A multi-cycle injection and production simulation method for multi-layer gas storage with different inclination angles

Abstract

The present invention discloses a multi-cycle injection and production simulation method for a multi-layer gas storage with different inclination angles, and belongs to the technical field of natural gas extraction. The steps of the method are S1, preparing a gas storage reservoir model: obtaining rock samples from different layers of the gas storage by drilling and crushing them into rock cuttings, using the rock cuttings of the corresponding layers as raw materials according to the reservoir distribution characteristics of the actual gas storage, and preparing each rock layer by stacking from bottom to top to form a multi-layer reservoir model; S2, coating the surface of the reservoir model with high temperature resistant silica gel to ensure the flow of fluid in the model; placing the wrapped model into a metal container to form a reservoir simulation unit; and then installing and connecting the whole set of experimental devices; S3, using the experimental device to conduct multiple rounds of injection and production simulation experiments of the gas storage. The method of the present invention can simulate the formation state of multi-layer gas storage with different porosity and permeability and fracture, simulate the injection and production conditions of the gas storage at different stages, and obtain an accurate simulation of the indoor experiment by analogy with the on-site injection and production method.

Description

Technical Field

[0001] The invention relates to the technical field of natural gas exploitation, in particular to a multi-cycle injection and production simulation method for a multi-layer gas storage with different inclination angles. Background Art

[0002] Natural gas is clean and efficient among many fuels, and is gradually becoming the main fuel in daily life. At the same time, the development of high-definition and clean energy is the need of the times, which helps to improve the supply side of the energy structure and is of great significance to achieving energy self-sufficiency and ensuring energy security. Natural gas is transported to thousands of households through pipelines, and gas storage plays a very important role in it.

[0003] Commonly used natural gas storages are divided into depleted gas reservoirs, depleted oil reservoirs and underground aquifers. The injection and production methods used in gas storages with different formations during construction and operation are also different. Therefore, it is necessary to conduct research on the construction and operation mechanism of gas storages for specific oil reservoirs. However, gas storages vary greatly. How to effectively simulate gas storages for different reservoirs is an urgent problem to be solved. Similarly, the development, expansion and operation of gas storages is also a major problem. There are two main problems in the existing related technical research: one is the lack of indoor accurate simulation of the formation structure of different gas storages; the other is the lack of an indoor experimental method to fully simulate the injection and expansion process of gas storages. Summary of the invention

[0004] In order to solve the problem that the prior art is still unable to perform multi-cycle injection and production simulation on gas storages of different types of reservoirs, the present invention provides a multi-cycle injection and production simulation method for gas storages with multiple layers and different inclination angles.

[0005] The multi-cycle injection and production simulation method of a multi-layer gas storage with different inclination angles provided by the present invention comprises the following steps:

[0006] S1. Prepare the gas storage reservoir model: obtain rock samples from different layers of the gas storage through drilling and crush them into rock cuttings. According to the reservoir distribution characteristics of the actual gas storage, use the rock cuttings of the corresponding layers as raw materials, and prepare each rock layer by stacking layer by layer from bottom to top to form a multi-layer reservoir model. Specifically, the following steps are included:

[0007] S11, firstly, the rock cuttings at the bottom layer are mixed with water-soluble inorganic salts and epoxy resin to form a mixture, and the mixture is filled into the bottom of the mold until the required thickness is reached; according to the actual reservoir fracture development, a metal sheet is embedded in the mold, and pressure is applied after loading to solidify the rock cuttings, and after solidification, a first artificial rock layer is obtained; according to the same method as above, the rock cuttings at the second layer are mixed with water-soluble inorganic salts and epoxy resin to form a mixture, and the mixture is laid on the first rock layer to obtain a second artificial rock layer; this is repeated multiple times, layer by layer, to form a reservoir model with a multi-layer structure;

[0008] When preparing each artificial rock layer, due to the different rock cuttings and permeabilities used in each rock layer, the pressure applied is different. The pressure value applied in preparing each artificial rock layer is determined through preliminary experiments. The preliminary experiment method is as follows:

[0009] (1) Based on all the rock samples obtained, draw a curve of the relationship between porosity and permeability;

[0010] (2) rock cuttings from a certain layer are mixed with water-soluble inorganic salts and epoxy resin to fill the mixture into a mold until the required thickness is reached; metal sheets are embedded in the mixture in the mold, and different pressures are applied after loading to prepare different artificial rock layers; the permeability of the rock layer is tested, and a curve of the relationship between pressure and permeability is drawn;

[0011] (3) If the actual reservoir porosity is , the permeability is K 1 The porosity of the solution pores is , the fracture porosity is , then the intergranular porosity of the reservoir to be prepared is , ; According to the relationship curve between porosity and permeability obtained in step (1), the porosity is calculated The corresponding permeability K 2 , which is the permeability of the rock formation to be prepared; then, according to the relationship curve between pressure and permeability obtained in step (2), the permeability K is calculated 2 The corresponding pressure value is the pressure P applied when preparing the artificial rock layer. 1 ; Using pressure P 1 The permeability of the prepared artificial rock layer is K 2 , the corresponding porosity is .

[0012] According to the actual reservoir interlayer conditions that need to be simulated, the wells to be used need to be arranged in advance during the preparation of artificial rock formations. For example, for a top horizontal well, when preparing the top model, it is necessary to bury a horizontal pipeline in advance as a well position for subsequent development; if it is a bottom inclined well that runs through multiple layers, it is necessary to connect the pipeline after one layer is prepared and when preparing the next layer, so as to achieve multi-layer penetration of the inclined well; if there is an inclination in the reservoir, the well angle should be reserved in advance, and in the later stage, by cutting the large model, the reservoir inclination can be achieved while meeting the requirements for well layout and angle. At the same time, it is also necessary to consider whether the actual reservoir has an inclination. If there is an inclination, the corresponding inclination needs to be set in the reservoir model.

[0013] The method for setting the inclination is: according to the actual reservoir conditions, if the actual reservoir has an inclination and the inclination is for the entire reservoir, the artificial rock layer is cut as a whole to meet the actual simulation requirements; if only part of the actual reservoir has an inclination, the mold is placed at an angle when preparing the artificial rock layer with an inclination to achieve the inclination setting only for this rock layer.

[0014] S12. Preparation of pore structure: The inorganic salts and metal flakes in the reservoir model are washed and dissolved to form a pore structure, and the porosity is increased to , as the porosity increases, the permeability increases to K 1 , that is, the reservoir model preparation is completed.

[0015] The specific method is to use formation water to flush the reservoir model until the weight of the model no longer changes, that is, the dissolution pore preparation is completed; use strong acid or strong alkali to continuously flush the reservoir model until no bubbles appear and the weight of the model no longer changes, and the fracture preparation is completed. When the pore structure is prepared, continue to flush with formation water to wash away the residual acid and alkali in the model.

[0016] S2. Load the model and install the experimental device; the method is as follows:

[0017] S21, coating the surface of the reservoir model prepared in step S1 with high temperature resistant silica gel to ensure that the fluid flows in the model;

[0018] S22, placing the wrapped model into a metal container to form a reservoir simulation unit; a heating resistor wire is arranged inside the side wall of the metal container to heat the reservoir model, and reserved channels are arranged on the upper and lower end covers of the metal container to facilitate the connection of the fluid injection port and the discharge port of the model with external equipment;

[0019] S23. Install the whole set of experimental equipment, and use distilled water as the confining pressure application liquid. The experimental equipment includes a reservoir simulation unit, a fluid injection unit, a production control back pressure valve, a liquid collection device, and a gas collection device; various fluids are injected into the reservoir simulation unit through the fluid injection unit, the outlet of the reservoir simulation unit is connected to the liquid collection device, and the liquid collection device is connected to the gas collection device; the fluid injection unit includes a natural gas injection device, a formation water injection device, a formation oil injection device, a confining pressure water injection device, and a nitrogen injection device.

[0020] S3. Use the experimental device to conduct multiple rounds of injection and production simulation experiments in gas storage; the steps are as follows:

[0021] S31, reservoir stratigraphic state reproduction;

[0022] After heating the reservoir model, the whole model was evacuated to -0.1MPa for 5 hours, and then formation water was injected from the bottom; after injecting 3 times the pore volume, the water output from the top was stable, and the model pressure was raised to the experimental pressure; because the model was too large, the live oil displacement fluid might lead to incomplete sweep, so the ground degassed crude oil was used, heated and pressurized to the experimental conditions, and then the viscosity of the degassed crude oil was reduced to that of the formation crude oil by adding low-viscosity white oil. The dead oil with reduced viscosity was slowly injected from the bottom to displace the water in the model until no water was seen at the outlet, and the saturated dead oil was completed; the prepared live oil was slowly injected from the bottom at 0.1ml / min, and the pressure at the top was kept above the saturation pressure. The top oil-gas-oil ratio was recorded every 0.1PV displacement until the gas-oil ratio was appropriate, and the saturated live oil was considered to be completed.

[0023] S32. Simulation of the gas storage reservoir construction stage: Simulate according to the injection and production plan before the actual gas storage reservoir is built. For example, water drive at high parts and oil production at low parts; or first exhaustion production at low parts, then gas injection at high parts, etc. For example, before the construction of a gas storage reservoir, water drive at high parts and oil production at low parts, after the recovery rate reaches 10%, gas is injected at high parts, and liquid is produced at low parts until no liquid is produced, and then the gas storage reservoir is switched to operation. In the simulation of the reservoir construction stage, water should be injected at high parts first, and the produced liquid at low parts should be collected, and the production should be stopped after 10% is produced; then gas should be injected from high parts and liquid should be produced from low parts until no liquid is produced; the clamp and inlet and outlet pressures should be controlled by the back pressure valve during the whole process.

[0024] S33, Simulation of the gas storage operation stage: Indoor simulation is performed according to the actual gas storage operation plan. For example, in the operation stage of a gas storage, gas is injected from the top and gas is produced from the top. The upper limit pressure of gas injection is 45MPa and the lower limit pressure is 12MPa. According to the reservoir shut-in time, the laboratory model is inferred to be shut-in for 250 minutes based on the similarity criterion. When simulating the operation stage of the gas storage, the bottom outlet is closed, gas is injected from the top to the upper limit pressure, and after shut-in for 250 minutes, the top is produced to the lower limit pressure; repeat multiple rounds, record the liquid and gas production conditions, and reverse the changes in the internal space of the model, so that the expansion capacity and spatial changes of the gas storage under this operation mode can be known.

[0025] Preferably, in step S11, the water-soluble inorganic salt is NaCl crystals.

[0026] Preferably, the metal sheet used in step S11 is an aluminum foil or a thin iron sheet. The aluminum foil is used for carbonate reservoirs, and the thin iron sheet is used for sandstone reservoirs.

[0027] Preferably, in step S31, when the dead oil is saturated, the viscosity of the degassed crude oil is reduced to that of the formation crude oil by adding low-viscosity white oil, and then the water in the dead oil displacement model is injected from the bottom of the reservoir model until no water is seen at the outlet, and the saturation of the dead oil is completed; then the prepared live oil is injected from the bottom of the reservoir model, and the pressure at the top is maintained above the saturation pressure. The gas-oil ratio of the top oil output is recorded every 0.1PV displacement. When the gas-oil ratio reaches the gas-oil ratio of the prepared well flow, the saturation of the live oil is completed.

[0028] Compared with the prior art, the present invention is beneficial in that:

[0029] The method of the present invention can simulate the formation state of multi-layer gas storage with different porosity and permeability and fractures, and accurately reproduce the formation state of the gas storage by saturating the formation fluid, etc. The injection and production conditions of the gas storage at different stages are simulated, and the accurate simulation of the indoor experiment is obtained by analogy with the injection and production methods on site.

[0030] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a curve diagram showing the relationship between actual reservoir porosity and permeability.

[0032] Figure 2 is the relationship between pressure and permeability in artificial rock formations.

[0033] Figure 3 This is a schematic diagram of the reservoir model.

[0034] Figure 4Schematic diagram of metal container and reservoir model loading. (a) is the appearance of the metal container, (b) is the structure of the metal container; (c) is the schematic diagram of the reservoir model being loaded into the metal container.

[0035] Numbers in the figure: sealing cover plate 1-1, bolt 1-2, heating resistance wire 1-3, temperature sensor 1-4, pressure sensor 1-5, reservoir model 1-6, reserved channel 1-7.

[0036] Figure 5 This is a schematic diagram of the experimental device connection.

[0037] Numbers in the figure: reservoir simulation unit 1, fluid injection device 2, 3, 4, 5, 6, back pressure valve 7, 8, 9, pumps 10, 11, 12, 13, pressure gauges 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, liquid collecting device 28, 29, 30, gas collecting device 31, 32, 33, control valves 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52.

[0038] Figure 6 It is a recovery factor diagram drawn according to the experimental result data in the embodiment. DETAILED DESCRIPTION

[0039] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0040] The multi-cycle injection and production simulation method of a multi-layer gas storage with different inclination angles provided by the present invention includes three steps:

[0041] Step S1, in the process of preparing the gas storage reservoir model, after the obtained rock sample is crushed, the oversized particles are roughly screened out according to the size of the actual reservoir rock cuttings, and used as the raw material for preparing the rock formation, and the rock cuttings are solidified by epoxy resin to form a rock formation. When there are large gaps and cracks in the actual reservoir, inorganic salt crystals (such as NaCl crystals) and metal sheets (aluminum foil or thin iron sheets) are added, pressed and then flushed with a solution. The preparation process adopts a layer-by-layer preparation and slow stacking method, and the preparation is done layer by layer.

[0042] In this embodiment, the mass ratio of rock cuttings to epoxy resin is controlled to be 7: 1. After loading is completed, a metal mold is used to apply pressure of 2-20 MPa on the top, and the specific value of the applied pressure is determined by preliminary experiments.

[0043] Taking a rock sample from a certain area as an example, a porosity-permeability relationship curve is drawn based on all the rock samples obtained, and the approximate relationship between porosity and permeability is obtained as follows: Figure 1 shown.

[0044] Preliminary experiments were conducted based on actual rock cuttings to explore the permeability of artificial rock formations prepared under different pressures in the reservoir rock cuttings when the mass ratio of rock cuttings to epoxy resin was 7:1. Multiple groups of preliminary experiments were conducted and the experimental results were as follows: Figure 2 shown.

[0045] If the actual reservoir porosity is , the permeability is K 1 The porosity of the solution pores is , the fracture porosity is , then the intergranular porosity of the reservoir to be prepared is , ;according to Figure 1 The relationship curve between porosity and permeability is used to calculate the porosity. The corresponding permeability K 2 , which is the permeability of the rock formation to be prepared; then according to Figure 2 The relationship curve between pressure and permeability, calculate the permeability K 2 The corresponding pressure value is the pressure P applied when preparing the artificial rock layer. 1 ; According to the pressure P 1 , to prepare the artificial rock formation. Using pressure P 1 The permeability of the prepared artificial rock layer is K 2 , the corresponding porosity is After washing and dissolving the sodium chloride and metal flakes in the rock formation, the porosity increases to As the porosity increases, the permeability also increases to K 1 .

[0046] The porosity of dissolved pores in the prepared rock formation , the calculation formula is as follows:

[0047] ,

[0048] In the formula, is the volume of the prepared rock layer; m 2 is the mass of NaCl used; is the density of NaCl.

[0049] The fracture porosity in the prepared rock formation is , the calculation formula is as follows:

[0050] ,

[0051] The number of metal sheets required is N;

[0052] ,

[0053] In the formula, m 1 is the mass of the metal sheet used; is the density of the metal flake used; The volume of the rock formation prepared; is the fracture density in the reservoir; is the crack size.

[0054] In this embodiment, the structure of the reservoir model prepared in step S1 is shown in Figure 3 .

[0055] Step S2: After the reservoir model is prepared, the model is loaded and the experimental device is installed.

[0056] Since the reservoir model prepared by the present invention is relatively large, it needs to be loaded in a specially made high-temperature and high-pressure metal container. The reservoir model wrapped with high-temperature resistant silica gel is loaded into the metal container to form a reservoir simulation unit. Figure 4 As shown, (a) is the appearance diagram of the metal container, (b) is the structural diagram of the metal container; (c) is a schematic diagram of the reservoir model being loaded into the metal container. The metal container is cylindrical, and a sealing cover plate 1-1 is provided at the upper and lower ends respectively, which is sealed and connected to the metal cylinder by bolts 1-2. A heating resistor wire 1-3 is installed inside the side wall of the cylinder to heat the inside of the metal container and thereby control the experimental temperature of the reservoir model 1-6; a temperature sensor 1-4 and a pressure sensor 1-5 are provided on the surface of the lower end cover plate facing the inside of the cylinder to monitor the temperature and pressure inside the metal container. In addition, reserved channels 1-7 are provided on the upper and lower cover plates to facilitate the connection of the fluid injection port and discharge port of the reservoir model with external equipment.

[0057] Further installation of the whole experimental device, such as Figure 5As shown, the experimental device includes a reservoir simulation unit 1 and pressure gauges 14, 15, 26, 27 connected thereto, a fluid injection unit, production control back pressure valves 7, 8, 9, liquid collection devices 28, 29, 30 and gas collection devices 31, 32, 33. The fluid injection unit includes a natural gas injection device 2, a formation water injection device 3, a formation oil injection device 4, a confining pressure water injection device 5 and a nitrogen injection device 6. The fluid injection unit is used to inject different fluids into the reservoir simulation unit 1. Among them, natural gas and formation water are injected from the bottom of the reservoir simulation unit 1 through a pump 12, and natural gas can also be injected from the top of the reservoir simulation unit 1; formation oil is injected from the top of the reservoir simulation unit 1 through a pump 11, and confining pressure water is injected from the top of the reservoir simulation unit 1 through a pump 10 to form a confining pressure. Since the silica gel used may be soluble in oil, distilled water is used as the confining pressure application liquid to ensure that the silica gel fits tightly with the model and the fluid only flows from the inside of the model. The pump 13 is connected to the nitrogen injection device 6, which is used to control the nitrogen injection pressure, and then control the back pressure valves 7, 8, and 9. The fluid extracted from the top of the reservoir simulation unit 1 is connected to the liquid collection device 30 through the pressure gauge 27, the control valve 49 and the back pressure valve 7, and the liquid collection device 30 is further connected to the gas collection device 31. The liquid collection device 30 and the gas collection device 31 can be used as long as they can collect and measure the volume of liquid and gas, and the specific structure is not limited. The fluid extracted from the bottom of the reservoir simulation unit 1 is divided into two paths, one of which is connected to the liquid collection device 29 through the pressure gauge 14, the pressure gauge 16, the control valve and the back pressure valve 9, and the liquid collection device 29 is further connected to the gas collection device 33; the other path is connected to the liquid collection device 32 through the pressure gauge 15, the pressure gauge 17, the control valve and the back pressure valve 8. All pumps used in this embodiment are ISCO pumps.

[0058] S3. Use the experimental device to conduct multiple rounds of injection and production simulation experiments in gas storage. The specific cases are as follows:

[0059] After years of development, a certain oil reservoir was initially developed with water and gas injection. After gas drive failed to improve the recovery rate, it was planned to be converted into a gas storage. The expansion and construction of the gas storage was completed through cyclic injection and production at different upper and lower pressure limits in the early stage, and the storage was operated at the upper and lower pressure limits after construction.

[0060] Detailed parameters: Reservoir inclination 11°, formation pressure 30MPa, formation temperature 120℃, volume coefficient 1.32m 3 / m 3 , gas-oil ratio 200m 3 / m 3Five strata are mainly used, with average permeabilities of 120 mD, 200 mD, 300 mD, 100 mD and 50 mD respectively. When producing oil, water is injected through the two vertical wells at the bottom, and the water drive recovery rate is 10%. At the same time, the pressure is reduced to 24 MPa. After switching to gas drive, gas is injected through the top horizontal well until no liquid is produced, and at the same time the pressure is increased to the formation pressure of 30 MPa.

[0061] It is now necessary to verify the impact of different injection and production methods on oil production and gas storage capacity expansion through indoor experiments.

[0062] Two gas storage operation plans are designed. It is expected that by comparing different operation plans, the multi-cycle injection and production operation of the gas storage can be simulated, so as to provide on-site guidance for later operations.

[0063] Option 1: After 10% water drive, switch to gas drive and when no more liquid can be produced, perform five rounds of injection and production at the upper limit pressure (30MPa) - lower limit pressure (14MPa).

[0064] Option 2: After 10% water drive, switch to gas drive and if no liquid can be discharged, then carry out cyclic injection and production with variable upper and lower limit pressures, which are five rounds of cyclic injection and production of upper limit pressure (30MPa) - lower limit pressure (24MPa) + five rounds of cyclic injection and production of upper limit pressure (30MPa) - variable lower limit pressure (27, 24, 21, 18, 14MPa) + five rounds of cyclic injection and production of upper limit pressure (30MPa) - lower limit pressure (14MPa).

[0065] The composition of well flow is shown in Table 1, the composition of injected gas is shown in Table 2, and the composition of formation water is shown in Table 3.

[0066] Table 1. Well flow composition

[0067]

[0068] Table 2. Injection gas composition

[0069]

[0070] Table 3. Formation water composition

[0071]

[0072] Experimental preparation: Select the actual formation core, crush it, and prepare the sample after removing the large particles; use NaCl crystals to make holes and thin iron sheets to make seams. First, take a small part of the cuttings and prepare a small model in proportion to master the pressure applied when compacting with different permeabilities. Then prepare the model according to the direction of reservoir fractures and the development of pores. After the model is prepared, it is washed with water and acid to complete the preparation of pore fractures; then load it according to the experimental device. Prepare water samples according to the mineralization and ion content of formation water; prepare formation well flow according to the formation pressure and temperature based on the obtained surface crude oil and degassed gas composition; prepare degassed oil according to the viscosity of formation crude oil.

[0073] Reproduction of formation state: After heating the reservoir simulation unit, evacuate it, inject formation water at 2MPa at the bottom, and keep the pressure constant for 12h. Record the water injection volume at this time, which can be regarded as the model pore volume PV; slowly inject degassed crude oil prepared with low-viscosity white oil at the bottom at 0.1 ml / min, and record the water output V at the top 1 and oil output V 2 ; Then inject the prepared active oil from the formation from the bottom, and record the gas-oil ratio at the outlet. When the gas-oil ratio reaches the prepared gas-oil ratio of the well flow, the process ends, and the water V at the outlet is collected at the same time. 3 , then V 1 + V 3 It can be considered as the model effective pore volume HCPV.

[0074] Simulation of oil production stage: The oil production stage of this reservoir is 10% water drive + gas drive without liquid production. Therefore, water is injected into two vertical wells at the bottom, and the water drive recovery rate is 10%. At the same time, the pressure is reduced to 24 MPa. During the water drive, the oil, water and gas production are recorded, and it ends when the recovery rate reaches 10%. After switching to gas drive, natural gas is injected through the top horizontal well until no liquid is produced. At the same time, the pressure is increased to the formation pressure of 30 MPa, and the water, oil and gas production are continuously recorded.

[0075] Simulation of the gas storage operation phase: For Scheme 1, the simulation of the operation phase requires that the three wells be exhausted to the lower limit pressure first to meet the pressure gap of subsequent natural gas injection; then the natural gas is slowly injected from the top, and the bottom production well is closed at this time. After the pressure rises to the upper limit pressure, it is stabilized for a period of time to allow the injected gas to fully spread to the pores, which also simulates the shut-in state during the operation of the gas storage. Then the three wells are opened to produce gas at the same time, and the flow rate and gas production time are controlled by the back pressure valve until the production reaches the lower limit pressure. The gas injection volume is recorded during the gas injection period, and the gas production, oil production and water production of different wells are recorded during the gas production period, and the cycle is repeated for 5 rounds. For Scheme 2, different lower limit pressures need to be controlled, that is, by controlling the pressure of the back pressure valve during exhaustion gas production and stabilizing it for a period of time, the lower limit pressure is continuously changed by controlling the back pressure valve pressure at different stages.

[0076] Relevant experimental data of different experimental stages are shown in Tables 4-10.

[0077] Table 4. Initial data of the model

[0078] Length cm Widthcm Thicknesscm Number of layers <![CDATA[Water volume in cm 3 > <![CDATA[Oil volume cm 3 > <![CDATA[Pore volume cm 3 > Bound water saturation% 50 50 3 5 2448.98 5144.77 7593.75 32.25

[0079] Table 5. Water flooding test data

[0080] HCPV injection <![CDATA[V oil (cm 3 ).]]> <![CDATA[V water (cm 3 )]]> <![CDATA[V gas (cm 3 )]]> Cumulative oil recovery rate (%) 0.7 384.298402 1.5 76859.6804 9.86

[0081] Table 6. Gas drive experimental data

[0082] Injection volume (HCPV) V oil (cm3) V water (cm3) V gas (cm3) Cumulative oil recovery rate (%) 0.5 290.76 10 58151 17.32 0.6 112.64 15 22528 20.21 0.8 136.02 13 27205 23.7

[0083] Table 7. Cyclic injection and production data for Scheme 1

[0084] Hypovolemic Volume Multiple (HCPV) V Oil V Water V-gas Cumulative oil recovery rate (%) First cycle of decompression 245.5456 6.9 49109.13 30.00 First cycle boost 0.32 316.481 6.1 63296.21 38.12 Second cycle of decompression 217.873 7.6 43574.61 43.71 Second cycle boost 0.29 35.4677 9.6 7093.54 44.62 The third cycle of blood pressure reduction 120.4343 8.3 24086.86 47.71 The third cycle boost 0.34 35.07795 6.6 7015.59 48.61 The 4th cycle of decompression 39.75501 3.1 7951.00 49.63 4th cycle boost 0.29 26.50334 7.5 5300.67 50.31 The 5th cycle of blood pressure reduction 90.0334 9.4 18006.68 52.62 The fifth cycle of boosting 0.53 39.36525 3.2 7873.05 53.63

[0085] Table 8. Five rounds of cyclic injection and production data of the upper limit pressure (30MPa) and lower limit pressure (24MPa) of the second scheme

[0086]

[0087] Table 9. Five rounds of cyclic injection and production data for Scheme 2 with upper limit pressure (30 MPa) and lower limit pressure (27, 24, 21, 18, 14 MPa)

[0088]

[0089] Table 10. Five-round cyclic injection and production data of the upper limit pressure (30MPa) and lower limit pressure (14MPa) of the second scheme

[0090]

[0091] Figure 6 This is a recovery diagram drawn based on the experimental results. In the figure, a represents the 10% water drive stage; b represents the gas drive stage, where no liquid is produced; c represents the five-cycle injection and production stage of the upper limit pressure of 30MPa-lower limit pressure of 14MPa in Scheme 1; d represents the five-cycle injection and production stage of the upper limit pressure of 30MPa-lower limit pressure of 24MPa in Scheme 2; e represents the five-cycle injection and production stage of the upper limit pressure of 30MPa-variable lower limit pressure (27, 24, 21, 18, 14MPa) in Scheme 2; and f represents the five-cycle injection and production stage of the upper limit pressure (30MPa)-lower limit pressure (14MPa) in Scheme 2.

[0092] The results are analyzed as follows:

[0093] Under the two experimental schemes, directly exploiting from 30MPa depletion to 14MPa can bring faster recovery speed, but after five rounds of cyclic injection and production, the recovery rate only reaches 53.63%; in scheme 2, the final recovery rate brought by gradient descent is higher, and the recovery rates obtained by the three different stages of exploitation are 46.8%, 56% and 61.6% respectively. Although the recovery rate is slightly increased by the higher lower limit pressure in the early stage, the final recovery rate is further expanded as the injection and production proceeds, which is much higher than the single cycle injection and production. Analysis shows that: the direct gas injection cycle injection and production in the early stage can obtain a greater recovery rate, but due to the sharp drop in pressure, the residual oil in the pores cannot be fully mobilized; while the gradient descent cyclic injection and production, although the higher upper limit pressure in the early stage makes the cyclic injection and production recovery rate may not be high, the slow use of pore space may bring a greater degree of utilization and further improve the oil recovery rate. It can be concluded that during the construction and operation of a gas storage facility, the effect of directly starting operation at a lower pressure may be insufficient, and a step-by-step reduction in the lower limit pressure may bring about a greater degree of crude oil recovery and storage space.

[0094] The above description is only a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A multi-cycle injection and production simulation method for multi-layer gas storage with different inclination angles, characterized in that: Here are the steps: S1. Preparation of gas storage reservoir model: rock samples from different layers of the gas storage are obtained by drilling and crushed into rock cuttings. According to the reservoir distribution characteristics of the actual gas storage, the rock cuttings of the corresponding layers are used as raw materials, and each rock layer is prepared by stacking layer by layer from bottom to top to form a multi-layer reservoir model; specifically, the following steps are included: S11, firstly, the rock cuttings at the bottom layer are mixed with water-soluble inorganic salts and epoxy resin to form a mixture, and the mixture is filled into the bottom of the mold until the required thickness is reached; according to the actual reservoir fracture development, a metal sheet is embedded in the mold, and pressure is applied after loading to solidify the rock cuttings, and after solidification, a first artificial rock layer is obtained; according to the same method as above, the rock cuttings at the second layer are mixed with water-soluble inorganic salts and epoxy resin to form a mixture, and the mixture is laid on the first rock layer to obtain a second artificial rock layer; this is repeated multiple times, layer by layer, to form a reservoir model with a multi-layer structure; When preparing each artificial rock layer, due to the different rock cuttings and permeabilities used in each rock layer, the pressure requirements applied are different. The pressure value applied in preparing each artificial rock layer is determined through preliminary experiments. The preliminary experiment method is as follows: (1) Based on all the rock samples obtained, draw a curve of the relationship between porosity and permeability; (2) rock cuttings from a certain layer are mixed with water-soluble inorganic salts and epoxy resin to fill the mixture into a mold until the required thickness is reached; metal sheets are embedded in the mixture in the mold, and different pressures are applied after loading to prepare different artificial rock layers; the permeability of the rock layer is tested, and a curve of the relationship between pressure and permeability is drawn; (3) If the actual reservoir porosity is , the permeability is K1, and the porosity of the solution pores is , the fracture porosity is , then the intergranular porosity of the reservoir to be prepared is , ; According to the relationship curve between porosity and permeability obtained in step (1), the porosity is calculated The corresponding permeability K2 is the permeability of the rock layer to be prepared; then, according to the relationship curve between pressure and permeability obtained in step (2), the pressure value corresponding to the permeability K2 is calculated, that is, the pressure P1 applied when preparing the artificial rock layer is obtained; the permeability of the artificial rock layer prepared with the pressure P1 is K2, and the corresponding porosity is ; According to the actual reservoir interlayer conditions to be simulated, the wells to be used need to be arranged in advance during the preparation of artificial rock formations; at the same time, it is necessary to consider whether the actual reservoir has a dip. If so, the corresponding dip needs to be set in the reservoir model; S12. Preparation of pore structure: The inorganic salts and metal flakes in the reservoir model are washed and dissolved to form a pore structure, and the porosity is increased to , as the porosity increases, the permeability increases to K1, and the preparation of the reservoir model is completed; S2, loading of reservoir model and installation of experimental device; S3. Use experimental equipment to conduct multiple rounds of injection and production simulation experiments in gas storage.

2. The multi-cycle injection and production simulation method for multi-layer gas storage with different inclination angles according to claim 1 is characterized in that: In step S11, the water-soluble inorganic salt is NaCl crystals.

3. The multi-cycle injection and production simulation method for multi-layer gas storage with different inclination angles according to claim 1 is characterized in that: The metal sheet used in step S11 is an aluminum foil or a thin iron sheet. Aluminum foil is used for carbonate reservoirs, and thin iron sheet is used for sandstone reservoirs.

4. The multi-cycle injection and production simulation method for multi-layer gas storage with different inclination angles according to claim 1 is characterized in that: In step S11, the method for setting the inclination angle is: according to the actual reservoir conditions, if the actual reservoir has an inclination angle and the inclination angle is for the entire reservoir, the artificial rock formation is cut as a whole to meet the actual simulation requirements; if only part of the actual reservoir has an inclination angle, the mold is placed at an angle when preparing the artificial rock formation with an inclination angle to achieve the inclination angle setting only for this rock formation.

5. The multi-cycle injection and production simulation method for multi-layer gas storage with different inclination angles according to claim 1 is characterized in that: In step S12, formation water is used to flush the reservoir model until the weight of the model no longer changes, that is, the pore preparation is completed; strong acid or strong alkali is used to continuously flush the reservoir model until no bubbles appear and the weight of the model no longer changes, and the fracture preparation is completed.

6. The multi-cycle injection and production simulation method for multi-layer gas storage with different inclination angles according to claim 1 is characterized in that: The method of step S2 is as follows: S21, coating the reservoir model prepared in step S1 with high temperature resistant silica gel to ensure that the fluid flows in the model; S22, placing the wrapped model into a metal container to form a reservoir simulation unit; a heating resistor wire is arranged inside the side wall of the metal container to heat the reservoir model, and reserved channels are arranged on the upper and lower end covers of the metal container to facilitate the connection of the fluid injection port and the discharge port of the model with external equipment; S23. Install the entire experimental apparatus and use distilled water as the confining pressure application liquid.

7. The multi-cycle injection and production simulation method for multi-layer gas storage with different inclination angles according to claim 6 is characterized in that: In step S23, the experimental device includes a reservoir simulation unit, a fluid injection unit, a production control back pressure valve, a liquid collecting device and a gas collecting device; various fluids are injected into the reservoir simulation unit through the fluid injection unit, the outlet of the reservoir simulation unit is connected to the liquid collecting device, and the liquid collecting device is connected to the gas collecting device; the fluid injection unit includes a natural gas injection device, a formation water injection device, a formation oil injection device, a confining pressure water injection device and a nitrogen injection device.

8. The multi-cycle injection and production simulation method for multi-layer gas storage with different inclination angles as claimed in claim 7, characterized in that: The steps of the multi-round injection and production simulation experiment of the gas storage in step S3 are as follows: S31, reservoir stratigraphic state reproduction; After heating the reservoir model, evacuate it, inject formation water from the bottom of the model until the water output from the top is stable, and then increase the pressure of the model to the experimental pressure; then saturate the model with dead oil and live oil in turn; S32, gas storage construction stage simulation: simulation is performed based on the actual injection and production plan before the gas storage is built; S33. Gas storage operation phase simulation: indoor simulation is conducted based on the actual gas storage operation plan.

9. The multi-cycle injection and production simulation method for multi-layer gas storage with different inclination angles according to claim 7, characterized in that: In step S31, when the dead oil is saturated, the viscosity of the degassed crude oil is reduced to that of the formation crude oil by adding low-viscosity white oil, and then the water in the dead oil displacement model is injected from the bottom of the reservoir model until no water is seen at the outlet, and the saturation of the dead oil is completed; then the prepared live oil is injected from the bottom of the reservoir model, and the pressure at the top is kept above the saturation pressure. The gas-oil ratio of the top oil is recorded every 0.1PV displacement. When the gas-oil ratio reaches the prepared gas-oil ratio of the well flow, the saturation of the live oil is completed.

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