Method and device for evaluating water blocking damage rate of drilling fluid

Abstract

The invention discloses a method for evaluating the water blocking damage rate of drilling fluid. The method comprises the following steps: performing rock sample saturation and pore volume measurement on a first rock core in a plurality of rock cores from the same area; performing a critical flow test on the first rock core to obtain a critical flow bearable by the first rock core; determining irreducible water saturation for a second rock core in the plurality of rock cores from the same area, and testing initial oil phase permeability based on conditions of the irreducible water saturation; contaminating the second core with a drilling fluid filtrate; testing the oil phase permeability of the polluted second rock core; according to the initial oil phase permeability and the polluted oil phase permeability of the second rock core, the drilling fluid water blocking damage rate is calculated. The low-permeability sandstone hydrocarbon reservoir drilling fluid water blocking damage rate evaluation method is constructed from the aspects of invasion mechanism analysis, invasion mode simulation, experimental process design and the like, and data support is provided for drilling fluid reservoir damage diagnosis and targeted protection technology selection.

Description

Technical Field

[0001] The invention relates to the technical field of drilling fluid in the process of oil and natural gas development, and in particular to an evaluation method and device for the water lock damage rate of drilling fluid. Background Art

[0002] Water lock damage is the capillary resistance caused by the displacement of the wetting phase by the non-wetting phase, which leads to a decrease in the permeability of the oil phase. During the drilling process, the drilling fluid damages the reservoir in the form of solid phase blockage and liquid phase damage. In low-permeability and ultra-low-permeability oil and gas layers, water lock damage is one of the main forms of damage.

[0003] Since the 1990s, some scholars at home and abroad have conducted a certain degree of research on water lock damage and water lock damage removal and mitigation of condensate oil and gas wells, but the focus is on gas layer water lock, and the mechanism research is mainly carried out, and the water lock experimental research method is rarely involved. Due to the existence of various wettabilities in actual reservoirs, water-based drilling fluids invading oil and gas layers are likely to produce water lock effects under different rock wettability conditions, forming resistance to oil flow and reducing oil well production. There is no standard for the evaluation method of drilling fluid oil and gas layer water lock damage rate, and no relevant patents have been published. Summary of the invention

[0004] In view of the difficulty in evaluating the water lock damage rate of drilling fluid, the present invention is proposed to provide a method for evaluating the water lock damage rate of drilling fluid that overcomes the above problem or at least partially solves the above problem.

[0005] On the one hand, an embodiment of the present invention provides a method for evaluating the water lock damage rate of drilling fluid, comprising:

[0006] Saturate the first core of multiple cores from the same area and determine the pore volume;

[0007] Performing a critical flow test on the first core to obtain a critical flow that the first core can withstand;

[0008] determining irreducible water saturation for a second core among the plurality of cores from the same region, and testing initial oil phase permeability based on the irreducible water saturation;

[0009] Contaminating the second core with drilling fluid filtrate; and testing the oil phase permeability of the second core after contamination;

[0010] The drilling fluid water lock damage rate was calculated based on the initial oil phase permeability and the oil phase permeability after contamination of the second core.

[0011] In one embodiment, before the steps of saturating the first core among the multiple cores from the same area and measuring the pore volume, the method for evaluating the water lock damage rate of the drilling fluid further includes:

[0012] A plurality of rock cores from the same area are pre-processed; the pre-processing comprises: cleaning the plurality of rock cores with a cleaning solvent under pressure and heating conditions.

[0013] In one embodiment, determining irreducible water saturation and testing initial oil phase permeability of the second core among the multiple cores from the same area includes:

[0014] measuring the length and diameter of the second core;

[0015] Drying the second core to a constant weight, and recording the dry weight of the second core;

[0016] Performing negative pressure evacuation and saturation on the second core, and recording the wet weight of the second core after the negative pressure evacuation and saturation;

[0017] The second core is placed in a core holder, and at the formation temperature, a displacement solvent is used to displace the second core at a preset multiple of a critical flow rate until no water is produced and a stable pressure is achieved in the second core, and an actual flow rate and equilibrium pressure of the displacement solvent are measured when no water is produced and the pressure is stable;

[0018] measuring the weight of the second core after displacement with the displacement solvent;

[0019] Calculating irreducible water saturation according to the dry weight of the second core, the wet weight of the second core after saturation by negative pressure evacuation, the weight of the second core after displacement by the displacement solvent, the density of formation water and the density of the displacement solvent;

[0020] The initial oil phase permeability is calculated based on the actual flow rate and equilibrium pressure of the displacement solvent when no water is produced and the pressure is stable, the viscosity of the displacement solvent, and the length and diameter of the second core.

[0021] In one embodiment, the step of loading the second core into a core holder, displacing the second core with a displacement solvent at a preset multiple of a critical flow rate until no water is produced in the second core and the pressure is stable, and measuring the actual flow rate and equilibrium pressure of the displacement solvent when no water is produced and the pressure is stable, comprises:

[0022] The second core is placed in a core holder, and driven with a displacement solvent at 0.4 times the critical flow rate at formation temperature until no water is produced and the pressure is stable;

[0023] The second core is placed in a core holder, and driven with a displacement solvent at 0.8 times the critical flow rate at formation temperature until no water is produced and the pressure is stable;

[0024] At the formation temperature, the displacement solvent is driven at 0.5 times the critical flow rate until no water is produced in the second core and the pressure is stable, and the actual flow rate and equilibrium pressure of the solvent when no water is produced and the pressure is stable are measured.

[0025] In one embodiment, the calculating of irreducible water saturation according to the dry weight of the second core, the wet weight of the second core after saturation by negative pressure evacuation, the weight of the second core after displacement by a displacement solvent, the density of formation water and the density of the displacement solvent includes:

[0026] Substitute the dry weight of the second core, the wet weight of the second core after saturation by negative pressure evacuation, the weight of the second core after displacement by the displacement solvent, the density of the formation water and the density of the displacement solvent into the following formula to calculate the irreducible water saturation of the second core:

[0027]

[0028] Where: S wi is the irreducible water saturation, G3 is the weight of the second core after displacement with the displacement solvent, G1 is the dry weight of the second core, ρ 模拟地层水 is the density of simulated formation water, G2 is the wet weight of the second core after saturation by negative pressure evacuation, ρ 驱替溶剂 is the density of the displacing solvent.

[0029] In one embodiment, the contaminating the second core with drilling fluid filtrate comprises:

[0030] preparing drilling fluid filtrate;

[0031] Test the contents of various fluid ions in the drilling fluid filtrate, and count the contents of all fluid ions in the drilling fluid filtrate as the mineralization of the drilling fluid filtrate;

[0032] Comparing the mineralization of the drilling fluid filtrate with the preset mineralization thresholds corresponding to each fluid ion, adjusting the content of the fluid ions in the drilling fluid filtrate so that the mineralization of the drilling fluid filtrate is not lower than the mineralization thresholds corresponding to each fluid ion;

[0033] The drilling fluid filtrate is used to reverse displace a preset multiple of the pore volume of the second core at the formation temperature.

[0034] In one embodiment, testing the post-contamination oil phase permeability of the second core comprises:

[0035] Under the conditions of formation temperature and preset multiple of critical flow rate, use the displacement solvent to displace until no water is produced and the pressure is stable in the second core, measure the actual flow rate and equilibrium pressure of the displacement solvent when no water is produced and the pressure is stable, and calculate the post-contamination oil phase permeability based on the actual flow rate and equilibrium pressure of the displacement solvent when no water is produced and the pressure is stable, the displacement solvent viscosity, and the length and diameter of the second core.

[0036] In one embodiment, the calculation of the initial oil phase permeability and the calculation of the oil phase permeability after contamination are performed as follows:

[0037] Substitute the actual flow rate of the displacement solvent when no water is produced and the pressure is stable, the equilibrium pressure when no water is produced and the pressure is stable, the viscosity of the displacement solvent, and the length and diameter of the second core into the following formula:

[0038]

[0039] Where: μ is the viscosity of the displacement solvent, L is the length of the second core, q is the actual flow rate of the displacement solvent when there is no water and the pressure is stable, A is the area of ​​the core end face, P0 is the equilibrium pressure when there is no water and the pressure is stable, π is the circumference, and d is the diameter of the second core.

[0040] In one embodiment, the calculating the drilling fluid water lock damage rate according to the initial oil phase permeability and the oil phase permeability after contamination of the second core includes:

[0041] Calculate the difference between the oil phase permeability after contamination and the initial oil phase permeability;

[0042] The percentage of the difference and the initial oil phase permeability is calculated to obtain the drilling fluid water lock damage rate.

[0043] In one embodiment, the steps are performed while also comprising:

[0044] The length, diameter, wet weight after saturation by negative pressure evacuation, dry weight and density of simulated formation water of the second core are substituted into the following formula to calculate the porosity of the second core:

[0045]

[0046] in: is the porosity of the second core, V 孔隙 is the pore volume, V 岩心 is the total volume of the core, G2 is the wet weight of the second core after vacuum saturation, G1 is the dry weight of the second core, ρ 模拟地层水 is the density of simulated formation water, π is the circumference of a circle, d is the diameter of the second core, and L is the length of the second core.

[0047] The beneficial effects of the above technical solution provided by the embodiment of the present invention include at least:

[0048] An embodiment of the present invention provides a method and device for evaluating the water lock damage rate of drilling fluid, comprising: saturating a first core among multiple cores from the same area and measuring the pore volume; performing a critical flow test on the first core to obtain a critical flow that the first core can withstand; determining the irreducible water saturation of a second core among the multiple cores from the same area, and testing the initial oil phase permeability based on the irreducible water saturation; contaminating the second core with drilling fluid filtrate; testing the oil phase permeability of the second core after contamination; and calculating the water lock damage rate of drilling fluid according to the initial oil phase permeability and the oil phase permeability after contamination of the second core. The embodiment of the present invention is suitable for evaluating the water lock damage rate of drilling fluid on reservoirs. The embodiment of the present invention uses drilling fluid filtrate for reverse displacement, fully considering the influence of surfactant components contained in the drilling fluid filtrate on the wettability of the core, and the water lock damage rate result of the test is more realistic; moreover, the experimental process considers the influence of water-sensitive damage, and reduces the pollution by adjusting the mineralization of the contaminated fluid during the experiment; it is suitable for grassroots oil and gas layer protection technology research laboratories and is suitable for future standard formulation. The experimental process constructed by the present invention and the equipment and materials involved are easy to implement in grassroots oil and gas layer protection technology research laboratories.

[0049] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description, claims, and drawings.

[0050] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0052] Figure 1 A flow chart of a method for evaluating the water lock damage rate of drilling fluid provided by an embodiment of the present invention;

[0053] Figure 2 A flow chart of a method for testing initial oil phase permeability based on irreducible water saturation provided in an embodiment of the present invention;

[0054] Figure 3 Flow chart of the method for testing the permeability of oil phase after pollution provided by the embodiment of the present invention

[0055] Figure 4 This is a structural block diagram of a displacement device provided in an embodiment of the present invention.

[0056] Description of reference numerals:

[0057] 1- horizontal flow pump, 2- first valve, 3- intermediate device, 4- second valve, 5- third valve, 6- first displacement tank, 7- first piston, 8- first pressure gauge, 9- fourth valve, 10- second displacement tank, 11- second piston, 12- second pressure gauge, 13- fifth valve, 14- core holder, 15- core, 16- sixth valve, 17- measuring cylinder. DETAILED DESCRIPTION

[0058] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0059] In order to solve the problem that the water lock damage rate of the drilling fluid filtrate is difficult to evaluate, an embodiment of the present invention provides a method for evaluating the water lock damage rate of the drilling fluid, and its flow chart is as follows: Figure 1 As shown, including:

[0060] Step S11, saturating the first core among multiple cores from the same area and measuring the pore volume;

[0061] Step S12, performing a critical flow test on the first core to obtain a critical flow that the first core can withstand;

[0062] Step S13, determining irreducible water saturation of a second core among the multiple cores from the same area, and testing initial oil phase permeability based on the irreducible water saturation;

[0063] Step S14, using drilling fluid filtrate to contaminate the second core; testing the oil phase permeability of the second core after contamination;

[0064] Step S15: Calculate the drilling fluid water lock damage rate according to the initial oil phase permeability and the oil phase permeability after contamination of the second core.

[0065] For the convenience of distinction, different cores representing the same area are respectively referred to as the first core and the second core.

[0066] The above-mentioned drilling fluid water lock damage rate evaluation method provided in the embodiment of the present invention is aimed at the problem that there is currently a lack of effective evaluation methods for evaluating the degree of water lock damage of drilling fluid on oil and gas layers. A low-permeability sandstone oil and gas layer drilling fluid water lock damage rate evaluation method is constructed from the aspects of invasion mechanism analysis, invasion mode simulation, experimental process design, etc., to provide data support for the diagnosis of drilling fluid reservoir damage and the selection of targeted protection technology.

[0067] At the same time, the experimental process constructed by the present invention, the equipment and materials involved can be realized in the grassroots oil and gas layer protection technology research laboratory, which is convenient for further establishing the water lock damage rate evaluation standard.

[0068] In order to clean hydrocarbons and salts in the cores, before the above step S11, the evaluation method of the drilling fluid water lock damage rate can also perform preliminary processing on multiple cores from the same area;

[0069] The above-mentioned preliminary treatment may, for example, be to clean the multiple cores using a cleaning solvent under pressurized and heated conditions; the magnitude of the applied pressure and the temperature may, for example, depend on the lithology of the cores, which may include permeability and porosity; the cleaning solvent may be selected based on the composition of the rock sample, and if the composition of the rock sample is unknown, for example, a mixture of toluene and ethanol may be used; for example, the cleaning may be terminated when the extract shows kerosene fluorescence under fluorescence.

[0070] Before the first core is saturated in the above step S11, and after the above-mentioned pre-treatment of the core, the core may be dried to reduce the influence of the cleaning solvent on the saturation of the rock sample; the drying treatment may be carried out by placing the core in an oven, and the oven may be a conventional oven, a vacuum oven, etc.; the drying standard may be, for example, taking out the core and weighing it at a preset time interval, and the difference between the weight values ​​of the two weighings is lower than a preset value;

[0071] The preset time interval may be, for example, 4 hours, 8 hours or 16 hours; the preset value of the difference between the weight values ​​of two weighings may be, for example, 10 mg.

[0072] In the above step S11, the rock sample saturation of the first core may be performed, for example, in the following manner:

[0073] Under negative pressure evacuation conditions, the dried first core is immersed in a saturated liquid for saturation. The saturation time is not less than a preset saturation time threshold, which may be 40 hours, for example.

[0074] The pore volume of the first core after saturation is measured. For example, the dry weight of the first core can be recorded by weighing it after drying, and the wet weight of the first core can be recorded by weighing it after saturation. The dry weight of the first core, the wet weight of the first core and the density of the saturated liquid at the temperature when the core is saturated are substituted into the following formula to calculate the pore volume:

[0075]

[0076] Where V p is the pore volume, m1 is the wet weight of the first core, m0 is the dry weight of the first core, and ρ is the density of the saturated fluid at the temperature when the above core is saturated.

[0077] In the above step S12, the length and diameter of the first core are first measured, and then the saturated first core is placed in a core holder. Under a preset pressure and temperature, the fluid is passed through the core at a preset flow rate, and the end surface pressure at one end of the core into which the fluid flows is measured. A pressurization test is performed according to a certain flow gradient until the end surface pressure is greater than a preset threshold value; wherein the fluid may be, for example, formation brine or 8% (mass fraction) standard brine with a formula of 7:0.6:0.4 of NaCl:CaCl2:MgCl2·6H2O; the critical flow condition may be, for example, a point before the core permeability change rate is greater than 20%, and the corresponding displacement rate is the critical flow, and the pressure difference at both ends of the first core and the volume of the fluid passing through the first core per unit time under this condition are recorded.

[0078] The first core permeability can be calculated, for example, in the following manner:

[0079] Substitute the viscosity of the fluid under the test conditions, the length of the first core, the diameter of the first core, the volume of the fluid passing through the first core per unit time, and the pressure difference at both ends of the first core into the following formula:

[0080]

[0081] Where μ is the viscosity of the fluid under the test conditions, L1 is the length of the first core, A is the end surface area of ​​the first core, d1 is the diameter of the first core, Q is the volume of the fluid passing through the first core per unit time, and Δp is the pressure difference at both ends of the first core.

[0082] Finally, the permeability change rate of the first core can be calculated, for example, in the following way:

[0083] Substitute the first core permeability and the first core initial permeability into the following formula:

[0084]

[0085] Where Kn0 is the initial permeability of the first core, K n1 is the first core permeability.

[0086] The above-mentioned first core initial permeability is the first core permeability calculated when the test is just started.

[0087] In the above step S13, determining the irreducible water saturation of the second core among the multiple cores from the same area, and testing the initial oil phase permeability based on the irreducible water saturation condition specifically includes the following steps, and its flow chart is as follows: Figure 2 As shown:

[0088] Step S21, measuring the length and diameter of the second core;

[0089] Step S22, drying the second core to a constant weight, and recording the dry weight of the second core;

[0090] Step S23, vacuum evacuating and saturating the second core, and recording the wet weight of the second core after vacuum evacuating and saturating;

[0091] Step S24, loading the second core into a core holder, displacing the second core with a displacement solvent at a preset multiple critical flow rate at formation temperature until no water is produced in the second core and the pressure is stable, and measuring the actual flow rate and equilibrium pressure of the displacement solvent when no water is produced and the pressure is stable;

[0092] Step S25, measuring the weight of the second core after displacement by the displacement solvent;

[0093] Step S26, calculating irreducible water saturation according to the dry weight of the second core, the wet weight of the second core after saturation by negative pressure evacuation, the weight of the second core after displacement by the displacement solvent, the density of formation water and the density of the displacement solvent;

[0094] Step S27, calculating the initial oil phase permeability according to the actual flow rate and equilibrium pressure of the displacement solvent when no water is produced and the pressure is stable, the viscosity of the displacement solvent, and the length and diameter of the second core.

[0095] Since the negative pressure evacuation and saturation of the core in the above step S23 is similar to the method of saturating the first core in the above step S12, it will not be described in detail here.

[0096] Specifically, in the above step S24, for example, the following three stages may be included:

[0097] Stage 1: Load the second core into the core holder and drive it with a displacement solvent at 0.4 times the critical flow rate at formation temperature until no water is produced and the pressure is stable;

[0098] Stage 2: Load the second core into a core holder and drive it with a displacement solvent at 0.8 times the critical flow rate at formation temperature until no water is produced and the pressure is stable;

[0099] Stage 3: At formation temperature, the displacement solvent is driven at 0.5 times the critical flow rate until no water is produced in the second core and the pressure is stable. The actual flow rate and equilibrium pressure of the solvent are measured when no water is produced and the pressure is stable.

[0100] Among them, stable pressure refers to the pressure on the end face of the core that contacts the displacement solvent. The end face pressure will become larger and larger as the displacement proceeds. When the end face pressure remains unchanged during the displacement, the value on the pressure gauge is the value of the stable pressure.

[0101] In the above step S26, the irreducible water saturation is calculated, for example, in the following manner:

[0102] Substitute the dry weight of the second core, the wet weight of the second core after saturation by negative pressure evacuation, the weight of the second core after displacement by the displacement solvent, the density of the formation water and the density of the displacement solvent into the following formula to calculate the irreducible water saturation of the second core:

[0103]

[0104] Where: S wi is the irreducible water saturation, G3 is the weight of the second core after displacement with the displacement solvent, G1 is the dry weight of the second core, ρ 模拟地层水 is the density of simulated formation water, G2 is the wet weight of the second core after saturation by negative pressure evacuation, ρ 驱替溶剂 is the density of the displacing solvent.

[0105] In the above step S14, the second core is contaminated with drilling fluid filtrate, for example, by following four steps, as shown in the flow chart. Figure 3 As shown:

[0106] Step S31, preparing drilling fluid filtrate;

[0107] Step S32, testing the contents of various fluid ions in the drilling fluid filtrate, and calculating the contents of all fluid ions in the drilling fluid filtrate as the mineralization of the drilling fluid filtrate;

[0108] Step S33, comparing the mineralization of the drilling fluid filtrate with the preset mineralization thresholds corresponding to the fluid ions, and adjusting the content of the fluid ions in the drilling fluid filtrate so that the mineralization of the drilling fluid filtrate is not lower than the mineralization thresholds corresponding to the fluid ions;

[0109] Step S34: using the drilling fluid filtrate to reversely displace a preset multiple of the pore volume of the second core at the formation temperature.

[0110] Specifically, in step S34, the drilling fluid filtrate is used to reversely displace a preset multiple of the pore volume of the second core, and the preset multiple may be, for example, 2 or 3 times.

[0111] Similarly, in the above step S14, the post-contamination oil phase permeability of the second core can be tested, for example, in the following manner:

[0112] Under the conditions of formation temperature and preset multiple of critical flow rate, use the displacement solvent to displace until no water is produced and the pressure is stable in the second core, measure the actual flow rate and equilibrium pressure of the displacement solvent when no water is produced and the pressure is stable, and calculate the post-contamination oil phase permeability based on the actual flow rate and equilibrium pressure of the displacement solvent when no water is produced and the pressure is stable, the displacement solvent viscosity, and the length and diameter of the second core.

[0113] Specifically, the calculation of the initial oil phase permeability and the oil phase permeability after contamination may be performed, for example, in the following manner:

[0114] Substitute the actual flow rate of the displacement solvent when no water is produced and the pressure is stable, the equilibrium pressure when no water is produced and the pressure is stable, the viscosity of the displacement solvent, and the length and diameter of the second core into the following formula:

[0115]

[0116] Where: μ is the viscosity of the displacement solvent, L is the length of the second core, q is the actual flow rate of the displacement solvent when there is no water and the pressure is stable, A is the area of ​​the core end face, P0 is the equilibrium pressure when there is no water and the pressure is stable, π is the circumference, and d is the diameter of the second core.

[0117] In the above step S15, calculating the drilling fluid water lock damage rate includes the following two steps:

[0118] Calculate the difference between the oil phase permeability after contamination and the initial oil phase permeability;

[0119] The percentage of the difference and the initial oil phase permeability is calculated to obtain the drilling fluid water lock damage rate.

[0120] In the above-mentioned evaluation method of the drilling fluid water lock damage rate, for example, the porosity of the second core can also be calculated. The porosity can be calculated, for example, in the following manner:

[0121] The length, diameter, wet weight after saturation by negative pressure evacuation, dry weight and density of simulated formation water of the second core are substituted into the following formula to calculate the porosity of the second core:

[0122]

[0123] in: is the porosity of the second core, V 孔隙 is the pore volume, V 岩心 is the total volume of the core, G2 is the wet weight of the second core after vacuum saturation, G1 is the dry weight of the second core, ρ 模拟地层水 is the density of simulated formation water, π is the circumference of a circle, d is the diameter of the second core, and L is the length of the second core.

[0124] In the above-mentioned method for evaluating the water lock damage rate of drilling fluid, for example, kerosene can be used as a displacement solvent, for example, Figure 4 The device shown displaces the core:

[0125] Reference Figure 4 As shown, the forward displacement process is as follows: during forward displacement, the first valve 2, the second valve 4, the fourth valve 9 and the sixth valve 16 are opened, and the core 15 is placed in the core holder 14; the horizontal flow pump 1 gives a steady pressure to the intermediate device 3, squeezing the first piston 7 in the first displacement tank 6 upward, thereby pressing the displacement solvent toward the core holder 14, and the core 15 in the core holder 14 is displaced by the displacement solvent, wherein the first pressure gauge 8 is used to detect the end face pressure of the core 15 receiving the displacement solvent displacement end, and the measuring cylinder 17 is used to receive the liquid flowing out of the core 15.

[0126] The reverse displacement process is as follows: during reverse displacement, the first valve 2, the third valve 5, the fifth valve 13 and the sixth valve 16 are opened, and the core 15 is placed in the core holder 14 in the opposite direction to the forward displacement; the horizontal flow pump 1 gives a steady pressure to the intermediate device 3, squeezing the first piston 7 in the first displacement tank 6 upward, thereby pressing the displacement solvent toward the core holder 14, and the core 15 in the core holder 14 is displaced by the displacement solvent, wherein the second pressure gauge 12 is used to detect the end face pressure of the core 15 receiving the displacement solvent, and the measuring cylinder 17 is used to receive the liquid flowing out of the core 15.

[0127] In the above two displacement processes, the intermediate device 3 is used to store liquid for driving the first piston 7 and the second piston 11 .

[0128] Next, two examples are used to describe in detail the evaluation method of the drilling fluid water lock damage rate:

[0129] Embodiment 1:

[0130] The water lock damage degree of drilling fluid in oil and gas layers is tested by the method of the present invention at 90°C using the core of site A and the drilling fluid of site A. The method specifically comprises the following steps:

[0131] (1) Core pretreatment: direct pressurized solvent flushing, cleaning hydrocarbons and salts in the rock sample under pressurized and heated conditions (the cleaning solvents are toluene and ethanol), the pressure is 500 psi, and the rock sample cleaning is completed after the extracting fluid shows no fluorescence under fluorescence.

[0132] (2) Conduct critical flow test;

[0133] The test results of critical flow are as follows:

[0134] Table 1 Results of velocity sensitivity test of rock in A site

[0135]

[0136] It can be seen from Table 1 that the displacement rate corresponding to a point before the permeability change rate is 20% is 0.75 mL / min, that is, the critical flow rate is 0.75 mL / min.

[0137] Speed-sensitive damage rate: 29.2%. The speed-sensitive damage rate is the largest of the above permeability change rates. The damage degree is weakly speed-sensitive. The damage degree can be confirmed, for example, by the following method:

[0138] When the speed-sensitive damage rate is less than or equal to 5%, it is no speed-sensitive; when the speed-sensitive damage rate is greater than 5% and less than or equal to 30%, it is weak speed-sensitive; when the speed-sensitive damage rate is greater than 30% and less than or equal to 50%, it is medium-weak speed-sensitive; when the speed-sensitive damage rate is greater than 50% and less than or equal to 70%, it is medium-strong speed-sensitive; when the speed-sensitive damage rate is greater than 70%, it is strong speed-sensitive.

[0139] (3) Determine bound water saturation and conduct initial oil phase permeability test:

[0140] Table 2A Determined irreducible water saturation and initial oil phase permeability

[0141]

[0142] In Table 2 above, L refers to the length of the core, d refers to the diameter of the core, φ refers to the porosity of the core, P0 refers to the stable pressure before the pollution displacement, q0 refers to the actual flow rate at the end of the measurement process, and K o Refers to the initial oil phase permeability, S wi refers to the irreducible water saturation, G1 refers to the dry weight of the core, G2 refers to the wet weight of the core after saturation, and G3 refers to the weight of the core after kerosene displacement.

[0143] (4) Conduct oil phase permeability test after pollution:

[0144] Table 3A Oil phase permeability test after ground pollution

[0145] Core number <![CDATA[P 01 ,MPa]]> <![CDATA[q 01 ,cm 3 / s]]> <![CDATA[K o1 ,10 -3 μm 2 ]]> 1-18 / 39 0.40 0.006 1.15

[0146] In Table 3 above, P 01 refers to the stable pressure of post-pollution displacement, q 01 Refers to the actual flow at the end of the measurement process, K o1 Refers to the oil phase permeability after pollution.

[0147] (5) Calculate the damage rate of penetration rate

[0148] R s1 (%) = (K o -K o1 )×100% / K o =(2.40-1.15)×100% / 2.40=52.1%

[0149] The water lock damage rate of the drilling fluid of site A tested by the present invention to the rock core of site A at 90° C. is 52.1%.

[0150] Embodiment 2:

[0151] The water lock damage degree of drilling fluid in oil and gas layers is tested by the method of the present invention at 100°C using the core of site B and the drilling fluid of site B. The method comprises the following steps:

[0152] (1) Core pretreatment: The core pretreatment is similar to that in Example 1 and will not be described in detail here.

[0153] (2) Test the critical flow rate:

[0154] Table 4B Rock velocity sensitivity test results

[0155]

[0156] It can be seen from Table 1 that the displacement rate corresponding to a point before the permeability change rate is 20% is 0.78 mL / min, that is, the critical flow rate is 0.78 mL / min.

[0157] Speed-sensitive damage rate: 16%, damage level is weakly speed-sensitive. The speed-sensitive damage rate and damage level are determined in a similar way to the speed-sensitive damage rate and damage level in Table 1, and will not be repeated here.

[0158] (3) Determine bound water saturation and conduct initial oil phase permeability test:

[0159] Table 5B Determined irreducible water saturation and initial oil phase permeability

[0160]

[0161] In Table 5, L refers to the length of the core, d refers to the diameter of the core, φ refers to the porosity of the core, and P 02refers to the stable pressure before pollution displacement, q 02 Refers to the actual flow at the end of the measurement process, K o2 Refers to the initial oil phase permeability, S wi refers to the irreducible water saturation, G1 refers to the dry weight of the core, G2 refers to the wet weight of the core after saturation, and G3 refers to the weight of the core after kerosene displacement.

[0162] (4) Conduct oil phase permeability test after pollution

[0163] Table 6B Oil phase permeability test after ground pollution

[0164] Core number <![CDATA[P 03 ,MPa]]> <![CDATA[q 03 ,cm 3 / s]]> <![CDATA[K o3 ,10 -3 μm 2 ]]> 1-18 / 39 0.023 0.00867 22.5

[0165] In Table 6, P 03 refers to the stable pressure of post-pollution displacement, q 03 Refers to the actual flow at the end of the measurement process, K o3 Refers to the oil phase permeability after pollution.

[0166] (5) Calculate the damage rate of penetration rate

[0167] R s1 (%) = (K o3 -K o2 )×100% / K o2 =(30.5-22.5)×100% / 30.5=26.2%.

[0168] By using the above method provided by the embodiment of the present invention, the water lock damage rate of the drilling fluid at site B to the core of site B at 90° C. was tested to be 26.2%.

[0169] Since the principles of solving the problems in these embodiments are similar to the aforementioned method for evaluating the water lock damage rate of drilling fluid, the implementation of these embodiments can refer to the implementation of the aforementioned method, and the repeated parts will not be repeated.

[0170] An embodiment of the present invention provides a method and device for evaluating the water lock damage rate of drilling fluid, comprising: saturating a first core among multiple cores from the same area and measuring the pore volume; performing a critical flow test on the first core to obtain a critical flow that the first core can withstand; determining the irreducible water saturation of a second core among the multiple cores from the same area, and testing the initial oil phase permeability based on the irreducible water saturation; contaminating the second core with drilling fluid filtrate; testing the oil phase permeability of the second core after contamination; and calculating the water lock damage rate of drilling fluid according to the initial oil phase permeability and the oil phase permeability after contamination of the second core. The embodiment of the present invention is suitable for evaluating water lock damage of oil and gas layers. The displacement fluid used in the present invention is anhydrous kerosene, and the test results are characterized by the degree of damage to the oil phase permeability, simulating the water lock damage caused by the invasion of water-based drilling fluid into the oil and gas layer; the embodiment of the present invention is suitable for evaluating the water lock damage rate of the drilling fluid on the reservoir. The embodiment of the present invention uses the drilling fluid filtrate for reverse displacement, and fully considers the influence of the surfactant components contained in the drilling fluid filtrate on the wettability of the core, and the water lock damage rate result of the test is more realistic; and the experimental process considers the influence of water-sensitive damage, and reduces the pollution by adjusting the mineralization of the contaminated fluid during the experiment; it is suitable for grassroots oil and gas layer protection technology research laboratories and is suitable for the formulation of standards in the future. The experimental process constructed by the present invention and the equipment and materials involved are easy to implement in grassroots oil and gas layer protection technology research laboratories.

[0171] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for evaluating the water lock damage rate of drilling fluid, characterized in that: include: Saturate the first core of multiple cores from the same area and determine the pore volume; Performing a critical flow test on the first core to obtain a critical flow that the first core can withstand; determining irreducible water saturation for a second core among the plurality of cores from the same region, and testing initial oil phase permeability based on the irreducible water saturation; contaminating the second core with drilling fluid filtrate; Testing the post-contamination oil phase permeability of the second core; The drilling fluid water lock damage rate was calculated based on the initial oil phase permeability and the oil phase permeability after contamination of the second core.

2. The method according to claim 1, characterized in that Before the steps of saturating the first core among the multiple cores from the same area and measuring the pore volume, the method for evaluating the water lock damage rate of the drilling fluid further includes: A plurality of rock cores from the same area are pre-processed; the pre-processing comprises: cleaning the plurality of rock cores with a cleaning solvent under pressure and heating conditions.

3. The method according to claim 1, characterized in that For the second core among the multiple cores from the same area, determining the irreducible water saturation and testing the initial oil phase permeability includes: measuring the length and diameter of the second core; Drying the second core to a constant weight, and recording the dry weight of the second core; Performing negative pressure evacuation and saturation on the second core, and recording the wet weight of the second core after the negative pressure evacuation and saturation; The second core is placed in a core holder, and at the formation temperature, a displacement solvent is used to displace the second core at a preset multiple of a critical flow rate until no water is produced and a stable pressure is achieved in the second core, and an actual flow rate and equilibrium pressure of the displacement solvent are measured when no water is produced and the pressure is stable; measuring the weight of the second core after displacement with the displacement solvent; Calculating irreducible water saturation according to the dry weight of the second core, the wet weight of the second core after saturation by negative pressure evacuation, the weight of the second core after displacement by the displacement solvent, the density of formation water and the density of the displacement solvent; The initial oil phase permeability is calculated based on the actual flow rate and equilibrium pressure of the displacement solvent when no water is produced and the pressure is stable, the viscosity of the displacement solvent, and the length and diameter of the second core.

4. The method according to claim 3, characterized in that The step of placing the second core into a core holder, displacing the second core with a displacement solvent at a preset multiple critical flow rate until no water is produced in the second core and the pressure is stable, and measuring the actual flow rate and equilibrium pressure of the displacement solvent when no water is produced and the pressure is stable, comprises: The second core is placed in a core holder, and driven with a displacement solvent at 0.4 times the critical flow rate at formation temperature until no water is produced and the pressure is stable; The second core is placed in a core holder, and driven with a displacement solvent at 0.8 times the critical flow rate at formation temperature until no water is produced and the pressure is stable; At the formation temperature, the displacement solvent is driven at 0.5 times the critical flow rate until no water is produced in the second core and the pressure is stable, and the actual flow rate and equilibrium pressure of the solvent when no water is produced and the pressure is stable are measured.

5. The method according to claim 3, characterized in that The calculating of irreducible water saturation according to the dry weight of the second core, the wet weight of the second core after saturation by negative pressure evacuation, the weight of the second core after displacement by the displacement solvent, the density of formation water and the density of the displacement solvent comprises: Substitute the dry weight of the second core, the wet weight of the second core after saturation by negative pressure evacuation, the weight of the second core after displacement by the displacement solvent, the density of the formation water and the density of the displacement solvent into the following formula to calculate the irreducible water saturation of the second core: Where: S wi is the irreducible water saturation, G3 is the weight of the second core after displacement with the displacement solvent, G1 is the dry weight of the second core, ρ 模拟地层水 is the density of simulated formation water, G2 is the wet weight of the second core after saturation by negative pressure evacuation, ρ 驱替溶剂 is the density of the displacing solvent.

6. The method according to claim 3, characterized in that The step of contaminating the second core with drilling fluid filtrate comprises: preparing drilling fluid filtrate; Test the contents of various fluid ions in the drilling fluid filtrate, and count the contents of all fluid ions in the drilling fluid filtrate as the mineralization of the drilling fluid filtrate; Comparing the mineralization of the drilling fluid filtrate with the preset mineralization thresholds corresponding to each fluid ion, adjusting the content of the fluid ions in the drilling fluid filtrate so that the mineralization of the drilling fluid filtrate is not lower than the mineralization thresholds corresponding to each fluid ion; The drilling fluid filtrate is used to reverse displace a preset multiple of the pore volume of the second core at the formation temperature.

7. The method according to claim 1, characterized in that The testing of the post-contamination oil phase permeability of the second core comprises: Under the conditions of formation temperature and preset multiple of critical flow rate, use the displacement solvent to displace until no water is produced and the pressure is stable in the second core, measure the actual flow rate and equilibrium pressure of the displacement solvent when no water is produced and the pressure is stable, and calculate the post-contamination oil phase permeability based on the actual flow rate and equilibrium pressure of the displacement solvent when no water is produced and the pressure is stable, the displacement solvent viscosity, and the length and diameter of the second core.

8. The method according to any one of claims 3 and 7, characterized in that The calculation of the initial oil phase permeability and the calculation of the oil phase permeability after contamination are performed as follows: Substitute the actual flow rate of the displacement solvent when no water is produced and the pressure is stable, the equilibrium pressure when no water is produced and the pressure is stable, the viscosity of the displacement solvent, and the length and diameter of the second core into the following formula: Where: μ is the viscosity of the displacement solvent, L is the length of the second core, q is the actual flow rate of the displacement solvent when there is no water and the pressure is stable, A is the area of ​​the core end face, P0 is the equilibrium pressure when there is no water and the pressure is stable, π is the circumference, and d is the diameter of the second core.

9. The method according to claim 1, characterized in that The calculation of the drilling fluid water lock damage rate according to the initial oil phase permeability and the oil phase permeability after pollution of the second core includes: Calculate the difference between the oil phase permeability after contamination and the initial oil phase permeability; The percentage of the difference and the initial oil phase permeability is calculated to obtain the drilling fluid water lock damage rate.

10. The method according to claim 3, characterized in that The steps of claim 3 also include: The length, diameter, wet weight after saturation by negative pressure evacuation, dry weight and density of simulated formation water of the second core are substituted into the following formula to calculate the porosity of the second core: in: is the porosity of the second core, V 孔隙 is the pore volume, V 岩心 is the total volume of the core, G2 is the wet weight of the second core after vacuum saturation, G1 is the dry weight of the second core, ρ 模拟地层水 is the density of simulated formation water, π is the circumference of a circle, d is the diameter of the second core, and L is the length of the second core.

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