Method for calculating gas amount of gas storage cushion

Abstract

The invention provides a method for calculating the gas amount of a gas storage cushion, and belongs to the technical field of natural gas storage. The method comprises the following steps: calculating the minimum water content saturation according to the requirements of the gas storage and the operation conditions of the gas storage; establishing a capillary force curve of the corresponding rock stratum; on the basis of the capillary force curve, determining a capillary force value according to the minimum water content saturation; drawing a water-phase pressure-depth curve and a gas-phase pressure-depth curve; according to the water phase pressure depth curve and the gas phase pressure depth curve, the gas saturation and the formation volume coefficient of the corresponding rock stratum are calculated; based on the rock stratum parameters of the corresponding rock stratum and the gas saturation and the stratum volume coefficient of the corresponding rock stratum, the air cushion amount of the corresponding rock stratum is calculated; compared with the prior art, the method can be suitable for calculating the cushion gas amount of the water-containing gas storage, the current operation requirement of the large waterlogging dam gas storage can be met, and the water content of output natural gas does not exceed a standard value; and meanwhile, the economic cost is also saved.

Description

Technical Field

[0001] The present invention belongs to the technical field of natural gas storage, and in particular relates to a method for calculating the cushion gas volume of a gas storage reservoir. Background Art

[0002] Aqueous gas storage (AGS) is an important type of gas storage facility. It is formed by injecting high-pressure natural gas beneath a reliably sealed caprock to displace water from the rock formation. Examples of this type of gas storage currently under construction include the Dalaoba and Yakela gas reservoirs in the Kuqa region of northwest China. This type of gas storage boasts a large gas storage capacity, second only to depleted oil and gas reservoirs. The stored gas consists of both working gas and cushion gas. Working gas refers to the gas that is stored and released during the storage cycle, while cushion gas refers to the gas that remains within the reservoir or acts as a buffer between the working gas and the water. Therefore, determining the cushion gas volume is a crucial step in establishing an AGS.

[0003] The cushion gas in a water-bearing gas storage facility plays a crucial role. Its primary purpose is to maintain a certain volume and pressure, prevent water intrusion, and act as a buffer between the working gas and the cushion gas. Cushion gas accounts for 30%-70% of the total gas volume and 1 / 3-2 / 3 of the total investment. When a gas storage facility is abandoned, a significant amount of cushion gas cannot be recovered, resulting in a significant waste of resources. Therefore, calculating the appropriate cushion gas volume is crucial for improving the economic efficiency of a gas storage facility.

[0004] Technical solutions for calculating / simulating the amount of gas storage or cushion gas have been disclosed in the prior art.

[0005] Patent application CN112434474A relates to a method for evaluating the working gas volume of a gas storage reservoir by setting a lower limit pressure. The method establishes three curves, namely, a working gas volume relationship curve for evaluating the material balance of the gas storage reservoir, a working gas volume relationship curve for evaluating the daily injection capacity of the gas injection well, and a working gas volume relationship curve for evaluating the daily production capacity of the gas production well. The three established curves are then placed in the same coordinate system to obtain an intersection curve diagram, thereby determining the upper limit pressure of the gas storage reservoir when the injection and production balance is achieved, thereby determining the working gas volume and storage capacity of the gas storage reservoir. The determined upper limit pressure, working gas volume and storage capacity of the gas storage reservoir are applied to the determination of the construction type of the gas storage reservoir and the design and implementation of the gas storage drilling project and ground engineering. This can achieve optimal configuration of the engineering facilities and the storage and peak-shaving capacity of the gas storage reservoir during production operation, avoid construction waste or restrictions, and maximize economic benefits.

[0006] The paper "Optimal Design of Reservoir-Based Gas Storage Based on Chance-Constrained Programming" addresses the difficulty of traditional deterministic optimization methods for gas storage to cope with fluctuations in natural gas user demand. This paper uses a chance-constrained programming approach to develop a design optimization model for gas reservoir-based gas storage under demand uncertainty, with the goal of minimizing total investment costs. The optimization model uses the volume of cushion gas, number of wells, number of compressors, and number of dehydration units as decision variables, and incorporates constraints such as inventory changes, single-well injection and production capacity, and demand uncertainty. Taking into account the uncertainty of user demand, a chance-constrained programming approach is used to preprocess the uncertainty. The optimization model is then applied to the W23 gas storage reservoir in an oilfield, and solved using the GAMS modeling system and the DICOPT solver.

[0007] However, in some areas of water-containing gas storage, gas and water are distributed in the same layer, and the natural gas injected into the gas storage is expelled in a non-piston manner. The cushion gas volume of the gas storage needs to take into account the coexistence of injected gas and formation water. However, the traditional gas storage cushion gas volume calculation method does not take this factor into account.

[0008] Therefore, how to provide a targeted calculation method for the cushion gas volume applicable to water-containing gas storage is of great significance for improving the economic benefits of gas storage and is one of the practical issues studied by those skilled in the art. Summary of the Invention

[0009] In response to the problem that the calculation / simulation methods of cushion gas volume in the existing technology are difficult to apply to water-containing gas storage reservoirs, the present invention provides a method for calculating the cushion gas volume of gas storage reservoirs. This method calculates the cushion gas volume differently from conventional methods. This method takes into account the heterogeneity of the reservoir, the gas-water distribution in the same layer formed under the action of gravity and capillary force, calculates the natural gas saturation in a specified area of the gas storage reservoir to meet the specified requirements, and then determines what amount of natural gas to inject as cushion gas is more reasonable.

[0010] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0011] A method for calculating the cushion gas volume of a gas storage reservoir comprises the following steps:

[0012] S1. Calculate the minimum water content saturation based on gas storage requirements and gas storage operating conditions;

[0013] S2. Establishing a capillary force curve for the corresponding rock formation;

[0014] S3. Based on the capillary force curve obtained in step S2, the capillary force value is determined according to the minimum water saturation obtained in step S1;

[0015] S4. Draw a water phase pressure-depth curve and a gas phase pressure-depth curve;

[0016] S5. Calculate the gas saturation and formation volume coefficient of the corresponding rock formation according to the water pressure depth curve and the gas pressure depth curve drawn in step S4;

[0017] S6. Calculate the cushion gas volume of the corresponding rock formation based on the rock formation parameters of the corresponding rock formation and the gas saturation and formation volume coefficient of the corresponding rock formation obtained in step S5.

[0018] Preferably, the gas storage requirements in step S1 include the water content of natural gas.

[0019] Preferably, the calculation method of the minimum moisture saturation in step S1 is as follows:

[0020] (1) Establish the relationship curve between gas saturation and water saturation;

[0021] (2) Construct f according to the relationship curve obtained in step (1) g (S g )-S g Curve, based on minimum water content saturation In the f g (S g )-S g Determine the minimum gas saturation on the curve The f g (S g )-S g The curve is:

[0022]

[0023] Where S g Indicates gas saturation, dimensionless; k rw Represents the relative permeability of water, dimensionless; k rg Represents gas relative permeability, dimensionless; μ w 、μ g represent the viscosities of water and gas phase, mPa·s, respectively;

[0024] If the gas storage reservoir includes multiple rock layers, it is necessary to calculate the minimum water content saturation of each rock layer to determine the minimum gas saturation of each rock layer.

[0025] Preferably, the method for determining the capillary force value in step S3 is: for the corresponding rock formation, the minimum gas saturation The intersection point with the capillary force curve is the corresponding capillary force value

[0026] Preferably, step S4 specifically includes the following steps:

[0027] On the Pressure-Depth (pD) graph:

[0028] S401. Draw the water phase pressure depth curve P w -D;

[0029] S402. Draw the gas phase pressure depth curve

[0030] Further preferably, the specific method of drawing in step S402 is: for each rock layer involved in injection and production, the top depth of the rock layer is determined and recorded as calculate On the pD chart, draw the following function curve:

[0031]

[0032] Where ρ g is the gas phase density, g is the acceleration due to gravity

[0033] Determine the maximum value p in the depth range of gas storage distribution g,k ~D curve, denoted as

[0034] Preferably, the calculation method in step S5 is:

[0035] The water phase pressure value and the gas phase pressure value of the corresponding rock formation are calculated, the corresponding gas saturation is calculated based on the difference between the water phase pressure value and the gas phase pressure value, and the formation volume coefficient of the corresponding rock formation is calculated based on the gas phase pressure value.

[0036] Further preferably, the specific method of calculation in step S5 is:

[0037] S501: Calculate the middle depth of all rock layers in the gas storage reservoir and record it as exist On the curve, determine the depth The corresponding gas phase pressure value is recorded as And in p w The corresponding water phase pressure value on the ~D curve

[0038] S502: Capillary force curve p corresponding to the layer cgw,k -S w On the capillary force The corresponding gas saturation S g,k (k=1..N;N≥n);

[0039] S503: Based on the natural gas formation volume coefficient curve B g ~p confirmed The corresponding formation volume coefficient

[0040] Preferably, the rock formation parameters in step S6 include rock formation volume and rock formation porosity.

[0041] Preferably, the formula used in the calculation in step S6 is:

[0042]

[0043] The above formula is used to calculate the gas cushion volume of the corresponding rock layer, where: V b Indicates the volume of rock layer, m 3 ; φ represents porosity, dimensionless; Indicates the cushion air volume, m 3 .

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] The present invention provides a method for calculating the cushion gas volume of a gas storage reservoir for water-bearing lithologic oil and gas reservoirs. The method takes into account the heterogeneity of the reservoir and the gas-water distribution in the same layer formed under the action of gravity and capillary force. The method can be applied to the calculation of the cushion gas volume of water-bearing gas storage reservoirs. It can not only meet the current operating requirements of the Dalaoba gas storage reservoir and ensure that the water content of the output natural gas does not exceed the standard value; it also saves economic costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a schematic diagram of determining gas saturation based on water content output from gas storage operation according to an embodiment of the present invention;

[0047] Figure 2 A schematic diagram of determining capillary force based on gas saturation according to an embodiment of the present invention;

[0048] Figure 3 This is a schematic diagram of determining the operating pressure of a gas storage based on a specified gas saturation according to an embodiment of the present invention. DETAILED DESCRIPTION

[0049] Example: A method for calculating the cushion gas volume of a gas storage reservoir

[0050] S1. According to the requirements of gas storage operation on the water content of produced natural gas The minimum water saturation is calculated based on the gas-water relative permeability curve and the viscosity of natural gas and formation water.

[0051] Specifically, the formula is as follows:

[0052]

[0053] Where S g Indicates gas saturation, dimensionless; k rw Represents the relative permeability of water, dimensionless; k rgRepresents gas relative permeability, dimensionless; μ w 、μ g Represent the viscosity of water and gas phase, mPa·s, respectively.

[0054] Figure 1 The figure shows a schematic diagram of determining gas saturation based on the water content output from the gas storage operation. Figure 2 As shown, in f g (S g )-S g On the curve, determine Corresponding minimum gas saturation

[0055] The injection and production layers of the gas storage include multiple rock layers. The above operations need to be performed on each rock layer to determine the minimum gas saturation.

[0056] S2. Establish a capillary force curve for the corresponding rock formation.

[0057] S3. According to the capillary force curve of the corresponding rock formation, the minimum gas saturation Determine the corresponding capillary force value and record it as

[0058] Specifically, if Figure 2 As shown, for the corresponding rock layer, the minimum gas saturation The intersection point with the capillary force curve is the corresponding capillary force value.

[0059] S4. On the pressure-depth curve (pD) board, draw the water phase pressure-depth curve P w -D and gas phase pressure depth curves; including:

[0060] Step S401: Draw a water phase pressure depth curve P w -D.

[0061] Step S402: Draw a gas phase pressure depth curve For each rock formation involved in injection and production, the top depth of the rock formation is determined and recorded as calculate On the pD chart, draw the following function curve:

[0062]

[0063] Determine the maximum value p in the depth range of gas storage distribution g,k ~D curve, denoted as like Figure 3 In the previous step, draw two p g ~D curve, take the curve at the top as

[0064] S5. Calculate the water phase pressure value and gas phase pressure value of the corresponding rock formation, calculate the corresponding gas saturation based on the difference between the water phase pressure value and the gas phase pressure value, and calculate the bottom volume coefficient of the corresponding rock formation based on the gas phase pressure value, including:

[0065] S501: Calculate the middle depth of all rock layers in the gas storage reservoir and record it as exist On the curve, determine the depth The corresponding gas phase pressure value is recorded as And in p w The corresponding water phase pressure value on the ~D curve

[0066] S502: Capillary force curve p corresponding to the layer cgw,k -S w On the capillary force The corresponding gas saturation S g,k (k=1..N;N≥n);

[0067] S503: Based on the natural gas formation volume coefficient curve B g ~p confirmed The corresponding formation volume coefficient

[0068] S6. Calculate the cushion gas volume of the corresponding rock formation based on the rock formation volume, rock formation porosity, formation volume coefficient, and gas saturation of the corresponding rock formation.

[0069]

[0070] The above formula is used to calculate the gas cushion volume of the corresponding rock layer, where: V b Indicates the volume of rock layer, m 3 ; φ represents porosity, dimensionless; Indicates the cushion air volume, m 3 .

[0071] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A method for calculating the cushion gas volume of a gas storage reservoir, characterized in that: The following steps are involved: S1. Calculate the minimum water content saturation based on gas storage requirements and gas storage operating conditions; S2. Establishing a capillary force curve for the corresponding rock formation; S3. Based on the capillary force curve obtained in step S2, the capillary force value is determined according to the minimum water saturation obtained in step S1; S4. Draw a water phase pressure-depth curve and a gas phase pressure-depth curve; S5. Calculate the gas saturation and formation volume coefficient of the corresponding rock formation according to the water pressure depth curve and the gas pressure depth curve drawn in step S4; S6. Calculate the cushion gas volume of the corresponding rock formation based on the rock formation parameters of the corresponding rock formation and the gas saturation and formation volume coefficient of the corresponding rock formation obtained in step S5.

2. The method according to claim 1, wherein: The gas storage requirements in step S1 include the water content of natural gas.

3. The method according to claim 1, wherein: The calculation method of the minimum moisture saturation in step S1 is as follows: (1) Establish the relationship curve between gas saturation and water saturation; (2) Construct f according to the relationship curve obtained in step (1) g (S g )-S g Curve, based on minimum water content saturation In the f g (S g )-S g Determine the minimum gas saturation on the curve The f g (S g )-S g The curve is: Where S g Indicates gas saturation, dimensionless; k rw Represents the relative permeability of water, dimensionless; k rg Represents gas relative permeability, dimensionless; μ w 、μ g Represent the viscosities of water and gas phase, mPa·s, respectively.

4. The method according to claim 1, wherein The method for determining the capillary force value in step S3 is: for the corresponding rock formation, the minimum gas saturation The intersection point with the capillary force curve is the corresponding capillary force value 5. The method according to claim 1, wherein Step S4 specifically includes the following steps: On the pressure-depth curve (pD) chart: S401. Draw the water phase pressure depth curve P w -D; S402. Draw the gas phase pressure depth curve 6. The method according to claim 5, characterized in that The specific method of drawing in step S402 is: for each rock layer involved in injection and production, determine the top depth of the rock layer and record it as calculate On the pD chart, draw the following function curve: Where ρ g is the gas phase density, g is the acceleration due to gravity; Determine the maximum value p in the depth range of gas storage distribution g,k ~D curve, denoted as 7. The method according to claim 1, characterized in that The calculation method in step S5 is: The water phase pressure value and the gas phase pressure value of the corresponding rock formation are calculated, the corresponding gas saturation is calculated based on the difference between the water phase pressure value and the gas phase pressure value, and the formation volume coefficient of the corresponding rock formation is calculated based on the gas phase pressure value.

8. The method according to claim 1, characterized in that The calculation method in step S5 is: S501: Calculate the middle depth of all rock layers in the gas storage reservoir and record it as exist On the curve, determine the depth The corresponding gas phase pressure value is recorded as And in p w The corresponding water phase pressure value on the ~D curve S502: Capillary force curve p corresponding to the rock formation cgw,k -S w On the capillary force The corresponding gas saturation S g,k (k=1..N;N≥n); S503: Based on the natural gas formation volume coefficient curve B g ~p confirmed The corresponding formation volume coefficient 9. The method according to claim 1, characterized in that The rock formation parameters in step S6 include rock formation volume and rock formation porosity.

10. The method according to claim 1, characterized in that The formula used in the calculation in step S6 is: Where V b Indicates the volume of rock layer, m 3 ; φ represents porosity and is dimensionless; Indicates the cushion air volume, m 3 .

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