Method suitable for fluid saturation of tight oil core

Abstract

The invention discloses a method for fluid saturation of a tight oil rock core, which is specifically implemented according to the following steps of: washing the rock core with oil, heating and drying, measuring the length and the diameter of the rock core by adopting a vernier caliper, and performing repeated dry sweeping treatment by adopting high-precision nuclear magnetism until the nuclear magnetism semaphore is stable and tends to 0; carrying out nuclear magnetic detection on the used fluid, enabling nuclear magnetic signals to be stable by adjusting parameters, and recording nuclear magnetic signal values; a tight reservoir rock core saturated fluid system is built, and vacuumizing is carried out; emptying detection is carried out, and a tight reservoir core saturated fluid system is pressurized; performing high-pressure water saturation; and repeating the operation until the difference of the measured fluid saturation is less than 1%. The problem that in the prior art, tight oil reservoir fluid is difficult to inject is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of tertiary oil recovery in oil and gas field development, and relates to a method suitable for saturating tight oil cores with fluid. Background Art

[0002] Tight oil reservoirs have attracted great attention from the global oil industry due to their huge reserves. However, due to the extremely low microscopic pore size (usually at the nanometer level) and high pore-throat ratio (>100) of this type of oil and gas resources, conventional water injection development is difficult to meet the development needs of this type of reservoir.

[0003] The extreme resistance to oil-water flow makes injection difficult, hindering timely replenishment of formation energy, further leading to low well productivity and rapid decline, the so-called "no injection, no production." While tight oil reservoir research has primarily been conducted indoors, the study of fluid seepage patterns is urgently needed, and accurate simulation of reservoir saturated fluids is a prerequisite.

[0004] Currently, conventional methods for determining fluid saturation in these tight reservoirs are no longer applicable, and there is an urgent need to develop "targeted" fluid saturation methods suitable for tight oil reservoirs. Research on tight oil reservoirs has primarily been conducted in-house, but the study of fluid seepage patterns is crucial, and reservoir saturation with fluid is a prerequisite. Conventional methods for determining fluid saturation are no longer applicable to tight oil samples. Fluid saturation in these reservoirs still relies on conventional methods, and there is an urgent need to develop "targeted" fluid saturation methods. Summary of the Invention

[0005] The purpose of the present invention is to provide a method suitable for saturating tight oil cores with fluid, thereby solving the problem of "difficulty in injecting fluid into tight oil reservoirs" existing in the prior art.

[0006] The technical solution adopted by the present invention is a method for saturating a tight oil core with fluid, which is specifically implemented according to the following steps:

[0007] Step 1: Wash the core with oil, heat and dry it, measure the length and diameter of the core with a vernier caliper, and perform repeated dry scanning with high-precision nuclear magnetic resonance until the nuclear magnetic resonance signal is stable and approaches 0;

[0008] Step 2: Perform nuclear magnetic resonance (NMR) testing on the fluid, adjust the parameters to make the NMR signal stable, and record the NMR signal value;

[0009] Step 3: Build a tight reservoir core saturation fluid system and perform vacuum extraction;

[0010] Step 4: emptying test and pressurizing the tight reservoir core saturated fluid system;

[0011] Step 5: high pressure saturated water;

[0012] Step 6: Repeat steps 4 to 6 until the measured fluid saturations differ by less than 1%.

[0013] The present invention is also characterized in that:

[0014] In step 1, the core is washed with oil and placed in an oven for heating and drying at 80°C to 120°C for 12 hours to 24 hours.

[0015] In step 3, the tight reservoir core saturation fluid system includes an injection pump, one outlet of the injection pump is connected to the CO2 storage, and the other outlet of the injection pump is connected to the intermediate container. The core treated in step 1 is placed in the intermediate container. The injection pump supplies a pressure of 0-72 MPa. The CO2 storage is connected to the top of the intermediate container through a pipeline, and the bottom of the intermediate container is connected to the vacuum pump through a pipeline. Valves are set on each connecting pipeline for switch control.

[0016] The pressure provided by the vacuum pump in step 4 is -0.1MPa-0Mpa.

[0017] The vacuuming time in step 4 is 24h-48h.

[0018] Step 5: Perform a routine venting test by opening the valve on the CO2 storage to ensure that all pipelines, valves and intermediate containers are filled with CO2 gas; start the injection pump, adjust the injection pressure to 3MPa-5Mpa, pressurize the intermediate container filled with CO2, and continue for 12h-24h, and close the valve on the CO2 storage.

[0019] Step 6: Set the injection pump pressure of the injection pump to the formation pressure, perform high-pressure saturation water for 48 hours to 72 hours, and detect the CO2 concentration until the concentration remains unchanged; remove the sample from the intermediate container and perform nuclear magnetic resonance detection.

[0020] The beneficial effects of the present invention are as follows: the method for saturating tight oil cores with fluid combines the high-pressure saturation method and the mechanism that CO2 is easily soluble in water, allowing the fluid to enter the pores in both directions, effectively solving the difficult problems of "difficult injection and incomplete injection" in tight oil reservoirs; in addition, the present invention uses CO2 as the gas medium, and the solution formed after dissolving in water has little change in the overall pH value, and will not cause acid-sensitive damage to the reservoir. The solubility of the gas medium causes local negative pressure to be formed in the pores, promoting the fluid to enter the pores and increasing the fluid saturation in the reservoir. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic structural diagram of the tight reservoir core saturated fluid system of the present invention;

[0022] Figure 2 This is a comparison chart of experimental data using conventional saturated fluid and the saturated fluid method of the present invention in Example 3 of the present invention;

[0023] Figure 3 3 is a comparison chart of experimental data using conventional saturated fluid and the saturated fluid method of the present invention in Example 4 of the present invention.

[0024] In the figure, 1. Injection pump, 2. CO2 storage, 3. Intermediate container, 4. High-precision nuclear magnetic resonance, 5. Vacuum pump, 6. Valve. DETAILED DESCRIPTION

[0025] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] Example 1

[0027] The method for saturating a tight oil core with fluid according to the present invention is specifically implemented according to the following steps:

[0028] Step 1: Wash the core with oil, heat and dry it, measure the length and diameter of the core with a vernier caliper, and perform repeated dry scanning with a high-precision nuclear magnetic resonance 4 until the nuclear magnetic resonance signal is stable and approaches 0;

[0029] Step 2: Perform nuclear magnetic resonance (NMR) testing on the fluid, adjust the parameters to make the NMR signal stable, and record the NMR signal value;

[0030] Step 3: Build a tight reservoir core saturation fluid system and perform vacuum extraction;

[0031] Step 4: emptying test and pressurizing the tight reservoir core saturated fluid system;

[0032] Step 5: high pressure saturated water;

[0033] Step 6: Repeat steps 4 to 6 until the measured fluid saturations differ by less than 1%.

[0034] Example 2

[0035] The method for saturating a tight oil core with fluid according to the present invention is specifically implemented according to the following steps:

[0036] Step 1: Wash the core with oil, heat and dry it, measure the length and diameter of the core with a vernier caliper, and perform repeated dry scanning with a high-precision nuclear magnetic resonance 4 until the nuclear magnetic resonance signal is stable and approaches 0;

[0037] In step 1, the core is washed with oil and placed in an oven for 12 hours to 24 hours at 80 to 120 degrees Celsius.

[0038] Step 2: Perform nuclear magnetic resonance (NMR) testing on the fluid, adjust the parameters to make the NMR signal stable, and record the NMR signal value;

[0039] Step 3: Building a tight reservoir core saturation fluid system;

[0040] like Figure 1 As shown, the tight reservoir core saturation fluid system includes an injection pump 1, one outlet of the injection pump 1 is connected to the CO2 storage 2, and the other outlet of the injection pump 1 is connected to the intermediate container 3. The core treated in step 1 is placed in the intermediate container 3, and the injection pump 1 provides a pressure of 0-72 MPa. The CO2 storage 2 is connected to the top of the intermediate container 3 through a pipeline, and the bottom of the intermediate container 3 is connected to a vacuum pump 5 through a pipeline. Valves 6 are provided on each connecting pipeline for on-off control; the vacuum pump 5 is turned on to vacuum the intermediate container 3 containing the core; the pressure provided by the vacuum pump 5 is -0.1 MPa-0 MPa; and the vacuuming time is 24h-48h;

[0041] The CO2 storage 2 is made of corrosion-resistant material with a maximum temperature resistance of 120°C and a maximum pressure resistance of 75 MPa; the intermediate container 3 has a maximum temperature resistance of 120°C and a maximum pressure resistance of 75 MPa; the minimum recognition accuracy of the high-precision nuclear magnetic resonance 4 is 2 nm.

[0042] Step 4: emptying test and pressurizing the tight reservoir core saturated fluid system;

[0043] Step 4: Perform a routine venting test by opening the valve 6 on the CO2 storage 2 to ensure that all pipelines, valves 6 and the intermediate container 3 are filled with CO2 gas; start the injection pump 1 and adjust the injection pressure to 3MPa-5MPa to pressurize the intermediate container 3 filled with CO2, and continue the injection pressure for 12h-24h, and then close the valve 6 on the CO2 storage 2;

[0044] Step 5: high pressure saturated water;

[0045] Step 5: The injection pump pressure of the injection pump 1 is set to the formation pressure, and high-pressure water saturation is performed for 48 hours to 72 hours, and the CO2 concentration is detected until the concentration remains unchanged; the sample in the intermediate container 3 is taken out and subjected to nuclear magnetic resonance detection using a high-precision nuclear magnetic resonance 4;

[0046] Step 6: Repeat steps 4 to 6 until the measured fluid saturations differ by less than 1%.

[0047] The present invention's method for saturating tight oil cores with fluids, demonstrated through indoor saturated fluid experimental simulations, demonstrates that using CO2 as the gas medium, its solubility creates a localized negative pressure within the pores, promoting fluid entry, further increasing fluid saturation by 5% to 15% on top of high-pressure saturation. Furthermore, when CO2 is dissolved in water, the resulting solution changes the overall pH value between 0.3 and 0.5, with negligible impact on the reservoir. This saturated fluid method provides important technical support for indoor research on tight oil reservoirs. Building on the traditional pressurized saturation method, the introduction of CO2's water solubility allows bidirectional fluid entry into the pores, effectively resolving the challenges of difficult and incomplete injection in tight oil reservoirs.

[0048] Example 3

[0049] The method for saturating a tight oil core with fluid according to the present invention is specifically implemented according to the following steps:

[0050] Step 1: Using a dense sandstone with a permeability of 0.03 mD, a length of 5 cm, and a diameter of 2.5 cm, the core was washed with oil and dried under room temperature. The length and diameter of the core were measured with a vernier caliper. A high-precision nuclear magnetic resonance (NMR) 4 was used for repeated dry scanning until the NMR signal was stable and approached 0. After washing the core with oil, the core was placed in an oven and dried at 80°C for 12 hours.

[0051] Step 2: In this embodiment, oil is used to simulate water in the Daqing formation, and nuclear magnetic resonance detection is performed. The parameters are adjusted to make the nuclear magnetic signal stable, and the nuclear magnetic signal value is recorded;

[0052] Step 3: Build a tight reservoir core saturation fluid system; place the core processed in step 1 into the intermediate container 3, turn on the vacuum pump 5, and evacuate the intermediate container 3 containing the core; the pressure of the vacuum pump 5 is -0.1 MPa; and the evacuation time is 24 hours;

[0053] Step 4: Perform a routine venting test by opening the valve 6 on the CO2 storage 2 to ensure that all pipelines, valves 6, and the intermediate container 3 are filled with CO2 gas; start the injection pump 1 and adjust the injection pressure to 3 MPa to pressurize the intermediate container 3 filled with CO2 for 12 hours, and then close the valve 6 on the CO2 storage 2;

[0054] Step 5: Set the injection pump pressure of the injection pump 1 to the formation pressure of 25 MPa, perform high-pressure saturation water for 48 hours, and detect the CO2 concentration until the concentration remains unchanged; take out the sample in the intermediate container 3 and perform nuclear magnetic resonance detection;

[0055] Step 6: Repeat steps 4 to 6 until the measured fluid saturations differ by less than 1%.

[0056] The experimental data were compared using conventional saturated fluid and the saturated fluid method of the present invention. After the comparison, the nuclear magnetic T2 spectra were established for the two methods respectively, as shown in FIG. Figure 2 The smaller the T2 relaxation time, the smaller the core pore diameter. The amplitude reflects the T2 value and can also indicate the volume of fluid in the pores. That is, the larger the amplitude, the more fluid. Figure 2 It can be shown that for the same sample, the volume of fluid stored in the porous medium after adopting the method of this patent is much higher than that of the conventional method. Through data comparison and analysis, it can be concluded that after conventional high-pressure saturated water, the water saturation is 41%, and after adopting the embodiment of the present invention, the water saturation is 63%, an increase of 22 percentage points.

[0057] Example 4

[0058] The method for saturating a tight oil core with fluid according to the present invention is specifically implemented according to the following steps:

[0059] Step 1: Using Xinjiang shale with a permeability of 0.015 mD, a length of 4 cm, and a diameter of 2.5 cm, the experimental temperature was 65°C. The core was washed with oil, heated and dried, and the length and diameter of the core were measured with a vernier caliper. A high-precision nuclear magnetic resonance 4 was used for repeated dry scanning until the nuclear magnetic resonance signal was stable and approached 0. After washing the oil, the core was placed in an oven at 120°C for 24 hours.

[0060] Step 2: In this embodiment, the oil used is the degassed crude oil from Mahu Ma 131 well. The fluid is subjected to nuclear magnetic resonance (NMR) detection. The parameters are adjusted to make the NMR signal stable, and the NMR signal value is recorded.

[0061] Step 3: Build a tight reservoir core saturation fluid system; place the core processed in step 1 into the intermediate container 3, turn on the vacuum pump 5, and evacuate the intermediate container 3 containing the core; the pressure provided by the vacuum pump 5 is 0 MPa; and the evacuation time is 48 hours;

[0062] Step 4: Perform a routine venting test by opening the valve 6 on the CO2 storage 2 to ensure that all pipelines, valves 6, and the intermediate container 3 are filled with CO2 gas; start the injection pump 1 and adjust the injection pressure to 5 MPa to pressurize the intermediate container 3 filled with CO2, and continue this for 24 hours, then close the valve 6 on the CO2 storage 2;

[0063] Step 5: Set the injection pump pressure of the injection pump 1 to the formation pressure of 18 MPa, perform high-pressure saturation water for 72 hours, and detect the CO2 concentration until the concentration remains unchanged; remove the sample from the intermediate container 3 and perform nuclear magnetic resonance detection using a high-precision nuclear magnetic resonance 4;

[0064] Step 6: Repeat steps 4 to 6 until the measured fluid saturations differ by less than 1%.

[0065] The experimental data were compared using conventional saturated fluid and the saturated fluid method of the present invention. After the comparison, the nuclear magnetic T2 spectra were established for the two methods respectively, as shown in FIG. Figure 3 As shown, the volume of fluid stored in the porous medium after adopting the method of the present invention is much higher than that of the conventional method. Through data comparison and analysis, it can be concluded that after conventional high-pressure saturation, the oil saturation is 24%, and after adopting the embodiment of the present invention, the oil saturation is 40%, an increase of 16 percentage points.

[0066] The present invention addresses the problem of fluid injection difficulties in tight oil reservoirs by combining a high-pressure saturation method with the mechanism of CO2's solubility in water. This allows bidirectional fluid entry into pores. The resulting solution exhibits minimal changes in the overall pH, preventing acid-sensitive damage to the reservoir. The solubility of the gas medium creates localized negative pressure within the pores, promoting fluid entry and improving fluid saturation in tight reservoir cores, thereby enhancing the accuracy of experimental data. This method not only addresses the difficulty of fluid injection into tight oil reservoirs, but also improves the fluid's storage capacity, effectively increasing oil / water saturation and ensuring smooth laboratory research on tight oil reservoirs. It effectively enhances the storage capacity of fluids (oil / water) within porous media, effectively increasing oil / water saturation and accurately reconstructing the original horizontal and vertical fluid distribution in the reservoir. Building on traditional methods, the method incorporates the similar dissolution mechanism of CO2, allowing CO2 to dissolve into the fluid, creating localized negative pressure within the porous medium, providing motive force for fluid entry. This addresses the difficulty of fluid injection into tight oil reservoirs, while also ensuring safe, environmentally friendly, and universal applicability.

Claims

1. A method for saturating a tight oil core with a fluid, characterized in that: Please follow the steps below to implement it: Step 1: Wash the core with oil, heat and dry it, measure the length and diameter of the core with a vernier caliper, and perform repeated dry scanning with a high-precision nuclear magnetic resonance 4 until the nuclear magnetic resonance signal is stable and approaches 0; Step 2: Perform nuclear magnetic resonance (NMR) testing on the fluid, adjust the parameters to make the NMR signal stable, and record the NMR signal value; Step 3: Build a tight reservoir core saturation fluid system and perform vacuum extraction; Step 4: emptying test and pressurizing the tight reservoir core saturated fluid system; Step 5: high pressure saturated water; Step 6: Repeat steps 4 to 6 until the measured fluid saturations differ by less than 1%.

2. The method for saturating tight oil core with fluid according to claim 1, characterized in that: In step 1, the core is washed with oil and placed in an oven for heating and drying at 80° C. to 120° C. for 12 hours to 24 hours.

3. The method for saturating tight oil core with fluid according to claim 2, characterized in that: The tight reservoir core saturation fluid system in step 3 includes an injection pump (1), one outlet of the injection pump (1) is connected to a CO2 storage device (2), and the other outlet of the injection pump (1) is connected to an intermediate container (3). The core treated in step 1 is placed in the intermediate container (3). The injection pump (1) supplies a pressure of 0-72 MPa. The CO2 storage device (2) is connected to the top of the intermediate container (3) through a pipeline. The bottom of the intermediate container (3) is connected to a vacuum pump (5) through a pipeline. Valves (6) are provided on each connecting pipeline for on-off control.

4. The method for saturating tight oil core with fluid according to claim 3, characterized in that: The pressure provided by the vacuum pump (5) in step 4 is -0.1 MPa-0 MPa.

5. The method for saturating tight oil core with fluid according to claim 3, characterized in that: The vacuuming time in step 4 is 24h-48h.

6. The method for saturating tight oil core with fluid according to claim 3, characterized in that: In step 5, a routine venting test is performed by opening the valve (6) on the CO2 storage (2) to ensure that all pipelines, valves (6) and intermediate containers (3) are filled with CO2 gas; the injection pump (1) is started, the injection pressure is adjusted to 3MPa-5Mpa, the intermediate container (3) filled with CO2 is pressurized, and the pressurization is continued for 12h-24h, and the valve (6) on the CO2 storage (2) is closed.

7. The method for saturating tight oil core with fluid according to claim 6, characterized in that: In step 6, the injection pump pressure of the injection pump (1) is set to the formation pressure, high-pressure water saturation is performed for 48 hours to 72 hours, and the CO2 concentration is detected until the concentration remains unchanged; the sample in the intermediate container (3) is taken out and subjected to nuclear magnetic resonance detection.

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