Shale gas development evaluation method and system

Abstract

The application discloses a shale gas development evaluation method and system, wherein the method comprises the following steps: obtaining the static characteristics of a favorable reservoir before fracturing in a build-up area according to geochemical identification of the favorable layer section, reservoir quality classification evaluation and reservoir distribution evaluation; based on the static characteristics of the favorable reservoir before fracturing in the build-up area and production dynamic data, the fracture network parameters after fracturing of a shale gas well are inverted, gas well productivity evaluation and classification evaluation are carried out, and the characteristics of the reservoir after fracturing are obtained; the reservoir connectivity after fracturing is analyzed by using qualitative and quantitative technical methods, and the optimal development well spacing in the build-up area is determined; on the basis of the fracture network form analysis, the longitudinal well pattern deployment in the build-up area is evaluated; and based on the quantitative characterization of the stress sensitivity of the shale reservoir in the build-up area, the reasonable development mode of the gas well and real-time production allocation are determined. The application can comprehensively understand the shale gas, so that the key development technical policy of the shale gas is determined, and efficient development of the shale gas is realized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of natural gas development, and particularly relates to a shale gas development evaluation method and system. BACKGROUND

[0002] Shale gas refers to unconventional natural gas existing in organic matter-rich shale and interbeds in an adsorbed and free state as the main existence mode, and has a large distribution area, no obvious gas reservoir boundary, and extremely poor reservoir permeability, with a surface permeability of 10 -4 ~10 -6 mD, relatively homogeneous in macroscopic view and strong heterogeneity in microscopic view. At the exploration stage, the parameters, standards and precision of reservoir evaluation using seismic data and a small amount of exploration wells cannot meet the needs of the development stage. Therefore, at the development stage, establishing reservoir quantitative characterization parameters and standards is the basis for identifying shale reservoirs from micro and macro perspectives, and evaluating the spatial distribution characteristics of different types of reservoirs is the premise of fracturing design and development technology policy optimization.

[0003] Compared with conventional gas reservoirs, shale reservoirs have self-sealing characteristics, and only through long horizontal wells + large-scale volume fracturing to form a complex fracture network can single wells be effectively developed, so the shale gas development concept is different. Practice has proved that moderate interference between wells and clusters is appropriate, and horizontal and vertical composite flow is appropriate. The matrix reservoir permeability of marine shale is extremely low, the reservoir bedding joints are developed, and the higher the content of siliceous, carbonaceous and organic matter in the reservoir, the more developed the bedding joints. The bedding joint density of Wufeng Formation-Longyi 1 Submember is large, reaching 20-50 per meter, directly affecting the extension of the hydraulic fracture height, and the vertical utilization height is limited, so the matching relationship between the hydraulic fracture network parameters and the horizontal well spacing and vertical well pattern is the key to affecting the vertical and horizontal reservoir utilization degree. In addition, marine shale is distributed in thin layers and belongs to soft strata, and different scale fracture networks are developed after fracturing, which is easy to cause stress sensitivity effect, especially in the micro-fracture and near-fracture zone matrix area without proppant, the stress sensitivity is extremely strong, so the production system is the key to affecting the shale gas recovery degree in the SRV area. SUMMARY

[0004] In view of the above problems, the present application provides a shale gas development evaluation method and system to quantitatively understand the essential characteristics of shale gas reservoirs, evaluate shale gas production capacity, and determine a reasonable shale gas development technology policy.

[0005] The shale gas development evaluation method comprises the following steps: obtaining the static characteristics of the favorable reservoirs in the development area before fracturing according to the geochemical identification of the favorable intervals, the reservoir quality classification evaluation and the reservoir distribution evaluation; based on the static characteristics of the favorable reservoirs in the development area before fracturing and the production dynamic data, the fracture network parameters after fracturing of the shale gas well are inverted, the gas well productivity evaluation and classification evaluation are carried out, and the reservoir characteristics after fracturing are obtained; the reservoir connectivity after fracturing is analyzed by using qualitative and quantitative various technical methods, and the optimal development well spacing of the development area is determined; based on the fracture network form analysis, the longitudinal well pattern deployment of the development area is evaluated; based on the quantitative characterization of the stress sensitivity of the shale reservoir in the development area, the reasonable development mode and real-time production allocation of the gas well are determined.

[0006] Further, the obtaining of the static characteristics of the favorable reservoirs in the development area before fracturing according to the geochemical identification of the favorable intervals, the reservoir quality classification evaluation and the reservoir distribution evaluation comprises the following steps:

[0007] According to the geochemical parameters, the geophysical parameters and the geological comprehensive parameters, the micro-pore structure characterization and the mineral composition of the development area are obtained;

[0008] According to the micro-pore structure characterization and the mineral composition, the shale geochemical evaluation index and the classification standard of the favorable intervals are determined;

[0009] According to the gas content which is the index reflecting the macroscopic material basis of the reservoir and the brittleness index which is the index reflecting the compressibility, the reservoir classification of the development area is comprehensively determined;

[0010] According to the reservoir data of the horizontal well point, the fracture number and the mechanical data, and the seismic data, the mechanical data and the fracturing prediction data between wells, the macroscopic distribution of each main layer in the regional space of the development area is determined.

[0011] Further, the obtaining of the static characteristics of the favorable reservoirs in the development area before fracturing according to the geochemical identification of the favorable intervals, the reservoir quality classification evaluation and the reservoir distribution evaluation comprises the following steps:

[0012] According to the well test data, the production dynamic data and various production models of the development area, the apparent parameters of the reservoir after fracturing are inverted;

[0013] According to the production dynamic data and the distribution law of the key productivity characterization parameters in the effective reservoir parameters after fracturing, the probability distribution range of the single well productivity is determined;

[0014] According to the gas well classification evaluation standard oriented by benefit at different stages, the single well with the determined productivity is classified.

[0015] Further, the obtaining of the static characteristics of the favorable reservoirs in the development area before fracturing according to the geochemical identification of the favorable intervals, the reservoir quality classification evaluation and the reservoir distribution evaluation comprises the following steps:

[0016] According to the relationship between the microseismic event and the effective fracture network length, the interference probability is determined;

[0017] According to the interference test result, the communication mode is determined;

[0018] According to the production dynamic evaluation of productivity index change, the interference strength is determined;

[0019] Based on the interference probability, the communication mode and the interference strength, taking the single well productivity index as the objective function and taking the fracturing scale as the constraint condition, the multi-fracture network parameters are optimized to obtain the gas well spacing under the condition of maximizing the single well productivity index;

[0020] Taking the multi-well dynamic cumulative production as the optimization target, taking the total proppant volume as the internal constraint condition and taking the gas well development economy as the external constraint condition, the well spacing and the fracture network parameters are globally optimized.

[0021] Further, on the basis of the fracture network morphology analysis, the evaluation of the vertical well pattern deployment in the production area includes the following steps:

[0022] The fracture network parameters of the shale gas well are analyzed by the finite element method to obtain the fracture network morphology of the shale gas well;

[0023] Based on the physical simulation experiment of hydraulic fracturing, the field tracer dynamic monitoring and the evaluation results of the gas well production dynamic of the target body position in the adjacent layer, the reserve distribution of each high-quality small layer in the vertical direction of the gas well is obtained;

[0024] According to the fracture network morphology of the shale gas well and the reserve distribution of each high-quality small layer in the vertical direction of the gas well, a mathematical model of the star-shaped fracture network section is established;

[0025] According to the mathematical model of the star-shaped fracture network section, the vertical well pattern deployment in the production area is evaluated.

[0026] Further, based on the quantitative characterization of the stress sensitivity of the shale reservoir in the production area, the reasonable development mode and the real-time production allocation of the gas well include the following steps:

[0027] According to the mechanism analysis and the core experiment, the stress sensitivity coefficient γ of the shale reservoir is determined as a function of the production pressure difference of the soft formation, and the stress sensitivity curve of the shale permeability is obtained;

[0028] According to the stress sensitivity curve of the shale permeability, a physical model of the gas well after fracturing is established, a bilinear flow mathematical model of the gas flowing from the formation into the fracture and from the fracture into the wellbore is established by taking the single main fracture as a unit, and the instantaneous inflow dynamic curve of the shale gas well is obtained by superimposing the production and the stress sensitivity curve of the shale permeability;

[0029] Based on the instantaneous inflow dynamic curve of the shale gas well in the production area, the economic evaluation is combined to comprehensively optimize the production allocation of the gas well, and the reasonable development mode and the real-time production allocation of the gas well are determined.

[0030] Furthermore, the mathematical model for the star-shaped seam mesh cross-section is as follows:

[0031]

[0032] In the formula: y is the vertical distance of the volume element, m; b is the maximum vertical distance of the volume element from the wellbore, m; x is the lateral extension length of the crack at a distance of height y from the wellbore, m; a is the maximum lateral extension length of the crack at a distance of height y from the wellbore, m.

[0033] Furthermore, the specific gas well production pressure differential function is as follows:

[0034]

[0035] In the formula: γ is the stress sensitivity coefficient of shale reservoir; Δp is the production pressure difference; A, B, and C are constants.

[0036] Furthermore, the instantaneous inflow dynamic curve of the shale gas well is as follows:

[0037]

[0038] In the formula: Q g The gas well production is m / s; m is the pseudo-pressure, P. a 2 ;p i p wf These are the original formation pressure and the bottom hole flowing pressure, respectively, P a ;K m K f Permeability of the matrix and fracture system, respectively, in m 2 ;t a The equilibrium time is given in seconds; γ m γ mi The stress sensitivity coefficients at a given moment and in the initial state are respectively; w f x f P represents the width and half-length of the main fracture zone, respectively, in meters; B is the volume factor; μ is the gas viscosity at a certain formation pressure, in meters. a ·s;h is the effective reservoir thickness, in meters.

[0039] This invention also provides a shale gas development evaluation system, comprising:

[0040] Static reservoir identification unit before fracturing: Based on favorable interval geochemical identification, reservoir quality classification and evaluation, and reservoir distribution evaluation, obtain the static characteristics of favorable reservoirs in the production area before fracturing.

[0041] The reservoir dynamic understanding unit after fracturing reconstruction is based on the static characteristics and production dynamic data of the favorable reservoir before fracturing in the construction area, inverses the fracture network parameters after fracturing of the shale gas well, performs productivity evaluation and classification evaluation of the gas well, and obtains the reservoir characteristics after fracturing;

[0042] The plane well spacing evaluation unit uses qualitative and quantitative technical methods to analyze the reservoir connectivity after fracturing, and determines the optimal development well spacing in the construction area;

[0043] The longitudinal well pattern evaluation unit evaluates the deployment of the longitudinal well pattern in the construction area based on the fracture network form analysis;

[0044] The production system evaluation unit determines the reasonable development mode and real-time proration of the gas well based on the quantitative characterization of the stress sensitivity of the shale reservoir in the construction area.

[0045] Further, the reservoir static understanding unit before fracturing reconstruction is specifically used for:

[0046] According to the geochemical parameters, geophysical parameters and comprehensive geological parameters, the micro-pore structure characterization and mineral composition of the construction area are obtained;

[0047] According to the micro-pore structure characterization and mineral composition, the shale geochemical evaluation index and classification standard of the favorable layer are determined;

[0048] According to the index of gas content and the index of brittleness index reflecting the compressibility, the reservoir classification of the construction area is comprehensively determined;

[0049] According to the reservoir data of the horizontal well point, the number of fractures and mechanical data, and the interwell seismic data, mechanical data and fracturing prediction data, the macroscopic distribution of each main layer in the regional space of the construction area is determined.

[0050] Further, the reservoir dynamic understanding unit after fracturing reconstruction is specifically used for:

[0051] According to the well test data, production dynamic data and various production models of the construction area, the apparent parameters of the reservoir after fracturing are inversely determined;

[0052] According to the production dynamic data and the distribution rule of the key characterization parameters of the productivity in the effective reservoir parameters after fracturing, the probability distribution range of the single well productivity is determined;

[0053] According to the benefit-oriented gas well classification evaluation standard at different stages, the single well with determined productivity is classified.

[0054] Further, the plane well spacing evaluation unit is specifically used for:

[0055] The interference probability is determined according to the relationship between the microseismic event and the effective fracture network length;

[0056] The connectivity mode is determined according to the interference well test result;

[0057] According to the production dynamic evaluation capacity index change determines the interference intensity;

[0058] Based on the interference probability, the connected mode and the interference intensity, taking the single well capacity index as a target function, taking the fracturing scale as a constraint condition, the multi-fracture network parameters are optimized, and the gas well spacing under the condition of the maximum single well capacity index is obtained.

[0059] Taking the multi-well dynamic cumulative production as an optimization target, taking the total proppant volume as an internal constraint condition, and taking the gas well development economy as an external constraint condition, the well spacing and the fracture network parameters are globally optimized.

[0060] The shale gas can be comprehensively understood, so that the key development technology policy of the shale gas is determined, and the shale gas is developed efficiently.

[0061] Other features and advantages of the present application will be set forth in the following description, and in part will become apparent to those skilled in the art from the description, or can be learned by practice of the present application. The objects and other advantages of the present application can be realized and achieved by the structure as indicated in the description, claims and drawings. BRIEF DESCRIPTION OF DRAWINGS

[0062] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0063] Figure 1 A flowchart of a shale gas development evaluation method according to an embodiment of the present application is shown;

[0064] Figure 2 A specific operation flowchart of a shale gas development evaluation method according to an embodiment of the present application is shown;

[0065] Figure 3 A fracture network cross section perpendicular to a horizontal wellbore in an embodiment of the present application is shown;

[0066] Figure 4 A stress sensitivity curve of a shale sample of Longyi 1 submember in South Sichuan after being soaked in a fracturing fluid according to an embodiment of the present application is shown;

[0067] Figure 5 A shale gas well physical model after fracturing according to an embodiment of the present application is shown;

[0068] Figure 6A structural schematic diagram of a shale gas development evaluation system according to an embodiment of the present application is shown. DETAILED DESCRIPTION

[0069] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts should fall into the scope of the present application.

[0070] Plane well spacing evaluation, longitudinal well pattern evaluation and production system evaluation are the keys to efficient development of shale gas. The shale gas development evaluation method and flow processing system provided by the embodiments of the present application can represent the characteristics of the shale reservoir before and after fracturing, evaluate the production capacity of the shale gas well after fracturing, and determine the reasonable development technical policy of the shale gas.

[0071] Please refer to Figure 1 , Figure 1 A flow schematic diagram of a shale gas development evaluation method according to an embodiment of the present application is shown.

[0072] A shale gas development evaluation method, comprising the following steps:

[0073] S1, obtaining the static characteristics of the favorable reservoir before fracturing in the build-up area according to the geochemical identification of the favorable interval, the reservoir quality classification evaluation and the reservoir distribution evaluation.

[0074] S2, based on the static characteristics of the favorable reservoir before fracturing in the build-up area and the production dynamic data, inverting the fracture network parameters after fracturing of the shale gas well, performing the gas well productivity evaluation and the classification evaluation, and obtaining the characteristics of the reservoir after fracturing.

[0075] In this step, based on a large amount of production dynamic data of the gas well in the build-up area, the effective artificial fracture network characteristics after fracturing are inverted by means of various theoretical models; based on the inversion of the effective artificial fracture network characteristics after fracturing, the gas well productivity evaluation and the gas well classification evaluation are performed, so as to comprehensively understand the distribution characteristics and flow capacity of the reservoir after fracturing from the dynamic aspect.

[0076] S3, using qualitative and quantitative various technical methods to analyze the connectivity of the reservoir after fracturing, and determining the optimal development well spacing in the build-up area.

[0077] S4, based on the fracture network form analysis, evaluating the longitudinal well pattern deployment in the build-up area.

[0078] S5, based on the quantitative representation of the stress sensitivity of the shale reservoir in the build-up area, determining the reasonable development mode and real-time production allocation of the gas well.

[0079] The shale gas development evaluation method can comprehensively understand shale gas, so as to determine key shale gas development technology policies and realize efficient shale gas development.

[0080] Please refer to Figure 2 , Figure 2 The shale gas development evaluation method according to the embodiment of the application is shown.

[0081] In specific implementation, the shale gas development evaluation method includes two aspects of comprehensively understanding shale gas and efficiently developing shale gas. Favorable interval geochemical identification, reservoir quality classification evaluation and reservoir distribution fine evaluation are used to understand the shale reservoir before fracturing reconstruction from the static aspect; well testing or production dynamic evaluation, gas well productivity evaluation and gas well classification evaluation are used to understand the shale reservoir after fracturing reconstruction from the dynamic aspect. Plane well spacing evaluation, vertical well pattern evaluation and production system evaluation are keys to efficiently develop shale gas. The shale gas development evaluation technology method and process provided by the embodiment of the application can understand the shale reservoir characteristics before and after fracturing, evaluate the production capacity of the shale gas well after fracturing and determine the reasonable shale gas development technology policy.

[0082] Specifically, according to the favorable interval geochemical identification, reservoir quality classification evaluation and reservoir distribution evaluation, the static characteristics of the favorable reservoir before fracturing in the construction area are obtained by the following steps.

[0083] S11, the micro-pore structure representation and mineral composition of the construction area are obtained according to the geochemical parameters, geophysical parameters and geological comprehensive parameters.

[0084] S12, the shale geochemical evaluation index and classification standard of the favorable interval are determined according to the micro-pore structure representation and mineral composition.

[0085] S13, the reservoir classification of the construction area is comprehensively determined according to the gas content which reflects the macro-reflecting material basis of the reservoir and the brittleness index which reflects the compressibility.

[0086] S14, the macro-distribution of each main small layer in the regional space of the construction area is determined according to the reservoir data, fracture quantity and mechanical data of the horizontal well point and the inter-well seismic data, mechanical data and fracturing prediction data.

[0087] In specific implementation, the static characteristics before fracturing include microscopic identification, macroscopic reservoir classification and three-dimensional spatial distribution. First, the shale reservoir micro-pore structure representation and the nano-pore development law of shale reservoirs rich in organic matter are studied, and the relationship between pore development and reservoir mineral composition is finely described, the main control factors of pore development and mineral composition are studied, and the geochemical evaluation index and classification standard of the favorable interval are comprehensively established. On this basis, the well point core, logging (including imaging special logging) and other data are used to optimize the shale reservoir macro-classification index, and the development dynamic response of the single well is established to establish the shale reservoir macro-classification standard. Based on the reservoir data, fracture quantity and mechanical data of multiple well points, especially the reservoir data, fracture quantity and mechanical data of multiple crossing points of horizontal wells, the interwell seismic data, microseismic monitoring results and regional stress distribution are comprehensively used to predict the three-dimensional spatial distribution of the reservoir and identify the original reservoir before fracturing.

[0088] Based on the static characteristics of the favorable reservoir before fracturing in the built-up area and the production dynamic data, the fracture network parameters after fracturing of the shale gas well are inverted, the productivity evaluation and classification evaluation of the gas well are performed, and the reservoir characteristics after fracturing are obtained by the following steps:

[0089] S21. Inverting the apparent parameters of the reservoir after fracturing according to the well testing data, production dynamic data and various production models.

[0090] It should be noted that the apparent parameters of the reservoir are the artificial fracture network parameters. The shale gas is developed by the artificial fracture network, and the artificial fracture network after fracturing is affected by the original reservoir stress distribution, artificial reconstruction technology, various parameters, pressure distribution in the wave range of adjacent wells and other factors. The influencing factors are complex and the main control factors are not clear, and it is difficult to forward the artificial fracture network distribution. The effective artificial fracture network characteristics are inverted by using a large amount of production dynamic data and various production theoretical models.

[0091] In specific implementation, due to the large difference in the scale of the artificial fracture network, the theoretical model is established for scale representation. The main fracture near the wellbore is represented by a discrete model, and the core parameter is the fracture shape parameter; the secondary fracture in the SRV area is mainly controlled by the stress distribution, is complex and has certain regularity, is represented by a fractal model, and the core parameter is the fractal dimension of the secondary fracture system. The empirical value can be obtained according to the core or outcrop mechanical experiment; the micro-fracture in the far-wellbore area is small in scale and is not supported by proppant, and is represented by the same continuous model as the matrix, and the core parameter is the effective permeability of the mixed flow with the matrix, which can be obtained according to the core experiment.

[0092] S22. Determining the probability distribution range of the single-well productivity according to the production dynamic data and the productivity key representation parameter distribution law in the effective reservoir parameters after fracturing;

[0093] S23, according to the benefit-oriented gas well classification evaluation standard in different stages, the single well with determined productivity is classified.

[0094] It should be noted that the single well with determined productivity in this step is classified according to the fracture network volume size of the single well.

[0095] When the gas well productivity evaluation is specifically implemented, through the production dynamic data in the early linear flow stage, the product of the half length of the fracture system and the effective permeability of the 0.5th power of the percolation zone after fracturing is a determined value However, since the effective permeability of the percolation zone after fracturing and the half length of the fracture system are difficult to accurately obtain, a probability method is used to determine the distribution range of one of the parameters, for example, taking the effective permeability as an example, the minimum effective permeability is the matrix permeability, and the maximum effective permeability is the permeability when the boundary is reached tomorrow, after determining the range and distribution form of the effective permeability, a probability distribution curve is generated after multiple simulations, and a probability distribution curve of the half length of the fracture system is also generated, that is, a probability distribution curve and a cumulative probability distribution curve representing the EUR of the single well can be calculated, and P10, P50 and P90 on the cumulative probability distribution curve are taken as the conservative value, the median value and the optimistic value, respectively.

[0096] Specifically, the reservoir connectivity after fracturing is analyzed by using qualitative and quantitative technical methods, and the optimal development well spacing of the production area is determined, including the following steps:

[0097] S31, determining the interference probability according to the relationship between the microseismic event and the effective fracture network length;

[0098] S32, determining the connectivity mode according to the interference test result;

[0099] S33, determining the interference strength according to the productivity index change in the production dynamic evaluation;

[0100] S34, based on the interference probability, the connectivity mode and the interference strength, taking the single well productivity index as the target function, taking the fracturing scale as the constraint condition, optimizing the multi-fracture network parameters, and obtaining the gas well spacing under the condition of maximizing the single well productivity index;

[0101] S35, taking the multi-well dynamic cumulative production as the optimization target, taking the total proppant volume as the internal constraint condition, and taking the gas well development economy as the external constraint condition, globally optimizing the well spacing and the fracture network parameters.

[0102] It should be noted that the total proppant volume is related to the fracturing scale.

[0103] Specifically, on the basis of the fracture network form analysis, the vertical well pattern deployment in the production area is evaluated, including the following steps:

[0104] S41, analyze the fracture network parameters of the shale gas well by the finite element method, and obtain the fracture network form of the shale gas well.

[0105] S42, based on the hydraulic fracturing physical simulation experiment, the field tracer dynamic monitoring, and the evaluation results of the gas well production dynamic of the target body position in the adjacent layer, obtain the reserve distribution of each high-quality small layer in the longitudinal direction of the gas well.

[0106] S43, according to the fracture network form of the shale gas well and the reserve distribution of each high-quality small layer in the longitudinal direction of the gas well, establish a star-shaped fracture network cross-section mathematical model, and the specific process is as follows:

[0107]

[0108] In the formula, y is the vertical distance of the volume element distance, m; b is the maximum vertical distance of the volume element distance from the wellbore, m; x is the lateral extension length of the fracture at the height y position from the wellbore, m; and a is the maximum lateral extension length of the fracture at the height y position from the wellbore, m.

[0109] S44, according to the star-shaped fracture network cross-section mathematical model, evaluate the longitudinal well pattern deployment in the construction area.

[0110] It should be noted that the development of the longitudinal stratification seam limits the extension of the fracture network in the height, and the fracture network height away from the perforation point decreases exponentially with the distance.

[0111] Please refer to Figure 3 , Figure 3 The figure shows a schematic diagram of the fracture network cross section perpendicular to the horizontal wellbore in the embodiment of the application.

[0112] Based on the researches of the hydraulic fracturing physical simulation experiment, the field tracer dynamic monitoring, the comparative evaluation results of the target body position in the adjacent layer, and the shale gas well fracture network simulation by the finite element method, the embodiment of the application comprehensively proposes the understanding of the star-shaped fracture network cross section perpendicular to the horizontal wellbore, and establishes a star-shaped fracture network cross-section mathematical model. Based on this, the longitudinal well pattern deployment is optimized, and the staggered deployment can effectively reduce the interference of the fracture network and improve the reserve producing degree.

[0113] Specifically, based on the quantitative characterization of the stress sensitivity of the shale reservoir in the construction area, the reasonable development mode of the gas well and the real-time production allocation include the following steps:

[0114] S51, according to the mechanism analysis and the core experiment, determine that the stress sensitivity coefficient γ of the shale reservoir is a function of the production pressure difference of the soft formation, and obtain the stress sensitivity curve of the shale permeability.

[0115] In this step, there is the following relationship between the core permeability and the effective stress or the production pressure difference:

[0116] K (σ eff) = A exp[- γ(σ eff )] or

[0117]

[0118] wherein K is the permeability, m 2 ; A is a coefficient; γ is the stress sensitivity coefficient of shale permeability; σ eff is the effective stress, P a ; p is the formation pressure, P a ; p i is the original formation pressure, Pa; α is the Biot coefficient; υ is the Poisson's ratio of rock; Δp is the production pressure difference, P a .

[0119] In this step, the gas well production pressure difference function is specifically as follows:

[0120]

[0121] wherein γ is the stress sensitivity coefficient of shale reservoir; Δp is the production pressure difference; A, B and C are constants.

[0122] Please refer to Figure 4 and Figure 5 , Figure 4 shows the stress sensitivity curve after the shale sample of the Chuannan Longyi 1 sub-section is soaked with the fracturing fluid according to the embodiment of the present application, Figure 5 shows the schematic diagram of the physical model of the gas well after the shale is fractured according to the embodiment of the present application.

[0123] S52, according to the stress sensitivity curve of shale permeability, a physical model of the gas well after the shale is fractured is established, a bilinear flow mathematical model of gas flowing from the formation into the fracture and from the fracture into the wellbore is established by taking the single-section main fracture as a unit, and the instantaneous inflow performance curve of the shale gas well is obtained by superimposing the production and the stress sensitivity curve of shale permeability.

[0124] In this step, the instantaneous inflow performance curve of the shale gas well is specifically as follows:

[0125]

[0126] wherein Q g is the gas well production, m / s; m is the pseudo-pressure, P a 2 ; p i , p wf are the original formation pressure and the bottom-hole flowing pressure, P a ; K m , K f are the matrix and fracture system permeability, m 2 ; t a is the material balance time, s; γm , gamma mi , respectively, are stress sensitivity coefficients at a certain time and an original state; w f , x f , respectively, are width and half length of a main fracture zone, m; B is a volume coefficient; mu is gas viscosity under formation pressure at a certain time, P a ·s; h is effective reservoir thickness, m.

[0127] S53, based on the instantaneous inflow performance curve of the shale gas well in the build-up area, combined with economic evaluation, the gas well production allocation is optimized comprehensively, and the reasonable development mode and real-time production allocation of the gas well are determined.

[0128] In the implementation, the shale gas well instantaneous inflow performance curve chart is drawn by theoretically calculating based on the shale permeability stress sensitivity curve obtained through the experiment, combined with economic evaluation, the gas well production allocation is optimized comprehensively, and the cumulative production and recovery degree in the SRV area are maximized.

[0129] It should be noted that in the SRV area of the shale gas well, a large amount of gas is still stored in the matrix block and needs to be produced through the fracture network seepage channel, so maintaining the effectiveness of the seepage channel is also one of the core means to improve the recovery rate. Mechanism analysis shows that the characteristics of the thin-layered shale reservoir structure and the soft formation determine that the shale reservoir has strong stress sensitivity, and the stress sensitivity degree changes with the change of the effective stress. The experiment shows that the key parameter between the shale core permeability and the production pressure difference, that is, the shale permeability stress sensitivity coefficient, is a function of the production pressure difference in the soft formation, and is not a fixed value. The shale permeability stress sensitivity curve can be obtained through the experiment. Based on this, the physical and mathematical models are established, the shale gas well instantaneous inflow performance curve chart is calculated and drawn, combined with economic evaluation, the gas well production allocation is optimized comprehensively, and the cumulative production and recovery degree in the SRV area are maximized.

[0130] The shale gas development evaluation method of the embodiment of the present application can first identify the reservoir before fracturing from the static aspect according to the micro-geological identification, macro-classification evaluation and spatial distribution. Then the reservoir after fracturing can be understood from the dynamic aspect through well testing or production dynamic theory inversion, gas well probabilistic productivity evaluation and gas well classification evaluation. Finally, the key parameters for improving the shale gas recovery and development benefit can be determined through the optimization of key development technical policies such as plane well spacing, longitudinal well pattern and gas well production system.

[0131] Please refer to Figure 6 , Figure 6 Fig. 1 shows a structure schematic diagram of a shale gas development evaluation system according to an embodiment of the present application.

[0132] The embodiment of the present application further provides a shale gas development evaluation system, comprising:

[0133] The reservoir static understanding unit before fracturing reconstruction obtains the static characteristics of the favorable reservoir before fracturing in the built production area according to the geochemical identification, reservoir quality classification evaluation and reservoir distribution evaluation of the favorable interval.

[0134] The reservoir dynamic understanding unit after fracturing reconstruction obtains the reservoir characteristics after fracturing by inverting the fracture network parameters after fracturing of the shale gas well, performing gas well productivity evaluation and classification evaluation based on the static characteristics of the favorable reservoir before fracturing in the built production area and production dynamic data.

[0135] The plane well spacing evaluation unit determines the optimal development well spacing in the built production area by analyzing the reservoir connectivity after fracturing by using various qualitative and quantitative technical methods.

[0136] The longitudinal well pattern evaluation unit evaluates the longitudinal well pattern deployment in the built production area based on the fracture network form analysis.

[0137] The production system evaluation unit determines the reasonable development mode and real-time proration of the gas well based on the quantitative characterization of the stress sensitivity of the shale reservoir in the built production area.

[0138] Further, the reservoir static understanding unit before fracturing reconstruction is specifically used to obtain the micro-pore structure characterization and mineral composition of the built production area according to the geochemical parameters, geophysical parameters and comprehensive geological parameters; determine the shale geochemical evaluation index and classification standard of the favorable interval according to the micro-pore structure characterization and mineral composition; comprehensively determine the reservoir classification of the built production area according to the gas content which reflects the macro-substance basis of the reservoir and the brittleness index which reflects the compressibility; and determine the macro-distribution of each main layer in the regional space of the built production area according to the reservoir data of the horizontal well point, the number of fractures and mechanical data, and the inter-well seismic data, mechanical data and fracturing prediction data.

[0139] Further, the reservoir dynamic understanding unit after fracturing reconstruction is specifically used to invert the apparent parameters of the reservoir after fracturing according to the well test data, production dynamic data and various production models of the built production area; determine the probability distribution range of the single-well productivity according to the production dynamic data and the distribution law of the key characterization parameters of the productivity in the effective reservoir parameters after fracturing; and classify the single well with determined productivity according to the gas well classification evaluation standard oriented to the benefit at different stages.

[0140] Further, the plane well spacing evaluation unit is specifically used to determine the interference probability according to the relationship between the microseismic event and the effective fracture network length; determine the connectivity mode according to the interference well test result; determine the interference intensity according to the productivity index change in the production dynamic evaluation; based on the interference probability, the connectivity mode and the interference intensity, take the single-well productivity index as the objective function, take the fracturing scale as the constraint condition, optimize the multi-fracture network parameters, and obtain the gas well spacing under the condition of maximizing the single-well productivity index; and globally optimize the well spacing and fracture network parameters by taking the multi-well dynamic cumulative production as the optimization target, taking the total proppant volume as the internal constraint condition, and taking the economic efficiency of the gas well development as the external constraint condition.

[0141] Although the present application has been described in detail with reference to the foregoing embodiments, it should be understood that modifications can be made to the foregoing embodiments, or additional implementations can be implemented, without departing from the spirit and scope of the inventive subject matter. Accordingly, the present application is not limited to the implementations described herein, but is intended to cover all modifications and equivalents falling within the spirit and scope of the inventive subject matter.

Claims

1. A method for evaluating shale gas development, characterized in that, Includes the following steps: Based on the geochemical identification of favorable strata, reservoir quality classification and evaluation, and reservoir distribution evaluation, the static characteristics of favorable reservoirs in the production area before fracturing are obtained, including the following steps: Based on geochemical parameters, geophysical parameters, and comprehensive geological parameters, the microscopic pore structure and mineral composition of the production area are obtained; based on the microscopic pore structure and mineral composition, the geochemical evaluation indicators and classification standards for favorable shale strata are determined; based on the gas content, an indicator reflecting the material basis of the reservoir, and the brittleness index, an indicator reflecting compressibility, the reservoir classification of the production area is comprehensively determined; based on reservoir data, fracture quantity and mechanical data at horizontal well points, as well as seismic data, mechanical data, and fracturing prediction data between wells, the macroscopic distribution of each major sub-layer in the regional space of the production area is determined. Based on the static characteristics and production dynamics data of favorable reservoirs in the production area before fracturing, the fracture network parameters of shale gas wells after fracturing are inverted to conduct gas well productivity evaluation and classification evaluation, and obtain the reservoir characteristics after fracturing. This includes the following steps: inverting the apparent parameters of the reservoir after fracturing based on well test data, production dynamics data, and various production models in the production area; determining the probability distribution range of single-well productivity based on the distribution patterns of key productivity characterization parameters in the effective reservoir parameters after fracturing, according to the production dynamics data and the effective reservoir parameters after fracturing; and classifying single wells with determined productivity according to the benefit-oriented gas well classification evaluation standards at different stages. The post-fracturing reservoir connectivity was analyzed using a combination of qualitative and quantitative techniques to determine the optimal well spacing for the production area. This involved the following steps: determining the interference probability based on the relationship between microseismic events and effective fracture network length; determining the connectivity mode based on interference well test results; determining the interference intensity based on changes in the production capacity index; optimizing multi-fracture network parameters based on the interference probability, connectivity mode, and interference intensity, using the single-well production capacity index as the objective function and fracturing scale as the constraint, to obtain the well spacing under the condition of maximizing the single-well production capacity index; and globally optimizing the well spacing and fracture network parameters using the dynamic cumulative production of multiple wells as the optimization objective, the total proppant volume as the internal constraint, and the economic efficiency of gas well development as the external constraint. Based on the analysis of fracture network morphology, the evaluation of the vertical well network deployment in the production area includes the following steps: Analyzing the fracture network parameters of shale gas wells using the finite element method to obtain the fracture network morphology; obtaining the reserve distribution of each high-quality sub-layer in the vertical direction of the gas wells based on the results of hydraulic fracturing physical simulation experiments, on-site tracer dynamic monitoring, and dynamic evaluation of gas well production at adjacent layers with target locations; establishing a mathematical model of the star-shaped fracture network cross-section based on the shale gas well fracture network morphology and the reserve distribution of each high-quality sub-layer in the vertical direction of the gas wells; and evaluating the vertical well network deployment in the production area based on the star-shaped fracture network cross-section mathematical model. Based on the quantitative characterization of stress sensitivity in shale reservoirs in the production area, the rational development mode and real-time production allocation of gas wells are determined, including the following steps: Based on mechanism analysis and core experiments, the stress sensitivity coefficient γ of the shale reservoir is determined as a function of the gas well production pressure differential in soft formations, and the shale permeability stress sensitivity curve is obtained; based on the shale permeability stress sensitivity curve, a physical model of the gas well after fracturing is established. Taking a single main fracture as a unit, a bilinear flow mathematical model of gas flowing from the formation into the fracture and from the fracture into the wellbore is established. By superimposing the production rate onto the shale permeability stress sensitivity curve, the instantaneous inflow dynamic curve of the shale gas well is obtained; based on the instantaneous inflow dynamic curve of the shale gas well in the production area, combined with economic evaluation, the gas well production allocation is comprehensively optimized to determine the rational development mode and real-time production allocation of gas wells.

2. The shale gas development evaluation method according to claim 1, characterized in that, The specific mathematical model of the star-shaped seam mesh cross-section is as follows: In the formula: y is the vertical distance of the volume element, m; b is the maximum vertical distance of the volume element from the wellbore, m; x is the lateral extension length of the crack at a distance of height y from the wellbore, m; a is the maximum lateral extension length of the crack at a distance of height y from the wellbore, m.

3. The shale gas development evaluation method according to claim 1, characterized in that, The specific production pressure differential function for gas wells is as follows: In the formula: γ is the stress sensitivity coefficient of shale reservoir; Δp is the production pressure difference; A, B, and C are constants.

4. The shale gas development evaluation method according to claim 1, characterized in that, The instantaneous inflow dynamic curve of shale gas wells is as follows: In the formula: The gas well production rate is expressed in m / s. To simulate pressure, P a 2 ; p i 、p wf These are the original formation pressure and the bottom hole flowing pressure, respectively, P a ; K m , K f Permeability of the matrix and fracture system, respectively, in m 2 ; t a The equilibrium time is given in seconds; γ m γ mi These are the stress sensitivity coefficients at a certain moment and in the original state, respectively; w f , x f Hereinafter, the width and half-length of the main fracture zone are respectively, in meters (m). B This is the volume factor; Let P be the gas viscosity at a certain formation pressure. a ·s; The effective reservoir thickness is in meters (m).

5. A shale gas development evaluation system, characterized in that, include: The static reservoir identification unit before fracturing involves obtaining the static characteristics of favorable reservoirs in the production area before fracturing, based on favorable strata geochemical identification, reservoir quality classification and evaluation, and reservoir distribution evaluation. This includes the following steps: obtaining the microscopic pore structure characterization and mineral composition of the production area based on geochemical parameters, geophysical parameters, and comprehensive geological parameters; determining the favorable shale geochemical evaluation indicators and classification standards based on the microscopic pore structure characterization and mineral composition; comprehensively determining the reservoir classification of the production area based on the gas content (an indicator reflecting the macroscopic material basis of the reservoir) and the brittleness index (an indicator reflecting compressibility); and determining the macroscopic distribution of each major sub-layer in the production area in the regional space based on reservoir data, fracture quantity and mechanical data at horizontal well points, as well as seismic data, mechanical data, and fracturing prediction data between wells. The reservoir dynamics assessment unit after fracturing, based on the static characteristics and production dynamics data of favorable reservoirs in the production area before fracturing, inverts the fracture network parameters of shale gas wells after fracturing, conducts gas well productivity evaluation and classification evaluation, and obtains reservoir characteristics after fracturing. This includes the following steps: inverting the apparent parameters of the reservoir after fracturing based on well test data, production dynamics data, and various production models in the production area; determining the probability distribution range of single-well productivity based on the distribution patterns of key productivity characterization parameters in the effective reservoir parameters after fracturing, according to the production dynamics data and the effective reservoir parameters after fracturing; and classifying single wells with determined productivity according to the benefit-oriented gas well classification evaluation standards at different stages. The planar well spacing evaluation unit utilizes a combination of qualitative and quantitative techniques to analyze reservoir connectivity after fracturing and determine the optimal well spacing for production development. This includes the following steps: determining the interference probability based on the relationship between microseismic events and effective fracture network length; determining the connectivity mode based on interference well test results; determining the interference intensity based on changes in the production capacity index; optimizing multi-fracture network parameters based on the interference probability, connectivity mode, and interference intensity, using the single-well production capacity index as the objective function and fracturing scale as the constraint, to obtain the well spacing under the condition of maximizing the single-well production capacity index; and globally optimizing the well spacing and fracture network parameters using the dynamic cumulative production of multiple wells as the optimization objective, the total proppant volume as the internal constraint, and the economic efficiency of gas well development as the external constraint. The vertical well network evaluation unit, based on fracture network morphology analysis, evaluates the vertical well network deployment in the production area, including the following steps: Analyzing shale gas well fracture network parameters using the finite element method to obtain the fracture network morphology; obtaining the reservoir distribution of each high-quality sub-layer in the vertical direction of the gas well based on hydraulic fracturing physical simulation experiments, on-site tracer dynamic monitoring, and gas well production dynamic evaluation results at target locations in adjacent layers; establishing a mathematical model of the star-shaped fracture network cross-section based on the shale gas well fracture network morphology and the reservoir distribution of each high-quality sub-layer in the vertical direction of the gas well; and evaluating the vertical well network deployment in the production area based on the star-shaped fracture network cross-section mathematical model. The production system evaluation unit, based on the quantitative characterization of stress sensitivity of shale reservoirs in the production area, determines the reasonable development mode and real-time production allocation of gas wells, including the following steps: Based on mechanism analysis and core experiments, the stress sensitivity coefficient γ of the shale reservoir is determined as a function of the gas well production pressure difference in soft formations, obtaining the shale permeability stress sensitivity curve; based on the shale permeability stress sensitivity curve, a physical model of the gas well after fracturing is established, using a single main fracture as a unit, establishing a bilinear flow mathematical model of gas flowing from the formation into the fracture and from the fracture into the wellbore; by superimposing the production rate onto the shale permeability stress sensitivity curve, the instantaneous inflow dynamic curve of the shale gas well is obtained; based on the instantaneous inflow dynamic curve of the shale gas well in the production area, combined with economic evaluation, the gas well production allocation is comprehensively optimized to determine the reasonable development mode and real-time production allocation of gas wells.

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