Method for calculating gas storage capacity of aquifer gas storage

Abstract

The application relates to the fields of natural gas underground storage, gas reservoir engineering and indoor experiment technology, and discloses a water-bearing layer gas storage reservoir gas storage capacity calculation method, which comprises the following steps: obtaining water-bearing layer structure water body volume, stratum pressure, temperature and reservoir rock mineral characteristic data, and the maximum volume of natural gas dissolved in the stratum water under the condition of the reservoir temperature and pressure; obtaining cumulative water production and pressure data, and determining the cumulative water production and pressure function relationship; according to the material balance principle, the gas storage capacity of the gas storage reservoir at any time is divided into the sum of the pore volume contributed by the cumulative water production after the high-pressure gas injection into the stratum, the water body elastic compression amount and the rock pore expansion amount, and the dissolved gas amount. According to the pore volume of the gas storage and the gas volume dissolved in the stratum water, the gas storage capacity of the water-bearing layer gas storage reservoir is determined, and the dynamic calculation method of the natural gas storage capacity for the design of the undeveloped water-bearing layer is provided.

Description

Technical Field

[0001] This invention relates to the fields of underground natural gas storage, gas reservoir engineering, and indoor experimental technology, specifically to a method for calculating the gas storage capacity of an aquifer gas storage facility. Background Technology

[0002] Aquifer gas storage facilities, artificial gas reservoirs formed by injecting natural gas into underground aquifers with suitable storage conditions through high-pressure gas injection and water displacement, are core facilities for ensuring strategic natural gas reserves and peak-shaving supply, occupying a crucial position in the energy security system. Storage capacity, as a core indicator for measuring the storage and regulation capabilities of aquifer gas storage facilities, requires accurate and scientific calculation as a prerequisite and foundation for planning the construction of aquifer gas storage facilities and achieving efficient and economical operation.

[0003] Calculating the gas storage capacity of aquifer gas storage facilities faces unique technical challenges. During high-pressure gas injection, phenomena such as water compression and elastic rebound of rock pores directly alter the gas storage space, and this dynamic change has a crucial impact on the gas storage capacity.

[0004] However, there is a significant lack of dedicated calculation methods for aquifer gas storage facilities in the existing technology. The existing calculation methods for the capacity of depleted oil and gas reservoirs do not take into account the dynamic changes of the gas storage space under high pressure, such as water compression and rock pore expansion. These methods are not suitable for the geological characteristics and operating mechanisms of aquifer gas storage facilities, resulting in large deviations between the calculation results and the actual situation. Summary of the Invention

[0005] The purpose of this invention is to provide a method for calculating the gas storage capacity of aquifer gas storage facilities, in order to solve the technical problem that existing methods for calculating the capacity of depleted oil and gas reservoirs do not take into account the dynamic changes of the gas storage space under high pressure, and therefore cannot adapt to the geological characteristics and operating mechanisms of aquifer gas storage facilities, resulting in a large deviation between the calculated results and the actual situation.

[0006] To solve the above-mentioned technical problems, the present invention specifically provides the following technical solution:

[0007] A method for calculating the gas storage capacity of an aquifer gas storage facility includes the following steps:

[0008] Step 100: Based on 2D / 3D seismic data, drilling, logging, well logging and core reservoir physical property test and analysis data, obtain the structural water volume of the aquifer gas reservoir; and based on the determined pressure, temperature and reservoir rock mineral characteristics data of the aquifer gas reservoir, determine the water compressibility coefficient, water volume coefficient, rock compressibility coefficient and natural gas solubility in formation water.

[0009] Step 200: Through drilling pressure and extraction test of the aquifer gas reservoir, obtain the cumulative water production and pressure data of the aquifer gas reservoir, establish the functional relationship between cumulative water production and pressure, and characterize the change relationship between the remaining water and pressure of the aquifer gas reservoir under different pressure injection and production conditions through the functional relationship.

[0010] Step 300: Based on the obtained volume of the tectonic water body and the rock compressibility coefficient, calculate the rock pore expansion volume V due to the increased pressure and rock pore expansion after the high-pressure gas is injected into the aquifer gas storage tank. f ;

[0011] Step 400: Determine the pore volume V that can store gas after the formation water is released from the aquifer gas reservoir based on the volume of the tectonic water body. w The remaining water volume of the aquifer gas reservoir is calculated based on the difference between the sculpted water volume and the cumulative water production. The pore volume V provided by the water volume due to pressure increase and contraction after high-pressure gas injection into the formation is then calculated by multiplying this value with the water volume's compressibility coefficient. wr ;

[0012] Step 500: Based on the difference between the volume of the sculpted water body and the cumulative water production, and the solubility of natural gas in formation water, calculate the dissolved volume V in the remaining water of the aquifer gas reservoir. s ;

[0013] Step 600: Based on the obtained rock pore expansion volume V f The pore volume V that can store gas after formation water is released from the aquifer gas reservoir. w 1. Set the pore volume V provided by the water body due to the increased pressure and contraction after high-pressure gas is injected into the formation. wr and the volume of dissolution V s The formula for calculating the gas storage capacity of an aquifer gas storage facility is as follows:

[0014] G = (V f +V w +V wr +V s ) / B g ;

[0015] B g =Z×T×P0 / (P×T0);

[0016] Where Z is the gas compressibility factor; T is the formation temperature; P is the formation pressure; P0 is the surface standard pressure; and T0 is the surface standard temperature.

[0017] As a preferred embodiment of the present invention, in step 100, the trap type of the aquifer is identified by seismic profile or horizontal slice, and the trap boundary interpreted by seismic analysis is obtained. Then, the trap boundary interpreted by seismic analysis is projected onto the planar structural map, and the area of ​​the closed region is calculated to obtain the preliminary trap area.

[0018] For any initial trap area of ​​any shape, take the geometric center of the isochronous slice of the initial trap area as the origin, and gradually cover the entire aquifer boundary through a series of concentric circular traps. Each circular trap corresponds to an effective radius interval, and calculate the effective trap area belonging to the aquifer boundary within each effective radius interval.

[0019] Let R be the maximum circumradius of the isochronous slice of the initial closed area. max Divide it into n equal radius intervals [r i-1 r i ],(i=1,2,…,n,r0=0,r n =R max );

[0020] The final total effective trap area A is obtained by superposition. w ;

[0021]

[0022] Where, k i This represents the percentage of effective traps within the i-th interval calculated using the grid method.

[0023] As a preferred embodiment of the present invention, coherence analysis of three-dimensional seismic data is used to delineate boundaries in areas with coherence values ​​below a threshold, identifying independent connected regions in the reservoir and obtaining m independent reservoir groups; then, the effective trap area A corresponding to the m independent reservoir groups is calculated. w,s For the total effective trap area A w The correction is made, and the correction formula is:

[0024]

[0025] As a preferred embodiment of the present invention, based on the sedimentary facies diagram interpreted by seismic analysis, favorable and unfavorable facies zones of the reservoir are determined and assigned different weights;

[0026] For the i-th annular region, first calculate the initial value using the mesh method. Then, combine the sedimentary facies weights to calculate the corrected k. i , Where w i This represents the sedimentary phase weight within the effective radius range.

[0027] As a preferred embodiment of the present invention, the trap type of the aquifer is identified by seismic profile or horizontal slice, and the lowest closure point of the trap is determined; based on the lowest closure point, the aquifer is vertically divided into an effective segment above the lowest closure point and an ineffective segment below the lowest closure point, and the thickness of the effective segment is calculated only by depth layering.

[0028] The effective section thickness and effective trap ratio are integrated by volume integration to obtain the total effective reservoir volume V of the aquifer. total ;

[0029]

[0030] in, h represents the effective area of ​​the j-th grid within the i-th radius interval. ij The effective segment thickness at the corresponding position;

[0031] Determine the water volume W of the aquifer structure. total The calculation formula is:

[0032] W total =V total ×φ×ρ w / ρ w Where Φ represents the effective porosity of the aquifer; ρ w B represents the density of the aquifer water. w It represents the water volume factor under formation temperature and pressure conditions.

[0033] As a preferred embodiment of the present invention, the cumulative water production and pressure data are obtained by using the drilling pressure-production test of the proposed aquifer gas storage, and a functional relationship between the cumulative water production and pressure of the aquifer gas storage is established to characterize the relationship between the remaining water and pressure of the aquifer gas storage under different pressure injection and production conditions.

[0034] Cumulative water production Q w Functional relationship with pressure:

[0035] Q w = f(P), where P is the surface gas injection pressure;

[0036] The functional relationship between the remaining water volume and pressure in an aquifer gas storage facility is as follows:

[0037] Q w =W total -f(P).

[0038] As a preferred embodiment of the present invention, the lowest closure point of the trap is used as the critical benchmark, and combined with time dynamics, the cumulative water production Q is corrected by establishing a function in stages. w The functional relationship between pressure and the remaining water volume of an aquifer gas storage reservoir, and the specific stages include:

[0039] When the gas injection pressure does not exceed the critical pressure corresponding to the lowest closure point of the trap, the water in the reservoir is mainly elastically compressed.

[0040] When the injection pressure exceeds the critical pressure of the lowest closure point of the trap, the water body breaks through the lowest closure point of the trap and begins to be produced.

[0041] As a preferred embodiment of the present invention, when the injection pressure P(t) does not exceed the critical pressure P corresponding to the lowest closure point of the loop. e At that time, the cumulative water production Q w The functional relationship with pressure is as follows:

[0042] Q w (P,t)=k1·(P(t)-P0)·t α ;

[0043] When the injection pressure P(t) exceeds the critical pressure P at the lowest closure point of the loop. e At that time, the cumulative water production Q w The functional relationship with pressure is as follows:

[0044] Q w (P,t)=Q w1 +k2·(P(t)-P0)·(1-e -βt );

[0045] Among them, P e P(t) represents the critical pressure corresponding to the lowest closure point, and P(t) represents the change of surface injection pressure with time; t represents the injection time in days; Q w (P,t) represents the cumulative water production; P0 represents the initial formation pressure; α represents the time exponent, and 0 < α < 1; Q w1 Represents P(t) <P e The cumulative water production after the end of the state; k2 represents the overflow water production coefficient; β represents the time decay coefficient, reflecting the stable trend of water production rate over time. The larger the β value, the earlier the stable water production state is reached.

[0046] As a preferred embodiment of the present invention, if there are multiple critical pressure conditions corresponding to the lowest closure points, the pressure range is subdivided into stages, with each stage corresponding to different k2 and β.

[0047] Among them, k2 is obtained from drilling tests and is positively correlated with the channel permeability at the lowest closure point.

[0048] Compared with the prior art, the present invention has the following advantages:

[0049] This invention provides a method for calculating the storage capacity of aquifer gas storage facilities. Addressing the impact of high-pressure gas injection on water compression and rock pore rebound in aquifer gas storage, this method proposes a solution based on the principle of mass balance. It divides the storage capacity into the pore volume contributed by the cumulative water production after high-pressure gas injection, the elastic compression of the water, and the expansion of rock pores, along with the volume of gas dissolved in the formation water. This method significantly improves the accuracy of aquifer gas storage capacity calculation. Attached Figure Description

[0050] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0051] Figure 1 This is a schematic diagram of the overall structure of an embodiment of the present invention. Detailed Implementation

[0052] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0053] like Figure 1 As shown, the present invention provides a method for calculating the gas storage capacity of an aquifer gas storage facility, comprising the following steps:

[0054] Step 100: Based on 2D / 3D seismic data, drilling, logging, well logging and core reservoir physical property test and analysis data, obtain the structural water volume of the aquifer gas reservoir; and based on the determined pressure, temperature and reservoir rock mineral characteristics data of the aquifer gas reservoir, determine the water compressibility coefficient, water volume coefficient, rock compressibility coefficient and natural gas solubility in formation water.

[0055] Step 200: Through drilling pressure and extraction test of the aquifer gas reservoir, obtain the cumulative water production and pressure data of the aquifer gas reservoir, establish the functional relationship between cumulative water production and pressure, and characterize the change relationship between the remaining water and pressure of the aquifer gas reservoir under different pressure injection and production conditions through the functional relationship.

[0056] Step 300: Based on the obtained volume of the tectonic water body and the rock compressibility coefficient, calculate the rock pore expansion volume V due to the increased pressure and rock pore expansion after the high-pressure gas is injected into the aquifer gas storage tank. f ;

[0057] Step 400: Determine the pore volume V that can store gas after the formation water is released from the aquifer gas reservoir based on the volume of the tectonic water body. w The remaining water volume of the aquifer gas reservoir is calculated based on the difference between the sculpted water volume and the cumulative water production. The pore volume V provided by the water volume due to pressure increase and contraction after high-pressure gas injection into the formation is then calculated by multiplying this value with the water volume's compressibility coefficient.wr ;

[0058] Step 500: Based on the difference between the volume of the sculpted water body and the cumulative water production, and the solubility of natural gas in formation water, calculate the dissolved volume V in the remaining water of the aquifer gas reservoir. s ;

[0059] Step 600: Based on the obtained rock pore expansion volume V f The pore volume V that can store gas after formation water is released from the aquifer gas reservoir. w 1. Set the pore volume V provided by the water body due to the increased pressure and contraction after high-pressure gas is injected into the formation. wr and the volume of dissolution V s The formula for calculating the gas storage capacity of an aquifer gas storage facility is as follows:

[0060] G = (V f +V w +V wr +V s ) / B g ;

[0061] B g =Z×T×P0 / (P×T0);

[0062] Where Z is the gas compressibility factor; T is the formation temperature; P is the formation pressure; P0 is the surface standard pressure; and T0 is the surface standard temperature.

[0063] Using 2D / 3D seismic data as the core, well calibration and verification are conducted. The area of ​​a structural trap is "the area of ​​a closed region underground that can hold water / gas." The structural morphology needs to be identified through seismic data, and the effectiveness of the trap needs to be confirmed by well drilling.

[0064] 2D / 3D seismic data processing and interpretation: Determining trap boundaries:

[0065] Step 1: Seismic Data Preprocessing

[0066] Denoising, stacking, and migration processing of the raw seismic data (such as pre-stack depth migration of 3D seismic data) are performed to ensure clear subsurface structural morphology (such as the top of anticline traps and the fault strike of fault-blocked traps), which is the basis for trap identification.

[0067] Step 2: Trap Type Identification and Boundary Delineation

[0068] Identify aquifer trap types (commonly anticline traps or fault-lithological traps) using seismic profiles (2D) or horizontal slices (3D):

[0069] If it is an anticline trap: trace the "lowest closure point" of the anticline on the seismic profile (the lowest closure point of the trap, below which water / gas will escape) to determine the closure range from the top of the anticline to the lowest closure point;

[0070] If the trap is blocked by a fault: determine the strike and dip of the fault through seismic interpretation, combine it with the structural map of the top surface of the reservoir, find the boundary between the fault and the reservoir, and then determine the lowest closure point;

[0071] Step 3: Calculation of the enclosed area

[0072] Projecting the seismic trap boundary (the area above the lowest closure point) onto a planar structural map, and using geographic information software (such as ArcGIS) to calculate the area of ​​the closed region, yields the preliminary trap area.

[0073] In step 100, the trap type of the aquifer is identified by seismic profile or horizontal slice, and the trap boundary interpreted by seismic analysis is obtained. The trap boundary interpreted by seismic analysis is then projected onto the planar structural map, and the area of ​​the closed region is calculated to obtain the preliminary trap area.

[0074] To obtain the volume of the tectonic water body, the following parameters are required:

[0075] I. Effective Enclosed Area A w :

[0076] Drilling data calibration: Verify trap validity and determine the effective trap area. Deploy 1-2 exploratory wells within the initial trap area. If the drilling encounters the target aquifer (water layer observed in well logging and water layer characteristics shown), and adjacent wells outside the trap do not encounter the aquifer (or encounter it but without closure), the trap is considered effective. If drilling reveals a "leakage layer" within the trap (e.g., fracture development leading to water escape), the trap boundary determined by seismic interpretation needs to be revised based on the drilling data, invalid areas are eliminated, and the final effective trap area A is obtained. w .

[0077] II. Effective thickness of water-bearing reservoir (h): Drilling to a certain depth, logging to divide into effective sections, and logging-assisted lithology identification. The effective thickness of the water-bearing reservoir is "the actual thickness of the reservoir that can effectively store water (excluding non-reservoir sections such as clay interlayers)", which needs to be achieved through "drilling to a fixed point + continuous logging division".

[0078] (1) Drilling data: Determine the top and bottom depths of the reservoir by direct observation through drilling cores (core data): When drilling encounters aquifers, the cores are mostly porous rocks such as sandstone and conglomerate (the description of logging cuttings can be helpful, such as sandstone cuttings accounting for >80%). Record the well depth corresponding to the cores to determine the preliminary top and bottom depths of the reservoir (such as top depth 1500m, bottom depth 1550m, preliminary thickness 50m).

[0079] (2) Well logging data: Divide the "effective reservoir section" and remove invalid interlayers;

[0080] The effective reservoir is distinguished based on well logging curves, with the following three types of curves being the core:

[0081] Gamma logging (GR): Identifying mudstone interlayers (mudstone has high gamma values, generally >80 API; sandstone and other reservoirs have low gamma values, generally <60 API);

[0082] Resistivity logging (RT): Confirms the "water-bearing" attribute (the resistivity of the water-bearing layer is lower than that of the oil / gas layer, such as the freshwater layer, where the RT is generally 5-50 Ω·m. Combined with the negative anomaly of spontaneous potential logging (SP), the water layer is further verified).

[0083] Acoustic transit time logging (AC): helps determine reservoir effectiveness (effective reservoirs have moderate acoustic transit time, generally 250-350 μs / m, while tight interlayers have small acoustic transit time <200 μs / m).

[0084] Steps: Within the reservoir top and bottom depth range determined by drilling, use gamma curves to remove mudstone interlayers (e.g., if 1520-1525m is mudstone, remove 5m). The remaining section (1500-1520m, 1525-1550m, a total of 45m) is the effective thickness (h) of the water-bearing reservoir.

[0085] (3) Logging data: The logging data is used to verify whether the effective thickness of the well logging division is reasonable and avoid misjudgment. The description of rock cuttings (such as "1500-1550m is mainly light gray fine sandstone with occasional mudstone bands") and the drilling fluid loss (there may be slight loss of water aquifer) are used to verify the effectiveness of the well logging division.

[0086] III. Effective porosity (φ): The true value of core testing. The effective porosity of the continuous model established by well logging is the proportion of pores in the rock that can be connected to store water.

[0087] It is necessary to combine direct core testing and indirect well logging calculations:

[0088] (1) Core reservoir physical property testing: Obtain "direct porosity data" according to the reservoir parameter testing logic. Select 3-5 representative samples (avoiding fractures and clay interlayers) from the core of the aquifer obtained from drilling and test them with a helium porosimeter.

[0089] Principle: Helium molecules are small and can enter all connected pores. By measuring the injection volume and pressure changes of helium, the effective porosity of the rock can be calculated (excluding dead pores, i.e., non-connected pores).

[0090] The resulting discrete effective porosity data (e.g., 18%, 20%, 19%, average 19%) are used as the "standard true value".

[0091] (2) Well logging data: Establishing a "continuous porosity calculation model" Since core testing only involves discrete points, well logging curves are needed to calculate the continuous porosity of the entire well section. The core method uses density logging (ρb) or neutron logging (CNL): Density logging model (most commonly used):

[0092] The effective porosity (φ) is calculated based on the principle of rock volume balance.

[0093] Effective porosity (φ) calibration and correction:

[0094] The porosity calculated from well logging (e.g., 18.5% at a certain depth) is compared with the porosity from core testing at the corresponding depth (19%). The model parameters are then corrected to ensure that the error is less than 3%. Finally, the corrected model is used to calculate the continuous effective porosity of the entire effective thickness of the water-bearing reservoir, and the average value is taken as the effective porosity.

[0095] Aquifer water density (ρ) w Water density is measured directly from core samples and indirectly calculated from well logs for subsequent water quality calculations. There are two methods for obtaining this density:

[0096] (1) Direct testing of core water samples (accurate): During drilling and coring, a formation water sample is collected from the aquifer using a sealed core sampler (to avoid drilling fluid contamination) and sent to the laboratory. The density of the water sample under formation temperature and pressure is directly measured using a densitometer (e.g., 1.03 g / cm³). 3 Because formation water has a high mineral content, its density is slightly higher than that of pure water. If it is not possible to obtain core samples in a sealed environment, formation water samples can be obtained through well testing (such as DST testing) and then the density can be measured.

[0097] (2) Indirect calculation of logging data (for backup when no water sample is available) Utilize the correlation between density logging and effective porosity: When the reservoir is completely water-bearing (no gas / oil), the water density is inversely calculated from the density logging formula.

[0098] For any initial trap area of ​​any shape, with the geometric center of the isochronous slice of the initial trap area as the origin, the entire aquifer boundary is gradually covered by a series of concentric circular traps. Each circular trap corresponds to an effective radius interval, and the effective trap area belonging to the aquifer boundary within each effective radius interval is calculated.

[0099] Compared to a single geometric model (circle / ellipse), multi-circle enclosing can approximate any irregular closed loop by increasing the number of intervals, offering greater flexibility.

[0100] The spatial integral of area multiplied by thickness is directly calculated by the fusion method, avoiding the non-homogeneity error (such as the contribution of thin edge regions to the total volume) that is ignored in the product of average thickness and total area.

[0101] Defining the effective thickness based on the lowest closure point aligns with the fundamental principles of trapped reservoirs and ensures the geological rationality of the thickness calculation.

[0102] Therefore, let the maximum circumcircle radius of the isochronous slice of the initial closed area be R. max Divide it into n equal radius intervals [r i-1 r i ],(i=1,2,…,n,r0=0,r n =R max );

[0103] The final total effective trap area A is obtained by superposition. w ;

[0104]

[0105] Where, k i This represents the percentage of effective traps within the i-th interval calculated using the grid method.

[0106] k i The effective proportion of reservoirs within the annular region is determined by seismic grid analysis. However, due to limitations in seismic resolution (typically ≥25m), boundary areas are prone to misjudgment, leading to variations in k... i deviation.

[0107] Using coherence volume analysis from 3D seismic data, boundaries are delineated for regions with coherence values ​​below a threshold to identify independent connected regions within the reservoir, resulting in m independent reservoir clusters. The effective trap area A corresponding to these m independent reservoir clusters is then calculated. w,s For the total effective trap area A w The correction is made, and the correction formula is:

[0108]

[0109] Based on the sedimentary facies diagram interpreted by seismic analysis, favorable and unfavorable facies zones of the reservoir are identified and assigned different weights.

[0110] For the i-th annular region, first calculate the initial value using the mesh method. Then, combine the sedimentary facies weights to calculate the corrected k. i , Where w i This represents the sedimentary phase weight within the effective radius range.

[0111] By using seismic profiles or horizontal slices, the trap type of the aquifer is identified, and the lowest closure point of the trap is determined. Based on the lowest closure point, the aquifer is vertically divided into an effective segment above the lowest closure point and an ineffective segment below the lowest closure point. The thickness of the effective segment is calculated only by depth.

[0112] Let the elevation of the lowest closure point be H0, the elevation function of the top surface of the reservoir be H(x,y) (x,y are horizontal coordinates), and the effective thickness function be h(x,y) (only valid when H(x,y)>H0);

[0113] Effective thickness of a single mesh cell (Δx×Δy):

[0114] h ij =h(x i ,y i )×I(H(x i ,y j )≥H0), where I is an indicator function, which is 1 when the condition is met and 0 otherwise.

[0115] Integral of effective thickness (total effective volume contribution) V h :

[0116]

[0117] m×n is A w The number of grid cells within.

[0118] The effective section thickness and effective trap ratio are integrated by volume integration to obtain the total effective reservoir volume V of the aquifer. total ;

[0119]

[0120] in, h represents the effective area of ​​the j-th grid within the i-th radius interval. ij This represents the effective segment thickness at the corresponding position.

[0121] Fusion is achieved through volume integration, meaning that the total effective storage volume is the accumulation of the effective thickness of each point within the effective enclosed area, reflecting the spatial matching relationship between area and thickness, that is, the area and thickness at the same horizontal position correspond.

[0122] Determine the water volume W of the aquifer structure. total The calculation formula is:

[0123] W total =V total ×φ×ρ w / B w Where φ represents the effective porosity of the aquifer; ρ w B represents the density of the aquifer water. w It represents the water volume factor under formation temperature and pressure conditions.

[0124] Of course, in the above application of volume integral fusion of the effective trap area and effective section thickness of the aquifer gas storage, the actual effective thickness of the reservoir and the trap area do not have a "concentric correspondence" relationship (e.g., the area is large in a certain direction but the thickness is thin), and the concentric circle division will destroy the real spatial relationship between the two.

[0125] Therefore, this embodiment can also use an irregular grid that adapts to the reservoir thickness distribution to ensure uniform thickness within each grid, thus achieving a true spatial match between area and thickness.

[0126] Mesh the mesh based on the gradient (thickness change rate) of the effective thickness function (h(x,y)):

[0127] Larger grids (e.g., 100m×100m) are used in areas with gentle thickness changes, while smaller grids (e.g., 25m×25m) are used in areas with drastic thickness changes.

[0128] The effective area S of each grid (i,j) is i,j h represents the actual area of ​​the grid and its effective thickness. i,j The average thickness within the grid; the total effective storage volume is corrected as follows:

[0129]

[0130] The mesh shape adapts to the thickness distribution, preserving the true spatial relationship between area and thickness, and avoiding the forced symmetry error of concentric circles.

[0131] By integrating the effective trap area and effective section thickness of the aquifer gas reservoir as described above, this method is applicable to discontinuous reservoirs (such as multi-section channel sand bodies), reservoirs with drastic lateral thickness variations (such as delta front reservoirs), and complex traps cut by faults. It solves the unreasonable assumptions of the original method regarding "continuity" and "concentric symmetry".

[0132] By using drilling pressure-production test experiments of the proposed aquifer gas storage, cumulative water production and pressure data were obtained, and a functional relationship between cumulative water production and pressure of the aquifer gas storage was established to characterize the relationship between the remaining water and pressure of the aquifer gas storage under different pressure injection and production conditions.

[0133] Cumulative water production Q w Functional relationship with pressure:

[0134] Q w = f(P), where P is the surface gas injection pressure;

[0135] The functional relationship between the remaining water volume and pressure in an aquifer gas storage facility is as follows:

[0136] Q w =W total -f(P).

[0137] Using the lowest closure point of the trap as the critical benchmark, and combining time dynamics, the cumulative water production Q is corrected by establishing a function in stages. w The functional relationship between pressure and the remaining water volume of an aquifer gas storage reservoir, and the specific stages include:

[0138] When the gas injection pressure does not exceed the critical pressure corresponding to the lowest closure point of the trap, the water in the reservoir is mainly elastically compressed.

[0139] When the injection pressure exceeds the critical pressure of the lowest closure point of the trap, the water body breaks through the lowest closure point of the trap and begins to be produced.

[0140] When the injection pressure P(t) does not exceed the critical pressure P corresponding to the lowest closure point of the loop. e At that time, the injection pressure only compressed the water body and rock pores, without forming an effective water-driving force. The cumulative water production mainly came from elastic compression, which increased slowly over time and was affected by both the pressure increase and time. The cumulative water production Q w The functional relationship with pressure follows a quadratic growth model:

[0141] Q w (P,t)=k1·(P(t)-P0)·t α ;

[0142] When the injection pressure P(t) exceeds the critical pressure P at the lowest closure point of the loop. e When the pressure exceeds the minimum closure point, water is driven by gravity to flow along the minimum closure point channel. The cumulative water production increases rapidly over time and is positively correlated with the extent to which the pressure exceeds the critical value. The cumulative water production Q w The functional relationship with pressure follows an exponential growth model:

[0143] Q w (P,t)=Q w1 +k2·(P(t)-P0)·(1-e -βt );

[0144] Among them, P e P(t) represents the critical pressure corresponding to the lowest closure point, and P(t) represents the change of surface injection pressure with time; t represents the injection time in days; Q w (P,t) represents the cumulative water production; P0 represents the initial formation pressure; α represents the time exponent, and 0 < α < 1; Q w1 Represents P(t) <P eThe cumulative water production after the end of the state; k1 represents the elastic water production coefficient, which is obtained by core experiment measurement and is positively correlated with the water compressibility coefficient and the rock compressibility coefficient; k2 represents the overflow water production coefficient; β represents the time decay coefficient, which reflects the stable trend of water production rate over time. The larger the β value, the earlier the stable water production state is reached.

[0145] Correspondingly, the functional relationship Q between the remaining water volume and pressure of the aquifer gas storage tank. s (P,t):

[0146] When the injection pressure exceeds the critical pressure at the lowest closure point of the loop:

[0147] Q s (P,t)=W total -k1·(P(t)-P0)·t α ;

[0148] When the injection pressure P(t) exceeds the critical pressure P at the lowest closure point of the loop. e hour:

[0149] Q s (P,t)=W total -(Q w1 +k2·(P(t)-P0)·(1-e -βt ));

[0150] If there are multiple critical pressure conditions corresponding to the lowest closure points, the pressure range is subdivided into stages, with each stage corresponding to different k2 and β.

[0151] Among them, k2 is obtained from drilling tests and is positively correlated with the channel permeability at the lowest closure point.

[0152] The lowest closure point represents the minimum limit that the reservoir can accommodate fluids. Water will only be produced in large quantities after the pressure exceeds this value. The staged model fits the actual water production mechanism of elastic compression-gravity water drive.

[0153] In actual gas injection, even with the same pressure, the longer the gas injection time, the more significant the difference in cumulative water production. This is especially true in stage 2, where time determines whether the water body is fully displaced. Introducing the time dimension makes the calculation more relevant to the actual situation.

[0154] However, in actual aquifer gas storage facilities, the reservoir may have multiple minimum closure points due to the influence of faults. The critical pressures of different minimum closure points are different, so it is necessary to modify the multi-minimum closure point piecewise model, which increases the function complexity.

[0155] In this embodiment, the actual injection pressure P(t) is dynamically adjusted over time and is not a constant value. The specific form of P(t) needs to be known, for example, linear boosting P(t) = P0 + rt, where r is the daily boosting rate.

[0156] Furthermore, this implementation method, compared to the original static function Q, w =f(P), which can predict the cumulative water production at any time and pressure, such as the water production after 30 days of gas injection at a pressure of 25 MPa, providing a quantitative basis for the design of injection and production schemes for undeveloped gas storage facilities. It also provides a dynamic calculation method for the natural gas storage capacity of undeveloped aquifers.

[0157] This implementation method demonstrates the control of reservoir structure on water production through the minimum closure of the reservoir and the division of points, avoiding errors caused by ignoring geological boundaries.

[0158] In this embodiment, reservoir numerical simulation software (such as Eclipse) is used to simulate water production under different pressure-time combinations, and parameters such as k1, k2, α, and β are inverted to improve the accuracy of the function.

[0159] This invention, through the analysis of the water volume within the aquifer structure, determines the contribution of the pore volume provided by the expansion of rock pores due to increased pressure after high-pressure gas injection into the formation to the gas storage capacity of the aquifer gas reservoir. By establishing a functional relationship between cumulative water production and pressure, the cumulative water production under different injection pressures is determined. Based on this cumulative water production, the contributions of the cumulative water production within the aquifer gas reservoir trap, the pore volume provided by the contraction of the remaining water body due to increased pressure, and the dissolved volume of natural gas in the remaining formation water to the gas storage capacity of the aquifer gas reservoir are determined, effectively improving the accuracy of gas reservoir storage capacity calculation. This embodiment significantly improves the calculation accuracy of aquifer gas reservoir storage capacity.

[0160] Using the aquifer structure, the volume of the trapped water body, and the rock compressibility coefficient of the aquifer gas reservoir, the pore volume V provided by the rock pore expansion due to increased pressure after high-pressure gas injection into the formation can be determined. f The calculation formula is:

[0161] V f =W×C f ×ΔP;

[0162] Among them, V f The pore volume provided for rock pore expansion; C f ΔP is the rock compressibility coefficient; ΔP is the change in formation pressure after gas injection.

[0163] Based on the relationship between cumulative water production and pressure data, and the water volume factor, the pore volume V of the gas reservoir after formation water releases water from the aquifer is determined, which affects the gas storage capacity of the reservoir. w The calculation formula is:

[0164] V w =Q w ×B w ;

[0165] Among them, Q w To accumulate water production, B w This is the water volume coefficient.

[0166] Based on the water volume and water compressibility coefficient of the aquifer gas reservoir, the pore volume V provided by the water body due to pressure increase and contraction after high-pressure gas injection into the formation is determined. wr The calculation formula is:

[0167] V wr =(WQ w )×C w ;

[0168] Among them, C w Q is the water compressibility coefficient. w This refers to the cumulative water production.

[0169] The dissolved volume V of natural gas in formation water is determined based on the reservoir temperature, the solubility of natural gas in formation water at a set pressure, and the remaining water volume in the water-bearing structural trap. s The calculation formula is:

[0170] V s =(WQ w )×S g / ρ g ;

[0171] Among them, S g ρ represents the solubility of natural gas in formation water. g This represents the density of natural gas under the given formation temperature and pressure conditions.

[0172] The above embodiments are merely exemplary embodiments of this application and are not intended to limit this application. The scope of protection of this application is defined by the claims. Those skilled in the art can make various modifications or equivalent substitutions to this application within its substance and scope of protection, and such modifications or equivalent substitutions should also be considered to fall within the scope of protection of this application.

Claims

1. A method for calculating the gas storage capacity of an aquifer gas storage facility, characterized in that, Includes the following steps: Step 100: Based on 2D / 3D seismic data, drilling, logging, well logging and core reservoir physical property test and analysis data, obtain the structural water volume of the aquifer gas reservoir; and based on the determined pressure, temperature and reservoir rock mineral characteristics data of the aquifer gas reservoir, determine the water compressibility coefficient, water volume coefficient, rock compressibility coefficient and natural gas solubility in formation water. Step 200: Through drilling pressure and extraction test of the aquifer gas reservoir, obtain the cumulative water production and pressure data of the aquifer gas reservoir, establish the functional relationship between cumulative water production and pressure, and characterize the change relationship between the remaining water and pressure of the aquifer gas reservoir under different pressure injection and production conditions through the functional relationship. Step 300: Based on the obtained volume of the tectonic water body and the rock compressibility coefficient, calculate the rock pore expansion volume due to the increased pressure after the high-pressure gas is injected into the aquifer gas storage tank. ; Step 400: Determine the pore volume that can store gas after the formation water is released from the aquifer gas reservoir based on the volume of the tectonic water body. The remaining water volume of the aquifer gas reservoir is calculated based on the difference between the volume of the sculpted water body and the cumulative water production. The pore volume provided by the water body due to pressure increase and contraction after high-pressure gas injection is then calculated by multiplying this value with the water body's compressibility coefficient. ; Step 500: Based on the difference between the volume of the sculpted water body and the cumulative water production, as well as the solubility of natural gas in formation water, calculate the dissolved volume in the remaining water of the aquifer gas reservoir. ; Step 600: Based on the obtained rock pore expansion volume The pore volume that can store gas after formation water is released from the aquifer gas reservoir.

1. Set the pore volume provided by the water body due to the increased pressure and contraction after high-pressure gas is injected into the formation. and the volume of dissolution The formula for calculating the gas storage capacity of an aquifer gas storage facility is as follows: ； ； in, It is the gas compressibility factor; Formation temperature; Formation pressure; This is the standard ground pressure; The ground standard temperature; In step 100, the trap type of the aquifer is identified by seismic profile or horizontal slice, and the trap boundary interpreted by seismic analysis is obtained. The trap boundary interpreted by seismic analysis is then projected onto the planar structural map, and the area of ​​the closed region is calculated to obtain the preliminary trap area. For any initial trap area of ​​any shape, take the geometric center of the isochronous slice of the initial trap area as the origin, and gradually cover the entire aquifer boundary through a series of concentric circular traps. Each circular trap corresponds to an effective radius interval, and calculate the effective trap area belonging to the aquifer boundary within each effective radius interval. Let the maximum circumcircle radius of the isochronous slice of the initial closed area be... Divide it into equal parts a radius interval , ; The final sum of the total effective trap area ; ； in, Represents the first calculation based on the grid method The percentage of effective traps within each interval; Using coherence volume analysis from 3D seismic data, boundaries are defined for regions with coherence values ​​below a threshold, identifying independent connected regions within the reservoir and obtaining... Individual storage groups; recalculation Effective enclosure area corresponding to each independent storage group For the total effective enclosed area The correction is made, and the correction formula is: ， ； Based on the sedimentary facies diagram interpreted by seismic analysis, favorable and unfavorable facies zones of the reservoir are identified and assigned different weights. For the For each annular region, the initial calculation is first performed using the mesh method. Then, the corrected value is calculated by combining the sedimentary facies weights. , ;in The sedimentary phase weights represent the effective radius range; By using seismic profiles or horizontal slices, the trap type of the aquifer is identified, and the lowest closure point of the trap is determined. Based on the lowest closure point, the aquifer is vertically divided into an effective segment above the lowest closure point and an ineffective segment below the lowest closure point. The thickness of the effective segment is calculated only by depth. The effective section thickness and effective trap ratio are integrated by volume integration to obtain the total effective reservoir volume of the aquifer. ; ； in, Indicates the first The radius interval, the first The effective area of ​​each grid The effective segment thickness at the corresponding position; Determine the volume of water in an aquifer structure. The calculation formula is: ;in, Indicates the effective porosity of the aquifer; This indicates the density of the water in the aquifer. It represents the water volume factor under formation temperature and pressure conditions.

2. The method for calculating the gas storage capacity of an aquifer gas storage facility according to claim 1, characterized in that, By using drilling pressure-production test experiments of the proposed aquifer gas storage, cumulative water production and pressure data were obtained, and a functional relationship between cumulative water production and pressure of the aquifer gas storage was established to characterize the relationship between the remaining water and pressure of the aquifer gas storage under different pressure injection and production conditions. Cumulative water production Functional relationship with pressure: ,in, The ground injection pressure; The functional relationship between the remaining water volume and pressure in an aquifer gas storage facility is as follows: 。 3. The method for calculating the gas storage capacity of an aquifer gas storage facility according to claim 2, characterized in that, Using the lowest closure point of the trap as the critical benchmark, and combining time dynamics, the cumulative water production is corrected by establishing a function in stages. The functional relationship between pressure and the remaining water volume of an aquifer gas storage reservoir, and the specific stages include: When the gas injection pressure does not exceed the critical pressure corresponding to the lowest closure point of the trap, the water in the reservoir is mainly elastically compressed. When the injection pressure exceeds the critical pressure of the lowest closure point of the trap, the water body breaks through the lowest closure point of the trap and begins to be produced.

4. The method for calculating the gas storage capacity of an aquifer gas storage facility according to claim 3, characterized in that, When the injection pressure The critical pressure corresponding to the lowest closure point of the trap has not been exceeded. At that time, the cumulative water production The functional relationship with pressure is as follows: ； When the injection pressure Critical pressure exceeding the lowest closure point of the trap At that time, the cumulative water production The functional relationship with pressure is as follows: ； in, This represents the critical pressure corresponding to the lowest closure point. This represents a function that expresses the change in surface gas injection pressure over time. Indicates the gas injection time, in days; Indicates cumulative water production; Indicates the original formation pressure; Represents the time index, and ; express Cumulative water production after the end of the state; Indicates the overflow production coefficient; This represents the time decay coefficient, reflecting the steady-state trend of the water production rate over time. The higher the value, the sooner a stable water production state is reached.

5. The method for calculating the gas storage capacity of an aquifer gas storage facility according to claim 4, characterized in that, If there are multiple critical pressure conditions corresponding to the lowest closure points, the pressure range is subdivided into stages, with each stage corresponding to different... and ; in, Obtained from drilling tests, it is positively correlated with the channel permeability at the lowest closure point.

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