Reservoir sand production risk prediction method under gas storage injection-production circulation

Abstract

The invention discloses a reservoir sand production risk prediction method under gas storage injection-production circulation. The reservoir sand production risk prediction method sequentially comprises the following steps that S1, a sandstone reservoir is machined into a standard cylindrical rock core sample; s2, selecting a first group of rock core samples, carrying out a uniaxial compression test, and calculating uniaxial compressive strength and uniaxial compression elasticity modulus; s3, selecting a second group of rock core samples, carrying out a triaxial compression test, and calculating triaxial compressive strength; s4, selecting a third group of rock core samples, performing a triaxial cyclic loading and unloading test, and drawing a cyclic loading and unloading stress-strain curve; s5, preliminarily evaluating the sand production of the sandstone under cyclic loading and unloading, and calculating damage factors in the cyclic loading and unloading process of the rock core; and S6, predicting the reservoir sand production risk through the compressive strength after cyclic damage. The reservoir sand production risk prediction method under the gas storage injection-production circulation provides a scientific basis for guiding gas storage injection-production operation in actual production, is expected to effectively reduce negative effects of a sand production phenomenon on production, and improves production efficiency and operation safety.

Description

Technical Field

[0001] The invention relates to an underground gas storage, and in particular to a method for predicting sand production risk in a reservoir during injection-production cycle of a gas storage, and belongs to the technical field of construction and operation of underground gas storage. Background Art

[0002] In the field of oil production, gas storage injection and production cycle is a common operation method used to improve oil and gas production efficiency. However, during the injection and production cycle, the mechanical properties of the reservoir rock may change, resulting in sand shedding, which in turn affects the normal operation and production efficiency of the production equipment. Therefore, the prediction of the critical pressure difference of reservoir sand production under cycle has become an important topic.

[0003] In the prior art, the research on the sand production problem of the reservoir under the injection-production cycle of the gas storage mainly has the following problems:

[0004] 1. The prediction of critical pressure difference of sand production in existing gas storage reservoirs mainly relies on empirical methods and local test data, which lacks systematicity and scientificity.

[0005] 2. The existing indoor test simulation method for reservoir sand production cannot accurately consider the operating characteristics of the gas storage reservoir, that is, the impact of the injection and production cycle of the gas storage reservoir on the reservoir sand production, nor can it consider the damage caused by the alternating load of the confining pressure to the gas storage reservoir, resulting in sand production in the gas storage reservoir.

[0006] 3. Most of the existing reservoir critical pressure difference prediction methods for sand production are based on indoor test results or numerical simulation results. Most of the indoor test results cannot take into account the triaxial stress state of the reservoir.

[0007] Based on the above background, this prediction method makes up for the shortcomings of existing technologies and establishes a scientific and reliable prediction model through systematic experiments and analysis. Summary of the invention

[0008] The purpose of this section is to summarize some aspects of embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the specification abstract and the invention title of this application to avoid blurring the purpose of this section, the specification abstract and the invention title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0009] In view of the above problems and / or the problems existing in the prior art, the present invention is proposed.

[0010] The purpose of the present invention is to overcome the problems existing in the prior art and provide a method for predicting the risk of sand production in a reservoir during the injection and production cycle of a gas storage reservoir, which can comprehensively consider the impact of the three-dimensional stress state of the formation and the damage caused to the reservoir by the operating characteristics of the injection and production process of the gas storage reservoir.

[0011] In order to solve the above technical problems, the method for predicting the risk of sand production in a gas storage reservoir during injection and production cycle of the present invention comprises the following steps in sequence:

[0012] S1. Process the sandstone reservoir into a standard cylindrical core sample;

[0013] S2. Select the first group of core samples and conduct uniaxial compression test to obtain the uniaxial compressive strength UCS0 and uniaxial compressive elastic modulus Ee;

[0014] S3, select the second group of core samples, conduct triaxial compression test, and obtain the triaxial compressive strength TCS0;

[0015] S4, selecting the third group of core samples, conducting triaxial cyclic loading and unloading tests, and drawing cyclic loading and unloading stress-strain curves;

[0016] S5. Preliminary evaluation of sand production of sandstone under cyclic loading and unloading and calculation of damage factors during cyclic loading and unloading of cores;

[0017] S6. Predict the risk of reservoir sand production by compressive strength after cyclic damage.

[0018] Furthermore, step S2 specifically includes the following sub-steps:

[0019] S2.1. Place the core sample vertically on the pressure plate of the rock multi-field coupled triaxial testing machine to ensure that the axis of the core is consistent with the loading direction;

[0020] S2.2, start the testing machine and load with displacement control until the core sample is destroyed. During the whole process, continuously record the load and the corresponding displacement or deformation, and record the maximum load F and the corresponding displacement during the test;

[0021] S2.3. Draw the stress-strain curve of the core sample according to the axial deformation and radial deformation of the core sample in the uniaxial compression test;

[0022] S2.4. Calculate the uniaxial compressive strength UCS0 and the uniaxial compressive elastic modulus Ee based on the stress-strain curve of the uniaxial compression test.

[0023] Furthermore, in step S2.4, the calculation formula of the uniaxial compressive strength UCS0 of sandstone is as follows:

[0024]

[0025] Where UCS0 is the uniaxial compressive strength of sandstone, MPa; F is the maximum failure load of sandstone core during loading, N; A is the cross-sectional area of ​​the core sample, mm 2 .

[0026] Furthermore, in step S2.4, the calculation formula of the uniaxial compression elastic modulus Ee is as follows:

[0027]

[0028] Wherein, Ee is the elastic modulus of sandstone in uniaxial stress, MPa; σa is the stress value at the starting point of the straight line segment on the uniaxial stress-axial strain curve, MPa; σb is the stress value at the end point of the straight line segment on the uniaxial stress-axial strain curve, MPa; εha represents the axial strain value at stress at σa; εhb represents the axial strain value at stress at σb.

[0029] Furthermore, step S3 specifically includes the following sub-steps:

[0030] S3.1. Place the core sample vertically in the confining pressure chamber of the rock multi-field coupled triaxial testing machine, start the testing machine, use displacement control to load, and continuously record the axial load until the core fails, and record the maximum failure load F. tri , and continuously record the axial strain and lateral strain during the test;

[0031] S3.2. Draw the stress-strain curve of the triaxial compression test according to the axial deformation and lateral deformation of the core sample in the triaxial compression test;

[0032] S3.3. According to the stress-strain curve of the triaxial compression test, calculate the triaxial compressive strength TCS0.

[0033] Furthermore, in step S3.3, the triaxial compressive strength TCS0 of sandstone is calculated as follows:

[0034]

[0035] TCS0=σ1-σ3 (5)

[0036] Where, TCS0 is the triaxial compressive strength of the core sample, MPa; F tri is the maximum failure load during the core sample loading process (N); σ1 is the maximum principal stress, MPa; σ3 is the confining pressure, MPa; A is the cross-sectional area of ​​the core sample, mm 2 .

[0037] Furthermore, the calculation formula of confining pressure is as follows:

[0038] σ3=h×ρ×g (6)

[0039] Where σ3 represents the confining pressure, MPa; h represents the depth of the reservoir rock, m; ρ represents the density of the overlying stratum, kg / m 3 ; g represents the acceleration due to gravity, m / s 2 .

[0040] Furthermore, step S4 specifically includes the following sub-steps:

[0041] S4.1. Select core samples, check and calibrate triaxial test equipment;

[0042] S4.2, simulate the injection and production cycle of the gas storage, set the upper limit stress of the cycle to 70% of the triaxial compressive strength TCS0, set the lower limit stress of the cycle to 30% of the triaxial compressive strength TCS0, and set the operating life of the gas storage to the number of cycles;

[0043] S4.3. Collect the loading force and displacement during the cyclic loading and unloading test in real time and draw the cyclic loading and unloading stress-strain curve.

[0044] Furthermore, step S5 specifically includes the following sub-steps:

[0045] S5.1. Calculate the dynamic elastic modulus E based on the cyclic loading and unloading stress-strain curve d , taking the uniaxial compression elastic modulus Ee as the critical standard value, when the dynamic elastic modulus E d When the uniaxial compression elastic modulus Ee is greater than the uniaxial compression elastic modulus Ee, it is judged that there is no risk of sand production; when the dynamic elastic modulus Ee is greater than the uniaxial compression elastic modulus Ee, it is judged that there is no risk of sand production. d When it is less than the uniaxial compression elastic modulus Ee, it is preliminarily determined that there is a risk of sand production in the core section, and the next step is continued for judgment;

[0046] S5.2. Calculation of the damage factor D during the core cyclic loading and unloading process i .

[0047] Furthermore, in step S5.1, the dynamic elastic modulus E d The following formula is used for calculation:

[0048]

[0049] Where: E d is the average dynamic elastic modulus during cyclic loading and unloading, MPa; σ dmax is the maximum stress value of a hysteresis loop during cyclic loading and unloading, MPa; σ dmin is the minimum stress value of a hysteresis loop during cyclic loading and unloading, MPa; ε dmin is the minimum strain value of a hysteresis loop during cyclic loading and unloading; ε ds is the initial strain value of a hysteresis loop during the cyclic loading and unloading process; ε de It is the strain value at the end of a hysteresis loop during the cyclic loading and unloading process.

[0050] Furthermore, in step S5.2, the damage factor D i The calculation formula is as follows:

[0051]

[0052] Where: i is the number of cyclic loading and unloading; ε0 is the axial strain at the beginning of the cycle; ε n is the axial strain at the end of the cycle; ε i is the axial strain at the peak point of the i-th cycle.

[0053] Furthermore, step S6 specifically includes the following sub-steps:

[0054] S6.1. Obtain the relationship between the core uniaxial compression strength and the core density by linear fitting method;

[0055] S6.2. Based on the relationship between the core uniaxial compression strength and the core density and combined with the density distribution of the entire well section, the distribution curve of the rock uniaxial compressive strength of the entire well section is calculated;

[0056] S6.3. Damage factor D obtained from cyclic loading and unloading test i The relationship between the number of cycles and the UCS distribution curve after formation damage in the entire well section under different injection and production cycles of the gas storage is obtained.

[0057] Furthermore, in step S6.3, the uniaxial compressive strength formula of the gas storage reservoir after the i-th injection and production cycle is as follows:

[0058] UCS i =(1-D i )·UCS0 (9)

[0059] P cr =UCS i (10)

[0060] Among them: UCS i is the uniaxial compressive strength of the rock formation after considering damage reduction, MPa; D i is the damage factor after the injection and production cycle i; UCS0 is the uniaxial compressive strength, MPa, P cr It is defined as the post-cyclic damage compressive strength considering the rock damage after cyclic injection and production;

[0061] According to P cr The critical sand pressure difference curve of the whole well section is drawn based on the calculation results, and the design compressive strength P determined when designing the gas storage is used. pro The red line is the reference. When the compressive strength after cyclic damage is P cr Lower than the design compressive strength P pro When , it means that there is a risk of sand production in the well section.

[0062] Compared with the prior art, the present invention has achieved the following beneficial effects: 1. This prediction method, through indoor tests, takes into account the operation characteristics of the injection-production cycle of the gas storage reservoir, and simulates the damage effect of the injection-production cycle of the gas storage reservoir on the reservoir; based on the results of the indoor tests, the existing theory is revised to establish a prediction method for the critical pressure difference of the gas storage reservoir taking into account the reservoir damage, which is systematic and scientific;

[0063] 2. This prediction method takes into account the three-dimensional stress state of the reservoir and the damage caused by the injection and production cycle operation characteristics of the gas storage reservoir. The triaxial cyclic loading and unloading test system is used to measure the changes in the mechanical properties of the reservoir rock during the injection and production cycle of the gas storage reservoir, further revealing the damage evolution characteristics of the rock under cyclic loading and unloading, and simulating and predicting the compressive strength after cyclic damage under actual working conditions;

[0064] 3. Combining experimental data and calculation of damage factors, a method for predicting the risk of sand production under the injection and production cycle of gas storage reservoirs was established, which provides a scientific basis for guiding the injection and production operations of gas storage reservoirs in actual production. It is expected to effectively reduce the negative impact of sand production on production and improve production efficiency and operational safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without creative work. The accompanying drawings are only provided for reference and explanation, and are not used to limit the present invention.

[0066] in:

[0067] Figure 1 This is a flow chart of a method for predicting reservoir sand production risk during injection-production cycle of a gas storage facility of the present invention;

[0068] Figure 2 is a schematic diagram of a sandstone specimen in the present invention;

[0069] Figure 3 It is a schematic diagram of the principle of the uniaxial compression test in the present invention;

[0070] Figure 4 is a stress-strain curve diagram of the UCS-1 core in the uniaxial compression test of the present invention;

[0071] Figure 5 It is a schematic diagram of the principle of the triaxial cyclic loading and unloading test in the present invention;

[0072] Figure 6 is a stress-strain curve diagram of the TCS-1 core in the triaxial compression test of the present invention;

[0073] Figure 7 It is a curve diagram showing the relationship between the formation depth of the gas storage reservoir and the density change of the test piece in the present invention;

[0074] Figure 8 is the loading and unloading path diagram of the TCL-1 core in the cyclic loading and unloading test of the present invention;

[0075] Fig. 9 It is a morphological comparison diagram of the TCL-1 core before and after destruction in the cyclic loading and unloading test of the present invention;

[0076] Fig.10 is a stress-strain curve diagram of the TCL-1 core in the cyclic loading and unloading test of the present invention;

[0077] Fig.11 is a graph showing the dynamic elastic modulus change of the TCL-1 core in the cyclic loading and unloading test of the present invention;

[0078] Fig.12 is the damage evolution diagram of the TCL-1 core in the cyclic loading and unloading test of the present invention;

[0079] Fig.13 is a curve diagram showing the fitting relationship between the density of the specimen and the UCS of the specimen in the uniaxial compression test of the present invention;

[0080] Fig.14 It is the UCS distribution curve diagram of the formation rock in the whole well section in the present invention;

[0081] Fig.15 It is a UCS distribution curve diagram after formation damage in the entire well section under different times of injection and production cycles of the gas storage in the present invention. DETAILED DESCRIPTION

[0082] In order to make the technical means, creative features, objectives and effects of the present invention easier to understand, the present invention is further described below in conjunction with specific diagrams. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them.

[0083] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0084] like Figure 1 As shown, the method for predicting the risk of sand production in a gas storage reservoir during injection and production cycle of the present invention comprises the following steps in sequence:

[0085] S1. Process the sandstone reservoir into a standard cylindrical core sample. The specific steps are as follows:

[0086] S1.1. On-site core sampling: select representative locations in the sandstone reservoir to drill holes, process the core samples to remove impurities, cut them into standard cylindrical sandstone core samples with a diameter of 25 mm and a height of 50 mm, and perform standardized processing on the cut sandstone core samples to ensure that the size and shape of the sandstone core samples meet the test requirements;

[0087] S1.2. Take nine standard cylindrical specimens and number them, such as Figure 2 The specific arrangement and numbering are as follows:

[0088] three for uniaxial compression tests, numbered UCS-1, UCS-2, and UCS-3;

[0089] three for triaxial compression tests, numbered TCS-1, TCS-2, and TCS-3;

[0090] Three are used for triaxial cyclic loading tests and are numbered TCL-1, TCL-2, and TCL-3.

[0091] S2. Select core samples numbered UCS-1, UCS-2, and UCS-3 to conduct uniaxial compression tests. The specific steps and example analysis are as follows:

[0092] S2.1, such as Figure 3 As shown, the UCS-1 core sample is selected and placed vertically on the pressure plate of the YDO-500G rock multi-field coupled triaxial testing machine to ensure that the axis of the core is consistent with the loading direction.

[0093] S2.2. Start the testing machine. The experiment uses displacement-controlled loading at a rate of 0.001 mm / s until the core sample is damaged. During the whole process, the load and the corresponding displacement or deformation are continuously recorded. The maximum load F, the corresponding displacement and the appearance of the core when it is damaged are recorded during the test.

[0094] S2.3. According to the axial deformation and radial deformation of the core sample in the uniaxial compression test, draw the stress-strain curve of the core sample, such as Figure 4 shown.

[0095] S2.4. Based on the stress-strain curve of the uniaxial compression test, the following mechanical parameters are calculated, including: uniaxial compressive strength UCS0, uniaxial compression elastic modulus Ee, and Poisson's ratio μe.

[0096] Among them, the calculation formula of the uniaxial compressive strength UCS0 of sandstone is as follows:

[0097]

[0098] Where UCS0 is the uniaxial compressive strength of sandstone, MPa; F is the maximum failure load of sandstone core during loading, N; A is the cross-sectional area of ​​the core sample, mm 2 .

[0099] The uniaxial compression elastic modulus Ee and Poisson's ratio μe are calculated as follows:

[0100]

[0101] Where, Ee is the elastic modulus of sandstone in uniaxial compression, MPa;

[0102] μe is the Poisson’s ratio in the uniaxial sandstone;

[0103] σa is the stress value at the starting point of the straight line segment on the uniaxial stress-axial strain curve, MPa;

[0104] σb is the stress value at the end point of the straight line segment on the uniaxial stress-axial strain curve, MPa;

[0105] εha represents the axial strain value of stress at σa;

[0106] εhb represents the axial strain value of stress at σb;

[0107] εda represents the radial strain value of stress at σa;

[0108] εdb represents the radial strain value of stress at σb.

[0109] Taking the UCS-1 core sample as an example, the core information and mechanical parameters obtained by uniaxial compression are as follows:

[0110]

[0111] Select UCS-2 and UCS-3 core samples, repeat the above steps, and calculate the average values ​​of uniaxial compressive strength and elastic modulus.

[0112] S3. Select core samples numbered TCS-1, TCS-2, and TCS-3 to conduct triaxial compression tests. The specific steps and example analysis are as follows:

[0113] S3.1, if Figure 5 As shown, a core sample numbered TCS-1 was selected and placed vertically in the confining pressure chamber of the YDO-500G rock multi-field coupled triaxial testing machine. The testing machine was started. The experiment adopted displacement control loading, with a loading rate of 0.001 mm / s and a confining pressure loading rate of 0.05 MPa / s. During the whole process, the axial load was continuously recorded until the core was damaged, and the maximum damage load F was recorded. tri , and continuously record the axial strain and lateral strain during the test.

[0114] S3.2. According to the axial deformation and lateral deformation of the core sample in the triaxial compression test, draw the stress-strain curve of the triaxial compression test, such as Figure 6 shown.

[0115] S3.3. Based on the stress-strain curve of the triaxial compression test, calculate the triaxial compressive strength, elastic modulus, Poisson's ratio and other mechanical parameters.

[0116] The calculation formula of triaxial compressive strength TCS0 of sandstone is as follows:

[0117]

[0118] Where, TCS0 is the triaxial compressive strength of the core sample, MPa;

[0119] F tri is the maximum failure load during the core sample loading process (N);

[0120] σ1 is the maximum principal stress, MPa;

[0121] σ3 is the confining pressure, MPa;

[0122] A is the cross-sectional area of ​​the core sample, mm 2 .

[0123] The confining pressure calculation formula is as follows:

[0124] σ3=h×ρ×g (6)

[0125] Where σ3 represents the confining pressure, MPa; h represents the depth of the reservoir rock, m; ρ represents the density of the overlying stratum, kg / m 3 ; g represents the acceleration due to gravity, m / s 2 .

[0126] Figure 7 The figure shows the relationship between the depth and density of the gas storage reservoir. The depth of the formation where the core is located is 3770m. According to the above formula, the confining pressure σ3 is 47.6MPa, and the confining pressure loading rate is 0.05MPa / s.

[0127] Taking the TCS-1 core sample as an example, the core information and mechanical parameters obtained by triaxial compression are as follows:

[0128]

[0129] The TCS-2 and TCS-3 core samples were operated in the same manner as above.

[0130] S4. Conduct triaxial cyclic loading and unloading tests to determine the mechanical properties of reservoir rock during the injection and production cycle of the gas storage reservoir. The specific steps are as follows:

[0131] S4.1. In order to determine the mechanical properties of reservoir rocks during the injection and production cycle of the gas storage facility, core samples numbered TCL-1, TCL-2, and TCL-3 were selected to ensure their representativeness and integrity.

[0132] Check all parts of the triaxial testing instrument to ensure normal operation and calibration.

[0133] S4.2. During the injection and production process of the gas storage, the reservoir rock will be subjected to cyclic stress from gas injection and production. In order to simulate this stress state, the upper limit stress of the cycle is set to 70% of the triaxial compressive strength TCS0, and the lower limit stress of the cycle is set to 30% of the triaxial compressive strength TCS0. The operating life of the gas storage is 60 years, and the reservoir rock will experience 60 such stress cycles. Therefore, the cycles applied in the test are set to 60 times.

[0134] S4.3, taking TCL-1 core sample as an example, Figure 8 The loading and unloading paths are shown. Cyclic loads are applied to simulate the operating cycles in the gas storage reservoir and to determine the frequency and amplitude of the loading.

[0135] Fig. 9 The figure shows the morphological comparison of the TCL-1 core sample before and after failure. During the loading process, the deformation and failure process of the TCL-1 core sample was observed and recorded.

[0136] The mechanical parameters during the cyclic loading and unloading test, including loading force and displacement, are collected in real time through the sensors or data acquisition system of the loading equipment. The cyclic loading and unloading stress-strain curve is drawn based on the recorded loading and unloading data. Fig.10 shown.

[0137] S5. Preliminary evaluation of sand production under cyclic loading and unloading and calculation of damage factors during cyclic loading and unloading of cores

[0138] S5.1. Based on experimental observation and analysis, preliminarily evaluate whether the TCL-1 core sample has sand production. Focus on factors such as stability, particle consolidation, and internal stress distribution during the cyclic loading and unloading process of the core sample. Calculate the dynamic elastic modulus of the core sample based on the experimental results. Fig.10 In the cyclic loading and unloading stress-strain curve shown, the area of ​​the hysteresis loop reflects the degree of energy loss during the loading and unloading process. The average slope, that is, the dynamic elastic modulus, is calculated using the following formula:

[0139]

[0140] Where: E dis the average dynamic elastic modulus during cyclic loading and unloading, MPa; σ dmax is the maximum stress value of a hysteresis loop during cyclic loading and unloading, MPa; σ dmin is the minimum stress value of a hysteresis loop during cyclic loading and unloading, MPa; ε dmin is the minimum strain value of a hysteresis loop during cyclic loading and unloading; ε ds is the initial strain value of a hysteresis loop during the cyclic loading and unloading process; ε de It is the strain value at the end of a hysteresis loop during the cyclic loading and unloading process.

[0141] The dynamic elastic modulus of the TCL-1 core sample changes as follows Fig.11 As shown. Taking the uniaxial compression elastic modulus Ee as the critical standard value, when the dynamic elastic modulus E d When the uniaxial compression elastic modulus Ee is greater than the uniaxial compression elastic modulus Ee, it is judged that there is no risk of sand production; when the dynamic elastic modulus Ee is greater than the uniaxial compression elastic modulus Ee, it is judged that there is no risk of sand production. d When it is less than the uniaxial compression elastic modulus Ee, it is preliminarily determined that the core section may have the risk of sand production, and the next step is proceeded to make further judgment.

[0142] S5.2. Calculation of damage factors during core cyclic loading and unloading

[0143] During the injection-production cycle of the gas storage reservoir, the mechanical integrity of the reservoir rock at the injection-production stress peak point is an important basis for judging sand production. Considering the damage development conditions of the entire fatigue process, the stress peak point of each cycle is selected as the observation point. Based on this, the calculation expression of the damage factor during the core cyclic loading and unloading process is as follows:

[0144]

[0145] Where: D i is the damage factor of the core during cyclic loading and unloading; i is the number of cyclic loading and unloading; ε0 is the axial strain at the beginning of the cycle, at which the damage factor D0 = 0; ε n is the axial strain at the end of the cycle, and the damage factor D n =1;ε i is the axial strain at the peak point of the i-th cycle. Thus, the curve of the damage factor changing with the number of cycles under cyclic loading and unloading of the core is calculated, as shown in Fig.12 shown.

[0146] S6. Predicting the risk of reservoir sand production by compressive strength after cyclic damage

[0147] S6.1. Fitting of uniaxial compression strength and density logging curves

[0148] The relationship curve between the uniaxial compression strength UCS and the core density obtained by the uniaxial compression experiment is plotted and fitted, as shown in Fig.13 The relationship between the core uniaxial compression strength and the core density is obtained by linear fitting method, which provides basic data for the subsequent analysis of the prediction of the uniaxial compressive strength of the rock in the whole well section.

[0149] S6.2. Calculate the uniaxial compressive strength distribution curve of the rock in the entire well section

[0150] by Fig.13 Based on the relationship between the uniaxial compression strength of the core and the core density, combined with Figure 7 The density distribution of the entire well section is shown, and the uniaxial compressive strength distribution curve of the rock in the entire well section is calculated, as shown in Fig.14 shown.

[0151] S6.3. Distribution of uniaxial compressive strength of the entire well section considering formation damage after cyclic injection and production

[0152] Using the damage factor calculation results and combining them with the damage factor D obtained in the cyclic loading and unloading test i The relationship between the damage factor and the number of cycles is extracted after 20, 40, and 60 cycles, and the UCS curve is updated to obtain the following: Fig.15 The UCS distribution curve of the whole well section after formation damage under different injection and production cycles of the gas storage is shown. Based on the upper and lower limit stresses of the gas storage operation, it can be judged whether sand production will occur in the reservoir. The uniaxial compressive strength formula of the gas storage after the i-th injection and production cycle is as follows:

[0153] UCS i =(1-D i )·UCS0 (9)

[0154] P cr =UCS i (10)

[0155] Among them: UCS i is the uniaxial compressive strength of the rock formation after considering damage reduction, MPa; D i is the damage factor after the injection and production cycle i; UCS0 is the uniaxial compressive strength, MPa, P cr The post-cyclic damage compressive strength is calculated to consider the damage of rock after cyclic injection and production.

[0156] S6.4. Identification of sand-producing well sections after injection-production cycle rock damage

[0157] Fig.15 The uniaxial compressive strength distribution curve of the whole well section under different injection and production cycles of the gas storage, where the red line is the design compressive strength P determined when designing the gas storage. pro .

[0158] According to the calculation results of formula (10), the compressive strength curve P of the whole well section after cyclic damage is drawn cr, when the compressive strength after cyclic damage P cr Lower than the design compressive strength P pro When , it means that there is a risk of sand production in the well section.

[0159] This method can effectively evaluate the stability of gas storage in long-term injection-production cycles and provide a scientific basis for reservoir management and optimization.

[0160] The above is only a preferred embodiment of the present invention, which shows and describes the basic principles, main features and advantages of the present invention, but does not limit the scope of patent protection of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. In addition to the above embodiments, the present invention may have other implementation modes without departing from the spirit and scope of the present invention. The present invention may also have various changes and improvements, and all technical solutions formed by equivalent substitution or equivalent transformation fall within the scope of protection required by the present invention. The scope of protection required by the present invention is defined by the attached claims and their equivalents. The technical features not described in the present invention can be realized by or using existing technologies, which will not be repeated here.

Claims

1. A method for predicting the risk of sand production in a gas storage reservoir during injection and production cycles, characterized in that: The steps are as follows: S1. Process the sandstone reservoir into a standard cylindrical core sample; S2. Select the first group of core samples and conduct uniaxial compression test to obtain the uniaxial compressive strength UCS0 and uniaxial compressive elastic modulus Ee; S3, select the second group of core samples, conduct triaxial compression test, and obtain the triaxial compressive strength TCS0; S4, selecting the third group of core samples, conducting triaxial cyclic loading and unloading tests, and drawing cyclic loading and unloading stress-strain curves; S5. Preliminary evaluation of sand production of sandstone under cyclic loading and unloading and calculation of damage factors during cyclic loading and unloading of cores; S6. Predict the risk of reservoir sand production by compressive strength after cyclic damage.

2. The method for predicting the risk of sand production in a gas storage reservoir during injection and production cycle according to claim 1, characterized in that: Step S2 specifically includes the following sub-steps: S2.

1. Place the core sample vertically on the pressure plate of the rock multi-field coupled triaxial testing machine to ensure that the axis of the core is consistent with the loading direction; S2.2, start the testing machine and load with displacement control until the core sample is destroyed. During the whole process, continuously record the load and the corresponding displacement or deformation, and record the maximum load F and the corresponding displacement during the test; S2.

3. Draw the stress-strain curve of the core sample according to the axial deformation and radial deformation of the core sample in the uniaxial compression test; S2.

4. Calculate the uniaxial compressive strength UCS0 and the uniaxial compressive elastic modulus Ee based on the stress-strain curve of the uniaxial compression test.

3. The method for predicting sand production risk in a gas storage reservoir during injection-production cycle according to claim 2, characterized in that: In step S2.4, the calculation formula of the uniaxial compressive strength UCS0 of sandstone is as follows: Where UCS0 is the uniaxial compressive strength of sandstone, MPa; F is the maximum failure load of sandstone core during loading, N; A is the cross-sectional area of ​​the core sample, mm 2 .

4. The method for predicting sand production risk in a gas storage reservoir during injection-production cycle according to claim 2, characterized in that: In step S2.4, the calculation formula of the uniaxial compression elastic modulus Ee is as follows: Wherein, Ee is the elastic modulus of sandstone in uniaxial stress, MPa; σa is the stress value at the starting point of the straight line segment on the uniaxial stress-axial strain curve, MPa; σb is the stress value at the end point of the straight line segment on the uniaxial stress-axial strain curve, MPa; εha represents the axial strain value at stress at σa; εhb represents the axial strain value at stress at σb.

5. The method for predicting sand production risk in a gas storage reservoir during injection-production cycle according to claim 2, characterized in that: Step S3 specifically includes the following sub-steps: S3.

1. Place the core sample vertically in the confining pressure chamber of the rock multi-field coupled triaxial testing machine, start the testing machine, use displacement control to load, and continuously record the axial load until the core fails, and record the maximum failure load F. tri , and continuously record the axial strain and lateral strain during the test; S3.

2. Draw the stress-strain curve of the triaxial compression test according to the axial deformation and lateral deformation of the core sample in the triaxial compression test; S3.

3. According to the stress-strain curve of the triaxial compression test, calculate the triaxial compressive strength TCS0.

6. The method for predicting sand production risk in a gas storage reservoir during injection-production cycle according to claim 5, characterized in that: In step S3.3, the triaxial compressive strength TCS0 of sandstone is calculated as follows: TCS0=σ1-σ3 (5) Where, TCS0 is the triaxial compressive strength of the core sample, MPa; F tri is the maximum failure load during the core sample loading process (N); σ1 is the maximum principal stress, MPa; σ3 is the confining pressure, MPa; A is the cross-sectional area of ​​the core sample, mm 2 .

7. The method for predicting sand production risk in a gas storage reservoir during injection-production cycle according to claim 6, characterized in that: The calculation formula of confining pressure is as follows: σ3=h×ρ×g (6) Where σ3 represents the confining pressure, MPa; h represents the depth of the reservoir rock, m; ρ represents the density of the overlying stratum, kg / m 3 ; g represents the acceleration due to gravity, m / s 2 .

8. The method for predicting sand production risk in a gas storage reservoir during injection-production cycle according to claim 6, characterized in that: Step S4 specifically includes the following sub-steps: S4.

1. Select core samples, check and calibrate triaxial test equipment; S4.2, simulate the injection and production cycle of the gas storage, set the upper limit stress of the cycle to 70% of the triaxial compressive strength TCS0, set the lower limit stress of the cycle to 30% of the triaxial compressive strength TCS0, and set the operating life of the gas storage to the number of cycles; S4.

3. Collect the loading force and displacement during the cyclic loading and unloading test in real time and draw the cyclic loading and unloading stress-strain curve.

9. The method for predicting the risk of sand production in a gas storage reservoir during injection and production cycles according to claim 1, characterized in that: Step S5 specifically includes the following sub-steps: S5.

1. Calculate the dynamic elastic modulus E based on the cyclic loading and unloading stress-strain curve d , taking the uniaxial compression elastic modulus Ee as the critical standard value, when the dynamic elastic modulus E d When the uniaxial compression elastic modulus Ee is greater than the uniaxial compression elastic modulus Ee, it is judged that there is no risk of sand production; when the dynamic elastic modulus Ee is greater than the uniaxial compression elastic modulus Ee, it is judged that there is no risk of sand production. d When it is less than the uniaxial compression elastic modulus Ee, it is preliminarily determined that there is a risk of sand production in the core section, and the next step is continued for judgment; S5.

2. Calculation of the damage factor D during the core cyclic loading and unloading process i .

10. The method for predicting the risk of sand production in a gas storage reservoir during injection and production cycles according to claim 9, characterized in that: In step S5.1, the dynamic elastic modulus E d The following formula is used for calculation: Where: E d is the average dynamic elastic modulus during cyclic loading and unloading, MPa; σ dmax is the maximum stress value of a hysteresis loop during cyclic loading and unloading, MPa; σ dmin is the minimum stress value of a hysteresis loop during cyclic loading and unloading, MPa; ε dmin is the minimum strain value of a hysteresis loop during cyclic loading and unloading; ε ds is the initial strain value of a hysteresis loop during the cyclic loading and unloading process; ε de It is the strain value at the end of a hysteresis loop during the cyclic loading and unloading process.

11. The method for predicting sand production risk in a gas storage reservoir during injection-production cycle according to claim 9, characterized in that: In step S5.2, the damage factor D i The calculation formula is as follows: Where: i is the number of cyclic loading and unloading; ε0 is the axial strain at the beginning of the cycle; ε n is the axial strain at the end of the cycle; ε i is the axial strain at the peak point of the i-th cycle.

12. The method for predicting sand production risk in a gas storage reservoir during injection-production cycle according to claim 1, characterized in that: Step S6 specifically includes the following sub-steps: S6.

1. Obtain the relationship between the core uniaxial compression strength and the core density by linear fitting method; S6.

2. Based on the relationship between the core uniaxial compression strength and the core density and combined with the density distribution of the entire well section, the distribution curve of the rock uniaxial compressive strength of the entire well section is calculated; S6.

3. Damage factor D obtained from cyclic loading and unloading test i The relationship between the number of cycles and the UCS distribution curve after formation damage in the entire well section under different injection and production cycles of the gas storage is obtained.

13. The method for predicting sand production risk in a gas storage reservoir during injection-production cycle according to claim 12, characterized in that: In step S6.3, the uniaxial compressive strength formula of the gas storage after the i-th injection and production cycle is as follows: UCS i =(1-D i )·UCS0 (9) P cr =UCS i (10) Among them: UCS i is the uniaxial compressive strength of the rock formation after considering damage reduction, MPa; D i is the damage factor after the injection and production cycle i; UCS0 is the uniaxial compressive strength, MPa, P cr It is defined as the post-cyclic damage compressive strength considering the rock damage after cyclic injection and production; According to P cr The critical sand pressure difference curve of the whole well section is drawn based on the calculation results, and the design compressive strength P determined when designing the gas storage is used. pro The red line is the reference. When the compressive strength after cyclic damage is P cr Lower than the design compressive strength P pro When , it means that there is a risk of sand production in the well section.

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