Method for determining lower limit pressure of weak water drive gas reservoir gas storage

Abstract

This invention discloses a method for determining the lower limit pressure of a gas storage facility in a weak water-drive oil and gas reservoir. The method includes the following steps: 1. Determining the effective gas storage pore volume of the reservoir and the storage capacity under different formation pressures; 2. Calculating the working gas volume of the gas storage facility corresponding to different lower limit pressures; 3. Calculating the average daily gas production during the winter peak-shaving gas production period of the gas storage facility; 4. Evaluating the reasonable production capacity of gas wells corresponding to different lower limit pressures; 5. Calculating the number of gas wells required for winter peak-shaving production of the gas storage facility to meet the coordination requirements of gas well production nodes; 6. Calculating the well-controlled seepage area of ​​a single gas well at different lower limit pressures; 7. Calculating the number of gas wells required for winter peak-shaving production of the gas storage facility to meet the requirements for effective control of the effective oil and gas-bearing area of ​​the reservoir. This method solves the problems of lower limit pressure design not considering effective storage capacity control and the optimal coordination between efficient gas export at the end of production and effective storage capacity control.

Description

Technical Field

[0001] This invention relates to the field of underground natural gas storage technology, and more specifically, to a method for determining the lower limit pressure of a gas storage facility in a weak water-drive oil and gas reservoir. Background Technology

[0002] Oil and gas reservoir-type gas storage facilities are underground natural gas storage facilities converted from oil and gas reservoirs in the mid-to-late stages of development or those that have been depleted. They have functions such as natural gas peak shaving and supply guarantee, pipeline accident emergency response, and strategic energy reserves. Currently, oil and gas reservoir-type gas storage facilities (hereinafter referred to as gas storage facilities) are the type of gas storage facilities with the highest proportion of working gas volume among the four types of gas storage facilities worldwide. They have multiple advantages, such as large natural gas storage scale, relatively clear understanding of underground geological characteristics, and the availability of some existing engineering facilities in the oil and gas field. Water-driven oil and gas reservoirs are the first choice and the best target for converting them into gas storage facilities.

[0003] The lower limit pressure (hereinafter referred to as the lower limit pressure) refers to the lowest formation pressure that a gas storage facility can achieve during winter peak-shaving gas production. The lower the lower limit pressure, the larger the working gas volume of the gas storage facility. However, the lower formation pressure at the end of the gas production period will result in lower well productivity. To achieve the working gas volume in 120-150 days, more new injection and production wells need to be drilled, and the total investment in the gas storage facility construction project will be higher. At the same time, a lower lower limit pressure may cause the wellhead pressure at the end of the gas storage facility to be lower than the minimum pressure required by the natural gas transmission pipeline, resulting in the need to use compressors to reverse pressurize and transmit natural gas at the end of the gas production period, which will increase the operating cost of the gas storage facility. On the other hand, a higher lower limit pressure will result in a smaller working gas volume of the gas storage facility, making it impossible to maximize the utilization of underground gas storage space and wasting the storage capacity.

[0004] Clearly, the design of the lower limit pressure of gas storage facilities is closely related to the number of injection and production wells and the pressure requirements of natural gas export wellheads. The technical lower limit pressure design of gas storage facilities needs to consider multiple factors simultaneously, including the scale of working gas production (peak-shaving capacity), efficient natural gas export at the end of production, effective control of storage capacity, and the number of new wells drilled for storage construction, to comprehensively optimize and determine a reasonable lower limit pressure. However, currently, there is a lack of design methods for the lower limit pressure of gas storage facilities that consider the above multiple factors, especially those considering effective control of storage capacity (such as the article "A New Method for Designing the Lower Limit Pressure of Gas Storage Facilities for Reservoir Reconstruction" in the November 2020 issue of *Natural Gas Geoscience*, Volume 31). This method only considers the impact of the number of wells drilled and engineering investment on the lower limit pressure, and particularly fails to consider the impact of single-well control during winter peak-shaving production on the lower limit pressure, thus having certain limitations in technical application. Summary of the Invention

[0005] The purpose of this invention is to provide a method for determining the lower limit pressure of a gas storage facility in a weak water-driven oil and gas reservoir, so as to obtain the lower limit pressure that achieves the synergy between efficient gas output and effective storage capacity control during winter peak shaving. This solves the problem in the prior art that the lower limit pressure design does not consider effective storage capacity control and the optimal synergy between efficient gas output and effective storage capacity control at the end of gas production.

[0006] The technical solution provided by this invention is: a method for determining the lower limit operating pressure of a gas storage facility in a weak water-drive oil and gas reservoir, comprising the following steps:

[0007] Step 1: Based on the geological and development dynamics of the oil and gas reservoir and the results of laboratory simulation, determine the effective gas storage pore volume of the reservoir and the inventory under different formation pressures.

[0008] Step 2: Based on the gas storage capacity and the determined upper limit pressure, calculate the working gas volume of the gas storage corresponding to different lower limit pressures.

[0009] Step 3: Based on the working gas volume corresponding to different lower limit pressures, and according to the number of days of peak-shaving gas production during winter as determined by the gas storage construction plan, calculate the average daily gas production during the winter peak-shaving gas production period of the gas storage facility.

[0010] Step 4: Based on the binomial production capacity equation of the gas wells in the gas storage facility, use the nodal analysis method to evaluate the reasonable production capacity of the gas wells corresponding to different lower limit pressures;

[0011] Step 5: Divide the average daily gas production during the winter peak-shaving gas production period of the gas storage facility corresponding to different lower limit pressures by the reasonable production capacity of the gas wells at the corresponding lower limit pressures to calculate the number of gas wells required for the winter peak-shaving production of the gas storage facility to meet the coordination requirements of the gas well production nodes.

[0012] Step 6: Based on the reasonable production capacity of gas wells in the gas storage facility corresponding to different lower limit pressures, the high-speed unstable seepage equation is used to calculate the well-controlled seepage area of ​​gas wells at different lower limit pressures.

[0013] Step 7: Divide the effective oil and gas-bearing area of ​​the reservoir into the well control seepage area of ​​the gas wells in the gas storage facility at different lower limit pressures to calculate the number of gas wells required for winter peak-shaving production of the gas storage facility to meet the requirements for effective control of the effective oil and gas-bearing area of ​​the reservoir.

[0014] Step 8: Using the lower limit pressure as the horizontal axis and the number of production wells as the vertical axis, overlay the relationship curve of the number of wells required for winter peak-shaving production of gas storage facilities to meet the coordination requirements of gas well production nodes and the relationship curve of the number of wells required for winter peak-shaving production of gas storage facilities to meet the requirements of effective control of the effective oil and gas-bearing area of ​​the reservoir on the same coordinate system.

[0015] Step 9: Based on the intersection characteristics of the two curves mentioned above, design the lower limit pressure for gas storage operation, specifically as follows:

[0016] If the two curves mentioned above intersect, the wellhead pressure corresponding to the lower limit pressure at the intersection point is calculated using the gas well pipeline flow and the average daily gas production during the winter peak-shaving gas production period of the gas storage facility. It is then determined whether the wellhead pressure at this point meets the minimum wellhead pressure required by the natural gas surface transmission pipeline. If it does, then the intersection point is the lower limit pressure that simultaneously meets the triple requirements of coordinated gas well production nodes for peak-shaving gas production in the gas storage facility, effective control of the gas-bearing area of ​​the reservoir, and the minimum wellhead pressure required by the natural gas surface transmission pipeline.

[0017] B. If the two curves mentioned above intersect, the wellhead pressure corresponding to the lower limit pressure at the intersection point is calculated using the gas well pipeline flow and the average daily gas production during the winter peak-shaving gas production period of the gas storage facility. It is then determined whether the wellhead pressure at this point meets the minimum wellhead pressure required by the natural gas surface transmission pipeline. If the calculated wellhead pressure is less than the minimum wellhead pressure required by the natural gas surface transmission pipeline, but as the lower limit pressure increases, the number of production wells required for the coordination of gas well nodes during the winter peak-shaving gas production period of the gas storage facility is higher than the number of production wells required for effective control of the effective oil and gas area of ​​the reservoir, then based on the former and combined with the working gas volume corresponding to different lower limit pressures, the average daily gas production per well and its corresponding wellhead pressure during the winter peak-shaving gas production period of the gas storage facility are calculated. Then, according to the minimum external transmission wellhead pressure required by the natural gas surface transmission pipeline, the lower limit pressure of the gas storage facility is calculated using the gas well pipeline flow and production capacity equations.

[0018] C. If the two curves mentioned above intersect, the wellhead pressure corresponding to the lower limit pressure at the intersection point is calculated using the gas well pipeline flow and the average daily gas production during the winter peak-shaving gas production period of the gas storage facility. It is then determined whether the wellhead pressure at this point meets the minimum wellhead pressure required by the natural gas surface transmission pipeline. If the calculated wellhead pressure is less than the minimum wellhead pressure required by the natural gas surface transmission pipeline, but as the lower limit pressure increases, the number of production wells required for the coordination of gas well nodes during the winter peak-shaving gas production period of the gas storage facility is lower than the number of production wells required for effective control of the effective oil and gas area of ​​the reservoir, then based on the latter and combined with the working gas volume corresponding to different lower limit pressures, the average daily gas production per well and its corresponding wellhead pressure during the winter peak-shaving gas production period of the gas storage facility are calculated. Then, according to the minimum external transmission wellhead pressure required by the natural gas surface transmission pipeline, the lower limit pressure of the gas storage facility is calculated using the gas well pipeline flow and production capacity equations.

[0019] D. If the two curves mentioned above do not intersect, and the curve of the number of production wells that meets the requirements for coordination of gas well nodes in winter peak-shaving gas production of the gas storage is higher than the curve of the number of production wells that meets the requirements for effective control of the effective oil and gas area of ​​the reservoir, then based on the former, combined with the working gas volume and number of gas wells corresponding to different lower limit pressures, the average daily gas production of a single well and its corresponding wellhead pressure during the winter peak-shaving gas production of the gas storage are calculated. Then, based on the minimum wellhead pressure required by the natural gas surface transmission pipeline, the lower limit pressure of the gas storage is calculated by using the gas well pipeline flow and production capacity equation.

[0020] If the two curves mentioned above do not intersect, and the number of production wells that meet the requirements for coordinating gas well nodes during winter peak-shaving gas production in the gas storage facility is lower than the number of production wells that meet the requirements for effective control of the effective oil and gas area of ​​the reservoir, then based on the latter, and combined with the working gas volume and number of gas wells corresponding to different lower limit pressures, the average daily gas production of a single well and its corresponding wellhead pressure during the winter peak-shaving gas production period of the gas storage facility are calculated. Then, based on the minimum wellhead pressure required by the natural gas surface transmission pipeline, the lower limit pressure of the gas storage facility is calculated by using the gas well pipeline flow and production capacity equation.

[0021] Step 1, which involves determining the effective gas storage pore volume of the reservoir and the storage capacity under different formation pressures, includes:

[0022] Using data on reservoir development dynamics, laboratory gas injection displacement, and high-pressure physical properties of crude oil and natural gas, for weak water-drive reservoirs, according to formula V... ge =(N oi ×B oi )×η og ×E og For weak water-driven gas reservoirs, according to formula V ge = (G×B gri )-V wflux ×(1-E wg )-V lowpg The effective gas-bearing pore volume of the reservoir was calculated separately; using formula I e =V ge / B ginj The gas storage inventory curve was calculated.

[0023] Among them, V ge For the effective gas storage pore volume of the reservoir for oil and gas reservoir construction, N oi To assess the dynamic crude oil reserves of an oil reservoir based on material balance evaluation, B oi η is the crude oil volume factor under the original formation pressure of the reservoir. og E represents the macroscopic sweep efficiency of gas drive reservoir construction, determined based on indoor simulation experiments or reservoir numerical simulations. ogG represents the reservoir's microscopic gas drive efficiency determined based on indoor simulation experiments, and B represents the dynamic gas reservoir reserves based on material balance evaluation. gri B is the natural gas volume factor of the gas reservoir under the original formation pressure. ging V is the natural gas volume factor of the gas reservoir at any pressure. wflux E represents the gas-bearing pore volume affected by edge and bottom water intrusion during gas reservoir development. wg To determine the microscopic gas drive efficiency in the water-flooded zone of a gas reservoir based on indoor simulation experiments, V lowpg I represents the gas-bearing pore volume of the reservoir with poor physical properties, as determined by geological evaluation. e This represents the inventory levels under different formation pressures.

[0024] Step 2 involves calculating the working gas volume of the gas storage facility corresponding to different lower pressure limits, based on the formula... Calculated;

[0025] Among them, B ginjmax Let Q be the gas reservoir volume factor under the upper limit pressure of the gas storage facility. wg The working gas volume of the gas storage facility corresponding to different lower pressure limits.

[0026] Step 3 describes the calculation of the average daily gas extraction volume during the winter peak-shaving gas extraction period of the gas storage facility, based on the formula Q. pg =Q wg / t is calculated.

[0027] Where t represents the number of days of peak-shaving gas production in the gas storage facility during winter, and Q... pg This represents the average daily gas extraction volume during the winter peak-shaving gas extraction period of the gas storage facility.

[0028] The binomial productivity equation mentioned in step 4 is: p R 2 -p wf 2 =Aq sc +Bq sc 2 ,

[0029] Among them, coefficients A and B are obtained based on Darcy's flow theory or well test data from the mine, and their mathematical expressions calculated based on Darcy's flow theory are as follows:

[0030]

[0031]

[0032] Where, p R Formation pressure; p wf The bottom-hole flowing pressure; q scR is the daily production of the gas well; K is the effective permeability of the gas phase in the reservoir; h is the effective thickness of the reservoir; r e Provide the radius for the gas well; r w γ is the radius of the gas wellbore; g The relative density of the gas; The average viscosity of the gas; is the gas average deviation factor; β is the velocity coefficient; S is the skin coefficient; T is the reservoir temperature.

[0033] Step 5 describes using node analysis to evaluate the reasonable production capacity of gas wells under different lower limit pressures. This includes plotting inflow (binomial production capacity equation) and outflow (wellbore flow dynamics) curves for different lower limit pressures. Under the same lower limit pressure, the inflow and outflow curves intersect at a series of points. Further considering the constraints of critical sand production differential, critical fluid carrying capacity, and erosion flow rate, the gas well production capacity must be less than the production capacity limited by the critical sand production differential and erosion flow rate, while simultaneously being greater than the production capacity limited by the critical fluid carrying capacity. A comprehensive evaluation of the reasonable production capacity q under different lower limit pressures is then conducted. npg .

[0034] Step 6 involves calculating the number of gas wells required for winter production in the gas storage facility to meet the coordination requirements of gas well production nodes. This number is then calculated using the formula N. nw =Q pg / q npg Calculated;

[0035] Where, N nw To meet the coordination requirements of gas well production nodes and the number of gas wells required for winter production in gas storage facilities, Q pg q represents the average daily gas production during the winter peak-shaving gas production period of the gas storage facility, corresponding to different lower pressure limits. npg To Q pg Reasonable production capacity of gas wells at different lower pressure limits.

[0036] The equation for high-speed unsteady seepage is:

[0037]

[0038] Among them, pseudo-pressure The mathematical expression is:

[0039]

[0040] Where, p min p is the lower limit pressure of the gas storage facility. max T represents the upper limit pressure of the gas storage facility. sc φ is the surface standard temperature; t is the number of days of peak-shaving production in the gas storage facility during winter; φ is the reservoir porosity; μ is the gas viscosity; C t R is the overall compressibility coefficient of the formation; K is the effective gas permeability of the reservoir;e r is the radius of the controlled seepage flow of a gas well. w B is the radius of the gas well shaft; g is the gas volume factor; h is the effective reservoir thickness; r D t is the dimensionless radial distance; D Dimensionless time; Q D This is dimensionless output.

[0041] Step 7 describes the calculation of the well-controlled seepage area of ​​a gas well at different lower limit pressures, based on the formula... Calculated.

[0042] Among them, A w R represents the well-controlled seepage area of ​​a single gas well in a gas storage facility. e The seepage radius is used to control the seepage radius of gas wells and gas production wells in gas storage facilities.

[0043] The number of gas production wells required for winter peak-shaving production of the gas storage facility, as described in step 8, to meet the effective control requirements of the effective oil and gas-bearing area of ​​the reservoir, is calculated according to formula N. rw =A r / A w Calculated.

[0044] Where, N rw To meet the requirements for effective control of the effective oil and gas-bearing area of ​​the reservoir, the number of gas production wells needed for winter peak-shaving production of the gas storage facility, A r For the effective oil and gas-bearing area of ​​the reservoir, A w This refers to the well-controlled seepage area of ​​a single gas well in a gas storage facility.

[0045] The well-controlled seepage area of ​​a gas well at different lower limit pressures is as follows: when the lower limit pressure of the gas storage is different, the well control radius of the gas well calculated according to the high-speed unstable seepage theory is different, and the number of wells that can effectively control the oil and gas area and storage capacity is also different.

[0046] The beneficial effects of this invention are:

[0047] 1. Existing methods, when designing the lower limit pressure of gas storage facilities, fail to consider the impact of well control radius, seepage area, and well network on the effective utilization of storage capacity due to limited-time peak-shaving production during winter. This fails to reflect the influence of the number of wells on the lower limit pressure and the economic benefits of storage facility construction. During high-speed, limited-time production operations, lower lower limit pressures and smaller well control radii and seepage areas require more wells to effectively utilize storage capacity, resulting in higher total investment in the storage facility construction project. Therefore, there is a direct and close correlation between the lower limit pressure of gas storage facilities and the number of production wells. Existing methods, by neglecting the control of individual production wells, may lead to large errors in the design of the number of new wells drilled for storage facility construction, resulting in excessive drilling or insufficient well control, causing wasted investment or insufficient utilization of underground gas storage space. This method, through high-speed unstable seepage theory, evaluates the well control radius and well-controlled seepage area under different lower limit pressures during high-speed, limited-time production in gas storage facilities. It can accurately determine the number of wells required to achieve effective oil and gas area and effective storage capacity control, providing a scientific basis for the optimized design of the lower limit pressure.

[0048] 2. Compared with existing methods that only consider meeting the requirements of natural gas pipeline transportation during winter peak-shaving gas production from gas storage facilities or minimizing drilling engineering investment based on the experience of existing gas storage facilities, this method proposes to simultaneously meet the two core factors of efficient natural gas pipeline transportation and effective storage capacity control during winter peak-shaving gas production from gas storage facilities. It plots the number of gas production wells that meet both natural gas transportation (node ​​coordination) and effective storage capacity control on the same coordinate system. The lower limit pressure of the gas storage facility is designed by comprehensively analyzing the intersection of the two curves and their corresponding number of wells, the final wellhead pressure, etc., or by analyzing the relationship between the two curves and the lower limit pressure (when there is no intersection), and the relationship between the number of wells, the final wellhead pressure, and the natural gas transportation pressure requirements, to design and determine the lower limit pressure of the gas storage facility. This method overcomes the shortcomings of conventional design methods that do not consider factors such as the limited-rate peak-shaving gas production radius of single wells in winter gas storage facilities and its decrease with decreasing lower limit pressure, and the coordination between effective storage capacity control and gas production transportation, significantly improving the scientificity and accuracy of the lower limit pressure design of gas storage facilities.

[0049] 3. This method differs from conventional methods in that, based on the geological characteristics of converting weak water-driven oil and gas reservoirs into gas storage facilities, it employs the high-speed unstable seepage theory to calculate the well control radius and seepage area of ​​gas production wells at different lower limit pressures, thereby determining the number of wells required to achieve effective storage capacity control. Furthermore, the curves of the number of wells required to achieve efficient gas production and external transmission during winter peak shaving in the gas storage facility and the number of wells required for effective storage capacity control are overlaid and plotted on the same coordinate system. The lower limit pressure of the gas storage facility is designed by comprehensively analyzing the intersection of the two curves and their corresponding number of wells, the final wellhead pressure of gas production, etc. Attached Figure Description

[0050] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, are not intended to limit the scope of the invention. In the drawings:

[0051] Figure 1 This is a schematic diagram of the process of the present invention;

[0052] Figure 2 This is a graph showing the inventory curves of the oil and gas reservoirs in this invention.

[0053] Figure 3 This is a diagram showing the relationship between formation pressure and reasonable production capacity of a typical single well, as presented in this invention.

[0054] Figure 4 This is a diagram showing the relationship between gas reservoir formation pressure and reasonable production capacity of a typical single well, as presented in this invention.

[0055] Figure 5 This is a diagram showing the relationship between formation pressure and well control radius according to the present invention;

[0056] Figure 6 This is a schematic diagram illustrating the design of the lower limit operating pressure of the gas storage facility according to the present invention.

[0057] Figure 7 This is the design diagram of the lower limit operating pressure of the Bohai Gas Storage Facility according to the present invention;

[0058] Figure 8 This is a comparison chart of the lower limit pressure and working gas volume of the gas storage facility calculated by different methods of the present invention. Detailed Implementation

[0059] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0060] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0061] refer to Figure 1 As shown, this invention provides a method for determining the lower operating limit pressure of a gas storage facility in a weak water-drive oil and gas reservoir, comprising the following steps:

[0062] Step S101: Based on dynamic data of oil and gas reservoir development, determine the effective gas storage pore volume of the reservoir and the gas storage capacity under different formation pressures. Specifically:

[0063] Using data on reservoir development dynamics, laboratory gas injection displacement, and high-pressure physical properties of crude oil and natural gas, for weak water-drive reservoirs, according to formula V... ge =(N oi ×B oi )×η og ×E ogFor weak water-driven gas reservoirs, according to formula V ge = (G×B gri )-V wflux ×(1-E wg )-V lowpg The effective gas-bearing pore volume of the reservoir was calculated separately; using formula I e =V ge / B ginj The gas storage inventory curve was calculated.

[0064] Among them, V ge For the effective gas storage pore volume of the reservoir for oil and gas reservoir construction, N oi To assess the dynamic crude oil reserves of an oil reservoir based on material balance evaluation, B oi η is the crude oil volume factor under the original formation pressure of the reservoir. og E represents the macroscopic sweep efficiency of gas drive reservoir construction, determined based on indoor simulation experiments or reservoir numerical simulations. og G represents the reservoir's microscopic gas drive efficiency determined based on indoor simulation experiments, and B represents the dynamic gas reservoir reserves based on material balance evaluation. gri B is the natural gas volume factor of the gas reservoir under the original formation pressure. ging V is the natural gas volume factor of the gas reservoir at any pressure. wflux E represents the gas-bearing pore volume affected by edge and bottom water intrusion during gas reservoir development. wg To determine the microscopic gas drive efficiency in the water-flooded zone of a gas reservoir based on indoor simulation experiments, V lowpg I represents the gas-bearing pore volume of the reservoir with poor physical properties, as determined by geological evaluation. e This represents the inventory levels under different formation pressures.

[0065] Taking the Bohai Gas Storage Facility as an example, based on reservoir geology and development dynamics data, the dynamic crude oil reserves of the Bohai Gas Storage Facility were calculated using the mass balance method to be 479.84 × 10⁻⁶. 4 Based on the high-pressure physical properties of natural gas, the crude oil volume factor under the original formation pressure is 1.375. The macroscopic sweep efficiency of gas drive for reservoir construction is 65%, and the microscopic gas drive efficiency is 71.6%. According to the formula V... ge =(N oi ×B oi )×η og ×E og The effective gas-bearing pore volume of the reservoir was calculated to be 374.94 × 10⁻⁶. 4 m 3 According to formula I e =V ge / B ginj Calculate the inventory levels under different formation pressures and obtain the gas storage inventory curve (e.g.) Figure 2 (As shown in the oil reservoir inventory curve).

[0066] Based on oil and gas reservoir geology and development dynamics data, the dynamic reserves of the Bohai gas reservoir were calculated using the mass balance method to be 8.1 × 10⁻⁶. 8 m 3 Based on the high-pressure physical properties of natural gas, the natural gas volume factor of the gas reservoir under the original formation pressure is 0.00454, and the gas-bearing pore volume affected by edge and bottom water intrusion during the development of the gas reservoir is 25.44 × 10⁻⁶. 4 m 3 The microscopic gas drive efficiency in the water-flooded area of ​​the gas reservoir was 59.32%, and the gas-bearing pore volume in the reservoir with poor permeability was 15.33 × 10⁻⁶. 4 m 3 According to formula V ge = (G×B gri )-V wflux ×(1-E wg )-V lowpg The effective gas-bearing pore volume of the reservoir was calculated to be 327 × 10⁻⁶. 4 m 3 According to formula I e =V ge / B ginj Calculate the inventory levels under different formation pressures and obtain the gas storage inventory curve (e.g.) Figure 2 (As shown in the gas reservoir inventory curve).

[0067] Step S102: Based on the gas storage tank's inventory and the determined upper operating pressure, calculate the working gas volume of the gas storage tank corresponding to different lower pressure limits. Specifically:

[0068] According to the formula Calculated. Where, B ginjmax Q is the volume factor of natural gas in an oil and gas reservoir under the upper limit pressure. wg The working gas volume of the gas storage facility corresponding to different lower pressure limits.

[0069] In specific application examples, the upper limit pressure is generally taken as the original formation pressure of the oil and gas reservoir or determined through geomechanical analysis; in this example, it is 27 MPa. Based on the high-pressure physical properties of natural gas, the natural gas volume factor of the oil and gas reservoir under the upper limit pressure is 0.00387, and the natural gas volume factor under different formation pressures can be obtained. According to the formula... The working gas volume of the gas storage tank corresponding to different lower pressure limits was calculated.

[0070] Step S103: Based on the number of winter peak-shaving gas production days determined in the gas storage construction plan, calculate the average daily gas production during the winter peak-shaving gas production period of the gas storage facility. Specifically:

[0071] According to formula Q pg =Q wg / t calculates the average daily gas extraction volume during the winter peak-shaving gas extraction period of the gas storage facility. Where t is the number of days of peak-shaving gas extraction production in winter, and Q... pg This represents the average daily gas extraction volume during the winter peak-shaving gas extraction period of the gas storage facility.

[0072] In this invention example, the winter peak-shaving gas production days determined by the gas storage construction plan are 120 days, and then according to formula Q... pg =Q wg The average daily gas extraction volume during the winter peak-shaving gas extraction period of the gas storage facility was calculated using / t, as shown in Table 1.

[0073] Table 1. Results of natural gas volume factor, working gas volume, and average daily gas production for different formation pressures in the Bohai Gas Storage Reservoir.

[0074]

[0075]

[0076] Step S104: Based on the binomial production capacity equation of the gas well in the gas storage facility, establish the relationship between the inflow rate from the formation to the bottom of the well and the production pressure differential. Specifically:

[0077] According to the binomial capacity equation p R 2 -p wf 2 =Aq sc +Bq sc 2 The inflow dynamics during the gas injection process in the gas storage facility are calculated. Coefficients A and B are obtained based on Darcy's flow theory or well test data from the mine. Their mathematical expressions, calculated using Darcy's flow theory, are as follows:

[0078] Where, p R Formation pressure; p wf The bottom-hole flowing pressure; q sc R is the daily production of the gas well; K is the effective permeability of the gas phase in the reservoir; h is the effective thickness of the reservoir; r e Provide the radius for the gas well; r w γ is the radius of the gas wellbore; g The relative density of the gas; The average viscosity of the gas; is the gas average deviation factor; β is the velocity coefficient; S is the skin coefficient; T is the reservoir temperature.

[0079] In this embodiment of the invention, coefficients A and B are obtained based on well test data from the mine, and then the binomial productivity equation p is applied.R 2 -p wf 2 =Aq sc +Bq sc 2 Establish the relationship between the inflow rate from the formation to the bottom of the well and the production pressure differential.

[0080] Step S105: The nodal analysis method is used to evaluate the reasonable production capacity of gas wells corresponding to different lower pressure limits. Specifically:

[0081] Plot the inflow (binomial productivity equation) and outflow (wellbore flow dynamics) curves of gas wells under different lower limit pressures. Under the same lower limit pressure, the inflow and outflow curves intersect at a series of points. Further considering the constraints of the critical sand production differential, critical fluid carrying capacity, and erosion flow rate, the gas well productivity must be less than the productivity limited by the critical sand production differential and erosion flow rate, while simultaneously being greater than the productivity limited by the critical fluid carrying capacity. A comprehensive evaluation of the reasonable productivity q under different lower limit pressures is then conducted. npg (like Figure 3 , 4 As shown, Figure 3 This diagram shows the relationship between formation pressure in the Bohai gas storage reservoir and the reasonable production capacity of a typical single well. Figure 4 (This is a diagram showing the relationship between formation pressure in the Bohai gas reservoir and the reasonable production capacity of a typical single well).

[0082] Step S106: Using the average daily gas production during the winter peak-shaving gas production period of the gas storage facility corresponding to different lower limit pressures and the reasonable production capacity of gas wells, calculate the number of gas wells required for the winter peak-shaving production of the gas storage facility to meet the coordination requirements of gas well production nodes. Specifically:

[0083] According to formula N nw =Q pg / q npg The number of gas wells required for winter production of the gas storage facility to meet the coordination requirements of gas well production nodes was calculated.

[0084] Where, N nw To meet the coordination requirements of gas well production nodes and the number of gas wells required for winter production in gas storage facilities, Q pg q represents the average daily gas production during the winter peak-shaving gas production period of the gas storage facility, corresponding to different lower pressure limits. npg To Q pg Reasonable production capacity of gas wells at different lower pressure limits.

[0085] In this embodiment of the invention, the number of gas wells required for winter production of the gas storage facility to meet the coordination requirements of gas well production nodes can be obtained by dividing the average daily gas production during the winter peak-shaving gas production period of the gas storage facility obtained in step S103 by the reasonable production capacity of gas wells corresponding to different lower limit pressures obtained in step S105.

[0086] Table 2. Working gas volume and number of gas wells meeting the coordination requirements of different lower pressure limits at the Bohai Gas Storage Facility.

[0087]

[0088] Step S107: Based on the reasonable production capacity of gas wells in the gas storage facility corresponding to different lower limit pressures, the high-speed unsteady flow equation is used to calculate the well-controlled seepage area of ​​the gas well at different lower limit pressures. Specifically:

[0089] Based on actual production data, according to the formula Calculate the well control radius R under different lower limit pressures. e .

[0090] Among them, pseudo-pressure The mathematical expression is:

[0091]

[0092] Where, p min p is the lower limit pressure of the gas storage facility. max T represents the upper limit pressure of the gas storage facility. sc φ is the surface standard temperature; t is the number of days of peak-shaving production in the gas storage facility during winter; φ is the reservoir porosity; μ is the gas viscosity; C t R is the overall compressibility coefficient of the formation; K is the effective gas permeability of the reservoir; e r is the radius of the controlled seepage flow of a gas well. w B is the radius of the gas well shaft; g is the gas volume factor; h is the effective reservoir thickness; r D t is the dimensionless radial distance; D Dimensionless time; Q D This is dimensionless output.

[0093] In this embodiment of the invention, based on actual production data and the high-speed unsteady seepage equation... Among them, pseudo-pressure The mathematical expression is Calculate the corresponding well control radius under different formation pressures (e.g.) Figure 5 ).

[0094] Step S108: Calculate the well-controlled seepage area of ​​the gas well at different lower limit pressures based on the well-controlled seepage radius of the gas well at different lower limit pressures. Specifically:

[0095] According to the formula Calculations were performed to obtain the well-controlled seepage area of ​​a single gas well under different lower limit pressures (e.g., Figure 5 (and Table 3).

[0096] Among them, Aw R represents the well-controlled seepage area of ​​a single gas well in a gas storage facility. e The seepage radius is used to control the seepage radius of gas wells and gas production wells in gas storage facilities.

[0097] Step S109: Based on the effective oil and gas-bearing area of ​​the reservoir and the well-controlled seepage area of ​​the gas wells in the gas storage facility under different lower limit pressures, calculate the number of gas production wells required for winter peak-shaving production of the gas storage facility to meet the requirements for effective control of the effective oil and gas-bearing area of ​​the reservoir.

[0098] According to formula N rw =A r / A w Calculate the number of gas production wells required for winter peak-shaving production of the gas storage facility to meet the requirements for effective control of the effective oil and gas-bearing area of ​​the reservoir.

[0099] In this embodiment of the invention, the effective oil and gas-bearing area of ​​the reservoir for building a gas storage facility is obtained based on production data. By dividing the effective oil and gas-bearing area of ​​the reservoir for building a gas storage facility by the well-controlled seepage area of ​​the gas wells in the gas storage facility under different lower limit pressures, the number of gas production wells required for winter peak-shaving production of the gas storage facility that meets the requirements for effective control of the effective oil and gas-bearing area of ​​the reservoir can be obtained (as shown in Table 3).

[0100] Table 3. Controlled seepage area of ​​single wells in Bohai gas storage under different lower limit pressures and the number of gas production wells required for winter peak-shaving production of gas storage to meet the requirements of effective control of effective oil and gas-bearing area of ​​the reservoir.

[0101]

[0102] Step S110: The relationship curve between the number of wells required for winter peak-shaving production and the lower limit pressure of the gas storage facility to meet the coordination requirements of gas well production nodes is overlaid with the relationship curve between the number of wells required for winter peak-shaving production and the lower limit pressure of the gas storage facility to meet the requirements of effective control of the effective oil and gas-bearing area of ​​the reservoir, and plotted on the same coordinate system. Based on the intersection characteristics of the above two curves, the lower limit pressure for gas storage facility operation is designed as follows:

[0103] ① If the two curves mentioned above intersect, the wellhead pressure corresponding to the lower limit pressure at the intersection point is calculated using the gas well pipeline flow and the average daily gas production during the winter peak-shaving gas production period of the gas storage facility. It is then determined whether the wellhead pressure at this point meets the minimum wellhead pressure required by the natural gas surface transmission pipeline. If it does, then the intersection point is the lower limit pressure that simultaneously meets the triple requirements of coordinated gas well production nodes for peak-shaving gas production in the gas storage facility, effective control of the gas-bearing area of ​​the reservoir, and the minimum wellhead pressure required by the natural gas surface transmission pipeline.

[0104] ② If the two curves intersect, the wellhead pressure corresponding to the lower limit pressure at the intersection point is calculated using the gas well pipeline flow and the average daily gas production during the winter peak-shaving gas production period of the gas storage facility. It is then determined whether the wellhead pressure at this point meets the minimum wellhead pressure required by the natural gas surface transmission pipeline. If the calculated wellhead pressure is less than the minimum wellhead pressure required by the natural gas surface transmission pipeline, but the number of production wells required for the coordination of gas well nodes during the winter peak-shaving gas production period of the gas storage facility is higher than the number of production wells required for effective control of the effective oil and gas area of ​​the reservoir, then based on the former and combined with the working gas volume corresponding to different lower limit pressures, the average daily gas production per well and its corresponding wellhead pressure during the winter peak-shaving gas production period of the gas storage facility are calculated. Then, according to the minimum export wellhead pressure required by the natural gas surface transmission pipeline, the lower limit pressure of the gas storage facility is calculated using the gas well pipeline flow and production capacity equations.

[0105] ③ If the above two curves intersect, the wellhead pressure corresponding to the lower limit pressure at the intersection point is calculated using the gas well pipeline flow and the average daily gas production during the winter peak-shaving gas production period of the gas storage facility. It is then determined whether the wellhead pressure at this point meets the minimum wellhead pressure required by the natural gas surface transmission pipeline. If the calculated gas wellhead pressure is less than the minimum wellhead pressure required by the natural gas surface transmission pipeline, but as the lower limit pressure increases, the number of production wells required for the coordination of gas well nodes during the winter peak-shaving gas production period of the gas storage facility is lower than the number of production wells required for effective control of the effective oil and gas area of ​​the reservoir, then based on the latter and combined with the working gas volume corresponding to different lower limit pressures, the average daily gas production per well and its corresponding wellhead pressure during the winter peak-shaving gas production period of the gas storage facility are calculated. Then, according to the minimum external transmission wellhead pressure required by the natural gas surface transmission pipeline, the lower limit pressure of the gas storage facility is calculated using the gas well pipeline flow and production capacity equations.

[0106] ④ If the two curves mentioned above do not intersect, and the number of production wells that meet the requirements for coordinating the production well nodes of the gas storage facility during winter peak-shaving gas production is higher than the number of production wells that meet the requirements for effective control of the effective oil and gas area of ​​the reservoir, then based on the former, combined with the working gas volume and number of gas wells corresponding to different lower limit pressures, the average daily gas production of a single well and its corresponding wellhead pressure during the winter peak-shaving gas production period of the gas storage facility are calculated. Then, based on the minimum wellhead pressure required by the natural gas surface transmission pipeline, the lower limit pressure of the gas storage facility is calculated by using the gas well pipeline flow and production capacity equation.

[0107] ⑤ If the two curves mentioned above do not intersect, and the number of production wells meeting the coordination requirements for peak-shaving gas production nodes in the gas storage facility during winter is lower than the number of production wells meeting the requirements for effective control of the effective oil and gas-bearing area of ​​the reservoir, then based on the latter, and combined with the working gas volume and number of gas wells corresponding to different lower limit pressures, the average daily gas production per well and its corresponding wellhead pressure during the peak-shaving gas production period in winter are calculated. Then, according to the minimum wellhead pressure required by the natural gas surface transmission pipeline, the lower limit pressure of the gas storage facility is calculated back using the gas well pipe flow and production capacity equation. Figure 6 (This is a diagram illustrating the five scenarios mentioned above).

[0108] In this embodiment of the invention, for the Bohai gas storage facility, it is the first of the five scenarios mentioned above, namely, the lower limit pressure that simultaneously meets the triple requirements of coordinating the production nodes of the gas storage facility's peak-shaving gas production wells, effectively controlling the gas-bearing area of ​​the reservoir, and meeting the minimum wellhead pressure requirements of the natural gas surface transmission pipeline. The calculated lower limit operating pressure is 11.3 MPa (e.g., Figure 7 (As shown).

[0109] Comparison of the effects and advantages of the new method of this invention with existing methods

[0110] Table 4 and Figure 8 The lower limit pressure for operation of the Bohai gas storage facility is calculated using existing methods and the new method of this invention.

[0111] Table 4. Lower operating pressure of Bohai Gas Storage Calculated by Different Methods

[0112]

[0113] The existing design for the lowest wellhead pressure required for gas storage operation (Method A) to meet the coordination requirements of gas well production nodes and the requirements of natural gas surface transmission pipelines is adopted. The calculated lower limit pressure is 10 MPa. However, this method only considers the wellhead pressure requirements for natural gas pipeline transmission, but does not consider the effective control of the effective oil and gas-bearing area of ​​the reservoir. This results in the number of newly drilled wells (12) exceeding the number of wells required for storage capacity control (11 wells, as shown in Table 3). This leads to inter-well interference and overlapping well control areas in gas storage production, and in particular, it results in a waste of engineering investment and fails to achieve the optimal lower limit pressure for gas storage operation.

[0114] Using the novel method proposed in this invention, which simultaneously considers the requirements for coordination of gas well production nodes, effective control of the effective oil and gas-bearing area of ​​the reservoir, and the minimum wellhead pressure design requirements for natural gas surface transmission pipelines, the calculated lower limit pressure for gas storage operation (Method B) is 11.3 MPa, with 11 new wells drilled. This method meets the above-mentioned triple lower limit pressure design requirements. The new method also considers two core factors: efficient external transmission of natural gas from gas storage pipelines during winter peak-shaving and effective control of storage capacity. It considers more comprehensive factors, improves the accuracy of lower limit pressure design, and provides a more reliable basis for lower limit pressure design.

Claims

1. A method for determining the lower limit pressure of a gas storage facility in a weak water-drive oil and gas reservoir, characterized in that, The method includes the following steps: Step 1: Based on the geological and development dynamics of the oil and gas reservoir and the results of laboratory simulation, determine the effective gas storage pore volume of the reservoir and the inventory under different formation pressures. Step 2: Based on the gas storage capacity and the determined upper limit pressure, calculate the working gas volume of the gas storage corresponding to different lower limit pressures. Step 3: Based on the working gas volume corresponding to different lower limit pressures, and according to the number of days of peak-shaving gas production during winter as determined by the gas storage construction plan, calculate the average daily gas production during the winter peak-shaving gas production period of the gas storage facility. Step 4: Based on the binomial production capacity equation of the gas wells in the gas storage facility, use the nodal analysis method to evaluate the reasonable production capacity of the gas wells corresponding to different lower limit pressures; Step 5: Divide the average daily gas production during the winter peak-shaving gas production period of the gas storage facility corresponding to different lower limit pressures by the reasonable production capacity of the gas wells at the corresponding lower limit pressures to calculate the number of gas wells required for the winter peak-shaving production of the gas storage facility to meet the coordination requirements of the gas well production nodes. Step 6: Based on the reasonable production capacity of gas wells in the gas storage facility corresponding to different lower limit pressures, the high-speed unstable seepage equation is used to calculate the well-controlled seepage area of ​​gas wells at different lower limit pressures. Step 7: Divide the effective oil and gas-bearing area of ​​the reservoir into the well control seepage area of ​​the gas wells in the gas storage facility at different lower limit pressures to calculate the number of gas wells required for winter peak-shaving production of the gas storage facility to meet the requirements for effective control of the effective oil and gas-bearing area of ​​the reservoir. Step 8: Using the lower limit pressure as the horizontal axis and the number of production wells as the vertical axis, overlay the relationship curve of the number of wells required for winter peak-shaving production of gas storage facilities to meet the coordination requirements of gas well production nodes and the relationship curve of the number of wells required for winter peak-shaving production of gas storage facilities to meet the requirements of effective control of the effective oil and gas-bearing area of ​​the reservoir on the same coordinate system. Step 9: Based on the intersection characteristics of the two curves mentioned above, design the lower limit pressure for gas storage operation, specifically as follows: A. If the two curves mentioned above intersect, the wellhead pressure corresponding to the lower limit pressure at the intersection point is calculated using the gas well pipeline flow and the average daily gas production during the winter peak-shaving gas production period of the gas storage facility. It is then determined whether the wellhead pressure at this point meets the minimum wellhead pressure required by the natural gas surface transmission pipeline. If it does, then the intersection point is the lower limit pressure that simultaneously meets the triple requirements of coordinating the gas well production nodes for peak-shaving gas production in the gas storage facility, effectively controlling the gas-bearing area of ​​the reservoir, and meeting the minimum wellhead pressure required by the natural gas surface transmission pipeline. B. If the two curves intersect, the wellhead pressure corresponding to the lower limit pressure at the intersection point is calculated using the gas well pipeline flow and the average daily gas production during the winter peak-shaving gas production of the gas storage facility. It is then determined whether the wellhead pressure at this point meets the minimum wellhead pressure required by the natural gas surface transmission pipeline. If the calculated gas wellhead pressure is less than the minimum wellhead pressure required by the natural gas surface transmission pipeline, but as the lower limit pressure increases, the number of production wells required for the coordination of gas well nodes during the winter peak-shaving gas production of the gas storage facility is higher than the number of production wells required for effective control of the effective oil and gas area of ​​the reservoir, then based on the former and combined with the working gas volume corresponding to different lower limit pressures, the average daily gas production of a single well and its corresponding wellhead pressure during the winter peak-shaving gas production of the gas storage facility are calculated. Then, according to the minimum external transmission wellhead pressure required by the natural gas surface transmission pipeline, the lower limit pressure of the gas storage facility is calculated by using the gas well pipeline flow and production capacity equation. C. If the two curves mentioned above intersect, the wellhead pressure corresponding to the lower limit pressure at the intersection point is calculated using the gas well pipeline flow and the average daily gas production during the winter peak-shaving gas production of the gas storage facility. It is then determined whether the wellhead pressure at this point meets the minimum wellhead pressure required by the natural gas surface transmission pipeline. If the calculated gas wellhead pressure is less than the minimum wellhead pressure required by the natural gas surface transmission pipeline, but as the lower limit pressure increases, the number of production wells required for the coordination of gas well nodes during the winter peak-shaving gas production of the gas storage facility is lower than the number of production wells required for effective control of the effective oil and gas area of ​​the reservoir, then based on the latter and combined with the working gas volume corresponding to different lower limit pressures, the average daily gas production of a single well and its corresponding wellhead pressure during the winter peak-shaving gas production of the gas storage facility are calculated. Then, according to the minimum external transmission wellhead pressure required by the natural gas surface transmission pipeline, the lower limit pressure of the gas storage facility is calculated by using the gas well pipeline flow and production capacity equations. D. If the two curves mentioned above do not intersect, and the curve of the number of production wells that meets the requirements for coordination of gas well nodes in winter peak-shaving gas production of the gas storage is higher than the curve of the number of production wells that meets the requirements for effective control of the effective oil and gas area of ​​the reservoir, then based on the former, combined with the working gas volume and number of gas wells corresponding to different lower limit pressures, the average daily gas production of a single well and its corresponding wellhead pressure during the winter peak-shaving gas production of the gas storage are calculated. Then, based on the minimum wellhead pressure required by the natural gas surface transmission pipeline, the lower limit pressure of the gas storage is calculated by using the gas well pipeline flow and production capacity equation. If the two curves mentioned above do not intersect, and the number of production wells that meet the requirements for coordinating gas well nodes during winter peak-shaving gas production in the gas storage facility is lower than the number of production wells that meet the requirements for effective control of the effective oil and gas area of ​​the reservoir, then based on the latter, and combined with the working gas volume and number of gas wells corresponding to different lower limit pressures, the average daily gas production of a single well and its corresponding wellhead pressure during the winter peak-shaving gas production period of the gas storage facility are calculated. Then, based on the minimum wellhead pressure required by the natural gas surface transmission pipeline, the lower limit pressure of the gas storage facility is calculated by using the gas well pipeline flow and production capacity equation.

2. The method for determining the lower limit operating pressure of a gas storage tank in a weak water-drive oil and gas reservoir according to claim 1, characterized in that, Step 1, which involves determining the effective gas storage pore volume of the reservoir and the storage capacity under different formation pressures, includes: Using data on oil and gas reservoir development dynamics, laboratory gas injection displacement, and high-pressure physical properties of crude oil and natural gas, for weak water-drive reservoirs, according to the formula... For weak water-driven gas reservoirs, according to the formula The effective gas-bearing pore volume of the reservoir was calculated separately; using the formula The gas storage inventory curve was calculated. Among them, V ge To determine the effective gas storage pore volume of the reservoir for oil and gas reservoir construction, To determine the dynamic crude oil reserves of the reservoir based on the material balance assessment. The crude oil volume factor under the original formation pressure of the reservoir. The macroscopic sweep efficiency of reservoir gas drive for reservoir construction is determined based on indoor simulation experiments or reservoir numerical simulations. The microscopic gas drive efficiency for reservoir construction was determined based on indoor simulation experiments. This refers to the dynamic reserves of gas reservoirs based on material balance assessment. This represents the natural gas volume factor of the gas reservoir under its original formation pressure. Let be the natural gas volume factor of the gas reservoir at any pressure. This refers to the gas-bearing pore volume affected by edge and bottom water intrusion during gas reservoir development. The microscopic gas drive efficiency in the water-flooded area of ​​a gas reservoir, as determined by indoor simulation experiments, is as follows. This refers to the gas-bearing pore volume of the reservoir with poor physical properties, as determined by geological evaluation. This represents the inventory levels under different formation pressures.

3. The method for determining the lower limit operating pressure of a gas storage tank in a weak water-drive oil and gas reservoir according to claim 2, characterized in that, Step 2 involves calculating the working gas volume of the gas storage facility corresponding to different lower pressure limits, based on the formula... Calculated; in, This is the gas reservoir natural gas volume factor under the upper limit pressure of the gas storage facility. The working gas volume of the gas storage facility corresponding to different lower pressure limits.

4. The method for determining the lower limit operating pressure of a gas storage tank in a weak water-drive oil and gas reservoir according to claim 1, characterized in that, Step 3 involves calculating the average daily gas extraction volume during the winter peak-shaving gas extraction period of the gas storage facility, based on the formula... Calculated; in, The number of days for peak gas extraction and production at the gas storage facility during winter. This represents the average daily gas extraction volume during the winter peak-shaving gas extraction period of the gas storage facility.

5. The method for determining the lower limit operating pressure of a gas storage tank in a weak water-drive oil and gas reservoir according to claim 1, characterized in that, The binomial production capacity equation mentioned in step 4 is: ； Among them, coefficients A and B are obtained based on Darcy's flow theory or well test data in the mine, and their mathematical expressions calculated based on Darcy's flow theory are as follows: ； ； in, Formation pressure; Bottom hole flowing pressure; K represents the daily production of the gas well; K represents the effective permeability of the gas phase in the reservoir. The effective thickness of the reservoir; Provide radius for gas wells; The radius of the gas well shaft; The relative density of the gas; The average viscosity of the gas; This is the gas average deviation factor; The velocity coefficient; For epidermal coefficient; Reservoir temperature; The method of evaluating the reasonable production capacity of gas wells under different lower limit pressures using node analysis includes: plotting the inflow binomial production capacity equation and the outflow dynamic curve of the wellbore under different lower limit pressures; under the same lower limit pressure, the inflow and outflow curves have a series of intersection points; further considering the constraints of the critical sand production pressure differential, critical fluid carrying capacity, and erosion flow rate, the gas well production capacity must be less than the gas well production capacity limited by the critical sand production pressure differential and erosion flow rate, and must be greater than the gas well production capacity limited by the critical fluid carrying capacity; and comprehensively evaluating the reasonable production capacity q under different lower limit pressures. npg .

6. The method for determining the lower limit operating pressure of a gas storage tank in a weak water-drive oil and gas reservoir according to claim 1, characterized in that, Step 5 calculates the number of gas wells required for winter production in the gas storage facility to meet the coordination requirements of gas well production nodes. This number is then calculated using the formula N. nw =Q pg / q npg Calculated; Where, N nw To meet the coordination requirements of gas well production nodes and the number of gas wells required for winter production in gas storage facilities, Q pg q represents the average daily gas production during the winter peak-shaving gas production period of the gas storage facility, corresponding to different lower pressure limits. npg To Q pg Reasonable production capacity of gas wells at different lower pressure limits.

7. The method for determining the lower limit operating pressure of a gas storage tank in a weak water-drive oil and gas reservoir according to claim 1, characterized in that, The high-speed unsteady seepage equation mentioned in step 6 is: ； Among them, pseudo-pressure The mathematical expression is: ； in, This refers to the lower limit pressure of the gas storage facility. This refers to the upper limit pressure of the gas storage facility; Ground standard temperature; The number of days for peak-shaving production in gas storage facilities during winter; Reservoir porosity; Gas viscosity; The total compressibility coefficient of the formation; The effective permeability of the reservoir gas phase; The seepage radius is used to control the seepage radius of gas wells and gas production wells; The radius of the gas well shaft; This is the gas volume coefficient; The effective thickness of the reservoir; The radial distance is dimensionless. Dimensionless time; This is dimensionless output.

8. The method for determining the lower limit operating pressure of a gas storage tank in a weak water-drive oil and gas reservoir according to claim 1, characterized in that, Step 7 describes the calculation of the well-controlled seepage area of ​​a gas well at different lower limit pressures, based on the formula... Calculated; Among them, A w R represents the well-controlled seepage area of ​​a single gas well in a gas storage facility. e The seepage radius is used to control the seepage radius of gas wells and gas production wells in gas storage facilities.

9. The method for determining the lower limit operating pressure of a gas storage tank in a weak water-drive oil and gas reservoir according to claim 1, characterized in that, The number of wells required for winter peak-shaving production of the gas storage facility, as described in step 8, to meet the requirements for effective control of the effective oil and gas-bearing area of ​​the reservoir, is calculated according to formula N. rw =A r / A w Calculated; in, To meet the requirements for effective control of the effective oil and gas-bearing area of ​​the reservoir, the number of gas production wells needed for winter peak-shaving production of the gas storage facility, A r For the effective oil and gas-bearing area of ​​the reservoir, A w This refers to the well-controlled seepage area of ​​a single gas well in a gas storage facility.

10. The method for determining the lower limit operating pressure of a gas storage tank in a weak water-drive oil and gas reservoir according to claim 9, characterized in that, The well-controlled seepage area of ​​a gas well at different lower limit pressures is as follows: when the lower limit pressure of the gas storage is different, the well control radius of the gas well calculated according to the high-speed unstable seepage theory is different, and the number of wells that can effectively control the oil and gas area and storage capacity is also different.

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