A method and system for testing the salt solubility strength of inter-salt shale reservoirs

Abstract

The application discloses a method for testing salt-dissolution strength of inter-salt shale reservoirs, which comprises the following steps: collecting inter-salt shale cores of a current area to be researched, and preparing experimental rock samples with a saturated oil state; configuring the experimental rock samples with a carbonic acid solution, and converting the carbonic acid solution into a supercritical carbonic acid solution with a supercritical state according to preset supercritical characteristic parameters; removing soluble salt in the experimental rock samples by using the supercritical carbonic acid solution to obtain first rock samples, then injecting a target injection gas medium into the first rock samples to carry out oil displacement, and collecting output water in the oil displacement process; and performing component analysis on the output water to obtain the salt-dissolution strength. The application realizes acquisition of soluble salt types and salt-dissolution rates of inter-salt shale reservoirs, and can provide optimal injection-production parameters for oil development of inter-salt shale reservoirs in different regions.

Description

Technical Field

[0001] This invention belongs to the field of shale oil development technology, and in particular relates to a method and system for testing the intensity of salt dissolution in intersalt shale reservoirs. Background Technology

[0002] Shale oil is an unconventional petroleum resource with a coexisting source and reservoir, typically existing in free, adsorbed, and partially dissolved states within shale formations. While shale oil resources are abundant, the poor physical properties of shale reservoirs, along with extremely low pore-throat ratios and permeability, result in very low recovery rates during the depletion phase of shale oil production. Therefore, conventional secondary water injection to enhance oil recovery is not an effective method; shale oil development necessitates reservoir fracturing and permeability enhancement. Currently, horizontal well fracturing, hydraulic fracturing, and CO2 fracturing technologies are primarily used domestically and internationally to improve shale oil recovery rates.

[0003] The inter-salt shale oil in the Qianjiang Depression is a typical example of inter-salt shale oil in my country. The Qianjiang Depression is not only rich in source rocks but is also the most important salt-forming area. Its reservoirs contain two sets of salt rock layers. With the advancement of development processes such as hydraulic fracturing and water injection / pumping, the salt crystals in the reservoir (mainly composed of Na₂SO₄·CaSO₄) can decompose into highly soluble Na₂SO₄ and slightly soluble CaSO₄ under water dissolution. Salt crystals in the water (such as CaSO₄) will also precipitate when they accumulate to a certain extent. This dynamic reaction ultimately leads to an increase in some pore spaces in the reservoir, i.e., salt dissolution occurs. Salt dissolution is of great significance for the effective development of inter-salt shale oil.

[0004] Shale samples exposed to fracturing fluid and dry CO2 or CO2-saturated water undergo barite precipitation, calcite dissolution / precipitation, and pore size changes. These precipitations and changes can, to some extent, enhance reservoir flow pathways. Furthermore, under high temperature and pressure, minerals such as dolomite in shale samples do not react with anhydrous supercritical CO2, but react with saturated water supercritical CO2, causing some minerals in the shale samples to dissolve and recrystallize. The reaction temperature and reaction time are key parameters affecting the composition, morphology, and degree of reaction of the newly formed minerals. Summary of the Invention

[0005] To address the aforementioned problems, this invention proposes a method for testing the salt dissolution intensity of intersalt shale reservoirs, comprising: collecting intersalt shale core samples from the area under study and preparing experimental rock samples with saturated oil; preparing a carbonic acid solution for the experimental rock samples and converting the carbonic acid solution into a supercritical carbonic acid solution with a supercritical state according to preset supercritical characteristic parameters; using the supercritical carbonic acid solution to remove soluble salts from the experimental rock samples to obtain a first rock sample, then injecting a target gas injection medium into the first rock sample to perform oil displacement and collecting the produced water during the oil displacement process; and performing component analysis on the produced water to obtain the salt dissolution intensity.

[0006] Preferably, the step of preparing the experimental rock sample includes: washing the shale core with oil, then evacuating the washed shale core under vacuum, and then pressurizing the evacuated shale core with saturated crude oil to obtain the experimental rock sample.

[0007] Preferably, the carbonic acid solution is obtained by mixing a first solution and carbon dioxide. The process of converting the carbonic acid solution into a supercritical carbonic acid solution with a supercritical state includes: heating and pressurizing the first solution according to a preset first temperature threshold and a first pressure threshold, and then injecting the carbon dioxide into the current first solution according to a preset injection ratio parameter to form the supercritical carbonic acid solution. The first pressure threshold is higher than 23 MPa and the first temperature threshold is higher than 375°C.

[0008] Preferably, after carbon dioxide is completely injected into the first solution, the optimal supercritical carbonic acid solution is obtained by discharging the undissolved carbon dioxide gas.

[0009] Preferably, the steps of injecting the target gas injection medium into the first rock sample to drive oil and collecting the produced water during the oil displacement process include: pressurizing the target gas injection medium to the preset first pressure threshold, then using the current target gas injection medium to drive oil in the experimental rock sample, and after the oil displacement is completed, reducing the back pressure generated during the oil displacement process according to the preset second pressure threshold, wherein the preset second pressure threshold is lower than the preset first pressure threshold, and the second pressure threshold is preferably 20 MPa.

[0010] Preferably, the process of obtaining the salt dissolution intensity includes: performing soluble salt removal and oil displacement steps on the experimental rock sample multiple times in succession, obtaining the ion solubility of the produced water each time, and calculating the salt dissolution rate characterizing the salt dissolution intensity.

[0011] Preferably, the salt solubility is calculated using the following expression:

[0012]

[0013] in, Indicates salt solubility. α This indicates the total ion concentration in the output water from each test. L This indicates the volume of water produced in each test. n The sequence number represents the number of tests. M Indicates the dry weight of the core. α c This indicates the initial ion concentration.

[0014] On the other hand, the present invention also provides a system for testing the salt dissolution intensity of intersalt shale reservoirs. The system includes: an experimental rock sample clamp for clamping and fixing an experimental rock sample with a saturated oil state, prepared from intersalt shale cores collected from the current area under study; and a reaction vessel for removing soluble salts from the experimental rock sample using the supercritical carbonic acid solution to obtain a first rock sample, and then injecting a target gas injection medium into the first rock sample for oil displacement; a supercritical carbonic acid solution preparation device for preparing a carbonic acid solution for the experimental rock sample and converting the carbonic acid solution into a supercritical carbonic acid solution with a supercritical state according to preset supercritical characteristic parameters; and a salt dissolution intensity calculation device for collecting produced water during the oil displacement process and performing component analysis on the produced water to obtain the salt dissolution intensity.

[0015] Preferably, the system further includes a backpressure device, which is used to reduce the backpressure generated inside the experimental rock sample holder during the oil displacement process after the oil displacement process is completed.

[0016] Preferably, the salt dissolution intensity calculation device includes: a three-phase separation device for separating the produced water from the products of the oil displacement process; an ion composition analysis device for performing component analysis on the produced water separated by the three-phase separation device to generate water ion solubility; and a salt dissolution rate generation device for calculating the salt dissolution rate based on the water ion solubility.

[0017] Compared with the prior art, one or more embodiments of the above solutions may have the following advantages or beneficial effects:

[0018] This invention proposes a method for testing the salt dissolution intensity of intersalt shale reservoirs. The method involves preparing a carbonated solution from experimental rock samples originating from the study area, and converting the carbonated solution into a supercritical carbonated solution with a supercritical state according to preset supercritical characteristic parameters. Then, the supercritical carbonated solution is used to remove soluble salts from the experimental rock samples. Next, a selected target gas injection medium is injected into the first rock sample to perform oil displacement. Finally, the salt dissolution intensity of the intersalt shale reservoir is obtained based on the composition of the produced water during the oil displacement process. This invention enables the acquisition of soluble salt types and salt dissolution rates in intersalt shale reservoirs, providing optimal injection and production parameters for crude oil development in intersalt shale reservoirs in different regions, and offering a new direction for reservoir development and enhanced oil recovery after shale water injection fracturing.

[0019] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the description, claims, and drawings. Attached Figure Description

[0020] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0021] Figure 1 This is a step diagram of a method for testing the salt dissolution intensity of intersalt shale reservoirs according to an embodiment of this application.

[0022] Figure 2 This is a schematic diagram illustrating the changes in ionic composition in the produced water before and after the huff and puff process of a method for testing the intensity of salt dissolution in intersalt shale reservoirs, as described in an embodiment of this application.

[0023] Figure 3 This is a schematic diagram showing the changes in NMR T2 spectra before and after the huff and puff process of a method for testing the intensity of salt dissolution in intersalt shale reservoirs, as described in an embodiment of this application.

[0024] Figure 4 This is a schematic diagram of a system for testing the intensity of salt dissolution in intersalt shale reservoirs, according to an embodiment of this application.

[0025] In this application, all drawings are schematic and are used only to illustrate the principles of the invention, and are not drawn to scale.

[0026] The list of reference numerals in the attached figures is as follows:

[0027] 10: Experimental rock sample holder

[0028] 11: Experimental rock samples

[0029] 20: Supercritical carbonic acid solution preparation apparatus

[0030] 21: Reactant replenishment device

[0031] 22: Injection device

[0032] 23: Mixing device

[0033] 30: Salt dissolution intensity calculation device

[0034] 31: Three-phase separation device

[0035] 32: Ion composition analysis device

[0036] 40: Back pressure device

[0037] 50: Nuclear Magnetic Resonance Testing Device

[0038] 60: Temperature control device Detailed Implementation

[0039] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings and examples, so that the process of how the present invention uses technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly. It should be noted that, as long as there is no conflict, the various embodiments and features in the various embodiments of the present invention can be combined with each other, and the resulting technical solutions are all within the protection scope of the present invention.

[0040] Furthermore, the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0041] Shale oil is an unconventional petroleum resource with a coexisting source and reservoir, typically existing in free, adsorbed, and partially dissolved states within shale formations. While shale oil resources are abundant, the poor physical properties of shale reservoirs, along with extremely low pore-throat ratios and permeability, result in very low recovery rates during the depletion phase of shale oil production. Therefore, conventional secondary water injection to enhance oil recovery is not an effective method; shale oil development necessitates reservoir fracturing and permeability enhancement. Currently, horizontal well fracturing, hydraulic fracturing, and CO2 fracturing technologies are primarily used domestically and internationally to improve shale oil recovery rates.

[0042] The inter-salt shale oil in the Qianjiang Depression is a typical example of inter-salt shale oil in my country. The Qianjiang Depression is not only rich in source rocks but is also the most important salt-forming area. Its reservoirs contain two sets of salt rock layers. With the advancement of development processes such as hydraulic fracturing and water injection / pumping, the salt crystals in the reservoir (mainly composed of Na₂SO₄·CaSO₄) can decompose into highly soluble Na₂SO₄ and slightly soluble CaSO₄ under water dissolution. Salt crystals in the water (such as CaSO₄) will also precipitate when they accumulate to a certain extent. This dynamic reaction ultimately leads to an increase in some pore spaces in the reservoir, i.e., salt dissolution occurs. Salt dissolution is of great significance for the effective development of inter-salt shale oil.

[0043] Shale samples exposed to fracturing fluid and dry CO2 or CO2-saturated water undergo barite precipitation, calcite dissolution / precipitation, and pore size changes. These precipitations and changes can, to some extent, enhance reservoir flow pathways. Furthermore, under high temperature and pressure, minerals such as dolomite in shale samples do not react with anhydrous supercritical CO2, but react with saturated water supercritical CO2, causing some minerals in the shale samples to dissolve and recrystallize. The reaction temperature and reaction time are key parameters affecting the composition, morphology, and degree of reaction of the newly formed minerals.

[0044] Therefore, to address the aforementioned problems, this invention proposes a method for testing the salt dissolution intensity of inter-salt shale reservoirs. This method involves preparing a carbonated solution from experimental rock samples originating from the current study area, and converting the carbonated solution into a supercritical carbonated solution with a supercritical state according to preset supercritical characteristic parameters. Then, the supercritical carbonated solution is used to remove soluble salts from the experimental rock samples. Next, the selected target gas injection medium is injected into the first rock sample to perform oil displacement. Finally, the salt dissolution intensity of the inter-salt shale reservoir is obtained based on the composition of the produced water during the oil displacement process. This invention enables the acquisition of soluble salt types and salt dissolution rates in inter-salt shale reservoirs, providing optimal injection and production parameters for crude oil development in inter-salt shale reservoirs in different regions, and offering a new direction for reservoir development and enhanced oil recovery after shale water injection fracturing.

[0045] Example 1

[0046] Figure 1 This is a step diagram illustrating a method for testing the salt dissolution intensity of inter-salt shale reservoirs according to an embodiment of this application. See below for reference. Figure 1 The following will be used to explain each step of this method.

[0047] like Figure 1As shown, in step S110, intersalt shale cores are collected from the current area under study, and experimental rock samples with saturated oil are prepared. In this embodiment, intersalt shale cores are collected from the intersalt shale reservoir in the current area under study, and the intersalt shale cores are processed to prepare experimental rock samples with saturated oil.

[0048] In the process of preparing an experimental rock sample with saturated oil, firstly, the intersalt shale core is washed with oil. Then, the washed intersalt shale core is evacuated and pressurized with saturated crude oil to obtain the experimental rock sample. Specifically, the intersalt shale core collected in step S110 is washed with oil to obtain an oil-free intersalt shale core. Next, the oil-free intersalt shale core is evacuated according to a preset time threshold to remove gas from the core, thus providing conditions for creating a saturated oil state in the experimental rock sample. Finally, the evacuated oil-free intersalt shale core is pressurized with saturated crude oil according to the preset time threshold until the crude oil in the core reaches saturation, thereby obtaining an experimental rock sample with saturated oil. The preset time threshold is preferably 36 hours. It should be noted that the present invention does not specifically limit the preset time threshold; those skilled in the art can set it according to actual needs.

[0049] After the experimental rock samples were prepared, they were subjected to heating and pressurization treatment to give them the same environmental parameters (temperature and pressure parameters) as the reservoir in which they were located. Nuclear magnetic resonance (NMR) tests were then performed on the experimental rock samples to obtain the NMR T2 spectrum of the experimental rock samples under saturated oil conditions.

[0050] Further, in step S120, a carbonic acid solution is prepared for the experimental rock sample, and the carbonic acid solution is converted into a supercritical carbonic acid solution with a supercritical state according to preset supercritical characteristic parameters. This invention injects carbonated water into the experimental rock sample under high pressure, utilizing the characteristics of supercritical carbonated water to enter the micro-nano pores of the experimental rock sample, causing the supercritical carbonated water to react with the crude oil in the experimental rock sample, thereby displacing the crude oil and obtaining produced oil. Accordingly, this embodiment prepares a carbonic acid solution for the experimental rock sample, and presets the supercritical characteristic parameters (temperature and pressure parameters) required for the carbonic acid solution to reach a supercritical state. The preset supercritical characteristic parameters create a reaction environment for the carbonic acid solution to form a supercritical carbonic acid solution, thereby converting the carbonic acid solution into a supercritical carbonic acid solution with a supercritical state.

[0051] The carbonic acid solution is obtained by mixing a first solution and carbon dioxide. In one specific embodiment of this application, a manganese aqueous solution is used as the first solution, and then carbon dioxide is injected into the manganese aqueous solution to fully mix the carbon dioxide and manganese aqueous solution to form a manganese carbonate solution. It should be noted that the present invention does not specifically limit the type of the first solution, and those skilled in the art can select a first solution that can react with carbon dioxide to form a carbonic acid solution according to the actual situation.

[0052] Next, in the process of converting the carbonic acid solution into a supercritical carbonic acid solution with a supercritical state, firstly, the first solution is heated and pressurized according to a preset first temperature threshold and a first pressure threshold. Then, according to a preset injection ratio parameter, carbon dioxide is injected into the first solution to form a supercritical carbonic acid solution, wherein the first pressure threshold is higher than 23 MPa and the first temperature threshold is higher than 375°C. Specifically, the first solution is heated and pressurized according to the preset first temperature threshold and first pressure threshold that enable the first solution to reach a supercritical state, resulting in a first solution with a supercritical state. Next, a preset injection ratio parameter (the injection ratio parameter is the ratio of the first solution to carbon dioxide) is set, and carbon dioxide is injected into the first solution according to the preset ratio parameter. After the first solution and carbon dioxide have fully reacted, a supercritical carbonic acid solution is obtained. In this embodiment, the preset injection ratio parameter is 2.5. It should be noted that the present invention does not specifically limit the injection ratio parameter, and those skilled in the art can set it according to the actual reaction conditions.

[0053] After carbon dioxide is completely injected into the first solution, the optimal supercritical carbonic acid solution is obtained by discharging the undissolved carbon dioxide gas cap. Specifically, after all carbon dioxide is injected into the first solution, the supercritical carbonic acid solution is further heated and pressurized to achieve the same environmental parameters (temperature and pressure) as the current experimental rock sample. In actual operation, after all carbon dioxide is injected into the first solution, there may be excess carbon dioxide; in other words, not all carbon dioxide participates in the reaction to form the carbonic acid solution. Therefore, in this embodiment, after the reaction is complete and the pressure inside the experimental rock sample stabilizes, the undissolved carbon dioxide gas cap is discharged. When liquid is produced in the current supercritical carbonic acid solution, it is determined that the carbon dioxide gas cap has been completely discharged, thus obtaining the optimal supercritical carbonic acid solution with sufficient reaction and no excess reactants.

[0054] Next, in step S130, soluble salts in the experimental rock sample are removed using a supercritical carbonic acid solution to obtain a first rock sample. Then, the target gas injection medium is injected into the first rock sample to perform oil displacement, and the produced water during the oil displacement process is collected. In this embodiment, an optimal supercritical carbonic acid solution is injected into the experimental rock sample to dissolve the soluble salts, thus removing them. The experimental rock sample after complete dissolution of the soluble salts is used as the first rock sample. Next, gas injection is performed on the first rock sample, injecting the target gas injection medium to perform oil displacement, obtaining products (produced oil, produced gas, and produced water). Because the combination of supercritical fluid and carbon dioxide has stronger diffusion, dissolution, and extraction capabilities, this invention uses carbon dioxide as the target gas injection medium, significantly improving the oil displacement efficiency.

[0055] After dissolving soluble salts in the experimental rock sample by injecting the optimal supercritical carbonic acid solution, the pressure of the environment surrounding the experimental rock sample is increased to a preset first pressure threshold to dissolve the soluble salts. Once the soluble salts are completely dissolved, the target gas injection medium is pressurized to the preset first pressure threshold, and then the experimental rock sample is displaced using the target gas injection medium. After displacement, the back pressure generated during the displacement process is reduced according to a preset second pressure threshold, wherein the preset second pressure threshold is lower than the preset first pressure threshold, and the second pressure threshold is preferably 20 MPa. Specifically, during the displacement of the experimental rock sample, a certain back pressure is generated, resulting in the pressure of the environment surrounding the experimental rock sample after displacement being much higher than the preset first pressure threshold. Therefore, this embodiment reduces the back pressure generated during the displacement process by adjusting the displacement environment according to the preset second pressure threshold, thereby reducing the viscosity of the produced oil and enabling better collection of the produced oil.

[0056] Furthermore, in step S140, the produced water is subjected to compositional analysis to obtain the salt dissolution intensity. After obtaining the oil displacement product, this embodiment separates the produced water from the product and collects it. After collection, the produced water is subjected to compositional analysis to obtain the changes in ion solubility in the produced water. Then, based on the changes in ion solubility, the salt dissolution intensity of the intersalt shale reservoir where the experimental rock sample is located is determined.

[0057] Next, the experimental rock samples underwent multiple cycles of soluble salt removal and oil displacement (i.e., multiple rounds of huff and puff). The ion solubility of the produced water was obtained for each round, and the salt dissolution rate, characterizing the intensity of salt dissolution, was calculated based on the ion solubility of the produced water for each round. This allowed for the tracking of changes in the intensity of salt dissolution. Each round of huff and puff began when the pressure of the experimental rock sample decreased to match the environmental parameters of the reservoir containing the experimental rock sample.

[0058] Furthermore, in this embodiment, the dry weight of the oil-free intersalt shale core in step S110 is weighed before vacuuming, and the wet weight of the experimental rock sample after obtaining the experimental rock sample with saturated oil is weighed, so that the weighing results are applied to the calculation of karst rate and the nuclear magnetic resonance test process.

[0059] Next, this embodiment uses the following expression to calculate the karst ratio:

[0060] (1)

[0061] in, Indicates salt solubility. α This indicates the total ion concentration in the output water from each test. L This indicates the volume of water produced in each test. n The sequence number represents the number of tests. M Indicates the dry weight of the core. α c This indicates the initial ion concentration.

[0062] Figure 2 This is a schematic diagram illustrating the changes in ionic composition in the produced water before and after the huff and puff process of a method for testing the intensity of salt dissolution in intersalt shale reservoirs, as described in an embodiment of this application. (Refer to...) Figure 2 In this embodiment, the soluble salts are dissolved by injecting carbonic acid solution into the experimental rock sample in each round of huff and puff, which increases the pore space inside the experimental rock sample. The crude oil is replaced into the large pores by gas injection, which improves the core recovery rate of intersalt shale.

[0063] Figure 3 This is a schematic diagram illustrating the changes in NMR T2 spectra before and after the huff and puff process of a method for testing the intensity of salt dissolution in inter-salt shale reservoirs, as described in this embodiment of the application. This embodiment also generates NMR T2 spectra of the soluble salt dissolution process and the oil displacement process in real time using NMR testing (see reference). Figure 3 Then, based on the NMR T2 spectrum, the throughput efficiency per round is calculated using the following expression:

[0064] (2)

[0065] in, This represents the total signal amount when the oil is saturated. Φ represents the total amount of crude oil signal after throughput, and Φ represents throughput efficiency.

[0066] Example 2

[0067] Based on the method for testing the salt dissolution intensity of inter-salt shale reservoirs described in Embodiment 1 above, this embodiment of the invention also provides a system for testing the salt dissolution intensity of inter-salt shale reservoirs (hereinafter referred to as the "salt dissolution intensity testing system"). Figure 4 This is a schematic diagram of a system for testing the salt dissolution intensity of inter-salt shale reservoirs according to an embodiment of this application. The structure and function of the system for testing the salt dissolution intensity of inter-salt shale reservoirs will be described in detail below with reference to embodiments of the present invention.

[0068] like Figure 4 As shown, the salt dissolution intensity testing system includes at least: an experimental rock sample clamp 10, a supercritical carbonic acid solution preparation device 20, and a salt dissolution intensity calculation device 30. The experimental rock sample clamp 10 is used to clamp and fix experimental rock samples prepared from inter-salt shale cores collected from the area under study, forming a saturated oil state. It also serves as a reaction vessel for removing soluble salts from the experimental rock sample using a supercritical carbonic acid solution to obtain a first rock sample, into which the target gas injection medium is then injected for oil displacement. The supercritical carbonic acid solution preparation device 20 is used to prepare a carbonic acid solution for the experimental rock sample and, according to preset supercritical characteristic parameters, converts the carbonic acid solution into a supercritical carbonic acid solution with a supercritical state. The salt dissolution intensity calculation device 30 is used to collect produced water during the oil displacement process and perform component analysis on the produced water to obtain the salt dissolution intensity.

[0069] Specifically, the experimental rock sample holder 10 contains an experimental rock sample 11 prepared from intersalt shale cores collected from the area under study, and is in a saturated oil state. The experimental rock sample holder 10 is used to clamp and fix the experimental rock sample 11. On the other hand, inside the experimental rock sample holder 10, the space between the inner wall of the experimental rock sample and the experimental rock sample is filled with a supercritical carbonic acid solution and a target gas injection medium. That is, the experimental rock sample holder 10 also serves as a reaction vessel for preparing the first rock sample using the supercritical carbonic acid solution and injecting the target gas injection medium into the first rock sample for oil displacement. The supercritical carbonic acid solution preparation device 20 is connected to the experimental rock sample holder 10 and is used to prepare a carbonic acid solution for the experimental rock sample 11, and to prepare a supercritical carbonic acid solution in a supercritical state according to preset supercritical characteristic parameters, and to provide the supercritical carbonic acid solution to the experimental rock sample holder 10 to realize the reaction inside the experimental rock sample holder 10. The salt dissolution intensity calculation device 30 is connected to the supercritical carbonic acid solution preparation device 20. It is used to collect the produced water during the oil displacement process inside the experimental rock sample holder 10 and perform component analysis on the produced water to obtain the salt dissolution intensity.

[0070] The salt dissolution intensity testing system of this embodiment also includes a back pressure device 40, which is disposed between the experimental rock sample clamp 10 and the salt dissolution intensity calculation device 30. It is used to reduce the back pressure generated inside the experimental rock sample clamp 10 during the oil displacement process after the oil displacement process is completed.

[0071] Furthermore, the salt dissolution intensity calculation device 30 includes: a three-phase separation device 31, an ion composition analysis device 32, and a salt dissolution rate generation device (not shown). The three-phase separation device 31 is located between the back pressure device 40 and the ion composition analysis device 32, and is used to separate produced water from the products of the oil displacement process. The ion composition analysis device 32 is used to analyze the composition of the produced water separated by the three-phase separation device 31 and generate water ion solubility. The salt dissolution rate generation device (not shown) is used to calculate the salt dissolution rate based on the water ion solubility generated by the three-phase separation device 31.

[0072] The supercritical carbonic acid solution preparation apparatus 20 includes: multiple reactant replenishment devices 21, an injection device 22, and a mixing device 23. The multiple reactant replenishment devices 21 are used to store the reactants required for preparing the supercritical carbonic acid solution. The injection device 22, connected to each reactant replenishment device 21, is used to pressurize the reactants stored in each reactant replenishment device 21 into the mixing device for reaction. The mixing device 23 provides the reaction space for preparing the supercritical carbonic acid solution.

[0073] The salt dissolution intensity testing system of this embodiment also includes: a nuclear magnetic resonance (NMR) testing device 50 and a temperature control device 60. The NMR testing device 50 is used to generate NMR T2 spectra of the soluble salt dissolution process and the oil displacement process in real time, as well as the NMR T2 spectrum of the experimental rock sample under saturated oil conditions after the experimental rock sample is prepared. The temperature control device 60 is connected to the experimental rock sample clamp 10 and is used to maintain a constant temperature after the reaction conditions inside the experimental rock sample clamp 10 reach the expected temperature.

[0074] Example 3

[0075] The following section uses an experimental rock sample made from a core of intersalt shale in a certain region as an example to explain in detail the testing method for the salt dissolution intensity of intersalt shale reservoirs.

[0076] After collecting intersalt shale cores, the cores were first washed with oil, and the dry weight of the washed cores was measured. Then, the washed cores were vacuum-sealed for 36 hours. Next, the vacuum-sealed cores were pressurized with saturated crude oil for 36 hours to obtain experimental rock samples. Simultaneously, the wet weight of the experimental rock samples now in a saturated oil state was measured.

[0077] Next, the experimental rock sample was placed in the experimental rock sample holder 10, and the internal temperature of the experimental rock sample holder 10 was raised to 65°C and the pressure increased to 25 MPa. Then, nuclear magnetic resonance (NMR) testing was performed to obtain the NMR T2 spectrum of the experimental rock sample in saturated oil condition (refer to...). Figure 3 ).

[0078] Open the reactant replenishment device storing manganese aqueous solution, and inject 0.25 PV of manganese aqueous solution into the mixing device 23 using the injection device 22. Quickly heat the inside of the mixing device 23 to 380°C and pressurize it to 25 MPa. Then, open the reactant replenishment device storing carbon dioxide, and inject 0.1 PV of carbon dioxide fluid into the mixing device 23 at a constant flow rate using the injection device 22. After the pressure inside the mixing device 23 stabilizes, discharge the excess gas at the top until liquid is produced. Then close the injection valve of the reactant replenishment device storing carbon dioxide.

[0079] After the pressure inside the mixing device 23 stabilizes, manganese carbonate solution prepared inside the mixing device 23 is injected into the experimental rock sample holder 10, and the pressure inside the experimental rock sample holder 10 is increased to 30 MPa. After injection, the injection valve of the mixing device 23 is closed. After the pressure inside the mixing device 23 stabilizes, the nuclear magnetic resonance (NMR) T2 spectrum related to the dissolution process of soluble salts is generated by the NMR testing device 50 (refer to...). Figure 3 Next, the injection device 22 is reopened to inject carbon dioxide fluid into the experimental rock sample holder 10, and the pressure in the experimental rock sample holder 10 is increased to 30 MPa. After the internal pressure of the experimental rock sample holder 10 stabilizes again, the nuclear magnetic resonance testing device 50 generates a nuclear magnetic resonance T2 spectrum related to the oil displacement process (refer to...). Figure 3 ).like Figure 3 As shown, each round of inrush and outflow in this embodiment can increase the pore radius of the intersalt shale reservoir, and the pore radius is basically the same in each round.

[0080] Next, the backpressure device 40 is turned on to reduce the backpressure inside the experimental rock sample holder 10 to 20 MPa. Then, the three-phase separation device 31 collects the products from the oil displacement process and separates the produced oil, produced gas, and produced water. Next, the produced water is directed to the ion composition analysis device 32 to analyze changes in ion solubility. Finally, the experimental rock sample undergoes multiple soluble salt removal and oil displacement steps consecutively, and the changes in ion solubility in the produced water are analyzed each time to determine the intensity of salt dissolution for each step.

[0081] This invention proposes a method for testing the salt dissolution intensity of intersalt shale reservoirs. The method involves preparing a carbonated solution from experimental rock samples originating from the study area, and converting the solution into a supercritical carbonated solution with a supercritical state according to preset supercritical characteristic parameters. Then, the supercritical carbonated solution is used to remove soluble salts from the experimental rock samples. Next, a selected target gas injection medium is injected into the first rock sample to drive oil flow. Finally, the salt dissolution intensity of the intersalt shale reservoir is obtained based on the composition of the produced water during the oil displacement process. This invention enables the acquisition of soluble salt types and salt dissolution rates in intersalt shale reservoirs. By utilizing the water-soluble properties of reservoir salts to increase pore throat space, and combining this with the injected target gas injection medium (carbon dioxide), the huff and puff efficiency is significantly improved. This provides optimal injection and production parameters for crude oil development in intersalt shale reservoirs in different regions, offering a new direction for reservoir development and enhanced oil recovery after shale water injection fracturing.

[0082] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

[0083] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the claims of the present invention.

[0084] Those skilled in the art will understand that the modules or steps of the present invention described above can be implemented using general-purpose computing devices. They can be centralized on a single computing device or distributed across a network of multiple computing devices. Optionally, they can be implemented using computer-executable program code, thereby storing them in a storage device for execution by a computing device, or fabricating them separately as individual integrated circuit modules, or fabricating multiple modules or steps as a single integrated circuit module. Thus, the present invention is not limited to any particular hardware and software combination.

[0085] While the embodiments disclosed in this invention are as described above, the content is merely for the purpose of facilitating understanding of the invention and is not intended to limit the invention. Any person skilled in the art to which this invention pertains may make any modifications and variations in form and detail of the implementation without departing from the spirit and scope disclosed herein; however, the scope of patent protection for this invention shall still be determined by the scope defined in the appended claims.

Claims

1. A method for testing the intensity of salt dissolution in intersalt shale reservoirs, characterized in that, include: Collect intersalt shale cores from the area to be studied and prepare experimental rock samples with saturated oil. A carbonic acid solution is prepared for the experimental rock sample, and the carbonic acid solution is converted into a supercritical carbonic acid solution with a supercritical state according to preset supercritical characteristic parameters. The carbonic acid solution is obtained by mixing a first solution and carbon dioxide. The first solution is heated and pressurized according to preset first temperature threshold and first pressure threshold. Then, carbon dioxide is injected into the first solution according to preset injection ratio parameters to form the supercritical carbonic acid solution. The first pressure threshold is higher than 23 MPa and the first temperature threshold is higher than 375°C. The supercritical carbonic acid solution is used to remove soluble salts from the experimental rock sample to obtain a first rock sample. Then, the target gas injection medium is injected into the first rock sample to perform oil displacement, and the produced water during the oil displacement process is collected. The target gas injection medium is pressurized to a preset first pressure threshold, and then the experimental rock sample is subjected to oil displacement using the current target gas injection medium. After the oil displacement is completed, the back pressure generated during the oil displacement process is reduced according to a preset second pressure threshold. The preset second pressure threshold is lower than the preset first pressure threshold, and the second pressure threshold is 20 MPa. The composition of the produced water is analyzed to obtain the intensity of salt dissolution.

2. The method according to claim 1, characterized in that, The steps for preparing the experimental rock sample include: The shale core was washed with oil, then the washed shale core was evacuated, and then pressurized with saturated crude oil to obtain the experimental rock sample.

3. The method according to claim 1, characterized in that, After carbon dioxide is completely injected into the first solution, the optimal supercritical carbonic acid solution is obtained by discharging the undissolved carbon dioxide gas head in the first solution.

4. The method according to claim 2 or 3, characterized in that, The process of obtaining the strength of salt dissolution includes: The experimental rock sample was subjected to soluble salt removal and oil displacement steps multiple times in succession. The ion solubility of the produced water was obtained each time, and the salt dissolution rate, which characterizes the intensity of salt dissolution, was calculated.

5. The method according to claim 4, characterized in that, The salt solubility rate is calculated using the following expression: in, Indicates salt solubility. α This indicates the total ion concentration in the output water from each test. L This indicates the volume of water produced in each test. n The sequence number represents the number of tests. M Indicates the dry weight of the core. α c This indicates the initial ion concentration.

6. A system for testing the intensity of salt dissolution in intersalt shale reservoirs, characterized in that, The system is used to implement the method as described in any one of claims 1 to 5, and the system comprises: An experimental rock sample clamp is used to clamp and fix an experimental rock sample with saturated oil, which is made from intersalt shale cores collected from the current area under study. It also serves as a reaction vessel for removing soluble salts from the experimental rock sample using the supercritical carbonic acid solution to obtain a first rock sample, and then injecting a target gas injection medium into the first rock sample to drive oil. The target gas injection medium is pressurized to the preset first pressure threshold, and then the experimental rock sample is driven for oil displacement using the target gas injection medium. A supercritical carbonic acid solution preparation device is used to prepare a carbonic acid solution for the experimental rock sample and convert the carbonic acid solution into a supercritical carbonic acid solution with a supercritical state according to preset supercritical characteristic parameters. The carbonic acid solution is obtained by mixing a first solution and carbon dioxide. The first solution is heated and pressurized according to preset first temperature threshold and first pressure threshold. Then, carbon dioxide is injected into the first solution according to preset injection ratio parameters to form the supercritical carbonic acid solution. The first pressure threshold is higher than 23 MPa and the first temperature threshold is higher than 375°C. A back pressure device is used to reduce the back pressure generated inside the experimental rock sample holder during the oil displacement process according to a preset second pressure threshold after the oil displacement process is completed. The preset second pressure threshold is lower than the preset first pressure threshold, and the second pressure threshold is 20 MPa. A salt dissolution intensity calculation device is used to collect the produced water during the oil displacement process and perform component analysis on the produced water to obtain the salt dissolution intensity.

7. The system according to claim 6, characterized in that, The salt dissolution intensity calculation device includes: A three-phase separation device is used to separate the produced water from the products of an oil displacement process; An ion composition analysis device is used to analyze the composition of the product water separated by the three-phase separation device and generate water ion solubility; A salt solubility rate generating device, which is used to calculate the salt solubility rate based on the water ion solubility.

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