Method for evaluating sensitivity of low-permeability reservoir

Abstract

Provided is a method for evaluating sensitivity of a low-permeability reservoir. The method comprises: using a full-diameter core of a target reservoir to prepare a test sample of the target reservoir; separately performing a standard brine permeability test on each test sample, determining a minimum flow at which each test sample is able to achieve the permeability test to be an initial flow, and then grouping each test sample according to the magnitude of the initial flow; performing a sensitivity test on a same group of samples, comprising: taking a test sample A from a group to be tested, and carrying out a flow rate sensitivity test using the initial flow thereof as a minimum flow, to determine a critical flow rate of the group to be tested; taking test samples B, C, D, E and F from the group to perform water sensitivity, salinity sensitivity, acid sensitivity, alkali sensitivity and stress sensitivity tests, respectively, to obtain water sensitivity, salinity sensitivity, acid sensitivity, alkali sensitivity, and stress sensitivity of the group to be tested, and selecting a critical flow corresponding to the critical flow rate of the group to be tested during each sensitivity test process.

Description

Low permeability reservoir sensitivity evaluation method

[0001] Cross-reference information

[0002] The present application claims priority to the Chinese patent application No. 202410757191.X, filed on June 12, 2024, and entitled "Low permeability reservoir sensitivity evaluation method", the entire content of which is incorporated herein by reference. TECHNICAL FIELD

[0003] The present application relates to the field of oil and gas field development engineering, in particular to a low permeability reservoir sensitivity evaluation method. BACKGROUND

[0004] In recent years, the center of the world's oil and gas exploration and development field is gradually shifting from conventional oil and gas, which accounts for 20% of the total oil and gas resources, to unconventional oil and gas, which accounts for 80% of the total oil and gas resources. The poor permeability, low single well production, high decline rate, low oil and gas field recovery, difficulty in stable production, and poor economic benefit of unconventional oil and gas reservoirs are mainly due to the fact that the reservoirs of unconventional oil and gas reservoirs belong to low permeability reservoirs (matrix permeability ≤ 0.1 × 10 -3 μm 2 ). Large-scale horizontal well volume fracturing technology is a key means to realize the economic and effective development of unconventional oil and gas reservoirs. Through hydraulic fracturing, the "artificial permeability" of the reservoir is "broken" and a complex fracture network is formed. With the continuous innovation of drilling and completion technology and straight well fine segmentation fracturing, horizontal well segmented multi-cluster fracturing and other reservoir reconstruction technologies, unconventional oil and gas reservoirs have realized large-scale and efficient development, but have also exposed the problems of rapid production decline and low single well EUR. Due to the complexity of the reservoir conditions and the difference in development methods, there is strong uncertainty in the reservoir reconstruction method and effect in the actual development process of unconventional oil and gas reservoirs.

[0005] Overall, in the current development process, the problems of large damage to low permeability reservoirs and rapid production decline still exist, and the stimulation effect has not been substantially broken through. The existing reservoir sensitivity experimental evaluation results cannot effectively support the efficient development of low permeability oil and gas reservoirs.

[0006] In different stages of oil and gas field development, the reservoirs will be contacted with different external fluids. When the external fluids are incompatible with the reservoir rocks and / or formation water, and the technical measures are unreasonable, the reservoirs will be sensitive, various physical and chemical reactions will occur, and the flow capacity of oil and gas in the reservoirs will be reduced, and the production capacity of the reservoirs will be damaged to different degrees. Drilling fluid will be used in the drilling process. The drilling fluid has a certain salinity and pH value. When the drilling fluid invades the reservoir, physical and chemical reactions will occur between the drilling fluid and the reservoir rocks, and the permeability of the reservoir will be changed. In the well completion process, in order to improve the production of oil and gas wells, the reservoirs of low permeability usually need to be reconstructed. The working fluid such as preflush, slickwater and acid fluid is needed in the reservoir reconstruction. When the working fluid enters the reservoir and reacts with the water-sensitive minerals, acid-sensitive minerals and reservoir fluid, or the fluid flow rate is too high, the sedimentation, release of particles and migration of formation particles will occur, and the pore throat will be blocked, so that the permeability of the reservoir will be changed. In the process of oil and gas production, with the production of oil and gas in the reservoir, the pore pressure of the reservoir is reduced, and the effective stress of the reservoir rock is changed. The change of the effective stress state from one state to another state will inevitably cause the deformation of the reservoir rock, and the deformation of the reservoir rock will inevitably cause the change of the pore structure and pore volume of the reservoir, such as the reduction of the pore volume, the closure of the pore throat and the fracture, etc. These changes will change the permeability of the rock. In summary, accurate evaluation of the reservoir sensitivity and analysis of the reservoir damage mechanism will provide an important reference for the formulation of oil and gas production process. Deepening the understanding of the reservoir sensitivity will help to prevent the damage of the reservoir in each construction link, fully develop the production capacity of the reservoir, and achieve the purpose of scientific development of oil and gas field.

[0007] The current experimental evaluation method of reservoir sensitivity is aimed at conventional oil and gas reservoirs (matrix permeability > 1 x 10 -3 μm 2) are usually columnar samples with a diameter of about 2.54 cm or 3.81 cm and a length of not less than 1.5 times the diameter, which are processed from downhole cores of oil and gas reservoirs, and the experimental medium can directly penetrate the test sample to carry out the experiment (the test sample cannot be artificially jointed). When the test sample has a low dense permeability, the experimental medium cannot penetrate the test sample to carry out the sensitivity experiment evaluation, and at this time, the current reservoir sensitivity experiment evaluation method has obvious inadaptability; when this situation occurs, the test sample can only be discarded, and a new test sample needs to be drilled and processed again until a test sample that can be directly penetrated by the experimental medium is found, so that a large amount of precious downhole cores are wasted, and even if a test sample that can be directly penetrated by the experimental medium is found, the test sample often cannot represent the typical physical property characteristics of the low-permeability reservoir, and the sensitivity experiment result cannot truly reflect the sensitivity characteristics of the low-permeability reservoir. Different sensitivities have mutual influences (for example, the salinity sensitivity has influences on the acid sensitivity, the alkali sensitivity and the stress sensitivity), and there is superimposed damage to the reservoir. The current reservoir sensitivity experiment evaluation method has the problem that the experimental conditions (room temperature, confining pressure conditions) do not match the reservoir state. In short, the current reservoir sensitivity experiment evaluation method has obvious inadaptability when evaluating the sensitivity of the low-permeability reservoir.

[0008] In summary, at present, it is urgent to further study a low-permeability reservoir sensitivity evaluation method that can accurately evaluate the sensitivity of the low-permeability reservoir and provide data support for formulating an efficient development plan for the low-permeability oil and gas reservoir. SUMMARY

[0009] The purpose of the present application is to provide a low-permeability reservoir sensitivity evaluation method that can accurately evaluate the sensitivity of the low-permeability reservoir and provide strong data support for formulating a development plan for the low-permeability reservoir, so as to ensure safe, economic and efficient exploration and development of the low-permeability oil and gas reservoir.

[0010] In order to achieve the above purpose, the present application provides a low-permeability reservoir sensitivity evaluation method, which comprises the following steps:

[0011] Step 1, preparing test samples of a target reservoir by using a full-diameter core of the target reservoir; during the preparation of the test samples, the diameter of the full-diameter core is not changed (that is, the test samples retain the original diameter of the full-diameter core) ;

[0012] Step 2, respectively performing a standard saltwater permeability test on each test sample to determine the minimum flow rate that can achieve the permeability test of each test sample, that is, the initial flow rate, and then grouping the test samples according to the size of the initial flow rate;

[0013] Step 3, performing a sensitivity test on the test samples in the same group, which comprises the following steps:

[0014] Take a certain group of samples as the to-be-tested group; take A test samples in the to-be-tested group to perform a flow rate sensitivity test, and obtain the critical flow rate of the A test samples as the critical flow rate of the to-be-tested group, wherein the initial flow rate of the A test samples is taken as the minimum flow rate during the flow rate sensitivity test;

[0015] Take B test samples in the to-be-tested group to perform a water sensitivity test, and obtain the water sensitivity of the B test samples as the water sensitivity of the to-be-tested group, wherein the critical flow rate of the to-be-tested group is selected as the critical flow rate of the B test samples during the water sensitivity test; and / or take C test samples in the to-be-tested group to perform a salinity sensitivity test, and obtain the salinity sensitivity of the C test samples as the salinity sensitivity of the to-be-tested group, wherein the critical flow rate of the to-be-tested group is selected as the critical flow rate of the C test samples during the salinity sensitivity test; and / or take D test samples in the to-be-tested group to perform an acid sensitivity test, and obtain the acid sensitivity of the D test samples as the acid sensitivity of the to-be-tested group, wherein the critical flow rate of the to-be-tested group is selected as the critical flow rate of the D test samples during the acid sensitivity test; and / or take E test samples in the to-be-tested group to perform an alkali sensitivity test, and obtain the alkali sensitivity of the E test samples as the alkali sensitivity of the to-be-tested group, wherein the critical flow rate of the to-be-tested group is selected as the critical flow rate of the E test samples during the alkali sensitivity test; and / or take F test samples in the to-be-tested group to perform a stress sensitivity test, and obtain the stress sensitivity of the F test samples as the stress sensitivity of the to-be-tested group, wherein the critical flow rate of the to-be-tested group is selected as the critical flow rate of the F test samples during the stress sensitivity test.

[0016] The low-permeability reservoir sensitivity evaluation method provided by the application can determine the critical flow rate, water sensitivity, salinity sensitivity, acid sensitivity, alkali sensitivity and stress sensitivity of the to-be-tested group, which can reflect the sensitivity of the region with the permeability of the to-be-tested group in the target reservoir.

[0017] According to the preferred embodiment of the low-permeability reservoir sensitivity evaluation method, the length of the test sample is not less than 1.5 times the diameter; more preferably, the preparation of the test sample of the target reservoir from the full-diameter core of the target reservoir comprises: length cutting of the full-diameter core of the target reservoir to obtain a core with a length of not less than 1.5 times the diameter as the test sample of the target reservoir.

[0018] According to the preferred embodiment of the low-permeability reservoir sensitivity evaluation method, the length of the test sample is 0.5-1 times the diameter; more preferably, the preparation of the test sample of the target reservoir from the full-diameter core of the target reservoir comprises: length cutting of the full-diameter core of the target reservoir to obtain a core with a length of 0.5-1 times the diameter as the test sample of the target reservoir.

[0019] According to the preferred embodiment of the low-permeability reservoir sensitivity evaluation method, the method further comprises: obtaining the reservoir temperature, the overburden pressure, and the reservoir pore pressure of the target reservoir; taking the reservoir temperature of the target reservoir as the simulation temperature of the test sample during the standard salt water permeability test, the water sensitivity test, the salinity sensitivity test, the acid sensitivity test, the alkali sensitivity test, and the stress sensitivity test; taking the overburden pressure as the experimental confining pressure of the test sample during the standard salt water permeability test, the water sensitivity test, the salinity sensitivity test, the acid sensitivity test, the alkali sensitivity test, and the stress sensitivity test; and taking the reservoir pore pressure as the experimental back pressure of the test sample during the standard salt water permeability test, the water sensitivity test, the salinity sensitivity test, the acid sensitivity test, and the alkali sensitivity test.

[0020] According to the preferred embodiment of the low-permeability reservoir sensitivity evaluation method, in step 2, the standard salt water permeability test is performed on each test sample to determine the minimum flow rate at which the permeability test can be performed, i.e., the initial flow rate, which comprises:

[0021] The standard salt water permeability test is performed on each test sample at the first flow rate, and the initial flow rate of each test sample that can perform the permeability test is the first flow rate, and each test sample that cannot perform the permeability test is recorded as a remaining test sample.

[0022] The standard salt water permeability test is performed on each remaining test sample at the second flow rate, which is greater than the first flow rate, and the initial flow rate of each test sample that can perform the permeability test is the second flow rate, and each test sample that cannot perform the permeability test is recorded as a remaining test sample.

[0023] The standard salt water permeability test is performed on each remaining test sample at the (i+1)th flow rate, which is greater than the ith flow rate, and the initial flow rate of each test sample that can perform the permeability test is the (i+1)th flow rate, and each test sample that cannot perform the permeability test is recorded as a remaining test sample, until the number of remaining test samples is 0.

[0024] According to the preferred embodiment of the low-permeability reservoir sensitivity evaluation method, the method further comprises: performing a flow rate sensitivity test on A test samples in the to-be-tested group to obtain the flow rate sensitivity damage rate of the A test samples as the flow rate sensitivity damage rate of the to-be-tested group.

[0025] More preferably, the method further comprises: performing a flow rate sensitivity damage degree evaluation on the A test samples based on the flow rate sensitivity damage rate of the A test samples, and taking the flow rate sensitivity damage degree evaluation result of the A test samples as the flow rate sensitivity damage degree evaluation result of the to-be-tested group; and further preferably, the flow rate sensitivity damage degree evaluation standard is shown in Table 1.

[0026] Table 1

[0027] According to the preferred embodiment of the low-permeability reservoir sensitivity evaluation method, wherein, in the group to be tested, A test samples are taken for flow rate sensitivity test, which comprises:

[0028] In the group to be tested, A test samples are taken, and standard saline permeability tests are performed on the A test samples under different flow rates to obtain the permeability of the A test samples under different flow rates; wherein, the standard saline permeability test under low flow rate is performed first, and then the standard saline permeability test under high flow rate is performed, and the minimum flow rate is the initial flow rate of the A test sample;

[0029] More preferably, the critical flow rate of the A test sample is determined by the following method:

[0030] Based on the permeability data of the A test sample under different flow rates, the permeability retention rate of the A test sample under different flow rates is determined; wherein, the permeability retention rate is based on the permeability under the initial flow rate; the highest flow rate corresponding to the permeability retention rate not less than 80% is taken as the critical flow rate of the A test sample, and the critical flow rate corresponding to the critical flow rate of the A test sample is taken as the critical flow rate of the A test sample;

[0031] Wherein, the permeability retention rate is determined by the following formula:

[0032] In the formula, vn is the permeability retention rate, unit %; Kn is the permeability under a certain flow rate, unit 10 -3 μm 2 ; Kin is the reference permeability, unit 10 -3 μm 2 ;

[0033] Wherein, the flow rate corresponding to the flow rate is determined by the following formula:

[0034] In the formula, v is the flow rate, unit cm / min; Q is the flow rate, unit cm 3 / min; d is the diameter of the test sample, unit cm.

[0035] More preferably, the flow rate sensitivity damage rate of the A test sample is determined by the following method:

[0036] Based on the permeability data of the A test sample under different flow rates, the flow rate sensitivity damage rate of the A test sample under different flow rates is determined; wherein, the flow rate sensitivity damage rate is based on the permeability under the initial flow rate;

[0037] Wherein, the flow rate sensitivity damage rate is determined by the following formula:

[0038] Dn = (Kn - Kin) / Kin × 100% -3 μm 2 ; Kn is the permeability under a certain flow rate, unit 10 -3 μm 2 ;

[0039] According to the preferred embodiment of the low-permeability reservoir sensitivity evaluation method, wherein the water sensitivity of the B test sample is obtained as the water sensitivity of the group to be tested.

[0040] The water sensitivity damage rate of the B test sample is obtained as the water sensitivity damage rate of the group to be tested.

[0041] More preferably, the water sensitivity of the B test sample is obtained as the water sensitivity of the group to be tested.

[0042] The water sensitivity damage degree evaluation of the B test sample is performed based on the water sensitivity damage rate of the B test sample, and the water sensitivity damage degree evaluation result of the B test sample is obtained as the water sensitivity damage degree evaluation result of the group to be tested; further preferably, the water sensitivity damage degree evaluation standard is shown in Table 2; and more preferably, when the water sensitivity damage degree evaluation result of the group to be tested is none or weak during the sensitivity test of the same group of samples, the step of "taking C test samples in the group to be tested to perform salinity sensitivity test to obtain the salinity sensitivity of the C test samples as the salinity sensitivity of the group to be tested" is not performed.

[0043] Table 2

[0044] More preferably, the water sensitivity test of the B test sample in the group to be tested comprises:

[0045] The B test sample is taken in the group to be tested; first, the standard salt water permeability test is performed on the B test sample at the critical flow rate of the test sample corresponding to the critical flow rate of the group to be tested, and the standard salt water permeability of the B test sample is obtained; then, the 1 / 2 standard salt water permeability test is performed on the B test sample at the critical flow rate of the test sample corresponding to the critical flow rate of the group to be tested, and the 1 / 2 standard salt water permeability of the B test sample is obtained; and further, the distilled water permeability test is performed on the B test sample at the critical flow rate of the test sample corresponding to the critical flow rate of the group to be tested, and the distilled water permeability of the B test sample is obtained.

[0046] Further preferably, the water sensitivity damage rate of the B test sample is determined by the following method:

[0047] Based on the standard salt water permeability of the B test sample and the distilled water permeability of the B test sample, the water sensitivity damage rate of the B test sample is determined as the water sensitivity damage rate of the group to be tested; wherein the water sensitivity damage rate is determined by the following formula:

[0048] In the formula, Dw is the water sensitivity damage rate, in %; Kiw is the standard saline permeability, in 10 -3 μm 2 ; Kw is the distilled water permeability, in 10 -3 μm 2 ;

[0049] According to the preferred embodiment of the low-permeability reservoir sensitivity evaluation method, wherein C test samples are taken from the group to be tested for salt sensitivity test, and the critical salinity of the C test samples is taken as the critical salinity of the group to be tested.

[0050] The critical salinity of the C test samples is taken as the critical salinity of the group to be tested.

[0051] More preferably, the critical salinity of the C test samples is taken as the critical salinity of the group to be tested.

[0052] C test samples are taken from the group to be tested.

[0053] The C test samples are respectively subjected to different salt concentration saline permeability tests at the critical flow rate of the test sample corresponding to the critical flow rate of the group to be tested, to obtain the permeability of the C test samples under different salt concentrations; wherein, the high-salt-concentration saline permeability test is performed first, and then the low-salt-concentration saline permeability test is performed, and the highest salt concentration saline is taken as the standard saline, and the lowest salt concentration saline is taken as the distilled water.

[0054] Based on the permeability of the C test samples under different salt concentrations, the permeability retention rate of the C test samples under different salt concentrations is determined respectively; wherein, the permeability retention rate is taken as the reference permeability under the standard saline.

[0055] The critical salinity of the C test samples is taken as the critical salinity of the group to be tested.

[0056] Wherein, the permeability retention rate is determined by the following formula:

[0057] In the formula, vsn is the permeability retention rate, in %; Ks is the permeability under a certain salt concentration, in 10 -3 μm 2 ; Kis is the permeability under the standard saline, i.e. the initial permeability, in 10 -3 μm 2 .

[0058] According to the preferred embodiment of the low-permeability reservoir sensitivity evaluation method, wherein the permeability test fluid has a salinity equal to the critical salinity of the group to be tested during the acid sensitivity test.

[0059] According to the preferred embodiment of the low-permeability reservoir sensitivity evaluation method, wherein the acid sensitivity of the D test sample is obtained as the acid sensitivity of the group to be tested, which comprises:

[0060] The acid sensitivity damage rate of the D test sample is obtained as the acid sensitivity damage rate of the group to be tested.

[0061] More preferably, obtaining the acid sensitivity of the D test sample as the acid sensitivity of the group to be tested further comprises: performing an acid sensitivity damage degree evaluation of the D test sample based on the acid sensitivity damage rate of the D test sample, and obtaining the acid sensitivity damage degree evaluation result of the D test sample as the acid sensitivity damage degree evaluation result of the group to be tested; and further preferably, the acid sensitivity damage degree evaluation criteria are shown in Table 3:

[0062] Table 3

[0063] More preferably, the acid sensitivity test of the D test sample in the group to be tested comprises:

[0064] The D test sample is taken from the group to be tested; first, the D test sample is subjected to a brine permeability test at the critical flow rate of the group to be tested, to obtain the permeability of the D test sample before acid action; then, the acid liquid is displaced into the D test sample and the D test sample is reacted with the acid liquid for a period of time; further, the D test sample is subjected to a brine permeability test at the critical flow rate of the group to be tested, to obtain the permeability of the D test sample after acid action.

[0065] Further preferably, the acid liquid is displaced into the D test sample until the acid liquid stops flowing out of the liquid flow outlet, and the acid injection is stopped.

[0066] Further preferably, the acid sensitivity damage rate of the D test sample is determined by the following method:

[0067] Based on the permeability before acid action and the permeability after acid action of the D test sample, the acid sensitivity damage rate of the D test sample is determined as the acid sensitivity damage rate of the group to be tested; wherein the acid sensitivity damage rate is determined by the following formula:

[0068] In the formula, Dac is the acid sensitivity damage rate, unit %; Kiac is the permeability before acid action, unit 10 -3 μm 2 ; Kac is the permeability after acid action, unit 10 -3 μm 2;

[0069] According to the preferred embodiment of the low-permeability reservoir sensitivity evaluation method, the permeability test fluid has a salinity equal to the critical salinity of the group to be tested during the alkali sensitivity test.

[0070] According to the preferred embodiment of the low-permeability reservoir sensitivity evaluation method, obtaining the alkali sensitivity of the E test sample as the alkali sensitivity of the group to be tested comprises:

[0071] obtaining the critical pH value of the E test sample as the critical pH value of the group to be tested, and / or obtaining the alkali sensitivity damage rate of the E test sample as the alkali sensitivity damage rate of the group to be tested;

[0072] More preferably, obtaining the alkali sensitivity of the E test sample as the alkali sensitivity of the group to be tested further comprises: performing an alkali sensitivity damage degree evaluation of the E test sample based on the alkali sensitivity damage rate of the E test sample, and obtaining the alkali sensitivity damage degree evaluation result of the E test sample as the alkali sensitivity damage degree evaluation result of the group to be tested; and further preferably, the alkali sensitivity damage degree evaluation criteria are shown in Table 4:

[0073] Table 4

[0074] More preferably, the alkali sensitivity test of the E test sample in the group to be tested obtains the following results:

[0075] The E test sample is taken from the group to be tested; the permeability of the E test sample under different pH value solutions is obtained by performing permeability tests of the E test sample under different pH value solutions at the critical flow rate of the test sample corresponding to the critical flow rate of the group to be tested; wherein, the permeability test under a low pH value solution is performed first, and then the permeability test under a high pH value solution is performed; the pH value of the solution is 7-14, the pH value of the solution with the lowest pH value is 7, and the salinity of the solution is equal to the critical salinity of the group to be tested; and the reference permeability of the E test sample;

[0076] Further preferably, the critical pH value of the E test sample is determined by the following method:

[0077] Based on the permeability of the E test sample under different pH value solutions, the permeability retention rate of the E test sample under different pH value solutions is determined respectively; wherein, the reference permeability is the permeability of the E test sample under a solution with a pH value of 7;

[0078] The pH value of the solution with the highest pH value corresponding to a permeability retention rate not lower than 80% is taken as the critical pH value of the E test sample;

[0079] wherein, the permeability retention rate is determined by the following formula:

[0080] wherein: val is the permeability retention rate, unit %; Kal is the permeability under certain pH value alkali solution, unit 10 -3 μm 2 ; Kial is the reference permeability, unit 10 -3 μm 2 ;

[0081] Further preferably, the alkali sensitivity damage rate of the E test sample is determined by the following way:

[0082] Based on the permeability of the E test sample under different pH value solutions, the alkali sensitivity damage rate of the E test sample is determined; wherein, the alkali sensitivity damage rate takes the permeability of the E test sample under the solution with pH value of 7 as the reference permeability; wherein, the alkali sensitivity damage rate is determined by the following formula:

[0083] wherein: Dal is the alkali sensitivity damage rate, unit %; Kial is the reference permeability, unit 10 -3 μm 2 ; Kal is the permeability under certain pH value alkali solution, unit 10 -3 μm 2 .

[0084] According to the preferred embodiment of the low permeability reservoir sensitivity evaluation method, wherein the fluid used for permeability test during the stress sensitivity test process uses the critical salinity brine of the group to be tested.

[0085] According to the preferred embodiment of the low permeability reservoir sensitivity evaluation method, wherein the stress sensitivity of the F test sample is obtained as the stress sensitivity of the group to be tested, which includes:

[0086] The critical stress of the F test sample is obtained as the critical stress of the group to be tested, and / or the irreversible stress sensitivity damage rate of the F test sample is obtained as the irreversible stress sensitivity damage rate of the group to be tested, and / or the stress sensitivity damage rate of the F test sample is obtained as the stress sensitivity damage rate of the group to be tested;

[0087] More preferably, the stress sensitivity of the F test sample is obtained as the stress sensitivity of the group to be tested, which further includes: based on the stress sensitivity damage rate of the F test sample, the stress sensitivity damage degree evaluation of the F test sample is carried out, and the stress damage degree evaluation result of the F test sample is obtained as the stress sensitivity damage degree evaluation result of the group to be tested; further preferably, the stress sensitivity damage degree evaluation standard is shown in Table 5:

[0088] Table 5

[0089] More preferably, the stress sensitivity test is performed on F test samples taken from the group to be tested to obtain:

[0090] F test samples are taken from the group to be tested; the permeability of the F test samples under different stresses is tested to obtain the permeability of the F test samples under different stresses; during the permeability test, the flow rate is selected as the critical flow rate of the test sample corresponding to the critical flow rate of the group to be tested; the fluid used in the permeability test is the critical salinity brine of the group to be tested; the permeability test is first performed under an initial stress, then the stress is gradually increased to a maximum stress value, and then gradually decreased to a final stress, and the permeability test is performed under each stress value for a predetermined time; the initial stress is the effective stress of the target reservoir, and the final stress is equal to the initial stress;

[0091] Further preferably, during the permeability test of the F test samples under different stresses, the confining pressure remains unchanged, and the appropriate back pressure is determined according to the stress value (the difference between the confining pressure and the back pressure is the stress);

[0092] Further preferably, the critical stress of the F test sample is determined by the following method:

[0093] Based on the permeability of the F test samples under different stresses, the permeability under the initial stress is taken as the reference permeability, and the permeability retention rate of the F test samples under different stresses is determined; when the permeability retention rate measured during the process of gradually increasing the stress to the maximum stress value is not less than 80%, the maximum stress corresponding to the permeability retention rate is taken as the critical stress of the F test sample;

[0094] Wherein, the permeability retention rate is determined by the following formula:

[0095] In the formula: vp is the permeability retention rate, unit %; Kp is the permeability under a certain stress, unit 10 -3 μm 2 ; Kip is the reference permeability, unit 10 -3 μm 2 ;

[0096] Further preferably, the irreversible stress sensitivity damage rate of the F test sample is determined by the following method:

[0097] Based on the permeability of the F test samples under the initial stress and the final stress, the permeability under the initial stress is taken as the reference permeability, and the irreversible stress sensitivity damage rate of the F test sample is determined as the irreversible stress sensitivity damage rate of the group to be tested; wherein, the irreversible stress sensitivity damage rate is determined by the following formula:

[0098] Dpn = (Kp - Kip) / Kip x 100 -3 μm 2 Kip is the reference permeability, unit 10 -3 μm 2 ;

[0099] Further preferably, the stress sensitivity damage rate of the F test sample is determined by the following way:

[0100] Based on the permeability of the F test sample under different stresses, taking the permeability under the initial stress as the reference permeability, the stress sensitivity damage rate of the F test sample is determined as the stress sensitivity damage rate of the test group;

[0101] Wherein, the stress sensitivity damage rate is determined by the following formula:

[0102] Dp = (Kp - Kip) / Kip x 100 -3 μm 2 Kip is the reference permeability, unit 10 -3 μm 2 .

[0103] According to the preferred embodiment of the low permeability reservoir sensitivity evaluation method, wherein,

[0104] The standard brine refers to a NaCl aqueous solution with a mass content of 8% of NaCl;

[0105] The 3 / 4 standard brine refers to a NaCl aqueous solution with a mass content of 6% of NaCl;

[0106] The 1 / 2 standard brine refers to a NaCl aqueous solution with a mass content of 4% of NaCl;

[0107] The 1 / 4 standard brine refers to a NaCl aqueous solution with a mass content of 2% of NaCl.

[0108] According to the preferred embodiment of the low permeability reservoir sensitivity evaluation method, wherein, the solution used in the sensitivity test process is provided with salinity by NaCl, alkalinity by NaOH, and acidity by HCl.

[0109] According to the preferred embodiment of the low permeability reservoir sensitivity evaluation method, wherein, the permeability test adopts an ultra-low permeability tester, and the lower limit of the test of the ultra-low permeability tester is not more than 10 -4 mD, and the upper limit of the confining pressure is not less than 80 MPa.

[0110] The technical scheme provided by the present application solves the problem that the existing experimental method cannot evaluate the sensitivity of low-permeability reservoirs.

[0111] 1. The technical scheme provided by the present application uses the test sample prepared by retaining the original diameter of the full-diameter core to perform the sensitivity test, retains the original seepage channel of the downhole core of the oil and gas reservoir, avoids the problem that the data is inaccurate due to the fact that the loose area (i.e., the seepage channel area) of the downhole core of the oil and gas reservoir is artificially avoided to ensure the success of the processing during the processing of the downhole core of the oil and gas reservoir (usually processed into a columnar sample with a diameter of about 2.54 cm or 3.81 cm), and can well adapt to the sensitivity evaluation of low-permeability reservoirs.

[0112] 2. The technical scheme provided by the present application proposes a new sensitivity test process for the special sample used in the technical scheme, can eliminate the mutual influence between different sensitivities, and can accurately evaluate the sensitivity damage of low-permeability reservoirs.

[0113] 3. The technical scheme provided by the present application can effectively solve the problem of waste of downhole cores caused by the fact that the existing reservoir sensitivity experimental evaluation method is not applicable to low-permeability reservoirs. BRIEF DESCRIPTION OF DRAWINGS

[0114] FIG. 1 is a flow rate sensitivity experimental curve diagram in the embodiment 1 of the present application.

[0115] FIG. 2 is a salinity sensitivity curve diagram in the embodiment 1 of the present application. DETAILED DESCRIPTION

[0116] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear and explicit, the embodiments of the present application will be further described in detail below in combination with the drawings. Herein, the schematic embodiments of the present application and the descriptions thereof are used to explain the present application, but not as a limitation on the present application.

[0117] A low-permeability reservoir sensitivity evaluation method is provided in a specific embodiment of the present application, and the method comprises:

[0118] Step 101, a test sample of a target reservoir is prepared by using a full-diameter core of the target reservoir; during the preparation of the test sample, the diameter of the full-diameter core is not changed (i.e., the test sample retains the original diameter of the full-diameter core);

[0119] Step 102, standard salt water permeability tests are performed on each test sample to determine the minimum flow rate at which the permeability test can be performed, i.e., the initial flow rate, and then the test samples are grouped according to the size of the initial flow;

[0120] Step 103, sensitivity tests are performed on the same group of samples, including:

[0121] taking A test sample in the to-be-tested group to perform a flow rate sensitivity test to obtain a critical flow rate of the A test sample as the critical flow rate of the to-be-tested group, and taking the initial flow rate of the A test sample as the minimum flow rate during the flow rate sensitivity test;

[0122] taking B test sample in the to-be-tested group to perform a water sensitivity test to obtain the water sensitivity of the B test sample as the water sensitivity of the to-be-tested group, and selecting the critical flow rate of the B test sample corresponding to the critical flow rate of the to-be-tested group as the flow rate during the water sensitivity test; and / or taking C test sample in the to-be-tested group to perform a salinity sensitivity test to obtain the salinity sensitivity of the C test sample as the salinity sensitivity of the to-be-tested group, and selecting the critical flow rate of the C test sample corresponding to the critical flow rate of the to-be-tested group as the flow rate during the salinity sensitivity test; and / or taking D test sample in the to-be-tested group to perform an acid sensitivity test to obtain the acid sensitivity of the D test sample as the acid sensitivity of the to-be-tested group, and selecting the critical flow rate of the D test sample corresponding to the critical flow rate of the to-be-tested group as the flow rate during the acid sensitivity test; and / or taking E test sample in the to-be-tested group to perform an alkali sensitivity test to obtain the alkali sensitivity of the E test sample as the alkali sensitivity of the to-be-tested group, and selecting the critical flow rate of the E test sample corresponding to the critical flow rate of the to-be-tested group as the flow rate during the alkali sensitivity test; and / or taking F test sample in the to-be-tested group to perform a stress sensitivity test to obtain the stress sensitivity of the F test sample as the stress sensitivity of the to-be-tested group, and selecting the critical flow rate of the F test sample corresponding to the critical flow rate of the to-be-tested group as the flow rate during the stress sensitivity test.

[0123] In the low-permeability reservoir sensitivity evaluation method provided in the specific implementation, the critical flow rate, the water sensitivity, the salinity sensitivity, the acid sensitivity, the alkali sensitivity, and the stress sensitivity of the to-be-tested group obtained in step 103 can reflect the sensitivity of the region with the permeability of the to-be-tested group in the target reservoir.

[0124] In one embodiment, the length of the test sample is not less than 1.5 times the diameter.

[0125] Further, the preparation of the test sample of the target reservoir from the full-diameter core of the target reservoir includes: length cutting on the full-diameter core of the target reservoir to obtain a core with a length not less than 1.5 times the diameter as the test sample of the target reservoir.

[0126] In one embodiment, the method further comprises: obtaining the reservoir temperature, the overburden pressure, and the reservoir pore pressure of the target reservoir, taking the reservoir temperature of the target reservoir as the simulation temperature of the test sample in the process of the standard salt water permeability test, the water sensitivity test, the salinity sensitivity test, the acid sensitivity test, the alkali sensitivity test, and the stress sensitivity test, taking the overburden pressure as the experimental confining pressure of the test sample in the process of the standard salt water permeability test, the water sensitivity test, the salinity sensitivity test, the acid sensitivity test, the alkali sensitivity test, and the stress sensitivity test, and taking the reservoir pore pressure as the experimental back pressure of the test sample in the process of the standard salt water permeability test, the water sensitivity test, the salinity sensitivity test, the acid sensitivity test, and the alkali sensitivity test.

[0127] In one embodiment, step 102 comprises: performing the standard salt water permeability test on each test sample in the test group to determine the minimum flow rate at which each test sample can achieve the permeability test, and taking the minimum flow rate as the initial flow rate of each test sample.

[0128] In one embodiment, step 102 comprises: performing the standard salt water permeability test on each test sample in the test group to determine the minimum flow rate at which each test sample can achieve the permeability test, and taking the minimum flow rate as the initial flow rate of each test sample.

[0129] In one embodiment, step 102 comprises: performing the standard salt water permeability test on each test sample in the test group to determine the minimum flow rate at which each test sample can achieve the permeability test, and taking the minimum flow rate as the initial flow rate of each test sample.

[0130] In one embodiment, step 102 comprises: performing the standard salt water permeability test on each test sample in the test group to determine the minimum flow rate at which each test sample can achieve the permeability test, and taking the minimum flow rate as the initial flow rate of each test sample.

[0131] For example, the first flow rate is 0.1 cm 3 / min, the second flow rate is 0.5 cm 3 / min, and the third flow rate is 1 cm 3 / min.

[0132] In one embodiment, step 103 comprises: taking A test samples from the test group to perform the flow rate sensitivity test, and taking the critical flow rate of the A test samples as the critical flow rate of the test group.

[0133] The A test sample is taken from the to-be-tested group, and a standard saline permeability test is performed on the A test sample under different flow rates to obtain the permeability of the A test sample under different flow rates; wherein, the standard saline permeability test is first performed under a low flow rate, and then the standard saline permeability test is performed under a high flow rate, and the lowest flow rate is the initial flow rate of the A test sample;

[0134] Based on the permeability of the A test sample under different flow rates, the permeability retention rate of the A test sample under different flow rates is determined; wherein, the permeability retention rate is based on the permeability under the initial flow rate as the reference permeability;

[0135] The highest flow rate corresponding to the permeability retention rate not less than 80% is taken as the critical flow rate of the A test sample, and the critical flow rate corresponding to the critical flow rate of the A test sample is taken as the critical flow rate of the A test sample, that is, the critical flow rate of the to-be-tested group;

[0136] Wherein, the permeability retention rate is determined by the following formula:

[0137] In the formula: vn is the permeability retention rate, unit %; Kn is the permeability under a certain flow rate, unit 10 -3 μm 2 ; Kin is the reference permeability, unit 10 -3 μm 2 ;

[0138] Wherein, the flow rate corresponding to the flow rate is determined by the following formula:

[0139] In the formula: v is the flow rate, unit cm / min; Q is the flow rate, unit cm 3 / min; d is the diameter of the test sample, unit cm.

[0140] In one embodiment, step 103 further comprises: based on the flow rate sensitivity test data of the A test sample, determining the flow rate sensitivity damage rate of the A test sample as the flow rate sensitivity damage rate of the to-be-tested group; wherein, the flow rate sensitivity damage rate is based on the permeability under the initial flow rate as the reference permeability;

[0141] Wherein, the flow rate sensitivity damage rate is determined by the following formula:

[0142] In the formula: Dn is the flow rate sensitivity damage rate, unit %; Kin is the reference permeability, unit 10 -3 μm 2 ; Kn is the permeability under a certain flow rate, unit 10 -3 μm 2 ;

[0143] Further, the step 103 further comprises: evaluating the flow rate sensitivity damage degree of the A test sample based on the flow rate sensitivity damage rate of the A test sample, and taking the evaluation result of the flow rate sensitivity damage degree of the A test sample as the evaluation result of the flow rate sensitivity damage degree of the to-be-tested group; and further preferably, wherein the evaluation standard of the flow rate sensitivity damage degree is shown in Table 6:

[0144] Table 6

[0145] In one embodiment, the water sensitivity of the to-be-tested group is obtained by taking the B test sample in the to-be-tested group to perform the water sensitivity test, and taking the water sensitivity of the B test sample as the water sensitivity of the to-be-tested group.

[0146] The water sensitivity damage rate of the to-be-tested group is obtained by taking the B test sample in the to-be-tested group to perform the water sensitivity test, and taking the water sensitivity damage rate of the B test sample as the water sensitivity damage rate of the to-be-tested group.

[0147] Further, the water sensitivity damage rate of the to-be-tested group is obtained by taking the B test sample in the to-be-tested group to perform the water sensitivity test, and taking the water sensitivity damage rate of the B test sample as the water sensitivity damage rate of the to-be-tested group.

[0148] The water sensitivity damage rate of the to-be-tested group is obtained by taking the B test sample in the to-be-tested group; first, the standard saline permeability of the B test sample is obtained by taking the B test sample to perform the standard saline permeability test at the critical flow rate of the to-be-tested group corresponding to the critical flow of the test sample; then, the 1 / 2 standard saline permeability of the B test sample is obtained by taking the B test sample to perform the 1 / 2 standard saline permeability test at the critical flow rate of the to-be-tested group corresponding to the critical flow of the test sample; further, the distilled water permeability of the B test sample is obtained by taking the B test sample to perform the distilled water permeability test at the critical flow rate of the to-be-tested group corresponding to the critical flow of the test sample; and the water sensitivity damage rate of the B test sample is determined based on the standard saline permeability of the B test sample and the distilled water permeability of the B test sample, and taken as the water sensitivity damage rate of the to-be-tested group; wherein the water sensitivity damage rate is obtained by the following formula:

[0149] In the formula, Dw is the water sensitivity damage rate, unit %; Kiw is the standard saline permeability, unit 10 -3 μm 2 ; Kw is the distilled water permeability, unit 10 -3 μm 2 ;

[0150] Further, the water sensitivity of the B test sample is obtained as the water sensitivity of the to-be-tested group, and the water sensitivity damage degree of the B test sample is evaluated based on the water sensitivity damage rate of the B test sample, and the evaluation result of the water sensitivity damage degree of the B test sample is taken as the evaluation result of the water sensitivity damage degree of the to-be-tested group; further, the water sensitivity damage degree evaluation standard is shown in Table 7; further, when the evaluation result of the water sensitivity damage degree of the to-be-tested group is none or weak during the sensitivity test of the same group of samples, the step of “taking C test samples in the to-be-tested group to perform salinity sensitivity test to obtain the salinity sensitivity of the C test sample as the salinity sensitivity of the to-be-tested group” is not performed.

[0151] Table 7

[0152] In one embodiment, the salinity sensitivity of the C test sample is obtained as the salinity sensitivity of the to-be-tested group, and the salinity sensitivity damage degree of the C test sample is evaluated based on the salinity sensitivity damage rate of the C test sample, and the evaluation result of the salinity sensitivity damage degree of the C test sample is taken as the evaluation result of the salinity sensitivity damage degree of the to-be-tested group.

[0153] The critical salinity of the C test sample is obtained as the critical salinity of the to-be-tested group.

[0154] Further, the critical salinity of the C test sample is obtained as the critical salinity of the to-be-tested group, and the critical salinity damage degree of the C test sample is evaluated based on the critical salinity damage rate of the C test sample, and the evaluation result of the critical salinity damage degree of the C test sample is taken as the evaluation result of the critical salinity damage degree of the to-be-tested group.

[0155] The C test sample is taken in the to-be-tested group.

[0156] The permeability of the C test sample under different salt concentrations of salt water is obtained by performing different salt concentration salt water permeability tests on the C test sample respectively at the critical flow rate of the test sample corresponding to the critical flow rate of the to-be-tested group; wherein, the high salt concentration salt water permeability test is performed first, and then the low salt concentration salt water permeability test is performed, the highest salt concentration salt water is taken as the standard salt water, and the lowest salt concentration salt water is taken as the distilled water.

[0157] The permeability retention rate of the C test sample under different salt concentrations of salt water is determined respectively based on the permeability of the C test sample under different salt concentrations of salt water; wherein, the permeability retention rate is taken as the reference permeability under the standard salt water.

[0158] The critical salinity of the C test sample is obtained as the critical salinity of the to-be-tested group, and the critical salinity damage degree of the C test sample is evaluated based on the critical salinity damage rate of the C test sample, and the evaluation result of the critical salinity damage degree of the C test sample is taken as the evaluation result of the critical salinity damage degree of the to-be-tested group.

[0159] The permeability retention rate is determined by the following formula:

[0160] In the formula, vsn is the permeability retention rate, unit %; Ks is the permeability under a certain salinity, unit 10 -3 μm 2 ; Kis is the permeability under standard brine, i.e. the initial permeability, unit 10 -3 μm 2 .

[0161] In one embodiment, during the acid sensitivity test, the permeability test fluid is the critical salinity brine of the test group (i.e. the brine with the salinity of the critical salinity of the test group).

[0162] In one embodiment, the acid sensitivity of the D test samples in the test group is obtained by acid sensitivity test, and the acid sensitivity of the D test samples is taken as the acid sensitivity of the test group, which includes:

[0163] The acid sensitivity of the D test samples in the test group is obtained by acid sensitivity test, and the acid sensitivity damage rate of the D test samples is taken as the acid sensitivity damage rate of the test group.

[0164] Further, the acid sensitivity damage rate of the D test samples in the test group is obtained by acid sensitivity test, and the acid sensitivity damage rate of the D test samples is taken as the acid sensitivity damage rate of the test group, which includes:

[0165] The D test samples in the test group are taken.

[0166] Firstly, the permeability of the D test samples under the critical salinity of the test group is tested by using the critical flow of the test sample corresponding to the critical flow rate of the test group, and the permeability of the D test samples before acid action is obtained; then, the acid liquid is displaced into the D test samples and the D test samples are reacted with the acid liquid for a period of time; further, the permeability of the D test samples under the critical salinity of the test group is tested by using the critical flow of the test sample corresponding to the critical flow rate of the test group, and the permeability of the D test samples after acid action is obtained.

[0167] Based on the permeability of the D test samples before acid action and the permeability of the D test samples after acid action, the acid sensitivity damage rate of the D test samples is determined as the acid sensitivity damage rate of the test group.

[0168] The acid sensitivity damage rate is determined by the following formula:

[0169] In the formula, Dac is the acid sensitivity damage rate, unit %; Kiac is the permeability before acid action, unit 10 -3 μm 2 ; Kac is the permeability after acid action, unit 10 -3 μm 2 ;

[0170] Further, the acid liquid is displaced into the D test samples until the acid liquid flow stops at the liquid flow outlet, and the acid injection is stopped.

[0171] Further, the acid sensitivity of the D test samples is obtained as the acid sensitivity of the group to be tested, and the acid sensitivity damage degree of the D test samples is evaluated based on the acid sensitivity damage rate of the D test samples, and the evaluation result of the acid sensitivity damage degree of the D test samples is taken as the evaluation result of the acid sensitivity damage degree of the group to be tested. Further, the acid sensitivity damage degree evaluation criteria are shown in Table 8:

[0172] Table 8

[0173] In one embodiment, the permeability test fluid has a salinity equal to the critical salinity of the group to be tested during the base sensitivity test.

[0174] In one embodiment, E test samples are taken from the group to be tested for base sensitivity test, and the base sensitivity of the E test samples is obtained as the base sensitivity of the group to be tested, which includes:

[0175] The critical pH value of the E test samples is obtained as the critical pH value of the group to be tested.

[0176] Further, the critical pH value of the E test samples is obtained as the critical pH value of the group to be tested, which includes:

[0177] E test samples are taken from the group to be tested.

[0178] The permeability of the E test samples under different pH value solutions is obtained by performing permeability tests on the E test samples with the critical flow rate of the test samples corresponding to the critical flow rate of the group to be tested, wherein the permeability test is first performed on a low pH value solution, and then on a high pH value solution, the pH value of the solution is 7-14, the pH value of the lowest pH value solution is 7, and the salinity of the solution is equal to the critical salinity of the group to be tested.

[0179] The permeability retention rate of the E test samples under different pH value solutions is determined based on the permeability of the E test samples under different pH value solutions, wherein the permeability retention rate is based on the permeability of the E test samples under a solution with a pH value of 7 as the reference permeability.

[0180] The pH value of the highest pH value solution corresponding to the permeability retention rate not less than 80% is taken as the critical pH value of the E test samples.

[0181] The permeability retention rate is determined by the following formula:

[0182] In the formula, val is the permeability retention rate, in %; Kal is the permeability under an alkali solution of a certain pH value, in 10 -3 μm 2 ; Kial is the reference permeability, in 10 -3 μm 2 .

[0183] In one embodiment, E test samples are taken from the group to be tested to perform the alkali sensitivity test, and the alkali sensitivity of the E test samples is obtained as the alkali sensitivity of the group to be tested, which includes:

[0184] In one embodiment, E test samples are taken from the group to be tested to perform the alkali sensitivity test, and the alkali sensitivity of the E test samples is obtained as the alkali sensitivity of the group to be tested, which includes:

[0185] Further, in one embodiment, E test samples are taken from the group to be tested to perform the alkali sensitivity test, and the alkali sensitivity of the E test samples is obtained as the alkali sensitivity of the group to be tested, which includes:

[0186] In one embodiment, E test samples are taken from the group to be tested to perform the alkali sensitivity test, and the alkali sensitivity of the E test samples is obtained as the alkali sensitivity of the group to be tested, which includes:

[0187] In one embodiment, E test samples are taken from the group to be tested to perform the alkali sensitivity test, and the alkali sensitivity of the E test samples is obtained as the alkali sensitivity of the group to be tested, which includes:

[0188] In one embodiment, E test samples are taken from the group to be tested to perform the alkali sensitivity test, and the alkali sensitivity of the E test samples is obtained as the alkali sensitivity of the group to be tested, which includes:

[0189] In one embodiment, E test samples are taken from the group to be tested to perform the alkali sensitivity test, and the alkali sensitivity of the E test samples is obtained as the alkali sensitivity of the group to be tested, which includes:

[0190] In the formula, val is the permeability retention rate, in %; Kal is the permeability under an alkali solution of a certain pH value, in 10 -3 μm 2 ; Kial is the reference permeability, in 10 -3 μm 2 ;

[0191] Further, the alkali sensitivity of the E test samples is obtained as the alkali sensitivity of the test group, and the alkali sensitivity damage degree of the E test samples is evaluated based on the alkali sensitivity damage rate of the E test samples, and the evaluation result of the alkali sensitivity damage degree of the E test samples is taken as the evaluation result of the alkali sensitivity damage degree of the test group.

[0192] Further, the evaluation standard of the alkali sensitivity damage degree is shown in Table 9.

[0193] Table 9

[0194] In one embodiment, the fluid used in the permeability test during the stress sensitivity test process uses the critical salinity brine of the test group.

[0195] In one embodiment, the stress sensitivity of the F test samples in the test group is obtained as the stress sensitivity of the test group.

[0196] The critical stress of the F test samples in the test group is obtained as the critical stress of the test group.

[0197] Further, the critical stress of the F test samples in the test group is obtained as the critical stress of the test group.

[0198] The F test samples in the test group are taken.

[0199] The permeability of the F test samples under different stresses is obtained, and the fluid used in the permeability test uses the critical salinity brine of the test group; the permeability test is first performed under an initial stress, then the stress is gradually increased to a maximum stress value, and then gradually reduced to a final stress, and the permeability test is performed under each stress value for a predetermined time, and the initial stress is the effective stress of the target reservoir, and the final stress is equal to the initial stress.

[0200] Based on the permeability of the F test samples under different stresses, the permeability retention rate of the F test samples under different stresses is determined respectively, taking the permeability under the initial stress as the reference permeability.

[0201] The maximum stress corresponding to the permeability retention rate not less than 80% during the process of gradually increasing the stress to the maximum stress value is taken as the critical stress of the F test samples, which is the critical stress of the test group.

[0202] The permeability retention rate is determined by the following formula:

[0203] In the formula, vp is the permeability retention rate, in %; Kp is the permeability under a certain stress, in 10 -3 μm 2 ; Kip is the reference permeability, in 10 -3 μm 2 ;

[0204] Further, in the permeability test under different stresses on the F test sample, the confining pressure is kept unchanged, and the back pressure is determined according to the stress value (the difference between the confining pressure and the back pressure is the stress).

[0205] In one embodiment, the F test sample is taken from the to-be-tested group to perform the stress sensitivity test, and the stress sensitivity of the F test sample is obtained as the stress sensitivity of the to-be-tested group, which includes:

[0206] The F test sample is taken from the to-be-tested group to perform the stress sensitivity test, and the irreversible stress sensitivity damage rate of the F test sample is obtained as the irreversible stress sensitivity damage rate of the to-be-tested group.

[0207] Further, the F test sample is taken from the to-be-tested group to perform the stress sensitivity test, and the irreversible stress sensitivity damage rate of the F test sample is obtained as the irreversible stress sensitivity damage rate of the to-be-tested group, which includes:

[0208] The F test sample is taken from the to-be-tested group.

[0209] The permeability test under different stresses is performed on the F test sample, and the permeability of the F test sample under different stresses is obtained; in the permeability test, the flow rate is selected as the critical flow rate of the test sample corresponding to the critical flow rate of the to-be-tested group; the fluid used in the permeability test is the critical salinity brine of the to-be-tested group; the permeability test under the initial stress is performed first, then the stress is gradually increased to the maximum stress value, and then the stress is gradually reduced to the final stress, and the permeability test is performed under each stress value for a rated time, and the initial stress is the reservoir effective stress of the target reservoir, and the final stress is equal to the initial stress.

[0210] Based on the reference permeability of the F test sample and the permeability under the final stress, the irreversible stress sensitivity damage rate of the F test sample is determined as the irreversible stress sensitivity damage rate of the to-be-tested group.

[0211] The irreversible stress sensitivity damage rate is determined by the following formula:

[0212] In the formula, Dpn is the irreversible stress sensitivity damage rate, in %; Kpn is the permeability under the final stress, in 10 -3μm 2 ; Kip is the reference permeability, unit 10 -3 μm 2 .

[0213] In one embodiment, F test samples are taken from the group to be tested to test the stress sensitivity, and the stress sensitivity of the F test samples is obtained as the stress sensitivity of the group to be tested, which includes:

[0214] In one embodiment, F test samples are taken from the group to be tested to test the stress sensitivity, and the stress sensitivity of the F test samples is obtained as the stress sensitivity of the group to be tested, which includes:

[0215] Further, in the group to be tested, F test samples are taken to test the stress sensitivity, and the stress sensitivity damage rate of the F test samples is obtained as the stress sensitivity damage rate of the group to be tested, which includes:

[0216] F test samples are taken from the group to be tested;

[0217] The permeability of the F test samples under different stresses is obtained by testing the permeability of the F test samples under different stresses. During the permeability test, the critical flow rate of the test sample corresponding to the critical flow rate of the group to be tested is selected; the fluid used for the permeability test is the critical salinity brine of the group to be tested; the permeability test is first carried out under an initial stress, then the stress is gradually increased to a maximum stress value, and then gradually reduced to a final stress, and the permeability test is carried out under each stress value for a predetermined time, and the initial stress is the effective stress of the target reservoir, and the final stress is equal to the initial stress;

[0218] Based on the permeability of the F test samples under different stresses, the stress sensitivity damage rate of the F test samples is determined as the stress sensitivity damage rate of the group to be tested;

[0219] Wherein, the stress sensitivity damage rate is determined by the following formula:

[0220] In the formula: Dp is the stress sensitivity damage rate, unit %; Kp is the permeability under a certain stress, unit 10 -3 μm 2 ; Kip is the reference permeability, unit 10 -3 μm 2 ;

[0221] Further, in the group to be tested, F test samples are taken to test the stress sensitivity, and the stress sensitivity of the F test samples is obtained as the stress sensitivity of the group to be tested, which includes: based on the stress sensitivity damage rate of the F test samples, the stress sensitivity damage degree of the F test samples is evaluated, and the stress damage degree evaluation result of the F test samples is taken as the stress sensitivity damage degree evaluation result of the group to be tested;

[0222] Still further, the stress sensitivity damage degree evaluation criteria are shown in Table 10:

[0223] Table 10

[0224] In one embodiment, standard brine refers to a NaCl aqueous solution with a mass content of NaCl of 8%; 3 / 4 standard brine refers to a NaCl aqueous solution with a mass content of NaCl of 6%; 1 / 2 standard brine refers to a NaCl aqueous solution with a mass content of NaCl of 4%; and 1 / 4 standard brine refers to a NaCl aqueous solution with a mass content of NaCl of 2%.

[0225] In one embodiment, the solution used in the sensitivity test process is mineralized by NaCl, alkaline by NaOH, and acidic by HCl.

[0226] For example, the solution used in the sensitivity test process is a NaCl aqueous solution or a NaOH aqueous solution or an HCl aqueous solution or a mixed solution of a NaCl aqueous solution and a NaOH aqueous solution or a mixed solution of a NaCl aqueous solution and an HCl aqueous solution.

[0227] Embodiment 1

[0228] The embodiment provides a low-permeability reservoir sensitivity evaluation method, which comprises the following steps:

[0229] 1. Length cutting is performed on a full-diameter core of a target reservoir to obtain a core with both ends flat and a length not less than 1.5 times the diameter as a test sample of the target reservoir.

[0230] 2. The reservoir temperature, overburden pressure, and reservoir pore pressure of the target reservoir are obtained, the reservoir temperature of the target reservoir is 140℃, the overburden pressure is 98MPa, and the reservoir pore pressure is 69MPa. The reservoir temperature of the target reservoir is used as the simulation temperature of the test sample in the process of standard brine permeability test, water sensitivity test, salinity sensitivity test, acid sensitivity test, alkali sensitivity test, and stress sensitivity test, the overburden pressure is used as the experimental confining pressure of the test sample in the process of standard brine permeability test, water sensitivity test, salinity sensitivity test, acid sensitivity test, alkali sensitivity test, and stress sensitivity test, and the reservoir pore pressure is used as the experimental back pressure of the test sample in the process of standard brine permeability test, water sensitivity test, salinity sensitivity test, acid sensitivity test, and alkali sensitivity test.

[0231] 3. The first flow rate (0.1cm 3The flow rate of standard saline (NaCl aqueous solution with a mass content of 8% NaCl) was tested at a rate of 1 / min. The initial flow rate of each test sample that could achieve the permeability test was the first flow rate, and the test samples that could not achieve the permeability test were recorded as the remaining test samples.

[0232] For each remaining test sample, a second flow rate (0.5 cm⁻¹) greater than the first flow rate was used. 3 The standard saline permeability test was conducted at a flow rate of 1000 m / min. The initial flow rate of each test sample that could achieve the permeability test was the second flow rate, and the test samples that could not achieve the permeability test were recorded as the remaining test samples.

[0233] For each remaining test sample, a third flow rate (1 cm) greater than the second flow rate was applied. 3 The standard saline permeability test is performed at a flow rate of 0 / min. The initial flow rate of each test sample that can achieve the permeability test is the third flow rate, and the test samples that cannot achieve the permeability test are recorded as the remaining test samples; at this time, the number of remaining test samples is 0.

[0234] The test samples were then grouped according to the initial flow rate. The first group included test samples 1, 2, 3, 4, 5, 6, and 7; the second group included test samples 8, 9, 10, 11, 12, 13, and 14; and the third group included test samples 15, 16, 17, 18, 19, and 20. The initial flow rate of the first group was 0.1 cm³. 3 / min, the initial flow rate of the second group of test samples was 0.5 cm³ / min. 3 / min, the initial flow rate of the third group of test samples was 1cm 3 / min.

[0235] 4. Using the first group of test samples (the average permeability of the first group of test samples is approximately 0.896 × 10⁻⁶), -3 μm 2 As the test group, sensitivity testing was conducted, and the permeability of the target reservoir was determined to be 0.896 × 10⁻⁶. -3 μm 2 Sensitivity in the left and right regions. Specifically, this includes:

[0236] 4.1 Take test sample 1 from the test group and conduct standard saline permeability tests on test sample 1 at different flow rates to obtain the permeability of test sample 1 at different flow rates; wherein, the standard saline permeability test is conducted first at a low flow rate and then at a high flow rate, and the lowest flow rate is taken as the initial flow rate of test sample 1.

[0237] Based on the permeability of the A test sample at different flow rates, the permeability retention rate of the test sample 1 at different flow rates was determined respectively; wherein the permeability retention rate was based on the permeability at the initial flow rate as the reference permeability. The results are shown in Table 11 and Figure 1. Wherein the permeability retention rate is determined by the following formula:

[0238] In the formula: vn is the permeability retention rate, unit %; Kn is the permeability at a certain flow rate, unit 10 -3 μm 2 ; Kin is the reference permeability, unit 10 -3 μm 2 .

[0239] The highest flow rate corresponding to the permeability retention rate not less than 80% was taken as the critical flow rate of the test sample 1, and the critical flow rate corresponding to the critical flow rate of the test sample 1 was taken as the critical flow rate of the test sample 1, that is, the critical flow rate of the group to be tested. In this embodiment, as shown in Table 11 and Figure 1, the flow rate corresponding to the flow rate of 0.1 cm 3 / min is the critical flow rate, the diameter of the test sample 1 is 6.5 cm, and the critical flow rate is 0.003 cm / min. Wherein the flow rate corresponding to the flow rate is determined by the following formula:

[0240] In the formula: v is the flow rate, unit cm / min; Q is the flow rate, unit cm 3 / min; d is the diameter of the test sample, unit cm.

[0241] Based on the flow rate sensitivity test data of the test sample 1, the flow rate sensitivity damage rate of the test sample 1 was determined as the flow rate sensitivity damage rate of the group to be tested; wherein the flow rate sensitivity damage rate was based on the permeability at the initial flow rate as the reference permeability. The results are shown in Table 11. Wherein the flow rate sensitivity damage rate is determined by the following formula:

[0242] In the formula: Dn is the flow rate sensitivity damage rate, unit %; Kin is the reference permeability, unit 10 -3 μm 2 ; Kn is the permeability at a certain flow rate, unit 10 -3 μm 2 .

[0243] Table 11

[0244] The flow rate sensitivity damage degree of the test sample 1 is evaluated based on the flow rate sensitivity damage rate of the test sample 1, and the evaluation result of the flow rate sensitivity damage degree of the test sample 1 is taken as the evaluation result of the flow rate sensitivity damage degree of the test group; wherein the evaluation standard of the flow rate sensitivity damage degree is shown in Table 12:

[0245] Table 12

[0246] Example flow rate 0.25 cm 3 / min, the permeability damage rate is 30 < Dn (30.2%) ≤ 50, and the flow rate sensitivity damage degree is moderate to weak.

[0247] 4.2, taking test sample 2 in the test group; first, the standard salt water permeability of the test sample 2 is tested at the critical flow rate of the test sample corresponding to the critical flow rate of the test group, to obtain the standard salt water permeability of the test sample 2; then, the 1 / 2 standard salt water (NaCl aqueous solution with a mass content of 4% NaCl) permeability of the test sample 2 is tested at the critical flow rate of the test sample corresponding to the critical flow rate of the test group, to obtain the 1 / 2 standard salt water permeability of the test sample 2; further, the distilled water permeability of the test sample 2 is tested at the critical flow rate of the test sample corresponding to the critical flow rate of the test group, to obtain the distilled water permeability of the test sample 2. The results are shown in Table 13.

[0248] Table 13

[0249] Based on the standard salt water permeability of the test sample 2 and the distilled water permeability of the test sample 2, the water sensitivity damage rate of the test sample 2 is determined as the water sensitivity damage rate of the test group, and the water sensitivity damage rate is 47.37%. Wherein, the water sensitivity damage rate is determined by the following formula:

[0250] In the formula: Dw is the water sensitivity damage rate, unit %; Kiw is the standard salt water permeability, unit 10 -3 μm 2 ; Kw is the distilled water permeability, unit 10 -3 μm 2 .

[0251] The water sensitivity damage degree of the test sample 2 is evaluated based on the water sensitivity damage rate of the test sample 2, and the evaluation result of the water sensitivity damage degree of the test sample 2 is taken as the evaluation result of the water sensitivity damage degree of the test group; wherein the evaluation standard of the water sensitivity damage degree is shown in Table 14;

[0252] Table 14

[0253] The water sensitivity damage rate is 30 < Dw (47.37%) < 50, and the water sensitivity damage degree is medium to weak.

[0254] 4.3, the evaluation result of the water sensitivity damage degree of the test group is medium to weak, therefore, the salinity sensitivity experiment needs to be carried out. The test sample 3 is taken from the test group; the different salinity brine permeability tests are carried out on the test sample 3 at different salinity concentrations respectively with the critical flow rate of the test sample corresponding to the critical flow rate of the test group, to obtain the permeability of the test sample 3 under different salinity concentrations; wherein, the high salinity concentration brine permeability test is carried out first, and then the low salinity concentration brine permeability test is carried out, the highest salinity concentration brine is the standard brine, and the lowest salinity concentration brine is distilled water. Based on the permeability of the test sample 3 under different salinity concentrations, the permeability retention rate of the test sample 3 under different salinity concentrations is determined respectively; wherein, the permeability retention rate takes the permeability under the standard brine as the reference permeability. The results are shown in Table 15 and FIG. 2. The salinity of the lowest concentration brine corresponding to the permeability retention rate not less than 80% is taken as the critical salinity of the test sample 3, that is, the critical salinity of the test group, and the critical salinity is 80000 mg / L. Wherein, the permeability retention rate is determined by the following formula:

[0255] In the formula: vsn is the permeability retention rate, unit %; Ks is the permeability under a certain salinity concentration, unit 10 -3 μm 2 ; Kis is the permeability under the standard brine, that is, the initial permeability, unit 10 -3 μm 2 .

[0256] Table 15

[0257] 4.4, the test sample 4 is taken from the test group. First, the test sample 4 is tested for the permeability of the test group under the critical salinity, to obtain the permeability of the test sample 4 before acid action; then, the acid liquid is displaced into the test sample 4 until the acid liquid stops flowing out of the liquid flow outlet, the acid injection is stopped, and the test sample 4 is reacted with the acid liquid for a period of time; further, the test sample 4 is tested for the permeability of the test group under the critical salinity, to obtain the permeability of the test sample 4 after acid action. Based on the permeability of the test sample 4 before acid action and the permeability after acid action, the acid sensitivity damage rate of the test sample 4 is determined as the acid sensitivity damage rate of the test group, and the result is shown in Table 16. The acid sensitivity damage degree evaluation of the test sample 4 is carried out based on the acid sensitivity damage rate of the test sample 4, and the acid sensitivity damage degree evaluation result of the test sample 4 is taken as the acid sensitivity damage degree evaluation result of the test group, wherein, the acid sensitivity damage degree evaluation standard is shown in Table 17.

[0258] The acid sensitivity damage rate is determined by the following formula:

[0259] In the formula, Dac is the acid sensitivity damage rate, in %; Kiac is the permeability before acid action, in 10 -3 μm 2 ; Kac is the permeability after acid action, in 10 -3 μm 2 .

[0260] Table 16

[0261] Table 17

[0262] The acid sensitivity damage rate is 30 < Dac (28.99%) < 50, and the acid sensitivity damage degree is weak.

[0263] 4.5, five test samples 5 are taken from the test group. The permeability of the test sample 5 under different pH solutions is obtained by performing permeability tests on the test sample 5 under the critical flow of the test sample corresponding to the critical flow rate of the test group and different pH solutions, respectively. Among them, the permeability tests are performed using solutions with pH values of 7, 8.5, 10, 11.5 and 13 in sequence, and the mineralization degree of the solution is equal to the critical mineralization degree of the test group. The solution with a pH value of 7 is a NaCl aqueous solution, and the solutions with pH values of 8.5, 10, 11.5 and 13 are mixed solutions of NaCl aqueous solution and NaOH aqueous solution.

[0264] Based on the permeability of the test sample 5 under different pH solutions, the permeability retention rate of the test sample 5 under different pH solutions is determined, respectively. Among them, the permeability retention rate takes the permeability of the test sample 5 under the solution with a pH value of 7 as the reference permeability. The results are shown in Table 18. The pH value of the highest pH solution corresponding to the permeability retention rate not less than 80% is taken as the critical pH value of the test sample 5, and the critical pH value is 7. The permeability retention rate is determined by the following formula:

[0265] In the formula, val is the permeability retention rate, in %; Kal is the permeability under a certain pH alkaline solution, in 10 -3 μm 2 ; Kial is the reference permeability, in 10 -3 μm 2 .

[0266] Based on the permeability of test sample 5 in different pH value solutions, the alkali sensitivity damage rate of test sample 5 is determined as the alkali sensitivity damage rate of the test group; wherein, the alkali sensitivity damage rate is based on the permeability of test sample 5 in the solution with pH value of 7 as the reference permeability, and the results are shown in Table 18. Wherein, the alkali sensitivity damage rate is determined by the following formula:

[0267] In the formula: Dal is the alkali sensitivity damage rate, unit %; Kial is the reference permeability, unit 10 -3 μm 2 ; Kal is the permeability under the alkali solution of a certain pH value, unit 10 -3 μm 2 .

[0268] Table 18

[0269] Based on the alkali sensitivity damage rate of test sample 5, the alkali sensitivity damage degree evaluation of test sample 5 is carried out, and the alkali sensitivity damage degree evaluation result of test sample 5 is taken as the alkali sensitivity damage degree evaluation result of the test group. The alkali sensitivity damage degree evaluation standard is shown in Table 19.

[0270] Table 19

[0271] When the pH value is 10, the alkali sensitivity damage rate is 30 < Dal (40.012%) ≤ 50, and the damage degree is medium weak.

[0272] 4.6, F test samples are taken in the test group. The permeability of test sample 6 under different stresses is obtained by permeability test under different stresses. In the permeability test process, the flow rate is selected as the critical flow rate of the test sample corresponding to the critical flow rate of the test group; the fluid for permeability test is the critical salinity brine of the test group; the permeability test under initial stress is carried out first, then the stress is gradually increased to the maximum stress value, and then the stress is gradually reduced to the final stress, and the permeability test is carried out under each stress value for a certain time, the initial stress is the reservoir effective stress of the target reservoir, the final stress is equal to the initial stress, the confining pressure is kept unchanged, and the appropriate back pressure is determined according to the stress value (the difference between confining pressure and back pressure is stress).

[0273] Based on the permeability of test sample 6 under different stresses, the permeability under initial stress is taken as the reference permeability, and the permeability retention rate of test sample 6 under different stresses is determined respectively, and the results are shown in Table 20. When the permeability retention rate measured in the process of gradually increasing the stress to the maximum stress value is not less than 80%, the maximum stress corresponding to the critical stress of test sample 6 is taken as the critical stress of the test group; the critical stress is 29 MPa. Wherein, the permeability retention rate is determined by the following formula:

[0274] wherein: vp is the permeability retention rate, unit %; Kp is the permeability under a certain stress, unit 10 -3 μm 2 ; Kip is the reference permeability, unit 10 -3 μm 2 .

[0275] Based on the permeability of the test sample 6 under different stresses, the stress sensitivity damage rate of the test sample 6 is determined as the stress sensitivity damage rate of the test group, and the results are shown in Table 20. Among them, the stress sensitivity damage rate is determined by the following formula:

[0276] wherein: Dp is the stress sensitivity damage rate, unit %; Kp is the permeability under a certain stress, unit 10 -3 μm 2 ; Kip is the reference permeability, unit 10 -3 μm 2 .

[0277] Table 20

[0278] In the test group, the stress sensitivity of the test sample 6 is determined, and the stress sensitivity of the test sample 6 is determined as the stress sensitivity of the test group. The stress sensitivity damage degree of the test sample 6 is evaluated based on the stress sensitivity damage rate of the test sample F, and the stress damage degree evaluation result of the test sample 6 is taken as the stress damage degree evaluation result of the test group. Among them, the stress sensitivity damage degree evaluation standard is shown in Table 21:

[0279] Table 21

[0280] For example, when the effective stress is 36.5 MPa, the stress sensitivity damage rate is Dp(78.48%)>70, and the damage degree is strong.

[0281] Based on the reference permeability and the permeability under the final stress of the test sample 6, the irreversible stress sensitivity damage rate of the test sample 6 is determined as the irreversible stress sensitivity damage rate of the test group, and the irreversible permeability damage rate is 45.57%. Among them, the irreversible stress sensitivity damage rate is determined by the following formula:

[0282] wherein: Dpn is the irreversible stress sensitivity damage rate, unit %; Kpn is the permeability under the final stress, unit 10 -3 μm 2 ; Kip is the reference permeability, unit 10-3 μm 2 .

[0283] The above-described specific embodiments further illustrate the objects, technical solutions, and advantages of the present application. It should be understood that the above-described specific embodiments are merely illustrative of the present application and are not intended to limit the scope of protection of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A method for evaluating sensitivity of a low permeability reservoir, the method comprising: Step 1, preparing test samples of a target reservoir using a full diameter core of the target reservoir; During the preparation of the test samples, the diameter of the full diameter core is not changed; Step 2, performing standard salt water permeability tests on each test sample respectively to determine the minimum flow rate at which each test sample can achieve a permeability test, i.e. the initial flow rate, and then grouping the test samples according to the size of the initial flow rate; Step 3, performing sensitivity tests on the test samples in the same group, including: taking a certain group of samples as a test group; taking A test samples from the test group to perform a flow rate sensitivity test, obtaining the critical flow rate of the A test samples as the critical flow rate of the test group, and using the initial flow rate of the A test samples as the minimum flow rate during the flow rate sensitivity test; taking B test samples from the test group to perform a water sensitivity test, obtaining the water sensitivity of the B test samples as the water sensitivity of the test group, and using the critical flow rate of the test group corresponding to the critical flow rate of the B test samples as the flow rate during the water sensitivity test; and / or taking C test samples from the test group to perform a salinity sensitivity test, obtaining the salinity sensitivity of the C test samples as the salinity sensitivity of the test group, and using the critical flow rate of the test group corresponding to the critical flow rate of the C test samples as the flow rate during the salinity sensitivity test; and / or taking D test samples from the test group to perform an acid sensitivity test, obtaining the acid sensitivity of the D test samples as the acid sensitivity of the test group, and using the critical flow rate of the test group corresponding to the critical flow rate of the D test samples as the flow rate during the acid sensitivity test; and / or taking E test samples from the test group to perform an alkali sensitivity test, obtaining the alkali sensitivity of the E test samples as the alkali sensitivity of the test group, and using the critical flow rate of the test group corresponding to the critical flow rate of the E test samples as the flow rate during the alkali sensitivity test; and / or taking F test samples from the test group to perform a stress sensitivity test, obtaining the stress sensitivity of the F test samples as the stress sensitivity of the test group, and using the critical flow rate of the test group corresponding to the critical flow rate of the F test samples as the flow rate during the stress sensitivity test.

2. The method of claim 1, wherein, The preparation of the test samples of the target reservoir using the full diameter core of the target reservoir includes: length cutting the full diameter core of the target reservoir to obtain a core with a length not less than 1.5 times the diameter as the test sample of the target reservoir.

3. The method of claim 1, wherein, The preparation of the test samples of the target reservoir using the full diameter core of the target reservoir includes: length cutting the full diameter core of the target reservoir to obtain a core with a length of 0.5-1 times the diameter as the test sample of the target reservoir.

4. The method of claim 1, wherein, The standard salt water permeability tests performed on each test sample respectively to determine the minimum flow rate at which each test sample can achieve a permeability test, i.e. the initial flow rate, include: performing standard salt water permeability tests on each test sample respectively at a first flow rate, and the initial flow rate of each test sample that can achieve a permeability test is the first flow rate, and test samples that cannot achieve a permeability test are recorded as remaining test samples; respectively, and the initial flow rate of each test sample capable of achieving the permeability test is the second flow rate, and each test sample incapable of achieving the permeability test is recorded as a remaining test sample; The step of repeatedly performing the standard saline permeability test on each remaining test sample at a flow rate greater than the ith flow rate is repeated until the number of remaining test samples is 0.

5. The method of claim 1, wherein, The step of taking A test samples in the to-be-tested group to perform the flow rate sensitivity test comprises: The step of taking A test samples in the to-be-tested group to perform the standard saline permeability test at different flow rates respectively to obtain the permeability of the A test samples at different flow rates comprises: first performing the standard saline permeability test at a low flow rate, and then performing the standard saline permeability test at a high flow rate, wherein the lowest flow rate is the initial flow rate of the A test samples; The critical flow rate of the A test samples is determined by the following method: The step of determining the permeability retention rate of the A test samples at different flow rates based on the permeability data of the A test samples at different flow rates comprises: taking the permeability at the initial flow rate as the reference permeability. The highest flow rate corresponding to the permeability retention rate not lower than 80% is taken as the critical flow rate of the A test samples, and the critical flow rate corresponding to the critical flow rate of the A test samples is taken as the critical flow rate of the A test samples.

6. The method of claim 5, wherein, The method further comprises: determining, based on the permeability data of the A test sample at different flow rates, the flow rate sensitivity damage rate of the A test sample at different flow rates as the flow rate sensitivity damage rate of the to-be-tested group; wherein the flow rate sensitivity damage rate takes the permeability at the initial flow rate as the reference permeability, and the flow rate sensitivity damage rate is determined by the following formula: In the formula: Dn is the flow rate sensitivity damage rate, unit %; Kin is the reference permeability, unit 10 -3 μm 2 ; Kn is the permeability under a certain flow rate, unit 10 -3 μm 2 .

7. The method of claim 6, wherein, The method further comprises: performing the flow rate sensitivity damage degree evaluation of the A test samples based on the flow rate sensitivity damage rate of the A test samples, and taking the flow rate sensitivity damage degree evaluation result of the A test samples as the flow rate sensitivity damage degree evaluation result of the to-be-tested group.

8. The method of claim 1, wherein, The step of taking B test samples in the to-be-tested group to perform the water sensitivity test comprises: The step of taking B test samples in the to-be-tested group comprises: First, performing the standard saline permeability test on the B test samples at the critical flow rate of the to-be-tested group to obtain the standard saline permeability of the B test samples; then, performing the 1 / 2 standard saline permeability test on the B test samples at the critical flow rate of the to-be-tested group to obtain the 1 / 2 standard saline permeability of the B test samples; and further, performing the distilled water permeability test on the B test samples at the critical flow rate of the to-be-tested group to obtain the distilled water permeability of the B test samples; The step of obtaining the water sensitivity of the B test samples as the water sensitivity of the to-be-tested group comprises: obtaining the water sensitivity damage rate of the B test samples as the water sensitivity damage rate of the to-be-tested group; The water sensitivity damage rate of the B test sample is determined as the water sensitivity damage rate of the to-be-tested group based on the standard saline permeability of the B test sample and the distilled water permeability of the B test sample; wherein the water sensitivity damage rate is determined by the following formula: wherein: Dw is the water sensitivity damage rate, in %; Kiw is the standard brine permeability, in 10 -3 μm 2 ; Kw is the distilled water permeability, in 10 -3 μm 2 .

9. The method of claim 1, wherein, The step of obtaining the water sensitivity of the B test samples as the water sensitivity of the to-be-tested group further comprises: performing the water sensitivity damage degree evaluation of the B test samples based on the water sensitivity damage rate of the B test samples, and obtaining the water sensitivity damage degree evaluation result of the B test samples as the water sensitivity damage degree evaluation result of the to-be-tested group.

10. The method of claim 1, wherein, C test samples are taken from the group to be tested to perform the salt sensitivity test, and the salt sensitivity of the C test samples is obtained as the salt sensitivity of the group to be tested, including: C test samples are taken from the group to be tested; The C test samples are respectively subjected to different salt concentration brine permeability tests at the critical flow rate of the test sample corresponding to the critical flow rate of the group to be tested, and the permeability of the C test samples under different salt concentrations is obtained; wherein, the high salt concentration brine permeability test is performed first, and then the low salt concentration brine permeability test is performed, the highest salt concentration brine is standard salt water, and the lowest salt concentration brine is distilled water; Based on the permeability of the C test samples under different salt concentrations, the permeability retention rates of the C test samples under different salt concentrations are determined respectively; wherein, the permeability retention rate is based on the permeability under standard salt water as the reference permeability; The salinity of the minimum concentration brine corresponding to the permeability retention rate of not less than 80% is taken as the critical salinity of the test sample, that is, the critical salinity of the group to be measured; wherein the permeability retention rate is determined by the following formula: wherein: vsn is the permeability retention rate, unit %; Ks is the permeability under a certain salt concentration brine, unit 10 -3 μm 2 ; Kis is the permeability under standard brine, i.e. initial permeability, unit 10 -3 μm 2 .

11. The method of claim 1, wherein, During the acid sensitivity test, the permeability test fluid has a salinity equal to the critical salinity of the group to be tested; D test samples are taken from the group to be tested to perform the acid sensitivity test, including: D test samples are taken from the group to be tested; First, the D test samples are subjected to a group to be tested critical salinity brine permeability test at the critical flow rate of the test sample corresponding to the critical flow rate of the group to be tested, and the permeability of the D test samples before acid action is obtained; then, the acid liquid is displaced into the D test samples and the D test samples are reacted with the acid liquid for a period of time; further, the D test samples are subjected to a group to be tested critical salinity brine permeability test at the critical flow rate of the test sample corresponding to the critical flow rate of the group to be tested, and the permeability of the D test samples after acid action is obtained; The acid sensitivity of the D test samples is obtained as the acid sensitivity of the group to be tested, including: the acid sensitivity damage rate of the D test samples is obtained as the acid sensitivity damage rate of the group to be tested; The acid sensitivity damage rate of the test sample D is determined as the acid sensitivity damage rate of the to-be-tested group based on the permeability of the test sample D before acid action and the permeability of the test sample D after acid action, wherein the acid sensitivity damage rate is determined by the following formula: wherein: Dac is the acid sensitive damage rate in %; Kiac is the permeability before acid action in 10 -3 μm 2 ; Kac is the permeability after acid action in 10 -3 μm 2 .

12. The method of claim 10, wherein, The acid sensitivity of the D test samples is obtained as the acid sensitivity of the group to be tested, including: the acid sensitivity damage rate of the D test samples is obtained as the acid sensitivity damage rate of the group to be tested; The acid sensitivity of the D test samples is obtained as the acid sensitivity of the group to be tested, including: the acid sensitivity damage rate of the D test samples is obtained as the acid sensitivity damage rate of the group to be tested.

13. The method of claim 1, wherein, During the base sensitivity test, the permeability test fluid has a salinity equal to the critical salinity of the group to be tested; E test samples are taken from the group to be tested to perform the base sensitivity test, including: E test samples are taken from the group to be tested; The E test samples are respectively subjected to different pH solution permeability tests at the critical flow rate of the test sample corresponding to the critical flow rate of the group to be tested, and the permeability of the E test samples under different pH solutions is obtained; wherein, the low pH solution permeability test is performed first, and then the high pH solution permeability test is performed, the pH of the solution is 7-14, the pH of the lowest pH solution is 7, and the salinity of the solution is equal to the critical salinity of the group to be tested; the reference permeability of the E test samples; The base sensitivity of the E test samples is obtained as the base sensitivity of the group to be tested, including: the critical pH value of the E test samples is obtained as the critical pH value of the group to be tested, and / or the base sensitivity damage rate of the E test samples is obtained as the base sensitivity damage rate of the group to be tested; The critical pH value of the E test sample is determined by the following method: Based on the permeability of the E test sample in different pH value solutions, the permeability retention rate of the E test sample in different pH value solutions is determined respectively, wherein the permeability retention rate is based on the permeability of the E test sample in the solution with a pH value of 7 as the reference permeability; The pH value of the highest pH value solution corresponding to the permeability retention rate not less than 80% is taken as the critical pH value of the E test sample; The alkali sensitivity damage rate of the E test sample is determined based on the permeability of the E test sample in solutions with different pH values, wherein the alkali sensitivity damage rate is determined based on the permeability of the E test sample in a solution with a pH value of 7 as the reference permeability, and the alkali sensitivity damage rate is determined by the following formula: In the formula: Dal is the base-sensitivity damage rate, unit %; Kial is the reference permeability, unit 10 -3 μm 2 ; Kal is the permeability under a certain pH value of alkali solution, unit 10 -3 μm 2 .

14. The method of claim 13, wherein, The alkali sensitivity of the E test sample is obtained as the alkali sensitivity of the test group, and the alkali sensitivity damage degree evaluation of the E test sample is performed based on the alkali sensitivity damage rate of the E test sample, and the alkali sensitivity damage degree evaluation result of the E test sample is obtained as the alkali sensitivity damage degree evaluation result of the test group.

15. The method of claim 1, wherein, The fluid used in the permeability test during the stress sensitivity test process is the critical salinity brine of the test group; The F test sample is taken from the test group to perform the stress sensitivity test, and the stress sensitivity of the F test sample is obtained as the stress sensitivity of the test group. The F test sample is taken from the test group; The permeability of the F test sample under different stresses is tested, and the permeability of the F test sample under different stresses is obtained; during the permeability test, the flow rate is selected as the critical flow rate of the test sample corresponding to the critical flow rate of the test group; the fluid used in the permeability test is the critical salinity brine of the test group; the permeability test under the initial stress is performed first, then the stress is gradually increased to the maximum stress value, and then the stress is gradually reduced to the final stress, and the permeability test is performed under each stress value for a predetermined time and under each stress value, respectively; the initial stress is the reservoir effective stress of the target reservoir, and the final stress is equal to the initial stress; During the permeability test of the F test sample under different stresses, the confining pressure remains unchanged, and the appropriate back pressure is determined according to the stress value.

16. The method of claim 15, wherein, The stress sensitivity of the F test sample is obtained as the stress sensitivity of the test group, including obtaining the critical stress of the F test sample as the critical stress of the test group, and / or obtaining the irreversible stress sensitivity damage rate of the F test sample as the irreversible stress sensitivity damage rate of the test group; The critical stress of the F test sample is determined by the following method: Based on the permeability of the F test sample under different stresses, the permeability retention rate of the F test sample under different stresses is determined, and the permeability under the initial stress is taken as the reference permeability; The maximum stress corresponding to the permeability retention rate not less than 80% during the process of gradually increasing the stress to the maximum stress value is taken as the critical stress of the F test sample; The irreversible stress sensitivity damage rate of the F test sample is determined by taking the permeability under the initial stress as the reference permeability based on the permeability under the initial stress and the permeability under the final stress of the F test sample, and the irreversible stress sensitivity damage rate of the F test sample is taken as the irreversible stress sensitivity damage rate of the group to be measured. wherein: Dpn is the irreversible stress-sensitive damage rate, in %; Kpn is the permeability at the final stress, in 10 -3 μm 2 ; Kip is the reference permeability, in 10 -3 μm 2 .

17. The method of claim 15, wherein, The stress sensitivity of the F test sample is obtained as the stress sensitivity of the test group, including obtaining the critical stress of the F test sample as the critical stress of the test group, and / or obtaining the irreversible stress sensitivity damage rate of the F test sample as the irreversible stress sensitivity damage rate of the test group, and / or obtaining the stress sensitivity damage rate of the F test sample as the stress sensitivity damage rate of the test group; The stress sensitivity damage rate of the F test sample is determined based on the permeability of the F test sample under different stresses, with the permeability under the initial stress as the reference permeability, to obtain the stress sensitivity damage rate of the F test sample as the stress sensitivity damage rate of the group to be measured; wherein the stress sensitivity damage rate is determined by the following formula: wherein: Dp is the stress sensitivity damage rate, unit %; Kp is the permeability under certain stress, unit 10 -3 μm 2 ; Kip is the reference permeability, unit 10 -3 μm 2 .

18. The method of claim 17, wherein, The stress sensitivity of the F test sample is obtained as the stress sensitivity of the test group, and further includes: evaluating the stress sensitivity damage degree of the F test sample based on the stress sensitivity damage rate of the F test sample, and obtaining the stress damage degree evaluation result of the F test sample as the stress sensitivity damage degree evaluation result of the test group.

19. The method of any one of claims 1-18, wherein, The solutions used during the sensitivity test process have a salinity provided by NaCl, an alkalinity provided by NaOH, and an acidity provided by HCl.

20. The method of any one of claims 1-18, wherein, The permeability test adopts an ultra-low permeability tester, wherein the lower limit of the test is not more than 10 -4 MPa, and the upper limit of the confining pressure is not less than 80 MPa.

Images