A method for evaluating effective working gas volume of gas storage
By monitoring the T2 spectrum signal intensity value of the core through nuclear magnetic resonance and combining it with simulated formation conditions, the error problem of working gas volume assessment during multiple injection and production processes in water-intrusive gas reservoirs was solved, achieving accurate working gas volume assessment and rational operation of the gas reservoir.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- PETROCHINA CO LTD
- Filing Date
- 2024-05-10
- Publication Date
- 2026-07-03
Smart Images
Figure CN120925904B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the technical field of oil and gas field development, and in particular to a method for evaluating the effective working gas volume of a gas storage facility. Background Technology
[0002] Among various peak-shaving methods, underground gas storage is the most important natural gas storage method and peak-shaving means in the world today. Since the first gas storage experiment was conducted in the Wellland gas field in Canada in 1915, 715 underground gas storage facilities have been built globally, with a total of 23,007 production wells and a total working gas volume of 3930 × 10⁻⁶. 8 m 3 The average hourly output is 2.35 × 10 8 m 3 natural gas.
[0003] China's natural gas industry has entered a phase of rapid development. With the increasing demand for natural gas, the continued rapid growth of imported gas, and the accelerated construction of large-scale long-distance pipelines, the contradiction between natural gas storage and peak-shaving has become increasingly prominent. In recent years, to address the tight natural gas supply, the government has proposed accelerating the construction of regional gas storage facilities.
[0004] Statistics show that the main types of underground gas storage facilities worldwide include gas reservoirs, aquifers, salt caverns, and oil reservoirs. Among them, gas reservoirs have the largest working gas volume, accounting for about 75% of the total working gas volume. However, most gas reservoirs are converted from original developed gas reservoirs, and most gas reservoirs have certain water intrusion characteristics in the late stage of development. After formation water intrudes into the gas reservoir, it leads to problems such as the formation of trapped gas and reduced gas well production capacity.
[0005] Furthermore, after converting a water-inundated gas reservoir into a gas storage facility, the distribution of the intruding water body changes during multiple injection and production cycles. This alters key parameters such as the working gas volume, cushion gas volume, and movable cushion gas volume, leading to significant discrepancies between the storage facility's operating parameters and the design parameters, and resulting in unsatisfactory economic benefits. Therefore, before converting a water-inundated gas reservoir into a gas storage facility, it is necessary to conduct an assessment of the effective working gas volume after multiple rounds of injection and production to guide the rational construction of such storage facilities.
[0006] Currently, research on the water intrusion patterns in multi-round injection and production of gas storage facilities mainly relies on physical simulation and numerical simulation. However, these methods have the following drawbacks:
[0007] 1) Most physical simulations use monitoring changes in core water to simulate changes in the working gas volume of a gas storage facility. However, the actual inventory of a gas reservoir includes working gas, movable cushion gas, and unmovable inventory. Since the cushion gas controlled by the water phase trap is not considered, there is a certain difference between it and the actual storage capacity.
[0008] 2) Most physical simulations utilize nitrogen to displace water at normal temperature and pressure. The experimental conditions differ significantly from the formation conditions, and therefore fail to effectively reflect the impact of factors such as gas expansion on the working gas volume during multi-cycle injection and production.
[0009] 3) Numerical simulations mainly simulate macroscopic gas and water distribution changes, and the accuracy of the geological model and the microscopic change patterns differ significantly from the actual gas reservoirs.
[0010] Assessing the effective working gas volume during multiple injection and production cycles in underground gas storage facilities is a crucial foundation for storage facility construction and a key element in evaluating their economic benefits. However, current assessment methods differ significantly from actual gas-water migration patterns during multiple injection and production cycles, and the assessment patterns do not align with the changes in working gas volume during these cycles. Therefore, developing a method for assessing the effective working gas volume during multiple injection and production cycles in water-inundated underground gas storage facilities is of great significance for storage facility construction. Summary of the Invention
[0011] The purpose of this invention is to overcome the aforementioned problems in the existing technology and provide a method for evaluating the effective working gas volume of a gas storage facility. This invention employs nuclear magnetic resonance (NMR) to monitor the T2 spectrum signal intensity values of core samples at the end of different injection and production stages. The T2 spectrum signal intensity values reflect changes in gas saturation within the core, and the gas content ratio at the end of production and injection stages is analyzed to obtain the change in working gas volume within the core over an injection-production cycle. This allows for a realistic and accurate reflection of the working gas volume variation patterns of water-inundated gas storage facilities across multiple injection-production cycles. The simulation process of this invention is consistent with the changes in parameters such as pressure and time during gas storage facility operation. Furthermore, by using NMR to detect fluid changes within microscopic pore throats, the complex process of conventional working gas volume evaluation is simplified, and a basis for the rational operation of water-inundated gas storage facilities is provided.
[0012] To achieve the above objectives, the technical solution adopted by the present invention is as follows:
[0013] A method for evaluating the effective working gas volume of a gas storage facility, comprising the following steps:
[0014] S1: Basic Signal Acquisition
[0015] Reservoir cores were selected and pressurized to the original formation pressure using simulated natural gas. The nuclear magnetic resonance T2 spectrum of the saturated simulated natural gas cores was tested using a nuclear magnetic resonance acquisition instrument to obtain the total signal intensity value Rt of the core's basic T2 spectrum.
[0016] S2: Simulated hydrocarbon accumulation
[0017] The gas reservoir formation process was simulated using core samples. After the water saturation of the core sample reached the original saturation of the gas reservoir, the pore pressure of the core sample was pressurized using simulated natural gas to restore the pore pressure of the core sample to the original formation pressure.
[0018] S3: Gas reservoir development
[0019] The gas reservoir development and production process was simulated, and the nuclear magnetic resonance T2 spectrum of the core at the end of the development and production stage was tested to obtain the total signal intensity value Rm of the core T2 spectrum under gas saturation at the end of the gas reservoir development stage.
[0020] S4: Gas injection into the gas storage facility
[0021] The first simulation of the gas injection process of the gas storage was conducted, and the equilibrium was maintained under the upper limit pressure of the gas storage. The nuclear magnetic resonance T2 spectrum of the core at the end of the first gas injection was tested, and the total signal intensity value Ro-1 of the core T2 spectrum at the end of the first gas injection was obtained.
[0022] S5: Gas extraction from gas storage facility
[0023] The first simulation of gas extraction process in the gas storage facility was conducted, and the equilibrium was maintained under the lower limit pressure of the gas storage facility. The nuclear magnetic resonance T2 spectrum of the core at the end of the first gas extraction was tested, and the total signal intensity value Rp-1 of the core T2 spectrum at the end of the first gas extraction was obtained.
[0024] S6: Multi-round injection and extraction
[0025] Repeat steps S4 and S5. Each repetition constitutes one injection-production cycle of the gas storage facility. The total signal intensity value Ro-n of the core T2 spectrum at the end of the nth round of gas injection and the total signal intensity value Rp-n of the core T2 spectrum at the end of the nth round of gas production are obtained respectively.
[0026] S7: Effective Working Gas Volume Assessment
[0027] The residual gas volume ratio at the end of the gas reservoir development period is calculated based on the total signal intensity value Rt of the basic T2 spectrum of the core and the total signal intensity value Rm of the core under gas saturation at the end of the gas reservoir development period. The working gas volume ratio of the nth round is calculated based on the total signal intensity value Rt of the basic T2 spectrum of the core, the total signal intensity value Ro-n of the core at the end of the nth round of gas injection, and the total signal intensity value Rp-n of the core at the end of the nth round of gas production in the gas storage facility. An evaluation is then conducted based on the residual gas volume ratio and the working gas volume ratio of the nth round.
[0028] The core holder is equipped with a nuclear magnetic resonance acquisition instrument for testing the total signal intensity value of the T2 spectrum. The left end of the core holder is connected to a gas production backpressure valve and an intermediate container A that can provide simulated natural gas via a three-way valve. The right end is connected to an exhaust backpressure valve and an intermediate container B that can provide simulated formation water via a three-way valve. The components work together to realize the basic signal acquisition, simulated reservoir formation, gas reservoir development, gas injection into the gas storage facility, and gas production from the gas storage facility.
[0029] The simulated formation water is formed by adding 2% manganese chloride to formation water and stirring until fully dissolved, resulting in simulated formation water without NMR signals.
[0030] The simulated natural gas is obtained by adding 10% contrast gas to experimental nitrogen and mixing them to obtain simulated natural gas with nuclear magnetic resonance signals.
[0031] The imaging gas is methane, ethane, or xenon, which has a nuclear magnetic resonance signal.
[0032] In step S2, the specific method for simulating the gas reservoir formation process using core samples is as follows: after saturating the core sample with simulated formation water, it is placed into the core holder. The two ends of the core holder are connected to the intermediate container A and the exhaust back pressure valve respectively through a three-way valve. After connection, the core sample saturated with simulated formation water is displaced by simulated natural gas to simulate the gas reservoir formation process.
[0033] In step S3, the specific method for simulating the gas reservoir development and gas production process is as follows: the two ends of the core holder are connected to the gas production back pressure valve and the intermediate container B respectively through the three-way valve. After the connection is made, the gas production back pressure valve is turned on, so that the core pore pressure is slowly reduced to the pressure at the end of the gas production period, thereby realizing the simulated gas reservoir development and gas production process.
[0034] In step S4, the specific method for simulating the gas injection process of the gas storage is as follows: the two ends of the core holder are connected to intermediate container A and intermediate container B respectively through a three-way valve. After connection, the core holder is pressurized to the upper limit pressure of the gas storage using simulated natural gas, thereby realizing the gas injection process of the simulated gas storage.
[0035] In step S5, the specific method for simulating the gas extraction process of the gas storage is as follows: the two ends of the core holder are connected to the gas extraction back pressure valve and the intermediate container B respectively through the three-way valve. After the connection is made, the gas extraction back pressure valve is turned on to reduce the pressure of the gas storage to the lower limit pressure of the gas storage operation, thereby realizing the simulation of the gas extraction process of the gas storage.
[0036] In step S7, the method for calculating the proportion of residual gas volume at the end of the gas reservoir development stage is as follows:
[0037] S gr =R m / R t
[0038] The calculation method for the proportion of working gas volume in the nth round is as follows:
[0039] W n =S o-n -S p-n
[0040] in,
[0041] S o-n =R o-n / R t
[0042] Sp-n =R p-n / R t
[0043] In the formula, S gr W represents the percentage of residual gas at the end of the gas reservoir development phase. n S represents the proportion of working gas volume in the nth round. o-n S represents the percentage of gas content at the end of the nth round of gas injection. p-n This represents the percentage of gas content at the end of the nth round of gas extraction.
[0044] The advantages of using this invention are:
[0045] 1. This invention uses nuclear magnetic resonance to monitor the T2 spectrum signal intensity values of core samples at the end of different gas injection and gas production stages. The T2 spectrum signal intensity values reflect the changes in gas saturation in the core, and the gas content ratio at the end of gas production and the gas content ratio at the end of gas injection are analyzed to obtain the changes in the working gas volume in the core within one injection-production cycle. This allows for a true and accurate reflection of the changes in the working gas volume of water-inundated gas storage tanks across multiple injection-production cycles.
[0046] 2. In the evaluation process, this invention establishes pressure, water saturation, gas storage injection and production cycle time, upper operating pressure, and lower operating pressure that are consistent with the formation conditions. The entire simulation process is consistent with the changes in parameters such as pressure and time during the operation of the gas storage, which is conducive to obtaining more accurate evaluation results.
[0047] 3. In the evaluation process, this invention obtains simulated natural gas with nuclear magnetic resonance (NMR) signals by adding a contrast agent (contrast gas) to nitrogen. The strength of the contrast agent's NMR signal can represent the amount of natural gas in the gas storage facility, thereby accurately reflecting the changes in the working gas volume and bottom gas volume of the gas storage facility. This avoids the complex gas content calculation process caused by pressure changes and makes the calculation of the proportion of working gas volume in the gas storage facility relatively simple.
[0048] 4. Before and after injection and production, this invention uses nuclear magnetic resonance to test the distribution of imaging gas in the core, further clarifying the fluid variation law of natural gas in the microscopic pore throat, and providing a basis for optimizing the construction parameters of the gas storage facility.
[0049] 5. This invention obtains simulated formation water without nuclear magnetic resonance signals by adding 2% manganese chloride to the formation water. This simulated formation water does not generate nuclear magnetic resonance signals. During the nuclear magnetic resonance signal acquisition process, the nuclear magnetic signals generated by the water can be shielded, and only the signals of simulated natural gas can be acquired. This enables accurate monitoring of the working gas volume in multiple injection and production cycles.
[0050] 6. The simulated natural gas used in this invention is composed of nitrogen and contrast gas, and does not directly use combustible gases such as methane as experimental gases, which makes it safer; in addition, the 10% contrast gas added to the simulated natural gas has a low contrast gas concentration, which also makes it safer. Attached Figure Description
[0051] Figure 1 This is a flowchart of the multi-round injection and production effective working gas volume assessment of the present invention;
[0052] Figure 2 This is a schematic diagram of the experimental equipment for monitoring the effective working gas volume in multiple rounds of injection and production according to the present invention.
[0053] Figure 3 This is the nuclear magnetic resonance T2 spectrum corresponding to the working gas volume monitored during the first injection-production cycle of this invention.
[0054] The following are marked in the diagram: 1. Intermediate container A, 2. Intermediate container B, 3. Gas sampling backpressure valve, 4. Exhaust backpressure valve, 5. Three-way valve, 6. Core holder, 7. Nuclear magnetic resonance acquisition instrument. Detailed Implementation
[0055] Example 1
[0056] This embodiment provides a method for evaluating the effective working gas volume of a gas storage facility. This method is implemented based on the following experimental equipment, such as... Figure 2 As shown, it includes a core holder 6, an intermediate container A1, an intermediate container B2, a gas sampling backpressure valve 3, an exhaust backpressure valve 4, a three-way valve 5, a nuclear magnetic resonance (NMR) acquisition instrument 7, and related pipelines. Among them,
[0057] The nuclear magnetic resonance (NMR) acquisition instrument 7 is fixed on the core holder 6 to test the total signal intensity value of the T2 spectrum. The left end of the core holder 6 is connected to the gas production backpressure valve 3 and the intermediate container A1 via a three-way valve 5 and a pipeline, respectively. The right end is connected to the exhaust backpressure valve 4 and the intermediate container B2 via a three-way valve 5 and a pipeline, respectively. The intermediate container A1 stores simulated natural gas, which can provide simulated natural gas to the core holder 6. The intermediate container B2 stores simulated formation water, which can provide simulated formation water to the core holder 6. After all components are connected, through the relevant control and coordination of the three-way valve 5, the basic signal acquisition, simulated reservoir formation, gas reservoir development, gas injection into the gas storage facility, and gas production process in the following process flow can be realized. It should be noted that the aforementioned three-way valve 5 can also be a six-way valve or other related valves.
[0058] It should be noted that the simulated formation water mentioned above is formation water without NMR signals, which can be obtained by adding 2% manganese chloride by mass to formation water and stirring until fully dissolved. The simulated natural gas mentioned above is natural gas with NMR signals, which can be obtained by adding 10% contrast agent gas by mass to experimental nitrogen and mixing thoroughly. Furthermore, the contrast agent gas can be methane, ethane, or xenon, which have NMR signals.
[0059] Based on the above-mentioned experimental equipment, the present invention is achieved through the following technical solutions, such as... Figure 1 As shown, it includes the following steps:
[0060] S1: Preliminary Material Preparation
[0061] Select representative reservoir cores, preferably full-diameter cores; and prepare simulated formation water without NMR signals and simulated natural gas with NMR signals.
[0062] S2: Preparation of Experimental Equipment
[0063] Complete the connection of the above experimental equipment.
[0064] S3: Basic Signal Acquisition
[0065] The dry core is placed into the core holder 6, and the intermediate container A1 is connected to the core holder 6. The simulated natural gas in the intermediate container A1 is used to pressurize the core pore pressure, so that the core pore pressure is restored to the original formation pressure. Then, the nuclear magnetic resonance T2 spectrum of the saturated simulated natural gas core is tested using the nuclear magnetic resonance acquisition instrument 7 to obtain the total signal intensity value Rt of the core basic T2 spectrum.
[0066] The purpose of this step is to test the nuclear magnetic resonance signal of a simulated natural gas-filled core, which can indirectly represent the total pore volume of the core, so as to serve as a benchmark for subsequent multiple rounds of injection and production nuclear magnetic resonance signals.
[0067] S4: Simulated hydrocarbon accumulation
[0068] First, the gas reservoir formation process is simulated using core samples. The specific method is as follows: the core sample is taken out from the core holder 6, saturated with simulated formation water, and then put back into the core holder 6. The two ends of the core holder 6 are connected to the intermediate container A1 and the exhaust back pressure valve 4 respectively through the three-way valve 5. After connection, the core sample saturated with simulated formation water is displaced by simulated natural gas to simulate the gas reservoir formation process.
[0069] Secondly, after the water saturation of the core reaches the original saturation of the gas reservoir, simulated natural gas is used to pressurize the pore pressure of the core, so that the pore pressure of the core is restored to the original formation pressure.
[0070] The purpose of this step is to establish the original stratigraphic conditions of the gas reservoir, so that the gas saturation, pore pressure and other conditions of the experimental core are consistent with the original conditions of the gas reservoir.
[0071] S5: Gas Reservoir Development
[0072] First, the gas reservoir development and gas production process is simulated. The specific method is as follows: the two ends of the core holder 6 are connected to the gas production back pressure valve 3 and the intermediate container B2 respectively through the three-way valve 5. After the connection is made, the gas production back pressure valve 3 is turned on, so that the core pore pressure is slowly reduced to the pressure at the end of the gas production period. This pressure reduction time is usually controlled within 20-30 hours to realize the simulated gas reservoir development and gas production process.
[0073] Secondly, the nuclear magnetic resonance T2 spectrum of the core at the end of the gas production stage was tested to obtain the total signal intensity value Rm of the core T2 spectrum at the gas saturation level at the end of the gas reservoir development stage.
[0074] The purpose of this step is to establish the stratigraphic conditions at the end of gas reservoir development, so that the gas saturation, pore pressure, and other conditions of the experimental core are consistent with the conditions at the end of gas reservoir development.
[0075] S6: Gas injection into the gas storage facility
[0076] First, the gas injection process of the gas storage facility is simulated for the first time. The specific method is as follows: the two ends of the core holder 6 are connected to the intermediate container A1 and the intermediate container B2 respectively through the three-way valve 5. After the connection is made, the core holder 6 is pressurized to the upper limit pressure of the gas storage facility using simulated natural gas. The pressurization time is usually controlled at about 30 minutes to realize the gas injection process of the simulated gas storage facility.
[0077] Secondly, the core holder 6 is kept connected to the intermediate container B2 and kept in balance under the upper limit pressure of the gas storage tank. The balance time can be about 5 minutes to simulate the balance period after gas injection in the gas storage tank.
[0078] Finally, the T2 nuclear magnetic resonance spectrum of the core at the end of the first gas injection of the gas storage was tested, and the total signal intensity value Ro-1 of the T2 spectrum of the core at the end of the first gas injection of the gas storage was obtained.
[0079] The purpose of this step is to simulate the change in gas saturation of the core after the gas storage facility starts injecting gas, so that the experimental core reaches the upper limit pressure of the gas storage facility and obtains the gas saturation under the corresponding conditions.
[0080] S7: Gas extraction from gas storage facility
[0081] First, the gas extraction process of the gas storage facility is simulated for the first time. The specific method is as follows: the two ends of the core holder 6 are connected to the gas extraction back pressure valve 3 and the intermediate container B2 respectively through the three-way valve 5. After the connection is made, the gas extraction back pressure valve 3 is turned on to reduce the pressure of the gas storage facility to the lower limit pressure of the gas storage facility. The pressure reduction time is usually controlled at about 20 minutes to realize the simulation of the gas extraction process of the gas storage facility.
[0082] Secondly, continue to keep the core holder 6 connected to the intermediate container B2 and maintain balance under the lower limit pressure of the gas storage tank. The balance time can be about 5 minutes to simulate the balance period after gas extraction from the gas storage tank.
[0083] Finally, the nuclear magnetic resonance T2 spectrum of the core at the end of the first gas production of the gas storage was tested, and the total signal intensity value Rp-1 of the T2 spectrum of the core at the end of the first gas production of the gas storage was obtained.
[0084] The purpose of this step is to simulate the change in gas saturation of the core sample after the gas storage facility begins gas extraction, so that the experimental core sample reaches the lower limit pressure of the gas storage facility and obtains the gas saturation under the corresponding conditions.
[0085] S8: Multi-round injection
[0086] Repeat steps S6 and S7. Each repetition constitutes one injection-production cycle of the gas storage facility. Obtain the total signal intensity value Ro-n of the core T2 spectrum at the end of the nth injection cycle and the total signal intensity value Rp-n of the core T2 spectrum at the end of the nth production cycle.
[0087] The purpose of this step is to simulate the change in gas saturation of the core during multiple injection and production processes in the gas storage facility, and to obtain the gas saturation of the experimental core after multiple injection and production processes.
[0088] S9: Effective Working Gas Volume Assessment
[0089] The residual gas volume ratio at the end of the gas reservoir development period is calculated based on the total signal intensity value Rt of the basic T2 spectrum of the core and the total signal intensity value Rm of the T2 spectrum of the core at the gas saturation level at the end of the gas reservoir development period. The specific calculation method is as follows:
[0090] S gr =R m / R t
[0091] In the formula, S gr This represents the percentage of residual gas at the end of the gas reservoir's development phase.
[0092] The percentage of gas content at the end of the nth round of gas injection is calculated based on the total signal intensity value Rt of the T2 spectrum of the core and the total signal intensity value Ro-n of the T2 spectrum of the core at the end of the nth round of gas injection. The specific calculation method is as follows:
[0093] S o-n =R o-n / R t
[0094] In the formula, S o-n This represents the percentage of gas content at the end of the nth round of gas injection.
[0095] The percentage of gas content at the end of the nth round of gas production is calculated based on the total signal intensity value Rt of the T2 spectrum of the core sample and the total signal intensity value Rp-n of the T2 spectrum of the core sample at the end of the nth round of gas production in the gas storage facility. The specific calculation method is as follows:
[0096] S p-n =Rp-n / R t
[0097] In the formula, S p-n This represents the percentage of gas content at the end of the nth round of gas extraction.
[0098] The proportion of working gas volume in the nth round is calculated based on the proportion of gas content at the end of the nth round of gas injection and the proportion of gas content at the end of the nth round of gas production. The specific calculation method is as follows:
[0099] W n =S o-n -S p-n
[0100] In the formula, W n This represents the percentage of working gas volume in the nth round.
[0101] Finally, an evaluation can be conducted based on the residual gas volume percentage calculated above and the working gas volume percentage in the nth round.
[0102] The purpose of this step is to assess the proportion of gas at the end of the injection phase, the proportion of gas at the end of the production phase, and the proportion of working gas in the experimental core during different injection and production cycles by using the nuclear magnetic resonance signal intensity values monitored during multiple injection and production processes.
[0103] Example 2
[0104] This embodiment verifies the method of Embodiment 1, such as... Figure 1 As shown, the details are as follows:
[0105] Taking the Maokou Formation gas reservoir in the LWC gas field as an example, representative core samples were selected, and the effective working gas volume was assessed through multiple rounds of injection and production using the method described in the example. The Maokou Formation gas reservoir in the LWC gas field has a burial depth of 2200–2600 m, an original formation pressure of 24 MPa, a formation temperature of 75 °C, and localized edge water at the reservoir's periphery. The upper limit pressure of the gas storage facility is 23.9 MPa, and the lower limit pressure is 9 MPa.
[0106] S1: Preliminary Material Preparation
[0107] Select representative reservoir cores, which are full-diameter cores with a length of 7.5 cm and a diameter of 12.5 cm.
[0108] Add 2% manganese chloride to the formation water, stir until fully dissolved, and prepare simulated formation water without NMR signals.
[0109] In the experiment, 10% contrast gas, namely methane gas with NMR signal, was added to nitrogen gas to prepare simulated natural gas with NMR signal.
[0110] S2: Preparation of Experimental Equipment
[0111] Connect the left end of the core holder 6 to the intermediate container A1 and the gas extraction back pressure valve 3, with the three-way valve 5 controlling the middle; connect the right end of the core holder 6 to the intermediate container B2 and the exhaust back pressure valve 4, with the three-way valve 5 controlling the middle.
[0112] S3: Basic Signal Acquisition
[0113] Place the dry core into the core holder 6, keeping the left end connected to the middle container A1.
[0114] The core pore pressure was increased by simulating natural gas, restoring it to the original formation pressure of 24 MPa.
[0115] The T2 nuclear magnetic resonance spectrum of saturated simulated natural gas core was tested to obtain the total signal intensity value Rt of the basic T2 spectrum of the core.
[0116] S4: Simulated hydrocarbon accumulation
[0117] The gas reservoir formation process was simulated, and when the water saturation of the core reached the original saturation of the gas reservoir, the pore pressure of the core was pressurized by simulating natural gas, so that the pore pressure of the core was restored to the original formation pressure of 24 MPa.
[0118] S5: Gas Reservoir Development
[0119] The gas reservoir development and production process was simulated, and the core nuclear magnetic resonance T2 spectrum at the end of the development and production stage was tested to obtain the total signal intensity value Rm of the core T2 spectrum under gas saturation at the end of the gas reservoir development stage.
[0120] S6: Gas injection into the gas storage facility
[0121] Keep intermediate containers A1 and B2 connected to core holder 6, and pressurize core holder 6 with simulated natural gas to the upper limit pressure of the gas storage facility, 23.9 MPa. The pressurization time is controlled within 30 minutes, and the first simulation of the gas injection process of the gas storage facility is carried out.
[0122] Keep intermediate container B2 connected to core holder 6, maintain the pressure at the upper limit of gas storage operation, and maintain the equilibrium time for 5 minutes to simulate the equilibrium period after gas injection into the gas storage.
[0123] The T2 nuclear magnetic resonance spectrum of the core at the end of the first gas injection of the gas storage was tested, and the total signal intensity value Ro-1 of the T2 spectrum of the core at the end of the first gas injection of the gas storage was obtained.
[0124] S7: Gas extraction from gas storage facility
[0125] Keep the gas extraction back pressure valve 3 and the intermediate container B2 connected to the core holder 6. Open the gas extraction back pressure valve 3 to reduce the pressure to the lower limit of the gas storage operation pressure of 9MPa. The pressure reduction time is about 20 minutes. This is the first simulation of the gas extraction process of the gas storage.
[0126] Keep intermediate container B2 connected to core holder 6, maintain the pressure at the lower limit of gas storage operation, and maintain the balance time for 5 minutes to simulate the balance period after gas extraction from the gas storage.
[0127] Test the T2 NMR spectrum of the core at the end of the first gas production stage of the gas storage facility, such as... Figure 3 As shown, the total signal intensity value Rp-1 of the T2 spectrum of the core at the end of the first gas extraction of the gas storage was obtained.
[0128] S8: Multi-round injection
[0129] Repeat steps S6 and S7 for 6 rounds of injection and production, and obtain the total signal intensity value Ro-n of the core T2 spectrum at the end of the 6 rounds of gas injection and the total signal intensity value Rp-n of the core T2 spectrum at the end of the 6 rounds of gas production.
[0130] S9: Effective Working Gas Volume Assessment
[0131] The residual gas volume ratio at the end of the gas reservoir development and the working gas volume ratio in each injection and production cycle were calculated and are shown in Table 1.
[0132] Table 1. Estimated percentage of working gas volume in each injection / production cycle.
[0133]
[0134]
[0135] As shown in the table above, after six rounds of simulated gas injection and production operations, the percentage of working gas volume in each cycle was 0.45, 0.41, 0.43, 0.50, 0.55, and 0.54, respectively. Due to water intrusion, the percentage of working gas volume in the gas storage ultimately stabilized at around 0.55. This demonstrates that the present invention can accurately reflect the changing patterns of working gas volume in water-intrusion-type gas storage facilities across multiple injection and production cycles, thus providing a basis for the rational operation of water-intrusion-type gas storage facilities.
[0136] The above description is merely a specific embodiment of the present invention. Any feature disclosed in this specification may be replaced by other equivalent or similar features unless otherwise specified. All features or steps in the disclosed methods or processes may be combined in any way, except for mutually exclusive features and / or steps.
Claims
1. A method for evaluating the effective working gas volume of a gas storage facility, characterized in that... Includes the following steps: S1: Basic Signal Acquisition Select reservoir cores, place the cores into a core holder, and restore them to the original formation pressure using simulated natural gas pressurization. Use a nuclear magnetic resonance acquisition instrument to test the nuclear magnetic resonance T2 spectrum of the saturated simulated natural gas cores to obtain the total signal intensity value Rt of the core basic T2 spectrum. S2: Simulated hydrocarbon accumulation The gas reservoir formation process was simulated using core samples. After the water saturation of the core sample reached the original saturation of the gas reservoir, the pore pressure of the core sample was pressurized using simulated natural gas to restore the pore pressure of the core sample to the original formation pressure. S3: Gas reservoir development The gas reservoir development and production process was simulated, and the nuclear magnetic resonance T2 spectrum of the core at the end of the development and production stage was tested to obtain the total signal intensity value Rm of the core T2 spectrum under gas saturation at the end of the gas reservoir development stage. S4: Gas injection into the gas storage facility The first simulation of the gas injection process of the gas storage was conducted, and the equilibrium was maintained under the upper limit pressure of the gas storage. The nuclear magnetic resonance T2 spectrum of the core at the end of the first gas injection was tested, and the total signal intensity value Ro-1 of the core T2 spectrum at the end of the first gas injection was obtained. S5: Gas extraction from gas storage facility The first simulation of gas extraction process in the gas storage facility was conducted, and the equilibrium was maintained under the lower limit pressure of the gas storage facility. The nuclear magnetic resonance T2 spectrum of the core at the end of the first gas extraction was tested, and the total signal intensity value Rp-1 of the core T2 spectrum at the end of the first gas extraction was obtained. S6: Multi-round injection and extraction Repeat steps S4 and S5. Each repetition constitutes one injection-production cycle of the gas storage facility. The total signal intensity value Ro-n of the core T2 spectrum at the end of the nth round of gas injection and the total signal intensity value Rp-n of the core T2 spectrum at the end of the nth round of gas production are obtained respectively. S7: Effective Working Gas Volume Assessment The residual gas volume ratio at the end of the gas reservoir development period is calculated based on the total signal intensity value Rt of the basic T2 spectrum of the core and the total signal intensity value Rm of the core under gas saturation at the end of the gas reservoir development period. The working gas volume ratio of the nth round is calculated based on the total signal intensity value Rt of the basic T2 spectrum of the core, the total signal intensity value Ro-n of the core at the end of the nth round of gas injection, and the total signal intensity value Rp-n of the core at the end of the nth round of gas production in the gas storage facility. An evaluation is then conducted based on the residual gas volume ratio and the working gas volume ratio of the nth round. The core holder is equipped with a nuclear magnetic resonance (NMR) instrument for testing the total signal intensity of the T2 spectrum. The left end of the core holder is connected to a gas production backpressure valve and an intermediate container A that can provide simulated natural gas via a three-way valve. The right end is connected to an exhaust backpressure valve and an intermediate container B that can provide simulated formation water via a three-way valve. The components work together to realize the basic signal acquisition, simulated reservoir formation, gas reservoir development, gas injection into the gas storage facility, and gas production from the gas storage facility. The simulated formation water is formed by adding 2% manganese chloride to formation water and stirring until fully dissolved, resulting in simulated formation water without nuclear magnetic resonance signals. The simulated natural gas is obtained by adding 10% contrast gas to experimental nitrogen and mixing it to obtain simulated natural gas with nuclear magnetic resonance signal; The imaging gas is methane, ethane, or xenon, which has a nuclear magnetic resonance signal.
2. The method for evaluating the effective working gas volume of a gas storage facility according to claim 1, characterized in that: In step S2, the specific method for simulating the gas reservoir formation process using core samples is as follows: after saturating the core sample with simulated formation water, it is placed into the core holder. The two ends of the core holder are connected to the intermediate container A and the exhaust back pressure valve respectively through a three-way valve. After connection, the core sample saturated with simulated formation water is displaced by simulated natural gas to simulate the gas reservoir formation process.
3. The method for evaluating the effective working gas volume of a gas storage facility according to claim 1, characterized in that: In step S3, the specific method for simulating the gas reservoir development and gas production process is as follows: the two ends of the core holder are connected to the gas production back pressure valve and the intermediate container B respectively through the three-way valve. After the connection is made, the gas production back pressure valve is turned on, so that the core pore pressure is slowly reduced to the pressure at the end of the gas production period, thereby realizing the simulated gas reservoir development and gas production process.
4. The method for evaluating the effective working gas volume of a gas storage facility according to claim 1, characterized in that: In step S4, the specific method for simulating the gas injection process of the gas storage is as follows: the two ends of the core holder are connected to intermediate container A and intermediate container B respectively through a three-way valve. After connection, the core holder is pressurized to the upper limit pressure of the gas storage using simulated natural gas, thereby realizing the gas injection process of the simulated gas storage.
5. The method for evaluating the effective working gas volume of a gas storage facility according to claim 1, characterized in that: In step S5, the specific method for simulating the gas extraction process of the gas storage is as follows: the two ends of the core holder are connected to the gas extraction back pressure valve and the intermediate container B respectively through the three-way valve. After the connection is made, the gas extraction back pressure valve is turned on to reduce the pressure of the gas storage to the lower limit pressure of the gas storage operation, thereby realizing the simulation of the gas extraction process of the gas storage.
6. The method for evaluating the effective working gas volume of a gas storage facility according to claim 1, characterized in that: In step S7, the method for calculating the proportion of residual gas volume at the end of the gas reservoir development stage is as follows: S gr =R m / R t The calculation method for the proportion of working gas volume in the nth round is as follows: W n = S o-n -S p-n in, S o-n =R o-n / R t S p-n =R p-n / R t In the formula, S gr W represents the percentage of residual gas at the end of the gas reservoir development phase. n S represents the proportion of working gas volume in the nth round. o-n S represents the percentage of gas content at the end of the nth round of gas injection. p-n This represents the percentage of gas content at the end of the nth round of gas extraction.