Method for testing fluid saturation through rock core displacement and testing device thereof

Abstract

The invention relates to the technical field of water flooding gas reservoirs, in particular to a rock core displacement fluid saturation testing method and a testing device thereof.The method comprises the steps that S1, the original formation pressure and temperature of a gas reservoir are obtained; s2, obtaining a rock core, and testing physical property data of the rock core; then carrying out nuclear magnetic testing on the rock core; s3, saturating the rock core with formation water, and then carrying out nuclear magnetic testing; s4, carrying out gas drive water seepage test on the rock core according to the data in the S1, and obtaining the drive water quantity; s5, performing nuclear magnetic test on the depleted rock core; s6, obtaining the irreducible water saturation of the depleted rock core according to the nuclear magnetic test results of the steps S2, S3 and S5; s7, the total irreducible water saturation of the rock core is obtained according to the rock core physical property data, the displacement water amount and the irreducible water saturation of the rock core after exhaustion; the device comprises a drying oven, a first container, a second container, a core holder, a confining pressure pump, a displacement pump, a back pressure assembly, a receiving container and an electronic balance. The accuracy of fluid saturation determination can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of water drive gas reservoirs, and more specifically, to a method for testing fluid saturation by core displacement and its testing device. Background Art

[0002] Most of the gas reservoirs developed currently are water drive gas reservoirs to varying degrees. Among them, for the gas reservoirs with active edge and bottom water, the reserves of gas reservoirs with water account for more than 80% of the total reserves. In the field of oil and gas exploration and production, accurately measuring fluid saturation is the key to evaluating reservoir characteristics and optimizing production strategies. Nuclear magnetic resonance (NMR) testing is a widely used measurement method that can simultaneously reflect pore and fluid information without damaging the sample. However, NMR testing equipment has certain temperature and pressure limitations. Therefore, in the prior art, most of the testing methods are the combination of core displacement and NMR testing under normal temperature and pressure. Although this testing method can be used to measure fluid saturation, since the actual original reservoir of the gas reservoir is not at normal temperature and pressure, and the NMR T2 spectra of fluids at different temperatures and pressures have certain differences, this will make the fluid saturation data measured under normal temperature and pressure have certain errors, resulting in certain errors between the reservoir characteristics evaluated based on this and the actual reservoir characteristics. Summary of the Invention

[0003] The purpose of the present invention is to overcome the deficiency that the fluid saturation measurement in the prior art under normal temperature and pressure has certain errors, and provide a method for testing fluid saturation by core displacement and its testing device, which can improve the accuracy of fluid saturation measurement.

[0004] To solve the above technical problems, the technical solution adopted by the present invention is: Provide a method for testing fluid saturation by core displacement, including the following steps: S1. Obtain the original formation pressure and original formation temperature of the gas reservoir; S2. Obtain a core, and test the physical properties data of the core through core analysis method; then perform NMR testing on the core; S3. Saturate the core with formation water, and then perform NMR testing on the core saturated with formation water; S4. Perform gas drive water seepage testing on the saturated core according to the original formation pressure and original formation temperature of the gas reservoir, the core is depleted, and the amount of water produced is obtained; S5. Perform NMR testing on the depleted core; S6. Obtain the irreducible water saturation of the depleted core according to the NMR testing results of steps S2, S3, and S5; S7. Obtain the total irreducible water saturation of the core according to the core physical properties data in step S2, the amount of water produced in step S4, and the irreducible water saturation of the depleted core in step S6.

[0005] The present invention includes a method for testing fluid saturation of cores. By obtaining the data of the original formation pressure and the original formation temperature of the gas reservoir, it is possible to conduct a gas drive water seepage test under simulated formation conditions, and perform nuclear magnetic tests on the cores before saturation, after saturation, and after the gas drive water seepage test to obtain the irreducible water saturation. It can overcome the limitation of nuclear magnetic testing under high temperature and high pressure, improve the accuracy and reliability of the determination of irreducible water saturation, thereby enabling the accurate determination of formation pore and fluid information, and further providing important reservoir characteristic data for oil and gas field development.

[0006] Further, step S4 includes the following steps: S41. Place the core in an environment with a temperature approximately equal to or the same as the original formation temperature of the gas reservoir; S42. Establish an initial confining pressure at the core; S43. Inject formation water into the core at a constant rate for displacement until the output pressure at the core reaches the original formation pressure of the gas reservoir, and then apply a constant pressure to the core to complete the pressure build-up; S44. Introduce nitrogen gas into the core; S45. Conduct a nitrogen gas drive water experiment test on the core at the displacement pressure difference determined according to the relative permeability test standard until the irreducible water state is reached; S46. After reaching the irreducible water state, reduce the pressure at the core and cool the environment where the core is located to room temperature. At this time, the core is depleted, and the displaced water volume V is obtained.

[0007] Further, step S41 includes: clamping the core with a core holder and placing the core holder in an oven; heating the oven to a temperature approximately equal to or the same as the original formation temperature of the gas reservoir; Step S42 includes: using a confining pressure pump to pump into the core holder to establish an initial confining pressure; Step S43 includes: placing formation water in a second container, and then using a displacement pump to inject the formation water in the second container into the core holder at a constant rate for displacement until the pressure at the output end of the core holder reaches the original formation pressure of the gas reservoir; then, using a back pressure component to apply a constant pressure to the core holder to complete the pressure build-up; Step S44 includes: placing nitrogen gas in a first container, and then using the displacement pump to introduce the nitrogen gas in the first container into the core holder; Step S46 includes: after reaching the irreducible water state, reducing the pressure at the output end of the core holder to zero through the back pressure component; at the same time, closing the oven to cool the temperature inside the oven to room temperature; at this time, the core is depleted, and the displaced water is collected at the output end of the core holder through the back pressure component to obtain the displaced water volume V.

[0008] Further, during the displacement process in step S43, keep the output pressure of the confining pressure pump always greater than the pressure at the input end of the core holder, and the pressure difference between the two is the same as the value of the initial confining pressure.

[0009] Further, in step S44, the displacement pump is pressurized until the pressure at the input end of the core holder reaches the original formation pressure of the gas reservoir.

[0010] Further, the back pressure assembly includes a back pressure valve and a back pressure pump. The back pressure end of the back pressure valve is connected to the back pressure pump, the inlet end of the back pressure valve is connected to the core holder, and the outlet end of the back pressure valve is connected to a receiving container. The constant pressure operation in step S43 includes: setting the back pressure pump to the constant pressure mode, and pumping into the back pressure end of the back pressure valve until the pressure at the back pressure end is equal to the pressure at the inlet end of the back pressure valve, and then connecting the back pressure pump to the core holder to complete the pressure build-up. In step S46, the pressure reduction is achieved by setting the back pressure pump to the constant speed mode, and the displaced water is collected through the receiving container at the outlet end of the back pressure valve to obtain the displaced water volume V.

[0011] Further, in step S1, it also includes obtaining the density of the original formation water. Step S3 specifically includes the following steps: S31. Prepare the formation water according to the mineral composition of the formation water and the density of the original formation water. S32. Saturate the core with the formation water obtained in step S31. S33. Wipe the surface of the saturated core dry and then conduct a nuclear magnetic test.

[0012] Further, in step S2, after the nuclear magnetic test on the core, the T2 spectrum is obtained and the dry core signal area S0 is obtained; in step S3, after the nuclear magnetic test on the saturated core, the T2 spectrum is obtained and the saturated core signal area S1 is obtained; in step S5, after the nuclear magnetic test on the depleted core, the T2 spectrum is obtained and the signal area S2 of the depleted core is obtained. In step S6, the irreducible water saturation S w1 of the depleted core is calculated as follows: S w1 = (S2 - S0) / (S1 - S0); In the formula, S0 represents the dry core signal area, S1 represents the saturated core signal area, and S2 represents the signal area of the depleted core.

[0013] Further, in step S7, the total irreducible water saturation S w2 of the core is calculated as follows: S w2 = S w1 +V / (D 2 / 4×π×L×Ф); In the formula, S w1 represents the irreducible water saturation of the core after depletion obtained in step S6, V represents the amount of displaced water obtained in step S4; D, L, Ф represent the physical property data of the core, where they represent the diameter, length, and porosity in the dry core state, respectively.

[0014] The present invention also provides a testing device, which is applied to the above-mentioned method for testing the fluid saturation of core displacement. The device includes an oven, a first container, a second container, and a core holder disposed in the oven, and both the first container and the second container are connected to the core holder; it further includes an confining pressure pump and a displacement pump, the confining pressure pump is connected to the core holder, and the displacement pump is connected to both the first container and the second container; it further includes a back pressure assembly, the back pressure assembly is connected to the core holder; it further includes a receiving container and an electronic balance, the receiving container is placed on the electronic balance, and the back pressure assembly is also connected to the receiving container.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. By obtaining the original formation pressure and original formation temperature data of the gas reservoir, it is possible to conduct gas flooding water seepage tests under simulated formation conditions, and perform nuclear magnetic resonance tests on the core before saturation, after saturation, and after gas flooding water seepage tests to obtain the irreducible water saturation, which can overcome the limitations of nuclear magnetic resonance tests under high temperature and high pressure, improve the accuracy of irreducible water saturation determination, and thus enable the accuracy and reliability of the determination of formation pore and fluid information, and further provide important reservoir characteristic data for oil and gas field development; 2. The present invention also includes a testing device, which can be applied to the method for testing the fluid saturation of core displacement and obtain a more accurate determination of irreducible water saturation. Description of the Drawings

[0016] Figure 1 is a flowchart of a method for testing the fluid saturation of core displacement according to the present invention; Figure 2 is a nuclear magnetic resonance test curve graph in steps S2, S3, and S5 of the present invention; Figure 3 is a structural schematic diagram of a testing device according to the present invention.

[0017] In the accompanying drawings: 100, oven; 110, first container; 120, second container; 130, core holder; 200, confining pressure pump; 300, displacement pump; 410, back pressure valve; 420, back pressure pump; 500, receiving container; 600, electronic balance; 710, first pressure gauge; 720, second pressure gauge; 730, third pressure gauge; 740, fourth pressure gauge; 810, first valve; 820, second valve; 830, third valve; 840, fourth valve; 850, fifth valve; 860, sixth valve; 870, seventh valve; 880, eighth valve; 890, ninth valve. Detailed implementation manners

[0018] The present invention will be further described below in conjunction with the detailed implementation manners. Among them, the accompanying drawings are only for illustrative purposes, showing only schematic diagrams, not physical diagrams, and should not be construed as a limitation to this patent; in order to better illustrate the embodiments of the present invention, some components in the accompanying drawings will be omitted, enlarged or reduced, which do not represent the dimensions of the actual product; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the accompanying drawings may be omitted.

[0019] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", etc. indicating the orientation or positional relationship, they are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the accompanying drawings are only for illustrative purposes and should not be construed as a limitation to this patent. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0020] Embodiment 1 As Figure 1 shown in the first embodiment of a method for testing fluid saturation in core displacement of the present invention, it includes the following steps: S1. Obtain the original formation pressure and original formation temperature of the gas reservoir; S2. Obtain a core, and test the physical properties data of the core through core analysis method; then perform nuclear magnetic resonance test on the core; S3. Saturate the core with formation water, and then perform nuclear magnetic resonance test on the core saturated with formation water; S4. Perform gas drive water seepage test on the saturated core according to the original formation pressure and original formation temperature of the gas reservoir, the core fails, and the water production is obtained; S5. Perform nuclear magnetic resonance test on the failed core; S6. Obtain the irreducible water saturation of the core after depletion based on the NMR test results of steps S2, S3, and S5; S7. Obtain the total irreducible water saturation of the core based on the core physical property data in step S2, the water production volume in step S4, and the irreducible water saturation of the core after depletion in step S6.

[0021] By obtaining the original formation pressure and original formation temperature data of the gas reservoir, the present invention can conduct gas drive water seepage tests under simulated formation conditions, and perform NMR tests on the core before saturation, after saturation, and after gas drive water seepage tests to obtain the irreducible water saturation, which can overcome the limitations of NMR tests under high temperature and high pressure, improve the accuracy of irreducible water saturation determination, and thus achieve the accuracy of determining formation pore and fluid information.

[0022] Example Two This example is the second example of a method for testing fluid saturation in core displacement. This example is similar to Example One, and the differences are as follows: In step S1, obtain the original formation pressure p0 of the gas reservoir, the original formation temperature T0 of the gas reservoir, and the density ρ of the original formation water.

[0023] In step S2, obtain a core from a typical production well in the gas reservoir and clean it with petroleum ether, then dry it. Next, test the core physical property data through core analysis methods, where the core physical property data includes porosity, length, and diameter. Then, send the core into a nuclear magnetic resonance analyzer for NMR testing to obtain a T2 spectrum, and obtain the dry core signal area S0.

[0024] In this example, step S3 specifically includes the following steps: S31. Determine the ion composition, concentration, and salinity of the reservoir formation water according to the produced formation water quality analysis report (see Table 1), and prepare the formation water according to the density ρ of the original formation water; S32. Saturate the core with the formation water in step S31; S33. Wipe the surface of the saturated core dry, then conduct NMR testing to obtain a T2 spectrum, and obtain the saturated core signal area S1.

[0025]

[0026] Table 1 The density in Table 1 is the density of the original formation water corresponding to the current core ρ.

[0027] And, step S4 includes the following steps: S41. Place the core in an environment approximately equal to or equal to the original formation temperature T0 of the gas reservoir; Specifically, a core holder 130 is used to hold the core, and the core holder 130 is placed in an oven 100; the oven 100 is heated to a temperature approximately equal to or the same as the original formation temperature T0 of the gas reservoir.

[0028] S42. Establish an initial confining pressure on the core; Specifically, a confining pressure pump 200 is used to pump fluid into the core holder 130 to establish an initial confining pressure.

[0029] S43. Inject formation water at a constant rate for displacement until the output pressure at the core reaches the original formation pressure p0 of the gas reservoir, and then apply a constant pressure to the core to complete pressure build-up; Specifically, formation water is placed in a second container 120, and then a displacement pump 300 is used to inject the formation water in the second container 120 into the core holder 130 at a constant rate for displacement until the pressure at the output end of the core holder 130 reaches the original formation pressure p0 of the gas reservoir; during the displacement process, the output pressure of the confining pressure pump 200 is kept greater than the pressure at the input end of the core holder 130, and the pressure difference between the two is the same as the value of the initial confining pressure; then, a backpressure assembly is used to apply a constant pressure to the core holder 130 to complete pressure build-up.

[0030] S44. Inject nitrogen gas into the core; Specifically, nitrogen gas is placed in a first container 110, and then a displacement pump 300 is used to inject the nitrogen gas in the first container 110 into the core holder 130, and the displacement pump 300 is pressurized until the pressure at the input end of the core holder 130 reaches the original formation pressure p0 of the gas reservoir.

[0031] S45. Conduct a nitrogen gas water displacement experiment test on the core under the displacement pressure difference determined according to the relative permeability test standard until the irreducible water state is reached.

[0032] S46. After reaching the irreducible water state, reduce the pressure on the core and cool the environment where the core is located to room temperature. At this time, the core is depleted, and the water production volume V is obtained; Specifically, after reaching the irreducible water state, the pressure at the output end of the core holder 130 is reduced to zero through the backpressure assembly; at the same time, the oven 100 is turned off to cool the temperature inside the oven 100 to room temperature; at this time, the core is depleted, and the displaced water is collected at the output end of the core holder 130 through the backpressure assembly to obtain the water production volume V.

[0033] In this embodiment, the backpressure assembly includes a backpressure valve 410 and a backpressure pump 420. The backpressure end of the backpressure valve 410 is communicated with the backpressure pump 420, the inlet end of the backpressure valve 410 is communicated with the core holder 130, and the outlet end of the backpressure valve 410 is communicated with a receiving container 500. Specifically, the constant pressure operation in step S43 includes: setting the backpressure pump 420 to a constant pressure mode and pumping until the pressure at the backpressure end of the backpressure valve 410 is equal to the pressure at the inlet end of the backpressure valve 410, and then conducting the backpressure pump 420 with the core holder 130 to complete pressure building. Specifically, in step S46, the pressure reduction is achieved by setting the backpressure pump 420 to a constant speed mode, and the displaced water is collected by the receiving container 500 at the outlet end of the backpressure valve 410 to obtain the displaced water volume V.

[0034] In step S5, nuclear magnetic resonance (NMR) testing is performed on the depleted core to obtain the T2 spectrum, and the signal area S2 of the depleted core is obtained. In step S6, the irreducible water saturation S of the depleted core w1 is calculated by the formula: S w1 = (S2 - S0) / (S1 - S0); In the formula, S0 represents the signal area of the dry core, S1 represents the signal area of the saturated core, and S2 represents the signal area of the depleted core.

[0035] In step S7, the total irreducible water saturation S of the core w2 is calculated by the formula: S w2 = S w1 + V / (D 2 / 4 × π × L × Ф); In the formula, S w1 represents the irreducible water saturation of the depleted core obtained in step S6, V represents the displaced water volume obtained in step S4; D, L, and Ф represent the physical property data of the core, where they represent the diameter, length, and porosity in the dry core state, respectively.

[0036] When implementing the present invention, it can be measured that the diameter of a core in the dry core state is 2.483 cm, the length is 5.04 cm, and the porosity is 15.89%, and the following Figure 2 shown curve graph can be obtained: Among them, the dry core curve is the curve obtained by NMR testing in step S2, and the signal area S0 of the dry core can be obtained as 1448.6986; the saturated formation water curve before displacement is the curve obtained by NMR testing in step S3, and the signal area S1 of the saturated core can be obtained as 16004.1552; the curve after gas displacing water is the curve obtained by NMR testing in step S5, and the signal area S2 of the depleted core can be obtained as 4455.0769.

[0037] The data obtained above are shown in Table 2 below.

[0038]

[0039] Table 2 As can be seen from Table 2, through the present invention, the irreducible water saturation closer to the actual formation conditions and its approximate distribution can be obtained, so as to realize a more accurate determination of the formation pore and fluid information. It should be noted that since the T2 spectrum can reflect the amount of hydrogen-containing substances in different spaces, when the hydrogen-containing substance is water, the water distribution can be obtained.

[0040] Example 3 As Figure 3 shown in the figure is an embodiment of a test device of the present invention, including an oven 100, a first container 110, a second container 120, and a core holder 130 disposed in the oven 100. The first container 110 and the second container 120 are both connected to the core holder 130; it further includes a confining pressure pump 200 and a displacement pump 300. The confining pressure pump 200 is connected to the core holder 130, and the displacement pump 300 is connected to both the first container 110 and the second container 120; it further includes a backpressure assembly connected to the core holder 130; it further includes a receiving container 500 and an electronic balance 600. The receiving container 500 is placed on the electronic balance 600, and the backpressure assembly is further connected to the receiving container 500. A test device of the present invention can be applied to the core displacement test fluid saturation method as described in Example 1 or 2.

[0041] Among them, the backpressure assembly includes a backpressure valve 410 and a backpressure pump 420 connected to the backpressure valve 410. The backpressure valve 410 is connected to the core holder 130; the receiving container 500 is a beaker, and the backpressure valve 410 is further connected to the beaker.

[0042] As Figure 3As shown in the figure, a first pressure gauge 710 and a first valve 810 are provided on the connecting pipe between the confining pressure pump 200 and the core holder 130. The displacement pump 300, the first container 110, and the second container 120 are connected through a tee. Among them, a fifth valve 850 is provided on the branch of the tee connected to the displacement pump 300, a sixth valve 860 is provided on the branch of the tee connected to the first container 110, and a seventh valve 870 is provided on the branch of the tee connected to the second container 120. The core holder 130, the first container 110, and the second container 120 are also connected through a tee. Among them, a second pressure gauge 720 and a second valve 820 are provided on the branch of the tee connected to the core holder 130, an eighth valve 880 is provided on the branch of the tee connected to the first container 110, and a ninth valve 890 is provided on the branch of the tee connected to the second container 120. A third pressure gauge 730 and a third valve 830 are provided on the connecting pipe between the core holder 130 and the back pressure valve 410. A fourth pressure gauge 740 and a fourth valve 840 are provided on the connecting pipe between the back pressure pump 420 and the back pressure valve 410.

[0043] When using the core displacement test fluid saturation method of the testing device of the present invention, step S4 specifically includes the following steps: S41. Transfer nitrogen into the first container 110, and transfer the formation water prepared in step S3 into the second container 120; set the temperature of the oven 100 to the same temperature as the original formation temperature T0 of the gas reservoir; use the core holder 130 to hold the core and heat it through the oven 100. In this embodiment, the nitrogen selected is nitrogen with a purity of 99%, and T0 is determined according to the original reservoir data, such as it can be determined to be 144°C.

[0044] S42. Set the confining pressure pump 200 to the inlet pump mode, then open the first valve 810, and the confining pressure pump 200 pumps in to establish the initial confining pressure. In this embodiment, the initial confining pressure is 3-5 MPa. Preferably, the initial confining pressure is selected as 3 MPa.

[0045] S43. Open the fifth valve 850, the seventh valve 870, the ninth valve 890, and the second valve 820. Start the displacement pump 300 and inject formation water at a constant speed into the core holder 130 for displacement. During the displacement process, ensure that the reading of the first pressure gauge 710 is always higher than that of the second pressure gauge 720, and the difference between the first pressure gauge 710 and the second pressure gauge 720 is the same as the value of the initial confining pressure until the reading of the third pressure gauge 730 reaches the original formation pressure p0 of the gas reservoir. Subsequently, close the fifth valve 850, the seventh valve 870, the ninth valve 890, and the second valve 820. Set the backpressure pump 420 to the constant pressure mode and start the pump until the reading of the fourth pressure gauge 740 is equal to the reading of the third pressure gauge 730. Then open the third valve 830 and the fourth valve 840 to complete the pressure build-up. In this embodiment, p0 is determined according to the original reservoir data and can be determined as 51.2 MPa, for example.

[0046] S44. Open the sixth valve 860 and the eighth valve 880. Start the displacement pump 300 and pressurize the nitrogen in the first container 110 until the reading of the third pressure gauge 730 reaches the original formation pressure p0 of the gas reservoir.

[0047] S45. Open the second valve 820 and the backpressure valve 410. According to the existing production data of the gas reservoir, conduct a nitrogen flooding experiment test on the core under the displacement pressure difference determined according to the relative permeability test standard until the irreducible water state is reached.

[0048] S46. After reaching the irreducible water state, stop the displacement pump 300. Set the backpressure pump 420 to the constant speed mode and withdraw the pump. The confining pressure pump 200 follows the backpressure pump 420 to withdraw the pump, maintaining the difference between the first pressure gauge 710 and the second pressure gauge 720 at 1 - 2 MPa until it drops to zero. At the same time, turn off the oven 100 to cool the temperature in the oven 100 to room temperature, and the readings of the third pressure gauge 730 and the fourth pressure gauge 740 drop to zero. At this time, the core is depleted. Record the displaced water collected in the receiving container 500, i.e., the beaker, and then calculate the volume V of the displaced water through the mass obtained by the electronic balance 600 and the density ρ of the original formation water.

[0049] In the specific content of the above specific implementation manner, each technical feature can be combined arbitrarily without contradiction. For the sake of concise description, not all possible combinations of the above technical features are described. However, as long as the combination of these technical features does not exist in contradiction, it should be considered as within the scope described in this specification.

[0050] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all implementation manners here. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the claims of the present invention.

Claims

1. A method for testing fluid saturation in core displacement, characterized in that It includes the following steps: S1. Obtain the original formation pressure and original formation temperature of the gas reservoir; S2. Obtain a core, and test the physical properties data of the core through core analysis method; then conduct nuclear magnetic test on the core; S3. Saturate the core with formation water, and then conduct nuclear magnetic test on the core saturated with formation water; S4. Conduct gas drive water seepage test on the saturated core according to the original formation pressure and original formation temperature of the gas reservoir, and the core fails, and obtain the water production volume; S5. Conduct nuclear magnetic test on the failed core; S6. Obtain the irreducible water saturation of the failed core according to the nuclear magnetic test results of steps S2, S3, and S5; S7. Obtain the total irreducible water saturation of the core according to the physical properties data of the core in step S2, the water production volume in step S4, and the irreducible water saturation of the failed core in step S6.

2. The method for testing fluid saturation in a core displacement according to claim 1, characterized in that, Step S4 includes the following steps: S41. Place the core in an environment approximately equal to or the same as the original formation temperature of the gas reservoir; S42. Establish an initial confining pressure on the core; S43. Inject formation water at a constant rate for displacement at the core until the output pressure at the core reaches the original formation pressure of the gas reservoir, and then apply constant pressure to the core to complete pressure build-up; S44. Inject nitrogen gas into the core; S45. Conduct nitrogen gas drive water experiment test on the core at the displacement pressure difference determined according to the relative permeability test standard until the irreducible water state is reached; S46. After reaching the irreducible water state, reduce the pressure at the core and cool the environment where the core is located to room temperature. At this time, the core fails, and obtain the water production volume V.

3. The method for testing fluid saturation in a core displacement according to claim 2, wherein Step S41 includes: clamping the core with a core holder (130), and placing the core holder (130) in an oven (100); the oven (100) is heated to a temperature approximately equal to or the same as the original formation temperature of the gas reservoir; Step S42 includes: using a confining pressure pump (200) to pump into the core holder (130) to establish an initial confining pressure; Step S43 includes: placing formation water in a second container (120), and then using a displacement pump (300) to inject the formation water in the second container (120) into the core holder (130) at a constant rate for displacement until the pressure at the output end of the core holder (130) reaches the original formation pressure of the gas reservoir; then, use a back pressure component to apply constant pressure to the core holder (130) to complete pressure build-up; Step S44 includes: placing nitrogen gas in a first container (110), and then using the displacement pump (300) to inject the nitrogen gas in the first container (110) into the core holder (130); Step S46 includes: after reaching the irreducible water state, use the back pressure component to reduce the pressure at the output end of the core holder (130) to zero; at the same time, turn off the oven (100) to cool the temperature in the oven (100) to room temperature; at this time, the core fails, and collect the displaced water at the output end of the core holder (130) through the back pressure component to obtain the water production volume V.

4. The method for testing fluid saturation in a core displacement according to claim 3, wherein During the displacement process in step S43, keep the output pressure of the confining pressure pump (200) always greater than the pressure at the input end of the core holder (130), and the pressure difference between the two is the same as the value of the initial confining pressure.

5. The method for testing fluid saturation in a core displacement according to claim 2, wherein, In step S44, the displacement pump (300) is pressurized until the pressure at the input end of the core holder (130) reaches the original formation pressure of the gas reservoir.

6. The method for testing fluid saturation of core displacement according to claim 3, characterized in that The back pressure assembly includes a back pressure valve (410) and a back pressure pump (420). The back pressure end of the back pressure valve (410) is connected to the back pressure pump (420), the inlet end of the back pressure valve (410) is connected to the core holder (130), and the outlet end of the back pressure valve (410) is connected to a receiving container (500). The constant pressure operation in step S43 includes: setting the back pressure pump (420) to the constant pressure mode and pumping into the back pressure end of the back pressure valve (410) until the pressure at the back pressure end is equal to the pressure at the inlet end of the back pressure valve (410), and then connecting the back pressure pump (420) to the core holder (130) to complete the pressure build-up. In step S46, the pressure reduction is achieved by setting the back pressure pump (420) to the constant speed mode, and the displaced water is collected through the receiving container (500) at the outlet end of the back pressure valve (410) to obtain the displaced water volume V.

7. The method for testing fluid saturation in a core displacement according to claim 1, characterized in that, In step S1, it also includes obtaining the density of the original formation water. Step S3 specifically includes the following steps: S31. Prepare the formation water according to the mineral composition of the formation water and the density of the original formation water. S32. Saturate the core with the formation water prepared in step S31. S33. Wipe the surface of the saturated core dry and then perform nuclear magnetic resonance testing.

8. The core displacement test fluid saturation method according to any one of claims 1 to 7, characterized in that, In step S2, after performing nuclear magnetic resonance testing on the core, a T2 spectrum is obtained and the dry core signal area S0 is obtained; in step S3, after performing nuclear magnetic resonance testing on the saturated core, a T2 spectrum is obtained and the saturated core signal area S1 is obtained; in step S5, after performing nuclear magnetic resonance testing on the depleted core, a T2 spectrum is obtained and the depleted core signal area S2 is obtained. In step S6, the calculation formula for the irreducible water saturation S of the core after depletion is: w1 ​ S w1 = (S2 - S0) / (S1 - S0); In the formula, S0 represents the dry core signal area, S1 represents the saturated core signal area, and S2 represents the depleted core signal area.

9. The core displacement test fluid saturation method according to any one of claims 1 to 7, characterized in that, In step S7, the total irreducible water saturation S w2 of the core is calculated by the following formula: S w2 = S w1 +V / (D 2 / 4×π×L×Ф); Wherein, S w1 represents the irreducible water saturation of the core after depletion obtained in step S6, V represents the water displacement obtained in step S4; D, L, Ф represent the physical property data of the core, where they respectively represent the diameter, length, and porosity in the dry core state.

10. A test device for the method of testing fluid saturation in core displacement according to any one of claims 1 to 9, characterized in that, It includes an oven (100), a first container (110), a second container (120), and a core holder (130) provided in the oven (100). The first container (110) and the second container (120) are both connected to the core holder (130); it also includes a confining pressure pump (200) and a displacement pump (300). The confining pressure pump (200) is connected to the core holder (130), and the displacement pump (300) is connected to both the first container (110) and the second container (120); it also includes a back pressure assembly, and the back pressure assembly is connected to the core holder (130); it also includes a receiving container (500) and an electronic balance (600). The receiving container (500) is placed on the electronic balance (600), and the back pressure assembly is also connected to the receiving container (500).

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