Integrated experiment method for core water locking, resistivity and capillary pressure

Abstract

The invention belongs to the field of low-permeability reservoir development experiments, and discloses an integrated experiment method for core water locking, resistivity and capillary pressure. Comprising rock resistivity, rock air permeability, core pore volume, core permeability test, porosity distribution, radius and fluid saturation. According to the method, through a brand-new thought, key methods in all experiment steps are necessarily improved, the number of experiment samples is reduced, the working efficiency is improved, and the efficiency is more than two times of the original efficiency. And meanwhile, the correlation of various experiments is ensured.

Description

Technical Field

[0001] This invention belongs to the field of low-permeability reservoir development experiments, specifically involving an integrated experimental method for core water lock, resistivity, and capillary pressure. Background Technology

[0002] The oilfield has now entered the low-permeability reservoir development stage, but water-locking and rock-electricity experiments in the development process face many challenges, the most significant being the uneven distribution of fluid saturation in rock pores. Current main techniques for studying fluid saturation in rock pores include mercury intrusion porosimetry (MIP) and nuclear magnetic resonance (NMR). However, MIP can contaminate the core and presents challenges in waste recovery; while NMR requires specialized equipment and is ineffective for testing small and micropores. Therefore, a new experimental method is urgently needed to study water-locking damage, rock resistivity, and changes in fluid saturation in rocks.

[0003] The closest existing technology is a method and apparatus for measuring capillary pressure in rocks under reservoir temperature and pressure conditions (CN112858367A). This method solves the problem that current techniques for measuring capillary pressure in rocks are mostly performed outside of reservoir temperature and pressure environments. It also solves the difficulty of distinguishing between matrix and fractures, and can measure the capillary pressure curve of the core matrix. Furthermore, it utilizes nuclear magnetic resonance (NMR) experiments to obtain multiple parameters in a single experiment, including porosity, permeability, and capillary pressure curves. However, this patent cannot provide integrated measurement of core water lock, resistivity, and capillary pressure parameters, thus lacking a combined measurement approach. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides an integrated experimental method for core water lock, resistivity, and capillary pressure. It utilizes a single core to conduct combined measurements of water lock, rock resistivity, and capillary pressure curves, and selects the optimal and reasonable experimental method. This achievement provides a novel approach for core experiments with a small number of cores.

[0005] The above-mentioned objective of this invention is achieved through the following technical solution: an integrated experimental method for core water lock, resistivity, and capillary pressure, comprising the following steps:

[0006] 1. Selection of experimental methods for rock resistivity;

[0007] 2. Selection of experimental method for capillary pressure curve;

[0008] 3. Cut both ends of the core sample using a wire cutting device;

[0009] 4. Weigh the dry weight of the rock and test its air permeability;

[0010] 5. Vacuum the core sample to saturate and simulate the bottom layer, then measure the weight of the wet core sample and calculate the core pore volume;

[0011] 6. Test the water resistivity and calculate the formation factor;

[0012] 7. Test core permeability;

[0013] 8. Optimize the porosity distribution range and the porosity-permeability relationship;

[0014] 9. Calculate the fluid saturation condition controlled by pore radius;

[0015] 10. Obtain the relationship between water saturation and resistivity increase coefficient;

[0016] 11. Obtain the resistivity increase factor and perform correction fitting;

[0017] 12. Establish a chart showing the breakthrough pressure required after waterlock damage with the same pore radius.

[0018] Furthermore, step 1 specifically involves selecting centrifugation as the experimental method for rock resistivity among oil-driven water method, gas-driven water method, semi-permeable diaphragm method, and centrifugation method.

[0019] Furthermore, step 2 specifically involves selecting the centrifugation method as the experimental method for capillary pressure curves from among the pump method, semi-permeable diaphragm method, and centrifugation method.

[0020] Furthermore, step 4 specifically involves: weighing the dry weight of the rock using a 1 / 10000 electronic balance, and testing the air permeability of the rock using a gas permeability meter.

[0021] Furthermore, step 6 specifically involves placing a rock sample saturated with formation water into a room-temperature and room-pressure holder, testing the 100% water content resistivity, and using the formula F=R o / R w Calculate the formation factors.

[0022] Furthermore, step 7 specifically involves: placing the rock sample into a centrifuge, gradually increasing the centrifuge speed, measuring the resistance at each speed point and the weight of the formation water removed by centrifugation, placing tin foil at both ends of the core, and testing the core permeability.

[0023] Furthermore, step 8 specifically involves: removing rock samples with significant deviations in porosity-permeability relationship during the experiment, increasing the correlation coefficient of the formation factor chart, and optimizing the porosity distribution range and porosity-permeability relationship.

[0024] Furthermore, step 9 specifically involves calculating the fluid saturation controlled by the pore radius based on the capillary force formula and the measured interfacial tension.

[0025] Furthermore, step 10 specifically involves obtaining different water saturation levels at different centrifugal speeds and measuring the corresponding resistivity R. tR o The resistivity of a fully saturated system can be expressed using the formula I = R. t / R o The relationship between water saturation and resistivity increase coefficient was obtained.

[0026] Furthermore, step 11 specifically involves: screening the resistivity increase coefficient of the core resistivity test, fitting the resistivity increase coefficient of each core with a power function to obtain the resistivity increase coefficient, and performing correction fitting.

[0027] Furthermore, step 12 specifically involves: using rock permeability data with different saturation levels to establish a breakthrough pressure chart required after water-lock damage with different pore radii, providing a reference for relieving water-lock damage.

[0028] The beneficial effects of this invention compared to existing technologies are as follows: This invention, through a novel approach, makes necessary improvements to the key methods in each experimental step, reducing the number of experimental samples and increasing work efficiency by more than twice. At the same time, it ensures the correlation between various experiments. Attached Figure Description

[0029] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0030] Figure 1 This is an experimental flowchart of the integrated experimental method for core water lock, resistivity, and capillary pressure.

[0031] Figure 2 This is a graph showing the resistivity increase coefficient in step 9 of Embodiment 1 of the present invention;

[0032] Figure 3 This is the formation factor diagram from step 9 of embodiment 1 of the present invention;

[0033] Figure 4 This is a graph showing the relationship between rotational speed and capillary pressure in step 8 of embodiment 1 of the present invention;

[0034] Figure 5 This is a diagram showing the correspondence between capillary pressure and the radius of the active pore in step 8 of embodiment 1 of the present invention;

[0035] Figure 6 This is a water-locking experiment data graph from step 10 of Embodiment 1 of the present invention.

[0036] Figure 1 shows: core cutting; 2 shows saturated formation water; 3 shows centrifugation to speed; 4 shows air permeability testing; 5 shows saturation testing and calculation; 6 shows rock resistivity testing; 7 shows plotting saturation and resistivity, permeability, and capillary pressure curves. Detailed Implementation

[0037] The present invention is described in detail below through specific embodiments, but this does not limit the scope of protection of the present invention. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can all be obtained commercially.

[0038] Example 1

[0039] An integrated experimental method for core water lock, resistivity, and capillary pressure is described below:

[0040] (1) Cut both ends of the core with a wire cutting device to ensure that the end faces are completely parallel and to reduce the degree of damage to the end faces, so as to ensure the accuracy of the test.

[0041] (2) Weigh the dry weight of the rock using a 1 / 10000 electronic balance and test the air permeability of the rock using a gas permeability meter.

[0042] (3) Use a vacuum pump to evacuate the core to -0.1MPa and maintain it for 2 hours to ensure that the air in the core is removed. Saturate the core with simulated formation water for 4 hours to ensure that the core is fully saturated. Use an electronic balance to test the weight of the wet core sample and calculate the core pore volume.

[0043] (4) Rock samples saturated with formation water are placed in a normal temperature and pressure holder, and the water resistance of 100% is tested. The formation factor is calculated using the formula.

[0044] F = R o / R w =a / Φ m

[0045] I = R t / R o =b / S w n

[0046] S w =[abR w (R t Φ m ) -1 ] 1 / n

[0047] Where: F—formation factor (relative resistivity), dimensionless;

[0048] I—Resistivity increase factor (resistivity index);

[0049] Rt, Ro, Rw—resistivity of oil-bearing rock sample, rock resistivity of formation water with 100% saturation resistivity of Rw, and formation water resistivity, in Ω·m;

[0050] a – proportionality coefficient, which is related to the tortuosity of rock pores;

[0051] b — coefficient;

[0052] m—cementation index, which varies with the degree of rock cementation;

[0053] n—Saturation index;

[0054] Φ—Rock connectivity porosity, %;

[0055] Sw – Water saturation, %.

[0056] (5) Place the rock sample in a centrifuge and centrifuge for 15 minutes. Gradually increase the centrifuge speed and measure the resistance and weight of the formation water removed at each speed point. To reduce contact resistance, place tin foil at both ends of the core. Test the core permeability quickly and accurately to prevent water evaporation caused by air flow.

[0057] (6) Rock samples with significant deviations in porosity-permeability relationship during the experiment were removed. The correlation coefficient of the formation factor plate was improved after the samples were removed. In order to improve the accuracy of rock electrical parameters, the porosity distribution range and porosity-permeability relationship were optimized.

[0058] (7) Based on the capillary force formula and the measured interfacial tension, the pore radius is used to calculate the fluid saturation.

[0059] The formulas for calculating capillary pressure and the radius of the active pore are as follows:

[0060] P ci =2σcosθ / r

[0061] In the formula:

[0062] P ci —Capillary pressure, Pa;

[0063] σ—Interfacial tension of the two-phase fluid, mN / m

[0064] θ — Contact angle between two phases.

[0065] (8) Different water saturation levels were obtained at different centrifugal speeds, and the corresponding resistivity Rt and Ro were measured. The resistivity at full saturation was then calculated using the formula I = Rt / Ro. The relationship between water saturation and the resistivity increase factor was then obtained. Figure 4 , Figure 5 .

[0066] (9) Core resistivity testing and resistivity increase coefficient screening to ensure accurate saturation index. To overcome human error caused by contact resistance during the experiment, a power function fit was performed between the resistivity increase coefficient of each core and the water saturation. The resulting resistivity increase coefficient was then corrected and fitted. Formation factors and resistivity increase charts were generated, see [link to chart]. Figure 2 , Figure 3 .

[0067] (10) Using rock permeability data at different saturations, establish a chart of the breakthrough pressure required after water-locking damage at different pore radii, see [reference needed]. Figure 6 This provides a reference for relieving waterlock damage.

[0068] The embodiments described above are merely preferred embodiments of the present invention, and not all feasible embodiments of the present invention. Any obvious modifications made by those skilled in the art without departing from the principles and spirit of the present invention should be considered to be included within the scope of protection of the claims of the present invention.

Claims

1. An integrated experimental method for core water lock, resistivity, and capillary pressure, characterized in that, The steps are as follows: S1. Selection of experimental methods for rock resistivity; S2. Selection of experimental method for capillary pressure curve; S3. Cut both ends of the core sample using a wire cutting device; S4. Weigh the dry weight of the rock and test its air permeability. S5. Vacuum the core sample, saturate the simulated bottom layer, then test the weight of the wet core sample and calculate the core pore volume; S6. Test the water-bearing resistance and calculate the formation factor; S7. Test core permeability; S8. Optimize the porosity distribution range and the porosity-permeability relationship; S9. Calculate the fluid saturation condition controlled by pore radius; S10. Obtain the relationship between water saturation and resistivity increase coefficient; S11. Obtain the resistivity increase coefficient and perform correction fitting; S12. Establish the breakthrough pressure chart required after waterlock damage with the same pore radius.

2. The integrated experimental method for core water lock, resistivity, and capillary pressure as described in claim 1, characterized in that, Specifically, step S1 involves selecting centrifugation as the experimental method for rock resistivity among oil-driven water method, gas-driven water method, semi-permeable diaphragm method, and centrifugation method.

3. The integrated experimental method for core water lock, resistivity, and capillary pressure as described in claim 1, characterized in that, Step S2 specifically involves selecting the centrifugation method as the experimental method for capillary pressure curves from among the pump method, semi-permeable diaphragm method, and centrifugation method.

4. The integrated experimental method for core water lock, resistivity, and capillary pressure as described in claim 1, characterized in that, Specifically, step S4 involves weighing the dry weight of the rock using a 1 / 10000 electronic balance and testing the air permeability of the rock using a gas permeability meter.

5. The integrated experimental method for core water lock, resistivity, and capillary pressure as described in claim 1, characterized in that, Step S6 specifically involves placing a rock sample saturated with formation water into a room-temperature and room-pressure holder, testing the 100% water content resistivity, and using the formula F=R o / R w Calculate the formation factors.

6. The integrated experimental method for core water lock, resistivity, and capillary pressure as described in claim 1, characterized in that, Step S7 specifically involves: placing the rock sample into a centrifuge, gradually increasing the centrifuge speed, measuring the resistance and weight of the formation water removed at each speed point, placing tin foil at both ends of the core, and testing the core permeability.

7. The integrated experimental method for core water lock, resistivity, and capillary pressure as described in claim 1, characterized in that, Step S8 specifically involves: removing rock samples with significant deviations in porosity-permeability relationship during the experiment, increasing the correlation coefficient of the formation factor chart, and optimizing the porosity distribution range and porosity-permeability relationship.

8. The integrated experimental method for core water lock, resistivity, and capillary pressure as described in claim 1, characterized in that, Specifically, step S9 involves calculating the fluid saturation level controlled by the pore radius based on the capillary force formula and the measured interfacial tension.

9. The integrated experimental method for core water lock, resistivity, and capillary pressure as described in claim 1, characterized in that, Step S10 specifically involves obtaining different water saturation levels at different centrifugal speeds and measuring the corresponding resistivity R. t R o The resistivity of a fully saturated system can be expressed using the formula I = R. t / R o The relationship between water saturation and resistivity increase coefficient was obtained.

10. The integrated experimental method for core water lock, resistivity, and capillary pressure as described in claim 1, characterized in that, Step S11 specifically involves: screening the resistivity increase coefficient of the core resistivity test, fitting the resistivity increase coefficient of each core with a power function to obtain the resistivity increase coefficient, and then performing a correction fit.

11. The integrated experimental method for core water lock, resistivity, and capillary pressure as described in claim 1, characterized in that, Step S12 specifically involves: using rock permeability data with different saturation levels to establish a breakthrough pressure chart required after water-lock damage with different pore radii, providing a reference for relieving water-lock damage.

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