A shale gas well production prediction method based on development experiments

Abstract

This invention provides a method for predicting shale gas well production based on development experiments. The method includes: a simulation experiment development curve determination step: conducting a depletion-type development laboratory simulation experiment using matrix-fracture coupling experimental cores of the target shale gas well, and establishing a curve showing the change in gas production rate with respect to production time, which is the simulation experiment development curve; a similarity relationship determination step: establishing similarity criteria for shale reservoir development considering the fracture network area, supply length, and dynamic permeability considering stress-sensitive effects of the matrix-fracture system, and establishing similarity relationships between the physical simulation experiment and the production time and gas production rate of the shale gas well in the mining area based on similarity theory; and a production prediction step: based on the simulation experiment development curve, using the similarity relationships between the physical simulation experiment and the production time and gas production rate of the shale gas well in the mining area, establishing a production decline curve for the shale gas well in the mining area, and completing the shale gas well production prediction.

Description

Technical Field

[0001] The present invention belongs to the technical field of shale gas exploration and development, and in particular relates to a method for predicting the full life cycle production of a shale gas well based on a matrix-fracture coupling development experiment. Background Art

[0002] Shale gas capacity evaluation and production decline analysis are the basis for efficient development of shale gas wells. At present, there are many methods for calculating shale gas well capacity and predicting production performance: most of them are purely theoretical models, which are based on many assumptions and are very different from actual development conditions; secondly, some key parameters used in the calculation process cannot be accurately obtained and lack the support of experimental physical parameters. The current capacity calculation and production performance prediction methods are difficult to reasonably explain the particularity of shale gas well production curves and cannot effectively guide the effective development of shale gas wells.

[0003] The shale gas development simulation experiment is based on the similarity theory. When the single-valued conditions of the same type of physical phenomena are similar and the corresponding similarity criteria (composed of the physical quantities in the single-valued conditions) are equal, these phenomena must be similar. By establishing an effective conversion relationship between the physical simulation experiment parameters and the mine parameters, the results of the physical simulation can be inverted into the gas reservoir to obtain the decline law of gas well production, thereby explaining the production curve characteristics and production decline law of shale gas wells, which has important theoretical guidance and practical significance for the efficient development of shale gas wells. Summary of the invention

[0004] The object of the present invention is to provide a shale gas well production prediction method based on a dynamic simulation experiment of shale gas well full life cycle depletion development.

[0005] In order to achieve the above object, the present invention provides a shale gas well production prediction method based on development experiments, wherein the method comprises:

[0006] Steps for determining the simulation experimental development curve: using the matrix-fracture coupling experimental core of the target shale gas well to conduct an indoor simulation experiment of depletion development, and establishing a curve of the change of gas production rate with respect to production time, which is the simulation experimental development curve;

[0007] Similarity relationship determination steps: establish similarity criteria for shale reservoir development that consider the fracture network area of ​​the matrix-fracture system, supply length, and dynamic permeability that considers stress sensitivity effects, and establish similarity relationships between the production time of the physical simulation experiment and the shale gas wells in the mine (i.e., the similarity relationship between the production time in the physical simulation experiment and the production time of the shale gas wells in the mine) and the gas production rate (i.e., the similarity relationship between the gas production rate in the physical simulation experiment and the gas production rate of the shale gas wells in the mine) based on similarity theory;

[0008] Production prediction step: Based on the simulation experiment development curve, using the physical simulation experiment and the similarity relationship between the production time and gas production rate of the shale gas wells in the mine, a production decline curve of the shale gas wells in the mine (i.e., the relationship curve of daily gas production with production time) is established to complete the shale gas well production prediction.

[0009] The technical solution provided by the present invention utilizes the exhaustion development dynamics of the entire life cycle of a shale gas well to determine the changing trend of the gas production rate with the production time during the exhaustion development process, that is, the gas production decline law; and considers the fracture network area, supply length and dynamic permeability of the matrix fracture system in the development dynamics considering the stress sensitivity effect, and establishes a similarity criterion (that is, the similarity relationship between the physical simulation parameters and the gas reservoir parameters); finally, using the similarity criterion, the changing trend of the gas production rate with the production time at the core scale is further inverted to the gas reservoir scale, and the dynamic decline curve of the shale gas well production in the mine is obtained; thus, a complete set of methods for obtaining the dynamic decline curve of the shale gas well production is formed.

[0010] In the above-mentioned shale gas well production prediction method based on development experiments, preferably, the matrix-fracture coupling experimental core of the target shale gas well is obtained by the following method:

[0011] Obtain a full-diameter core of a horizontal section of a target shale gas well development reservoir; create at least one artificial fracture along the bedding direction of the full-diameter core of a horizontal section of a target shale gas well development reservoir, thereby establishing a matrix-fracture coupling experimental core of the target shale gas well.

[0012] In the above-mentioned shale gas well production prediction method based on development experiment, preferably, the depletion development indoor simulation experiment is carried out using the matrix-fracture coupling experimental core of the target shale gas well to establish a curve of the change of gas production rate with respect to production time, i.e., the simulation experiment development curve, which includes:

[0013] The matrix-fracture coupling experimental core of the target shale gas well is loaded into the depletion development simulation experimental system, the experimental temperature is consistent with the temperature of the target shale gas well development reservoir or maintained at room temperature, the confining pressure of the experimental core is added to the overburden pressure of the target shale gas well development reservoir, and the experimental core is saturated with adsorbable methane gas to the pressure of the target shale gas well development reservoir;

[0014] After the experimental core is saturated with adsorbable methane gas, it is left to stand for a period of time to allow the adsorption to reach equilibrium;

[0015] Open the gas production outlet to start simulating the exhaustion development process and record the gas production rate at different production times;

[0016] Based on the gas production rate at different production times, a curve of the change of gas production rate with respect to production time is established, which is the simulation experiment development curve;

[0017] In a specific embodiment, the standing for a period of time is standing for more than 10 days.

[0018] In the above-mentioned shale gas well production prediction method based on development experiments, preferably, the production time similarity relationship is:

[0019]

[0020] In the formula, A t is the total seepage area of ​​the mine (usually refers to the total seepage area of ​​the fracture network after volume fracturing of shale gas wells); K t It is the comprehensive dynamic permeability of the mine taking into account the effects of slippage, diffusion and stress sensitivity; p it is the original formation pressure of the mine; T ft is the mine fluid temperature; l t is the seepage length from the mine matrix to the fracture surface; μ t is the viscosity of the mine fluid; is the reservoir porosity of the mine; S gt is the gas saturation of the mine; Z t is the mine fluid compressibility factor; K 0t is the mine matrix permeability; T Rt is the mine reservoir temperature; A m is the total experimental seepage area (usually refers to the total seepage area of ​​the seam network); K m is the comprehensive dynamic permeability considering the effects of slippage, diffusion, and stress sensitivity in the experiment; p im is the original formation pressure of the experimental simulation loading; T fm is the experimental fluid temperature; l m is the seepage length from the experimental matrix to the fracture surface; μ m is the experimental fluid viscosity; is the experimental reservoir porosity; S gm is the experimental gas saturation; Z m is the experimental fluid compressibility factor; K 0m is the experimental matrix permeability; T Rm is the experimental temperature; t m It is experimental production time.

[0021] In the above-mentioned shale gas well production prediction method based on development experiments, preferably, the gas production rate similarity relationship is:

[0022]

[0023] In the formula, A t is the total seepage area of ​​the mine (usually refers to the total seepage area of ​​the fracture network after volume fracturing of shale gas wells); K tIt is the comprehensive dynamic permeability of the mine taking into account the effects of slippage, diffusion and stress sensitivity; p it is the original formation pressure of the mine; μ t is the viscosity of the mine fluid; Z t is the mine fluid compressibility factor; l t is the seepage length from the mine matrix to the fracture surface; A m is the total experimental seepage area (usually refers to the total seepage area of ​​the seam network); K m is the comprehensive dynamic permeability considering the effects of slippage, diffusion, and stress sensitivity in the experiment; p im is the original formation pressure of the experimental simulation loading; μ m is the experimental fluid viscosity; Z m is the experimental fluid compressibility factor; l m is the seepage length from the experimental matrix to the fracture surface; q m is the experimental gas production rate.

[0024] In the above-mentioned shale gas well production prediction method based on development experiments, preferably, the similarity criteria for shale reservoir development considering the fracture network area of ​​the matrix-fracture system, the supply length and the dynamic permeability considering the stress sensitivity effect are established, and the similarity relationship between the production time and the gas production rate of the physical simulation experiment and the shale gas well in the mine are established according to the similarity theory, including:

[0025] Determine the main physical quantities related to stress sensitivity and gas flow, including the fracture network area of ​​the matrix-fracture system, the supply length, and the dynamic permeability considering the stress sensitivity effect;

[0026] Based on the main physical quantities, the similarity criterion is constructed using the second similarity theorem (i.e. the second law of similarity, i.e. the π theorem);

[0027] Based on the similarity criterion and using the dimensionless theory of well testing, expressions for dimensionless production time and dimensionless gas production rate are determined;

[0028] Based on the dimensionless production time expression, the similarity relationship between the physical simulation experiment and the production time of shale gas wells in the mine is determined;

[0029] Based on the dimensionless expression of gas production rate, the similarity between the physical simulation experiment and the gas production rate of shale gas wells in the mine is determined;

[0030] More preferably, the main physical quantities include the total seepage area (usually the total seepage area of ​​the fracture network), the seepage length from the matrix to the fracture surface, the comprehensive dynamic permeability considering the effects of slippage, diffusion, and stress sensitivity, the matrix permeability, the original formation pressure, the bottom hole pressure, the reservoir porosity, the gas saturation, the reservoir temperature, the fluid viscosity, the fluid temperature, the fluid compressibility factor, the gas production rate, and the production time;

[0031] Further preferably, based on the main physical quantities, the bottom hole pressure, the seepage length from the matrix to the fracture surface, the production time, and the reservoir temperature are used as characteristic physical quantities in the process of constructing similarity criteria using the second similarity theorem (i.e., the second law of similarity, i.e., the π theorem);

[0032] More preferably, the similarity criteria include: π1=φ, π2=S g ,π3=Z,

[0033] In the formula, p f is the bottom hole pressure, with the dimension [M·T -2 ·L -1 ]; p i is the original formation pressure, with the dimension [M·T -2 ·L -1 ]; K0 is the matrix permeability, with the dimension of [L 2 ]; K is the comprehensive dynamic permeability considering the effects of slippage, diffusion, and stress sensitivity, and its dimension is [L 2 ]; φ is the reservoir porosity, dimensionless; S g is the gas saturation, dimensionless; l is the seepage length from the matrix to the fracture surface, dimension [L]; A is the total seepage area (usually the total seepage area of ​​the fracture network), dimension [L 2 ]; q is the gas production rate, the dimension is [L 3 ·T -1 ]; T f is the fluid temperature, with the dimension [K]; t is the production time, with the dimension [T]; μ is the fluid viscosity, with the dimension [M·T -1 ·L -1 ]; Z is the fluid compressibility factor, dimensionless; T R Reservoir temperature, dimension is [K]; π1, π2, π3, π4, π5, π6, π7, π8, π9 and π 10 are all similarity criteria involved in the calculation;

[0034] Among them, π1, π2, and π3 are basic similarity criteria, which can achieve similarity with the original gas reservoir by restoring the original reservoir pressure and gas saturation and other conditions; π4 and π6 are dynamic similarity; π5 is geometric similarity; π7, π8, and π9 are motion similarity;

[0035] In a specific embodiment, the expression of the dimensionless production time is:

[0036]

[0037] In the formula, p i is the original formation pressure; K0 is the matrix permeability; K is the comprehensive dynamic permeability considering the effects of slippage, diffusion, and stress sensitivity; φ is the reservoir porosity; S g is the gas saturation; l is the seepage length from the matrix to the fracture surface; A is the total seepage area (usually refers to the total seepage area of ​​the fracture network); T f is the fluid temperature; t is the production time; μ is the fluid viscosity; Z is the fluid compressibility factor; T R Reservoir temperature; t D is the dimensionless production time;

[0038] In one specific embodiment, the dimensionless gas production rate is expressed as:

[0039]

[0040] In the formula, p i is the original formation pressure; K is the comprehensive dynamic permeability considering the effects of slippage, diffusion, and stress sensitivity; l is the seepage length from the matrix to the fracture surface; A is the total seepage area (usually the total seepage area of ​​the fracture network); μ is the fluid viscosity; Z is the fluid compressibility factor; q is the gas production rate; q D is the dimensionless gas production rate.

[0041] In the above-mentioned shale gas well production prediction method based on development experiments, preferably, the method further comprises:

[0042] Obtain the actual production curve of the target shale gas well;

[0043] Based on the comparison between the existing actual production curve of the target shale gas well and the established production decline curve of the shale gas well in the mine, it is determined whether the established production decline curve of the shale gas well in the mine is feasible.

[0044] The technical solution provided by the present invention takes the production dynamics of the whole life cycle of shale gas wells as the research object. First, the whole production process of the gas well is simulated by indoor simulation experiments to obtain the gas production decline law of the target shale gas well depletion development; then the similarity criteria for shale reservoir development considering the fracture network area of ​​the matrix-fracture system, the supply length and the dynamic permeability considering the stress sensitivity effect are established, and then the similarity relationship between production time and gas production rate is established; the constructed similarity relationship is used to more accurately invert the results of physical simulation into the gas reservoir to obtain the gas well production decline curve. The acquisition of the gas well production decline curve is the basis for explaining the production curve characteristics and production decline law of shale gas wells, and has important theoretical guidance and practical significance for the efficient development of shale gas wells. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 A schematic flow chart of a shale gas well production prediction method based on development experiments provided in one embodiment of the present invention.

[0046] Figure 2 This is the exhaustion-type development simulation experimental system in Example 1 of the present invention.

[0047] Figure 3 This is a graph showing the relationship between daily gas production, pressure and time during the exhaustion-type development indoor simulation experiment in Example 1.

[0048] Figure 4 This is the shale gas well production decline curve in Example 1. DETAILED DESCRIPTION

[0049] In order to make the purpose, technical solution and advantages of the embodiment of the present invention clearer, the technical solution in the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the protection scope of the present invention.

[0050] The principle and spirit of the present invention are described in detail below with reference to several representative embodiments of the present invention.

[0051] See also Figure 1 In order to achieve the above-mentioned purpose, the present invention provides a shale gas well production prediction method based on development experiments, wherein the method comprises:

[0052] Step S1: using the matrix-fracture coupling experimental core of the target shale gas well to conduct an indoor simulation experiment of depletion development, and establish a curve of the change of gas production rate with respect to production time, which is the simulation experiment development curve;

[0053] Step S2: establishing similarity criteria for shale reservoir development that consider the fracture network area of ​​the matrix-fracture system, the supply length, and the dynamic permeability that considers the stress sensitivity effect, and establishing similarity relationships between the production time of the physical simulation experiment and the shale gas wells in the mine (i.e., the similarity relationship between the production time in the physical simulation experiment and the production time of the shale gas wells in the mine) and the gas production rate (i.e., the similarity relationship between the gas production rate in the physical simulation experiment and the gas production rate of the shale gas wells in the mine) based on similarity theory;

[0054] Step S3: Based on the simulation experiment development curve, using the physical simulation experiment and the similarity relationship between the production time and gas production rate of the shale gas wells in the mine, establish the shale gas well production decline curve (i.e., the relationship curve between daily gas production and production time) to complete the shale gas well production prediction.

[0055] Generally speaking, shale gas well development can be divided into the fracture network control stage and the matrix supply stage. In the early stage of development, the production law is mainly controlled by the supply of the fracture network control area and the return of fracturing fluid, and the development law is relatively complex; in the fracture network control stage, the daily gas production curve fluctuates greatly due to the generation of free gas in the fractures and the return of fracturing fluid. In the matrix control stage, gas and water in the fractures are produced synchronously, the daily water production and daily gas production gradually decrease, the supply range gradually expands, and the gas production law is relatively uniform. In the late production stage, the matrix supply determines the production and stable production period of the gas well. In the matrix supply area near the fracture, it can be regarded as a one-dimensional flow of the matrix to the fracture. Using real reservoir cores, matrix depletion development simulation experiments are carried out to obtain the gas production law of the matrix under formation conditions. Combined with the gas well parameters, the gas well production can be predicted.

[0056] In one embodiment, step S1 includes:

[0057] The matrix-fracture coupling experimental core of the target shale gas well is loaded into the depletion development simulation experimental system. The experimental temperature is consistent with the temperature of the target shale gas well development reservoir or maintained at room temperature. The confining pressure of the experimental core is added to the overburden pressure of the target shale gas well development reservoir. The experimental core is saturated with adsorbable methane gas to the pressure of the target shale gas well development reservoir.

[0058] After the experimental core is saturated with adsorbable methane gas, it is left to stand for a period of time to allow the adsorption to reach equilibrium;

[0059] Open the gas production outlet to start simulating the exhaustion development process and record the gas production rate at different production times;

[0060] Based on the gas production rate at different production times, a curve of the change of gas production rate with respect to production time is established, which is the simulation experiment development curve;

[0061] Furthermore, the period of time of standing is 10 days or more.

[0062] In one embodiment, the matrix-fracture coupling experimental core of the target shale gas well is obtained by:

[0063] Obtain a full-diameter core of a horizontal section of a target shale gas well development reservoir; create at least one artificial fracture along the bedding direction of the full-diameter core of a horizontal section of a target shale gas well development reservoir, thereby establishing a matrix-fracture coupling experimental core of the target shale gas well.

[0064] In one embodiment, the production time similarity relationship is:

[0065]

[0066] In the formula, A tis the total seepage area of ​​the mine (usually refers to the total seepage area of ​​the fracture network after volume fracturing of shale gas wells); K t It is the comprehensive dynamic permeability of the mine taking into account the effects of slippage, diffusion and stress sensitivity; p it is the original formation pressure of the mine; T ft is the mine fluid temperature; l t is the seepage length from the mine matrix to the fracture surface; μ t is the viscosity of the mine fluid; is the reservoir porosity of the mine; S gt is the gas saturation of the mine; Z t is the mine fluid compressibility factor; K 0t is the mine matrix permeability; T Rt is the mine reservoir temperature; A m is the total experimental seepage area (usually refers to the total seepage area of ​​the seam network); K m is the comprehensive dynamic permeability considering the effects of slippage, diffusion, and stress sensitivity in the experiment; p im is the original formation pressure of the experimental simulation loading; T fm is the experimental fluid temperature; l m is the seepage length from the experimental matrix to the fracture surface; μ m is the experimental fluid viscosity; is the experimental reservoir porosity; S gm is the experimental gas saturation; Z m is the experimental fluid compressibility factor; K 0m is the experimental matrix permeability; T Rm is the experimental temperature; t m It is experimental production time.

[0067] In one embodiment, the gas production rate similarity relationship is:

[0068]

[0069] In the formula, A t is the total seepage area of ​​the mine (usually refers to the total seepage area of ​​the fracture network after volume fracturing of shale gas wells); K t It is the comprehensive dynamic permeability of the mine taking into account the effects of slippage, diffusion and stress sensitivity; p it is the original formation pressure of the mine; μ t is the viscosity of the mine fluid; Z t is the mine fluid compressibility factor; l t is the seepage length from the mine matrix to the fracture surface; A m is the total experimental seepage area (usually refers to the total seepage area of ​​the seam network); K m is the comprehensive dynamic permeability considering the effects of slippage, diffusion, and stress sensitivity in the experiment; p imis the original formation pressure of the experimental simulation loading; μ m is the experimental fluid viscosity; Z m is the experimental fluid compressibility factor; l m is the seepage length from the experimental matrix to the fracture surface; q m is the experimental gas production rate.

[0070] In one embodiment, step S2 includes:

[0071] Determine the main physical quantities related to stress sensitivity and gas flow, including the fracture network area of ​​the matrix-fracture system, the supply length, and the dynamic permeability considering the stress sensitivity effect;

[0072] Based on the main physical quantities, the similarity criterion is constructed using the second similarity theorem (i.e. the second law of similarity, i.e. the π theorem);

[0073] Based on similarity criteria and using the dimensionless theory of well testing, the expressions of dimensionless production time and dimensionless gas production rate are determined.

[0074] Based on the dimensionless production time expression, the similarity relationship between the physical simulation experiment and the production time of shale gas wells in the mine is determined;

[0075] Based on the dimensionless expression of gas production rate, the similarity between the physical simulation experiment and the gas production rate of shale gas wells in the mine is determined;

[0076] Furthermore, the main physical quantities include the total seepage area (usually the total seepage area of ​​the fracture network), the seepage length from the matrix to the fracture surface, the comprehensive dynamic permeability considering the effects of slippage, diffusion, and stress sensitivity, matrix permeability, original formation pressure, bottom hole pressure, reservoir porosity, gas saturation, reservoir temperature, fluid viscosity, fluid temperature, fluid compressibility factor, gas production rate, and production time;

[0077] Furthermore, based on the main physical quantities, the second similarity theorem (i.e., the second law of similarity, i.e., the π theorem) is used to construct similarity criteria, with bottom hole pressure, seepage length from matrix to fracture surface, production time, and reservoir temperature as characteristic physical quantities;

[0078] Furthermore, similar numbers include: π1 = φ, π2 = S g ,π3=Z,

[0079] In the formula, p f is the bottom hole pressure, with the dimension of [M·T -2 ·L -1 ]; pi is the original formation pressure, with the dimension [M·T -2 ·L -1 ]; K0 is the matrix permeability, with the dimension of [L 2 ]; K is the comprehensive dynamic permeability considering the effects of slippage, diffusion, and stress sensitivity, and its dimension is [L 2 ]; φ is the reservoir porosity, dimensionless; S g is the gas saturation, dimensionless; l is the seepage length from the matrix to the fracture surface, dimension [L]; A is the total seepage area (usually the total seepage area of ​​the fracture network), dimension [L 2 ]; q is the gas production rate, the dimension is [L 3 ·T -1 ]; T f is the fluid temperature, with the dimension [K]; t is the production time, with the dimension [T]; μ is the fluid viscosity, with the dimension [M·T -1 ·L -1 ]; Z is the fluid compressibility factor, dimensionless; T R Reservoir temperature, dimension is [K]; π1, π2, π3, π4, π5, π6, π7, π8, π9 and π 10 are all similar criteria involved in the calculation;

[0080] Among them, π1, π2, and π3 are basic similarity criteria, which can achieve similarity with the original gas reservoir by restoring the original reservoir pressure and gas saturation and other conditions; π4 and π6 are dynamic similarity; π5 is geometric similarity; π7, π8, and π9 are motion similarity;

[0081] For example, the expression for dimensionless production time is:

[0082]

[0083] In the formula, p i is the original formation pressure; K0 is the matrix permeability; K is the comprehensive dynamic permeability considering the effects of slippage, diffusion, and stress sensitivity; φ is the reservoir porosity; S g is the gas saturation; l is the seepage length from the matrix to the fracture surface; A is the total seepage area (usually refers to the total seepage area of ​​the fracture network); T f is the fluid temperature; t is the production time; μ is the fluid viscosity; Z is the fluid compressibility factor; T R Reservoir temperature; t D is the dimensionless production time;

[0084] For example, the expression for the dimensionless gas production rate is:

[0085]

[0086] In the formula, pi is the original formation pressure; K is the comprehensive dynamic permeability considering the effects of slippage, diffusion, and stress sensitivity; l is the seepage length from the matrix to the fracture surface; A is the total seepage area (usually the total seepage area of ​​the fracture network); μ is the fluid viscosity; Z is the fluid compressibility factor; q is the gas production rate; q D is the dimensionless gas production rate.

[0087] In one embodiment, the method further comprises:

[0088] Obtain the actual production curve of the target shale gas well;

[0089] Based on the comparison between the existing actual production curve of the target shale gas well and the established production decline curve of the shale gas well in the mine, it is determined whether the established production decline curve of the shale gas well in the mine is feasible.

[0090] Example 1

[0091] This embodiment provides a shale gas well production prediction method based on development experiments.

[0092] The method is used to predict the production of a shale gas well, and the method includes:

[0093] 1. Using the matrix-fracture coupling experimental core of the target shale gas well to conduct an indoor simulation experiment of depletion development, a curve of the change of gas production rate with respect to production time is established, which is the simulation experimental development curve; specifically, it includes:

[0094] 1.1 Obtain the full-diameter horizontal core of the target shale gas well development reservoir, place the prepared full-diameter horizontal core in a 105°C oven and dry it for more than 48 hours, weigh the dry weight to be 2640.36 g, measure the diameter to be 104.26 mm, and measure the length to be 125.50 mm; create an artificial fracture along the bedding direction of the full-diameter horizontal core and wrap it with a sealing tape to establish the matrix-fracture coupling experimental core of the target shale gas well.

[0095] 1.2 Load the matrix-fracture coupling experimental core of the target shale gas well into the depletion development simulation experimental system, and connect the depletion development simulation experimental system, such as Figure 2 As shown; debug the data acquisition software, test the air tightness of the experimental system, and measure the dead volume of external pipes and each interface.

[0096] The exhaustion development simulation experimental system is as follows: Figure 2As shown, it includes an ISCO pump, a high-pressure container for methane conversion, a core holder for loading cores, and a back pressure valve connected in sequence; wherein, a safety valve 1 and a regulating valve 1 are sequentially arranged on the connecting pipeline between the high-pressure container and the inlet of the core holder, a regulating valve 2 is arranged on the connecting pipeline between the outlet of the core holder and the back pressure valve, and a methane injection branch is arranged on the connecting pipeline between the regulating valve 2 and the back pressure valve, wherein the methane injection branch is provided with an ISCO pump, a high-pressure container for methane conversion, and a safety valve 2 connected once; the experimental system is further provided with a confining pressure application port connected to the core holder. pressure pump; pressure sensor 1, pressure sensor 2 and pressure sensor 3 are respectively arranged at the inlet, outlet and confining pressure application port of the core holder, and pressure sensor 1, pressure sensor 2 and pressure sensor 3 are connected to the indicator and then connected to the computer, so as to realize the collection of pressure data of pressure sensor 1, pressure sensor 2 and pressure sensor 3 by computer and display of pressure data of pressure sensor 1, pressure sensor 2 and pressure sensor 3 by indicator; the experimental system is further provided with a gas flow meter for detecting the output gas flow rate, and the detected gas flow rate is sold in real time by computer.

[0097] 1.3 The experimental temperature is room temperature, and the confining pressure and inlet pressure are loaded. The confining pressure is set to 50MPa, and the methane gas is continuously saturated to 30MPa. The pressure monitoring system records the pressure changes in real time. After the pressure balance is stable (not less than 10 days), it indicates that the adsorption has reached equilibrium.

[0098] 1.4 After the adsorption reaches equilibrium, open the regulating valve 2 to simulate the shale gas depletion development process. The software monitors the experimental data in real time, including the pressure at each pressure measuring point, production time, daily gas production (i.e. gas production rate), and cumulative gas production. The cumulative gas production is measured using the drainage gas production method.

[0099] 1.5 Based on the gas production rate at different production times, a curve of the gas production rate changing with respect to production time is established, which is the simulation experiment development curve; Figure 3 shown.

[0100] The experiment lasted for 6 months. The relationship between pressure, daily gas production and time is as follows: Figure 3 As shown, the gas production rate was high in the early stage, mainly from fractures, and then entered a high-speed decline stage, and then entered a low-production and stable production period, which lasted for 110 days.

[0101] 2. Establish similarity criteria for shale reservoir development that take into account the fracture network area of ​​the matrix-fracture system, supply length, and dynamic permeability that takes into account stress sensitivity effects. Based on similarity theory, establish similarity relationships between production time in physical simulation experiments and shale gas wells in mines (i.e., similarity relationships between production time in physical simulation experiments and production time of shale gas wells in mines) and gas production rate (i.e., similarity relationships between gas production rate in physical simulation experiments and gas production rate of shale gas wells in mines); specifically include:

[0102] Considering the stress sensitivity effect in shale reservoir development and the relationship between the main physical quantities related to gas flow, it can be expressed as:

[0103] f(p w ,p i ,K0,K,φ,S g ,l,A,q,T f ,t,μ,Z,T R )=0 Formula 1;

[0104] In the formula, p f is the bottom hole pressure, with the dimension [M·T -2 ·L -1 ]; p i is the original formation pressure, with the dimension [M·T -2 ·L -1 ]; K0 is the matrix permeability, with the dimension of [L 2 ]; K is the comprehensive dynamic permeability considering the effects of slippage, diffusion, and stress sensitivity, and its dimension is [L 2 ]; φ is the reservoir porosity, dimensionless; S g is the gas saturation, dimensionless; l is the seepage length from the matrix to the fracture surface, dimension [L]; A is the total seepage area (usually the total seepage area of ​​the fracture network), dimension [L 2 ]; q is the gas production rate, the dimension is [L 3 ·T -1 ]; T f is the fluid temperature, with the dimension [K]; t is the production time, with the dimension [T]; μ is the fluid viscosity, with the dimension [M·T -1 ·L -1 ]; Z is the fluid compressibility factor, dimensionless; T R Reservoir temperature, dimension is [K]; π1, π2, π3, π4, π5, π6, π7, π8, π9 and π 10 are all similar criteria involved in the calculation;

[0105] There are 14 physical quantities and 4 basic dimensions in total, among which p f , l, t and T Rare selected as four characteristic physical quantities; according to the principle of dimensional analysis, the relationship between physical quantities can be converted into dimensionless form, and the number of physical quantities can be reduced by using characteristic physical quantities to represent the remaining physical quantities; the second similarity theorem is used here, and the remaining 10 physical quantities can be represented by 4 characteristic physical quantities in formula 1 to obtain 10 similarity numbers; the dimensionless product is shown in the following formula:

[0106]

[0107] The similarity coefficients obtained are as follows: π1 = φ, π2 = S g ,π3=Z,

[0108] Among them, π1, π2, and π3 are basic similarity criteria, which can achieve similarity with the original gas reservoir by restoring the original reservoir pressure and gas saturation and other conditions; π4 and π6 are dynamic similarity; π5 is geometric similarity; π7, π8, and π9 are motion similarity;

[0109] According to the dimensionless theory of well testing, the dimensionless time t is derived by similarity criteria. D and the dimensionless yield q D As in the equation:

[0110]

[0111]

[0112] Based on the dimensionless production time expression, the similarity relationship between the physical simulation experiment and the production time of shale gas wells in the mine is determined;

[0113] The production time similarity relationship is:

[0114]

[0115] In the formula, A t is the total seepage area of ​​the mine (usually refers to the total seepage area of ​​the fracture network after volume fracturing of shale gas wells); K t It is the comprehensive dynamic permeability of the mine taking into account the effects of slippage, diffusion and stress sensitivity; p it is the original formation pressure of the mine; T ft is the mine fluid temperature; l t is the seepage length from the mine matrix to the fracture surface; μ t is the viscosity of the mine fluid; is the reservoir porosity of the mine; S gt is the gas saturation of the mine; Zt is the mine fluid compressibility factor; K 0t is the mine matrix permeability; T Rt is the mine reservoir temperature; A m is the total experimental seepage area (usually refers to the total seepage area of ​​the seam network); K m is the comprehensive dynamic permeability considering the effects of slippage, diffusion, and stress sensitivity in the experiment; p im is the original formation pressure of the experimental simulation loading; T fm is the experimental fluid temperature; l m is the seepage length from the experimental matrix to the fracture surface; μ m is the experimental fluid viscosity; is the experimental reservoir porosity; S gm is the experimental gas saturation; Z m is the experimental fluid compressibility factor; K 0m is the experimental matrix permeability; T Rm is the experimental temperature; t m is the experimental production time;

[0116] Based on the dimensionless expression of gas production rate, the similarity between the physical simulation experiment and the gas production rate of shale gas wells in the mine is determined;

[0117] The similarity relationship of the gas production rate is:

[0118]

[0119] In the formula, A t is the total seepage area of ​​the mine (usually refers to the total seepage area of ​​the fracture network after volume fracturing of shale gas wells); K t It is the comprehensive dynamic permeability of the mine taking into account the effects of slippage, diffusion and stress sensitivity; p it is the original formation pressure of the mine; μ t is the viscosity of the mine fluid; Z t is the mine fluid compressibility factor; l t is the seepage length from the mine matrix to the fracture surface; A m is the total experimental seepage area (usually refers to the total seepage area of ​​the seam network); K m is the comprehensive dynamic permeability considering the effects of slippage, diffusion, and stress sensitivity in the experiment; p im is the original formation pressure of the experimental simulation loading; μ m is the experimental fluid viscosity; Z m is the experimental fluid compressibility factor; l m is the seepage length from the experimental matrix to the fracture surface; q m is the experimental gas production rate.

[0120] 3. Based on the simulation experiment development curve, using the similarity relationship between the physical simulation experiment and the production time and gas production rate of the shale gas wells in the mine, a production decline curve of the shale gas wells in the mine (i.e., the relationship curve between daily gas production and production time) is established to complete the shale gas well production prediction.

[0121] The experimental physical simulation parameters and mine parameters are shown in Table 1.

[0122] Table 1

[0123] Mining experiment Seepage length / m 3.5 0.125 <![CDATA[Seepage area / m 2 > 2400000 0.0122656 Matrix permeability / mD 0.006 0.006 Fluid viscosity / mPa·s 0.02707 0.02534 Standard temperature / K 293.15 293.15 Original formation pressure / MPa 50 30 Fluid compressibility factor 0.899 0.899 Reservoir temperature / K 353.15 293.15 Standard atmospheric pressure / MPa 1.01 1.01 Reservoir porosity / % 6 6 Gas Saturation 0.7 0.7 Comprehensive dynamic permeability / mD 0.05 0.05 Fluid temperature / K 353.15 293.15

[0124] The production decline curve of shale gas wells in the mine is as follows: Figure 4 shown.

[0125] Fourth, the actual production data of the target shale gas well was fitted to obtain the production curve of the shale gas well that has been produced. The production decline curve of the mine shale gas well obtained by inversion of the physical simulation experiment was basically consistent with the production curve of the shale gas well that has been produced (the physical simulation experiment was from the 1.2th day to the 30th day, and the corresponding actual production was from the 25th day to the 630th day), which confirmed the rationality of the selection of mine parameters and physical simulation parameters, and showed that the experimental results can reasonably explain and predict the production dynamics of shale gas wells.

[0126] The production decline curve of shale gas wells in the mine is used to analyze the decline law of daily gas production in the whole life cycle of the target shale gas well. The production decline law of the target shale gas well is as follows: in the early stage of mining (the physical modeling experiment is the first 13 days, corresponding to the first 269 days of mine development), the daily gas production decreases rapidly; in the middle stage of mining (the physical modeling experiment is from the 13th day to the 58th day, corresponding to the 269th day to the 1214th day of mine development), the daily gas production decreases at a medium speed; in the late stage of mining (the physical modeling experiment is from the 58th day to the 173rd day, corresponding to the 1214th day to the 3637th day of mine development), the daily gas production shows a slow decay; and then it can be calculated that the annual decline rates are 65%, 40%, 25%, 15%, 14%...

[0127] The preferred embodiments of the present invention are described above with reference to the accompanying drawings. Many features and advantages of these embodiments are clear from this detailed description, and therefore the claims are intended to cover all such features and advantages of these embodiments that fall within their true spirit and scope. In addition, since many modifications and changes are easily conceivable to those skilled in the art, it is not intended to limit the embodiments of the present invention to the precise structure and operation illustrated and described, but all suitable modifications and equivalents falling within its scope may be covered.

Claims

1. A shale gas well production prediction method based on development experiments, wherein: The method includes: Steps for determining the simulation experimental development curve: using the matrix-fracture coupling experimental core of the target shale gas well to conduct an indoor simulation experiment of depletion development, and establishing a curve of the change of gas production rate with respect to production time, which is the simulation experimental development curve; Similarity relationship determination steps: Establish similarity criteria for shale reservoir development that consider the fracture network area of ​​the matrix-fracture system, supply length, and dynamic permeability that considers stress sensitivity effects; and establish similarity relationships between physical simulation experiments and production time and gas production rate of shale gas wells in the mine based on similarity theory; Production prediction step: Based on the simulation experiment development curve, using the physical simulation experiment and the similarity relationship between the production time and gas production rate of the shale gas wells in the mine, a production decline curve of the shale gas wells in the mine, that is, a curve of the relationship between the daily gas production and the production time, is established to complete the shale gas well production prediction; Among them, the similarity relationship of production time is: In the formula, A t is the total seepage area of ​​the mine; K t It is the comprehensive dynamic permeability of the mine taking into account the effects of slippage, diffusion and stress sensitivity; p it is the original formation pressure of the mine; T ft is the mine fluid temperature; l t is the seepage length from the mine matrix to the fracture surface; μ t is the viscosity of the mine fluid; is the reservoir porosity of the mine; S gt is the gas saturation of the mine; Z t is the mine fluid compressibility factor; K 0t is the mine matrix permeability; T Rt is the mine reservoir temperature; t t is the production time of the mine; A m is the total experimental seepage area; K m is the comprehensive dynamic permeability considering the effects of slippage, diffusion, and stress sensitivity in the experiment; p im is the original formation pressure of the experimental simulation loading; T fm is the experimental fluid temperature; l m is the seepage length from the experimental matrix to the fracture surface; μ m is the experimental fluid viscosity; is the experimental reservoir porosity; S gm is the experimental gas saturation; Z m is the experimental fluid compressibility factor; K 0m is the experimental matrix permeability; T Rm is the experimental temperature; t m It is the experimental production time; Among them, the similarity relationship of the gas production rate is: In the formula, A t is the total seepage area of ​​the mine; K t It is the comprehensive dynamic permeability of the mine taking into account the effects of slippage, diffusion and stress sensitivity; p it is the original formation pressure of the mine; μ t is the viscosity of the mine fluid; Z t is the mine fluid compressibility factor; l t is the seepage length from the mine matrix to the fracture surface; q t is the gas production rate of the mine; A m is the total experimental seepage area; K m is the comprehensive dynamic permeability considering the effects of slippage, diffusion, and stress sensitivity in the experiment; p im is the original formation pressure of the experimental simulation loading; μ m is the experimental fluid viscosity; Z m is the experimental fluid compressibility factor; l m is the seepage length from the experimental matrix to the fracture surface; q m is the experimental gas production rate.

2. The prediction method according to claim 1, wherein: The depletion development indoor simulation experiment is conducted using the matrix-fracture coupling experimental core of the target shale gas well to establish a curve of the change of gas production rate with respect to production time, which is the simulation experimental development curve, including: The matrix-fracture coupling experimental core of the target shale gas well is loaded into the depletion development simulation experimental system, the experimental temperature is consistent with the temperature of the target shale gas well development reservoir or maintained at room temperature, the confining pressure of the experimental core is added to the overburden pressure of the target shale gas well development reservoir, and the experimental core is saturated with adsorbable methane gas to the pressure of the target shale gas well development reservoir; After the experimental core is saturated with adsorbable methane gas, it is left to stand for a period of time to allow the adsorption to reach equilibrium; Open the gas production outlet to start simulating the exhaustion development process and record the gas production rate at different production times; Based on the gas production rate at different production times, a curve of the change of gas production rate with respect to production time is established, which is the simulation experiment development curve.

3. The prediction method according to claim 1 or 2, wherein: The matrix-fracture coupling experimental core of the target shale gas well is obtained by the following method: Obtain a full-diameter core of a horizontal section of a target shale gas well development reservoir; create at least one artificial fracture along the bedding direction of the full-diameter core of a horizontal section of a target shale gas well development reservoir, thereby establishing a matrix-fracture coupling experimental core of the target shale gas well.

4. The prediction method according to claim 1, wherein: The similarity criteria for shale reservoir development that consider the fracture network area of ​​the matrix-fracture system, the supply length, and the dynamic permeability that considers the stress sensitivity effect are established, and the similarity relationship between the production time and the gas production rate of the physical simulation experiment and the shale gas well in the mine are established based on the similarity theory, including: Determine the main physical quantities related to stress sensitivity and gas flow, including the fracture network area of ​​the matrix-fracture system, the supply length, and the dynamic permeability considering the stress sensitivity effect; Based on the main physical quantities, similarity criteria are constructed using the second similarity theorem; Based on the similarity criterion and using the dimensionless theory of well testing, expressions for dimensionless production time and dimensionless gas production rate are determined; Based on the dimensionless production time expression, the similarity relationship between the physical simulation experiment and the production time of shale gas wells in the mine is determined; Based on the dimensionless expression of gas production rate, the similarity relationship between the physical simulation experiment and the gas production rate of shale gas wells in the mine is determined.

5. The prediction method according to claim 4, wherein: The main physical quantities include the total seepage area, the seepage length from the matrix to the fracture surface, the comprehensive dynamic permeability considering the effects of slippage, diffusion and stress sensitivity, the matrix permeability, the original formation pressure, the bottom hole pressure, the reservoir porosity, the gas saturation, the reservoir temperature, the fluid viscosity, the fluid temperature, the fluid compressibility factor, the gas production rate and the production time.

6. The prediction method according to claim 5, wherein: Based on the main physical quantities, the bottom hole pressure, the seepage length from the matrix to the fracture surface, the production time and the reservoir temperature are used as characteristic physical quantities in the process of constructing similarity criteria using the second similarity theorem.

7. The prediction method according to claim 6, wherein: The similarity criteria include: π1=φ,π2=S g ,π3=Z, In the formula, p f is the bottom hole pressure; p i is the original formation pressure; K0 is the matrix permeability; K is the comprehensive dynamic permeability considering the effects of slippage, diffusion, and stress sensitivity; φ is the reservoir porosity; S g is the gas saturation; l is the seepage length from the matrix to the fracture surface; A is the total seepage area; q is the gas production rate; T f is the fluid temperature; t is the production time; μ is the fluid viscosity; Z is the fluid compressibility factor; T R Reservoir temperature; π1, π2, π3, π4, π5, π6, π7, π8, π9 and π 10 are all the similarity criteria involved in the calculation.

8. The prediction method according to any one of claims 4 to 7, wherein: The expression of the dimensionless production time is: In the formula, p i is the original formation pressure; K0 is the matrix permeability; K is the comprehensive dynamic permeability considering the effects of slippage, diffusion, and stress sensitivity; φ is the reservoir porosity; S g is the gas saturation; l is the seepage length from the matrix to the fracture surface; A is the total seepage area; T f is the fluid temperature; t is the production time; μ is the fluid viscosity; Z is the fluid compressibility factor; T R Reservoir temperature; t D is the dimensionless production time.

9. The prediction method according to any one of claims 4 to 7, wherein: The expression of the dimensionless gas production rate is: In the formula, p i is the original formation pressure; K is the comprehensive dynamic permeability considering the effects of slippage, diffusion, and stress sensitivity; l is the seepage length from the matrix to the fracture surface; A is the total seepage area; μ is the fluid viscosity; Z is the fluid compressibility factor; q is the gas production rate; q D is the dimensionless gas production rate.

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