Method for uniformly initializing heterogeneous large rock plate model to establish initial conditions of gas reservoir

Abstract

The invention discloses a method for establishing initial conditions of a gas reservoir through uniform initialization of a heterogeneous large rock plate model, and belongs to the technical field of gas reservoir development. On the basis that a conventional rock plate is provided with injection and production well inlets and outlets, the two sieve pipe injection channels are additionally arranged, the two ends of the sieve pipe are connected through the pipeline, and fluid can be injected into the sieve pipe; plugging or heating plugging removal operation is achieved by injecting a plugging agent into the four pipelines in good time, namely, an injection well and a production well are plugged firstly, formation water is injected through a screen pipe to make a rock plate saturated, and then formation water in the rock plate is displaced through gas injection of the screen pipe; the screen pipe is plugged, and a plugging removal injection and production well preparation experiment is carried out; the rock plate reaches an initial state of a gas drive / depletion experiment; the problem that the screen pipe becomes a high-permeability channel to affect a gas drive experiment and cause distortion of gas drive experiment data is avoided, the accuracy of a large flat plate model longitudinal heterogeneous gas reservoir water invasion failure or constant volume failure evaluation experiment can be improved, and the method has important significance on compact reservoir transformation and effective development.

Description

Technical Field

[0001] This invention belongs to the field of gas reservoir development technology, specifically relating to a pretreatment method for gas reservoir water intrusion depletion or constant volume depletion experiments using a large slab model. Background Technology

[0002] Before actually developing a development plan, conducting laboratory simulation experiments is an essential step. By constructing small-scale models similar to real geological conditions, such as using a large-scale model of a conventional oil reservoir slab for physical simulation experiments, we can conduct in-depth research on the effects of different production parameter settings on the development of specific reservoirs, thus providing a scientific basis and technical support for the development plan. However, when simulating reservoirs using slab models, interlayer heterogeneity exists. This causes fingering during the initial stage of slab modeling, i.e., the stage of obtaining bound water and initial gas saturation. During the process of establishing bound water through gas-driven water displacement, water remains untouched in the slab pores, leading to an overestimation of the measured bound water saturation and affecting subsequent experimental data, thus distorting the experimental data.

[0003] The invention patent "A device and method for testing the saturation of three phases of oil, gas and water in a high-temperature and high-pressure flat plate model" (CN112816394B) provides a device and method for testing the saturation of three phases of oil, gas and water in a large flat plate model. However, this method does not consider the interlayer heterogeneity of the rock plate model and does not perform pretreatment operations on the rock plate model. During the displacement process, gas channeling and fingering phenomena may occur, leading to a decrease in sweep efficiency and incomplete establishment of bound water conditions, thus causing experimental data distortion. The invention patent "A method for quantitative saturation of bound water in a large planar heterogeneous flat plate model" (CN112780241A) provides a method for quantitative saturation of bound water in a large flat plate model. However, this method requires the fabrication of sponges of corresponding rock plate size, making the operation relatively complex; and the determination of whether saturation has been reached by weighing the sponges during the saturation of bound water may cause over-saturation, affecting the experiment.

[0004] Patent (US2012316789A1) discloses a method for improving the sampling and characterization of heterogeneous unconventional hydrocarbon-bearing regions. This method is designed for consistent integration across measurements and scales. Furthermore, the method involves characterizing various scales, such as regional-scale heterogeneity, wellbore-scale heterogeneity, core-scale heterogeneity, sample-scale heterogeneity, and pore-scale heterogeneity. Patent (EP3006538A1) discloses a method for improving the injectability of underground gas reservoirs. The method for injecting into an underground gas reservoir includes performing a process of injecting a reducing agent to reduce the bound water saturation of the reservoir through a wellbore connected to the underground gas reservoir, which is composed of permeable rock material, and performing a process of injecting carbon dioxide into the reservoir after the injection of the reducing agent. Due to the injection of carbon dioxide, the reducing agent and water filling the pores of the reservoir are expelled together to reduce the non-reducible water saturation around the wellbore, thereby improving the carbon dioxide injectability of the reservoir. The patent (CN218848027U) provides an experimental instrument for establishing the initial water saturation of rock cores. It can simulate the initial water saturation of dense rock cores, is easy to use, facilitates the rapid establishment of the initial water saturation of rock cores to the formation, and effectively reduces damage to the rock cores.

[0005] Because the gas-driven experimental design introduces interlayer heterogeneity into the rock slab, the existing method of using gas-driven water injection between injection and production wells to reach the initial experimental state inevitably leads to phenomena such as gas fingering and flow around within the rock slab. This prevents some displaceable water from being reached, thus preventing the rock slab from achieving the initial conditions for bound water and original gas saturation. Therefore, this invention proposes a method of pre-embedding screen pipes in large rock slabs and using these screen pipes for gas-driven water injection to achieve multi-directional displacement within the rock slab, thus achieving sufficient displacement and mitigating the fingering phenomenon during the establishment of bound water, resulting in a uniform distribution of bound water. Furthermore, timely sealing with a plugging agent prevents the screen pipes from becoming high-permeability channels, thus not affecting subsequent displacement or attenuation experiments. The preparation process of the plugging agent is also very simple, facilitating the smooth progress of the experimental procedure. Summary of the Invention

[0006] This invention, based on the conventional rock slab with injection and production well inlets and outlets, adds two additional screen pipe injection channels. The two ends of the screen pipes are connected by pipelines, allowing fluid to be injected into them. By injecting a sealing agent into four pipes at appropriate times, sealing or unblocking operations are achieved through heating. Specifically, the injection and production wells are first sealed, formation water is injected through the screen pipes to saturate the rock slab, and then gas is injected through the screen pipes to displace the formation water within the rock slab. The screen pipes are then sealed again, and the injection and production wells are unblocked in preparation for the experiment. This achieves the initial state for the gas drive / depletion experiment on the rock slab.

[0007] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution:

[0008] A method for uniformly initializing a gas reservoir using a heterogeneous large slab model, the method comprising the following steps:

[0009] Step s1: Preparation of experimental materials, including the preparation of rock plates and sealing agents, and the preparation of sieve tubes;

[0010] Step s2: In the preparation stage of experimental equipment, connect the injection pump to the nitrogen, formation water, and sealing agent intermediate containers respectively using pipelines; connect the nitrogen and formation water intermediate containers to the three-way connecting valves, and then connect them to the injection, production wells, and screen pipes inside the rock slab model. The pipelines connecting the sealing agent intermediate container to the injection, production wells, and screen pipes inside the rock slab model should be separate from the pipelines connecting the nitrogen and formation water intermediate containers to the rock slab model to prevent the sealing agent from clogging the pipelines. Furthermore, the sealing agent pipelines and the rock slab model should both be included within the reactor heating device; then connect the outlet ends of the injection, production wells, and screen pipes to the back pressure valves respectively.

[0011] Step s3: Initialize the prepared rock slab and inject a plugging agent into the injection-production well to cool and form a seal;

[0012] Step s4: Saturate the rock slab with formation water through a sieve tube, and conduct acoustic and electrical tests by synchronously scanning the slab with electrodes connected to it to ensure that the rock slab is saturated with formation water.

[0013] Step s5: Once the rock slab is saturated with formation water, establish confining pressure, inject gas through the screen pipe to displace the formation water, and conduct acoustic and electrical tests by synchronously scanning through the electrode plates connected to the rock slab to obtain the uniform bound water saturation in different layers.

[0014] Step s6: Heating will unblock the injection and production wells, and a plugging agent will be injected into the screen pipe. Cooling will then form a seal.

[0015] Step s7: Conduct displacement or exhaustion experiments.

[0016] In a preferred embodiment of the present invention, in step s1:

[0017] The plugging agent is composed of one or more of the following: poly(N-isopropylacrylamide) (PNIPAM), polyvinyl alcohol (PVA) hydrogel, polyethylene glycol (PEG), poly(N,N-dimethylacrylamide) (PDMAAm), paraffin oil, and hot melt adhesive. The plugging agent should be obtained by mixing solid paraffin and liquid paraffin in a certain proportion, heating and stirring to obtain paraffin oil with a pour point of t1℃, the pour point of which is higher than the gas reservoir temperature t2℃. The obtained paraffin oil is then heated to a liquid state, which allows the paraffin oil to remain liquid above the pour point temperature and solidify below the pour point temperature to form a plug.

[0018] As a preferred embodiment of the present invention, in step s1: the rock slab is prepared by mixing 30-70 mesh coarse quartz sand and 70-140 mesh fine quartz sand with epoxy resin; according to experimental requirements, the mixing ratio of coarse and fine quartz sand can be adjusted according to the permeability required for different layers of the rock slab, so as to achieve different physical properties between different layers of the rock slab. Figure 2 The rock slab shown is composed of multiple layers (80-100cm long, 20-30cm wide, and 3-5cm thick), with each layer having a different permeability. Before preparation, two screen pipes are placed at the top and bottom ends of the rock slab model, and perforated pipes are placed on both sides laterally. These pipes simulate injection and production wells. Then, a mixture of quartz sand and epoxy resin is filled in, and the model is left to cure before use. The screen pipes should be made of stainless steel with a nominal diameter of 1 / 8 inch (≈3.175 mm) and a wall thickness of 0.2-0.28 mm. Circular holes with a diameter of 0.08-0.1 mm and a high pore density of 30-50 pores / cm are selected, with the holes arranged axially.

[0019] In a preferred embodiment of the present invention, in step s2, the prepared rock slab should be placed in the reaction vessel, then the rock slab should be placed vertically, and electrode plates should be placed on the upper and lower sides of the rock slab to conduct acoustic and electrical tests. The relevant pipelines should then be connected to the injection and production wells and the screen pipe. (See [link to relevant documentation]). Figure 2 .

[0020] As a preferred embodiment of the present invention, the initialization operation in step s3 should raise the temperature to above t1℃, at which point the sealing agent is injected into the injection and production wells, and then the temperature is naturally cooled to the reservoir temperature t2℃. After the sealing agent solidifies, the injection and production wells are sealed.

[0021] As a preferred embodiment of the present invention, when the formation water is saturated in step s4, water should be injected across the longitudinal interlayer through the lower screen pipe and water should be collected through the top screen pipe. The water drive front is stabilized by gravity, and the injection is stopped after the water production of the upper screen pipe is stable (about 4PV).

[0022] As a preferred embodiment of the present invention, the acoustic-electric testing in steps s4 and s5 includes the following sub-steps:

[0023] (a) Acoustic wave test

[0024] The reflection method is used, with a single-ended probe emitting and receiving reflected waves to calculate the round-trip time. By measuring the propagation time (Δt) of the ultrasonic wave in the core and the core length (L), the sound wave velocity and core density are calculated.

[0025] , ,

[0026] in: --- Longitudinal wave velocity; L--- Slab thickness; --- Sound wave propagation time; ---Slab density; ≈310, ≈0.25

[0027] (b) Resistivity test

[0028] Resistivity was measured at different saturation levels using electrodes, and S was directly calculated from the relationship between core resistivity and water saturation. w The formula is as follows:

[0029] ,

[0030] in: ---Resistivity of rock slab (including fluid); --- Formation water resistivity; ϕ--- Porosity; , , Lithology coefficient, cementation index, saturation index.

[0031] Acoustic data can constrain the compressibility of pore fluids, while resistivity data provides information on conductivity. Ultimately, combining acoustic and resistivity data improves... Calculation accuracy.

[0032] As a preferred embodiment of the present invention

[0033] In step s5, after the rock slab is saturated with formation water, hydraulic oil should be used to establish confining pressure. The confining pressure should always be 3 MPa higher than the internal pressure, and the internal pressure should be continuously increased to the gas reservoir pressure. After the pressure is established, gas is injected through the screen pipe located at the top of the rock slab to displace the formation water in the rock slab. Water is collected through the bottom screen pipe, and the displacement front is stabilized by gravity. The flow rate is adjusted to ensure that there is no fingering phenomenon in the vertical gravity displacement across the layers. When no water is displaced from the rock slab (approximately 8 PV), the injection is stopped.

[0034] As a preferred embodiment of the present invention

[0035] In step s6, the rock slab should first be heated to above the freezing point t1 of the plugging agent, and then gas should be introduced into the injection and production wells to displace the plugging agent and unblock it. After the injection and production wells are unblocked, the plugging agent is injected into the screen pipes, and the pipes are allowed to cool naturally to the reservoir temperature t2 to form a seal, preventing the two screen pipes from becoming high-permeability channels during the gas drive failure experiment, and ensuring that the presence of the two screen pipes will not affect the experimental results.

[0036] As a preferred embodiment of the present invention

[0037] Step s7 should simulate the production well's output by setting a constant flow rate using a mass flow meter to achieve fixed-output mining. The combined output of the production well is simulated by the main valve at the extraction end, while the output of each layer is measured by two other high-pressure mass flow meters. Production stops when the outlet pressure of the flat plate model deteriorates to the abandonment pressure.

[0038] The beneficial effects of this invention are:

[0039] 1) Due to the interlayer heterogeneity of artificial rock slabs, traditional gas-injection and water-injection methods can lead to gas channeling and fingering during the gas-driven water process, making it impossible to achieve the initial state required for the experiment. This invention uses cross-layer injection with sieve tubes to avoid fingering and enable the rock slab to reach the initial bound water and gas saturation conditions required for the experiment.

[0040] 2) This invention uses a plugging agent to seal the screen tubes. That is, after the initialization operation of the rock plate is completed, the plugging agent is injected into the screen tubes to perform the sealing operation. This avoids the two screen tubes becoming high-permeability channels during the gas drive depletion experiment, so that the presence of the two screen tubes will not affect the experimental results. This further improves the accuracy of the evaluation experiment of water intrusion depletion or constant volume depletion of vertical heterogeneous gas reservoirs in large rock plate models, which is of great significance for the stimulation and effective development of tight oil reservoirs. Attached Figure Description

[0041] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some implementation examples of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 A schematic diagram of the device for uniformly initializing a gas reservoir using a large slab model provided by the present invention.

[0043] Figure 2 This is a cross-sectional view of a large rock slab;

[0044] Figure 3 A schematic diagram of the initial conditions for water binding without pre-embedded screen pipes inside a large rock slab;

[0045] Figure 4 A schematic diagram showing how to achieve uniform initial conditions for binding water by pre-embedding screen pipes inside a large rock slab.

[0046] Figure 5 Flowchart of the method steps for establishing initial conditions for a gas reservoir;

[0047] The markings in the diagram are as follows:

[0048] 1-Injection pump; 2-Pipeline; 3-Nitrogen intermediate container; 4-Formation water intermediate container; 5-Sealing agent intermediate container; 6-Injection well; 7-Production well; 8, 9-Screen pipe; 10, 13-Back pressure valve; 11, 14-Intermediate container; 12, 15-Back pressure pump; 16-Reaction vessel heating device; 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31-Valve; 32-Three-way connecting valve; 33, 34, 35-Artificial rock slabs with different permeabilities. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0050] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0051] like Figure 5 As shown, this invention provides a method for uniformly initializing a gas reservoir using a heterogeneous large slab model, the method specifically including the following steps:

[0052] Step s1: Preparation of experimental materials, including the preparation of rock plates and sealing agents, and the preparation of sieve tubes;

[0053] Step s2: Preparation of experimental equipment; such as Figure 1 As shown, the injection pump 1 is connected to the intermediate containers of nitrogen 3, formation water 4, and sealing agent 5 via pipelines. The intermediate containers of nitrogen 3 and formation water 4 are connected to the three-way connecting valve 32, and then connected to the injection and production wells 6 and 7, and the screen pipes 8 and 9 inside the rock slab model. The pipeline connecting the intermediate container of sealing agent 5 to the injection and production wells 6 and 7, and the screen pipes 8 and 9 inside the rock slab model should be separate from the pipeline connecting the intermediate containers of nitrogen and formation water to the rock slab model to prevent the sealing agent from clogging the pipeline. The sealing agent pipeline and the rock slab model should both be included in the reactor heating device. The outlet ends of the injection and production wells and the screen pipes are then connected to the back pressure valves 10 and 13, respectively.

[0054] Step s3: Initialize the prepared rock slab and inject a plugging agent into the injection-production well to cool and form a seal;

[0055] Step s4: Saturate the rock slab with formation water through a sieve tube, and conduct acoustic and electrical tests by synchronously scanning the slab with electrodes connected to it to ensure that the rock slab is saturated with formation water.

[0056] Step s5: Once the rock slab is saturated with formation water, establish confining pressure, inject gas through the screen pipe to displace the formation water, and conduct acoustic and electrical tests by synchronously scanning through the electrode plates connected to the rock slab to obtain the uniform bound water saturation in different layers.

[0057] Step s6: Heating will unblock the injection and production wells, and a plugging agent will be injected into the screen pipe. Cooling will then form a seal.

[0058] Step s7: Conduct displacement or exhaustion experiments.

[0059] Furthermore, in step s1: the sealing agent is composed of one or more of the following: poly(N-isopropylacrylamide) (PNIPAM), polyvinyl alcohol (PVA) hydrogel, polyethylene glycol (PEG), poly(N,N-dimethylacrylamide) (PDMAAm), paraffin oil, and hot melt adhesive.

[0060] Furthermore, in step s1: the plugging agent should be obtained by mixing solid paraffin and liquid paraffin in a certain proportion and then heating and stirring to obtain paraffin oil with a pour point of t1℃ (the pour point of paraffin oil is higher than the gas reservoir temperature t2℃). The obtained paraffin oil is then heated to a liquid state, which means that the paraffin oil can be liquid at a temperature higher than its pour point and solidify at a temperature lower than its pour point to form a plug.

[0061] Furthermore, in step s1: the rock slab should be prepared by mixing coarse quartz sand (30-70 mesh) and fine quartz sand (70-140 mesh) with epoxy resin; according to experimental requirements, the mixing ratio of coarse and fine quartz sand can be adjusted according to the permeability required for different layers of the rock slab, so as to achieve different physical properties between different layers of the rock slab. Figure 2 The rock slab shown is divided into multiple layers (80-100cm long, 20-30cm wide, and 3-5cm thick), with different permeability in each layer. Before preparation, two screen pipes are placed at the top and bottom ends of the rock slab model, and perforated pipes are placed on both sides of the lateral direction. These pipes simulate injection and production wells. Then, a mixture of quartz sand and epoxy resin is filled in, and the rock slab is placed for later use after curing. The screen pipes should be stainless steel pipes with a nominal diameter of 1 / 8 inch (≈3.175 mm) and a wall thickness of 0.2-0.28 mm as the screen pipe body. The hole type should be circular, with a hole diameter of 0.08-0.1 mm and a high pore density of 30-50 holes / cm. The holes should be arranged axially.

[0062] Furthermore, in step s2, the prepared rock slab should be placed into the reactor, positioned vertically, and electrode plates should be placed on the top and bottom sides of the rock slab to conduct acoustic-electric testing. The relevant pipelines should then be connected to the injection and production wells and the screen pipe. (See...) Figure 2.

[0063] As a preferred embodiment of the present invention, the initialization operation in step s3 should raise the temperature to above t1℃. At this time, the sealing agent is injected into the injection and production wells, and then the temperature is naturally cooled to the reservoir temperature t2℃. After the sealing agent solidifies, the injection and production wells are sealed.

[0064] Furthermore, when the formation water is saturated in step s4, water should be injected across the longitudinal interlayer through the lower screen pipe, and water should be collected through the top screen pipe. The water drive front should be stabilized by gravity, and the injection should be stopped after the water production of the upper screen pipe is stable (about 4PV).

[0065] Furthermore, the acoustic-electric testing in steps s4 and s5 includes the following sub-steps:

[0066] (a) Acoustic wave test

[0067] The reflection method is used, with a single-ended probe emitting and receiving reflected waves to calculate the round-trip time. By measuring the propagation time (Δt) of the ultrasonic wave in the core and the core length (L), the sound wave velocity and core density are calculated.

[0068] ,

[0069] ,

[0070] in: --- Longitudinal wave velocity; L--- Slab thickness; --- Sound wave propagation time; ---Slab density; ≈310, ≈0.25

[0071] (b) Resistivity test

[0072] Resistivity was measured at different saturation levels using electrodes, and S was directly calculated from the relationship between core resistivity and water saturation. w The formula is as follows:

[0073] ,

[0074] in: ---Resistivity of rock slab (including fluid); --- Formation water resistivity; ϕ--- Porosity; , , Lithology coefficient, cementation index, saturation index.

[0075] Acoustic data can constrain the compressibility of pore fluids, while resistivity data provides information on conductivity. Ultimately, combining acoustic and resistivity data improves... Calculation accuracy.

[0076] Furthermore, in step s5, after the rock slab is saturated with formation water, hydraulic oil should be used to establish confining pressure. The confining pressure should always be 3 MPa higher than the internal pressure, and the internal pressure should be continuously increased to the gas reservoir pressure. After the pressure is established, gas is injected from the screen pipe located at the top of the rock slab to displace the formation water in the rock slab. Water is collected from the bottom screen pipe, and the displacement front is stabilized by gravity. The flow rate is adjusted to ensure that there is no fingering phenomenon in the vertical gravity displacement across the layers. When no water is driven out of the rock slab (about 8 PV), the injection is stopped.

[0077] Furthermore, in step s6, the rock slab should first be heated to above the freezing point t1 of the plugging agent, and then gas should be introduced into the injection and production wells to displace the plugging agent and unblock it. After the injection and production wells are unblocked, the plugging agent is injected into the screen pipes, and the pipes are allowed to cool naturally to the reservoir temperature t2 to form a seal, preventing the two screen pipes from becoming high-permeability channels during the gas drive failure experiment, and ensuring that the presence of the two screen pipes will not affect the experimental results.

[0078] Furthermore, step s7 should simulate the production well's output by setting a constant flow rate using a mass flow meter to achieve fixed-output mining; the combined output of the production well should be simulated using the main valve at the extraction end, while the output of the other two high-pressure mass flow meters should be measured by the layered output; production should be stopped when the outlet pressure of the flat plate model depletes to the abandonment pressure.

[0079] Implementation Case 1

[0080] This embodiment is a conventional practice, in which screen pipes are not pre-embedded inside the rock slab. The specific operation is as follows:

[0081] 1) Preparation of slabs: Prepare coarse quartz sand (30-70 mesh), fine quartz sand (70-140 mesh), and epoxy resin. Mix the quartz sand and epoxy resin according to the sand-to-resin ratio set in the experiment. Place perforated pipes on both sides of the transverse direction. These pipes simulate injection and production wells. Then fill them with the mixed quartz sand and epoxy resin. After the slabs have cured, set them aside for later use.

[0082] 2) Place the prepared rock slab into the reactor, and then position the rock slab vertically. Since no screen tube is pre-embedded inside the rock slab, no intermediate container for the sealing agent or related pipelines are installed, nor is a back pressure valve installed at the screen tube outlet. Figure 1 As shown, the injection pump 1 is connected to the intermediate containers of nitrogen gas 3 and formation water 4 via pipelines. The intermediate containers of nitrogen gas 3 and formation water 4 are connected to the three-way connecting valve 32, and then connected to the injection and production wells (6, 7) and screen pipes (8, 9) in the rock slab model. The outlet end of the injection and production wells is then connected to the back pressure valve 10.

[0083] 3) Use hydraulic oil to apply confining pressure to the reactor, ensuring the confining pressure is always 3 MPa higher than the internal pressure. After pressurization, turn the three-way connecting valve to the lower end to open it. Figure 1Valves 18, 20, 21, 28, and 29 are used to inject water into the injection well via an injection pump. Once the rock slab is saturated with formation water, the injection is stopped. Acoustic-electrical tests are then conducted using saturation probes located on the upper and lower sides of the rock slab to measure the water saturation of the rock slab and ensure that the rock slab is uniformly saturated with water.

[0084] 4) Close Figure 1 Open valves 18 and 20, and valves 17 and 19. Inject nitrogen gas from the injection well using the injection pump to displace formation water in the rock slab. Stop injection when no water is displaced from valve 14. Conduct acoustic-electric testing using saturation probes located on the upper and lower sides of the rock slab to measure the water saturation of the rock slab. Figure 3 As shown in the figure, the rock slab reaches the initial conditions for bound water at this time. The water saturation of the rock slab is measured to obtain the bound water saturation in different layers.

[0085] 5) A constant flow rate can be set using mass flow meters to simulate the production of a production well and achieve fixed-production extraction. The total valve at the extraction end simulates the combined production layer output of the production well, while two other high-pressure mass flow meters measure the output of each layer. Production stops when the outlet pressure of the flat plate model deteriorates to 5 MPa.

[0086] Implementation Case 2

[0087] This embodiment describes the pretreatment method of the present invention, namely, pre-embedding screen pipes inside the rock slab. The specific operation is as follows:

[0088] 1) Preparation of the sealing agent: Solid paraffin and liquid paraffin are mixed in a ratio of 3:7 and heated and stirred to obtain paraffin oil with a pour point of 50°C (the pour point of paraffin oil is 40°C higher than the gas reservoir temperature). The obtained paraffin oil is then heated to a liquid state. This paraffin oil can be liquid when the temperature is above the pour point and solidify to form a sealant when the temperature is below the pour point.

[0089] 2) Preparation of the slab: Prepare coarse quartz sand (30-70 mesh), fine quartz sand (70-140 mesh), and epoxy resin. Mix the quartz sand and epoxy resin according to the sand-to-resin ratio set in the experiment. Place two sieve pipes at the top and bottom ends of the slab model, and place perforated pipes on both sides laterally. These pipes simulate injection and production wells. Then fill the model with the mixed quartz sand and epoxy resin. After the slab has cured, set it aside for later use. The prepared slab is shown below. Figure 2 As shown.

[0090] 3) Place the prepared rock slab into the reactor, ensuring it is placed vertically, and connect the relevant pipelines. Raise the temperature inside the reactor to 50°C and open the valve. Figure 1 Valves 19, 22, 28, 29, 30, and 31 are used to inject liquid plugging agent into the injection and production wells. The mixture is then allowed to cool naturally to the reservoir temperature and left to stand for 2 hours until the plugging agent solidifies. This seals the injection and production wells, preventing liquid water from escaping from the rock slab through the well's channels during water injection.

[0091] 4) After the sealing agent has sealed the injection and production wells, use hydraulic oil to apply confining pressure to the reactor, ensuring the confining pressure is always 3 MPa higher than the internal pressure. Close the reactor after pressurization is complete. Figure 1 For valves 19, 22, 28, 29, 30, and 31, move the three-way connecting valve to the lower end to open. Figure 1 Valves 18, 20, 25, and 26 are used to inject water into the screen pipe located at the bottom of the rock slab via an injection pump. Once the rock slab is saturated with formation water, the injection is stopped, and acoustic and electrical tests are conducted to measure the water saturation of the rock slab and ensure that the rock slab is uniformly saturated with water.

[0092] 5) Close Figure 1 Open valves 18, 20, 25, and 26, and valves 17, 19, 24, and 27. Inject nitrogen gas through the injection pump into the screen pipe located at the top of the rock slab to displace the formation water. Stop injection when no water is displaced from valve 14, and conduct acoustic and electrical tests. Figure 3 As shown in the figure, the rock slab reaches the initial condition of uniformly bound water at this time. The water saturation of the rock slab is measured to obtain the bound water saturation in different layers.

[0093] 6) Close Figure 1 Valves 24 and 27 are used to heat the rock plate, raising the temperature of the injection and production wells to 50°C. At this point, the plugging agent in the well is in a flowable state. The three-way connecting valve is then turned to the upper end and opened. Figure 1 Gas is injected into the well through valves 21, 28, 29, 30, and 31 to drive out the plugging agent. At the same time, valves 19, 23, 24, 25, 26, and 27 are opened to inject the plugging agent into the screen pipe.

[0094] 7) Close after injection is complete Figure 1 Install valves 19, 23, 24, 25, 26, and 27, stop heating, and then allow the temperature to cool naturally to the reservoir temperature. Let it stand for 2 hours to allow the sealing agent in the screen tubes to solidify, at which point the screen tubes are sealed. After initialization, conduct an acoustic-electric saturation test. Figure 4 As shown in the figure, the rock slab reaches the initial conditions for bound water at this time. The water saturation of the rock slab is measured to obtain the bound water saturation in different layers.

[0095] 8) A constant flow rate can be set using a mass flow meter to simulate the production of a production well and achieve fixed-production extraction. The total valve at the extraction end simulates the combined production layer output of the production well, while two other high-pressure mass flow meters measure the output of each layer. Production stops when the outlet pressure of the flat plate model deteriorates to 5 MPa.

[0096] Compare the acoustic and electrical test results of the pretreated rock slabs in Example 1 and Example 2; see as follows Figure 3 and Figure 4 It can be seen Figure 3 No screen pipes were pre-embedded inside the rock slab, so water in some areas inside was not displaced. Figure 4After pre-embedding the screen pipe, a uniform bound water saturation was obtained; this indicates that the bound water saturation obtained by using the method of the present invention, i.e. through implementation case 2, is more uniform and significantly better than that of implementation case 1, which did not use the method of the present invention.

[0097] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of different aspects of the invention exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A method for uniformly initializing a gas reservoir using a heterogeneous large slab model, characterized in that: Includes the following steps: Step s1: The preparation stage of experimental materials, including the preparation of rock slabs and sealing agents, and the preparation of screen pipes; two screen pipes are placed at the top and bottom ends of the rock slab model, and perforated pipes are placed on both sides of the transverse direction. The perforated pipes simulate injection and production wells. Then, the mixed quartz sand and epoxy resin are filled in, and the rock slab is placed for later use after curing. Step s2: In the preparation stage of experimental equipment, connect the injection pump to the nitrogen, formation water, and sealing agent intermediate containers respectively using pipelines; connect the nitrogen and formation water intermediate containers to the three-way connecting valves, and then connect them to the injection, production wells, and screen pipes inside the rock slab model. The pipelines connecting the sealing agent intermediate container to the injection, production wells, and screen pipes inside the rock slab model should be separate from the pipelines connecting the nitrogen and formation water intermediate containers to the rock slab model to prevent the sealing agent from clogging the pipelines. Furthermore, the sealing agent pipelines and the rock slab model should both be included within the reactor heating device; then connect the outlet ends of the injection, production wells, and screen pipes to the back pressure valves respectively. Step s3: Initialize the prepared rock slab and inject a plugging agent into the injection-production well to cool and form a seal; Step s4: Saturate the rock slab with formation water through a sieve tube, and conduct acoustic and electrical tests by synchronously scanning the slab with electrodes connected to it to ensure that the rock slab is saturated with formation water. Step s5: Once the rock slab is saturated with formation water, establish confining pressure, inject gas through the screen pipe to displace the formation water, and conduct acoustic and electrical tests by synchronously scanning through the electrode plates connected to the rock slab to obtain the uniform bound water saturation in different layers. Step s6: Heating will unblock the injection and production wells, and a plugging agent will be injected into the screen pipe. Cooling will then form a seal. Step s7: Conduct displacement or exhaustion experiments.

2. The method for uniformly initializing and establishing initial conditions for a gas reservoir using a heterogeneous large slab model according to claim 1, characterized in that, In step s1: the plugging agent is composed of one or more of the following: poly(N-isopropylacrylamide) PNIPAM, polyvinyl alcohol (PVA) hydrogel, polyethylene glycol (PEG), poly(N,N-dimethylacrylamide) PDMAAm, paraffin oil, and hot melt adhesive; the plugging agent is obtained by mixing solid paraffin and liquid paraffin in a certain proportion and then heating and stirring to obtain paraffin oil with a pour point of t1℃, the pour point of which is higher than the gas reservoir temperature t2℃; the obtained paraffin oil is heated to a liquid state, which is liquid when the temperature is higher than the pour point temperature and solidifies to form a plug when the temperature is lower than the pour point temperature.

3. The method for uniformly initializing and establishing initial conditions for a gas reservoir using a heterogeneous large slab model according to claim 2, characterized in that, In step s1, the large slab is prepared by mixing 30-70 mesh coarse quartz sand and 70-140 mesh fine quartz sand with epoxy resin; the slab is three-layered, with dimensions of 80-100cm in length, 20-30cm in width, and 3-5cm in thickness, and the permeability of the three layers of slabs is different; the sieve tube should be a stainless steel tube with a nominal diameter of 1 / 8 inch and a wall thickness of 0.2-0.28 mm as the sieve tube body, with circular holes of 0.08-0.1mm in diameter and a high pore density of 30-50 pores / cm, and the holes arranged axially.

4. The method for uniformly initializing and establishing initial conditions for a gas reservoir using a heterogeneous large slab model according to claim 1, characterized in that, In step s2, the prepared rock slab is placed into the reaction vessel, then the rock slab is set to be placed vertically, and electrode plates are placed on the upper and lower sides of the rock slab to carry out acoustic and electrical tests, and the pipeline is connected to the injection well, production well and screen pipe.

5. The method for uniformly initializing and establishing initial conditions for a gas reservoir using a heterogeneous large slab model according to claim 1, characterized in that, In step s3, the initialization operation should raise the temperature to above t1℃. At this time, the sealing agent is injected into the injection and production wells, and then the temperature is naturally cooled to the reservoir temperature t2℃. After the sealing agent solidifies, the injection and production wells are sealed.

6. The method for uniformly initializing and establishing initial conditions for a gas reservoir using a heterogeneous large slab model according to claim 1, characterized in that, When the formation water is saturated in step s4, water is injected across the longitudinal interlayer through the lower screen pipe, and water is collected through the top screen pipe. The water drive front is stabilized by gravity, and the injection is stopped after the water production of the upper screen pipe is stable.

7. The method for uniformly initializing and establishing initial conditions for a gas reservoir using a heterogeneous large slab model according to claim 1, characterized in that, The acoustic-electric test includes the following sub-steps: Step s7.1: Acoustic wave test; transmit and receive reflected waves using a single-ended probe via the reflection method, calculate the round-trip time; measure the propagation time Δt of the ultrasonic wave in the core and the core length L, calculate the acoustic velocity and estimate the core density: ， ， in: --- Longitudinal wave velocity; L--- Slab thickness; ---Sound wave propagation time; ---Slab density; ≈310, ≈0.25 Step s7.2: Resistivity test; use electrodes to measure resistivity at different saturation levels, and directly calculate S based on the relationship between core resistivity and water saturation. w The calculation formula is as follows: ， in: ---Resistivity of rock slab (including fluid); --- Formation water resistivity; ϕ--- Porosity; , , Lithology coefficient, cementation index, and saturation index; among which acoustic waves constrain pore fluid compressibility, resistivity provides conductivity information, and the final combination of acoustic and resistivity data is used to improve... Calculation accuracy.

8. The method for uniformly initializing and establishing initial conditions for a gas reservoir using a heterogeneous large slab model according to claim 1, characterized in that, In step s5, after the rock slab is saturated with formation water, hydraulic oil should be used to establish confining pressure. The confining pressure should always be 3 MPa higher than the internal pressure, and the internal pressure should be continuously increased to the gas reservoir pressure. After the pressure is established, gas is injected from the screen pipe located at the top of the rock slab to displace the formation water in the rock slab. Water is collected from the bottom screen pipe. The displacement front is stabilized by gravity, and the flow rate is adjusted to ensure that there is no fingering phenomenon in the vertical gravity displacement across the layers. The injection is stopped when no water is driven out of the rock slab.

9. The method for uniformly initializing and establishing initial conditions for a gas reservoir using a heterogeneous large slab model according to claim 1, characterized in that, In step s6, the rock slab should first be heated to above the freezing point t1 of the plugging agent, and then gas should be introduced into the injection and production wells to displace the plugging agent and unblock it. After the injection and production wells are unblocked, the plugging agent should be injected into the screen pipes, and then the temperature should be naturally cooled to the gas reservoir temperature t2 to form a seal on the screen pipes. This prevents the two screen pipes from becoming high-permeability channels during the gas drive failure experiment, and ensures that the presence of the two screen pipes will not affect the experimental results.

10. The method for uniformly initializing and establishing initial conditions for a gas reservoir using a heterogeneous large slab model according to claim 1, characterized in that, In step s7, a constant flow rate is set using a mass flow meter to simulate the production distribution of the production well and achieve fixed-production mining. The combined production of the production well is simulated by the main valve at the extraction end, while the production output of each layer is measured by other high-pressure mass flow meters. Production stops when the outlet pressure of the flat plate model deteriorates to the abandonment pressure.

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