A method and system for determining fracture and cavity parameters in multi-branched fault-karst reservoirs

Abstract

The present invention discloses a method and system for determining fracture and cave parameters in a multi-branched fault-karst reservoir. The method comprises: obtaining measured data of the bottomhole pressure of a test well after shut-in, which changes over time; determining the initial parameters of a pre-constructed mathematical model of the bottomhole pressure of a multi-branched fault-karst combined production reservoir based on the basic geological data of the fracture and cave in the multi-branched fault-karst reservoir, using the initial parameters as the initial values of the fitting parameters, and solving to obtain the bottomhole pressure solution of the multi-branched fault-karst combined production reservoir; calculating the difference between the pressure of the measured data and the pressure solution obtained; if the difference is less than a preset fitting error, using the initial parameters as the final fitting parameters; if the difference is greater than or equal to the preset fitting error, correcting the fitting parameters until the difference is less than the preset fitting error, and obtaining the final fitting parameters. The present invention can determine the spatial distribution of fractures and caves in a multi-branched fault-karst reservoir by only acquiring pressure data once.

Description

Technical Field

[0001] The invention relates to a method and system for determining fracture and cavity parameters of a multi-branched fault-karst oil reservoir, belonging to the technical field of oil and gas field development. Background Art

[0002] Fault-karst reservoirs are a special type of highly heterogeneous, highly discrete, fracture-vuggy carbonate reservoir. Vertically, large-scale dissolution caves develop in a string-like pattern along deep, major, and secondary faults. Cross-sections show a tree-like structure with multiple intersecting fractures, caves, and faults (Lu Xinbian, Hu Wenge, Wang Yan, et al. Characteristics and development practices of fault-karst reservoirs in carbonate rocks in the Tahe region [J]. Petroleum and Natural Gas Geology, 2015, 36(03):347-355.). Fault-karst reservoirs have a tree-like, multi-branched structure, with fracture-vuggy reservoirs primarily distributed along branching faults. During on-site drilling, mud slurry often accumulates when drilling into fractures and caves, severely hindering normal drilling progress and potentially posing the risk of drilling empty holes (Chang Shaoying, Zhuang Xijin, Deng Xingliang, et al. High-efficiency well prediction methods and application results for fault-karst reservoirs [J]. Petroleum Geophysical Exploration, 2017, 52(S1):199-206.). Therefore, it is crucial to obtain information such as the number of fracture-vug branches and spatial structure of fault-karst reservoirs in a timely and accurate manner.

[0003] Currently, the commonly used method for obtaining reservoir information on site is shut-in unstable well testing. However, the existing technologies are all based on the seepage theory, which is mainly established when vertical wells are drilled into a single fault fracture-vug body. It does not consider the connectivity of different branch fracture-vug bodies and is not suitable for horizontal wells in multi-branch fault-karst reservoirs.

[0004] Chinese patent publication number CN113294147A, titled "A Well Test Interpretation Method for Single-Cavity Fault-Kalpa Reservoirs Considering the Influence of Gravity," proposes a well test interpretation method for single-cavity fault-karpast reservoirs based on the law of conservation of energy and cave fluctuations, while also considering the influence of gravity. By interpreting pressure buildup test curves, the method obtains well test interpretation parameters for single-cavity fault-karpast reservoirs and conducts a sensitivity analysis of the gravity coefficient. However, this method only considers the case of a vertical well encountering a vertical fracture-cavity reservoir, and thus falls within the seepage model of a single-branch fracture-cavity reservoir, making it unsuitable for interconnected multi-branch fault-karpast reservoirs.

[0005] Chinese patent publication number CN113919111A: A method for interpreting well test curves for fault-karst reservoirs, comprising: obtaining pressure buildup well test data for a target object; performing type analysis on the pressure buildup well test curve; determining the fracture / cavity combination model to which the target object belongs based on the curve type; and fitting key parameters based on the pressure buildup well test curve to obtain key parameters for the target object; inverting the key parameters in combination with an inversion formula to obtain application parameters characterizing reservoir characteristics, thereby interpreting the reservoir characteristics of the target object. Although this technology takes into account the situation where highly deviated wells encounter fractures and cavities, it still only considers single-branch fracture-cavity reservoirs and does not address the problem of seepage in multi-branch fault-karst reservoir commingled production wells.

[0006] Based on the cave characteristics of fault-karst reservoirs, a theoretical physical model of wells and caves was constructed. Combined with the actual flow characteristics of the fluid, the fluctuation coefficient and damping coefficient were introduced to construct a mathematical model (publication number CN113626969A). Dimensionless calculation formulas for the fluctuation coefficient and damping coefficient were obtained, and the radius (publication number CN113918866A) and cave height (publication number CN113919110A) that characterize the cave characteristics were obtained. A fitting calculation was performed based on the radius and height to obtain the cave volume characteristics. The model established by this method only considers the case where a vertical well encounters a single large cave, which does not conform to the interconnected characteristics of complex, multi-branched fault-karst reservoirs in reality. Summary of the Invention

[0007] The present invention aims to overcome the shortcomings of the prior art by providing a method and system for determining fracture-vug parameters in multi-branched fault-karst reservoirs. This method overcomes the current situation in which the existing seepage model is based on vertical wells encountering a single fault-vug, fails to consider the connectivity of different branching fractures and vugs, and is unsuitable for horizontal wells in multi-branched fault-karst reservoirs. The present invention expands existing seepage theory and well testing models to achieve this objective. The present invention employs the following technical solutions:

[0008] In a first aspect, the present invention provides a method for determining fracture-cavity parameters in a multi-branched fault-karst reservoir, comprising:

[0009] Obtain measured data on the bottom hole pressure of the test well after shut-in;

[0010] Based on the basic geological data of fractures and cavities in multi-branched fault-karst reservoirs, the initial parameters of the pre-constructed mathematical model of bottom-hole pressure in multi-branched fault-karst commingled production reservoirs are determined, and the initial parameters are used as the initial values of the fitting parameters to obtain the bottom-hole pressure solution of the multi-branched fault-karst commingled production reservoirs;

[0011] The difference between the pressure of the measured data and the pressure solution obtained by the solution is calculated; if the difference is less than the preset fitting error, the initial parameters are used as the final fitting parameters; if the difference is greater than or equal to the preset fitting error, the fitting parameters are revised until the difference is less than the preset fitting error, and the last revised fitting parameters are used as the final fitting parameters; the final fitting parameters are the parameters of the fractures and cavities in the multi-branched fault-karst reservoir.

[0012] In combination with the first aspect, further, the initial parameters of the pre-constructed mathematical model of the bottom hole pressure of the multi-branch fault-karst combined production reservoir include: the number of branch reservoirs j, the original formation pressure p i , reservoir permeability k j , porosity Comprehensive compression coefficient c tj .

[0013] In combination with the first aspect, further, the initial value of the fitting parameter is M0(d j0 ,A fj0 ,h j0 ), where d is the distance between the branch well and the reservoir, h is the depth of the cave area, and A f is the seepage area.

[0014] In combination with the first aspect, further, the pre-constructed mathematical model of bottom hole pressure of a multi-branch fracture-karst combined production reservoir is constructed based on the characteristics of horizontal pipe flow in a horizontal wellbore, linear seepage flow in a fracture area, and reservoir flow in a cave area, taking into account the initial conditions and boundary conditions of the fractures and caves;

[0015] According to the characteristics of horizontal pipe flow in horizontal wellbore, the relationship between the flow rate and the driving pressure difference of the horizontal wellbore stable full pipe laminar flow is characterized by the following mathematical model:

[0016]

[0017] In formula (1), △p w is the pressure difference corresponding to the wellbore length, Pa; q w is the flow rate in the wellbore area, m 3 / s; μ is viscosity, Pa·s; d is wellbore length, m; r w is the wellbore radius, m;

[0018] According to the characteristics of linear seepage in the fracture area, the mathematical differential equation describing fluid seepage is:

[0019]

[0020] In formula (2), k is the permeability of the fracture area, m 2 ; μ is viscosity, Pa·s; p fis the pressure in the fracture area, Pa; h is the depth, m; ρ is the fluid density, kg / m 3 ; g is the acceleration due to gravity, 9.8m / s 2 ;c l is the fluid compressibility coefficient, Pa -1 ; is the porosity, %; c t is the comprehensive compressibility coefficient of the reservoir, Pa -1 ; t is time, s;

[0021] The flow rate in the reservoir fracture area is obtained from the pressure change:

[0022]

[0023] In formula (3), q f is the flow rate in the crack area, m 3 / s;A f is the seepage area of the fracture region, m 2 ; k is the permeability of the fracture area, m 2 ;p f is the pressure in the crack area, Pa; t is the time, s;

[0024] According to the characteristics of reservoir flow in the cave area, the mathematical equation describing the relationship between the net flow rate of cave fluid and the change in cave pressure is:

[0025]

[0026] In formula (4), q v is the flow rate in the cave area, m 3 / s;C v is the cave storage coefficient, m 3 / Pa;p v is the pressure in the cave area, Pa; t is the time, s;

[0027] The initial condition of fractures and holes is that the pressure at all locations in the reservoir is the same and equal to the original reservoir pressure before well production. The mathematical model of the initial pressure is expressed as:

[0028] p tf (h,0)=p v (0) = p bf (h,0)=p i (5)

[0029] In formula (5), p tf is the pressure in the crack area above the cave, Pa; p v is the pressure in the cave area, Pa; p bf is the pressure in the crack area below the cave, Pa; p i is the original reservoir pressure, Pa; h is the depth, m;

[0030] The fracture-hole boundary conditions include:

[0031] Internal boundary conditions:

[0032] The wellbore production is equal to the sum of the flow rates in the fracture areas above the cave:

[0033]

[0034] The bottom hole pressure is equal to the sum of the pressure of the branch reservoir near the wellbore and the pressure difference of the horizontal section near the wellbore:

[0035] p w (t) = Δp w1 +p tf1 (t) (7)

[0036] In formulas (6) and (7), Q is the bottom hole flow rate, m 3 / s;q tf is the flow rate in the crack area above the cave, m 3 / s;p w is the bottom hole pressure, Pa; △p w1 is the pressure difference corresponding to the length of the wellbore near the wellbore, Pa; t is the time, s;

[0037] Interface connection conditions:

[0038] The fluid flows from the fracture system in the lower part of the cave, through the cave area, and into the fracture area in the upper part of the cave. At the interface between the cave and the upper and lower fracture areas, the flow rate is the same:

[0039]

[0040] At the interface between the cave and the upper and lower fracture areas, the pressure is the same:

[0041] p tf (h tv ,t)=p v (t) = p bf (h bv ,t) (9)

[0042] In formulas (8) and (9), C v is the cave storage coefficient, m 3 / Pa;h tv is the depth of the cave top, m; h bv is the depth of the cave bottom, m;

[0043] External boundary conditions:

[0044] The outer boundary of the reservoir is a closed boundary with no fluid flow.

[0045]

[0046] Where: h fb is the bottom depth of the crack area in the lower part of the cave, m.

[0047] In combination with the first aspect, further, the solution data for calculating the bottom hole pressure changing with time includes:

[0048] The parameters in the mathematical model are dimensionless, and we get: dimensionless pressure dimensionless time Dimensionless flow dimensionless storage coefficient Dimensionless depth Dimensionless gravity coefficient Dimensionless branch reservoir distance Dimensionless flow coefficient ratio Dimensionless pressure transmission coefficient ratio

[0049] After dimensionless transformation and Laplace space transformation, the pressure of the upper and lower fractures of any j-branch cave is:

[0050]

[0051] The flow equation of the upper fracture of any j-branch cave is:

[0052]

[0053] The flow equation of any j-branch cave is:

[0054]

[0055] The flow equation for any j-th section of the wellbore is:

[0056]

[0057] The wellbore flow conditions are:

[0058]

[0059] The wellbore pressure conditions are:

[0060]

[0061] For any j-branch lower fracture-cavern-upper fracture, the flow condition is:

[0062]

[0063] For any j-branch lower crack-cavern-upper crack, the pressure condition is:

[0064]

[0065] The outer boundary of the reservoir is a sealed boundary, and the flow rate is 0:

[0066]

[0067] The corresponding solution of equation (11) is in the form of:

[0068]

[0069] In formula (20), c is the coefficient to be determined, r is the conjugate characteristic root, and its expression is:

[0070]

[0071] Substituting equation (20) into the inner boundary conditions (15-16), the interface connection conditions (17-18), and the outer boundary conditions (19), we obtain the linear equations for the coefficient c to be determined:

[0072]

[0073] The matrix D is 4n×4n elements, and all elements except the following are 0.

[0074] The first row of elements is:

[0075]

[0076] The elements in rows 2 to n are:

[0077]

[0078] The elements in rows n+1 to 2n are:

[0079]

[0080] The elements in rows 2n+1 to 3n are:

[0081]

[0082] The elements in rows 3n+1 to 4n are:

[0083]

[0084] For the two-branch model, D is specifically:

[0085]

[0086] For a single branch, D is:

[0087]

[0088] Solve the equations (22) to obtain all the coefficients c t1 , then according to formula (16), the bottom hole pressure solution can be obtained as

[0089]

[0090] The dimensionless bottom hole pressure (23) in Laplace space is inverted by Stehfest numerical integration algorithm, and the solution data of the dimensionless bottom hole pressure changing with time in real space is obtained. wD .

[0091] In combination with the first aspect, further, the modified fitting parameters include: the reservoir distance d of each branch well j , the depth of each cave area h j , seepage area A of each branch reservoir fj .

[0092] In a second aspect, the present invention provides a system for determining fracture and vug parameters in a multi-branched fault-karst reservoir, comprising:

[0093] Acquisition module: used to obtain the measured data of the bottom hole pressure of the test well changing with time after the well is shut in;

[0094] Calculation module: used to determine the initial parameters of the pre-built mathematical model of bottom-hole pressure of multi-branched fault-karst combined production reservoir based on the basic geological data of fractures and cavities in multi-branched fault-karst combined production reservoirs, use the initial parameters as the initial values of the fitting parameters, and solve to obtain the bottom-hole pressure solution of the multi-branched fault-karst combined production reservoir;

[0095] Output module: used to calculate the difference between the pressure of the measured data and the pressure solution obtained by solving; if the difference is less than the preset fitting error, the initial parameters are used as the final fitting parameters; if the difference is greater than or equal to the preset fitting error, the fitting parameters are revised until the difference is less than the preset fitting error, and the last revised fitting parameters are used as the final fitting parameters; the final fitting parameters are the parameters of the fractures and cavities in the multi-branched fault-karst reservoir.

[0096] In a third aspect, the present invention provides a computing device comprising a processor and a storage medium;

[0097] The storage medium is used to store instructions;

[0098] The processor is configured to operate according to the instructions to execute the steps of the method of the first aspect.

[0099] In a fourth aspect, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method described in the first aspect.

[0100] Compared with the prior art, the method and system for determining fracture-vug parameters in a multi-branched fault-karst reservoir provided by the embodiments of the present invention have the following beneficial effects:

[0101] The present invention obtains measured data of the bottomhole pressure of the test well after shut-in; based on the basic geological data of the multi-branch fracture-karst oil reservoir fracture-cavity, the initial parameters of the pre-constructed mathematical model of the bottomhole pressure of the multi-branch fracture-karst oil reservoir are determined, and the initial parameters are used as the initial values of the fitting parameters to solve and obtain the bottomhole pressure solution of the multi-branch fracture-karst oil reservoir; the pre-constructed mathematical model of the bottomhole pressure of the multi-branch fracture-karst oil reservoir provided by the present invention takes into account the combined production conditions of multiple branch fracture-cavity reservoirs, and there is currently no multi-branch reservoir fracture-karst combined production model; the wellbore part of the pre-constructed mathematical model of the bottomhole pressure of the multi-branch fracture-karst oil reservoir introduces a horizontal well, and takes into account the horizontal flow of fluid in the horizontal wellbore and the existing flow pressure loss factors, and there is currently no seepage model for horizontal wells in fracture-karst reservoirs. The present invention takes into account the pressure and flow coupling between reservoir seepage, cave reservoir flow, and wellbore pipe flow. It expands the existing single-branch reservoir seepage model and enriches the unstable seepage theory of existing fracture-cavity carbonate oil and gas reservoirs.

[0102] The present invention calculates the difference between the pressure of the measured data and the pressure of the solved data; if the difference is less than a preset fitting error, the initial parameters are used as the final fitting parameters; if the difference is greater than or equal to the preset fitting error, the fitting parameters are revised until the difference is less than the preset fitting error, and the last revised fitting parameters are used as the final fitting parameters; the final fitting parameters are the parameters of the fractures and cavities in a multi-branched fault-karst reservoir. The present invention determines the number of fracture-cavity branches in a multi-branched fault-karst reservoir using bottomhole pressure measurement data. The present invention takes into account the interconnectedness of the multi-branched reservoir layers and is more consistent with the actual operating conditions of fault-karst reservoirs.

[0103] This method uses only a single pressure reading to determine the number of fracture-vuggy branches in the entire reservoir, reducing the operational costs of layered testing, improving testing efficiency, and significantly shortening shut-in testing time. This method is particularly effective for multi-branched fault-karst reservoirs produced using horizontal wells, highly deviated wells, and even vertical wells. It is also applicable to fracture-karst reservoirs, karst-vuggy reservoirs, and fractured oil and gas reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0104] Figure 1 This is a flow chart of a method for determining fracture and cavity parameters in a multi-branched fault-karst reservoir provided in Example 1;

[0105] Figure 2 This is the fitting effect and interpretation result of the present invention and the measured pressure of a single branch fracture in Example 2;

[0106] Figure 3This is the fitting effect and interpretation result of the present invention and the measured pressure of the double-branch fracture in Example 2. DETAILED DESCRIPTION

[0107] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0108] Example 1:

[0109] like Figure 1 As shown, an embodiment of the present invention provides a method for determining fracture-cavity parameters in a multi-branched fault-karst reservoir, comprising:

[0110] Obtain measured data on the bottom hole pressure of the test well after shut-in;

[0111] Based on the basic geological data of fractures and cavities in multi-branched fault-karst reservoirs, the initial parameters of the pre-constructed mathematical model of bottom-hole pressure in multi-branched fault-karst commingled production reservoirs are determined, and the initial parameters are used as the initial values of the fitting parameters to obtain the bottom-hole pressure solution of the multi-branched fault-karst commingled production reservoirs;

[0112] The difference between the pressure of the measured data and the pressure solution obtained by the solution is calculated; if the difference is less than the preset fitting error, the initial parameters are used as the final fitting parameters; if the difference is greater than or equal to the preset fitting error, the fitting parameters are revised until the difference is less than the preset fitting error, and the last revised fitting parameters are used as the final fitting parameters; the final fitting parameters are the parameters of the fractures and cavities in the multi-branched fault-karst reservoir.

[0113] The specific steps are as follows:

[0114] Step 1: Obtain the measured data of the bottom hole pressure of the test well after shut-in (t, P t0 ).

[0115] Step 2: Based on the basic geological data of fractures and cavities in multi-branched fault-karst reservoirs, determine the initial parameters M0 of the pre-constructed mathematical model of bottom hole pressure in multi-branched fault-karst commingled production reservoirs, and use the initial parameters as the initial values of the fitting parameters.

[0116] The initial parameters of the pre-built mathematical model of the bottom hole pressure of the multi-branch fault-karst combined production reservoir include: the number of branch reservoirs j, the original formation pressure p i , reservoir permeability k j , porosity Comprehensive compression coefficient c tj .

[0117] The initial values of the fitting parameters are expressed as M0(d j0 ,A fj0 ,h j0), where d is the distance between the branch well and the reservoir, h is the depth of the cave area, and A f is the seepage area.

[0118] The pre-built mathematical model of bottom hole pressure in multi-branch fracture-karst combined production reservoirs is constructed based on the characteristics of horizontal pipe flow in horizontal wellbore, linear seepage flow in fracture area, and reservoir flow in cave area, taking into account the initial conditions and boundary conditions of fractures and caves. Specifically, it includes:

[0119] According to the characteristics of horizontal pipe flow in horizontal wellbore: after the reservoir fluid enters the wellbore, it flows along the horizontal section of the wellbore from the far end to the bottom of the wellbore. The relationship between the flow rate of stable full pipe laminar flow and the driving pressure difference is characterized by the following mathematical model:

[0120]

[0121] In formula (1), △p w is the pressure difference corresponding to the wellbore length, Pa; q w is the flow rate in the wellbore area, m 3 / s; μ is viscosity, Pa·s; d is wellbore length, m; r w is the wellbore radius, m.

[0122] According to the characteristics of linear seepage in the fracture area, in the reservoir fracture area, the reservoir fluid mainly seeps through the fracture system. The mathematical differential equation describing the fluid seepage is:

[0123]

[0124] In formula (2), k is the permeability of the fracture area, m 2 ; μ is viscosity, Pa·s; p f is the pressure in the fracture area, Pa; h is the depth, m; ρ is the fluid density, kg / m 3 ; g is the acceleration due to gravity, 9.8m / s 2 ;c l is the fluid compressibility coefficient, Pa -1 ; is the porosity, %; c t is the comprehensive compressibility coefficient of the reservoir, Pa -1 ; t is time, s;

[0125] The flow rate in the reservoir fracture area is obtained from the pressure change:

[0126]

[0127] In formula (3), q f is the flow rate in the crack area, m 3 / s;A f is the seepage area of the fracture region, m 2; k is the permeability of the fracture area, m 2 ;p f is the pressure in the crack area, Pa; t is the time, s.

[0128] According to the characteristics of the reservoir flow in the cave area, the fluid in the cave will undergo elastic compression or expansion due to changes in reservoir pressure. The mathematical equation describing the relationship between the net flow rate of the cave fluid and the change in cave pressure is:

[0129]

[0130] In formula (4), q v is the flow rate in the cave area, m 3 / s;C v is the cave storage coefficient, m 3 / Pa;p v is the pressure in the cave area, Pa; t is the time, s.

[0131] The initial condition of fractures and holes is that the pressure at all locations in the reservoir is the same and equal to the original reservoir pressure before well production. The mathematical model of the initial pressure is expressed as:

[0132] p tf (h,0)=p v (0) = p bf (h,0)=p i (5)

[0133] In formula (5), p tf is the pressure in the crack area above the cave, Pa; p v is the pressure in the cave area, Pa; p bf is the pressure in the crack area below the cave, Pa; p i is the original reservoir pressure, Pa; h is the depth, m.

[0134] The fracture and hole boundary conditions include: internal boundary conditions, interface connection conditions and external boundary conditions.

[0135] Internal boundary conditions:

[0136] The wellbore production is equal to the sum of the flow rates in the fracture areas above the cave:

[0137]

[0138] The bottom hole pressure is equal to the sum of the pressure of the branch reservoir near the wellbore and the pressure difference of the horizontal section near the wellbore:

[0139] p w (t) = Δp w1 +p tf1 (t) (7)

[0140] In formulas (6) and (7), Q is the bottom hole flow rate, m3 / s;q tf is the flow rate in the crack area above the cave, m 3 / s;p w is the bottom hole pressure, Pa; △p w1 is the pressure difference corresponding to the wellbore length near the wellbore, Pa; t is the time, s.

[0141] Interface connection conditions:

[0142] The fluid flows from the fracture system in the lower part of the cave, through the cave area, and into the fracture area in the upper part of the cave. At the interface between the cave and the upper and lower fracture areas, the flow rate is the same:

[0143]

[0144] At the interface between the cave and the upper and lower fracture areas, the pressure is the same:

[0145] p tf (h tv ,t)=p v (t) = p bf (h bv ,t) (9)

[0146] In formulas (8) and (9), C v is the cave storage coefficient, m 3 / Pa;h tv is the depth of the cave top, m; h bv is the depth of the cave bottom, m.

[0147] External boundary conditions:

[0148] The outer boundary of the reservoir is a closed boundary with no fluid flow.

[0149]

[0150] Where: h fb is the bottom depth of the crack area in the lower part of the cave, m.

[0151] The pre-constructed mathematical model of bottom hole pressure of multi-branched fractured-karst combined production reservoir provided by the present invention takes into account the combined production conditions of multiple branched fractured-karst reservoirs. Currently, there is no multi-branched fractured-karst combined production model. The pre-constructed mathematical model of bottom hole pressure of multi-branched fractured-karst combined production reservoir introduces a horizontal well into the wellbore part, taking into account the horizontal flow of fluid in the horizontal wellbore and the existing flow pressure loss factors. Currently, there is no seepage model for horizontal wells in fractured-karst reservoirs. The present invention takes into account the pressure and flow coupling between reservoir seepage, cave reservoir flow, and wellbore pipe flow. It expands the existing single-branched reservoir seepage model and enriches the unstable seepage theory of existing fractured-karst carbonate oil and gas reservoirs.

[0152] Step 3: Based on the initial value M0 of the fitting parameter, the pre-constructed mathematical model of the bottom hole pressure of the multi-branch fault-melt commingled production reservoir is solved to obtain the bottom hole pressure solution of the multi-branch fault-melt commingled production reservoir.

[0153] The established mathematical model is solved through parameter dimensionless transformation, Laplace space transformation and numerical inversion.

[0154] Specifically:

[0155] The parameters in the mathematical model are dimensionless, and we get: dimensionless pressure dimensionless time Dimensionless flow dimensionless storage coefficient Dimensionless depth Dimensionless gravity coefficient Dimensionless branch reservoir distance Dimensionless flow coefficient ratio Dimensionless pressure transmission coefficient ratio

[0156] After dimensionless transformation and Laplace space transformation, the pressure of the upper and lower fractures of any j-branch cave is:

[0157]

[0158] The flow equation of the upper fracture of any j-branch cave is:

[0159]

[0160] The flow equation of any j-branch cave is:

[0161]

[0162] The flow equation for any j-th section of the wellbore is:

[0163]

[0164] The wellbore flow conditions are:

[0165]

[0166] The wellbore pressure conditions are:

[0167]

[0168] For any j-branch lower fracture-cavern-upper fracture, the flow condition is:

[0169]

[0170] For any j-branch lower crack-cavern-upper crack, the pressure condition is:

[0171]

[0172] The outer boundary of the reservoir is a sealed boundary, and the flow rate is 0:

[0173]

[0174] The corresponding solution of equation (11) is in the form of:

[0175]

[0176] In formula (20), c is the coefficient to be determined, r is the conjugate characteristic root, and its expression is:

[0177]

[0178] Substituting equation (20) into the inner boundary conditions (15-16), the interface connection conditions (17-18), and the outer boundary conditions (19), we obtain the linear equations for the coefficient c to be determined:

[0179]

[0180] The matrix D is 4n×4n elements, and all elements except the following are 0.

[0181] The first row of elements is:

[0182]

[0183] The elements in rows 2 to n are:

[0184]

[0185] The elements in rows n+1 to 2n are:

[0186]

[0187] The elements in rows 2n+1 to 3n are:

[0188]

[0189] The elements in rows 3n+1 to 4n are:

[0190]

[0191] For the two-branch model, D is specifically:

[0192]

[0193] For a single branch, D is:

[0194]

[0195] Solve the equations (22) to obtain all the coefficients c t1 , then according to formula (16), the bottom hole pressure solution can be obtained as

[0196]

[0197] The dimensionless bottom hole pressure (23) in Laplace space is inverted by Stehfest numerical integration algorithm, and the solution data of the dimensionless bottom hole pressure changing with time in real space is obtained. wD .

[0198] Step 4: Calculate the pressure P of the measured data to and the pressure solution P t The difference between |P t -P to |; If the difference is less than the preset fitting error e, the initial parameter M0 is used as the final fitting parameter M; if the difference is greater than or equal to the preset fitting error e, the fitting parameter is revised until the difference is less than the preset fitting error, and the last revised fitting parameter M is used as the final fitting parameter; the final fitting parameter is the parameter of the fracture-cavity of the multi-branched fault-karst reservoir.

[0199] The present invention determines the number of fracture-vug branches in a multi-branch fault-karst reservoir through bottom hole pressure measurement data. The present invention takes into account the interconnectivity of the multi-branch reservoirs of the fault-karst reservoir and is more in line with the actual working conditions of the actual fault-karst reservoir.

[0200] This method uses only a single pressure reading to determine the number of fracture-vuggy branches in the entire reservoir, reducing the operational costs of layered testing, improving testing efficiency, and significantly shortening shut-in testing time. This method is particularly effective for multi-branched fault-karst reservoirs produced using horizontal wells, highly deviated wells, and even vertical wells. It is also applicable to fracture-karst reservoirs, karst-vuggy reservoirs, and fractured oil and gas reservoirs.

[0201] Example 2:

[0202] This embodiment adopts the method for determining the fracture and cavity parameters of a multi-branched fault-karst reservoir described in the first embodiment to determine the parameters.

[0203] The method for determining the fracture-cavity parameters of multi-branch fault-karst reservoirs described in Example 1 is used to determine the fracture-cavity parameters of single-branch fracture-cavity ( Figure 2 (right figure) to determine the parameters. Figure 2 The left figure shows the fitting result of the single-branch model. The distance between the fracture-cavity branch and the wellhead is d1 = 135m, the cave depth is h1 = 50m, and the cave volume is V1 = 350m. 3 .

[0204] The method for determining the fracture-cavity parameters of multi-branch fault-karst reservoirs described in Example 1 was used to determine the fracture-cavity parameters of double-branch fracture-cavity ( Figure 3 (right figure) to determine the parameters. Figure 3 The left figure shows the fitting results of the double-branch model. The distance between fracture-cavity branch 1 and the wellhead is d1 = 35 m, the depth of cave 1 is h1 = 10 m, and the volume of cave 1 is V1 = 280 m 3 The distance between the fracture-cavity branch 2 and the wellhead is d2 = 50 m, the depth of the cave 2 is h2 = 15 m, and the volume of the cave 2 is V2 = 560 m 3 .

[0205] The results show that the method for determining the fracture and cavity parameters of a multi-branched fault-karst reservoir proposed in the present invention can quickly and accurately determine the fracture and cavity parameters of a multi-branched fault-karst reservoir, and determine the number of fracture and cavity branches and the spatial structure of the multi-branched fault-karst reservoir.

[0206] Example 3:

[0207] An embodiment of the present invention provides a system for determining fracture-cavity parameters in a multi-branched fault-karst reservoir, comprising:

[0208] Acquisition module: used to obtain the measured data of the bottom hole pressure of the test well changing with time after the well is shut in;

[0209] Calculation module: used to determine the initial parameters of the pre-built mathematical model of bottom-hole pressure of multi-branched fault-karst combined production reservoir based on the basic geological data of fractures and cavities in multi-branched fault-karst combined production reservoirs, use the initial parameters as the initial values of the fitting parameters, and solve to obtain the bottom-hole pressure solution of the multi-branched fault-karst combined production reservoir;

[0210] Output module: used to calculate the difference between the pressure of the measured data and the pressure solution obtained by solving; if the difference is less than the preset fitting error, the initial parameters are used as the final fitting parameters; if the difference is greater than or equal to the preset fitting error, the fitting parameters are revised until the difference is less than the preset fitting error, and the last revised fitting parameters are used as the final fitting parameters; the final fitting parameters are the parameters of the fractures and cavities in the multi-branched fault-karst reservoir.

[0211] Example 4:

[0212] An embodiment of the present invention provides a computing device, including a processor and a storage medium;

[0213] The storage medium is used to store instructions;

[0214] The processor is configured to operate according to the instructions to execute the steps of the method described in embodiment 1.

[0215] Embodiment 5:

[0216] An embodiment of the present invention further provides a computer-readable storage medium having a computer program stored thereon, which implements the steps of the method described in the first embodiment when the program is executed by a processor.

[0217] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0218] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the steps in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0219] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0220] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0221] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for determining fracture-cavity parameters in a multi-branched fault-karst reservoir, characterized in that: include: Obtain measured data on the bottom hole pressure of the test well after shut-in; Based on the basic geological data of fractures and cavities in multi-branched fault-karst reservoirs, the initial parameters of the pre-constructed mathematical model of bottom-hole pressure in multi-branched fault-karst commingled production reservoirs are determined, and the initial parameters are used as the initial values of the fitting parameters to obtain the bottom-hole pressure solution of the multi-branched fault-karst commingled production reservoirs; The pre-constructed mathematical model of bottom hole pressure in a multi-branch fracture-karst combined production reservoir is constructed based on the characteristics of horizontal pipe flow in the horizontal wellbore, linear seepage flow in the fracture area, and reservoir flow in the cave area, taking into account the initial conditions and boundary conditions of the fractures and caves; According to the characteristics of horizontal pipe flow in horizontal wellbore, the relationship between the flow rate and the driving pressure difference of the horizontal wellbore stable full pipe laminar flow is characterized by the following mathematical model: In formula (1), △p w is the pressure difference corresponding to the wellbore length, Pa; q w is the flow rate in the wellbore area, m 3 / s; μ is viscosity, Pa·s; d is wellbore length, m; r w is the wellbore radius, m; According to the characteristics of linear seepage in the fracture area, the mathematical differential equation describing fluid seepage is: In formula (2), k is the permeability of the fracture area, m 2 ; μ is viscosity, Pa·s; p f is the pressure in the fracture area, Pa; h is the depth, m; ρ is the fluid density, kg / m 3 ; g is the acceleration due to gravity, 9.8m / s 2 ;c l is the fluid compressibility coefficient, Pa -1 ;φ is porosity, %; c t is the comprehensive compressibility coefficient of the reservoir, Pa -1 ; t is time, s; The flow rate in the reservoir fracture area is obtained from the pressure change: In formula (3), q f is the flow rate in the crack area, m 3 / s;A f is the seepage area of the fracture region, m 2 ; k is the permeability of the fracture area, m 2 ;p f is the pressure in the crack area, Pa; t is the time, s; According to the characteristics of reservoir flow in the cave area, the mathematical equation describing the relationship between the net flow rate of cave fluid and the change in cave pressure is: In formula (4), q v is the flow rate in the cave area, m 3 / s;C v is the cave storage coefficient, m 3 / Pa;p v is the pressure in the cave area, Pa; t is the time, s; The initial condition of fractures and holes is that the pressure at all locations in the reservoir is the same and equal to the original reservoir pressure before well production. The mathematical model of the initial pressure is expressed as: p tf (h,0)=p v (0)=p bf (h,0)=p i (5) In formula (5), p tf is the pressure in the crack area above the cave, Pa; p v is the pressure in the cave area, Pa; p bf is the pressure in the crack area below the cave, Pa; p i is the original reservoir pressure, Pa; h is the depth, m; The fracture-hole boundary conditions include: Internal boundary conditions: The wellbore production is equal to the sum of the flow rates in the fracture areas above all caves: The bottom hole pressure is equal to the sum of the pressure of the branch reservoir near the wellbore and the pressure difference of the horizontal section near the wellbore: p w (t)=Δp w1 +p tf1 (t) (7) In formulas (6) and (7), Q is the bottom hole flow rate, m 3 / s;q tf is the flow rate in the crack area above the cave, m 3 / s;q tfj is the flow rate in the upper fracture area of the j-branch cave, m 3 / s;p w is the bottom hole pressure, Pa; △p w1 is the pressure difference corresponding to the wellbore length near the wellbore, Pa; t is the time, s; p tf1 is the pressure of the first branch fracture in the wellbore, Pa; Interface connection conditions: The fluid flows from the fracture system in the lower part of the cave, through the cave area, and into the fracture area in the upper part of the cave. At the interface between the cave and the upper and lower fracture areas, the flow rate is the same: At the interface between the cave and the upper and lower fracture areas, the pressure is the same: p tf (h tv ,t)=p v (t)=p bf (h bv ,t) (9) In formulas (8) and (9), C v is the cave storage coefficient, m 3 / Pa;h tv is the depth of the cave top, m; h bv is the depth of the cave bottom, m; External boundary conditions: The outer boundary of the reservoir is a closed boundary with no fluid flow: Where: h fb is the bottom depth of the crack area in the lower part of the cave, m; The solution to obtain the bottom hole pressure solution of a multi-branch fault-karst combined production reservoir includes: The parameters in the mathematical model are dimensionless, and we get: dimensionless pressure k1 is the permeability of the first branch reservoir, m 2 , A f1 is the projected area of the first branch reservoir, m 2 ; p is pressure, Pa; dimensionless time φ is porosity, %; j is the jth branch; dimensionless flow q is the flow rate, m 3 / d; dimensionless storage coefficient C is the storage coefficient, m 3 / Pa; dimensionless depth Dimensionless gravity coefficient Dimensionless branch reservoir distance Dimensionless flow coefficient ratio A fj is the projected area of the j-th branch reservoir, m 2 ; Dimensionless pressure transmission coefficient ratio After dimensionless transformation and Laplace space transformation, the pressure of the upper and lower fractures of any j-branch cave is: In formula (11), is the dimensionless pressure of the crack on the j-th branch in Laplace space, h D is the dimensionless depth in the vertical direction, dimensionless; is the dimensionless pressure of the crack at the lower part of the j-th branch in Laplace space, dimensionless; The flow equation of the upper fracture of any j-branch cave is: In formula (12), h tvDj is the dimensionless depth of the top surface of the j-th branch cave, dimensionless; The flow equation of any j-branch cave is: In formula (13), C vDj is the dimensionless storage coefficient of the j-th branch cave area, dimensionless; is the dimensionless pressure in the j-th branch cave region in Laplace space, dimensionless; The flow equation for any j-th section of the wellbore is: The wellbore flow conditions are: The wellbore pressure conditions are: In formula (16), is the dimensionless pressure in the crack region above the j-th branch in Laplace space, dimensionless; d D1 is the dimensionless distance from the first branch reservoir to the bottom of the well, dimensionless; is the dimensionless pressure at the bottom of the well in Laplace space, dimensionless; For any j-branch lower fracture-cavern-upper fracture, the flow condition is: In formula (17), C vDj is the dimensionless storage coefficient of the j-th branch cave area, dimensionless; for any j-branch lower fracture-cavity-upper fracture, the pressure condition is: In formula (18), h bvDj is the dimensionless depth of the bottom of the j-th branch cave, dimensionless; The outer boundary of the reservoir is a sealed boundary, and the flow rate is 0: In formula (19), h bfDj is the dimensionless depth of the bottom of the crack in the lower part of the j-th branch, dimensionless; The corresponding solution of equation (11) is in the form of: In formula (20), c is the coefficient to be determined, r is the conjugate characteristic root, and its expression is: In formula (21), is the characteristic root of the flow equation in the upper crack region of the jth branch, dimensionless; is the characteristic root of the flow equation in the crack region below the j-th branch, dimensionless; Substituting equation (20) into the inner boundary conditions (15-16), the interface connection conditions (17-18), and the outer boundary conditions (19), we obtain the linear equations for the coefficient c to be determined: In formula (22), c tj is the coefficient to be determined in the flow equation of the upper crack region of the j-th branch, dimensionless, subscript j = {1,…,n}; c bj is the coefficient to be determined in the flow equation of the lower fracture area of the j-th branch, dimensionless, subscript j = {1,…,n}; The matrix D is 4n×4n elements, all of which are 0 except for the following elements: The first row of elements is: The elements in rows 2 to n are: In formula (22-2), λ is the row number of matrix D, dimensionless, and its value is λ={2,…,n}; d Dj is the dimensionless distance from the j-th branch reservoir to the bottom of the well, dimensionless; the elements in the n+1~2n rows are: The elements in rows 2n+1 to 3n are: The elements in rows 3n+1 to 4n are: For the two-branch model, D is specifically: For a single branch, D is: Solve the equations (22) to obtain all the coefficients c t1 , then according to formula (16), the bottom hole pressure solution can be obtained as In formula (23), is the dimensionless bottom hole pressure in Laplace space, dimensionless; is the coefficient to be determined in the seepage equation of the upper fracture area of the first branch, dimensionless; is the conjugate coefficient to be determined in the seepage equation of the upper fracture area of the first branch, dimensionless; d D1 is the dimensionless distance from the first branch reservoir to the bottom of the well, dimensionless; The dimensionless bottom hole pressure (23) in Laplace space is inverted by Stehfest numerical integration algorithm, and the solution data of the dimensionless bottom hole pressure changing with time in real space is obtained. wD ; The difference between the pressure of the measured data and the pressure solution obtained by the solution is calculated; if the difference is less than the preset fitting error, the initial parameters are used as the final fitting parameters; if the difference is greater than or equal to the preset fitting error, the fitting parameters are revised until the difference is less than the preset fitting error, and the last revised fitting parameters are used as the final fitting parameters; the final fitting parameters are the parameters of the fractures and cavities in the multi-branched fault-karst reservoir.

2. The method for determining fracture-cavity parameters of a multi-branched fault-karst reservoir according to claim 1, characterized in that: The initial parameters of the pre-built mathematical model of the bottom hole pressure of the multi-branch fault-karst combined production reservoir include: the number of branch reservoirs j, the original formation pressure p i , reservoir permeability k, porosity φ, comprehensive compressibility c t .

3. The method for determining fracture-cavity parameters of a multi-branched fault-karst reservoir according to claim 2, characterized in that: The initial values of the fitting parameters are expressed as M0(d j0 ,A fj0 ,h j0 ), where d is the distance between the branch well and the reservoir, h is the depth of the cave area, and A f is the seepage area.

4. The method for determining fracture-cavity parameters of a multi-branched fault-karst reservoir according to claim 1, characterized in that: The modified fitting parameters include: the reservoir distance d of each branch well j , the depth of each cave area h j , seepage area A of each branch reservoir fj .

5. A system for determining fracture-cavity parameters of a multi-branched fault-karst reservoir based on the method for determining fracture-cavity parameters of a multi-branched fault-karst reservoir according to claim 1, characterized in that: include: Acquisition module: used to obtain the measured data of the bottom hole pressure of the test well changing with time after the well is shut in; Calculation module: used to determine the initial parameters of the pre-built mathematical model of bottom-hole pressure of multi-branched fault-karst combined production reservoir based on the basic geological data of fractures and cavities in multi-branched fault-karst combined production reservoirs, use the initial parameters as the initial values of the fitting parameters, and solve to obtain the bottom-hole pressure solution of the multi-branched fault-karst combined production reservoir; Output module: used to calculate the difference between the pressure of the measured data and the pressure solution obtained; If the difference is less than the preset fitting error, the initial parameters are used as the final fitting parameters; If the difference is greater than or equal to the preset fitting error, the fitting parameters are corrected until the difference is less than the preset fitting error, and the last corrected fitting parameters are used as the final fitting parameters; the final fitting parameters are the parameters of the fractures and cavities in the multi-branched fault-karst reservoir.

6. A computing device, characterized in that including processors and storage media; The storage medium is used to store instructions; The processor is configured to operate according to the instructions to execute the steps of the method according to any one of claims 1 to 4.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method according to any one of claims 1 to 4 are implemented.

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