Method for determining operation lower limit pressure of gas storage of weak water flooding oil and gas reservoir

Abstract

The invention discloses a method for determining the operation lower limit pressure of a gas storage of a weak water flooding oil and gas reservoir. The method comprises the following steps: 1, determining the effective gas storage pore volume of a reservoir building reservoir of the oil and gas reservoir and the stock under different formation pressures; 2, working gas volumes of the gas storage corresponding to different lower limit pressures are obtained through calculation; 3, the average daily gas production amount of the gas storage in the peak regulation gas production production period in winter is obtained through calculation; 4, evaluating the reasonable productivity of the gas well corresponding to different lower limit pressures; 5, the number of gas recovery wells required for winter peak regulation production of the gas storage and meeting the gas well gas recovery node coordination requirement is obtained through calculation; 6, the well control seepage area of the gas well gas production single well under the corresponding different lower limit pressures is obtained through calculation; 7, the number of gas recovery wells needed by peak regulation production in winter of the gas storage meeting the effective control requirement for the effective oil-gas containing area of the reservoir is obtained through calculation; the problems that effective reservoir capacity control is not considered in the lower limit pressure design, and efficient output and effective reservoir capacity control in the gas production last stage are coordinated optimally are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of underground natural gas storage, and in particular to a method for determining the lower limit operating pressure of a gas storage reservoir in a weak water drive oil and gas reservoir. Background Art

[0002] Oil and gas reservoir-type gas storage is an underground natural gas storage facility converted from mid-to-late-stage or depleted oil and gas reservoirs. It has functions such as natural gas peak-shaving and supply guarantee, pipeline accident emergency response and energy strategic reserve. At present, oil and gas reservoir-type gas storage (hereinafter referred to as gas storage) is the type of gas storage with the highest proportion of working gas volume among the four types of gas storage in the world. It has multiple advantages such as large scale of natural gas storage, relatively clear understanding of underground geological characteristics and some engineering facilities available in oil and gas fields. Weak water drive oil and gas reservoirs are the first choice and the best target for the reconstruction of gas storage.

[0003] The lower limit of operation pressure (hereinafter referred to as the lower limit pressure) refers to the lowest formation pressure that can be reached during the winter peak-shaving gas production operation of the gas storage. The lower the lower limit pressure, the greater the working gas volume of the gas storage. However, the lower formation pressure at the end of gas production will lead to a lower gas well production capacity. The more new wells are needed to achieve the working gas production within 120 to 150 days, the greater the total investment in the construction of the gas storage project. At the same time, a lower lower limit pressure may cause the wellhead pressure at the end of gas production in the gas storage to be lower than the minimum pressure required by the natural gas transmission pipeline, resulting in the need to use a compressor to reversely pressurize the natural gas for transmission at the end of gas production, which will increase the operating cost of the gas storage. However, a higher lower limit pressure will result in a smaller working gas volume in the gas storage, making it impossible to maximize the utilization of underground gas storage space, resulting in a waste of storage space.

[0004] Obviously, the design of the lower limit pressure of gas storage is closely related to the number of injection and production wells, the requirements for the wellhead pressure of natural gas transmission, etc. The design of the technical lower limit pressure of gas storage reservoirs needs to consider multiple factors such as the scale of working gas volume (peak shaving capacity), efficient transmission of natural gas at the end of gas production, effective control of storage capacity, and the number of new wells drilled for reservoir construction, and comprehensively optimize and determine the reasonable lower limit pressure. However, there is currently a lack of gas storage reservoir lower limit pressure design methods that take into account the above-mentioned multiple factors, especially those that take into account the effective control of storage capacity (such as the article "A New Method for Designing the Lower Limit Pressure of Gas Storage Reservoirs for Gas Reservoir Reconstruction" in the 11th issue of Natural Gas Geosciences, Volume 31, November 2020). It only considers the impact of the number of wells drilled in the gas storage reservoir and the investment in the project on the lower limit pressure, and especially does not consider the impact of the well control of a single well for peak production in the gas storage reservoir in winter on the lower limit pressure, which has certain limitations in technical application. Summary of the invention

[0005] The purpose of the present invention is to provide a method for determining the lower limit pressure of the operation of a gas storage reservoir in a weak water drive oil and gas reservoir, so as to obtain the lower limit pressure for realizing the coordination of efficient external transmission and effective control of storage capacity of the gas storage reservoir during winter peak-shaving gas production, thereby solving the problem that the lower limit pressure design in the background technology does not consider the effective control of storage capacity, and the optimal coordination of efficient external transmission and effective control of storage capacity at the end of gas production.

[0006] The technical solution provided by the present invention is: a method for determining the lower limit operating pressure of a weak water drive oil and gas reservoir gas storage reservoir comprises the following steps:

[0007] Step 1: According to the geological and development dynamic characteristics of the oil and gas reservoir and the laboratory simulation results, determine the effective gas storage pore volume of the reservoir and the storage volume under different formation pressures;

[0008] Step 2: According to the gas storage reservoir inventory and the determined upper limit pressure of operation, the working gas volume of the gas storage reservoir corresponding to different lower limit pressures is calculated;

[0009] Step 3: Based on the calculated working gas volumes corresponding to different lower limit pressures and the number of days for winter peak-shaving gas production determined in the gas storage construction plan, calculate the average daily gas production volume of the gas storage during the winter peak-shaving gas production period;

[0010] Step 4: Based on the binomial production capacity equation of the gas storage reservoir gas well, the node analysis method is used to evaluate the reasonable production capacity of the gas well corresponding to different lower limit pressures;

[0011] Step 5: The average daily gas production during the winter peak-shaving gas production period of the gas storage corresponding to different lower limit pressures is divided by the reasonable production capacity of the gas wells at the corresponding different lower limit pressures to calculate the number of gas wells required for the winter peak-shaving production of the gas storage that meets the coordination requirements of the gas well production nodes;

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

[0013] Step 7: The effective oil and gas area of ​​the reservoir is divided by the well-controlled seepage area of ​​the gas wells in the gas storage reservoir at different lower pressure limits to calculate the number of gas wells required for winter peak-shaving production in the gas storage reservoir to meet the effective control requirements for the effective oil and gas area of ​​the reservoir;

[0014] Step 8: With the lower limit pressure as the horizontal coordinate and the number of production wells as the vertical coordinate, the relationship curve between the number of wells required for winter peak-shaving production and production of gas storage facilities that meets the gas well production node coordination requirements and the lower limit pressure, and the relationship curve between the number of wells required for winter peak-shaving production and production of gas storage facilities that meets the requirements for effective control of the effective oil and gas-bearing area of ​​the reservoir and the lower limit pressure are superimposed and drawn in the same coordinate system;

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

[0016] AIf there is an intersection point between the above two curves, the well flow and the average daily gas production during the winter peak-shaving gas production of the gas storage are used to calculate the wellhead pressure corresponding to the lower limit pressure at the intersection point, and determine whether the wellhead pressure at this time meets the minimum wellhead pressure required by the natural gas surface pipeline. If so, the intersection point is the lower limit pressure that simultaneously meets the triple requirements of the coordination of production nodes of gas wells for gas storage peak-shaving gas production, effective control of gas-bearing area of ​​the reservoir, and the minimum wellhead pressure required by the natural gas surface pipeline.

[0017] B. If the above two curves have an intersection, then the wellhead pressure corresponding to the lower limit pressure at the intersection is calculated using the gas well pipe flow and the average daily gas production during the winter peak-shaving gas production of the gas storage reservoir, and it is determined whether the wellhead pressure at this time meets the minimum wellhead pressure required by the natural gas surface gas pipeline. If the calculated gas well wellhead pressure is lower than the minimum wellhead pressure required by the natural gas surface gas pipeline, but as the lower limit pressure increases, the production well number curve required by the coordination of the gas well node for the winter peak-shaving gas production of the gas storage reservoir is higher than the production well number curve 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 corresponding to different lower limit pressures, the average daily gas production of a single well during the winter peak-shaving gas production of the gas storage reservoir and its corresponding wellhead pressure are calculated, and then the lower limit pressure of the gas storage reservoir is obtained by reverse calculation using the gas well pipe flow and production capacity equation according to the minimum external transmission wellhead pressure required by the natural gas surface gas pipeline;

[0018] C If the above two curves have an intersection, then the wellhead pressure corresponding to the lower limit pressure at the intersection is calculated using the gas well pipe flow and the average daily gas production during the winter peak-shaving gas production of the gas storage reservoir, and it is determined whether the wellhead pressure at this time meets the minimum wellhead pressure required by the natural gas surface gas pipeline. If the calculated gas well wellhead pressure is lower than the minimum wellhead pressure required by the natural gas surface gas pipeline, but as the lower limit pressure increases, the production well number curve required by the coordination of gas well nodes for the winter peak-shaving gas production of the gas storage reservoir is lower than the production well number curve that meets the requirements for effective control of the effective oil and gas area of ​​the reservoir, then based on the latter, combined with the working gas volume corresponding to different lower limit pressures, the average daily gas production of a single well during the winter peak-shaving gas production of the gas storage reservoir and its corresponding wellhead pressure are calculated, and then the lower limit pressure of the gas storage reservoir is obtained by reverse calculation using the gas well pipe flow and production capacity equation according to the minimum external transmission wellhead pressure required by the natural gas surface gas pipeline;

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

[0020] EIf there is no intersection between the above two curves, and the curve of the number of production wells that meets the coordination requirements of the gas well nodes for the winter peak-shaving gas production of the gas storage reservoir is lower than 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 latter, combined with the working gas volume and the number of gas wells corresponding to different lower limit pressures, the average daily gas production of a single well during the winter peak-shaving gas production of the gas storage reservoir and its corresponding wellhead pressure are calculated, and then, based on the minimum wellhead pressure required by the natural gas surface gas pipeline, the gas well pipe flow and production capacity equation are used to reversely calculate the lower limit pressure of the gas storage reservoir.

[0021] The determination of the effective gas storage pore volume of the reservoir and the storage volume under different formation pressures in step 1 includes:

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

[0023] Among them, V ge The effective gas storage pore volume of the reservoir for oil and gas reservoirs, N oi is the dynamic reserves of crude oil in the reservoir evaluated based on material balance, B oi is the volume coefficient of crude oil at the original reservoir formation pressure, η og is the macroscopic sweep coefficient of gas flooding in reservoir construction determined by indoor simulation experiments or reservoir numerical simulation, E ogis the microscopic gas drive efficiency of reservoir construction determined by indoor simulation experiments, G is the dynamic reserves of gas reservoirs evaluated by material balance, and B is gri is the natural gas volume coefficient of the gas reservoir at the original formation pressure, B ging is the natural gas volume coefficient of the gas reservoir at any pressure, V wflux is the volume of gas-bearing pores affected by edge and bottom water intrusion during gas reservoir development, E wg is the microscopic gas drive efficiency of the flooded area of ​​the gas reservoir determined by indoor simulation experiments, V lowpg is the volume of gas-bearing pores with poor reservoir properties determined based on geological evaluation; I e is the inventory under different formation pressures.

[0024] The working gas volume of the gas storage corresponding to different lower limit pressures is calculated in step 2. According to the formula Calculated;

[0025] Among them, B ginjmax is the volume coefficient of natural gas in the gas reservoir under the upper limit pressure of the gas storage reservoir, Q wg The working gas volume of the gas storage corresponding to different lower limit pressures.

[0026] The average daily gas production during the winter peak-shaving period of the gas storage is calculated in step 3. According to the formula Q pg =Q wg / t is calculated.

[0027] Among them, t is the number of days of gas production for peak load regulation in winter in the gas storage, Q pg It is the average daily gas production during the winter peak-shaving gas production period of the gas storage facility.

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

[0029] Among them, coefficients A and B are obtained according to Darcy's seepage theory or field well test data, and their mathematical expressions calculated according to Darcy's seepage theory are:

[0030]

[0031]

[0032] Among them, p R is the formation pressure; p wf is the bottom hole flowing pressure; q scis the daily production of the gas well; K is the effective permeability of the reservoir gas phase; h is the effective thickness of the reservoir; r e is the gas well supply radius; r w is the radius of the gas wellbore; g is the relative density of gas; is 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] The node analysis method described in step 5 is used to evaluate the reasonable production capacity of gas wells corresponding to different lower limit pressures, including: drawing gas well inflow (binomial production capacity equation) and outflow (wellbore pipe flow dynamics) curves under different lower limit pressures. There are a series of intersections between the inflow and outflow curves under the same lower limit pressure. Further considering the constraints of the critical sand pressure difference, critical liquid carrying and erosion flow rate of the gas well, the gas well production capacity must be less than the gas well production capacity limited by the critical sand pressure difference and erosion flow rate, and must be greater than the gas well production capacity limited by the critical liquid carrying rate. Comprehensively evaluate the reasonable production capacity q under different lower limit pressures npg .

[0034] The calculation described in step 6 obtains the number of gas wells required for winter production in the gas storage facility to meet the coordination requirements of gas well production nodes. According to the formula N nw =Q pg / q npg Calculated;

[0035] Among them, N nw The number of gas wells required for winter production in a gas storage facility to meet the coordination requirements of gas well production nodes, Q pg is the average daily gas production during the winter peak-shaving gas production period of the gas storage corresponding to different lower limit pressures, q npg For Q pg Reasonable production capacity of gas wells at different lower pressure limits.

[0036] The high-speed unstable seepage equation is:

[0037]

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

[0039]

[0040] Among them, p min is the lower limit pressure of the gas storage; p max is the upper limit pressure of the gas storage; T sc is the standard ground temperature; t is the number of days of winter peak-shaving production in the gas storage; φ is the reservoir porosity; μ is the gas viscosity; C t is the total compression coefficient of the formation; K is the effective permeability of the reservoir gas phase; Re r is the controlled seepage radius of the gas well; w is the radius of the gas wellbore; B g is the gas volume coefficient; h is the effective thickness of the reservoir; r D is the dimensionless radial distance; t D is dimensionless time; Q D is dimensionless output.

[0041] The well-controlled seepage area of ​​a gas well under different lower limit pressures is calculated in step 7. Calculated.

[0042] Among them, A w is the well-controlled seepage area of ​​a single gas well in the gas storage reservoir, R e It is the controlled seepage radius of the gas well in the gas storage reservoir.

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

[0044] Among them, N rw The number of gas wells required for winter peak-shaving production of gas storage facilities to meet the effective control requirements of the effective oil and gas area of ​​the reservoir, A r is the effective oil and gas area of ​​the reservoir, A w It is the well-controlled seepage area of ​​a single gas well in the gas storage reservoir.

[0045] The well-controlled seepage area of ​​a single gas well under different lower limit pressures, when the lower limit pressure of the gas storage reservoir is different, the well-controlled radius of the single gas well calculated according to the high-speed unstable seepage theory is different, then the well-controlled seepage area is also different, and the number of wells that can achieve effective control of the effective oil and gas area and storage capacity is also different.

[0046] The beneficial effects of the present invention are:

[0047] 1. When designing the lower limit pressure of gas storage, the existing methods do not consider the influence of the well control radius, seepage area and well pattern of the gas storage's limited time rate peak gas production in winter on the effective use of storage capacity, and cannot reflect the influence of the number of wells on the lower limit pressure and the economic benefits of reservoir construction. During the operation of the gas storage with limited time rate and high speed gas production, the lower the lower limit pressure, the smaller the well control radius and seepage area of ​​the gas well, the more wells are required to achieve effective use of storage capacity, and the more total investment in the construction of the reservoir. Therefore, there is a direct and close relationship between the lower limit pressure of the gas storage and the number of gas production wells. The existing methods ignore the well control of the gas production well, which may lead to large errors in the design of the number of new wells for reservoir construction, resulting in too many wells or insufficient well control, causing waste of project investment or insufficient use of underground gas storage space. This method evaluates the well control radius and well control seepage area of ​​the gas storage with limited time rate and high speed gas production at different lower limit pressures through the high-speed unstable seepage theory, and can accurately obtain the number of wells required to achieve effective oil and gas area and effective control of storage capacity, providing a scientific basis for the optimization design of the lower limit pressure.

[0048] 2. Compared with the existing methods that only consider the winter peak-shaving gas production of gas storage to meet the requirements of natural gas pipeline transmission or the method of minimizing the drilling project investment based on the experience statistics of the existing storage, this method proposes to simultaneously meet the two core factors of efficient transmission of natural gas pipeline and effective control of storage capacity in winter peak-shaving gas production of gas storage, and plots the number of gas production wells that meet the requirements of natural gas transmission (node ​​coordination) and effective control of storage capacity in the same coordinate system. The lower limit pressure of the gas storage is designed by comprehensive analysis of the intersection of the above two curves and their corresponding number of wells, wellhead pressure at the end of gas production, etc., or according to the relationship between the above two curves with the change of the lower limit pressure (when there is no intersection between the two), the relationship between the number of wells, wellhead pressure at the end of gas production and the requirements of natural gas transmission pressure is analyzed to design and determine the lower limit pressure of the gas storage. This method makes up for the fact that the conventional design method does not consider the well control radius of the single well of the gas storage with limited time rate peak-shaving in winter and its decrease with the decrease of the lower limit pressure, effective control of storage capacity and coordination of gas production and transmission, and greatly improves the scientificity and accuracy of the lower limit pressure design of the gas storage.

[0049] 3. This method is different from the conventional method in that, according to the geological characteristics of the weak water drive oil and gas reservoir converted into a gas storage reservoir, the high-speed unstable seepage theory is adopted to calculate the well control radius and seepage area of ​​a single gas production well at different lower limit pressures, and determine the number of wells required to achieve effective control of the storage capacity; further, the curves of the number of wells required to achieve efficient external transmission of gas production during winter peak-shaving in the gas storage reservoir and the number of wells required for effective control of the storage capacity are superimposed and plotted in the same coordinate system, and the lower limit pressure of the gas storage reservoir is designed through a comprehensive analysis of the intersection of the two curves and their corresponding number of wells, the wellhead pressure at the end of gas production, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The drawings described herein are used to provide a further understanding of the present invention, constitute a part of the present application, and do not constitute a limitation of the present invention. In the drawings:

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

[0052] Figure 2 It is the inventory curve diagram of the oil layer and gas layer gas storage of the present invention;

[0053] Figure 3 The relationship diagram between the oil layer formation pressure and the reasonable production capacity of a typical single well of the present invention;

[0054] Figure 4 The relationship diagram between the gas layer formation pressure and the reasonable production capacity of a typical single well of the present invention;

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

[0056] Figure 6 This is a schematic diagram of the design of the lower limit pressure of the gas storage operation of the present invention;

[0057] Figure 7 This is the design diagram of the lower limit pressure of the Bohai gas storage operation of the present invention;

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

[0059] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to make the present invention more thorough and complete, and to fully convey the scope of the present invention to those skilled in the art.

[0060] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings.

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

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

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

[0064] Among them, V ge The effective gas storage pore volume of the reservoir for oil and gas reservoirs, N oi is the dynamic reserves of crude oil in the reservoir evaluated based on material balance, B oi is the volume coefficient of crude oil at the original reservoir formation pressure, η og is the macroscopic sweep coefficient of gas flooding in reservoir construction determined by indoor simulation experiments or reservoir numerical simulation, E og is the microscopic gas drive efficiency of reservoir construction determined by indoor simulation experiments, G is the dynamic reserves of gas reservoirs evaluated by material balance, and B is gri is the natural gas volume coefficient of the gas reservoir at the original formation pressure, B ging is the natural gas volume coefficient of the gas reservoir at any pressure, V wflux is the volume of gas-bearing pores affected by edge and bottom water intrusion during gas reservoir development, E wg is the microscopic gas drive efficiency of the flooded area of ​​the gas reservoir determined by indoor simulation experiments, V lowpg is the volume of gas-bearing pores with poor reservoir properties determined based on geological evaluation; I e is the inventory under different formation pressures.

[0065] Taking the Bohai Gas Storage as an example, based on the geological and development dynamic data of the oil and gas reservoirs, the dynamic reserves of crude oil in the oil layer of the Bohai Gas Storage are calculated by material balance method to be 479.84×10 4 t, according to the high-pressure physical property parameters of natural gas, the crude oil volume coefficient of the reservoir under the original formation pressure is 1.375, the macroscopic sweep coefficient of gas drive in 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 calculated effective gas-bearing pore volume of the reservoir is 374.94×10 4 m 3 According to Formula I e =V ge / B ginj Calculate the storage volume under different formation pressures and obtain the gas storage reservoir storage curve (such as Figure 2 The reservoir inventory curve shows the oil reservoir.

[0066] Based on the geological and development data of oil and gas reservoirs, the dynamic reserves of gas layers in Bohai Gas Storage are calculated by material balance method to be 8.1×10 8 m 3 According to the high-pressure physical property parameters of natural gas, the natural gas volume coefficient of the gas layer under the original formation pressure is 0.00454, and the gas-bearing pore volume affected by the intrusion of edge and bottom water during the development of the gas layer is 25.44×10 4 m 3 The microscopic gas drive efficiency in the flooded area of ​​the gas reservoir is 59.32%, and the volume of gas-bearing pores with poor reservoir permeability is 15.33×10 4 m 3 , according to the formula V ge =(G×B gri )-V wflux ×(1-E wg )-V lowpg The calculated effective gas-bearing pore volume of the reservoir is 327×10 4 m 3 According to Formula I e =V ge / B ginj Calculate the storage volume under different formation pressures and obtain the gas storage reservoir storage curve (such as Figure 2 gas reservoir inventory curve).

[0067] Step S102, based on the gas storage inventory and the determined upper limit pressure, calculate the gas storage working gas volume corresponding to different lower limit pressures. Specifically:

[0068] According to the formula Calculated. Among them, B ginjmax Q is the natural gas volume coefficient of the gas reservoir at the upper limit pressure; wg The working gas volume of the gas storage corresponding to different lower limit pressures.

[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 by geomechanical analysis, which is 27MPa in this example. According to the high-pressure physical parameters of natural gas, the volume coefficient of natural gas in the oil and gas reservoir under the upper limit pressure is 0.00387 and the volume coefficient of natural gas under different formation pressures. According to the formula The working gas volume of the gas storage corresponding to different lower limit pressures is calculated.

[0070] Step S103, according to the number of days of winter peak-shaving gas production 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. Specifically:

[0071] According to the formula Q pg =Q wg / t is used to calculate the average daily gas production during the winter peak-shaving gas production period of the gas storage. Among them, t is the number of days of winter peak-shaving gas production of the gas storage, Q pg It is the average daily gas production during the winter peak-shaving gas production period of the gas storage facility.

[0072] In the example of the present invention, the number of days for winter peak-shaving gas production determined by the gas storage construction planning scheme is 120 days. According to the formula Q pg =Q wg / tThe average daily gas production of the gas storage during the winter peak-shaving production period is calculated, as shown in Table 1.

[0073] Table 1 Results of natural gas volume coefficient, working gas volume of gas storage and average daily gas production corresponding to different formation pressures of oil and gas layers in Bohai gas storage

[0074]

[0075]

[0076] Step S104, based on the binomial production capacity equation of the gas storage reservoir gas well, establish the relationship between the inflow from the formation to the bottom of the well and the production pressure difference, specifically:

[0077] According to the binomial capacity equation p R 2 -p wf 2 =Aq sc +Bq sc 2 Calculate the inflow dynamics during the gas injection process of the gas storage, where coefficients A and B are obtained based on Darcy's seepage theory or field well test data. The mathematical expressions calculated based on Darcy's seepage theory are:

[0078] Among them, p R is the formation pressure; p wf is the bottom hole flowing pressure; q sc is the daily production of the gas well; K is the effective permeability of the reservoir gas phase; h is the effective thickness of the reservoir; r e is the gas well supply radius; r w is the radius of the gas wellbore; g is the relative density of gas; is 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 the embodiment of the present invention, the coefficients A and B are obtained according to the well test data of the mine, and then according to the binomial production capacity equation pR 2 -p wf 2 =Aq sc +Bq sc 2 Establish the relationship between the inflow from the formation to the bottom of the well and the production pressure difference.

[0080] Step S105, using a node analysis method to evaluate the reasonable production capacity of gas wells corresponding to different lower limit pressures. Specifically:

[0081] The gas well inflow (binomial production capacity equation) and outflow (wellbore pipe flow dynamics) curves under different lower limit pressures are plotted. There are a series of intersections between the inflow and outflow curves under the same lower limit pressure. Further considering the constraints of the critical sand pressure difference, critical liquid carrying and erosion flow rate of the gas well, the gas well production capacity must be less than the gas well production capacity limited by the critical sand pressure difference and erosion flow rate, and must be greater than the gas well production capacity limited by the critical liquid carrying rate. Comprehensively evaluate the reasonable production capacity q under different lower limit pressures npg (like Figure 3 , 4 As shown, Figure 3 This is the relationship between the formation pressure of the Bohai gas storage reservoir and the reasonable production capacity of a typical single well. Figure 4 (Figure 2 is the relationship between the formation pressure of the gas layer in the Bohai gas storage 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 corresponding to different lower limit pressures and the reasonable production capacity of the gas wells, calculate the number of gas wells required for the winter peak-shaving production of the gas storage that meets the gas well production node coordination requirements. Specifically:

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

[0084] Among them, N nw The number of gas wells required for winter production in a gas storage facility to meet the coordination requirements of gas well production nodes, Q pg is the average daily gas production during the winter peak-shaving gas production period of the gas storage corresponding to different lower limit pressures, q npg For Q pg Reasonable production capacity of gas wells at different lower pressure limits.

[0085] In the embodiment of the present invention, the number of gas wells required for winter production of the gas storage reservoir that meets 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 reservoir obtained in step S103 by the reasonable production capacity of the gas wells corresponding to the different lower limit pressures obtained in step S105.

[0086] Table 2 Working gas volume of Bohai gas storage with different lower limit pressures and the number of gas wells that meet the coordination requirements of gas production nodes

[0087]

[0088] Step S107, according to the reasonable production capacity of the gas well of the gas storage corresponding to different lower pressure limits, the high-speed unstable seepage equation is used to calculate the well-controlled seepage area of ​​the gas well production at the corresponding different lower pressure limits, specifically:

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

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

[0091]

[0092] Among them, p min is the lower limit pressure of the gas storage; p max is the upper limit pressure of the gas storage; T sc is the standard ground temperature; t is the number of days of winter peak-shaving production in the gas storage; φ is the reservoir porosity; μ is the gas viscosity; C t is the total compression coefficient of the formation; K is the effective permeability of the reservoir gas phase; R e r is the controlled seepage radius of the gas well; w is the radius of the gas wellbore; B g is the gas volume coefficient; h is the effective thickness of the reservoir; r D is the dimensionless radial distance; t D is dimensionless time; Q D is dimensionless output.

[0093] In the embodiment of the present invention, according to the actual production data and the high-speed unstable seepage equation The pseudo pressure The mathematical expression is Calculate the corresponding well control radius under different formation pressures (such as Figure 5 ).

[0094] Step S108, calculating the well-controlled seepage area of ​​a single well under different lower pressure limits according to the well-controlled seepage radius of a single well under different lower pressure limits, specifically:

[0095] According to the formula Calculate and obtain the well-controlled seepage area of ​​a single gas well under different lower limit pressures (such as Figure 5 and Table 3).

[0096] Among them, Aw is the well-controlled seepage area of ​​a single gas well in the gas storage reservoir, R e It is the controlled seepage radius of the gas well in the gas storage reservoir.

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

[0098] According to the formula N rw =A r / A w 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.

[0099] In the embodiment of the present invention, the effective oil and gas area of ​​the reservoir for oil and gas reservoir construction is obtained according to the production data, and the effective oil and gas area of ​​the reservoir for oil and gas reservoir construction is divided by the well-controlled seepage area of ​​the gas well of the gas storage reservoir under different lower limit pressures to obtain the number of gas production wells required for the winter peak-shaving production of the gas storage reservoir that meets the requirement of effectively controlling the effective oil and gas area of ​​the reservoir (as shown in Table 3).

[0100] Table 3 Single well controlled seepage area under different lower limit pressures in Bohai gas storage and the number of gas production wells required to effectively control the effective oil and gas area of ​​the reservoir for winter peak-shaving production in the gas storage

[0101]

[0102] Step S110, the relationship curve between the number of wells required for winter peak-shaving production and production of gas in the gas storage that meets the coordination requirements of gas well production nodes and the lower limit pressure, and the relationship curve between the number of wells required for winter peak-shaving production and production of gas in the gas storage that meets the requirements of effective control of the effective oil and gas area of ​​the reservoir and the lower limit pressure are superimposed and drawn in the same coordinate system. According to the intersection characteristics of the above two curves, the lower limit pressure of the gas storage operation is designed, specifically:

[0103] ① If there is an intersection point between the above two curves, the well flow and the average daily gas production during the winter peak-shaving gas production of the gas storage are used to calculate the wellhead pressure corresponding to the lower limit pressure at the above intersection point, and determine whether the wellhead pressure at this time meets the minimum wellhead pressure required by the natural gas surface pipeline. If so, the intersection point is the lower limit pressure that simultaneously meets the triple requirements of the coordination of production nodes of gas wells for gas storage peak-shaving gas production, effective control of the gas-bearing area of ​​the reservoir, and the minimum wellhead pressure required by the natural gas surface pipeline.

[0104] ② If the above two curves have an intersection, then the wellhead pressure corresponding to the lower limit pressure at the intersection is calculated using the gas well pipe flow and the average daily gas production during the winter peak-shaving gas production of the gas storage reservoir, and it is determined whether the wellhead pressure at this time meets the minimum wellhead pressure required by the natural gas surface gas pipeline. If the calculated gas well wellhead pressure is lower than the minimum wellhead pressure required by the natural gas surface gas pipeline, but as the lower limit pressure increases, the production well number curve required by the coordination of the gas well node for the winter peak-shaving gas production of the gas storage reservoir is higher than the production well number curve that meets the requirements 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 during the winter peak-shaving gas production of the gas storage reservoir and its corresponding wellhead pressure are calculated, and then the lower limit pressure of the gas storage reservoir is obtained by reverse calculation using the gas well pipe flow and production capacity equation according to the minimum external transmission wellhead pressure required by the natural gas surface gas pipeline;

[0105] ③ If the above two curves have an intersection, then the wellhead pressure corresponding to the lower limit pressure at the above intersection is calculated using the gas well pipe flow and the average daily gas production during the winter peak-shaving gas production of the gas storage reservoir, and it is determined whether the wellhead pressure at this time meets the minimum wellhead pressure required by the natural gas surface gas pipeline. If the calculated gas well wellhead pressure is lower than the minimum wellhead pressure required by the natural gas surface gas pipeline, but as the lower limit pressure increases, the production well number curve required by the coordination of the gas well node for the winter peak-shaving gas production of the gas storage reservoir is lower than the production well number curve that meets the requirements for effective control of the effective oil and gas area of ​​the reservoir, then based on the latter, combined with the working gas volume corresponding to different lower limit pressures, the average daily gas production of a single well during the winter peak-shaving gas production of the gas storage reservoir and its corresponding wellhead pressure are calculated, and then according to the minimum external transmission wellhead pressure required by the natural gas surface gas pipeline, the gas well pipe flow and production capacity equation are used to reversely calculate the lower limit pressure of the gas storage reservoir;

[0106] ④ If there is no intersection between the above two curves, and the curve of the number of production wells that meets the coordination requirements of the gas well nodes for the winter peak-shaving gas production of the gas storage reservoir 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 the number of gas wells corresponding to different lower limit pressures, the average daily gas production of a single well during the winter peak-shaving gas production of the gas storage reservoir and its corresponding wellhead pressure are calculated, and then, based on the minimum wellhead pressure required by the natural gas surface transmission pipeline, the gas well pipe flow and production capacity equation are used to reversely calculate the lower limit pressure of the gas storage reservoir;

[0107] ⑤ If the above two curves do not have an intersection point, and the number of production wells that meet the coordination requirements of the gas well nodes for the winter peak-shaving gas production of the gas storage reservoir 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, combined with the working gas volume and the number of gas wells corresponding to different lower limit pressures, the average daily gas production of a single well during the winter peak-shaving gas production of the gas storage reservoir and its corresponding wellhead pressure are calculated, and then according to the minimum wellhead pressure required by the natural gas surface gas pipeline, the gas well pipe flow and production capacity equation are used to reversely calculate the lower limit pressure of the gas storage reservoir, ( Figure 6 Schematic diagram of the five situations mentioned above).

[0108] In the embodiment of the present invention, for the Bohai gas storage, the first of the above five situations is adopted, that is, the lower limit pressure that satisfies the triple requirements of the coordination of the gas well production nodes for peak-shaving gas production in the gas storage, effective control of the gas-bearing area of ​​the reservoir, and the minimum wellhead pressure required by the natural gas surface transmission pipeline. The calculated operating lower limit pressure is 11.3MPa (e.g. Figure 7 shown).

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

[0110] Table 4 and Figure 8 The lower limit operating pressure of the Bohai gas storage calculated by the existing method and the new method of the present invention.

[0111] Table 4 Bohai gas storage operating lower limit pressure calculated by different methods

[0112]

[0113] The lower limit pressure of gas storage operation that meets the existing requirements of gas well production node coordination and the minimum wellhead pressure design requirements of natural gas surface gas pipelines (method A) is used. The calculated lower limit pressure is 10MPa. Since this method only considers the wellhead pressure requirements of natural gas pipeline transmission, but does not consider the effective control of the effective oil and gas area of ​​the reservoir, the number of newly drilled wells (12) for reservoir construction exceeds the number of wells required for storage capacity control (11, as shown in Table 3), resulting in well-to-well interference and well control area superposition in gas storage production, especially causing waste of engineering investment, and unable to achieve the optimal lower limit pressure of reservoir construction operation.

[0114] The new method proposed in the present invention takes into account the requirements for coordination of gas well production nodes, effective control of the effective oil and gas area of ​​the reservoir, and the minimum wellhead pressure design requirements of the natural gas surface transmission pipeline. The calculated lower limit pressure is 11.3MPa, and the number of new wells is 11. This method meets the above-mentioned triple lower limit pressure design requirements. The new method also considers the two core factors of efficient external transmission of natural gas pipelines and effective control of storage capacity for winter peak-shaving gas production in gas storage, and 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 the operation of a gas storage reservoir in a weak water drive oil and gas reservoir, characterized in that: The method comprises the following steps: Step 1: According to the geological and development dynamic characteristics of the oil and gas reservoir and the laboratory simulation results, determine the effective gas storage pore volume of the reservoir and the storage volume under different formation pressures; Step 2: According to the gas storage reservoir inventory and the determined upper limit pressure of operation, the working gas volume of the gas storage reservoir corresponding to different lower limit pressures is calculated; Step 3: Based on the calculated working gas volumes corresponding to different lower limit pressures and the number of days for winter peak-shaving gas production determined in the gas storage construction plan, calculate the average daily gas production volume of the gas storage during the winter peak-shaving gas production period; Step 4: Based on the binomial production capacity equation of the gas storage reservoir gas well, the node analysis method is used to evaluate the reasonable production capacity of the gas well corresponding to different lower limit pressures; Step 5: The average daily gas production during the winter peak-shaving gas production period of the gas storage corresponding to different lower limit pressures is divided by the reasonable production capacity of the gas wells at the corresponding different lower limit pressures to calculate the number of gas wells required for the winter peak-shaving production of the gas storage that meets the coordination requirements of the gas well production nodes; Step 6: Based on the reasonable production capacity of the gas wells in the gas storage corresponding to different lower pressure limits, the high-speed unstable seepage equation is used to calculate the well-controlled seepage area of ​​the gas well production at the corresponding different lower pressure limits; Step 7: The effective oil and gas area of ​​the reservoir is divided by the well-controlled seepage area of ​​the gas wells in the gas storage reservoir at different lower pressure limits to calculate the number of gas wells required for winter peak-shaving production in the gas storage reservoir to meet the effective control requirements for the effective oil and gas area of ​​the reservoir; Step 8: With the lower limit pressure as the horizontal coordinate and the number of production wells as the vertical coordinate, the relationship curve between the number of wells required for winter peak-shaving production and production of gas storage facilities that meets the gas well production node coordination requirements and the lower limit pressure, and the relationship curve between the number of wells required for winter peak-shaving production and production of gas storage facilities that meets the requirements for effective control of the effective oil and gas-bearing area of ​​the reservoir and the lower limit pressure are superimposed and drawn in the same coordinate system; Step 9: Based on the intersection characteristics of the above two curves, design the lower limit pressure of the gas storage operation, specifically: AIf there is an intersection point between the above two curves, the well flow and the average daily gas production during the winter peak-shaving gas production of the gas storage are used to calculate the wellhead pressure corresponding to the lower limit pressure at the above intersection point, and determine whether the wellhead pressure at this time meets the minimum wellhead pressure required by the natural gas surface transmission pipeline; if so, the intersection point is the lower limit pressure that simultaneously meets the triple requirements of the coordination of production nodes of the gas wells for peak-shaving gas production in the gas storage, the effective control of the gas-bearing area of ​​the reservoir, and the minimum wellhead pressure required by the natural gas surface transmission pipeline; B. If the above two curves have an intersection, then the wellhead pressure corresponding to the lower limit pressure at the intersection is calculated by using the gas well pipe flow and the average daily gas production during the winter peak-shaving gas production of the gas storage reservoir, and it is judged whether the wellhead pressure at this time meets the minimum wellhead pressure required by the natural gas surface gas transmission pipeline; if the calculated gas well wellhead pressure is lower than the minimum wellhead pressure required by the natural gas surface gas transmission pipeline, but with the increase of the lower limit pressure, the production well number curve required by the coordination of the gas well node of the winter peak-shaving gas production of the gas storage reservoir is higher than the production well number curve that meets the effective control requirements of the effective oil and gas area of ​​the reservoir, then based on the former, combined with the working gas volume corresponding to different lower limit pressures, the average daily gas production of a single well during the winter peak-shaving gas production of the gas storage reservoir and its corresponding wellhead pressure are calculated, and then according to the minimum external transmission wellhead pressure required by the natural gas surface gas transmission pipeline, the gas well pipe flow and production capacity equation are used to reversely calculate the lower limit pressure of the gas storage reservoir; C If the above two curves have an intersection, then the wellhead pressure corresponding to the lower limit pressure at the intersection is calculated by using the gas well pipe flow and the average daily gas production during the winter peak-shaving gas production of the gas storage reservoir, and it is judged whether the wellhead pressure at this time meets the minimum wellhead pressure required by the natural gas surface gas transmission pipeline; if the calculated gas well wellhead pressure is lower than the minimum wellhead pressure required by the natural gas surface gas transmission pipeline, but with the increase of the lower limit pressure, the production well number curve required by the coordination of the gas well node of the winter peak-shaving gas production of the gas storage reservoir is lower than the production well number curve that meets the effective control requirements of the effective oil and gas area of ​​the reservoir, then based on the latter, combined with the working gas volume corresponding to different lower limit pressures, the average daily gas production of a single well during the winter peak-shaving gas production of the gas storage reservoir and its corresponding wellhead pressure are calculated, and then according to the minimum external transmission wellhead pressure required by the natural gas surface gas transmission pipeline, the gas well pipe flow and production capacity equation are used to reversely calculate the lower limit pressure of the gas storage reservoir; D. If the above two curves do not have an intersection point, and the production well number curve that meets the coordination requirements of the gas well nodes for the gas storage reservoir's winter peak-shaving gas production is higher than the production well number curve that meets the requirements for effective control of the effective oil and gas-bearing area of ​​the reservoir, then based on the former, combined with the working gas volume and the number of gas wells corresponding to different lower limit pressures, the average daily gas production of a single well during the winter peak-shaving gas production period of the gas storage reservoir and its corresponding wellhead pressure are calculated, and then, based on the minimum wellhead pressure required by the natural gas surface transmission pipeline, the gas well pipe flow and production capacity equation are used to reversely calculate the lower limit pressure of the gas storage reservoir; EIf there is no intersection between the above two curves, and the curve of the number of production wells that meets the coordination requirements of the gas well nodes for the winter peak-shaving gas production of the gas storage reservoir is lower than 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 latter, combined with the working gas volume and the number of gas wells corresponding to different lower limit pressures, the average daily gas production of a single well during the winter peak-shaving gas production of the gas storage reservoir and its corresponding wellhead pressure are calculated, and then, based on the minimum wellhead pressure required by the natural gas surface gas pipeline, the gas well pipe flow and production capacity equation are used to reversely calculate the lower limit pressure of the gas storage reservoir.

2. The method for determining the lower limit operating pressure of a weak water drive oil and gas reservoir gas storage according to claim 1, characterized in that: The determination of the effective gas storage pore volume of the reservoir and the storage volume under different formation pressures in step 1 includes: Using data on reservoir development performance, laboratory gas injection displacement, and high-pressure physical properties of crude oil and natural gas, for weak water drive reservoirs, according to the formula V ge =(N oi ×B oi )×η og ×E og For weak water drive gas reservoirs, according to the formula V ge =(G×B gri )-V wflux ×(1-E wg )-V lowpg , respectively calculate the effective gas-bearing pore volume of the reservoir; using formula I e =V ge / B ginj The gas storage inventory curve is calculated; Among them, V ge The effective gas storage pore volume of the reservoir for oil and gas reservoirs, N oi is the dynamic reserves of crude oil in the reservoir evaluated based on material balance, B oi is the volume coefficient of crude oil at the original reservoir formation pressure, η og is the macroscopic sweep coefficient of gas flooding in reservoir construction determined by indoor simulation experiments or reservoir numerical simulation, E og is the microscopic gas drive efficiency of reservoir construction determined by indoor simulation experiments, G is the dynamic reserves of gas reservoirs evaluated by material balance, and B is gri is the natural gas volume coefficient of the gas reservoir at the original formation pressure, B ging is the natural gas volume coefficient of the gas reservoir at any pressure, V wflux is the volume of gas-bearing pores affected by edge and bottom water intrusion during gas reservoir development, E wg is the microscopic gas drive efficiency of the flooded area of ​​the gas reservoir determined by indoor simulation experiments, V lowpg is the volume of gas-bearing pores with poor reservoir properties determined based on geological evaluation; I e is the inventory under different formation pressures.

3. The method for determining the lower limit operating pressure of a weak water drive oil and gas reservoir gas storage according to claim 1, characterized in that: The working gas volume of the gas storage corresponding to different lower limit pressures is calculated in step 2. According to the formula Calculated; Among them, B ginjmax is the volume coefficient of natural gas in the gas reservoir under the upper limit pressure of the gas storage reservoir, Q wg The working gas volume of the gas storage corresponding to different lower limit pressures.

4. The method for determining the lower limit operating pressure of a weak water drive oil and gas reservoir gas storage according to claim 1, characterized in that: The average daily gas production during the winter peak-shaving period of the gas storage is calculated in step 3. According to the formula Q pg =Q wg / t calculated; Among them, t is the number of days of gas production for peak load regulation in winter in the gas storage, Q pg It is the average daily gas production during the winter peak-shaving gas production period of the gas storage facility.

5. The method for determining the lower limit operating pressure of a weak water drive oil and gas reservoir gas storage according to claim 1, characterized in that: The binomial capacity equation described in step 4 is: p R 2 -p wf 2 =Aq sc +Bq sc 2 Among them, coefficients A and B are obtained according to Darcy's seepage theory or field well test data, and their mathematical expressions calculated according to Darcy's seepage theory are: Among them, p R is the formation pressure; p wf is the bottom hole flowing pressure; q sc is the daily production of the gas well; K is the effective permeability of the reservoir gas phase; h is the effective thickness of the reservoir; r e is the gas well supply radius; r w is the radius of the gas wellbore; g is the relative density of gas; is 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; The node analysis method is used to evaluate the reasonable production capacity of gas wells corresponding to different lower limit pressures, including: drawing the gas well inflow binomial production capacity equation and the outflow wellbore pipe flow dynamic curve chart under different lower limit pressures, the inflow and outflow curves have a series of intersection points under the same lower limit pressure, and further considering the constraints of the critical sand production pressure difference, critical liquid carrying and erosion flow rate of the gas well, the gas well production capacity must be less than the gas well production capacity limited by the critical sand production pressure difference and erosion flow rate, and must be greater than the gas well production capacity limited by the critical liquid carrying, 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 weak water drive oil and gas reservoir according to claim 1, characterized in that: The calculation described in step 5 obtains the number of gas wells required for winter production in the gas storage reservoir that meets the coordination requirements of gas well production nodes. According to the formula N nw =Q pg / q npg Calculated; Among them, N nw The number of gas wells required for winter production in a gas storage facility to meet the coordination requirements of gas well production nodes, Q pg is the average daily gas production during the winter peak-shaving gas production period of the gas storage corresponding to different lower limit pressures, q npg For 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 weak water drive oil and gas reservoir according to claim 1, characterized in that: The high-speed unstable seepage equation in step 6 is: Among them, the pseudo pressure The mathematical expression is: Among them, p min is the lower limit pressure of the gas storage; p max is the upper limit pressure of the gas storage; T sc is the standard ground temperature; t is the number of days of winter peak-shaving production in the gas storage; φ is the reservoir porosity; μ is the gas viscosity; C t is the total compression coefficient of the formation; K is the effective permeability of the reservoir gas phase; R e r is the controlled seepage radius of the gas well; w is the radius of the gas wellbore; B g is the gas volume coefficient; h is the effective thickness of the reservoir; r D is the dimensionless radial distance; t D is dimensionless time; Q D is dimensionless output.

8. The method for determining the lower limit operating pressure of a weak water drive oil and gas reservoir gas storage according to claim 1, characterized in that: The well-controlled seepage area of ​​a gas well under different lower limit pressures is calculated in step 7. Calculated; Among them, A w is the well-controlled seepage area of ​​a single gas well in the gas storage reservoir, R e It is the controlled seepage radius of the gas well in the gas storage reservoir.

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

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

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