An experimental method for simulating high temperature and high pressure water invasion in gas reservoirs with interlayer

Abstract

The present application relates to a kind of experimental methods of high temperature and high pressure water invasion of gas reservoir simulating the existence of interlayer, comprising: (1) obtaining reservoir core, low-permeability interlayer core and closed interlayer core, permeability is K1, K2, K3 respectively;(2) preparation of interlayer full-diameter core: in the center position of low-permeability interlayer core and closed interlayer core with diameter d, along longitudinal direction, drill or carve out the core with diameter d1;In low-permeability interlayer core with diameter d and permeability K2, embed closed interlayer core with diameter d1 and permeability K3;(3) the interlayer full-diameter core, reservoir full-diameter core is placed in clamping device A, clamping device B respectively, after being connected in series, post in experimental device;(4) after carrying out gas reservoir water invasion experiment, remove reservoir full-diameter core and carry out nuclear magnetic resonance T2 spectrum scanning;(5) analysis the high temperature and high pressure water invasion law and characteristics of gas reservoir existing interlayer.The present application can provide theoretical guidance and technical support for improving natural gas recovery.

Description

Technical Field

[0001] This invention belongs to the field of gas reservoir development, specifically relating to an experimental method for simulating high-temperature and high-pressure water intrusion in gas reservoirs with strata. Background Technology

[0002] Most gas reservoirs in my country are water-driven reservoirs to varying degrees, with active edge-bottom water reservoirs accounting for approximately 40-50%. Water-driven gas reservoirs possess enormous resources and high exploitation value. However, their development is generally affected by water intrusion, severely impacting recovery rates. This is particularly true for a type of reservoir represented by the Yuanba Changxing Formation, where water is prevalent in the lower structural regions, but the water is confined to the high-permeability zone within the reef / shoal body and is not interconnected, resulting in a complex gas-water relationship. Based on this relationship, formation water distribution patterns can be categorized into layered (the main type) and unlayered types. Currently, high-temperature, high-pressure water intrusion experiments have not been conducted on gas reservoirs with layered structures.

[0003] Currently, most indoor gas reservoir water intrusion experiments focus on residual gas distribution, water intrusion patterns, fracture development, and water body size. For example, the invention patent "A method for simulating water intrusion caused by the expansion of a large water body during the exhaustion and exploitation of an oil and gas reservoir" (CN109707376A) achieves the goal of simulating the exhaustion and displacement of oil and gas reservoirs with large water bodies using a finite-volume intermediate container; the invention patent "An experimental device and method for simulating water intrusion in a gas reservoir" (CN105604545A) can obtain the distribution characteristics of residual gas after simulated water intrusion in a gas reservoir; the invention patent "An experimental device and method for studying the law of water intrusion in a fractured gas reservoir" (CN114482991A) simulates the distribution law of gas and water at different points in a porous medium model under high temperature and high pressure conditions in the formation by measuring points; and the invention patent "An experimental device and method for water intrusion under different fracture distribution patterns in a gas reservoir" (CN108505987A) can simulate the water intrusion process in gas reservoirs with different formation dip angles, different fracture distribution patterns, and different edge and bottom water energies.

[0004] Existing research on interlayers mostly focuses on areas such as artificial gas-water interface barriers, interlayer identification, and interlayer fracturing. The invention patent "A method for rapidly densifying artificial gas-water interface barriers in edge-bottom water gas reservoirs" (CN112943162B) first transforms the gas-water interface into an oil-water interface, forming a dense polymer water-blocking layer at the oil-water interface, and then utilizes crystallization to form an even denser polymer water-blocking layer, improving sealing efficiency. The invention patent "A method for identifying interlayers in biodegradable reservoirs" (CN109085272A) can effectively identify interlayers in biodegradable reservoirs. The invention patent "A method for fracturing interlayers in SAGD production" (CN113006755A) effectively solves the problem of interlayers obstructing the expansion and ascent of SAGD steam chambers and the downward flow of crude oil, leading to low oil production rates, low oil-steam ratios, and low recovery rates.

[0005] This invention is the first to study gas reservoirs with strata, and proposes an experimental method to simulate high-temperature and high-pressure water intrusion in gas reservoirs with strata, filling the gap in the existing technology and providing theoretical guidance and technical support for improving natural gas recovery. Summary of the Invention

[0006] The purpose of this invention is to provide an experimental method for simulating high-temperature and high-pressure water intrusion in gas reservoirs with strata. This method is based on reliable principles. First, a full-diameter core of the strata is prepared. Then, a full-diameter core holder for the strata and a full-diameter core holder for the reservoir are connected in series to conduct high-temperature and high-pressure water intrusion, thereby studying the laws and characteristics of high-temperature and high-pressure water intrusion in gas reservoirs with strata.

[0007] To achieve the above technical objectives, the present invention adopts the following technical solution.

[0008] An experimental method for simulating high-temperature and high-pressure water intrusion in a gas reservoir with strata includes the following steps:

[0009] (1) Based on the logging data of the target block, representative reservoir sections, low-permeability isolation sections and closed isolation sections were selected, and reservoir cores, low-permeability isolation cores and closed isolation cores were obtained. All of them are full-diameter cores with a height of h and a diameter of d. Their permeabilities are K1, K2 and K3, respectively.

[0010] (2) Preparation of full-diameter cores with interlayers, the process is as follows:

[0011] 1) Drill or haul out core samples with a diameter of d1 along the longitudinal direction from the center of both the low-permeability interlayer core and the sealed interlayer core, and extract 1 / 4d of the core sample. <d1<1 / 2d;

[0012] 2) Embed a closed-cell core with a diameter of d1 and a permeability of K3 into a low-permeability interlayer core with a diameter of d and a permeability of K2;

[0013] (3) The prepared interlayer full-diameter core and reservoir full-diameter core are placed in clamp A and clamp B respectively. Clamp A and clamp B are connected in series and placed in a simulated gas reservoir water intrusion test device. The inlet end of clamp A is connected to the gas intermediate container and the formation water intermediate container, and the outlet end of clamp B is connected to the back pressure valve. Clamp A and clamp B are connected to the confining pressure pump respectively. In clamp B, a diversion block is set at the inlet end of the reservoir full-diameter core. The diversion block has a diversion groove and a fluid channel to guide the fluid to fully contact the reservoir core. Clamp A, clamp B, gas intermediate container and formation water intermediate container are located in an oven.

[0014] (4) Conduct high-temperature and high-pressure water intrusion tests on gas reservoirs with strata, as follows:

[0015] 1) Configure formation water and natural gas in the target block gas reservoir;

[0016] 2) Use a vacuum pump to evacuate the experimental setup, inject water into the cores of the two clamps, and then inject gas into the cores of the two clamps until no more water comes out of the outlet to establish bound water. Take out the full diameter core of the reservoir for nuclear magnetic resonance T2 spectrum scanning.

[0017] 3) Use an oven to establish the reservoir temperature, and while raising the system pressure to the experimental pressure, the confining pressure and back pressure should also be raised to the appropriate pressure.

[0018] 4) Increase the pressure of the intermediate formation water container to the experimental pressure, open the valve of the intermediate formation water container, and use the pump withdrawal method to reduce the back pressure to realize the water intrusion attenuation experiment. During the attenuation process, appropriately reduce the confining pressure. After the attenuation experiment is completed, take out the full diameter core of the reservoir for nuclear magnetic resonance T2 spectrum scanning.

[0019] (5) Based on experimental data, analyze and study the high-temperature and high-pressure water intrusion patterns and characteristics of gas reservoirs with strata.

[0020] Furthermore, in step (2), the full-diameter core of the interlayer is a low-permeability closed interlayer designed according to the actual type of interlayer and the formation water distribution pattern.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) Selecting representative real full-diameter cores to prepare interlayers can ensure that the prepared interlayer cores are similar to the actual formation properties and more realistically reflect the development characteristics of the reservoir.

[0023] (2) Two full-diameter core holders are used to connect the interlayer and the reservoir in series to simulate a gas reservoir with an interlayer. A diversion block is placed at the front end of the reservoir core, and the problem of small contact area between the interlayer core and the reservoir core is solved by using a diversion channel.

[0024] (3) In the process of simulating the high temperature and high pressure water intrusion experiment of gas reservoir with strata, the influence of factors such as different decay rates, different water body sizes, and different core permeability on the water intrusion characteristics can be considered. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the experimental setup for simulating water intrusion in a gas reservoir.

[0026] Figure 2 for Figure 1 A schematic diagram of the drainage device.

[0027] Figure 3 This is a schematic diagram of a full-diameter core sample of a low-permeability, closed-cell type.

[0028] Figure 4 This is a graph showing the relationship between formation pressure and cumulative recovery rate in a water intrusion experiment of a low-permeability closed-cell model.

[0029] Figure 5 The T2 NMR spectra are for bound water and water-invaded water in a low-permeability closed-cell model.

[0030] Explanation of reference numerals in the attached drawings: 1, 2, 9 - Constant pressure pump; 3 - Vertical displacement pump; 4 - Gas intermediate container; 5 - Formation water intermediate container; 6, 7 - Clamping device; 8 - N2 intermediate container; 10 - Gas flow meter; 11 - Back pressure valve; 12 - Conical flask; 13, 14, 15, 16, 17, 18 - Pressure gauge; 19, 20, 21, 22 - Three-way valve; 23 - Full-diameter core of the interlayer; 24 - Fluid channel; 25 - Drainage block; 26 - Full-diameter core of the reservoir; 27, 28, 29, 30 - Valves; 31 - Drainage channel; 32 - High-temperature oven. Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings and examples to enable those skilled in the art to understand the invention. However, it should be understood that the present invention is not limited to the specific embodiments described herein. For those skilled in the art, any variations that fall within the spirit and scope of the invention as defined and determined by the appended claims are all within the scope of protection.

[0032] The gas reservoir water intrusion experimental apparatus (see) Figure 1 The left clamp 6 holds a full-diameter core 23 of the interlayer, and the inlet is connected to the gas intermediate container 4 and the formation water intermediate container 5. The right clamp 7 holds a diversion block 25 and a full-diameter core 26 of the reservoir, and the outlet is connected to the back pressure valve 11. Constant pressure pumps 1 and 2 are connected to clamps 7 and 6 respectively to provide confining pressure for the clamps. The two clamps are connected in series through pipelines and placed in a high-temperature and high-pressure oven 32.

[0033] At the start of the experiment (see) Figure 2The fluid flows through the full-diameter core 23 of the interlayer to the full-diameter core 26 of the reservoir in the pipeline. In the diversion block 25, the fluid enters the fluid channel 24 through the diversion groove 31, so that the fluid is in full contact with the full-diameter core 26 of the reservoir.

[0034] Preparation of low-permeability sealed barrier ( Figure 3 ): A closed interlayer core with a diameter of d1 and a permeability of K3 is embedded in a low-permeability interlayer core with a diameter of d and a permeability of K2; the cores are bonded together using high-temperature resistant adhesive and then dried in an oven for 12 hours.

[0035] Example

[0036] The high-temperature, high-pressure water intrusion experiment simulating a gas reservoir with strata using the above-mentioned apparatus and core samples includes the following steps:

[0037] (1) According to the experimental plan, the formation water and natural gas of the target gas reservoir were prepared;

[0038] (2) Figure 1 The experimental setup is connected as shown, and a vacuum pump is used to evacuate the device. A low-permeability closed-cell model is used for the experiment, and the specific information is shown in Table 1. Valves 27 and 29 are opened, and water is injected into the clamps 6 and 7 at 15 MPa and 5 mL / min using the vertical displacement pump 3 and the intermediate container 5 for formation water. Water injection is stopped after water flows steadily out of the conical flask. Valves 27 and 29 are closed, and valves 30 and 28 are opened. Water is injected into the clamps 6 and 7 at 15 MPa and 5 mL / min using the vertical displacement pump 3 and the intermediate container 4 for gas. Gas is injected until no more water is emitted from the outlet and gas flow meter 10 emits gas stably, indicating that the bound water has been established. During the water and gas injection process, constant pressure pumps 1 and 2 apply a confining pressure of about 5 MPa higher than the injection pressure of 15 MPa to clamps 7 and 6, respectively. At the same time, constant pressure pump 9 and N2 intermediate container 8 apply a back pressure of about 0.2 MPa higher than the injection pressure of 15 MPa to back pressure valve 11. Once the bound water has been established, the pressure is reduced and the reservoir core is removed for nuclear magnetic resonance T2 spectrum scanning. After the nuclear magnetic resonance scanning is completed, the reservoir core is put back into the clamp to restore the bound water state.

[0039] Table 1 Low-permeability closed-type interlayer model

[0040]

[0041] (3) Use an oven to establish a reservoir temperature of 150℃; close valves 27 and 29, open valves 30 and 28, and use vertical displacement pump 3 and gas intermediate container 4 to inject gas into clamps 6 and 7 at a rate of 5mL / min to pressurize to a formation pressure of 60MPa; during the pressurization process, use constant pressure pumps 1 and 2 to apply a confining pressure of about 5MPa higher than the formation pressure of 60MPa to clamps 7 and 6 respectively, and at the same time use constant pressure pump 9 and N2 intermediate container 8 to apply a back pressure of about 0.2MPa higher than the formation pressure of 60MPa to back pressure valve 11;

[0042] (4) Using the vertical displacement pump 3, the pressure in the intermediate container 5 of the formation water was increased to the formation pressure of 60 MPa. Valves 28 and 30 were closed, valve 27 was opened, and valve 29 was closed. The pump was withdrawn to reduce the back pressure, and the pressure was reduced to the abandonment pressure of 15 MPa at a rate of 5 MPa / h. During the attenuation process, the confining pressure was appropriately reduced. After the attenuation was completed, the pump was withdrawn to reduce the pressure, and the reservoir core was taken out for nuclear magnetic resonance T2 spectrum scanning. During the experiment, the gas production volume, water production, initial water breakthrough pressure, and outlet pressure were recorded. The experimental results are shown in Table 2.

[0043] Table 2. Water intrusion experimental data of the low-permeability closed-layer model.

[0044] Outlet pressure / MPa Water production / ml Gas production / ml Cumulative gas production / ml Cumulative recovery / % 60 / / / / 55 0 1421.2 1421.2 5.64 50 0 2972.3 3693.5 14.66 45 0 3462.5 6156 24.44 40 0 3024.8 8980.8 35.65 35 0 3805.2 11786 46.78 30 0 3107.6 14693.6 58.33 25 0.5 1908.7 16602.3 65.90 20 1.7 1578.2 18180.5 72.17 15 1.5 1689.4 19869.9 78.87

[0045] Based on experimental data, a curve showing the relationship between cumulative recovery rate and formation pressure was created (e.g., Figure 4 ), NMR T2 spectra of the bound water state and the post-water intrusion state (e.g. Figure 5 Comprehensive analysis shows that the water intrusion process of gas reservoirs with low permeability and closed interlayers is relatively low at 25 MPa, with a long waterless recovery period. After water intrusion, the reservoir with good physical properties also has good gas production capacity. During the water intrusion process, the water mainly intrudes along the large channels. When the core finally depletes to the abandonment pressure, the final cumulative recovery rate reaches 78.87%.

Claims

1. An experimental method for simulating high-temperature and high-pressure water intrusion in a gas reservoir with strata, comprising the following steps: (1) Based on the logging data of the target block, representative reservoir sections, low-permeability isolation sections and closed isolation sections were selected, and reservoir cores, low-permeability isolation cores and closed isolation cores were obtained. All of them are full-diameter cores with a height of h and a diameter of d. Their permeabilities are K1, K2 and K3, respectively. (2) Preparation of full-diameter cores with interlayers, the process is as follows: 1) Drill or haul out a core of diameter d1 longitudinally from the center of the low-permeability interlayer core and the closed interlayer core, respectively, where 1 / 4d < d1 < 1 / 2d; 2) Embed a closed-cell core with a diameter of d1 and a permeability of K3 into a low-permeability interlayer core with a diameter of d and a permeability of K2; (3) The prepared interlayer full-diameter core and reservoir full-diameter core are placed in clamp A and clamp B respectively. Clamp A and clamp B are connected in series and placed in a simulated gas reservoir water intrusion test device. The inlet end of clamp A is connected to the gas intermediate container and the formation water intermediate container. The outlet end of clamp B is connected to the back pressure valve. Clamp A and clamp B are connected to the confining pressure pump respectively. In clamp B, a diversion block is set at the inlet end of the reservoir full-diameter core. The diversion block has a diversion groove and a fluid channel to guide the fluid to fully contact the reservoir core. Clamp A, clamp B, gas intermediate container and formation water intermediate container are located in an oven. (4) Conduct high-temperature and high-pressure water intrusion experiments on gas reservoirs with strata, as follows: 1) Configure formation water and natural gas in the target block gas reservoir; 2) Use a vacuum pump to evacuate the experimental setup, inject water into the cores of the two clamps, and then inject gas into the cores of the two clamps until no more water comes out of the outlet to establish bound water. Take out the full diameter core of the reservoir for nuclear magnetic resonance T2 spectrum scanning. 3) Use an oven to establish the reservoir temperature, and at the same time raise the system pressure to the experimental pressure, the confining pressure and back pressure should also be raised to the appropriate pressure; 4) Increase the pressure of the intermediate formation water container to the experimental pressure, open the valve of the intermediate formation water container, and use the pump withdrawal method to reduce the back pressure to realize the water intrusion attenuation experiment. During the attenuation process, appropriately reduce the confining pressure. After the attenuation experiment is completed, take out the full diameter core of the reservoir for nuclear magnetic resonance T2 spectrum scanning. (5) Based on experimental data, analyze and study the high-temperature and high-pressure water intrusion patterns and characteristics of gas reservoirs with strata.

2. The experimental method for simulating high-temperature and high-pressure water intrusion in a gas reservoir with strata as described in claim 1, characterized in that, In step (2), the full-diameter core of the interlayer is a low-permeability closed interlayer designed according to the actual type of interlayer and the formation water distribution pattern.

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