Experimental apparatus and methods for simulating the development of carbonate bottom water gas reservoirs

Abstract

This invention discloses an experimental apparatus and method for simulating the development of carbonate bottom-water gas reservoirs, relating to the field of gas field development technology. The apparatus includes a reactor body, a core disposed within the reactor body, a temperature control unit wound around the outside of the reactor body, pressure monitoring units located at the top and bottom of the reactor body and inside the core wellbore, a bottom-water injection unit for injecting water into the bottom of the reactor body, a gas injection unit for injecting gas into the top of the reactor body, a horizontal wellbore simulation unit partially embedded in the core, an X-ray scanning unit covering the reactor body, a vacuum pump, a back pressure control unit, a gas-water flow metering unit, and a core pore water removal unit. The vacuum pump is connected to the gas injection unit via a pipeline for evacuating the reactor body. The inlet of the horizontal wellbore simulation unit is connected to the back pressure control unit and the gas-water flow metering unit via outlet valves. Using this invention, the physical simulation and evaluation of the development effect of carbonate bottom-water gas reservoirs can be conducted under laboratory conditions.

Description

Technical Field

[0001] This invention relates to the field of gas field development technology, and more specifically to the field of experimental apparatus and methods for simulating the development of carbonate bottom water gas reservoirs. Background Technology

[0002] Carbonate bottom-water gas reservoirs are highly heterogeneous with well-developed pores and fractures (cavities), and bottom water coning is a common problem during development, posing challenges to reservoir development and management. A balanced well deployment pattern and a rational production system are key to the efficient development of bottom-water gas reservoirs. Currently, domestic and international scholars mainly use microscopic visualization devices, three-dimensional sand-filled models, and full-diameter core samples to simulate the bottom water coning mechanism during reservoir development. These research devices and methods are primarily applicable to sandstone oil and gas reservoirs.

[0003] For carbonate gas reservoirs, due to limitations in experimental scale, microscopic visualization devices and full-diameter water intrusion experimental equipment are insufficient to accurately describe the water intrusion patterns under the complex multi-scale pore-fracture-vuggy relationships of the reservoir, especially the water intrusion patterns during horizontal well development. Furthermore, large-scale three-dimensional models with sand filling cannot be applied to carbonate reservoirs. Accurately simulating the development process of carbonate bottom-water gas reservoirs and optimizing reasonable gas well production regimes have always been a challenge and a key focus in the field of gas reservoir engineering.

[0004] Solving the aforementioned technical problems has become the focus of efforts for those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to solve the above-mentioned technical problems by providing an experimental apparatus and method for simulating the development of carbonate bottom water gas reservoirs. Using this invention, the physical simulation of the development effect of carbonate bottom water gas reservoirs can be carried out under laboratory conditions.

[0006] To achieve the above objectives, the present invention specifically adopts the following technical solution:

[0007] An experimental apparatus for simulating the development of carbonate bottom water gas reservoirs includes a vessel body, a core disposed within the vessel body, a temperature control unit wrapped around the outside of the vessel body, pressure monitoring units located at the top and bottom of the vessel body and inside the core wellbore, a bottom water injection unit for injecting water into the bottom of the vessel body, a gas injection unit for injecting gas into the top of the vessel body, a horizontal wellbore simulation unit partially embedded in the core, an X-ray scanning unit covering the vessel body, a vacuum pump, a back pressure control unit, a gas-water flow metering unit, and a core pore water removal unit. The vacuum pump is connected to the gas injection unit via a pipeline for evacuating the vessel body. The inlet of the horizontal wellbore simulation unit is connected to the back pressure control unit and the gas-water flow metering unit via outlet valves.

[0008] Furthermore, the bottom water injection unit includes a bottom water booster pump and a water storage intermediate container. The bottom water booster pump is connected to the water storage intermediate container via a pipeline. A control valve is installed on the pipeline between the bottom water booster pump and the water storage intermediate container. The water storage intermediate container is connected to the bottom of the vessel body via a pipeline. A control valve is installed on the pipeline between the water storage intermediate container and the vessel body.

[0009] Furthermore, the gas injection unit includes a high-pressure CH4 intermediate container and a high-pressure displacement pump. The high-pressure CH4 intermediate container is connected to the high-pressure displacement pump via a pipeline. A control valve is installed on the pipeline between the high-pressure CH4 intermediate container and the high-pressure displacement pump. The high-pressure CH4 intermediate container is connected to the top of the vessel via a pipeline. A control valve is installed on the pipeline between the high-pressure CH4 intermediate container and the top of the vessel.

[0010] Furthermore, the vessel body includes a bottom plate, a front plate, a left plate, a right plate, a rear plate, and a top plate. The bottom plate, front plate, left plate, right plate, rear plate, and top plate are respectively sealed and snapped together by sealing grooves. A bottom water injection valve is provided on the bottom plate, which is connected to the intermediate water storage container through a pipeline. An air injection valve is provided on the top plate, which is connected to the gas injection unit through a pipeline. Multiple outlet valves at different horizontal heights are provided on the right plate.

[0011] Furthermore, a core support bracket is provided at the bottom of the vessel body, and a core support screen is provided on the core support bracket. The space between the core support screen and the bottom plate forms a bottom water cavity, and the core is located on the core support screen.

[0012] Furthermore, the horizontal wellbore simulation unit includes multiple stainless steel hollow tubes at different horizontal heights, evenly distributed within the core at different horizontal heights. Each stainless steel hollow tube includes a horizontal wellbore at the front end that participates in the production simulation and a horizontal wellbore at the rear end that does not participate in the production simulation. The front end of the tube participating in the production simulation has multiple holes evenly distributed, which are used to simulate the perforation holes of the horizontal well. The front end of the tube that does not participate in the production simulation has no holes and the rear end is spiral-shaped, rotating and embedding into the right plate to connect with the corresponding outlet valve.

[0013] Furthermore, multiple holes that cooperate with the horizontal wellbore simulation unit are drilled at different heights on one side of the core. The core is surrounded by a rubber sleeve. The rubber sleeve has multiple holes at different horizontal heights on the side where the horizontal wellbore simulation unit is embedded, allowing the horizontal wellbore simulation unit to pass through. The core is an outcrop core from a field profile, cut into a cube shape.

[0014] Furthermore, the pressure monitoring unit includes a high-precision pressure gauge installed on the top and bottom plates, and a wireless pressure sensor located at the top of the horizontal wellbore simulation unit inside the core. The temperature control unit is a resistance heating wire wound around the outside of the vessel body, with an insulation layer provided on the outer edge of the resistance heating wire. The core pore water removal unit is an electric heating rod that can be inserted into the horizontal wellbore simulation unit, as well as an electric heating control system.

[0015] Furthermore, the back pressure control unit includes a back pressure valve, an N2 intermediate container, and a back pressure displacement pump. The back pressure displacement pump and the N2 intermediate container are connected by a pipeline. A control valve is installed on the pipeline between the back pressure displacement pump and the N2 intermediate container. The N2 intermediate container and the back pressure valve are connected by a pipeline. The horizontal wellbore simulation unit is connected to the back pressure valve in parallel through a pipeline. The gas and water flow metering unit is connected to the back pressure valve through a pipeline. A control valve is installed on the pipeline between the gas and water flow metering unit and the back pressure valve.

[0016] The experimental method for simulating the development of carbonate bottom water gas reservoirs includes the following steps:

[0017] Step 1: Select rock samples and drill holes: Based on the well test curves of the gas reservoir production wells, identify the typical reservoir physical properties and select outcrop cores that conform to the multi-scale pore-fracture-vuggy development characteristics of the reservoir; drill small core samples at the outcrop cores and measure their porosity, permeability and other physical properties. Then cut the cores and place them on the core support screen. Cover the cores with rubber sleeves. Use a drilling rig and drill bit to drill multiple wellbore holes evenly at different heights of the cores to simulate production wells. Clean the rock cuttings and residue inside the holes and embed a wireless pressure sensor at the top of the wellbore hole.

[0018] Step 2: Complete the assembly of the vessel body and the connection of the system pipelines: Add a small amount of lead powder to the inside of the plate slot of the vessel body. By using the slots and strips between the plates of the vessel body, assemble the left plate, right plate, front plate, rear plate and top plate of the vessel body in sequence. Seal the core with connecting screws.

[0019] Based on the experimental simulation scheme or the optimal well height and horizontal position of horizontal wells in actual gas reservoirs for production, the calculation formula for the height of the simulation unit of the horizontal wellbore used for production is as follows:

[0020] Hm = Hy * Hs / Hc

[0021] In the formula, Hm is the height of the horizontal wellbore simulation unit; Hy is the height of the experimental outcrop core; Hs is the actual well placement height of the horizontal well during gas reservoir development; and Hc is the target reservoir thickness during gas reservoir development.

[0022] Step 3, Vacuum treatment: Use a vacuum pump to evacuate the entire experimental setup for at least 48 hours;

[0023] Step 4, Bottom water injection: Open the bottom water injection valve, and use the bottom water booster pump and intermediate water storage container to inject formation water into the bottom water cavity. The intermediate water storage container contains a 10-20% sodium iodide solution. At the same time, turn on the X-ray scanner and use the computer imaging system to observe. Stop the injection of formation water when the bottom water cavity is full.

[0024] Step 5, Gas injection under reservoir conditions: Turn on the temperature control unit to raise the temperature of the reactor body to the reservoir temperature. At the same time, open the gas injection valve and inject CH4 gas into the core using the CH4 gas source and gas compressor. When the reading of the pressure monitoring device is close to the design reservoir pressure, stop the gas injection. At the same time, use the high-pressure CH4 intermediate container and high-pressure displacement pump to maintain the set gas pressure in the core for 12 hours to eliminate the pressure increase caused by the thermal expansion of the gas.

[0025] Step 6: Simulation of bottom water gas reservoir development. The simulation process includes the following steps:

[0026] Step a: Design the corresponding water volume in the intermediate water storage container and the bottom water cavity according to the actual gas reservoir water volume ratio. Use the bottom water booster pump to set the water pressure in the intermediate water storage container to the reservoir pressure. Open the bottom water injection valve to connect the bottom water cavity and the intermediate water storage container.

[0027] Step b: Open the switch valve of the horizontal wellbore unit used for production simulation, close the valves of the remaining horizontal wellbore simulation units, and reduce the outlet pressure using the back pressure valve, N2 intermediate container and back pressure displacement pump. Set different pressure drop rates according to actual production needs.

[0028] Step c: Measure the produced gas and water volume using a gas-water flow metering unit, monitor the pressure drop variation within the core using a pressure monitoring unit, and simultaneously detect the conical morphology and pattern of the water in the bottom water cavity using an X-ray scanner. The experiment ends when the reservoir pressure drops to the abandonment pressure. The gas and water volumes under different pressure reductions are statistically analyzed. The formula for calculating the recovery degree obtained from the simulation experiment is as follows:

[0029] S=Vc / Vz

[0030] In the formula: S is the recovery rate obtained from the simulation experiment; Vc is the produced gas volume; Vz is the gas volume injected into the core through the high-pressure CH4 intermediate container;

[0031] Step d: Use the bottom water injection valve and pipeline to drain the formation water from the bottom water chamber inside the reactor. Open the top cover of the reactor and turn on the temperature control system to set the temperature to 200℃. At the same time, take out the horizontal wellbore simulation unit and wireless pressure sensor. Insert the electric heating rod into the wellbore hole. In order to reduce damage to the core, the temperature of the electric heating rod is also set to 200℃. Continue drying for more than 48 hours. Stop the drying operation when the X-ray scanning device can no longer detect the presence of water in the core hole. At the same time, seal the reactor. After checking the sealing, perform vacuuming and repeat the bottom water injection and gas injection steps. At this time, set different gas well production systems and restart the bottom water gas reservoir development simulation experiment.

[0032] Repeat steps a and b until the simulation experiments under different production systems and development models are completed, and obtain gas recovery evaluation charts under different production systems and development models.

[0033] The beneficial effects of this invention are as follows:

[0034] 1. Most existing common three-dimensional large models are sand-filled models. The model of this invention realizes the simulation of the development process of horizontal wells in real carbonate bottom water gas reservoirs through a detachable vessel body and an embedded horizontal wellbore simulation system.

[0035] 2. The present invention enhances the high-pressure sealing and disassembly of the gas by using a slot design between the plates of the vessel body.

[0036] 3. The present invention simulates the contact relationship between bottom water and reservoir core to the maximum extent through the design of load-bearing screen, avoiding the uneven water propagation caused by single-point pipeline injection in conventional experiments. At the same time, the design of the bottom water cavity can simulate real water containing dissolved gas.

[0037] 4. This invention simulates the perforation production process in the development of horizontal wells by artificially creating holes at the front end of the horizontal well pipe. The threaded design at the tail end of the horizontal well allows for better embedding into the vessel body, maximizing the sealing performance of the vessel body.

[0038] 5. The device of the present invention can simulate the development effect of bottom water gas reservoirs under different production systems of horizontal wells and under the "balanced" and "non-balanced" development well network modes according to actual production needs. It can also optimize the water avoidance height of horizontal wells and the critical production system of gas wells in bottom water gas reservoirs. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the structure of the present invention;

[0040] Figure 2 This is a schematic diagram of a simulated horizontal wellbore structure.

[0041] Figure 3 This is a top view of the bottom plate structure of the vessel.

[0042] Reference numerals: 1-Core, 2-Rubber sleeve, 3-Left plate, 4-Right plate, 5-Top plate, 6-Bottom plate, 7-Core load-bearing support, 8-Core load-bearing screen, 9-Bottom water chamber, 10-Resistance heating wire, 11-Connecting screw, 12-High-precision pressure gauge, 13-Injection valve, 14-Bottom water injection valve, 15-Horizontal wellbore simulation unit, 16-Outlet valve, 17-Vacuum pump, 18-High-pressure CH4 intermediate container, 19-High-pressure displacement 20-Pump, 21-Back pressure valve, 22-N2 intermediate container, 23-Back pressure displacement pump, 24-Gas and water flow metering unit, 25-Water storage intermediate container, 26-Bottom water booster pump, 27-X-ray scanner, 28-Data imaging and receiving processing system, 29-Bottle body support bracket, 30-Pipeline switch, 31-Front plate, 32-Rear plate, 33-Wireless pressure sensor, 34-Perforation hole, 35-Inner slot, 36-Outer slot, 37-Threaded hole. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0044] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0045] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0046] In the description of the embodiments of the present invention, it should be noted that the terms "inner", "outer", "upper", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use. They are only for the convenience of describing the present 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 limiting the present invention.

[0047] Example 1

[0048] like Figures 1 to 3 As shown, this embodiment provides an experimental apparatus for simulating the development of carbonate bottom water gas reservoirs, including a vessel body, a core 1 housed within the vessel body, a temperature control unit wrapped around the outside of the vessel body, pressure monitoring units located at the top and bottom of the vessel body and inside the wellbore of the core 1, a bottom water injection unit for injecting water into the bottom of the vessel body, a gas injection unit for injecting gas into the top of the vessel body, a horizontal wellbore simulation unit 15 partially embedded within the core 1, an X-ray scanning unit 26 covering the vessel body, a vacuum pump 17, a back pressure control unit, a gas-water flow metering unit 23, and a core pore water removal unit; the vacuum pump 17 is connected to the pipeline of the gas injection unit for vacuuming the vessel body; the inlet end of the horizontal wellbore simulation unit 15 is connected to the back pressure control unit and the gas-water flow metering unit 23 respectively through an outlet valve 16; multiple vessel body support supports 28 are provided at the bottom of the vessel body; and the X-ray scanning unit 26 is electrically connected to an external data imaging and receiving processing system.

[0049] The bottom water injection unit includes a bottom water booster pump 25 and a water storage intermediate container 24. The bottom water booster pump 25 is connected to the water storage intermediate container 24 through a pipeline. A control valve is installed on the pipeline between the bottom water booster pump 25 and the water storage intermediate container 24. The water storage intermediate container 24 is connected to the bottom of the vessel body through a pipeline. A control valve is installed on the pipeline between the water storage intermediate container 24 and the vessel body.

[0050] The gas injection unit includes a high-pressure CH4 intermediate container 18 and a high-pressure displacement pump 19. The high-pressure CH4 intermediate container 18 is connected to the high-pressure displacement pump 19 via a pipeline. A control valve is installed on the pipeline between the high-pressure CH4 intermediate container 18 and the high-pressure displacement pump 19. The high-pressure CH4 intermediate container 18 is connected to the top of the vessel via a pipeline. A control valve is installed on the pipeline between the high-pressure CH4 intermediate container 18 and the top of the vessel.

[0051] The vessel body includes a bottom plate 6, a front plate 30, a left plate 3, a right plate 4, a rear plate 31, and a top plate 5. The bottom plate 6, the front plate 30, the left plate 3, the right plate 4, the rear plate 31, and the top plate 5 are respectively sealed and fastened by sealing grooves and connecting screws 11. A bottom water injection valve 14 is provided on the bottom plate 6, which is connected to the intermediate water storage container 24 through a pipeline. An air injection valve 13 is provided on the top plate 5, which is connected to the gas injection unit through a pipeline. Multiple outlet valves 16 at different horizontal heights are provided on the right plate 4.

[0052] The bottom of the vessel is provided with a core support bracket 7, and a core support screen 8 is provided on the core support bracket 7. The space between the core support screen 8 and the bottom plate 6 forms a bottom water cavity 9, and the core 1 is located on the core support screen 8.

[0053] The horizontal wellbore simulation unit 15 includes multiple stainless steel hollow tubes at different horizontal heights, evenly distributed within the core 1 at different horizontal heights. Each stainless steel hollow tube includes a horizontal wellbore at the front end that participates in the production simulation and a horizontal wellbore at the rear end that does not participate in the production simulation. The front end of the tube participating in the production simulation has multiple holes evenly distributed, which are used to simulate the perforation holes 33 of the horizontal well. The front end of the tube that does not participate in the production simulation has no holes and the rear end is spiral-shaped, rotating and embedding into the right plate 4 to connect with the corresponding outlet valve 16.

[0054] Multiple holes that cooperate with the horizontal wellbore simulation unit 15 are drilled at different heights on one side of the core 1. The core 1 is surrounded by a rubber sleeve 2. The rubber sleeve 2 has multiple holes at different horizontal heights on the side where the horizontal wellbore simulation unit 15 is embedded, allowing the horizontal wellbore simulation unit 15 to pass through. The core 1 is an outcrop core 1 from a field profile, cut into a cube shape.

[0055] The pressure monitoring unit includes a high-precision pressure gauge 12 installed on the top plate 5 and the bottom plate 6, and a wireless pressure sensor 32 located at the top of the horizontal well shaft simulation unit 15 inside the core 1. The temperature control unit is a resistance heating wire 10 wound around the outside of the vessel body, and the outer edge of the resistance heating wire 10 is provided with a heat insulation layer. The core pore water removal unit is an electric heating rod that can be inserted into the horizontal well shaft simulation unit 15 and an electric heating control system.

[0056] The back pressure control unit includes a back pressure valve 20, an N2 intermediate container 21, and a back pressure displacement pump 22. The back pressure displacement pump 22 is connected to the N2 intermediate container 21 via a pipeline. A control valve is installed on the pipeline between the back pressure displacement pump 22 and the N2 intermediate container 21. The N2 intermediate container 21 is connected to the back pressure valve 20 via a pipeline. The horizontal wellbore simulation unit 15 is connected to the back pressure valve 20 in parallel via a pipeline. The gas and water flow metering unit 23 is connected to the back pressure valve 20 via a pipeline. A control valve is installed on the pipeline between the gas and water flow metering unit 23 and the back pressure valve 20.

[0057] Example 2

[0058] This embodiment is a further optimization based on Embodiment 1, specifically:

[0059] The vessel body is a detachable high-temperature and high-pressure vessel made of aluminum alloy, capable of withstanding 80MPa pressure. The base plate contains one water injection valve, which connects to an intermediate water storage container via a pipeline. The base plate has threaded interfaces and eight sealing grooves at its edges (two grooves at each edge, divided into inner groove 34 and outer groove 35, located on both sides of thread 36). The grooves are 0.6cm deep and 0.3cm wide, and are filled with a small amount of lead powder for high-pressure sealing.

[0060] The core support frame is made of stainless steel and is connected to the base plate and the load-bearing screen by welding. The load-bearing screen has many round holes with a diameter of 1 cm to simulate the contact surface between the bottom water and the core to the greatest extent.

[0061] The top plate has a threaded interface and eight sealing grooves (two grooves at each edge, divided into inner and outer grooves, located on both sides of the thread). The grooves are filled with a small amount of lead powder for high-pressure sealing. There is a gas injection port at the top plate, which is connected to the gas injection valve via threads. A high-precision pressure gauge is also installed at the top plate.

[0062] The left plate has a threaded interface and four sealing grooves (two at the front and two at the rear). There are two raised retaining strips (0.6cm high and 0.3cm wide) at the top and bottom edges of the left plate for insertion into the grooves of the top and bottom plates. A microwave heating device is installed on the inner side of the left plate that contacts the core.

[0063] The right plate has a threaded interface and four sealing slots (two at the front and two at the rear). There are two raised strips at the top and bottom edges of the right plate. The strips are 0.6cm high and 0.3cm wide and are used to insert into the slots of the top and bottom plates. There are multiple horizontal well shaft simulation unit inlet valve interfaces at different positions on the right plate.

[0064] There are two raised retaining strips on the left, right, top, and bottom edges of the front and rear plates, which are inserted into the left, right, top, and bottom plates, respectively. The sealing of the autoclave body is mainly achieved through threads, nuts, bolts, and the engagement of the retaining strips and grooves at the edges of each plate under high pressure.

[0065] The horizontal wellbore simulation unit comprises multiple 0.6m long hollow stainless steel tubes with an outer diameter of 20mm, an inner diameter of 10mm, and a length of 0.6m. The tubes used in the production simulation have six evenly distributed holes at the front, simulating the perforations of a horizontal well, while the tubes not used in the production simulation have no holes. The tail end of the horizontal well stainless steel tube is spiral-shaped, allowing it to be rotatably embedded into the right side plate and connected to the outlet valve. In one embodiment, the horizontal well tube can be wrapped with raw rubber tape before being embedded into the core simulation wellbore to reduce the gap between the tube and the core.

[0066] The experimental core samples were outcrop cores from field profiles. A small number of representative core samples, each 5 cm long and 2.5 cm in diameter, were drilled from the outcrop cores to measure porosity and permeability. After cutting, each sample formed a cube with a side length of 1 m. At different heights on the right side of the core, 5×5 boreholes, each 0.7 m long and 20 mm in diameter, were drilled evenly along the height and horizontal length on the right side of the core using a drilling rig and drill bit. These boreholes were evenly distributed on one side of the rock mass for embedding the horizontal well casing. The core was placed inside the reactor vessel and surrounded by a rubber sleeve, which protected the core under high pressure and compressed excess voids. The rubber sleeve had a hole on the side where the well casing was embedded to facilitate the insertion of the well casing.

[0067] The pressure monitoring unit includes high-precision pressure gauges installed on the top and bottom plates, and a wireless pressure sensor located at the top of the horizontal wellbore within the core. The pressure gauges and pressure sensor have an accuracy of 0.001 MPa. In this implementation, the wireless pressure sensor is a custom-designed high-temperature resistant wireless pressure sensor with a diameter of 20 mm and a length of 0.1 m, which can be embedded into the core through the wellbore, i.e., at the top of the horizontal wellbore.

[0068] The temperature control unit consists of a resistance heating wire surrounding the outside of the vessel body. The outer edge of the heating wire has an insulation layer, and the temperature can be controlled between 20 and 300°C, meeting the temperature requirements of carbonate reservoirs in the Sichuan Basin.

[0069] The X-ray scanner is an industrial-grade X-ray scanner used in bottom water simulations to observe the macroscopic morphological characteristics of bottom water intrusion by adding sodium iodide to the water. The X-ray scanning unit includes an X-ray scanner and a computer imaging display system.

[0070] The back pressure control unit includes a back pressure valve, an N2 intermediate container, and a back pressure displacement pump. The gas-water flow metering unit includes a gas-water separator and metering device, which optimizes the critical production rate by recording the cumulative gas volume under different outlet pressure drops.

[0071] The core pore water removal unit is an electric heating rod that can be inserted into the borehole of a horizontal well, as well as an electric heating control system.

[0072] Example 3

[0073] The experimental method for simulating the development of carbonate bottom water gas reservoirs includes the following steps:

[0074] Step 1: Select rock samples and drill holes: Based on the well test curves of the gas reservoir production wells, identify the typical reservoir physical properties and select outcrop cores that conform to the multi-scale pore-fracture-vuggy development characteristics of the reservoir. Drill representative small core samples at the outcrop cores and measure their porosity, permeability and other physical properties. Then cut the cores and place them on the core support screen. Cover the cores with rubber sleeves. Use a drilling rig and drill bit to drill multiple wellbore holes at different heights of the cores to simulate production wells. Clean the rock cuttings and residue inside the holes and embed a wireless pressure sensor at the top of the wellbore hole.

[0075] Step 2: Complete the assembly of the vessel body and the connection of the system pipelines: Add a small amount of lead powder to the inside of the plate slot of the vessel body. By using the slots and strips between the plates of the vessel body, assemble the left plate, right plate, front plate, rear plate and top plate of the vessel body in sequence. Seal the core with connecting threads, nuts and bolts.

[0076] Based on experimental simulation schemes or the optimal wellbore height and horizontal position of horizontal wells in actual gas reservoirs for production, the calculation formula for the optimal wellbore simulation unit height for production is as follows:

[0077] Hm = Hy * Hs / Hc

[0078] In the formula, Hm is the height of the horizontal wellbore simulation unit; Hy is the height of the experimental outcrop core; Hs is the actual well placement height of the horizontal well during gas reservoir development; and Hc is the target reservoir thickness during gas reservoir development.

[0079] After selecting the optimal height and location of the horizontal wells, the wellbore for production simulation is embedded into the wellbore, while the remaining wellbores are embedded into the non-production wellbore. Pipelines and control valves are then connected, and the sealing of the experimental device system is checked.

[0080] Optionally, the development effect of single-well production or multi-well balanced production under the same water-avoidance height can be simulated according to the scheme requirements to select a reasonable production system. Alternatively, the development effect of horizontal wells with different water-avoidance heights under the same production system can be simulated according to the scheme requirements to select the water-avoidance height of horizontal wells.

[0081] Step 3, Vacuum treatment: Use a vacuum pump to evacuate the entire experimental setup for at least 48 hours;

[0082] Step 4, Bottom water injection: Open the bottom water injection valve, and use the bottom water booster pump and intermediate water storage container to inject formation water into the bottom water cavity. The intermediate water storage container contains a 10-20% sodium iodide solution. At the same time, turn on the X-ray scanner and use the computer imaging system to observe. Stop the injection of formation water when the bottom water cavity is full.

[0083] Step 5, Gas injection under reservoir conditions: Turn on the temperature control unit to raise the temperature of the reactor body to the reservoir temperature. At the same time, open the gas injection valve and inject CH4 gas into the core using the CH4 gas source and gas compressor. When the reading of the pressure monitoring device is close to the design reservoir pressure, stop the gas injection. At the same time, use the high-pressure CH4 intermediate container and high-pressure displacement pump to maintain the set gas pressure in the core for 12 hours to eliminate the pressure increase caused by the thermal expansion of the gas.

[0084] Step 6, Bottom Water Gas Reservoir Development Simulation: The simulation process includes the following steps:

[0085] Step a: Design the corresponding water volume in the intermediate water storage container and the bottom water cavity according to the actual gas reservoir water volume ratio. Use the bottom water booster pump to set the water pressure in the intermediate water storage container to the reservoir pressure. Open the bottom water injection valve to connect the bottom water cavity and the intermediate water storage container.

[0086] Step b: Open the preferred horizontal wellbore unit switch valve for production simulation, and close the valves of the remaining horizontal wellbore simulation units. Reduce the outlet pressure using the back pressure valve, N2 intermediate container, and back pressure displacement pump, setting different pressure drop rates according to actual production needs.

[0087] Step c: The produced gas and water volumes are measured using a gas-water flow metering unit, and the pressure drop variation within the core is monitored using a pressure monitoring unit. Simultaneously, an X-ray scanner is used to detect the conical morphology and pattern of the water in the bottom water cavity. The experiment ends when the reservoir pressure drops to the abandonment pressure. The gas and water volumes under different pressure reductions are statistically analyzed. Furthermore, the formula for calculating the recovery degree obtained from the simulation experiment is as follows:

[0088] S=Vc / Vz

[0089] In the formula: S is the recovery rate obtained from the simulation experiment; Vc is the produced gas volume; Vz is the gas volume injected into the core through the high-pressure CH4 intermediate container;

[0090] Step d: Use the bottom water injection valve and pipeline to drain the formation water from the bottom water chamber inside the reactor. Open the top cover of the reactor and turn on the temperature control system to set the temperature to 200℃. At the same time, take out the horizontal wellbore simulation unit and wireless pressure sensor. Insert the electric heating rod into the wellbore hole. In order to reduce damage to the core, the temperature of the electric heating rod is also set to 200℃. Continue drying for more than 48 hours. Stop the drying operation when the X-ray scanning device can no longer detect the presence of water in the core hole. At the same time, seal the reactor. After checking the sealing, perform vacuuming and repeat the bottom water injection and gas injection steps. At this time, set different gas well production systems and restart the bottom water gas reservoir development simulation experiment.

[0091] Repeat steps a and b until the simulation experiments under different production systems and development modes are completed, obtain gas recovery evaluation charts under different production systems and development modes, and optimize the deployment mode and production system of horizontal wells in bottom water gas reservoirs.

[0092] Example 4

[0093] Further optimizations were made based on Example 3, specifically the experimental method of the experimental apparatus for simulating the development of carbonate bottom water gas reservoirs, which includes the following steps:

[0094] Step 1: Select rock samples and drill holes:

[0095] Based on the well test curves of the gas reservoir production wells, typical reservoir physical properties are identified. Representative field outcrop cores are selected, which are actual reservoir outcrops. In one possible implementation, the field outcrop exhibits fracture-pore reservoir characteristics. A small number of representative small core samples, 5 cm long and 2.5 cm in diameter, are drilled from the outcrop cores to measure physical properties such as porosity and permeability. Preferably, a 1 m side length cube-shaped field core outcrop is cut. The field outcrop core 1 is placed on a core support screen 8. The core support screen 8 is connected to the bottom plate 6 of the reactor body by welding through a core support bracket 7. A rubber sleeve 2 is fitted around the core to reduce damage to the core under high pressure. The rubber sleeve has holes on the side where the wellbore is embedded to facilitate wellbore embedding. Using a drilling rig and drill bit, 5×5 wellbore holes, each 0.7m long and 20mm in diameter, are drilled evenly along the right side of the core sample, at both height and horizontal length, to remove rock cuttings and debris from the boreholes. A wireless pressure sensor is embedded at the top of the aforementioned core wellbore. In one embodiment, the wireless pressure sensor is a high-precision wireless pressure sensor with a diameter of 20mm and a length of 0.1m.

[0096] Step 2: Complete the assembly of the vessel body and the connection of system pipelines:

[0097] A small amount of lead powder is added to the inside of the plate slot of the vessel body. By using the slots and strips between the plates of the vessel body, the left plate, right plate, front plate, rear plate and top plate of the vessel body are assembled in sequence. The core is sealed by connecting threads, nuts and bolts. At the same time, the horizontal well shaft is embedded into the pre-drilled hole, and the well shaft and the vessel body are sealed by connecting valves at the outlet of the horizontal well. The unit systems are connected by pipelines, three-way valves and valves.

[0098] In one possible implementation, based on the selection of the production reservoir thickness and the water-avoidance height of the horizontal wells, the wellbore of the five production horizontal wells is determined by formula to be embedded in the wellbore approximately 0.6m from the bottom of the core, while the wellbore of the remaining wells is embedded with the wellbore of the non-production horizontal wells.

[0099] In one possible implementation, the five production horizontal wellbores are embedded in the five bottommost wellbores of the core sample, while the remaining wellbores are embedded with non-production horizontal wellbores.

[0100] During implementation, technicians can simulate the layout of actual production wells by flexibly adjusting the position of the horizontal wellbore used for production, and can obtain the pressure distribution pattern inside the core at different production times in real time by setting up wireless pressure sensors in each wellbore.

[0101] Step 3: System vacuuming process:

[0102] The entire simulation system was evacuated for 48 hours using a vacuum pump.

[0103] Step 4, Bottom water injection:

[0104] Open the bottom water injection valve and use the bottom water booster pump and intermediate water storage container to inject formation water into the bottom water cavity. The intermediate water storage container contains a 10% sodium iodide solution. Simultaneously turn on the X-ray scanning equipment and use the computer imaging system to observe. Stop the injection of formation water when the bottom water cavity is full.

[0105] Step 5, High-pressure gas injection:

[0106] The temperature control unit was activated to raise the reactor temperature to the reservoir temperature of 120°C. The gas injection valve was then opened, and CH4 gas was injected into the core using a high-pressure displacement pump and a high-pressure CH4 intermediate container. Gas injection was stopped when the reading on the high-precision pressure monitoring device approached the design reservoir pressure of 50 MPa. Simultaneously, the high-pressure CH4 intermediate container and high-pressure displacement pump were used to maintain the set gas pressure within the core for 12 hours to eliminate pressure increases caused by thermal expansion of the gas.

[0107] Step 6: Development simulation of bottom water gas reservoir water-sheltered height:

[0108] Based on the actual gas reservoir water volume ratio, design the corresponding water volume in the intermediate water storage container and the bottom water cavity. Use the bottom water booster pump to set the water pressure in the intermediate water storage container to the reservoir pressure, open the bottom water injection valve, and connect the bottom water cavity and the intermediate water storage container.

[0109] Open the on / off valve of the preferred horizontal wellbore simulation unit and close the valves of the remaining horizontal wellbore simulation units. Reduce the outlet pressure using the back pressure valve, N2 intermediate container, and back pressure displacement pump, setting different pressure drop rates according to actual production needs.

[0110] The produced gas and water volumes were measured using a gas-water flow metering unit, and the pressure drop variation within the core was monitored using a pressure monitoring unit. Simultaneously, an X-ray scanner was used to detect the conical morphology and pattern of the water in the bottom water cavity. The experiment ended when the reservoir pressure decreased to the abandonment pressure. The gas and water volumes under different pressure reductions were statistically analyzed. Furthermore, the recovery rate calculation formula obtained from the simulation experiment is as follows:

[0111] S=Vc / Vz

[0112] In the formula, S is the recovery rate obtained from the simulation experiment; Vc is the produced gas volume; and Vz is the gas volume injected into the core through the high-pressure CH4 intermediate container.

[0113] After the experiment was completed, the formation water in the bottom water chamber of the reactor was drained using the bottom water injection valve and pipeline. The top cover of the reactor was opened, and the core was dried using a microwave heating device. The drying operation was stopped when no moisture was detected by X-rays, and the reactor was sealed at the same time.

[0114] Perform vacuuming operations, and repeat the bottom water injection and gas injection steps. At this time, set different gas well production systems and restart the development simulation experiment of the bottom water gas reservoir.

[0115] Repeat the above steps until the simulation experiments under different production systems and development models are completed. Compare the gas recovery rates under different production systems and development models, and optimize the deployment mode and production system of horizontal wells in bottom water gas reservoirs.

Claims

1. An experimental apparatus for simulating the development of carbonate rock bottom water gas reservoirs, characterized in that, The system includes a vessel body, a core (1) housed within the vessel body, a temperature control unit wrapped around the outside of the vessel body, pressure monitoring units located at the top and bottom of the vessel body and inside the wellbore of the core (1), a bottom water injection unit for injecting water into the bottom of the vessel body, a gas injection unit for injecting gas into the top of the vessel body, a horizontal wellbore simulation unit (15) partially embedded within the core (1), an X-ray scanning unit (26) covering the vessel body, a vacuum pump (17), a back pressure control unit, a gas and water flow metering unit (23), and a core pore water removal unit; the vacuum pump (17) is connected to the pipeline of the gas injection unit for vacuuming the vessel body; the inlet end of the horizontal wellbore simulation unit (15) is connected to the back pressure control unit and the gas and water flow metering unit (23) respectively through the outlet valve (16); The bottom water injection unit includes a bottom water booster pump (25) and a water storage intermediate container (24) connected to the bottom water booster pump (25) via a pipeline. A control valve is installed on the pipeline between the bottom water booster pump (25) and the water storage intermediate container (24). The water storage intermediate container (24) is connected to the bottom of the vessel body via a pipeline. A control valve is installed on the pipeline between the water storage intermediate container (24) and the vessel body. A 10-20% sodium iodide solution is stored in the water storage intermediate container (24). The vessel body is made up of a bottom plate (6), a front plate (30), a left plate (3), a right plate (4), a rear plate (31), and a top plate (5), which are sealed and connected by sealing slots. A core support bracket (7) is provided at the bottom of the vessel body. A core support screen (8) is provided on the core support bracket (7). The space between the core support screen (8) and the bottom plate (6) forms a bottom water cavity (9). The core (1) is located on the core support screen (8). The horizontal wellbore simulation unit (15) includes multiple stainless steel hollow tubes at different horizontal heights, evenly distributed within the core (1) at different horizontal heights. Each stainless steel hollow tube includes a horizontal wellbore at the front end that participates in the production simulation and a horizontal wellbore at the rear end that does not participate in the production simulation. The front end of the tubes participating in the production simulation has multiple holes evenly distributed, which are used to simulate the perforation holes (33) of the horizontal well. The front end of the tubes not participating in the production simulation has no holes and the rear end is spiral-shaped. The rear end rotates and embeds into the right plate (4) and connects to the corresponding outlet valve (16). The calculation formula for the height of the horizontal wellbore simulation unit is as follows: Hm = Hy * Hs / Hc; In the formula, Hm is the height of the horizontal wellbore simulation unit; Hy is the height of the experimental outcrop core; Hs is the actual well placement height of the horizontal well during gas reservoir development; and Hc is the target reservoir thickness during gas reservoir development. The pressure monitoring unit includes a high-precision pressure gauge (12) set on the top plate (5) and the bottom plate (6), and a wireless pressure sensor (32) located at the top of the horizontal well shaft simulation unit (15) inside the core (1). The temperature control unit is a resistance heating wire (10) wrapped around the outside of the vessel body, and the outer edge of the resistance heating wire (10) is provided with a heat insulation interlayer. The core pore water removal unit is an electric heating rod inserted into the horizontal well shaft simulation unit (15) and an electric heating control system.

2. The experimental apparatus for simulating the development of carbonate rock bottom water gas reservoirs according to claim 1, characterized in that... A bottom water injection valve (14) is installed on the bottom plate (6). The bottom water injection valve (14) is connected to the water storage intermediate container (24) through a pipeline. An air injection valve (13) is installed on the top plate (5). The air injection valve (13) is connected to the gas injection unit through a pipeline. Multiple outlet valves (16) at different horizontal heights are installed on the right plate (4).

3. The experimental apparatus for simulating the development of carbonate bottom water gas reservoirs according to claim 2, characterized in that... The gas injection unit includes a high-pressure CH4 intermediate container (18) and a high-pressure displacement pump (19) connected to the high-pressure CH4 intermediate container (18) via a pipeline. A control valve is installed on the pipeline between the high-pressure CH4 intermediate container (18) and the high-pressure displacement pump (19). The high-pressure CH4 intermediate container (18) is connected to the top of the vessel body via a pipeline. A control valve is installed on the pipeline between the high-pressure CH4 intermediate container (18) and the top of the vessel body.

4. The experimental apparatus for simulating the development of carbonate bottom water gas reservoirs according to claim 3, characterized in that... Multiple holes that cooperate with the horizontal well shaft simulation unit (15) are drilled at different heights on one side of the core (1). The core (1) is surrounded by a rubber sleeve (2). The rubber sleeve (2) has multiple holes at different horizontal heights on the side where the horizontal well shaft simulation unit (15) is embedded, allowing the horizontal well shaft simulation unit (15) to pass through.

5. The experimental apparatus for simulating the development of carbonate bottom water gas reservoirs according to claim 4, characterized in that... The back pressure control unit includes a back pressure valve (20), an N2 intermediate container (21), and a back pressure displacement pump (22). The back pressure displacement pump (22) and the N2 intermediate container (21) are connected by a pipeline. A control valve is installed on the pipeline between the back pressure displacement pump (22) and the N2 intermediate container (21). The N2 intermediate container (21) and the back pressure valve (20) are connected by a pipeline. The horizontal wellbore simulation unit (15) is connected to the back pressure valve (20) in parallel through a pipeline. The gas and water flow metering unit (23) is connected to the back pressure valve (20) through a pipeline. A control valve is installed on the pipeline between the gas and water flow metering unit (23) and the back pressure valve (20).

6. An experimental method for simulating the development of carbonate bottom-water gas reservoirs, using the experimental apparatus for simulating the development of carbonate bottom-water gas reservoirs as described in claim 5, characterized in that... Includes the following steps: Step 1: Select rock samples and drill holes: Based on the well test curves of the gas reservoir production wells, identify the typical reservoir physical properties and select outcrop cores that conform to the multi-scale pore-fracture-vuggy development characteristics of the reservoir. Drill small core samples at the outcrop cores and measure their porosity and permeability. Then, cut the cores and place them on a core-supporting screen. Cover the cores with rubber sleeves. Use a drilling rig and drill bit to drill multiple wellbore holes at different heights of the cores to simulate production wells. Clean the rock cuttings and residue inside the holes and embed a wireless pressure sensor at the top of the wellbore hole. Step 2: Complete the assembly of the vessel body and the connection of the system pipelines: Add a small amount of lead powder to the inside of the plate slot of the vessel body. By using the slots and strips between the plates of the vessel body, assemble the left plate, right plate, front plate, rear plate and top plate of the vessel body in sequence. Seal the core with connecting screws. Step 3, Vacuum treatment: Use a vacuum pump to evacuate the entire experimental setup for at least 48 hours; Step 4, Bottom water injection: Open the bottom water injection valve, use the bottom water booster pump and the intermediate water storage container to inject formation water into the bottom water cavity, and at the same time turn on the X-ray scanner and use the computer imaging system to observe. Stop the injection of formation water when the bottom water cavity is full. Step 5, Gas injection under reservoir conditions: Turn on the temperature control unit to raise the temperature of the reactor body to the reservoir temperature. At the same time, open the gas injection valve and inject CH4 gas into the core using the CH4 gas source and gas compressor. When the reading of the pressure monitoring device is close to the design reservoir pressure, stop the gas injection. At the same time, use the high-pressure CH4 intermediate container and high-pressure displacement pump to maintain the set gas pressure in the core for 12 hours to eliminate the pressure increase caused by the thermal expansion of the gas. Step 6: Simulation of bottom water gas reservoir development. The simulation process includes the following steps: Step a: Design the corresponding water volume in the intermediate water storage container and the bottom water chamber according to the actual gas reservoir water volume ratio. Use the bottom water booster pump to set the water pressure in the intermediate water storage container to the reservoir pressure. Open the bottom water injection valve to connect the bottom water chamber and the intermediate water storage container. Step b: Open the switch valve of the horizontal wellbore unit used for production simulation, close the valves of the other horizontal wellbore simulation units, and use the back pressure valve, N2 intermediate container and back pressure displacement pump to reduce the outlet pressure. Set different pressure drop rates according to actual production needs. Step c: Measure the produced gas and water volume using a gas-water flow metering unit, monitor the pressure drop variation within the core using a pressure monitoring unit, and simultaneously detect the conical morphology and pattern of the water in the bottom water cavity using an X-ray scanner. The experiment ends when the reservoir pressure drops to the abandonment pressure. The gas and water volumes under different pressure reductions are statistically analyzed. The formula for calculating the recovery degree obtained from the simulation experiment is as follows: S = Vc / Vz; In the formula: S is the recovery rate obtained from the simulation experiment; Vc is the produced gas volume; Vz is the gas volume injected into the core through the high-pressure CH4 intermediate container; Step d: Use the bottom water injection valve and pipeline to drain the formation water from the bottom water chamber inside the reactor. Open the top cover of the reactor and turn on the temperature control system to set the temperature to 200℃. At the same time, take out the horizontal wellbore simulation unit and wireless pressure sensor. Insert the electric heating rod into the wellbore hole. In order to reduce damage to the core, the temperature of the electric heating rod is also set to 200℃. Continue drying for more than 48 hours. Stop the drying operation when the X-ray scanning device can no longer detect the presence of water in the core hole. At the same time, seal the reactor. After checking the sealing, perform vacuuming and repeat the bottom water injection and gas injection steps. At this time, set different gas well production systems and restart the bottom water gas reservoir development simulation experiment. Repeat steps a and b until the simulation experiments under different production systems and development modes are completed, and obtain gas recovery evaluation charts under different production systems and development modes.

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