Shale gas fracturing horizontal well production dynamic prediction method and computer equipment

Abstract

The invention discloses a shale gas fractured horizontal well production dynamic prediction method and computer equipment, and the method comprises the steps: building a shale gas reservoir material balance equation based on a material conservation principle of a closed gas reservoir and considering a shale gas adsorption effect; according to the gas well yield calculation model of the circular equal-thickness constant-pressure boundary homogeneous formation, an equivalent seepage resistance method is adopted, and a shale gas fractured horizontal well yield calculation model capable of considering fracture parameters is constructed; a shale gas reservoir material balance equation and a shale gas fractured horizontal well yield calculation model are combined, a shale gas fractured horizontal well yield calculation model based on the shale gas reservoir material balance equation is established, and the model is solved through a Newton iteration method and a dichotomy method. The method is mainly based on a material balance equation, correction is carried out according to the shale gas adsorption effect, the influence of the half length and the segment number of the crack is fully considered when a productivity calculation formula is constructed, the accuracy of final result prediction is greatly improved through combination of the two phases, and the calculation process is simple, clear, good in reliability and convenient to implement.

Description

Technical Field

[0001] The present invention belongs to the technical field of shale gas development, and in particular relates to a shale gas fracturing horizontal well production dynamic prediction method and computer equipment. Background Art

[0002] As an unconventional natural gas resource, shale gas is abundant in reserves. The Sichuan Basin and its surrounding areas are rich in shale gas resources and are currently the main battlefield for shale gas development in my country. In southern Sichuan, more than 80% of shale gas resources are buried in deep reservoirs above 3,500 meters. The production of deep marine shale gas has the conditions to build a production capacity of more than 30 billion cubic meters, which is the main body of future shale gas production growth.

[0003] However, shale reservoirs usually have low porosity and ultra-low permeability, which makes it very difficult for shale gas to flow in the reservoir. Currently, "volume fracturing + horizontal well" technology must be used to commercially develop shale gas. Affected by geological and engineering factors, shale gas wells usually have production variation characteristics of rapid initial production decline and low production in the later period, resulting in how to accurately predict the ultimate recoverable reserves (EUR) of shale gas wells is still a difficult problem in the industry.

[0004] At present, the commonly used shale gas well capacity evaluation methods include analytical method, numerical simulation method, empirical production decline method, modern production decline method, material balance method, probability method, and machine learning method. Among them, the model derivation of numerical simulation method, analytical model method, and modern production decline method is difficult, involving many physical parameters, and has high requirements on the theoretical level and operating experience of field operators; the material balance method is mainly used for geological reserve prediction, and it is difficult to predict the dynamic characteristics of gas wells; although the empirical production decline method is simple to apply, it lacks physical background; the probability method usually calculates the result of an interval range value with large uncertainty; the machine learning method is still in its infancy, and the method currently requires a large data body, and it is impossible to use a mathematical model to characterize the relationship between gas well production and influencing factors, and the prediction result is significantly affected by the learning effect.

[0005] For example, the Chinese invention patent with the patent number "CN202010636610.6" and the name "Method for determining the adaptability of production system in the variable pressure and variable production stage of shale gas wells" mainly uses the slope of the straight line fitted with production pressure and production data to obtain the pseudo-production index, which can be used to judge reservoir parameters. It mainly uses the simulation method, and its calculation process is relatively complex and still has large errors. Therefore, it is urgent to optimize the production dynamic calculation and prediction method of shale gas, improve the applicability of the method, enable it to be better applied and serve the site, and provide a strong technical reference for the formulation of gas reservoir development plans. Summary of the invention

[0006] In view of this, the present invention provides a shale gas fracturing horizontal well production dynamic prediction method and computer equipment to solve the problems in the prior art of complex physical model structure, cumbersome derivation and calculation, and inaccurate analysis of influencing factors for shale gas production dynamic prediction.

[0007] The technical solution is as follows:

[0008] A method for predicting the production dynamics of shale gas fracturing horizontal wells includes the following steps:

[0009] S1, based on the principle of conservation of matter, establish the material balance equation of closed gas reservoir;

[0010] S2, using the Langmuir model to characterize the shale gas adsorption model, correcting the material balance equation established in step S1 to obtain the shale gas reservoir material balance equation,

[0011]

[0012] Where P is the current formation pressure of the gas reservoir, MPa; Z is the current formation compression factor of the gas reservoir, dimensionless; P i is the original formation pressure of the gas reservoir, MPa; Z i is the original formation compression factor of the gas reservoir, dimensionless; is the cumulative gas production of shale reservoir without considering the effect of adsorption, m 3 ;c c is the compressibility factor of gas reservoir volume, MPa -1 ; ΔP is the gas reservoir pressure drop, ΔP=P i -P, MPa; is the original free gas volume of the gas reservoir, m 3 ;

[0013] S3, based on the gas well production calculation model of circular equal-thickness constant-pressure boundary homogeneous formation, the equivalent seepage resistance method is used to construct a shale gas fracturing horizontal well production calculation model that can take into account fracture parameters;

[0014] S4, by combining the shale gas reservoir material balance equation and the shale gas fracturing horizontal well production calculation model, a shale gas fracturing horizontal well production calculation model based on the shale gas reservoir material balance equation is established, the fluid physical properties and formation pressure under the two systems of fixed production rate production and fixed bottom hole pressure production are calculated, and the calculation results are output.

[0015] The above scheme is adopted mainly from the perspective of material balance, that is, the conservation of gas volume, and fully considers the shale gas adsorption effect to correct the material balance equation, thereby improving the accuracy of subsequent production capacity calculation and prediction. The overall idea is clearer, the model calculation is simple, and it has excellent applicability.

[0016] As a preferred embodiment, when correcting the material balance equation in step S2, the influence of shale gas adsorption on the material balance equation needs to be considered, which can further improve the reliability and accuracy of the correction.

[0017] As a preference: in step S3, the equivalent wellbore diameter r of the fracture in the fracturing area should first be determined according to the fracturing transformation characteristics of the vertical well section. wef The calculation formula of

[0018] Then, according to the fracture parameters of the horizontal section and the area equivalence principle, the equivalent circular driving boundary of the fracturing transformation area is obtained. Finally, the productivity calculation formula of the fracturing horizontal well is determined by the boundary conditions.

[0019] As a preferred embodiment: in step S4, the unknown production is processed by using the dichotomy method when performing the production calculation at a constant bottom hole pressure.

[0020] As a preferred method, the Newton iteration method is used to calculate the current formation pressure P of the gas reservoir.

[0021] As a preferred method, first input the basic parameters of the gas reservoir, the minimum bottom hole flow pressure P wf_min and the total forecast time T, and then calculate according to the production system of fixed production rate and fixed bottom flow pressure;

[0022] Among them, when calculating according to the fixed output production system, it includes the following steps:

[0023] S4.1, calculate the cumulative production of gas wells G at time t p ;

[0024] S4.2, calculating the current formation pressure P of the gas reservoir at time t+Δt based on the material balance equation of the shale gas reservoir;

[0025] S4.3, calculating the fluid physical property parameters under the current formation pressure P of the gas reservoir;

[0026] S4.4, based on the calculation formula for the productivity of fractured horizontal wells, calculate the bottom hole flow pressure P at t+Δt wf ;

[0027] According to the fixed bottom hole pressure production system, the following steps are included:

[0028] S4.a, calculating the current formation pressure P of the gas reservoir at time t+Δt based on the material balance equation of the shale gas reservoir;

[0029] S4.b, calculating the fluid physical property parameters under the current formation pressure P of the gas reservoir;

[0030] S4.c, based on the calculation formula of the production capacity of fractured horizontal wells, calculate the gas well production q at t+Δt sc ;

[0031] When the bottom hole pressure P calculated in S4.4 is wf Greater than the initial minimum bottom hole pressure P wf_min When t+Δt is greater than the total prediction time T, it is determined whether the calculation is terminated and the result is output. If the calculation is less than t, the calculation is continued in step S4.1.

[0032] When the bottom hole pressure P calculated in S4.4 is wf Less than or equal to the initial minimum bottom hole pressure P wf_min When , it directly enters S4.a for calculation.

[0033] Another aspect of the present application provides a computer device, the key of which is that the electronic device includes:

[0034] A memory storing executable instructions;

[0035] A processor runs the executable instructions in the memory to implement the above-mentioned shale gas fracturing horizontal well production dynamic prediction method.

[0036] On the other hand, the present application provides a computer-readable storage medium, the key of which is that the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the above-mentioned shale gas fracturing horizontal well production dynamic prediction method is implemented.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] The shale gas fracturing horizontal well production dynamic prediction method and computer equipment provided by the present invention are mainly based on the material balance principle. The material balance equation is corrected according to the shale gas adsorption effect, and the influence of the fracture half-length and the number of segments is fully considered when constructing the production capacity calculation formula. The combination of the two greatly improves the accuracy of the final result prediction, and the entire calculation process is relatively simpler and clearer, has good reliability, and is easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic diagram of the process of the present invention;

[0040] Figure 2 This is a schematic diagram of the production of a vertical well in the middle of a circular permeability mutation reservoir;

[0041] Figure 3 This is a schematic diagram of a shale gas fracturing horizontal well;

[0042] Figure 4 It is a schematic diagram of the calculation model;

[0043] Figure 5 It is a schematic diagram of production dynamic prediction;

[0044] Figure 6 This is a schematic diagram of the calculation model verification in this embodiment;

[0045] Figure 7 This is an analysis diagram of the impact of Langmuir volume on the productivity of shale gas fracturing horizontal wells;

[0046] Figure 8 This is an analysis diagram of the impact of Langmuir pressure on the productivity of shale gas fracturing horizontal wells;

[0047] Fig. 9 This is an analysis diagram of the impact of fracture half-length on the productivity of shale gas fracturing horizontal wells;

[0048] Fig.10 This is an analysis chart of the impact of the number of fracturing stages on the productivity of shale gas fracturing horizontal wells. DETAILED DESCRIPTION

[0049] The present invention will be further described in detail below in conjunction with the accompanying drawings.

[0050] refer to Figures 1 to 10 The shale gas fracturing horizontal well production dynamic prediction method shown mainly includes the following steps:

[0051] S1, based on the principle of conservation of matter, establish the material balance equation of closed gas reservoir;

[0052] S2, using the Langmuir model to characterize the shale gas adsorption model, correcting the material balance equation established in step S1 to obtain the shale gas reservoir material balance equation,

[0053]

[0054] Where P is the current formation pressure of the gas reservoir, MPa; Z is the current formation compression factor of the gas reservoir, dimensionless; P i is the original formation pressure of the gas reservoir, MPa; Z i is the original formation compression factor of the gas reservoir, dimensionless; is the cumulative gas production of shale reservoir without considering the effect of adsorption, m 3 ;c c is the compressibility factor of gas reservoir volume, MPa -1 ; ΔP is the gas reservoir pressure drop, ΔP=P i -P, MPa; is the original free gas volume of the gas reservoir, m 3 ;

[0055] S3, based on the gas well production calculation model of circular equal-thickness constant-pressure boundary homogeneous formation, the equivalent seepage resistance method is used to construct a shale gas fracturing horizontal well production calculation model that can take into account fracture parameters;

[0056] S4, by combining the shale gas reservoir material balance equation and the shale gas fracturing horizontal well production calculation model, a shale gas fracturing horizontal well production calculation model based on the shale gas reservoir material balance equation is established, the fluid physical properties and formation pressure under the two systems of fixed production rate production and fixed bottom hole pressure production are calculated, and the calculation results are output.

[0057] The pseudo-pressure corresponding to the formation pressure is calculated, and a schematic diagram of production dynamic characteristics is obtained based on the calculation results.

[0058] Usually, in the implementation process, the influence of shale gas adsorption is considered when correcting the material balance equation in step S2. In step S3, the equivalent wellbore r of the fracture in the fracturing area should be determined first according to the fracturing transformation characteristics of the vertical well section. wef The calculation formula is then used, and then according to the fracture parameters of the horizontal section and the area equivalence principle, the equivalent circular driving boundary of the fracturing transformation area is obtained. Finally, the calculation formula for the production capacity of the fractured horizontal well is determined through the boundary conditions.

[0059] The process of correcting the material balance equation in the specific implementation process is as follows:

[0060] Since shale gas reservoirs have extremely low porosity and permeability and have the characteristics of self-generation and self-storage, shale gas reservoirs are regarded as closed gas reservoirs in this embodiment. According to the principle of conservation of matter, the basic form of the material balance equation (gas volume conservation) of shale gas reservoirs can be obtained as follows:

[0061]

[0062] Where: G a is the current adsorbed gas volume in the gas reservoir, m 3 ; is the original adsorbed gas volume of the gas reservoir, m 3 ; G f is the current free gas volume in the gas reservoir, m 3 ; is the original free gas volume of the gas reservoir, m 3 ; G p is the cumulative gas output of the gas reservoir, m 3 .

[0063] Among them, the rock volume of shale gas reservoir is:

[0064] V b =A g h (2)

[0065] Where: V b is the gas reservoir volume, m 3 ; A g is the gas reservoir area, m 2 ; h is the thickness of the gas reservoir, m.

[0066] The pore volume of a shale gas reservoir is:

[0067] V p =A g hφ (3)

[0068] Where: V p is the pore volume, m 3 ; φ is the porosity, dimensionless.

[0069] The bound water volume of shale gas reservoir is:

[0070] V wc =A g h wc (4)

[0071] Where: V wc is the bound water volume, m 3 ; S wc is the bound water saturation and is dimensionless.

[0072] Therefore, the volume of shale gas reservoir under original conditions is:

[0073] V ci =V p -V wc =A g hφ(1-S wc ) (5)

[0074] Where: V ci is the initial volume of the gas reservoir, m 3 .

[0075] The original adsorbed gas volume of shale gas reservoir is:

[0076]

[0077] Where: is the amount of adsorbed gas under the original conditions of the shale reservoir, m 3 / t;ρ s is the density of shale rock, kg / m 3 .

[0078] When the formation pressure drops to a certain pressure P, the adsorbed gas volume of the shale gas reservoir is:

[0079]

[0080] Where: V a is the amount of gas adsorbed by the gas reservoir, m 3 / t.

[0081] Among them, the shale gas adsorption model is characterized by the Langmuir model:

[0082]

[0083] Where: P is the current formation pressure of the gas reservoir, MPa; V L is the Langmuir adsorption volume, m 3 / kg;

[0084] P L is the Langmuir pressure, MPa.

[0085] The change in pore volume of shale gas reservoir is:

[0086] △V p =V p c p △P (9)

[0087] Where: ΔV p is the compression (reduction) of the gas reservoir pore volume, m 3 ;c p is the rock compression coefficient, 1 / MPa; ΔP is the gas reservoir pressure drop, ΔP=P i -P, MPa.

[0088] The expansion of bound water volume in shale gas reservoirs is:

[0089] △V wc =V wc c w △P (10)

[0090] Where: ΔV wc is the volume expansion (increase) of bound water in gas reservoir, m 3 ;c w is the formation water compressibility coefficient, 1 / MPa.

[0091] When the formation pressure drops to a certain pressure P, the current volume of the shale gas reservoir is:

[0092] V c =V ci -△V p -△V wc (11)

[0093] Where: V c is the volume of the gas reservoir under current conditions, m 3 .

[0094] Substituting equation (9) and equation (10) into equation (11), we get:

[0095] V c =V ci -V p c p △PV wc cw △P (12)

[0096] From equations (3) to (5), the pore volume and irreducible water volume of the gas reservoir can be obtained as follows:

[0097]

[0098]

[0099] Substituting equations (6), (7), (13) and (14) into equation (12), we get:

[0100]

[0101] The original free gas volume in the shale gas reservoir is:

[0102]

[0103] Where: B gi is the gas volume compression coefficient under original conditions, 1 / MPa.

[0104] The current volume of free underground gas is:

[0105]

[0106] Where: V f is the underground volume of the remaining gas in the gas reservoir under current conditions, m 3 .

[0107] Convert the current underground free gas volume to the ground standard conditions, and the current ground free gas volume is:

[0108]

[0109] Where: B g is the gas volume compression coefficient under current conditions, 1 / MPa.

[0110] Substituting equations (6), (7), (16) and (18) into equation (1), we get:

[0111]

[0112] Substitute equation (16) into equation (19) and rearrange it to obtain:

[0113]

[0114] make

[0115]

[0116]

[0117] Where: is the cumulative gas production of the gas reservoir without considering the effect of adsorption, m 3 ;c c is the compressibility factor of gas reservoir volume, MPa -1 .

[0118] Substituting equation (21) and equation (22) into equation (20), we get:

[0119]

[0120] The volume coefficient of shale gas under original conditions can be expressed as:

[0121]

[0122] Where: P i is the original formation pressure of the gas reservoir, MPa; P sc is the standard pressure, MPa; Z sc is the standard state compression factor, dimensionless; T sc is the standard state temperature, K; Z i is the original formation compression factor of the gas reservoir, dimensionless; T i is the original formation temperature of the gas reservoir, K.

[0123] The volume coefficient of shale gas during production can be expressed as:

[0124]

[0125] Where: T is the current formation temperature of the gas reservoir, K; Z is the current formation compression factor of the gas reservoir, dimensionless;

[0126] Substituting equations (24) and (25) into equation (23), we can obtain the revised material balance equation, namely, the material balance equation for shale gas reservoirs:

[0127]

[0128] The specific implementation process of constructing the calculation formula for the production capacity of fractured horizontal wells is as follows:

[0129] First, based on the circular equal-thickness constant-pressure boundary homogeneous formation conditions, the gas well production calculation formula is defined as:

[0130]

[0131] Where: q sc is the daily gas production under ground conditions, 10 4 m 3 / d;; k is the reservoir permeability, mD; h is the reservoir thickness, m; r wis the wellbore radius, m; re is the reservoir radius, m; ψ(P) is the pseudo-pressure corresponding to the formation pressure, MPa 2 / (mPa·s);ψ(P wf ) is the pseudo pressure corresponding to the bottom hole flowing pressure, MPa 2 / (mPa·s).

[0132] Among them, the pseudo-pressure definition is:

[0133]

[0134] Where: μ is the gas viscosity, mPa·s.

[0135] As shown in 2, when there is a sudden change in the formation around the well, according to the equivalent seepage resistance method, it can be obtained:

[0136]

[0137] Where: r1 is the radius of reservoir zone 1, m; k1 and k2 are the permeabilities of reservoir zones 1 and 2, mD respectively.

[0138] When zone 1 represents the reformed zone of a hydraulically fractured vertical well, that is, there are hydraulic fractures in zone 1, the calculation formula for the equivalent wellbore diameter of a fracture with limited conductivity is:

[0139] r wef =x f e -F (30)

[0140] in,

[0141]

[0142]

[0143] Where: r wef is the equivalent radius of the crack, m; x f is the half length of the crack, m; F is the correction factor, dimensionless; C fD is the fracture conductivity, dimensionless; k f is the fracture permeability, mD; k m is the reservoir permeability, mD; w f is the crack width, m; x f is the half length of the crack, m.

[0144] refer to Figure 3 , assuming that the effective length of the fractured horizontal well is L and the number of fracture stages is N, according to the area equivalence principle, the equivalent circular driving boundaries of area 1 and area 2 are:

[0145]

[0146]

[0147] Right now:

[0148]

[0149] Where: L is the effective length of the horizontal well, m; N is the number of fracturing stages, stage; x e is the reservoir width, m.

[0150] Based on the boundary range given by formula (33) and formula (34), combined with formula (29), the productivity formula of fractured horizontal well can be expressed as:

[0151]

[0152] Under high pressure conditions, the following relationship exists:

[0153]

[0154] Where: L is the effective length of the horizontal well, m; N is the number of fracturing stages, stage; x e is the reservoir width, m; μ i is the gas viscosity at the original formation pressure, mPa·s.

[0155] Substituting formula (38) into formula (28), we get:

[0156]

[0157] Substituting formula (39) into formula (37) yields the calculation formula:

[0158]

[0159] The shale gas reservoir material balance equation shown in formula (26) and the fractured horizontal well productivity equation shown in formula (40) are combined to establish a shale gas fractured horizontal well production calculation model based on the shale gas reservoir material balance equation. The fluid physical parameters and pseudo-pressure corresponding to the formation pressure under the two systems of fixed production rate production and fixed bottom flow pressure production are calculated, and the calculation results are output. The calculation model is as follows: Figure 4 As shown. The modified material balance equation is used to calculate the current formation pressure P of the gas reservoir at the next time step using the Newton iteration method. Then, the production capacity model calculation formula (40) is used to calculate the fluid physical properties under the two production systems of fixed production and fixed bottom hole pressure production. In the calculation of fixed bottom hole pressure production, the unknown production is processed by the dichotomy method.

[0160] Specifically, when calculating, first input the basic parameters of the gas reservoir, the minimum bottom hole pressure P wf_minand the total prediction time T, where the basic parameters of the gas reservoir are geological and production data, directly obtained, and the minimum flow pressure P wf_min It can be the empirical value of the block, or it can be extrapolated from the existing mining data, and then calculated according to the system of fixed production output and fixed bottom hole pressure production.

[0161] As shown in the figure, when calculating according to the fixed output production system, it includes the following steps:

[0162] S4.1, calculate the cumulative production of gas wells G at time t p .

[0163] S4.2, based on the material balance equation (26) of the shale gas reservoir and the known original formation pressure P i The current formation pressure P of the gas reservoir at time t+Δt is calculated based on the same parameters.

[0164] S4.3, calculate the fluid physical property parameters under the current formation pressure P of the gas reservoir.

[0165] S4.4, based on the fractured horizontal well productivity calculation formula (40), first calculate the bottom hole flow pressure P at t+Δt wf .

[0166] When the bottom hole pressure P calculated in S4.4 is wf Greater than the initial minimum bottom hole pressure P wf_min , it is determined whether t+Δt is greater than the total predicted duration T. If so, the calculation is terminated and the result is output. If so, the calculation is looped into S4.1 to continue.

[0167] When the bottom hole pressure P calculated in S4.4 is wf Less than or equal to the initial set minimum bottom hole flow pressure P wf_min When , the calculation is directly performed according to the fixed bottom hole pressure production system, that is, the process goes to step S4.a.

[0168] According to the fixed bottom hole pressure production system, the following steps are included:

[0169] S4.a, shale gas reservoir material balance equation (26), and formula (40), given a hypothetical gas well production, calculate the current formation pressure P of the gas reservoir at two times t+Δt. By comparison, the closer the two values ​​are, the more accurate the hypothetical gas well production is, thereby determining the accurate value of the current formation pressure P of the gas reservoir at time t+Δt.

[0170] S4.b, based on the current formation pressure P of the gas reservoir obtained in S4.a, calculate the fluid physical property parameters under the current formation pressure P of the gas reservoir.

[0171] S4.c, based on the fractured horizontal well productivity calculation formula (40), calculate the gas well production q at t+Δt sc .

[0172] In the present application, a computer is used for calculation, so the present application also provides a computer device, which includes a memory and a processor, wherein the memory stores executable instructions; and the processor can run the executable instructions in the memory to implement the above-mentioned shale gas fracturing horizontal well production dynamic prediction method, which mainly implements the calculation process of the above-mentioned calculation model and outputs the results. For the convenience of intuitive observation, the output results in this embodiment are in graphical form, such as Figure 5 shown.

[0173] On the other hand, the present application provides a computer-readable storage medium, which stores a computer program. When the computer program is executed by a processor, it implements the above-mentioned shale gas fracturing horizontal well production dynamic prediction method, specifically mainly implements the calculation process of the above-mentioned calculation model and outputs the results.

[0174] This example uses the data of Well X1 in the Sichuan Basin as a reference. The formation temperature of the well is 110°C, the porosity is 5.5%, the actual fracturing length is 1426 meters, and the number of fracturing stages is 28. The above calculation model is used for calculation, and the output result is as follows: Figure 6 As shown, it includes the actual bottom hole flow pressure P wf Compared with the actual daily gas production data, it can be seen from the graph that the newly developed calculation model in this application is very similar to the actual results and can better fit the real gas well production and bottom hole pressure P wf Change characteristics, with higher reliability.

[0175] refer to Figures 1 to 10 The shale gas fracturing horizontal well production dynamic prediction method shown in the figure uses the parameters in the table below for calculation and verifies and analyzes the factors affecting shale gas production capacity.

[0176] Basic parameters unit Parameter Value Basic parameters unit Parameter Value Formation pressure MPa 50 Shale density <![CDATA[kg / m 3 ]]> 2500 Formation temperature K 373.15 Matrix compressibility <![CDATA[MPa -1 ]]> <![CDATA[0.4×10 -4 ]]> Reservoir effective length m 1800 Langmuir volume <![CDATA[m 3 / kg]]> 0.005 Reservoir effective width m 400 Langmuir Pressure MPa 5 Effective reservoir thickness m 30 Horizontal well length m 1500 Matrix permeability mD <![CDATA[5×10 -4 ]]> Fracturing stages part 15 Fracture permeability mD 100 Crack half length m 60 Porosity Decimal 0.05 Minimum bottom hole pressure MPa 5

[0177] From 7 and 8, we can see that if we do not consider the adsorption of shale gas, the productivity of shale gas wells will be underestimated. The impact of Langmuir volume on the productivity of shale gas wells is greater than that of Langmuir pressure. Specifically, when the Langmuir volume increases from 0.0005 kg / m 3 Reduce to 0kg / m 3 When the gas well productivity is 0.010kg / m 3When the Langmuir pressure drops from 5MPa to 1MPa, the gas well productivity will be underestimated by 5.45%, and when it increases to 15MPa, the gas well productivity will increase by 2.41%. Therefore, the shale gas adsorption effect cannot be ignored in the evaluation of shale gas well productivity, and reliable shale gas adsorption parameters are also very important for evaluating gas well productivity.

[0178] As shown in Figure 9, the fracture half-length has a significant impact on the productivity of shale gas wells. The productivity of shale gas wells increases with the increase of fracture half-length, and the impact of fracture half-length on shale gas wells is throughout the entire life cycle. The increase of fracture half-length will significantly increase the stable production period at the initial stage of gas well production and the production in the middle and late stages. Therefore, without considering economic constraints, appropriately increasing the fracture half-length will be beneficial to improving the productivity of gas wells.

[0179] As shown in Figure 10, the production capacity of shale gas wells increases with the increase of the number of fracturing stages, and the number of fracturing stages mainly affects the initial production of gas wells. When the gas well production enters the middle and late stages, the influence of the number of fracturing stages on the gas well production gradually decreases.

[0180] As shown above, because the calculation model of this application fully considers the influence of adsorption, fracture half-length and fracture segment number, and quantifies them, the reliability and accuracy of the calculation model are higher. In the process of formulating the later mining system, it can also be optimized according to the above analysis, which is conducive to the development and advancement of shale gas mining technology.

[0181] Finally, it should be noted that the above description is only a preferred embodiment of the present invention. Under the guidance of the present invention, ordinary technicians in this field can make various similar expressions without violating the purpose and claims of the present invention, and such changes all fall within the scope of protection of the present invention.

Claims

1. A method for predicting the production dynamics of shale gas fracturing horizontal wells. It is characterized in that The steps include: S1, based on the principle of conservation of matter, establish the material balance equation of closed gas reservoir; S2, using the Langmuir model to characterize the shale gas adsorption model, correcting the material balance equation established in step S1 to obtain the shale gas reservoir material balance equation, Where P is the current formation pressure of the gas reservoir, MPa; Z is the current formation compression factor of the gas reservoir, dimensionless; P i is the original formation pressure of the gas reservoir, MPa; Z i is the original formation compression factor of the gas reservoir, dimensionless; is the cumulative gas production of shale reservoir without considering the effect of adsorption, m 3 ;c c is the compressibility factor of gas reservoir volume, MPa -1 ; ΔP is the gas reservoir pressure drop, ΔP=P i -P, MPa; is the original free gas volume of the gas reservoir, m 3 ; S3, based on the gas well production calculation model of circular equal-thickness constant-pressure boundary homogeneous formation, the equivalent seepage resistance method is used to construct a shale gas fracturing horizontal well production calculation model that can take into account fracture parameters; S4, by combining the shale gas reservoir material balance equation and the shale gas fracturing horizontal well production calculation model, a shale gas fracturing horizontal well production calculation model based on the shale gas reservoir material balance equation is established, the fluid physical properties and formation pressure under the two systems of fixed production rate production and fixed bottom hole pressure production are calculated, and the calculation results are output.

2. The method for predicting the production dynamics of shale gas fracturing horizontal wells according to claim 1, Features: In step S2, the material balance equation is corrected by taking into account the shale gas adsorption effect.

3. The method for predicting the production dynamics of shale gas fracturing horizontal wells according to claim 1, Features: In step S3, the equivalent wellbore diameter r of the fracture in the fracturing area should be determined first according to the fracturing characteristics of the vertical well section. wef The calculation formula of Then, according to the fracture parameters of the horizontal section and the area equivalence principle, the equivalent circular driving boundary of the fracturing transformation area is obtained. Finally, the productivity calculation formula of the fracturing horizontal well is determined by the boundary conditions.

4. The method for predicting the production performance of shale gas fractured horizontal wells according to any one of claims 1 to 3, Features: In step S4, the unknown production is processed by using the dichotomy method when performing the production calculation under the constant bottom hole pressure.

5. The method for predicting the production performance of shale gas fractured horizontal wells according to any one of claims 1 to 3, Features: In step S4, the Newton iteration method is used to calculate the current formation pressure P of the gas reservoir at the next time step.

6. The method for predicting the production dynamics of shale gas fracturing horizontal wells according to claim 5, Features: First, input the basic parameters of the gas reservoir, the minimum bottom hole pressure P wf_min and the total forecast time T, and then calculate according to the production system of fixed production rate and fixed bottom flow pressure; Among them, when calculating according to the fixed output production system, it includes the following steps: S4.1, calculate the cumulative production of gas wells G at time t p ; S4.2, calculating the current formation pressure P of the gas reservoir at time t+Δt based on the material balance equation of the shale gas reservoir; S4.3, calculating the fluid physical property parameters under the current formation pressure P of the gas reservoir; S4.4, based on the calculation formula for the productivity of fractured horizontal wells, calculate the bottom hole flow pressure P at t+Δt wf ; According to the fixed bottom hole pressure production system, the following steps are included: S4.a, calculating the current formation pressure P of the gas reservoir at time t+Δt based on the material balance equation of the shale gas reservoir; S4.b, calculating the fluid physical property parameters under the current formation pressure P of the gas reservoir; S4.c, based on the calculation formula of the production capacity of fractured horizontal wells, calculate the gas well production q at t+Δt sc ; When the bottom hole pressure P calculated in S4.4 is wf Greater than the initial minimum bottom hole pressure P wf_min When t+Δt is greater than the total prediction time T, it is determined whether the calculation is terminated and the result is output. If the calculation is less than t, the calculation is continued in step S4.

1. When the bottom hole pressure P calculated in S4.4 is wf Less than or equal to the initial minimum bottom hole pressure P wf_min When , it directly enters S4.a for calculation.

7. A computer device, It is characterized in that include: A memory storing executable instructions; A processor, wherein the processor runs the executable instructions in the memory to implement the shale gas fracturing horizontal well production dynamic prediction method as described in any one of claims 1 to 6.

8. A computer-readable storage medium, It is characterized in that The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the method for predicting the production dynamics of a shale gas fracturing well described in any one of claims 1 to 6 is implemented.

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