WO2025256095A1 - 低渗储层敏感性评价方法 - Google Patents

低渗储层敏感性评价方法

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Publication number
WO2025256095A1
WO2025256095A1 PCT/CN2024/140892 CN2024140892W WO2025256095A1 WO 2025256095 A1 WO2025256095 A1 WO 2025256095A1 CN 2024140892 W CN2024140892 W CN 2024140892W WO 2025256095 A1 WO2025256095 A1 WO 2025256095A1
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Prior art keywords
test
sensitivity
permeability
test sample
stress
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English (en)
French (fr)
Inventor
高新平
杨建�
刘飞
韩慧芬
彭欢
朱世仁
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Petrochina Co Ltd
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Petrochina Co Ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/08—Investigating permeability, pore-volume, or surface area of porous materials
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/24—Earth materials

Definitions

  • This invention relates to the field of oil and gas field development engineering technology, specifically to a method for evaluating the sensitivity of low-permeability reservoirs.
  • reservoirs come into contact with various external fluids.
  • these external fluids have poor compatibility with reservoir rocks and/or formation water, or when technological measures are inappropriate, reservoir sensitivity can occur, leading to various physical and chemical reactions. This results in a decrease in the flow capacity of oil and gas in the reservoir, impairing its production capacity to varying degrees.
  • Drilling fluids with their specific salinity and pH value, are used during drilling. When these fluids penetrate the reservoir, they interact with the reservoir rocks, altering the reservoir's permeability.
  • reservoir stimulation is typically required for low-permeability reservoirs. This stimulation involves the use of working fluids such as pre-flush fluids, slickwater, and acid.
  • Test samples are typically cylindrical specimens, approximately 2.54 cm or 3.81 cm in diameter and at least 1.5 times the diameter in length, processed from oil and gas reservoir downhole cores.
  • the test medium must be able to directly penetrate the sample (artificial fractures cannot be created in the sample).
  • the test sample is dense and has low permeability, the test medium cannot penetrate it for sensitivity evaluation. In this case, the current reservoir sensitivity evaluation methods become clearly inadequate.
  • the test sample must be discarded, requiring re-drilling and processing of a new sample until a sample that the test medium can directly penetrate is found.
  • the purpose of this invention is to provide a method for evaluating the sensitivity of low-permeability reservoirs, which can accurately assess the sensitivity of low-permeability reservoirs, provide strong data support for the targeted development of low-permeability reservoirs, and ensure the safe, economical and efficient exploration and development of low-permeability oil and gas reservoirs.
  • the present invention provides a method for evaluating the sensitivity of low-permeability reservoirs, the method comprising:
  • Step 1 Prepare test samples of the target reservoir using full-diameter cores of the target reservoir; during the preparation of test samples, do not change the diameter of the full-diameter core (i.e., the test samples retain the original diameter of the full-diameter core);
  • Step 2 Perform standard saline permeability tests on each test sample to determine the minimum flow rate at which each test sample can achieve the permeability test, which is the initial flow rate. Then, group the test samples according to the magnitude of the initial flow rate.
  • Step 3 Perform sensitivity tests on the same group of samples, including:
  • test sample A is taken from the test group and a flow velocity sensitivity test is performed.
  • the critical flow velocity of test sample A is used as the critical flow velocity of the test group.
  • the initial flow rate of test sample A is used as the minimum flow rate during the flow velocity sensitivity test.
  • Water sensitivity testing is performed on sample B from the test group.
  • the water sensitivity of sample B is taken as the water sensitivity of the test group.
  • the flow rate is selected as the critical flow rate of sample B corresponding to the critical flow rate of the test group.
  • salinity sensitivity testing is performed on sample C from the test group.
  • the salinity sensitivity of sample C is taken as the salinity sensitivity of the test group.
  • the flow rate is selected as the critical flow rate of sample C corresponding to the critical flow rate of the test group.
  • acid sensitivity testing is performed on sample D from the test group.
  • the acid sensitivity of sample D is taken as the acid sensitivity of the test group.
  • the flow rate is selected as the critical flow rate of test sample D corresponding to the critical flow rate of the test group; and/or, test sample E is taken from the test group for alkali sensitivity testing, and the alkali sensitivity of test sample E is used as the alkali sensitivity of the test group, and the flow rate is selected as the critical flow rate of test sample E corresponding to the critical flow rate of the test group; and/or, test sample F is taken from the test group for stress sensitivity testing, and the stress sensitivity of test sample F is used as the stress sensitivity of the test group, and the flow rate is selected as the critical flow rate of test sample F corresponding to the critical flow rate of the test group.
  • step 3 determines the critical flow velocity, water sensitivity, salinity sensitivity, acid sensitivity, alkali sensitivity, and stress sensitivity of the test group, which can reflect the sensitivity of the area in the target reservoir where the permeability is the same as that of the test group.
  • the length of the test sample is not less than 1.5 times the diameter; more preferably, the preparation of the test sample of the target reservoir using the full-diameter core of the target reservoir includes: cutting the full-diameter core of the target reservoir to obtain a core with a length not less than 1.5 times the diameter as the test sample of the target reservoir.
  • the length of the test sample is 0.5-1 times the diameter; more preferably, the preparation of the test sample of the target reservoir using the full-diameter core of the target reservoir includes: cutting the full-diameter core of the target reservoir into a core with a length of 0.5-1 times the diameter as the test sample of the target reservoir.
  • the method further includes: obtaining the reservoir temperature, overlying formation pressure, and reservoir pore pressure of the target reservoir; using the reservoir temperature of the target reservoir as the simulated temperature of the test sample during standard brine permeability testing, water sensitivity testing, salinity sensitivity testing, acid sensitivity testing, alkali sensitivity testing, and stress sensitivity testing; using the overlying formation pressure as the experimental confining pressure of the test sample during standard brine permeability testing, water sensitivity testing, salinity sensitivity testing, acid sensitivity testing, alkali sensitivity testing, and stress sensitivity testing; and using the reservoir pore pressure as the experimental back pressure of the test sample during standard brine permeability testing, water sensitivity testing, salinity sensitivity testing, acid sensitivity testing, and alkali sensitivity testing.
  • step 2 involves performing standard brine permeability tests on each test sample to determine the minimum flow rate required for the permeability test of each test sample, which is the initial flow rate. This includes:
  • the standard saline permeability test was performed on each test sample at the first flow rate.
  • the initial flow rate of each test sample that could achieve the permeability test was the first flow rate, and the test samples that could not achieve the permeability test were recorded as the remaining test samples.
  • a standard saline permeability test was performed at a second flow rate greater than the first flow rate.
  • the initial flow rate of each test sample that could achieve the permeability test was the second flow rate, and the test samples that could not achieve the permeability test were recorded as the remaining test samples.
  • the method further includes: taking test sample A from the test group and performing flow velocity sensitivity testing to obtain the flow velocity sensitivity damage rate of test sample A as the flow velocity sensitivity damage rate of the test group.
  • the method further includes: evaluating the degree of flow velocity sensitivity impairment of test sample A based on the flow velocity sensitivity impairment rate of test sample A, and using the evaluation result of the degree of flow velocity sensitivity impairment of test sample A as the evaluation result of the degree of flow velocity sensitivity impairment of the test group; more preferably, the evaluation criteria for the degree of flow velocity sensitivity impairment are shown in Table 1:
  • the process of taking test sample A from the test group for flow velocity sensitivity testing includes:
  • test sample A Take test sample A from the test group and test the permeability of test sample A under different flow rates to obtain the permeability of test sample A under different flow rates. Specifically, the permeability of standard saline is tested first at a low flow rate and then at a high flow rate. The lowest flow rate is taken as the initial flow rate of test sample A.
  • test sample A is determined by the following method:
  • the permeability retention rate of test sample A at different flow rates was determined respectively; wherein, the permeability retention rate is based on the permeability at the initial flow rate; the highest flow rate corresponding to the permeability retention rate of not less than 80% is taken as the critical flow rate of test sample A, and the critical flow velocity corresponding to the critical flow rate of test sample A is taken as the critical flow velocity of test sample A.
  • the permeability retention rate is determined by the following formula:
  • vn is the permeability retention rate, in %
  • Kn is the permeability at a certain flow rate, in 10 ⁇ 3 ⁇ m2
  • Kin is the baseline permeability, in 10 ⁇ 3 ⁇ m2 .
  • the flow velocity corresponding to the flow rate is determined by the following formula:
  • the flow rate sensitivity damage rate of test sample A is determined by the following method:
  • the flow velocity sensitivity damage rate of test sample A at different flow rates was determined; wherein, the flow velocity sensitivity damage rate is based on the permeability at the initial flow rate.
  • the flow velocity-sensitive damage rate is determined by the following formula:
  • Dn is the flow velocity-sensitive damage rate, in %
  • Kin is the baseline permeability, in 10 ⁇ 3 ⁇ m2
  • Kn is the permeability at a certain flow rate, in 10 ⁇ 3 ⁇ m2 .
  • the water sensitivity of test sample B as the water sensitivity of the test group includes:
  • test sample B The water sensitivity damage rate of test sample B was obtained as the water sensitivity damage rate of the test group.
  • obtaining the water sensitivity of test sample B as the water sensitivity of the test group further includes:
  • the degree of water sensitivity damage to test sample B is evaluated based on the water sensitivity damage rate of test sample B, and the evaluation result of the water sensitivity damage to test sample B is used as the evaluation result of the water sensitivity damage to test group; more preferably, the evaluation criteria for the degree of water sensitivity damage are shown in Table 2; even more preferably, when the evaluation result of the degree of water sensitivity damage to test group is none or weak during the sensitivity test of the same group of samples, the step "taking test sample C from the test group for salinity sensitivity test and obtaining the salinity sensitivity of test sample C as the salinity sensitivity of the test group" is not performed.
  • test sample B from the test group includes:
  • test sample B Take test sample B from the test group; first, perform a standard saline permeability test on test sample B using the critical flow rate corresponding to the critical flow rate of the test group, to obtain the standard saline permeability of test sample B; then, perform a 1/2 standard saline permeability test on test sample B using the critical flow rate corresponding to the critical flow rate of the test group, to obtain the 1/2 standard saline permeability of test sample B; finally, perform a distilled water permeability test on test sample B using the critical flow rate corresponding to the critical flow rate of the test group, to obtain the distilled water permeability of test sample B.
  • test sample B is determined by the following method:
  • the water sensitivity damage rate of test sample B is determined as the water sensitivity damage rate of the test group; the water sensitivity damage rate is determined by the following formula:
  • Dw is the water-sensitive damage rate, in %
  • Kiw is the standard saline permeability, in 10 ⁇ 3 ⁇ m2
  • Kw is the distilled water permeability, in 10 ⁇ 3 ⁇ m2 .
  • the process of taking test sample C from the test group for salinity sensitivity testing, and obtaining the salinity sensitivity of test sample C as the salinity sensitivity of the test group includes:
  • the critical mineralization rate of the C test sample in the test group was obtained by taking the C test sample and performing a salinity sensitivity test. This critical mineralization rate was used as the critical mineralization rate of the test group.
  • the critical mineralization rate of the C test sample obtained by taking the C test sample from the test group and performing a salinity sensitivity test is used as the critical mineralization rate of the test group, including:
  • test sample C was tested with salt water of different concentrations at the critical flow rate corresponding to the critical flow rate of the test group.
  • the permeability of test sample C under different salt concentrations was obtained.
  • the permeability test of high salt concentration salt water was carried out first, followed by the permeability test of low salt concentration salt water.
  • the salt water with the highest salt concentration was taken as standard salt water, and the salt water with the lowest salt concentration was taken as distilled water.
  • the permeability retention rate of sample C under different salt concentrations was determined; the permeability retention rate was based on the permeability under standard saline.
  • the critical mineralization of the lowest concentration of brine when the permeability retention rate is not less than 80% is taken as the critical mineralization of the C test sample, which is also the critical mineralization of the test group.
  • the permeability retention rate is determined by the following formula:
  • vsn is the permeability retention rate, in %
  • Ks is the permeability of a certain salt concentration in saline solution, in 10 ⁇ 3 ⁇ m2
  • Kis is the permeability of the standard saline solution, which is the initial permeability, in 10 ⁇ 3 ⁇ m2 .
  • the mineralization of the fluid used for permeability testing is equal to the critical mineralization of the test group.
  • the acid sensitivity of test sample D as the acid sensitivity of the test group includes:
  • test sample D The acid sensitivity impairment rate of test sample D was obtained as the acid sensitivity impairment rate of the test group;
  • obtaining the acid sensitivity of test sample D as the acid sensitivity of the test group further includes: evaluating the degree of acid sensitivity damage of test sample D based on the acid sensitivity damage rate of test sample D, and obtaining the evaluation result of the degree of acid sensitivity damage of test sample D as the evaluation result of the degree of acid sensitivity damage of the test group; even more preferably, the evaluation criteria for the degree of acid sensitivity damage are shown in Table 3:
  • the acid sensitivity test performed on the D test sample from the test group includes:
  • test sample D Take test sample D from the test group; first, test the critical mineralization saline permeability of test sample D at the critical flow rate corresponding to the critical flow rate of the test group to obtain the permeability of test sample D before acid treatment; then, displace the acid solution into test sample D and allow test sample D to react with the acid solution for a period of time; then, test sample D again at the critical flow rate corresponding to the critical flow rate of the test group to obtain the permeability of test sample D after acid treatment.
  • acid is injected into the D test sample until acid flows out of the liquid outlet, at which point the acid injection is stopped;
  • the acid sensitivity damage rate of test sample D is determined by the following method:
  • the acid sensitivity damage rate of sample D is determined as the acid sensitivity damage rate of the test group; the acid sensitivity damage rate is determined by the following formula:
  • the alkali sensitivity of the E test sample as the alkali sensitivity of the test group includes:
  • the critical pH value of the E test sample is the critical pH value of the test group, and/or the alkali sensitivity impairment rate of the E test sample is the alkali sensitivity impairment rate of the test group.
  • obtaining the alkali sensitivity of the E test sample as the alkali sensitivity of the test group further includes: evaluating the degree of alkali sensitivity damage of the E test sample based on the alkali sensitivity damage rate of the E test sample, and obtaining the alkali sensitivity damage degree evaluation result of the E test sample as the alkali sensitivity damage degree evaluation result of the test group; even more preferably, the alkali sensitivity damage degree evaluation criteria are shown in Table 4:
  • an alkali sensitivity test is performed on an E test sample from the test group to obtain the following:
  • test sample E Take test sample E from the test group; test the permeability of test sample E with solutions at different pH values, using the critical flow rate of the test group corresponding to the critical flow rate of the test sample.
  • the permeability of test sample E under different pH values is obtained; the permeability test is performed first with low pH solutions, followed by high pH solutions.
  • the pH values of the solutions range from 7 to 14, with the lowest pH value being 7.
  • the mineralization of the solution is equal to the critical mineralization of the test group.
  • the baseline permeability of test sample E is also determined.
  • test sample E is determined by the following method:
  • the permeability retention rate of test sample E in solutions with different pH values was determined; wherein, the permeability retention rate was based on the permeability of test sample E in a solution with a pH value of 7.
  • the pH value of the solution with the highest pH value when the permeability retention rate is not less than 80% is taken as the critical pH value of the E test sample;
  • the permeability retention rate is determined by the following formula:
  • val is the permeability retention rate, in %
  • Kal is the permeability under alkaline solution at a certain pH value, in 10 ⁇ 3 ⁇ m2
  • Kial is the baseline permeability, in 10 ⁇ 3 ⁇ m2 .
  • the alkali sensitivity impairment rate of the E test sample is determined by the following method:
  • the alkali sensitivity damage rate of test sample E was determined; wherein, the alkali sensitivity damage rate is based on the permeability of test sample E in a solution with a pH value of 7; and the alkali sensitivity damage rate is determined by the following formula:
  • Dal is the alkali sensitivity damage rate, in %
  • Kial is the baseline permeability, in 10 ⁇ 3 ⁇ m2
  • Kal is the permeability of an alkaline solution at a certain pH value, in 10 ⁇ 3 ⁇ m2 .
  • the fluid used for permeability testing during stress sensitivity testing is brine with critical mineralization of the test group.
  • the stress sensitivity of the F test sample is obtained as the stress sensitivity of the test group, which includes:
  • the critical stress of the F test sample is obtained as the critical stress of the test group, and/or the irreversible stress sensitivity damage rate of the F test sample is obtained as the irreversible stress sensitivity damage rate of the test group, and/or the stress sensitivity damage rate of the F test sample is obtained as the stress sensitivity damage rate of the test group.
  • obtaining the stress sensitivity of the F test sample as the stress sensitivity of the test group further includes: evaluating the degree of stress sensitivity damage of the F test sample based on the stress sensitivity damage rate of the F test sample, and obtaining the stress sensitivity damage evaluation result of the F test sample as the stress sensitivity damage evaluation result of the test group; even more preferably, the stress sensitivity damage evaluation criteria are shown in Table 5:
  • stress sensitivity testing is performed on F test samples from the test group, including:
  • test sample F Take test sample F from the test group; conduct permeability tests on test sample F under different stresses to obtain the permeability of test sample F under different stresses; during the permeability test, the flow rate is selected as the critical flow rate of the test group corresponding to the critical flow rate of the test sample; the fluid used for the permeability test is the critical salinity brine of the test group; first conduct the permeability test under the initial stress, then gradually increase the stress to the maximum stress value, and then gradually decrease the stress to the final stress, and maintain the rated time at each stress value and conduct permeability tests at each stress value respectively.
  • the initial stress is the effective reservoir stress of the target reservoir, and the final stress is equal to the initial stress;
  • the confining pressure remains constant, and the appropriate back pressure is determined according to the stress value (the difference between the confining pressure and the back pressure is the stress);
  • the critical stress of the F test sample is determined by the following method:
  • the permeability under the initial stress is used as the benchmark permeability to determine the permeability retention rate of the F test sample under different stresses.
  • the maximum stress at which the permeability retention rate is not less than 80% during the process of gradually increasing the stress to the maximum stress value is taken as the critical stress of the F test sample.
  • the permeability retention rate is determined by the following formula:
  • vp is the permeability retention rate, in %
  • Kp is the permeability under a certain stress, in 10 ⁇ 3 ⁇ m2
  • Kip is the baseline permeability, in 10 ⁇ 3 ⁇ m2 .
  • the irreversible stress sensitivity damage rate of the F test sample is determined by the following method:
  • the irreversible stress sensitivity damage rate of test sample F is determined as the irreversible stress sensitivity damage rate of the test group; wherein, the irreversible stress sensitivity damage rate is determined by the following formula:
  • Dpn is the irreversible stress-sensitive damage rate, in %
  • Kpn is the permeability under final stress, in 10 ⁇ 3 ⁇ m2
  • Kip is the baseline permeability, in 10 ⁇ 3 ⁇ m2 .
  • the stress sensitivity damage rate of the F test sample is determined by the following method:
  • the stress sensitivity damage rate of the F test sample is determined as the stress sensitivity damage rate of the test group.
  • the stress sensitivity damage rate is determined by the following formula:
  • Dp is the stress-sensitive damage rate, in %
  • Kp is the permeability under a certain stress, in 10 ⁇ 3 ⁇ m2
  • Kip is the baseline permeability, in 10 ⁇ 3 ⁇ m2 .
  • Standard saline solution refers to an aqueous solution of NaCl with a NaCl content of 8% by mass.
  • 3/4 standard saline solution refers to a NaCl aqueous solution with a NaCl content of 6% by mass
  • 1/2 standard saline solution refers to a NaCl aqueous solution with a NaCl content of 4% by mass
  • 1/4 standard saline solution refers to an aqueous solution of NaCl with a NaCl mass content of 2%.
  • the solution used in the sensitivity test is provided with NaCl for mineralization, NaOH for alkalinity, and HCl for acidity.
  • the permeability test uses an ultra-low permeability tester, wherein the lower limit of the test of the ultra-low permeability tester is not more than 10 ⁇ 4 mD and the upper limit of the confining pressure is not less than 80 MPa.
  • the technical solution provided by this invention solves the problem that existing experimental methods cannot evaluate the sensitivity of low-permeability reservoirs. Compared with the prior art, the technical solution provided by this invention has the following beneficial effects:
  • the technical solution provided by this invention uses full-diameter core samples prepared with the original diameter retained for sensitivity testing. This preserves the original seepage channels in the oil and gas reservoir downhole core, avoiding the problem of inaccurate data caused by artificially avoiding loose areas (i.e. seepage channel areas) in the oil and gas reservoir downhole core during processing (usually processed into columnar samples with a diameter of about 2.54cm or 3.81cm) to ensure processing success. It can be well adapted to the sensitivity evaluation of low-permeability reservoirs.
  • the technical solution provided by this invention proposes a new sensitivity testing procedure for the special samples used in this technical solution, which can eliminate the mutual influence between different sensitivities and accurately evaluate the sensitivity damage of low-permeability reservoirs.
  • the technical solution provided by this invention can effectively solve the problem of waste of downhole cores caused by the inapplicability of the current reservoir sensitivity test evaluation method to low-permeability reservoirs.
  • Figure 1 is a flow velocity sensitivity experiment curve in Example 1 of the present invention.
  • Figure 2 is a salinity sensitivity curve in Example 1 of the present invention.
  • a specific embodiment of the present invention provides a method for evaluating the sensitivity of low-permeability reservoirs, the method comprising:
  • Step 101 Prepare test samples of the target reservoir using full-diameter cores of the target reservoir; during the preparation of test samples, do not change the diameter of the full-diameter cores (i.e., the test samples retain the original diameter of the full-diameter cores);
  • Step 102 Perform standard saline permeability tests on each test sample to determine the minimum flow rate at which each test sample can achieve the permeability test, which is the initial flow rate. Then, group the test samples according to the magnitude of the initial flow rate.
  • Step 103 Perform sensitivity testing on the same group of samples, including:
  • test sample A is taken from the test group and the flow velocity sensitivity test is performed to obtain the critical flow velocity of test sample A as the critical flow velocity of the test group.
  • the initial flow rate of test sample A is taken as the minimum flow rate during the flow velocity sensitivity test.
  • the water sensitivity of test sample B in the test group is used as the water sensitivity of the test group.
  • the flow rate is selected as the critical flow rate of test sample B corresponding to the critical flow rate of the test group.
  • the salinity sensitivity of test sample C in the test group is used as the salinity sensitivity of the test group.
  • the flow rate is selected as the critical flow rate of test sample C corresponding to the critical flow rate of the test group.
  • the acid sensitivity of test sample D in the test group is used as the acid sensitivity of the test group.
  • the flow rate is selected as the critical flow rate of test sample D corresponding to the critical flow rate of the test group.
  • the alkali sensitivity of test sample E in the test group is used as the alkali sensitivity of the test group.
  • the flow rate is selected as the critical flow rate of test sample E corresponding to the critical flow rate of the test group.
  • the stress sensitivity of test sample F in the test group is used as the stress sensitivity of the test group.
  • the flow rate is selected as the critical flow rate of test sample F corresponding to the critical flow rate of the test group.
  • step 103 determines the critical flow velocity, water sensitivity, salinity sensitivity, acid sensitivity, alkali sensitivity, and stress sensitivity of the test group, which can reflect the sensitivity of the area in the target reservoir where the permeability is the same as that of the test group.
  • the length of the test sample is not less than 1.5 times its diameter
  • the preparation of test samples of the target reservoir using full-diameter cores of the target reservoir includes: cutting the full-diameter cores of the target reservoir into cores with a length not less than 1.5 times the diameter as test samples of the target reservoir.
  • the method further includes: acquiring the reservoir temperature, overlying formation pressure, and reservoir pore pressure of the target reservoir; using the reservoir temperature of the target reservoir as the simulated temperature of the test sample during standard brine permeability testing, water sensitivity testing, salinity sensitivity testing, acid sensitivity testing, alkali sensitivity testing, and stress sensitivity testing; using the overlying formation pressure as the experimental confining pressure of the test sample during standard brine permeability testing, water sensitivity testing, salinity sensitivity testing, acid sensitivity testing, alkali sensitivity testing, and stress sensitivity testing; and using the reservoir pore pressure as the experimental back pressure of the test sample during standard brine permeability testing, water sensitivity testing, salinity sensitivity testing, acid sensitivity testing, and alkali sensitivity testing.
  • step 102 which involves performing a standard saline permeability test on each test sample to determine the minimum flow rate required for the permeability test of each test sample (i.e., the initial flow rate), includes:
  • the standard saline permeability test was performed on each test sample at the first flow rate.
  • the initial flow rate of each test sample that could achieve the permeability test was the first flow rate, and the test samples that could not achieve the permeability test were recorded as the remaining test samples.
  • a standard saline permeability test was performed at a second flow rate greater than the first flow rate.
  • the initial flow rate of each test sample that could achieve the permeability test was the second flow rate, and the test samples that could not achieve the permeability test were recorded as the remaining test samples.
  • the first flow rate is 0.1 cm3 /min
  • the second flow rate is 0.5 cm3 /min
  • the third flow rate is 1 cm3 /min.
  • step 103 taking test sample A from the test group and performing a flow velocity sensitivity test to obtain the critical flow velocity of test sample A as the critical flow velocity of the test group, includes:
  • test sample A Take test sample A from the test group and test the permeability of test sample A under different flow rates to obtain the permeability of test sample A under different flow rates. Specifically, the permeability of standard saline is tested first at a low flow rate and then at a high flow rate. The lowest flow rate is taken as the initial flow rate of test sample A.
  • the permeability retention rate of test sample A at different flow rates is determined respectively; wherein, the permeability retention rate is based on the permeability at the initial flow rate.
  • the highest flow rate corresponding to the permeability retention rate of not less than 80% is taken as the critical flow rate of test sample A, and the critical flow velocity corresponding to the critical flow rate of test sample A is taken as the critical flow velocity of test sample A, which is the critical flow velocity of the test group.
  • the permeability retention rate is determined by the following formula:
  • vn is the permeability retention rate, in %
  • Kn is the permeability at a certain flow rate, in 10 ⁇ 3 ⁇ m2
  • Kin is the baseline permeability, in 10 ⁇ 3 ⁇ m2 .
  • the flow velocity corresponding to the flow rate is determined by the following formula:
  • step 103 further includes: determining the flow rate sensitivity damage rate of test sample A as the flow rate sensitivity damage rate of the test group based on the flow rate sensitivity test data of test sample A; wherein the flow rate sensitivity damage rate is based on the permeability rate at the initial flow rate as the benchmark permeability rate;
  • the flow velocity-sensitive damage rate is determined by the following formula:
  • Dn is the flow velocity-sensitive damage rate, in %
  • Kin is the baseline permeability, in 10 ⁇ 3 ⁇ m2
  • Kn is the permeability at a certain flow rate, in 10 ⁇ 3 ⁇ m2 .
  • step 103 also includes: evaluating the degree of flow velocity sensitivity impairment of test sample A based on the flow velocity sensitivity impairment rate of test sample A, and using the evaluation result of the degree of flow velocity sensitivity impairment of test sample A as the evaluation result of the degree of flow velocity sensitivity impairment of the test group; more preferably, the evaluation criteria for the degree of flow velocity sensitivity impairment are shown in Table 6:
  • taking test sample B from the test group and performing a water sensitivity test, and obtaining the water sensitivity of test sample B as the water sensitivity of the test group includes:
  • a water sensitivity test was conducted on a sample B from the test group, and the water sensitivity damage rate of the sample B was taken as the water sensitivity damage rate of the test group.
  • sample B from the test group was obtained as the water sensitivity damage rate of the test group, including:
  • test sample B Take test sample B from the test group. First, perform a standard saline permeability test on test sample B using the critical flow rate corresponding to the critical flow rate of the test group, to obtain the standard saline permeability of test sample B. Then, perform a 1/2 standard saline permeability test on test sample B using the critical flow rate corresponding to the critical flow rate of the test group, to obtain the 1/2 standard saline permeability of test sample B. Next, perform a distilled water permeability test on test sample B using the critical flow rate corresponding to the critical flow rate of the test group, to obtain the distilled water permeability of test sample B. Based on the standard saline permeability and distilled water permeability of test sample B, determine the water sensitivity damage rate of test sample B as the water sensitivity damage rate of the test group. The water sensitivity damage rate is determined using the following formula:
  • Dw is the water-sensitive damage rate, in %
  • Kiw is the standard saline permeability, in 10 ⁇ 3 ⁇ m2
  • Kw is the distilled water permeability, in 10 ⁇ 3 ⁇ m2 .
  • taking test sample B from the test group for water sensitivity testing and obtaining the water sensitivity of test sample B as the water sensitivity of the test group also includes: evaluating the degree of water sensitivity damage of test sample B based on the water sensitivity damage rate of test sample B, and using the evaluation result of the degree of water sensitivity damage of test sample B as the evaluation result of the degree of water sensitivity damage of the test group; further still, the evaluation criteria for the degree of water sensitivity damage are shown in Table 7; and further still, when the evaluation result of the degree of water sensitivity damage of the test group is none or weak during the sensitivity testing of the same group of samples, the step "taking test sample C from the test group for salinity sensitivity testing and obtaining the salinity sensitivity of test sample C as the salinity sensitivity of the test group" is not performed.
  • taking test sample C from the test group and performing a salinity sensitivity test to obtain the salinity sensitivity of test sample C as the salinity sensitivity of the test group includes:
  • a C test sample was taken from the test group and subjected to a salinity sensitivity test.
  • the critical mineralization rate of the C test sample was taken as the critical mineralization of the test group.
  • test sample C was tested with salt water of different concentrations at the critical flow rate corresponding to the critical flow rate of the test group.
  • the permeability of test sample C under different salt concentrations was obtained.
  • the permeability test of high salt concentration salt water was carried out first, followed by the permeability test of low salt concentration salt water.
  • the salt water with the highest salt concentration was taken as standard salt water, and the salt water with the lowest salt concentration was taken as distilled water.
  • the permeability retention rate of sample C under different salt concentrations was determined; the permeability retention rate was based on the permeability under standard saline.
  • the critical mineralization of the lowest concentration of brine when the permeability retention rate is not less than 80% is taken as the critical mineralization of the C test sample, which is also the critical mineralization of the test group.
  • the permeability retention rate is determined by the following formula:
  • vsn is the permeability retention rate, in %
  • Ks is the permeability of a certain salt concentration in saline solution, in 10 ⁇ 3 ⁇ m2
  • Kis is the permeability of the standard saline solution, which is the initial permeability, in 10 ⁇ 3 ⁇ m2 .
  • the fluid used for the permeability test is selected as the critical mineralization brine of the test group (i.e., brine with a mineralization of the critical mineralization of the test group).
  • the acid sensitivity of test sample D is used as the acid sensitivity of the test group, including:
  • Acid sensitivity testing was performed on D test samples from the test group, and the acid sensitivity damage rate of D test samples was taken as the acid sensitivity damage rate of the test group.
  • the acid sensitivity impairment rate of test sample D in the test group is obtained by performing acid sensitivity testing on the test sample D, which is used as the acid sensitivity impairment rate of the test group.
  • test sample D the critical flow rate corresponding to the critical flow rate of the test group is used to test the critical mineralization of the brine before acid treatment, thus obtaining the permeability of test sample D before acid treatment. Then, acid is displaced into test sample D and the test sample D is allowed to react with the acid for a period of time. Subsequently, for test sample D, the critical mineralization of the test group is tested again at the critical flow rate corresponding to the critical flow rate of the test group, thus obtaining the permeability of test sample D after acid treatment.
  • the acid sensitivity damage rate of test sample D was determined as the acid sensitivity damage rate of the test group.
  • the acid sensitivity damage rate is determined by the following formula:
  • taking test sample D from the test group for acid sensitivity testing, and obtaining the acid sensitivity of test sample D as the acid sensitivity of the test group also includes: evaluating the degree of acid sensitivity damage of test sample D based on the acid sensitivity damage rate of test sample D, and using the evaluation result of the degree of acid sensitivity damage of test sample D as the evaluation result of the degree of acid sensitivity damage of the test group; furthermore, the evaluation criteria for the degree of acid sensitivity damage are shown in Table 8:
  • the mineralization of the fluid used for the permeability test is equal to the critical mineralization of the test group.
  • the alkali sensitivity of test sample E is obtained as the alkali sensitivity of the test group, including:
  • the critical pH value of E test sample is the critical pH value of the test group.
  • the critical pH value of the E test sample is the critical pH value of the test group, including:
  • the permeability of test sample E was tested at different pH values, corresponding to the critical flow rate of the test group.
  • the permeability of test sample E under different pH values was obtained.
  • the permeability test of low pH value solution was carried out first, followed by the permeability test of high pH value solution.
  • the pH value of the solution was 7-14, and the pH value of the lowest pH value solution was 7.
  • the mineralization of the solution was equal to the critical mineralization of the test group.
  • the permeability retention rate of test sample E in solutions with different pH values was determined; wherein, the permeability retention rate was based on the permeability of test sample E in a solution with a pH value of 7.
  • the pH value of the solution with the highest pH value when the permeability retention rate is not less than 80% is taken as the critical pH value of the E test sample;
  • the permeability retention rate is determined by the following formula:
  • val is the permeability retention rate, in %
  • Kal is the permeability under alkaline solution at a certain pH value, in 10 ⁇ 3 ⁇ m2
  • Kial is the baseline permeability, in 10 ⁇ 3 ⁇ m2 .
  • the alkali sensitivity of test sample E is obtained as the alkali sensitivity of the test group, including:
  • E test samples were taken from the test group and alkali sensitivity was tested.
  • the alkali sensitivity damage rate of the E test samples was taken as the alkali sensitivity damage rate of the test group.
  • the alkali sensitivity impairment rate of test sample E in the test group is obtained by conducting an alkali sensitivity test, and is used as the alkali sensitivity impairment rate of the test group. This includes:
  • the permeability of test sample E was tested at different pH values, corresponding to the critical flow rate of the test group.
  • the permeability of test sample E under different pH values was obtained.
  • the permeability test of low pH value solution was carried out first, followed by the permeability test of high pH value solution.
  • the pH value of the solution was 7-14, and the pH value of the lowest pH value solution was 7.
  • the mineralization of the solution was equal to the critical mineralization of the test group.
  • the alkali sensitivity damage rate of the E test sample was determined as the alkali sensitivity damage rate of the test group; among which, the permeability of the E test sample in a solution with a pH value of 7 was used as the baseline permeability.
  • the alkali sensitivity damage rate is determined by the following formula:
  • Dal is the alkali sensitivity damage rate, in %
  • Kial is the baseline permeability, in 10 ⁇ 3 ⁇ m2
  • Kal is the permeability of an alkaline solution at a certain pH value, in 10 ⁇ 3 ⁇ m2 .
  • taking test sample E from the test group for alkali sensitivity testing and obtaining the alkali sensitivity of test sample E as the alkali sensitivity of the test group also includes: evaluating the degree of alkali sensitivity damage of test sample E based on the alkali sensitivity damage rate of test sample E, and using the evaluation result of the degree of alkali sensitivity damage of test sample E as the evaluation result of the degree of alkali sensitivity damage of the test group.
  • the fluid used for permeability testing during stress sensitivity testing is the critical mineralization brine of the test group.
  • the stress sensitivity of test sample F is obtained as the stress sensitivity of the test group, including:
  • the permeability of test sample F under different stresses was obtained.
  • the flow rate was selected as the critical flow rate of the test sample corresponding to the critical flow rate of the test group.
  • the fluid used for the permeability test was brine with critical salinity of the test group.
  • the permeability test was first performed under the initial stress, then the stress was gradually increased to the maximum stress value, and then the stress was gradually decreased to the final stress. The rated time was maintained at each stress value and the permeability test was performed at each stress value.
  • the initial stress was the effective reservoir stress of the target reservoir, and the final stress was equal to the initial stress.
  • the permeability retention rate of the F test sample under different stresses was determined respectively.
  • the maximum stress at which the permeability retention rate is not less than 80% during the process of gradually increasing the stress to the maximum stress value is taken as the critical stress of the F test sample, which is also the critical stress of the test group.
  • the permeability retention rate is determined by the following formula:
  • vp is the permeability retention rate, in %
  • Kp is the permeability under a certain stress, in 10 ⁇ 3 ⁇ m2
  • Kip is the baseline permeability, in 10 ⁇ 3 ⁇ m2 .
  • the confining pressure remained constant, and the appropriate back pressure was determined based on the stress value (the difference between the confining pressure and the back pressure is the stress).
  • the stress sensitivity of test sample F is obtained as the stress sensitivity of the test group, including:
  • the F test sample was taken from the test group and subjected to stress sensitivity test.
  • the irreversible stress sensitivity damage rate of the F test sample was used as the irreversible stress sensitivity damage rate of the test group.
  • the permeability of test sample F under different stresses was obtained.
  • the flow rate was selected as the critical flow rate of the test sample corresponding to the critical flow rate of the test group.
  • the fluid used for the permeability test was brine with critical salinity of the test group.
  • the permeability test was first performed under the initial stress, then the stress was gradually increased to the maximum stress value, and then the stress was gradually decreased to the final stress. The rated time was maintained at each stress value and the permeability test was performed at each stress value.
  • the initial stress was the effective reservoir stress of the target reservoir, and the final stress was equal to the initial stress.
  • the irreversible stress sensitivity damage rate of the F test sample was determined as the irreversible stress sensitivity damage rate of the test group.
  • the irreversible stress sensitivity damage rate is determined by the following formula:
  • Dpn is the irreversible stress-sensitive damage rate, in %
  • Kpn is the permeability under final stress, in 10 ⁇ 3 ⁇ m2
  • Kip is the baseline permeability, in 10 ⁇ 3 ⁇ m2 .
  • the stress sensitivity of test sample F is obtained as the stress sensitivity of the test group, including:
  • the F test sample was taken from the test group and subjected to stress sensitivity test.
  • the stress sensitivity damage rate of the F test sample was taken as the stress sensitivity damage rate of the test group.
  • stress sensitivity tests were conducted on F test samples from the test group, and the stress sensitivity damage rate of F test samples was obtained as the stress sensitivity damage rate of the test group, including:
  • the permeability of test sample F under different stresses was obtained.
  • the flow rate was selected as the critical flow rate of the test sample corresponding to the critical flow rate of the test group.
  • the fluid used for the permeability test was brine with critical salinity of the test group.
  • the permeability test was first performed under the initial stress, then the stress was gradually increased to the maximum stress value, and then the stress was gradually decreased to the final stress. The rated time was maintained at each stress value and the permeability test was performed at each stress value.
  • the initial stress was the effective reservoir stress of the target reservoir, and the final stress was equal to the initial stress.
  • the stress sensitivity damage rate of the F test sample was determined as the stress sensitivity damage rate of the test group.
  • the stress sensitivity damage rate is determined by the following formula:
  • Dp is the stress-sensitive damage rate, in %
  • Kp is the permeability under a certain stress, in 10 ⁇ 3 ⁇ m2
  • Kip is the baseline permeability, in 10 ⁇ 3 ⁇ m2 .
  • taking F test samples from the test group for stress sensitivity testing and obtaining the stress sensitivity of F test samples as the stress sensitivity of the test group also includes: evaluating the stress sensitivity damage degree of F test samples based on the stress sensitivity damage rate of F test samples, and using the stress sensitivity damage degree evaluation result of F test samples as the stress sensitivity damage degree evaluation result of the test group.
  • standard saline refers to an aqueous solution of NaCl with a NaCl mass content of 8%; 3/4 standard saline refers to an aqueous solution of NaCl with a NaCl mass content of 6%; 1/2 standard saline refers to an aqueous solution of NaCl with a NaCl mass content of 4%; and 1/4 standard saline refers to an aqueous solution of NaCl with a NaCl mass content of 2%.
  • the solution used in the sensitivity test has mineralization provided by NaCl, alkalinity provided by NaOH, and acidity provided by HCl.
  • the solution used in the sensitivity test is an aqueous solution of NaCl, or an aqueous solution of NaOH, or an aqueous solution of HCl, or a mixed solution of NaCl and NaOH, or a mixed solution of NaCl and HCl.
  • This embodiment provides a method for evaluating the sensitivity of low-permeability reservoirs, the method comprising:
  • the target reservoir temperature is 140°C
  • the overlying formation pressure is 98MPa
  • the reservoir pore pressure is 69MPa.
  • the reservoir temperature is used as the simulated temperature of the test samples during standard brine permeability testing, water sensitivity testing, salinity sensitivity testing, acid sensitivity testing, alkali sensitivity testing, and stress sensitivity testing.
  • the overlying formation pressure is used as the experimental confining pressure of the test samples during these tests.
  • the reservoir pore pressure is used as the experimental back pressure of the test samples during these tests.
  • test samples For each test sample, the permeability of standard saline (NaCl aqueous solution with a NaCl mass content of 8%) was tested at the first flow rate (0.1 cm3 /min). The initial flow rate of each test sample that could achieve the permeability test was the first flow rate, and the test samples that could not achieve the permeability test were recorded as the remaining test samples.
  • standard saline NaCl aqueous solution with a NaCl mass content of 8%
  • a standard saline permeability test was conducted at a second flow rate (0.5 cm3 /min) that was greater than the first flow rate.
  • the initial flow rate of each test sample that could achieve the permeability test was the second flow rate, and the test samples that could not achieve the permeability test were recorded as the remaining test samples.
  • a standard saline permeability test was performed at a third flow rate (1 cm3 /min) that was greater than the second flow rate.
  • the initial flow rate of each test sample that could achieve the permeability test was the third flow rate, and the test samples that could not achieve the permeability test were recorded as the remaining test samples; at this time, the number of remaining test samples was 0.
  • test samples were then grouped according to the initial flow rate.
  • the first group of test samples included test sample 1, test sample 2, test sample 3, test sample 4, test sample 5, test sample 6, and test sample 7;
  • the second group of test samples included test sample 8, test sample 9, test sample 10, test sample 11, test sample 12, test sample 13, and test sample 14;
  • the third group of test samples included test sample 15, test sample 16, test sample 17, test sample 18, test sample 19, and test sample 20.
  • the initial flow rate of the first group of test samples was 0.1 cm3 /min
  • the initial flow rate of the second group of test samples was 0.5 cm3 /min
  • the initial flow rate of the third group of test samples was 1 cm3 /min.
  • sensitivity tests were conducted to determine the sensitivity of the region in the target reservoir with a permeability of approximately 0.896 ⁇ 10 ⁇ 3 ⁇ m2. Specifically, this included:
  • test sample 1 Take test sample 1 from the test group and conduct standard saline permeability tests on test sample 1 at different flow rates to obtain the permeability of test sample 1 at different flow rates; wherein, the standard saline permeability test is conducted first at a low flow rate and then at a high flow rate, and the lowest flow rate is taken as the initial flow rate of test sample 1.
  • the permeability retention rate of test sample 1 at different flow rates was determined; the permeability retention rate was based on the permeability at the initial flow rate. The results are shown in Table 11 and Figure 1.
  • the permeability retention rate was determined by the following formula:
  • vn is the permeability retention rate, in %
  • Kn is the permeability at a certain flow rate, in 10 ⁇ 3 ⁇ m2
  • Kin is the baseline permeability, in 10 ⁇ 3 ⁇ m2 .
  • the highest flow rate corresponding to a permeability retention rate of not less than 80% is taken as the critical flow rate of test sample 1, and the critical velocity corresponding to the critical flow rate of test sample 1 is taken as the critical velocity of test sample 1, which is the critical velocity of the test group.
  • the velocity corresponding to a flow rate of 0.1 cm3 /min is the critical velocity.
  • the diameter of test sample 1 is 6.5 cm, and the critical velocity is 0.003 cm/min.
  • the velocity corresponding to the flow rate is determined by the following formula:
  • the flow velocity sensitivity damage rate of test sample 1 was determined as the flow velocity sensitivity damage rate of the test group; wherein, the flow velocity sensitivity damage rate is based on the permeability at the initial flow rate.
  • the results are shown in Table 11.
  • the flow velocity sensitivity damage rate is determined by the following formula:
  • Dn is the flow velocity-sensitive damage rate, in %;
  • Kin is the baseline permeability, in 10 ⁇ 3 ⁇ m2 ;
  • Kn is the permeability at a certain flow rate, in 10 ⁇ 3 ⁇ m2 .
  • the degree of flow velocity sensitivity impairment of test sample 1 was evaluated based on the flow velocity sensitivity impairment rate of test sample 1, and the evaluation result of the flow velocity sensitivity impairment of test sample 1 was used as the evaluation result of the flow velocity sensitivity impairment of the test group; the evaluation criteria for the degree of flow velocity sensitivity impairment are shown in Table 12:
  • the permeability damage rate is 30 ⁇ Dn (30.2%) ⁇ 50, and the degree of flow velocity sensitivity damage is moderate to weak.
  • test sample 2 Take test sample 2 from the test group. First, for test sample 2, perform a standard saline permeability test at the critical flow rate corresponding to the critical flow rate of the test group to obtain the standard saline permeability of test sample 2. Then, for test sample 2, perform a 1/2 standard saline (NaCl aqueous solution with a NaCl mass content of 4%) permeability test at the critical flow rate corresponding to the critical flow rate of the test group to obtain the 1/2 standard saline permeability of test sample 2. Finally, for test sample 2, perform a distilled water permeability test at the critical flow rate corresponding to the critical flow rate of the test group to obtain the distilled water permeability of test sample 2. The results are shown in Table 13.
  • the water sensitivity damage rate of test sample 2 was determined as the water sensitivity damage rate of the test group, which was 47.37%.
  • the water sensitivity damage rate was determined using the following formula:
  • the degree of water sensitivity damage to test sample 2 was evaluated based on the water sensitivity damage rate of test sample 2, and the evaluation result of the degree of water sensitivity damage to test sample 2 was used as the evaluation result of the degree of water sensitivity damage to the test group; the evaluation criteria for the degree of water sensitivity damage are shown in Table 14.
  • the water sensitivity damage rate is 30 ⁇ Dw (47.37%) ⁇ 50, indicating a moderate to weak degree of water sensitivity damage.
  • Test sample 3 was taken from the test group.
  • the permeability of test sample 3 under different salinity concentrations was tested using the critical flow rate corresponding to the critical flow rate of the test group.
  • the permeability of test sample 3 under different salinity concentrations was obtained by first testing the permeability of high salinity concentrations, followed by low salinity concentrations. The highest salinity concentration was obtained from standard salinity, and the lowest salinity concentration was obtained from distilled water. Based on the permeability of test sample 3 under different salinity concentrations, the permeability retention rate of test sample 3 under different salinity concentrations was determined.
  • the permeability retention rate was based on the permeability under standard salinity. The results are shown in Table 15 and Figure 2. The mineralization of the lowest concentration of salinity corresponding to a permeability retention rate of not less than 80% was taken as the critical mineralization of test sample 3, which is also the critical mineralization of the test group, and the critical mineralization is 80000 mg/L.
  • the permeability retention rate was determined by the following formula:
  • vsn is the permeability retention rate, in %
  • Ks is the permeability of a certain salt concentration in saline solution, in 10 ⁇ 3 ⁇ m2
  • Kis is the permeability of the standard saline solution, which is the initial permeability, in 10 ⁇ 3 ⁇ m2 .
  • test sample 4 Take test sample 4 from the test group. First, test sample 4 is subjected to a critical flow rate test at the critical mineralization of the test group, corresponding to the critical flow rate of the test group, to obtain the permeability of test sample 4 before acid treatment. Then, acid is added to test sample 4 until acid flows out of the liquid outlet, and the acid injection is stopped, allowing test sample 4 to react with the acid for a period of time. Then, test sample 4 is subjected to a critical flow rate test at the critical mineralization of the test group, corresponding to the critical flow rate of the test group, to obtain the permeability of test sample 4 after acid treatment.
  • the acid sensitivity damage rate of test sample 4 is determined as the acid sensitivity damage rate of the test group, and the results are shown in Table 16.
  • the degree of acid sensitivity damage of test sample 4 is evaluated, and the evaluation result of the degree of acid sensitivity damage of test sample 4 is used as the evaluation result of the degree of acid sensitivity damage of the test group.
  • the evaluation criteria for the degree of acid sensitivity damage are shown in Table 17.
  • the acid sensitivity damage rate is determined by the following formula:
  • the acid sensitivity impairment rate is 30 ⁇ Dac (28.99%) ⁇ 50, indicating a weak degree of acid sensitivity impairment.
  • test sample 5 Take test sample 5 from the test group.
  • Test sample 5 was subjected to permeability tests at different pH values, using the critical flow rate corresponding to the critical flow rate of the test group. Specifically, solutions with pH values of 7, 8.5, 10, 11.5, and 13 were used for permeability testing in sequence. The mineralization of the solution was equal to the critical mineralization of the test group.
  • the solution with pH value 7 was an aqueous NaCl solution, and the solutions with pH values of 8.5, 10, 11.5, and 13 were mixed solutions of aqueous NaCl and aqueous NaOH solutions.
  • the permeability retention rate of test sample 5 in solutions with different pH values was determined respectively; among which, the permeability retention rate was based on the permeability of test sample 5 in a solution with a pH value of 7; the results are shown in Table 18.
  • the pH value of the highest pH value solution corresponding to a permeability retention rate of not less than 80% was taken as the critical pH value of test sample 5, and the critical pH value was 7.
  • the permeability retention rate was determined by the following formula:
  • val is the permeability retention rate, in %
  • Kal is the permeability under alkaline solution at a certain pH value, in 10 ⁇ 3 ⁇ m2
  • Kial is the baseline permeability, in 10 ⁇ 3 ⁇ m2 .
  • the alkali sensitivity damage rate of test sample 5 was determined as the alkali sensitivity damage rate of the test group; among which, the permeability of test sample 5 in a solution with a pH value of 7 was used as the baseline permeability, and the results are shown in Table 18.
  • the alkali sensitivity damage rate was determined by the following formula:
  • Dal is the alkali sensitivity damage rate, in %
  • Kial is the baseline permeability, in 10 ⁇ 3 ⁇ m2
  • Kal is the permeability of an alkaline solution at a certain pH value, in 10 ⁇ 3 ⁇ m2 .
  • the degree of alkali sensitivity impairment of test sample 5 was evaluated based on its alkali sensitivity impairment rate, and the evaluation result of the alkali sensitivity impairment of test sample 5 was used as the evaluation result of the alkali sensitivity impairment of the test group.
  • the evaluation criteria for the degree of alkali sensitivity impairment are shown in Table 19.
  • the alkali sensitivity damage rate is 30 ⁇ Dal (40.012%) ⁇ 50, indicating a moderate to weak degree of damage.
  • test sample F Take test sample F from the test group. Perform permeability tests on test sample F under different stresses to obtain the permeability of test sample 6 under different stresses.
  • the flow rate is selected as the critical flow rate of the test group corresponding to the critical flow velocity of the test sample; the fluid used for the permeability test is the critical salinity brine of the test group; first, perform the permeability test under the initial stress, then gradually increase the stress to the maximum stress value, and then gradually decrease the stress to the final stress, and maintain the rated time at each stress value and perform the permeability test at each stress value.
  • the initial stress is the effective reservoir stress of the target reservoir, and the final stress is equal to the initial stress.
  • the confining pressure remains unchanged, and the appropriate back pressure is determined according to the stress value (the difference between the confining pressure and the back pressure is the stress).
  • the permeability retention rate of test sample 6 under different stresses was determined, and the results are shown in Table 20.
  • the maximum stress at which the permeability retention rate is not less than 80% during the gradual increase of stress to the maximum stress value is taken as the critical stress of test sample 6, which is the critical stress of the test group; the critical stress is 29 MPa.
  • the permeability retention rate is determined by the following formula:
  • vp is the permeability retention rate, in %
  • Kp is the permeability under a certain stress, in 10 ⁇ 3 ⁇ m2
  • Kip is the baseline permeability, in 10 ⁇ 3 ⁇ m2 .
  • the stress sensitivity damage rate of test sample 6 was determined as the stress sensitivity damage rate of the test group, and the results are shown in Table 20.
  • the stress sensitivity damage rate was determined using the following formula:
  • Dp is the stress-sensitive damage rate, in %
  • Kp is the permeability under a certain stress, in 10 ⁇ 3 ⁇ m2
  • Kip is the baseline permeability, in 10 ⁇ 3 ⁇ m2 .
  • sample 6 was selected for stress sensitivity testing.
  • the stress sensitivity of sample 6 was used as the stress sensitivity of the test group.
  • This also included evaluating the degree of stress sensitivity damage of sample 6 based on the stress sensitivity damage rate of sample F, and using the evaluation result of the stress sensitivity damage of sample 6 as the evaluation result of the stress sensitivity damage of the test group.
  • the evaluation criteria for the degree of stress sensitivity damage are shown in Table 21.
  • the irreversible stress sensitivity damage rate of test sample 6 was determined as the irreversible stress sensitivity damage rate of the test group, which was 45.57%.
  • the irreversible stress sensitivity damage rate was determined using the following formula:
  • Dpn is the irreversible stress-sensitive damage rate, in %
  • Kpn is the permeability under final stress, in 10 ⁇ 3 ⁇ m2
  • Kip is the baseline permeability, in 10 ⁇ 3 ⁇ m2 .

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Abstract

提供了一种低渗储层敏感性评价方法，该方法包括：利用目标储层的全直径岩心制备目标储层的试验样品；对各试验样品分别进行标准盐水渗透率测试，以确定各试验样品能够实现渗透率测试的最小流量即为初始流量，进而按初始流的大小对各试验样品进行分组；对同一组样品进行敏感性测试，包括：在待测组中取A试验样品以其初始流量作为最小流量进行流速敏感性测试，确定待测组的临界流速；在待测组中分别取B、C、D、E、F试验样品进行水敏感性、盐度敏感性、酸敏感性、碱敏感性、应力敏感性测试，得到待测组的水敏感性、盐度敏感性、酸敏感性、碱敏感性、应力敏感性，各敏感性测试过程中流量选用待测组的临界流速对应的临界流量。

Description

低渗储层敏感性评价方法
交叉引用信息
本申请要求于2024年06月12日提交中国专利局、申请号为202410757191.X、发明名称为“低渗储层敏感性评价方法”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本发明涉及油气田开发工程技术领域，具体涉及一种低渗储层敏感性评价方法。
背景技术
近年，世界油气勘探开发领域的中心，正逐步从占油气资源总量20％的常规油气向占油气资源总量80％的非常规油气转变。非常规油气藏的渗流能力差、单井产量低、递减率大、油气田采收率低、稳产难度大、经济效益差，其主要原因在于：非常规油气藏的储层属于低渗透储层(基质渗透率≤0.1×10-3μm2)。大规模水平井体积压裂技术是实现非常规油气藏经济有效开发的关键手段，通过水力压裂“打碎”储层“人造渗透率”，并且形成复杂的裂缝网络。随着钻完井技术以及直井精细分段压裂、水平井分段多簇压裂等储层改造技术的不断创新，非常规油气藏实现了规模化效益开发，但也暴露出产量递减快、单井EUR低等工程难题。非常规油气藏由于储层条件复杂以及开发方式差异性，实际开发过程中存在储层改造方式及改造效果不确定性强问题。
总体而言，目前在开发过程中，低渗储层伤害大以及产量递减快等问题依旧存在，增产效果并未取得实质性突破，现有储层敏感性实验评价结果不能有效未支撑低渗油气藏的高效开发。
在油气田开发的不同阶段，储层会和不同的外来流体接触，当外来流体与储层岩石和/或地层水配伍性差、工艺措施不合理时，会引起储层敏感，发生各种物理、化学反应，导致储层中的油气流动能力下降，不同程度的损害储层生产能力。在钻井过程中会使用钻井液，钻井液具有一定的矿化度和pH值，当钻井液侵入储层后会与储层岩石发生理化作用，使储层渗流能力发生改变。在完井过程中，为提高油气井产量，通常需要对低渗储层进行储层改造，储层改造需要使用前置液、滑溜水、酸液等工作液，当工作液进入储层中与储层的水敏性矿物、酸敏性矿物及储层流体发生反应或者流体流动速度过大时，会产生沉淀、释放出微粒、引起地层微粒运移堵塞孔隙喉道，使储层渗流能力发生变化。在油气生产过程中，随着储层内部油气产出，储层孔隙压力降低，引起储层岩石有效应力变化，而有效应力状态从一个状态变化到另一个状态必然会引起储层岩石变形，储层岩石变形又必然会引起储层孔隙结构和孔隙体积的变化，如孔隙体积缩小、孔隙喉道和裂缝的闭合等，这些变化使岩石渗流能力变化。综上，准确评价储层敏感性、分析储层损伤机理，将会给采油气工艺方案的制订提供重要参考依据。加深对储层敏感性的理解有助于在各个施工环节防止储层损伤，充分发挥储层产能，达到科学开发油气田的目的。
现行的储层敏感性实验评价方法，均是针对常规油气储层(基质渗透率＞1×10-3μm2)的，试验样品多采用由油气储层井下岩心加工成的直径为2.54cm或3.81cm左右、长度不小于直径1.5倍的柱状样，实验介质能直接穿透试验样品开展实验(试验样品不能人工造缝)。当试验样品致密渗透率低时，实验介质就无法穿透试验样品开展敏感性实验评价，此时现行的储层敏感性实验评价方法就出现了明显的不适应性；当出现这种情况后，此试验样品就只能废弃，需要再重新钻取加工新的试验样品，直到找到实验介质能直接穿透的试验样品，如此不仅浪费了大量的珍贵的井下岩心，而且即便找到了实验介质能直接穿透的试验样品，此试验样品往往也不能代表低渗透储层的典型物性特征，敏感性实验结果也就不能真实的反应低渗透储层的敏感性特征。不同敏感性之间有相互影响(例如，盐度敏感性对酸敏感性、碱敏感性、应力敏感性均有影响)，对储层存在叠加损害。现行的储层敏感性实验评价方法多存在实验条件(室温、围压条件)与储层状态不符的问题。简言之，现行的储层敏感性实验评价方法在评价低渗储层敏感性时出现了明显的不适应性。
总之，目前亟待进一步研究能够准确评价低渗储层敏感性的低渗储层敏感性评价方法，为低渗油气藏制定高效开发方案提供数据支撑。
发明内容
本发明的目的在于提供能够准确评价低渗储层敏感性的低渗储层敏感性评价方法，为低渗储层针对性制定开发方案提供有力的数据支撑，确保安全、经济、高效地勘探开发低渗油气藏。
为了实现上述目的，本发明提供了一种低渗储层敏感性评价方法，该方法包括：
步骤1、利用目标储层的全直径岩心制备目标储层的试验样品；制备试验样品过程中，不改变全直径岩心的直径(即试验样品保留全直径岩心的原直径)；
步骤2、对各试验样品分别进行标准盐水渗透率测试，以确定各试验样品能够实现渗透率测试的最小流量即为初始流量，进而按初始流的大小对各试验样品进行分组；
步骤3、对同一组样品进行敏感性测试，包括：
以某一组样品作为待测组；在待测组中取A试验样品进行流速敏感性测试，得到A试验样品的临界流速作为待测组的临界流速，流速敏感性测试过程中以A试验样品的初始流量作为最小流量；
在待测组中取B试验样品进行水敏感性测试，得到B试验样品的水敏感性作为待测组的水敏感性，水敏感性测试过程中流量选用待测组的临界流速对应的B试验样品的临界流量；和/或在待测组中取C试验样品进行盐度敏感性测试，得到C试验样品的盐度敏感性作为待测组的盐度敏感性，盐度敏感性测试过程中流量选用待测组的临界流速对应的C试验样品的临界流量；和/或在待测组中取D试验样品进行酸敏感性测试，得到D试验样品的酸敏感性作为待测组的酸敏感性，酸敏感性测试过程中流量选用待测组的临界流速对应的D试验样品的临界流量；和/或在待测组中取E试验样品进行碱敏感性测试，得到E试验样品的碱敏感性作为待测组的碱敏感性，碱敏感性测试过程中流量选用待测组的临界流速对应的E试验样品的临界流量；和/或在待测组中取F试验样品进行应力敏感性测试，得到F试验样品的应力敏感性作为待测组的应力敏感性，应力敏感性测试过程中流量选用待测组的临界流速对应的F试验样品的临界流量。
本发明提供的低渗储层敏感性评价方法中，步骤3确定得到的待测组的临界流速、水敏感性、盐度敏感性、酸敏感性、碱敏感性、应力敏感性即可反应目标储层中渗透率为待测组渗透的区域的敏感性。
根据低渗储层敏感性评价方法的优选实施方式，其中，试验样品的长度不小于直径的1.5倍；更优选地，利用目标储层的全直径岩心制备目标储层的试验样品包括：对目标储层的全直径岩心进行长度切割得到长度不小于直径1.5倍的岩心作为目标储层的试验样品。
根据低渗储层敏感性评价方法的优选实施方式，其中，试验样品的长度为直径的0.5-1倍；更优选地，利用目标储层的全直径岩心制备目标储层的试验样品包括：对目标储层的全直径岩心进行长度切割得到长度为直径的0.5-1倍的岩心作为目标储层的试验样品。
根据低渗储层敏感性评价方法的优选实施方式，其中，该方法还包括：获取目标储层的储层温度、上覆地层压力、储层孔隙压力，以目标储层的储层温度作为标准盐水渗透率测试、水敏感性测试、盐度敏感性测试、酸敏感性测试、碱敏感性测试、应力敏感性测试过程中试验样品的模拟温度，以上覆地层压力作为标准盐水渗透率测试、水敏感性测试、盐度敏感性测试、酸敏感性测试、碱敏感性测试、应力敏感性测试过程中验样品的实验围压，以储层孔隙压力作为标准盐水渗透率测试、水敏感性测试、盐度敏感性测试、酸敏感性测试、碱敏感性测试过程中试验样品的实验回压。
根据低渗储层敏感性评价方法的优选实施方式，其中，步骤2，对各试验样品分别进行标准盐水渗透率测试，以确定各试验样品能够实现渗透率测试的最小流量即为初始流量，包括：
对各试验样品分别以第1流量进行标准盐水渗透率测试，能够实现渗透率测试的各试验样品的初始流量为第1流量，不能实现渗透率测试的各试验样品记为剩余试验样品；
对各剩余试验样品分别以大于第1流量的第2流量进行标准盐水渗透率测试，能够实现渗透率测试的各试验样品的初始流量为第2流量，不能实现渗透率测试的各试验样品记为剩余试验样品；
重复进行对各剩余试验样品分别以大于第i流量的第i+1流量进行标准盐水渗透率测试，能够实现渗透率测试的各试验样品的初始流量为第i+1流量，不能实现渗透率测试的各试验样品记为剩余试验样品，直至剩余试验样品数量为0。
根据低渗储层敏感性评价方法的优选实施方式，其中，该方法还包括：在待测组中取A试验样品进行流速敏感性测试，得到A试验样品的流速敏感性损害率作为待测组的流速敏感性损害率；
更优选地，该方法还包括：基于A试验样品的流速敏感性损害率进行A试验样品的流速敏感性损害程度评价，并将A试验样品的流速敏感性损害程度评价结果作为待测组的流速敏感性损害程度评价结果；进一步优选地，其中，流速敏感性损害程度评价标准如表1所示：
表1
根据低渗储层敏感性评价方法的优选实施方式，其中，在待测组中取A试验样品进行流速敏感性测试包括：
在待测组中取A试验样品，对A试验样品分别进行不同流量下的标准盐水渗透率测试，得到A试验样品在不同流量下的渗透率；其中，先进行低流量下的标准盐水渗透率测试，再进行高流量下的标准盐水渗透率测试，最低流量取A试验样品的初始流量；
更优选地，A试验样品的临界流速通过下述方式确定得到：
基于A试验样品在不同流量下的渗透率数据分别确定A试验样品在不同流量下的渗透率保持率；其中，渗透率保持率以初始流量下的渗透率为基准渗透率；将渗透率保持率不低于80％时对应的最高流量作为A试验样品的临界矿流量，将A试验样品的临界流量对应的临界流速作为A试验样品的临界流速；
其中，渗透率保持率通过下述公式确定得到：
式中：vn为渗透率保持率，单位％；Kn为某流量下的渗透率，单位10-3μm2；Kin为基准渗透率，单位10-3μm2；
其中，流量对应的流速通过下述公式确定得到：
式中：v为流速，单位cm/min；Q为流量，单位cm3/min；d为试验样品直径，单位cm。
更优选地，A试验样品的流速敏感性损害率通过下述方式确定得到：
基于A试验样品在不同流量下的渗透率数据分别确定A试验样品在不同流量下的流速敏感性损害率；其中，流速敏感性损害率以初始流量下的渗透率为基准渗透率；
其中，流速敏感性损害率通过下述公式确定得到：
式中：Dn为流速敏感性损害率，单位％；Kin为基准渗透率，单位10-3μm2；Kn为某流量下的渗透率，单位10-3μm2；
根据低渗储层敏感性评价方法的优选实施方式，其中，得到B试验样品的水敏感性作为待测组的水敏感性包括：
得到B试验样品的水敏感性损害率作为待测组的水敏感性损害率；
更优选地，得到B试验样品的水敏感性作为待测组的水敏感性还包括：
基于B试验样品的水敏感性损害率进行B试验样品的水敏感性损害程度评价，得到B试验样品的水敏感性损害程度评价结果作为待测组的水敏感性损害程度评价结果；进一步优选地，水敏感性损害程度评价标准如表2所示；再优选地，对同一组样品进行敏感性测试过程中当待测组的水敏感性损害程度评价结果为无或弱时，不进行步骤“在待测组中取C试验样品进行盐度敏感性测试得到C试验样品的盐度敏感性作为待测组的盐度敏感性”。
表2
更优选地，在待测组中取B试验样品进行水敏感性测试包括：
在待测组中取B试验样品；首先，对B试验样品，以待测组的临界流速对应的该试验样品的临界流量进行标准盐水渗透率测试，得到B试验样品标准盐水渗透率；然后，对B试验样品，以待测组的临界流速对应的该试验样品的临界流量进行1/2标准盐水渗透率测试，得到B试验样品1/2标准盐水渗透率；进而，对B试验样品，以待测组的临界流速对应的该试验样品的临界流量进行蒸馏水渗透率测试，得到B试验样品蒸馏水渗透率；
进一步优选地，B试验样品的水敏感性损害率通过下述方式确定得到：
基于B试验样品标准盐水渗透率和B试验样品蒸馏水渗透率，确定B试验样品的水敏感性损害率作为待测组的水敏感性损害率；其中，水敏感性损害率通过下述公式确定得到：
式中：Dw为水敏感性损害率，单位％；Kiw为标准盐水渗透率，单位10-3μm2；Kw为蒸馏水渗透率，单位10-3μm2；
根据低渗储层敏感性评价方法的优选实施方式，其中，在待测组中取C试验样品进行盐度敏感性测试，得到C试验样品的盐度敏感性作为待测组的盐度敏感性包括：
在待测组中取C试验样品进行盐度敏感性测试得到C试验样品的临界矿化度速作为待测组的临界矿化度；
更优选地，在待测组中取C试验样品进行盐度敏感性测试得到C试验样品的临界矿化度速作为待测组的临界矿化度包括：
在待测组中取C试验样品；
对C试验样品分别以待测组的临界流速对应的该试验样品的临界流量进行不同含盐浓度盐水渗透率测试，得到C试验样品在不同含盐浓度盐水下的渗透率；其中，先进行高含盐浓度盐水渗透率测试，再进行低含盐浓度盐水渗透率测试，最高含盐浓度盐水取标准盐水，最低含盐浓度盐水取蒸馏水；
基于C试验样品在不同含盐浓度盐水下的渗透率，分别确定C试验样品在不同含盐浓度盐水下的渗透率保持率；其中，渗透率保持率以标准盐水下的渗透率为基准渗透率；
将渗透率保持率不低于80％时对应的最低浓度盐水的矿化度作为C试验样品的临界矿化度即为待测组的临界矿化度；
其中，渗透率保持率通过下述公式确定得到：
式中：vsn为渗透率保持率，单位％；Ks为某含盐浓度盐水下的渗透率，单位10-3μm2；Kis为标准盐水下的渗透率即为初始渗透率，单位10-3μm2。
根据低渗储层敏感性评价方法的优选实施方式，其中，在酸敏感性测试过程中，渗透率测试用流体的矿化度等于待测组临界矿化度。
根据低渗储层敏感性评价方法的优选实施方式，其中，得到D试验样品的酸敏感性作为待测组的酸敏感性包括：
得到D试验样品的酸敏感性损害率作为待测组的酸敏感性损害率；
更优选地，得到D试验样品的酸敏感性作为待测组的酸敏感性还包括：基于D试验样品的酸敏感性损害率进行D试验样品的酸敏感性损害程度评价，得到D试验样品的酸敏感性损害程度评价结果作为待测组的酸敏感性损害程度评价结果；进一步优选地，酸敏感性损害程度评价标准如表3所示：
表3
更优选地，在待测组中取D试验样品进行酸敏感性测试包括：
在待测组中取D试验样品；首先，对D试验样品，以待测组的临界流速对应的该试验样品的临界流量进行待测组临界矿化度盐水渗透率测试，得到D试验样品酸作用前渗透率；然后，向D试验样品中驱替酸液并使D试验样品与酸液反应一段时间；进而，再对D试验样品，以待测组的临界流速对应的该试验样品的临界流量进行待测组临界矿化度盐水渗透率测试，得到D试验样品酸作用后渗透率；
进一步优选地，向D试验样品中驱替酸液至液流出口有酸液流出停止注酸；
进一步优选地，D试验样品的酸敏感性损害率通过下述方法确定得到：
基于D试验样品酸作用前渗透率和酸作用后渗透率，确定D试验样品的酸敏感性损害率作为待测组的酸敏感性损害率；其中，酸敏感性损害率通过下述公式确定得到：
式中：Dac为酸敏感性损害率，单位％；Kiac为酸作用前渗透率，单位10-3μm2；Kac为酸作用后渗透率，单位10-3μm2；
根据低渗储层敏感性评价方法的优选实施方式，其中，在碱敏感性测试过程中，渗透率测试用流体的矿化度等于待测组临界矿化度。
根据低渗储层敏感性评价方法的优选实施方式，其中，得到E试验样品的碱敏感性作为待测组的碱敏感性包括：
得到E试验样品的临界pH值即为待测组的临界pH值，和/或得到E试验样品的碱敏感性损害率作为待测组的碱敏感性损害率；
更优选地，得到E试验样品的碱敏感性作为待测组的碱敏感性还包括：基于E试验样品的碱敏感性损害率进行E试验样品的碱敏感性损害程度评价，得到E试验样品的碱敏感性损害程度评价结果作为待测组的碱敏感性损害程度评价结果；进一步优选地，碱敏感性损害程度评价标准如表4所示：
表4
更优选地，在待测组中取E试验样品进行碱敏感性测试得到包括：
在待测组中取E试验样品；对E试验样品分别以待测组的临界流速对应的该试验样品的临界流量进行不同pH值溶液渗透率测试，得到E试验样品在不同pH值溶液下的渗透率；其中，先进行低pH值溶液渗透率测试，再进行高pH值溶液渗透率测试，溶液的pH值为7-14，最低pH值溶液的pH值为7，溶液的矿化度等于待测组临界矿化度；E试验样品基准渗透率；
进一步优选地，E试验样品的临界pH值通过下述方式进行确定：
基于E试验样品在不同pH值溶液下的渗透率，分别确定E试验样品在不同pH值溶液下的渗透率保持率；其中，渗透率保持率以E试验样品在pH值为7的溶液下的渗透率为基准渗透率；
将渗透率保持率不低于80％时对应的最高pH值溶液的pH值作为E试验样品的临界pH值；
其中，渗透率保持率通过下述公式确定得到：
式中：val为渗透率保持率，单位％；Kal为某pH值碱液下的渗透率，单位10-3μm2；Kial为基准渗透率，单位10-3μm2；
进一步优选地，E试验样品的碱敏感性损害率通过下述方式进行确定：
基于E试验样品在不同pH值溶液下的渗透率，确定得到E试验样品的碱敏感性损害率；其中，碱敏感性损害率以E试验样品在pH值为7的溶液下的渗透率为基准渗透率；其中，碱敏感性损害率通过下述公式确定得到：
式中：Dal为碱敏感性损害率，单位％；Kial为基准渗透率，单位10-3μm2；Kal为某pH值碱液下的渗透率，单位10-3μm2。
根据低渗储层敏感性评价方法的优选实施方式，其中，进行应力敏感性测试过程中渗透率测试用流体使用待测组临界矿化度盐水。
根据低渗储层敏感性评价方法的优选实施方式，其中，得到F试验样品的应力敏感性作为待测组的应力敏感性包括：
得到F试验样品的临界应力作为待测组的临界应力，和/或得到F试验样品的不可逆应力敏感性损害率作为待测组的不可逆应力敏感性损害率，和/或得到F试验样品的应力敏感性损害率作为待测组的应力敏感性损害率；
更优选地，得到F试验样品的应力敏感性作为待测组的应力敏感性还包括：基于F试验样品的应力敏感性损害率进行F试验样品的应力敏感性损害程度评价，得到F试验样品的应力损害程度评价结果作为待测组的应力敏感性损害程度评价结果；进一步优选地，应力敏感性损害程度评价标准如表5所示：
表5

更优选地，在待测组中取F试验样品进行应力敏感性测试得包括：
在待测组中取F试验样品；对F试验样品进行不同应力下渗透率测试，得到F试验样品在不同应力下的渗透率；在渗透率测试过程中，流量选择待测组的临界流速对应的该试验样品的临界流量；渗透率测试用流体使用待测组临界矿化度盐水；先进行初始应力下渗透率测试，再逐步增大应力至最大应力值，进而逐步减小应力至最终应力，并分别在各应力值下保持额定时间且分别在各应力值下进行渗透率测试，初始应力为目标储层的储层有效应力，最终应力等于初始应力；
进一步优选地，对F试验样品进行不同应力下渗透率测试过程中，围压保持不变、根据应力值确定合适的回压(围压与回压差为应力)；
进一步优选地，F试验样品的临界应力通过下述方式进行确定：
基于F试验样品在不同应力下的渗透率，以初始应力下的渗透率作为基准渗透率，分别确定F试验样品在不同应力下的渗透率保持率；将逐步增大应力至最大应力值过程中测得的渗透率保持率不低于80％时对应的最大应力作为F试验样品的临界应力；
其中，渗透率保持率通过下述公式确定得到：
式中：vp为渗透率保持率，单位％；Kp为某应力下的渗透率，单位10-3μm2；Kip为基准渗透率，单位10-3μm2；
进一步优选地，F试验样品的不可逆应力敏感性损害率通过下述方式进行确定：
基于F试验样品在初始应力下的渗透率和在最终应力下的渗透率，以初始应力下的渗透率作为基准渗透率，确定得到F试验样品的不可逆应力敏感性损害率作为待测组的不可逆应力敏感性损害率；其中，不可逆应力敏感性损害率通过下述公式确定：
式中：Dpn为不可逆应力敏感性损害率，单位％；Kpn为最终应力下的渗透率，单位10-3μm2；Kip为基准渗透率，单位10-3μm2；
进一步优选地，F试验样品的应力敏感性损害率通过下述方式进行确定：
基于F试验样品在不同应力下的渗透率，以初始应力下的渗透率作为基准渗透率，确定得到F试验样品的应力敏感性损害率作为待测组的应力敏感性损害率；
其中，应力敏感性损害率通过下述公式确定得到：
式中：Dp为应力敏感性损害率，单位％；Kp为某应力下的渗透率，单位10-3μm2；Kip为基准渗透率，单位10-3μm2。
根据低渗储层敏感性评价方法的优选实施方式，其中，
标准盐水指NaCl质量含量为8％的NaCl水溶液；
3/4标准盐水指NaCl质量含量为6％的NaCl水溶液；
1/2标准盐水指NaCl质量含量为4％的NaCl水溶液；
1/4标准盐水指NaCl质量含量为2％的NaCl水溶液。
根据低渗储层敏感性评价方法的优选实施方式，其中，进行敏感性测试过程中使用的溶液，矿化度由NaCl提供，碱性由NaOH提供，酸性由HCl提供。
根据低渗储层敏感性评价方法的优选实施方式，其中，渗透率测试采用超低渗透率测试仪，所述超低渗透率测试仪的测试下限不超过10-4mD，围压上限不低于80MPa。
本发明提供的技术方案解决了现有实验方法无法评价低渗储层敏感性大小的问题。与现有技术相比，本发明提供的技术方案具备如下有益效果：
1、本发明提供的技术方案试验样品采用全直径岩心保留原直径制备得到的试验样品进行敏感性测试，保留了油气储层井下岩心原始渗流通道，避免了油气储层井下岩心在加工过程中(通常加工成直径为2.54cm或3.81cm左右的柱状样)为保证加工成功而人为避开油气储层井下岩心中松散区域(即渗流通道区域)从而导致数据不准确的问题，能够很好的适应低渗储层敏感性评价。
2、本发明提供的技术方案针对本技术方案使用的特殊样品提出了新的敏感性测试流程，能够消除不同敏感性之间的相互影响，能够准确的评价低渗储层敏感性损害。
3、本发明提供的技术方案能够有效解决由于现行的储层敏感性实验评价方法对低渗透储层不适用导致的井下岩心浪费问题。
附图说明
图1为本发明实施例1中流速敏感性实验曲线图。
图2为本发明实施例1中盐度敏感性曲线图。
具体实施方式
为使本发明实施例的目的、技术方案和优点更加清楚明白，下面结合附图对本发明实施例做进一步详细说明。在此，本发明的示意性实施例及其说明用于解释本发明，但并不作为对本发明的限定。
本发明一具体实施方式提供了一种低渗储层敏感性评价方法，该方法包括：
步骤101，利用目标储层的全直径岩心制备目标储层的试验样品；制备试验样品过程中，不改变全直径岩心的直径(即试验样品保留全直径岩心的原直径)；
步骤102、对各试验样品分别进行标准盐水渗透率测试，以确定各试验样品能够实现渗透率测试的最小流量即为初始流量，进而按初始流的大小对各试验样品进行分组；
步骤103、对同一组样品进行敏感性测试，包括：
以某一组样品作为待测组；在待测组中取A试验样品进行流速敏感性测试得到A试验样品的临界流速作为待测组的临界流速，流速敏感性测试过程中以A试验样品的初始流量作为最小流量；
在待测组中取B试验样品进行水敏感性测试得到B试验样品的水敏感性作为待测组的水敏感性，水敏感性测试过程中流量选用待测组的临界流速对应的B试验样品的临界流量；和/或在待测组中取C试验样品进行盐度敏感性测试得到C试验样品的盐度敏感性作为待测组的盐度敏感性，盐度敏感性测试过程中流量选用待测组的临界流速对应的C试验样品的临界流量；和/或在待测组中取D试验样品进行酸敏感性测试得到D试验样品的酸敏感性作为待测组的酸敏感性，酸敏感性测试过程中流量选用待测组的临界流速对应的D试验样品的临界流量；和/或在待测组中取E试验样品进行碱敏感性测试得到E试验样品的碱敏感性作为待测组的碱敏感性，碱敏感性测试过程中流量选用待测组的临界流速对应的E试验样品的临界流量；和/或在待测组中取F试验样品进行应力敏感性测试得到F试验样品的应力敏感性作为待测组的应力敏感性，应力敏感性测试过程中流量选用待测组的临界流速对应的F试验样品的临界流量。
具体实施方式提供的低渗储层敏感性评价方法中，步骤103确定得到的待测组的临界流速、水敏感性、盐度敏感性、酸敏感性、碱敏感性、应力敏感性即可反应目标储层中渗透率为待测组渗透的区域的敏感性。
在一个实施例中，试验样品的长度不小于直径的1.5倍；
进一步地，利用目标储层的全直径岩心制备目标储层的试验样品包括：对目标储层的全直径岩心进行长度切割得到长度不小于直径1.5倍的岩心作为目标储层的试验样品。
在一个实施例中，该方法还包括：获取目标储层的储层温度、上覆地层压力、储层孔隙压力，以目标储层的储层温度作为标准盐水渗透率测试、水敏感性测试、盐度敏感性测试、酸敏感性测试、碱敏感性测试、应力敏感性测试过程中试验样品的模拟温度，以上覆地层压力作为标准盐水渗透率测试、水敏感性测试、盐度敏感性测试、酸敏感性测试、碱敏感性测试、应力敏感性测试过程中验样品的实验围压，以储层孔隙压力作为标准盐水渗透率测试、水敏感性测试、盐度敏感性测试、酸敏感性测试、碱敏感性测试过程中试验样品的实验回压。
在一个实施例中，步骤102，对各试验样品分别进行标准盐水渗透率测试，以确定各试验样品能够实现渗透率测试的最小流量即为初始流量包括：
对各试验样品分别以第1流量进行标准盐水渗透率测试，能够实现渗透率测试的各试验样品的初始流量为第1流量，不能实现渗透率测试的各试验样品记为剩余试验样品；
对各剩余试验样品分别以大于第1流量的第2流量进行标准盐水渗透率测试，能够实现渗透率测试的各试验样品的初始流量为第2流量，不能实现渗透率测试的各试验样品记为剩余试验样品；
重复进行对各剩余试验样品分别以大于第i流量的第i+1流量进行标准盐水渗透率测试，能够实现渗透率测试的各试验样品的初始流量为第i+1流量，不能实现渗透率测试的各试验样品记为剩余试验样品，直至剩余试验样品数量为0；
举例而言，第1流量为0.1cm3/min、第2流量为0.5cm3/min、第3流量为1cm3/min。
在一个实施例中，步骤103，在待测组中取A试验样品进行流速敏感性测试得到A试验样品的临界流速作为待测组的临界流速包括：
在待测组中取A试验样品，对A试验样品分别进行不同流量下的标准盐水渗透率测试，得到A试验样品在不同流量下的渗透率；其中，先进行低流量下的标准盐水渗透率测试，再进行高流量下的标准盐水渗透率测试，最低流量取A试验样品的初始流量；
基于A试验样品在不同流量下的渗透率，分别确定A试验样品在不同流量下的渗透率保持率；其中，渗透率保持率以初始流量下的渗透率为基准渗透率；
将渗透率保持率不低于80％时对应的最高流量作为A试验样品的临界矿流量，将A试验样品的临界流量对应的临界流速作为A试验样品的临界流速即为待测组的临界流速；
其中，渗透率保持率通过下述公式确定得到：
式中：vn为渗透率保持率，单位％；Kn为某流量下的渗透率，单位10-3μm2；Kin为基准渗透率，单位10-3μm2；
其中，流量对应的流速通过下述公式确定得到：
式中：v为流速，单位cm/min；Q为流量，单位cm3/min；d为试验样品直径，单位cm。
在一个实施例中，步骤103还包括：基于A试验样品的流速敏感性测试数据，确定得到A试验样品的流速敏感性损害率作为待测组的流速敏感性损害率；其中，流速敏感性损害率以初始流量下的渗透率为基准渗透率；
其中，流速敏感性损害率通过下述公式确定得到：
式中：Dn为流速敏感性损害率，单位％；Kin为基准渗透率，单位10-3μm2；Kn为某流量下的渗透率，单位10-3μm2；
进一步地，步骤103还包括：基于A试验样品的流速敏感性损害率进行A试验样品的流速敏感性损害程度评价，并将A试验样品的流速敏感性损害程度评价结果作为待测组的流速敏感性损害程度评价结果；进一步优选地，其中，流速敏感性损害程度评价标准如表6所示：
表6
在一个实施例中，在待测组中取B试验样品进行水敏感性测试，得到B试验样品的水敏感性作为待测组的水敏感性包括：
在待测组中取B试验样品进行水敏感性测试，得到B试验样品的水敏感性损害率作为待测组的水敏感性损害率；
进一步地，在待测组中取B试验样品进行水敏感性测试，得到B试验样品的水敏感性损害率作为待测组的水敏感性损害率包括：
在待测组中取B试验样品；首先，对B试验样品，以待测组的临界流速对应的该试验样品的临界流量进行标准盐水渗透率测试，得到B试验样品标准盐水渗透率；然后，对B试验样品，以待测组的临界流速对应的该试验样品的临界流量进行1/2标准盐水渗透率测试，得到B试验样品1/2标准盐水渗透率；进而，对B试验样品，以待测组的临界流速对应的该试验样品的临界流量进行蒸馏水渗透率测试，得到B试验样品蒸馏水渗透率；基于B试验样品标准盐水渗透率和B试验样品蒸馏水渗透率，确定B试验样品的水敏感性损害率作为待测组的水敏感性损害率；其中，水敏感性损害率通过下述公式确定得到：
式中：Dw为水敏感性损害率，单位％；Kiw为标准盐水渗透率，单位10-3μm2；Kw为蒸馏水渗透率，单位10-3μm2；
更进一步地，在待测组中取B试验样品进行水敏感性测试，得到B试验样品的水敏感性作为待测组的水敏感性还包括：基于B试验样品的水敏感性损害率进行B试验样品的水敏感性损害程度评价，并将B试验样品的水敏感性损害程度评价结果作为待测组的水敏感性损害程度评价结果；再进一步地，水敏感性损害程度评价标准如表7所示；又进一步地，对同一组样品进行敏感性测试过程中当待测组的水敏感性损害程度评价结果为无或弱时，不进行步骤“在待测组中取C试验样品进行盐度敏感性测试得到C试验样品的盐度敏感性作为待测组的盐度敏感性”。
表7
在一个实施例中，在待测组中取C试验样品进行盐度敏感性测试，得到C试验样品的盐度敏感性作为待测组的盐度敏感性包括：
在待测组中取C试验样品进行盐度敏感性测试，得到C试验样品的临界矿化度速作为待测组的临界矿化度；
进一步地，在待测组中取C试验样品进行盐度敏感性测试，得到C试验样品的临界矿化度速作为待测组的临界矿化度包括：
在待测组中取C试验样品；
对C试验样品分别以待测组的临界流速对应的该试验样品的临界流量进行不同含盐浓度盐水渗透率测试，得到C试验样品在不同含盐浓度盐水下的渗透率；其中，先进行高含盐浓度盐水渗透率测试，再进行低含盐浓度盐水渗透率测试，最高含盐浓度盐水取标准盐水，最低含盐浓度盐水取蒸馏水；
基于C试验样品在不同含盐浓度盐水下的渗透率，分别确定C试验样品在不同含盐浓度盐水下的渗透率保持率；其中，渗透率保持率以标准盐水下的渗透率为基准渗透率；
将渗透率保持率不低于80％时对应的最低浓度盐水的矿化度作为C试验样品的临界矿化度即为待测组的临界矿化度；
其中，渗透率保持率通过下述公式确定得到：
式中：vsn为渗透率保持率，单位％；Ks为某含盐浓度盐水下的渗透率，单位10-3μm2；Kis为标准盐水下的渗透率即为初始渗透率，单位10-3μm2。
在一个实施例中，在酸敏感性测试过程中，渗透率测试用流体选用待测组临界矿化度盐水(即矿化度为待测组临界矿化度的盐水)。
在一个实施例中，在待测组中取D试验样品进行酸敏感性测试，得到D试验样品的酸敏感性作为待测组的酸敏感性包括：
在待测组中取D试验样品进行酸敏感性测试，得到D试验样品的酸敏感性损害率作为待测组的酸敏感性损害率；
进一步地，在待测组中取D试验样品进行酸敏感性测试得到D试验样品的酸敏感性损害率作为待测组的酸敏感性损害率包括：
在待测组中取D试验样品；
首先，对D试验样品，以待测组的临界流速对应的该试验样品的临界流量进行待测组临界矿化度盐水渗透率测试，得到D试验样品酸作用前渗透率；然后，向D试验样品中驱替酸液并使D试验样品与酸液反应一段时间；进而，再对D试验样品，以待测组的临界流速对应的该试验样品的临界流量进行待测组临界矿化度盐水渗透率测试，得到D试验样品酸作用后渗透率；
基于D试验样品酸作用前渗透率和酸作用后渗透率，确定D试验样品的酸敏感性损害率作为待测组的酸敏感性损害率；
其中，酸敏感性损害率通过下述公式确定得到：
式中：Dac为酸敏感性损害率，单位％；Kiac为酸作用前渗透率，单位10-3μm2；Kac为酸作用后渗透率，单位10-3μm2；
更进一步地，向D试验样品中驱替酸液至液流出口有酸液流出停止注酸；
更进一步地，在待测组中取D试验样品进行酸敏感性测试，得到D试验样品的酸敏感性作为待测组的酸敏感性还包括：基于D试验样品的酸敏感性损害率进行D试验样品的酸敏感性损害程度评价，并将D试验样品的酸敏感性损害程度评价结果作为待测组的酸敏感性损害程度评价结果；再进一步地，酸敏感性损害程度评价标准如表8所示：
表8
在一个实施例中，在碱敏感性测试过程中，渗透率测试用流体的矿化度等于待测组临界矿化度。
在一个实施例中，在待测组中取E试验样品进行碱敏感性测试，得到E试验样品的碱敏感性作为待测组的碱敏感性包括：
在待测组中取E试验样品进行碱敏感性测试，得到E试验样品的临界pH值即为待测组的临界pH值；
进一步地，在待测组中取E试验样品进行碱敏感性测试，得到E试验样品的临界pH值即为待测组的临界pH值包括：
在待测组中取E试验样品；
对E试验样品分别以待测组的临界流速对应的该试验样品的临界流量进行不同pH值溶液渗透率测试，得到E试验样品在不同pH值溶液下的渗透率；其中，先进行低pH值溶液渗透率测试，再进行高pH值溶液渗透率测试，溶液的pH值为7-14，最低pH值溶液的pH值为7，溶液的矿化度等于待测组临界矿化度；
基于E试验样品在不同pH值溶液下的渗透率，分别确定E试验样品在不同pH值溶液下的渗透率保持率；其中，渗透率保持率以E试验样品在pH值为7的溶液下的渗透率为基准渗透率；
将渗透率保持率不低于80％时对应的最高pH值溶液的pH值作为E试验样品的临界pH值；
其中，渗透率保持率通过下述公式确定得到：
式中：val为渗透率保持率，单位％；Kal为某pH值碱液下的渗透率，单位10-3μm2；Kial为基准渗透率，单位10-3μm2。
在一个实施例中，在待测组中取E试验样品进行碱敏感性测试，得到E试验样品的碱敏感性作为待测组的碱敏感性包括：
在待测组中取E试验样品进行碱敏感性测试，得到E试验样品的碱敏感性损害率作为待测组的碱敏感性损害率；
进一步地，在待测组中取E试验样品进行碱敏感性测试得到E试验样品的碱敏感性损害率作为待测组的碱敏感性损害率包括：
在待测组中取E试验样品；
对E试验样品分别以待测组的临界流速对应的该试验样品的临界流量进行不同pH值溶液渗透率测试，得到E试验样品在不同pH值溶液下的渗透率；其中，先进行低pH值溶液渗透率测试，再进行高pH值溶液渗透率测试，溶液的pH值为7-14，最低pH值溶液的pH值为7，溶液的矿化度等于待测组临界矿化度；
基于E试验样品在不同pH值溶液下的渗透率，确定得到E试验样品的碱敏感性损害率作为待测组的碱敏感性损害率；其中，碱敏感性损害率以E试验样品在pH值为7的溶液下的渗透率为基准渗透率；
其中，碱敏感性损害率通过下述公式确定得到：
式中：Dal为碱敏感性损害率，单位％；Kial为基准渗透率，单位10-3μm2；Kal为某pH值碱液下的渗透率，单位10-3μm2；
更进一步地，在待测组中取E试验样品进行碱敏感性测试，得到E试验样品的碱敏感性作为待测组的碱敏感性还包括：基于E试验样品的碱敏感性损害率进行E试验样品的碱敏感性损害程度评价，并将E试验样品的碱敏感性损害程度评价结果作为待测组的碱敏感性损害程度评价结果；
再进一步地，碱敏感性损害程度评价标准如表9所示：
表9

在一个实施例中，进行应力敏感性测试过程中渗透率测试用流体使用待测组临界矿化度盐水。
在一个实施例中，在待测组中取F试验样品进行应力敏感性测试，得到F试验样品的应力敏感性作为待测组的应力敏感性包括：
在待测组中取F试验样品进行应力敏感性测试，得到F试验样品的临界应力作为待测组的临界应力；
进一步地，在待测组中取F试验样品进行应力敏感性测试，得到F试验样品的临界应力作为待测组的临界应力包括：
在待测组中取F试验样品；
对F试验样品进行不同应力下渗透率测试，得到F试验样品在不同应力下的渗透率；在渗透率测试过程中，流量选择待测组的临界流速对应的该试验样品的临界流量；渗透率测试用流体使用待测组临界矿化度盐水；先进行初始应力下渗透率测试，再逐步增大应力至最大应力值，进而逐步减小应力至最终应力，并分别在各应力值下保持额定时间且分别在各应力值下进行渗透率测试，初始应力为目标储层的储层有效应力，最终应力等于初始应力；
基于F试验样品在不同应力下的渗透率，以初始应力下的渗透率作为基准渗透率，分别确定F试验样品在不同应力下的渗透率保持率；
将逐步增大应力至最大应力值过程中测得的渗透率保持率不低于80％时对应的最大应力作为F试验样品的临界应力即为待测组的临界应力；
其中，渗透率保持率通过下述公式确定得到：
式中：vp为渗透率保持率，单位％；Kp为某应力下的渗透率，单位10-3μm2；Kip为基准渗透率，单位10-3μm2；
更进一步地，对F试验样品进行不同应力下渗透率测试过程中，围压保持不变、根据应力值确定合适的回压(围压与回压差为应力)。
在一个实施例中，在待测组中取F试验样品进行应力敏感性测试，得到F试验样品的应力敏感性作为待测组的应力敏感性包括：
在待测组中取F试验样品进行应力敏感性测试，得到F试验样品的不可逆应力敏感性损害率作为待测组的不可逆应力敏感性损害率；
进一步地，在待测组中取F试验样品进行应力敏感性测试，得到F试验样品的不可逆应力敏感性损害率作为待测组的不可逆应力敏感性损害率包括：
在待测组中取F试验样品；
对F试验样品进行不同应力下渗透率测试，得到F试验样品在不同应力下的渗透率；在渗透率测试过程中，流量选择待测组的临界流速对应的该试验样品的临界流量；渗透率测试用流体使用待测组临界矿化度盐水；先进行初始应力下渗透率测试，再逐步增大应力至最大应力值，进而逐步减小应力至最终应力，并分别在各应力值下保持额定时间且分别在各应力值下进行渗透率测试，初始应力为目标储层的储层有效应力，最终应力等于初始应力；
基于F试验样品基准渗透率和在最终应力下的渗透率，确定得到F试验样品的不可逆应力敏感性损害率作为待测组的不可逆应力敏感性损害率；
其中，不可逆应力敏感性损害率通过下述公式确定得到：
式中：Dpn为不可逆应力敏感性损害率，单位％；Kpn为最终应力下的渗透率，单位10-3μm2；Kip为基准渗透率，单位10-3μm2。
在一个实施例中，在待测组中取F试验样品进行应力敏感性测试，得到F试验样品的应力敏感性作为待测组的应力敏感性包括：
在待测组中取F试验样品进行应力敏感性测试，得到F试验样品的应力敏感性损害率作为待测组的应力敏感性损害率；
进一步地，在待测组中取F试验样品进行应力敏感性测试，得到F试验样品的应力敏感性损害率作为待测组的应力敏感性损害率包括：
在待测组中取F试验样品；
对F试验样品进行不同应力下渗透率测试，得到F试验样品在不同应力下的渗透率；在渗透率测试过程中，流量选择待测组的临界流速对应的该试验样品的临界流量；渗透率测试用流体使用待测组临界矿化度盐水；先进行初始应力下渗透率测试，再逐步增大应力至最大应力值，进而逐步减小应力至最终应力，并分别在各应力值下保持额定时间且分别在各应力值下进行渗透率测试，初始应力为目标储层的储层有效应力，最终应力等于初始应力；
基于F试验样品在不同应力下的渗透率，确定得到F试验样品的应力敏感性损害率作为待测组的应力敏感性损害率；
其中，应力敏感性损害率通过下述公式确定得到：
式中：Dp为应力敏感性损害率，单位％；Kp为某应力下的渗透率，单位10-3μm2；Kip为基准渗透率，单位10-3μm2；
更进一步地，在待测组中取F试验样品进行应力敏感性测试，得到F试验样品的应力敏感性作为待测组的应力敏感性还包括：基于F试验样品的应力敏感性损害率进行F试验样品的应力敏感性损害程度评价，并将F试验样品的应力损害程度评价结果作为待测组的应力敏感性损害程度评价结果；
再进一步地，其中，应力敏感性损害程度评价标准如表10所示：
表10
在一个实施例中，标准盐水指NaCl质量含量为8％的NaCl水溶液；3/4标准盐水指NaCl质量含量为6％的NaCl水溶液；1/2标准盐水指NaCl质量含量为4％的NaCl水溶液；1/4标准盐水指NaCl质量含量为2％的NaCl水溶液。
在一个实施例中，进行敏感性测试过程中使用的溶液，矿化度由NaCl提供，碱性由NaOH提供，酸性由HCl提供；
举例而言，进行敏感性测试过程中使用的溶液为NaCl水溶液或NaOH水溶液或HCl水溶液或NaCl水溶液和NaOH水溶液的混合溶液或NaCl水溶液和HCl水溶液的混合溶液。
实施例1：
本实施例提供一种低渗储层敏感性评价方法，该方法包括：
1、对目标储层的全直径岩心进行长度切割，得到两端平整、长度不小于直径1.5倍的岩心作为目标储层的试验样品。
2、获取目标储层的储层温度、上覆地层压力、储层孔隙压力，目标储层的储层温度为140℃、上覆地层压力98MPa、储层孔隙压力69MPa。以目标储层的储层温度作为标准盐水渗透率测试、水敏感性测试、盐度敏感性测试、酸敏感性测试、碱敏感性测试、应力敏感性测试过程中试验样品的模拟温度，以上覆地层压力作为标准盐水渗透率测试、水敏感性测试、盐度敏感性测试、酸敏感性测试、碱敏感性测试、应力敏感性测试过程中验样品的实验围压，以储层孔隙压力作为标准盐水渗透率测试、水敏感性测试、盐度敏感性测试、酸敏感性测试、碱敏感性测试过程中试验样品的实验回压。
3、对各试验样品分别以第1流量(0.1cm3/min)进行标准盐水(NaCl质量含量为8％的NaCl水溶液)渗透率测试，能够实现渗透率测试的各试验样品的初始流量为第1流量，不能实现渗透率测试的各试验样品记为剩余试验样品；
对各剩余试验样品分别以大于第1流量的第2流量(0.5cm3/min)进行标准盐水渗透率测试，能够实现渗透率测试的各试验样品的初始流量为第2流量，不能实现渗透率测试的各试验样品记为剩余试验样品；
对各剩余试验样品分别以大于第2流量的第3流量(1cm3/min)进行标准盐水渗透率测试，能够实现渗透率测试的各试验样品的初始流量为第3流量，不能实现渗透率测试的各试验样品记为剩余试验样品；此时剩余试验样品数量为0；
进而按初始流的大小对各试验样品进行分组；第一组试验样品包括试验样品1、试验样品2、试验样品3、试验样品4、试验样品5、试验样品6、试验样品7，第二组试验样品包括试验样品8、试验样品9、试验样品10、试验样品11、试验样品12、试验样品13、试验样品14，第三组试验样品包括试验样品15、试验样品16、试验样品17、试验样品18、试验样品19、试验样品20，第一组试验样品的初始流量为0.1cm3/min，第二组试验样品的初始流量为0.5cm3/min，第三组试验样品的初始流量为1cm3/min。
4、以第一组试验样品(第一组试验样品的平均渗透率约为0.896×10-3μm2)作为待测组，进行敏感性测试，确定得到目标储层中渗透率为0.896×10-3μm2左右区域的敏感性。具体包括：
4.1、在待测组中取试验样品1，对试验样品1分别进行不同流量下的标准盐水渗透率测试，得到试验样品1在不同流量下的渗透率；其中，先进行低流量下的标准盐水渗透率测试，再进行高流量下的标准盐水渗透率测试，最低流量取试验样品1的初始流量。
基于A试验样品在不同流量下的渗透率，分别确定试验样品1在不同流量下的渗透率保持率；其中，渗透率保持率以初始流量下的渗透率为基准渗透率。结果如表11、图1所示。其中，渗透率保持率通过下述公式确定得到：
式中：vn为渗透率保持率，单位％；Kn为某流量下的渗透率，单位10-3μm2；Kin为基准渗透率，单位10-3μm2。
将渗透率保持率不低于80％时对应的最高流量作为试验样品1的临界矿流量，将试验样品1的临界流量对应的临界流速作为试验样品1的临界流速即为待测组的临界流速。本实施例中，如表11和图1所示，流量0.1cm3/min所对应的流速为临界流速，试验样品1直径6.5cm，临界流速为0.003cm/min。其中，流量对应的流速通过下述公式确定得到：
式中：v为流速，单位cm/min；Q为流量，单位cm3/min；d为试验样品直径，单位cm。
基于试验样品1的流速敏感性测试数据，确定得到试验样品1的流速敏感性损害率作为待测组的流速敏感性损害率；其中，流速敏感性损害率以初始流量下的渗透率为基准渗透率。结果如表11所示。其中，流速敏感性损害率通过下述公式确定得到：
式中：Dn为流速敏感性损害率，单位％；Kin为基准渗透率，单位10-3μm2；Kn为某流量下的渗透率，单位10-3μm2。
表11
基于试验样品1的流速敏感性损害率进行试验样品1的流速敏感性损害程度评价，并将试验样品1的流速敏感性损害程度评价结果作为待测组的流速敏感性损害程度评价结果；其中，流速敏感性损害程度评价标准如表12所示：
表12

例流量0.25cm3/min时，渗透率损害率30＜Dn(30.2％)≤50，流速敏感性损害程度为中等偏弱。
4.2、在待测组中取试验样品2；首先，对试验样品2，以待测组的临界流速对应的该试验样品的临界流量进行标准盐水渗透率测试，得到试验样品2标准盐水渗透率；然后，对试验样品2，以待测组的临界流速对应的该试验样品的临界流量进行1/2标准盐水(NaCl质量含量为4％的NaCl水溶液)渗透率测试，得到试验样品2的1/2标准盐水渗透率；进而，对试验样品2，以待测组的临界流速对应的该试验样品的临界流量进行蒸馏水渗透率测试，得到试验样品2蒸馏水渗透率。结果如表13所示。
表13
基于试验样品2标准盐水渗透率和试验样品2蒸馏水渗透率，确定试验样品2的水敏感性损害率作为待测组的水敏感性损害率，水敏感性损害率为47.37％。其中，水敏感性损害率通过下述公式确定得到：
式中：Dw为水敏感性损害率，单位％；Kiw为标准盐水渗透率，单位10-3μm2；Kw为蒸馏水渗透率，单位10-3μm2。
基于试验样品2的水敏感性损害率进行试验样品2的水敏感性损害程度评价，并将试验样品2的水敏感性损害程度评价结果作为待测组的水敏感性损害程度评价结果；其中，水敏感性损害程度评价标准如表14所示；
表14
水敏感性损害率30＜Dw(47.37％)≤50，水敏感性损害程度为中等偏弱。
4.3、待测组的水敏感性损害程度评价结果为中等偏弱，因此，需开展盐度敏感性实验。在待测组中取试验样品3；对试验样品3分别以待测组的临界流速对应的该试验样品的临界流量进行不同含盐浓度盐水渗透率测试，得到试验样品3在不同含盐浓度盐水下的渗透率；其中，先进行高含盐浓度盐水渗透率测试，再进行低含盐浓度盐水渗透率测试，最高含盐浓度盐水取标准盐水，最低含盐浓度盐水取蒸馏水。基于试验样品3在不同含盐浓度盐水下的渗透率，分别确定试验样品3在不同含盐浓度盐水下的渗透率保持率；其中，渗透率保持率以标准盐水下的渗透率为基准渗透率。结果如表15、图2所示。将渗透率保持率不低于80％时对应的最低浓度盐水的矿化度作为试验样品3的临界矿化度即为待测组的临界矿化度，临界矿化度为80000mg/L。其中，渗透率保持率通过下述公式确定得到：
式中：vsn为渗透率保持率，单位％；Ks为某含盐浓度盐水下的渗透率，单位10-3μm2；Kis为标准盐水下的渗透率即为初始渗透率，单位10-3μm2。
表15
4.4、在待测组中取试验样品4。首先，对试验样品4，以待测组的临界流速对应的该试验样品的临界流量进行待测组临界矿化度盐水渗透率测试，得到试验样品4酸作用前渗透率；然后，向试验样品4中驱替酸液至液流出口有酸液流出停止注酸并使试验样品4与酸液反应一段时间；进而，再对试验样品4，以待测组的临界流速对应的该试验样品的临界流量进行待测组临界矿化度盐水渗透率测试，得到试验样品4酸作用后渗透率。基于试验样品4酸作用前渗透率和酸作用后渗透率，确定试验样品4的酸敏感性损害率作为待测组的酸敏感性损害率，结果如表16所示。基于试验样品4的酸敏感性损害率进行试验样品4的酸敏感性损害程度评价，并将试验样品4的酸敏感性损害程度评价结果作为待测组的酸敏感性损害程度评价结果，其中，酸敏感性损害程度评价标准如表17所示。
其中，酸敏感性损害率通过下述公式确定得到：
式中：Dac为酸敏感性损害率，单位％；Kiac为酸作用前渗透率，单位10-3μm2；Kac为酸作用后渗透率，单位10-3μm2。
表16
表17
酸敏感性损害率30＜Dac(28.99％)≤50，酸敏感性损害程度为弱。
4.5、在待测组中取试验样品5。对试验样品5分别以待测组的临界流速对应的该试验样品的临界流量进行不同pH值溶液渗透率测试，得到试验样品5在不同pH值溶液下的渗透率。其中，依次使用pH值为7、8.5、10、11.5、13的溶液进行渗透率测试，溶液的矿化度等于待测组临界矿化度，pH值为7的溶液为NaCl水溶液，pH值为8.5、10、11.5、13的溶液为NaCl水溶液和NaOH水溶液的混合溶液。
基于试验样品5在不同pH值溶液下的渗透率，分别确定试验样品5在不同pH值溶液下的渗透率保持率；其中，渗透率保持率以试验样品5在pH值为7的溶液下的渗透率为基准渗透率；结果如表18所示。将渗透率保持率不低于80％时对应的最高pH值溶液的pH值作为试验样品5的临界pH值，临界pH值为7。其中，渗透率保持率通过下述公式确定得到：
式中：val为渗透率保持率，单位％；Kal为某pH值碱液下的渗透率，单位10-3μm2；Kial为基准渗透率，单位10-3μm2。
基于试验样品5在不同pH值溶液下的渗透率，确定得到试验样品5的碱敏感性损害率作为待测组的碱敏感性损害率；其中，碱敏感性损害率以试验样品5在pH值为7的溶液下的渗透率为基准渗透率，结果如表18所示。其中，碱敏感性损害率通过下述公式确定得到：
式中：Dal为碱敏感性损害率，单位％；Kial为基准渗透率，单位10-3μm2；Kal为某pH值碱液下的渗透率，单位10-3μm2。
表18
基于试验样品5的碱敏感性损害率进行试验样品5的碱敏感性损害程度评价，并将试验样品5的碱敏感性损害程度评价结果作为待测组的碱敏感性损害程度评价结果。碱敏感性损害程度评价标准如表19所示。
表19
例pH为10时，碱敏感性损害率30＜Dal(40.012％)≤50，损害程度为中等偏弱。
4.6、在待测组中取F试验样品。对F试验样品进行不同应力下渗透率测试，得到试验样品6在不同应力下的渗透率。在渗透率测试过程中，流量选择待测组的临界流速对应的该试验样品的临界流量；渗透率测试用流体使用待测组临界矿化度盐水；先进行初始应力下渗透率测试，再逐步增大应力至最大应力值，进而逐步减小应力至最终应力，并分别在各应力值下保持额定时间且分别在各应力值下进行渗透率测试，初始应力为目标储层的储层有效应力，最终应力等于初始应力，围压保持不变、根据应力值确定合适的回压(围压与回压差为应力)。
基于试验样品6在不同应力下的渗透率，以初始应力下的渗透率作为基准渗透率，分别确定试验样品6在不同应力下的渗透率保持率，结果如表20所示。将逐步增大应力至最大应力值过程中测得的渗透率保持率不低于80％时对应的最大应力作为试验样品6的临界应力即为待测组的临界应力；临界应力29MPa。其中，渗透率保持率通过下述公式确定得到：
式中：vp为渗透率保持率，单位％；Kp为某应力下的渗透率，单位10-3μm2；Kip为基准渗透率，单位10-3μm2。
基于试验样品6在不同应力下的渗透率，确定得到试验样品6的应力敏感性损害率作为待测组的应力敏感性损害率，结果表20所示。其中，应力敏感性损害率通过下述公式确定得到：
式中：Dp为应力敏感性损害率，单位％；Kp为某应力下的渗透率，单位10-3μm2；Kip为基准渗透率，单位10-3μm2。
表20
在待测组中取试验样品6进行应力敏感性测试，得到试验样品6的应力敏感性作为待测组的应力敏感性还包括：基于F试验样品的应力敏感性损害率进行试验样品6的应力敏感性损害程度评价，并将试验样品6的应力损害程度评价结果作为待测组的应力敏感性损害程度评价结果。其中，应力敏感性损害程度评价标准如表21所示：
表21

例：有效应力为36.5MPa时，应力敏感性损害率为Dp(78.48％)＞70，损害程度为强。
基于试验样品6基准渗透率和在最终应力下的渗透率，确定得到试验样品6的不可逆应力敏感性损害率作为待测组的不可逆应力敏感性损害率，不可逆渗透率损害率为45.57％。其中，不可逆应力敏感性损害率通过下述公式确定得到：
式中：Dpn为不可逆应力敏感性损害率，单位％；Kpn为最终应力下的渗透率，单位10-3μm2；Kip为基准渗透率，单位10-3μm2。
以上所述的具体实施例，对本发明的目的、技术方案和有益效果进行了进一步详细说明，所应理解的是，以上所述仅为本发明的具体实施例而已，并不用于限定本发明的保护范围，凡在本发明的精神和原则之内，所做的任何修改、等同替换、改进等，均应包含在本发明的保护范围之内。

Claims (20)

  1. 一种低渗储层敏感性评价方法，该方法包括：
    步骤1、利用目标储层的全直径岩心制备目标储层的试验样品；制备试验样品过程中，不改变全直径岩心的直径；
    步骤2、对各试验样品分别进行标准盐水渗透率测试，以确定各试验样品能够实现渗透率测试的最小流量即为初始流量，进而按初始流的大小对各试验样品进行分组；
    步骤3、对同一组样品进行敏感性测试，包括：
    以某一组样品作为待测组；在待测组中取A试验样品进行流速敏感性测试，得到A试验样品的临界流速作为待测组的临界流速，流速敏感性测试过程中以A试验样品的初始流量作为最小流量；
    在待测组中取B试验样品进行水敏感性测试，得到B试验样品的水敏感性作为待测组的水敏感性，水敏感性测试过程中流量选用待测组的临界流速对应的B试验样品的临界流量；和/或在待测组中取C试验样品进行盐度敏感性测试，得到C试验样品的盐度敏感性作为待测组的盐度敏感性，盐度敏感性测试过程中流量选用待测组的临界流速对应的C试验样品的临界流量；和/或在待测组中取D试验样品进行酸敏感性测试，得到D试验样品的酸敏感性作为待测组的酸敏感性，酸敏感性测试过程中流量选用待测组的临界流速对应的D试验样品的临界流量；和/或在待测组中取E试验样品进行碱敏感性测试，得到E试验样品的碱敏感性作为待测组的碱敏感性，碱敏感性测试过程中流量选用待测组的临界流速对应的E试验样品的临界流量；和/或在待测组中取F试验样品进行应力敏感性测试，得到F试验样品的应力敏感性作为待测组的应力敏感性，应力敏感性测试过程中流量选用待测组的临界流速对应的F试验样品的临界流量。
  2. 根据权利要求1所述的方法，其中，利用目标储层的全直径岩心制备目标储层的试验样品包括：对目标储层的全直径岩心进行长度切割得到长度不小于直径1.5倍的岩心作为目标储层的试验样品。
  3. 根据权利要求1所述的方法，其中，利用目标储层的全直径岩心制备目标储层的试验样品包括：对目标储层的全直径岩心进行长度切割得到长度为直径0.5-1倍的岩心作为目标储层的试验样品。
  4. 根据权利要求1所述的方法，其中，对各试验样品分别进行标准盐水渗透率测试，以确定各试验样品能够实现渗透率测试的最小流量即为初始流量，包括：
    对各试验样品分别以第1流量进行标准盐水渗透率测试，能够实现渗透率测试的各试验样品的初始流量为第1流量，不能实现渗透率测试的各试验样品记为剩余试验样品；
    对各剩余试验样品分别以大于第1流量的第2流量进行标准盐水渗透率测试，能够实现渗透率测试的各试验样品的初始流量为第2流量，不能实现渗透率测试的各试验样品记为剩余试验样品；
    重复进行对各剩余试验样品分别以大于第i流量的第i+1流量进行标准盐水渗透率测试，能够实现渗透率测试的各试验样品的初始流量为第i+1流量，不能实现渗透率测试的各试验样品记为剩余试验样品，直至剩余试验样品数量为0。
  5. 根据权利要求1所述的方法，其中，
    在待测组中取A试验样品进行流速敏感性测试包括：
    在待测组中取A试验样品，对A试验样品分别进行不同流量下的标准盐水渗透率测试，得到A试验样品在不同流量下的渗透率；其中，先进行低流量下的标准盐水渗透率测试，再进行高流量下的标准盐水渗透率测试，最低流量取A试验样品的初始流量；
    A试验样品的临界流速通过下述方式确定得到：
    基于A试验样品在不同流量下的渗透率数据分别确定A试验样品在不同流量下的渗透率保持率；其中，渗透率保持率以初始流量下的渗透率为基准渗透率；
    将渗透率保持率不低于80％时对应的最高流量作为A试验样品的临界矿流量，将A试验样品的临界流量对应的临界流速作为A试验样品的临界流速。
  6. 根据权利要求5所述的方法，其中，该方法还包括：基于A试验样品在不同流量下的渗透率数据分别确定A试验样品在不同流量下的流速敏感性损害率作为待测组的流速敏感性损害率；其中，流速敏感性损害率以初始流量下的渗透率为基准渗透率，流速敏感性损害率通过下述公式确定得到：
    式中：Dn为流速敏感性损害率，单位％；Kin为基准渗透率，单位10-3μm2；Kn为某流量下的渗透率，单位10-3μm2。
  7. 根据权利要求6所述的方法，其中，该方法还包括：基于A试验样品的流速敏感性损害率进行A试验样品的流速敏感性损害程度评价，并将A试验样品的流速敏感性损害程度评价结果作为待测组的流速敏感性损害程度评价结果。
  8. 根据权利要求1所述的方法，其中，
    在待测组中取B试验样品进行水敏感性测试包括：
    在待测组中取B试验样品；
    首先，对B试验样品，以待测组的临界流速对应的该试验样品的临界流量进行标准盐水渗透率测试，得到B试验样品标准盐水渗透率；然后，对B试验样品，以待测组的临界流速对应的该试验样品的临界流量进行1/2标准盐水渗透率测试，得到B试验样品1/2标准盐水渗透率；进而，对B试验样品，以待测组的临界流速对应的该试验样品的临界流量进行蒸馏水渗透率测试，得到B试验样品蒸馏水渗透率；
    得到B试验样品的水敏感性作为待测组的水敏感性包括：得到B试验样品的水敏感性损害率作为待测组的水敏感性损害率；
    其中，B试验样品的水敏感性损害率通过下述方式确定得到：基于B试验样品标准盐水渗透率和B试验样品蒸馏水渗透率，确定B试验样品的水敏感性损害率作为待测组的水敏感性损害率；其中，水敏感性损害率通过下述公式确定得到：
    式中：Dw为水敏感性损害率，单位％；Kiw为标准盐水渗透率，单位10-3μm2；Kw为蒸馏水渗透率，单位10-3μm2。
  9. 根据权利要求1所述的方法，其中，得到B试验样品的水敏感性作为待测组的水敏感性还包括：基于B试验样品的水敏感性损害率进行B试验样品的水敏感性损害程度评价，得到B试验样品的水敏感性损害程度评价结果作为待测组的水敏感性损害程度评价结果。
  10. 根据权利要求1所述的方法，其中，在待测组中取C试验样品进行盐度敏感性测试，得到C试验样品的盐度敏感性作为待测组的盐度敏感性包括：
    在待测组中取C试验样品；
    对C试验样品分别以待测组的临界流速对应的该试验样品的临界流量进行不同含盐浓度盐水渗透率测试，得到C试验样品在不同含盐浓度盐水下的渗透率；其中，先进行高含盐浓度盐水渗透率测试，再进行低含盐浓度盐水渗透率测试，最高含盐浓度盐水取标准盐水，最低含盐浓度盐水取蒸馏水；
    基于C试验样品在不同含盐浓度盐水下的渗透率，分别确定C试验样品在不同含盐浓度盐水下的渗透率保持率；其中，渗透率保持率以标准盐水下的渗透率为基准渗透率；
    将渗透率保持率不低于80％时对应的最低浓度盐水的矿化度作为C试验样品的临界矿化度即为待测组的临界矿化度；其中，渗透率保持率通过下述公式确定得到：
    式中：vsn为渗透率保持率，单位％；Ks为某含盐浓度盐水下的渗透率，单位10-3μm2；Kis为标准盐水下的渗透率即为初始渗透率，单位10-3μm2。
  11. 根据权利要求1所述的方法，其中，
    在酸敏感性测试过程中，渗透率测试用流体的矿化度等于待测组临界矿化度；
    在待测组中取D试验样品进行酸敏感性测试包括：
    在待测组中取D试验样品；
    首先，对D试验样品，以待测组的临界流速对应的该试验样品的临界流量进行待测组临界矿化度盐水渗透率测试，得到D试验样品酸作用前渗透率；然后，向D试验样品中驱替酸液并使D试验样品与酸液反应一段时间；进而，再对D试验样品，以待测组的临界流速对应的该试验样品的临界流量进行待测组临界矿化度盐水渗透率测试，得到D试验样品酸作用后渗透率；
    得到D试验样品的酸敏感性作为待测组的酸敏感性包括：得到D试验样品的酸敏感性损害率作为待测组的酸敏感性损害率；
    其中，D试验样品的酸敏感性损害率通过下述方法确定得到：基于D试验样品酸作用前渗透率和酸作用后渗透率，确定D试验样品的酸敏感性损害率作为待测组的酸敏感性损害率；其中，酸敏感性损害率通过下述公式确定得到：
    式中：Dac为酸敏感性损害率，单位％；Kiac为酸作用前渗透率，单位10-3μm2；Kac为酸作用后渗透率，单位10-3μm2。
  12. 根据权利要求10所述的方法，其中，得到D试验样品的酸敏感性作为待测组的酸敏感性还包括：基于D试验样品的酸敏感性损害率进行D试验样品的酸敏感性损害程度评价，得到D试验样品的酸敏感性损害程度评价结果作为待测组的酸敏感性损害程度评价结果。
  13. 根据权利要求1所述的方法，其中，
    在碱敏感性测试过程中，渗透率测试用流体的矿化度等于待测组临界矿化度；
    在待测组中取E试验样品进行碱敏感性测试包括：
    在待测组中取E试验样品；
    对E试验样品分别以待测组的临界流速对应的该试验样品的临界流量进行不同pH值溶液渗透率测试，得到E试验样品在不同pH值溶液下的渗透率；其中，先进行低pH值溶液渗透率测试，再进行高pH值溶液渗透率测试，溶液的pH值为7-14，最低pH值溶液的pH值为7，溶液的矿化度等于待测组临界矿化度；E试验样品基准渗透率；
    得到E试验样品的碱敏感性作为待测组的碱敏感性包括：得到E试验样品的临界pH值即为待测组的临界pH值，和/或得到E试验样品的碱敏感性损害率作为待测组的碱敏感性损害率；
    其中，E试验样品的临界pH值通过下述方式进行确定：
    基于E试验样品在不同pH值溶液下的渗透率，分别确定E试验样品在不同pH值溶液下的渗透率保持率；其中，渗透率保持率以E试验样品在pH值为7的溶液下的渗透率为基准渗透率；
    将渗透率保持率不低于80％时对应的最高pH值溶液的pH值作为E试验样品的临界pH值；
    其中，E试验样品的碱敏感性损害率通过下述方式进行确定：基于E试验样品在不同pH值溶液下的渗透率，确定得到E试验样品的碱敏感性损害率；其中，碱敏感性损害率以E试验样品在pH值为7的溶液下的渗透率为基准渗透率；其中，碱敏感性损害率通过下述公式确定得到：
    式中：Dal为碱敏感性损害率，单位％；Kial为基准渗透率，单位10-3μm2；Kal为某pH值碱液下的渗透率，单位10-3μm2。
  14. 根据权利要求13所述的方法，其中，得到E试验样品的碱敏感性作为待测组的碱敏感性还包括：基于E试验样品的碱敏感性损害率进行E试验样品的碱敏感性损害程度评价，得到E试验样品的碱敏感性损害程度评价结果作为待测组的碱敏感性损害程度评价结果。
  15. 根据权利要求1所述的方法，其中，
    进行应力敏感性测试过程中渗透率测试用流体使用待测组临界矿化度盐水；
    在待测组中取F试验样品进行应力敏感性测试得包括：
    在待测组中取F试验样品；
    对F试验样品进行不同应力下渗透率测试，得到F试验样品在不同应力下的渗透率；在渗透率测试过程中，流量选择待测组的临界流速对应的该试验样品的临界流量；渗透率测试用流体使用待测组临界矿化度盐水；先进行初始应力下渗透率测试，再逐步增大应力至最大应力值，进而逐步减小应力至最终应力，并分别在各应力值下保持额定时间且分别在各应力值下进行渗透率测试，初始应力为目标储层的储层有效应力，最终应力等于初始应力；
    其中，对F试验样品进行不同应力下渗透率测试过程中，围压保持不变、根据应力值确定合适的回压。
  16. 根据权利要求15所述的方法，其中，得到F试验样品的应力敏感性作为待测组的应力敏感性包括：得到F试验样品的临界应力作为待测组的临界应力，和/或得到F试验样品的不可逆应力敏感性损害率作为待测组的不可逆应力敏感性损害率；
    其中，F试验样品的临界应力通过下述方式进行确定：
    基于F试验样品在不同应力下的渗透率，以初始应力下的渗透率作为基准渗透率，分别确定F试验样品在不同应力下的渗透率保持率；
    将逐步增大应力至最大应力值过程中测得的渗透率保持率不低于80％时对应的最大应力作为F试验样品的临界应力；
    其中，F试验样品的不可逆应力敏感性损害率通过下述方式进行确定：基于F试验样品在初始应力下的渗透率和在最终应力下的渗透率，以初始应力下的渗透率作为基准渗透率，确定得到F试验样品的不可逆应力敏感性损害率作为待测组的不可逆应力敏感性损害率；其中，不可逆应力敏感性损害率通过下述公式确定得到：
    式中：Dpn为不可逆应力敏感性损害率，单位％；Kpn为最终应力下的渗透率，单位10-3μm2；Kip为基准渗透率，单位10-3μm2。
  17. 根据权利要求15所述的方法，其中，得到F试验样品的应力敏感性作为待测组的应力敏感性包括：得到F试验样品的临界应力作为待测组的临界应力，和/或得到F试验样品的不可逆应力敏感性损害率作为待测组的不可逆应力敏感性损害率，和/或得到F试验样品的应力敏感性损害率作为待测组的应力敏感性损害率；
    其中，F试验样品的应力敏感性损害率通过下述方式进行确定：基于F试验样品在不同应力下的渗透率，以初始应力下的渗透率作为基准渗透率，确定得到F试验样品的应力敏感性损害率作为待测组的应力敏感性损害率；其中，应力敏感性损害率通过下述公式确定得到：
    式中：Dp为应力敏感性损害率，单位％；Kp为某应力下的渗透率，单位10-3μm2；Kip为基准渗透率，单位10-3μm2。
  18. 根据权利要求17所述的方法，其中，得到F试验样品的应力敏感性作为待测组的应力敏感性还包括：基于F试验样品的应力敏感性损害率进行F试验样品的应力敏感性损害程度评价，得到F试验样品的应力损害程度评价结果作为待测组的应力敏感性损害程度评价结果。
  19. 根据权利要求1-18中任一项所述的方法，其中，进行敏感性测试过程中使用的溶液，矿化度由NaCl提供，碱性由NaOH提供，酸性由HCl提供。
  20. 根据权利要求1-18中任一项所述的方法，其中，渗透率测试采用超低渗透率测试仪，所述超低渗透率测试仪的测试下限不超过10-4mD，围压上限不低于80MPa。
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