A method for evaluating the recoverability of deep coalbed methane based on surrounding rock focusing effect

Abstract

The present invention discloses a method for evaluating the recoverability of deep coalbed methane based on the surrounding rock focusing effect, comprising the following steps: S1: establishing a numerical model of a typical well in a target area; S2: setting average parameters of multiple groups of fracturing conditions and performing numerical simulation of fracture expansion, and completing historical matching research to obtain the average fracture height and production intensity corresponding to each parameter; S3: establishing an initial calculation model, calculating the fracturing energy index and the energy focusing index; calculating the focusing effect evaluation parameters of the top and bottom plates on coalbed fractures; S4: adjusting the weight coefficient in the initial calculation model to obtain a production effect evaluation chart; S5: establishing a final calculation model for the fracturing energy index and the energy focusing index; S6: calculating the fracturing energy index and the energy focusing index of the target well in the target area, and combining the production effect evaluation chart to obtain the recoverability evaluation result of the target well. The present invention can more accurately evaluate the recoverability of deep coalbed methane and provide technical support for the development of deep coalbed methane.

Description

Technical Field

[0001] The invention relates to the technical field of deep coalbed methane development, and in particular to a deep coalbed methane recoverability evaluation method based on surrounding rock focusing effect. Background Art

[0002] my country has made a breakthrough in deep coalbed methane in the Daning-Jixian area, and is facing the problem of conducting deep coalbed methane pilot projects in other basins. In the Daning-Jixian area, the use of long horizontal wells and large-scale volume fracturing to increase production has successfully broken through the development of deep No. 8 coal in the area, but this technology has not achieved good results in other basins. This is due to the reservoir formation mechanism and roof and floor conditions of coalbed methane. The accumulation of coalbed methane does not depend on the formation of a dense roof (the preservation of coalbed methane depends on a dense roof), which leads to crack penetration during deep coalbed methane fracturing, thereby reducing the reservoir production increase and transformation effect of deep coalbed methane. Therefore, if the energy (displacement, liquid intensity, sand intensity, and maximum pump pressure) in the fracturing process is too large, it will cause crack penetration and a large amount of energy will be injected to form invalid cracks; if the energy in the fracturing process is too small, it will not increase production well and the production capacity of coalbed methane cannot be guaranteed.

[0003] At present, the influence of the mechanical effect of the roof and floor rocks on the deep coalbed methane fracturing process has not been clearly proposed, nor has the compressibility of deep coalbed methane been studied based on the mechanical characteristics of the roof and floor rocks. There has been no study that combines two factors (the effect of fracturing energy on productivity and the effect of surrounding rock constraints on productivity) to analyze the compressibility of deep coalbed methane, which has led to the current situation that the Daning-Jixian technology has not been completely successful in other basins. In response to this problem, there is an urgent need for a deep coalbed methane compressibility evaluation method that considers the influence of the roof and floor characteristics of deep coalbed methane on the fracturing effect of coal seams and integrates the energy of fracturing itself, so as to clearly give the influence of the physical properties of the roof and floor on the large-scale fracturing engineering design and deep coalbed methane development. Summary of the invention

[0004] In view of the above problems, the present invention aims to provide a method for evaluating the recoverability of deep coalbed methane based on the surrounding rock focusing effect.

[0005] The technical solution of the present invention is as follows:

[0006] A method for evaluating the recoverability of deep coalbed methane based on surrounding rock focusing effect comprises the following steps:

[0007] S1: Establishing a numerical model of a typical well in the target area, wherein the numerical model includes upper rock formation, roof, coal rock, floor, and lower rock formation from top to bottom;

[0008] S2: setting average parameters of multiple groups of fracturing conditions and performing numerical simulation of fracture extension in the numerical model, and completing history matching research to obtain average fracture height and production intensity corresponding to the average parameters of each fracturing condition;

[0009] S3: establishing an initial calculation model for the fracturing energy index and energy focusing index of deep coalbed methane, and calculating the fracturing energy index and energy focusing index of deep coalbed methane according to the initial calculation model;

[0010] Calculate the evaluation parameters of the focusing effect of the roof and floor plates on the coal seam fractures;

[0011] S4: adjusting the weight coefficient in the initial calculation model so that the fracturing energy index, energy focusing index, focusing effect evaluation parameter and production capacity intensity corresponding to the average parameters of each fracturing condition form four quadrants to obtain a production effect evaluation chart;

[0012] S5: determining the weight coefficient at this time according to the production effect evaluation chart, and establishing a final calculation model of the fracturing energy index and energy focusing index of deep coalbed methane with the weight coefficient at this time;

[0013] S6: Calculate the fracturing energy index and energy focusing index of the target well in the target area according to the final calculation model, determine the production effect quadrant to which the target well belongs in combination with the production effect evaluation chart, and obtain the recoverability evaluation result of the target well.

[0014] Preferably, in step S1, the numerical model is established by collecting geological models, geostress models and fracturing engineering parameters;

[0015] Alternatively, the numerical model is established by collecting parameters required for geological modeling, parameters required for geostress modeling, and fracturing engineering parameters.

[0016] Preferably, the geological model includes average porosity, permeability, gas saturation, adsorbed gas volume, well type, well coordinates and well trajectory;

[0017] The geostress model includes maximum principal stress, minimum principal stress, Young's modulus and Poisson's ratio;

[0018] The fracturing engineering parameters include fracturing fluid volume, construction process pressure and reservoir fracture pressure;

[0019] The parameters required for geological modeling include well logging interpretation results, seismic interpretation layer results, core description, sedimentary facies interpretation results and gas content;

[0020] The parameters required for the geostress modeling include logging stress interpretation results, seismic rock mechanics parameters and small pressure test results.

[0021] Preferably, in step S1, the upper rock layer and the lower rock layer are both 50 m.

[0022] Preferably, in step S2, the average parameters of the fracturing conditions include the amount of fracturing fluid, the total amount of sand, the average displacement, the maximum pump pressure and the viscosity of the fracturing fluid. When setting multiple groups of the average parameters of the fracturing conditions, they are grouped according to 85%, 90%, 95%, 100%, 105%, 110% and 115% of each average parameter to obtain a total of 7 5 The average parameters of the group fracturing conditions.

[0023] Preferably, in step S2, when performing the numerical simulation of fracture expansion, the bottom hole flow pressure is set to 0.1 MPa, and the numerical simulation is performed on a daily basis;

[0024] When the typical well is a horizontal well, the production intensity is calculated by the following formula:

[0025]

[0026] Where: C h is the production intensity of horizontal wells, cubic meters per day per hundred meters; Q h0 is the initial production capacity of the horizontal well, cubic meters per day; L h is the length of the horizontal well, hundred meters;

[0027] When the typical well is a vertical well, the production intensity is calculated by the following formula:

[0028]

[0029] Where: C v is the production intensity of vertical wells, cubic meters per day per ten meters; Q v0 is the initial production capacity of the vertical well, cubic meters per day; D v is the thickness of the vertical well, ten meters;

[0030] The initial production capacity of the horizontal well and the initial production capacity of the vertical well are both the average daily production in the first two months of the numerical simulation of the typical well.

[0031] Preferably, in step S3, the calculation model of the fracturing energy index is:

[0032]

[0033] Where: FE is the fracturing energy index, dimensionless; p max is the maximum pump pressure during fracturing, MPa; is the average fracture pressure of the coal seam, MPa; μ L is the average viscosity of the fracturing fluid, mPas; Q max is the maximum displacement during fracturing, m3 / min; σ c is the average minimum in-situ stress in the horizontal well section of the coal rock, MPa; is the porosity of coal rock, dimensionless; h c is the average thickness of coal rock, m; L is the length of the well section, km; x f is the average crack half length, m; α 1 and α 2 All are weight coefficients and are dimensionless;

[0034] The calculation model of the energy focusing index is:

[0035]

[0036] Where: EF is the energy focusing index, dimensionless; h tba is the average thickness of the top and bottom plates, m; σ tba is the average minimum in-situ stress of the top and bottom plates, MPa; is the average rupture pressure of the top and bottom plates, MPa; is the average fracture pressure of coal rock and roof and floor, MPa; β 1 , β 2 and β 3 All are weight coefficients and are dimensionless;

[0037] When the weight coefficients in the calculation model are all 1, the corresponding model is the initial calculation model;

[0038] The evaluation parameters of the focusing effect of the roof and floor plates on the coal seam fractures are calculated by the following formula:

[0039]

[0040] Where: λ is the evaluation parameter of the focusing effect of the roof and floor plates on the coal seam fractures, dimensionless; h b is the average thickness of the bottom plate below the horizontal section, m; h t is the average thickness of the top plate above the horizontal section, m; h f is the average fracture height of the hydraulic fracture, m.

[0041] Preferably, the average thickness of the top and bottom plates is calculated by the following formula:

[0042]

[0043] The average minimum ground stress of the top and bottom plates is calculated by the following formula:

[0044]

[0045] Where: bis the average minimum principal stress of the bottom plate below the horizontal section, MPa; σ t is the average minimum principal stress in the top plate above the horizontal section, MPa;

[0046] The average fracture pressure of the coal rock and the roof and floor is calculated by the following formula:

[0047]

[0048] The average bursting pressure of the top and bottom plates is calculated by the following formula:

[0049]

[0050] Where: p fb is the average rupture pressure of the bottom plate below the horizontal section, MPa; p ft is the average rupture pressure of the top plate above the horizontal section, MPa.

[0051] The beneficial effects of the present invention are:

[0052] The present invention takes into account the focusing effect of fracturing energy and surrounding rock energy, can more accurately evaluate the recoverability of deep coalbed methane, and provide technical support for the development of deep coalbed methane. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0054] Figure 1 It is a schematic diagram of the numerical model structure of a production well in a specific embodiment;

[0055] Figure 2 It is a schematic diagram of a production effect evaluation plate of a specific embodiment;

[0056] Figure 3 It is a structural schematic diagram of a wellbore structure and a three-dimensional geological model of a coalbed methane well in a specific embodiment;

[0057] Figure 4 It is a schematic diagram of the results of a fracturing model of a specific embodiment;

[0058] Figure 5 A schematic diagram of a model for completing a history matching study for a specific embodiment;

[0059] Figure 6 A schematic diagram of a plate calculated for the first time for a specific embodiment;

[0060] Figure 7 A schematic diagram of a production effect evaluation chart after adjusting the weight coefficient in a specific embodiment;

[0061] Figure 8 The figure is a schematic diagram of the evaluation results of a specific embodiment. DETAILED DESCRIPTION

[0062] The present invention is further described below in conjunction with the accompanying drawings and embodiments. It should be noted that, in the absence of conflict, the embodiments in this application and the technical features in the embodiments can be combined with each other. It should be noted that, unless otherwise specified, all technical and scientific terms used in this application have the same meanings as those generally understood by those of ordinary skill in the art to which this application belongs. The words "including" or "comprising" and the like used in the disclosure of the present invention mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects.

[0063] The present invention provides a method for evaluating the recoverability of deep coalbed methane based on surrounding rock focusing effect, comprising the following steps:

[0064] S1: Establish a numerical model of a typical well in the target area, wherein the numerical model includes upper rock formations, roof, coal rock, floor, and lower rock formations from top to bottom.

[0065] In the present invention, the typical well refers to a well that has successfully developed deep coalbed methane, which is generally a well with representative geological characteristics and production variation patterns, and is specifically determined based on the target area.

[0066] In a specific embodiment, the numerical model is established by collecting geological models, geostress models and fracturing engineering parameters, or by collecting parameters required for geological modeling, geostress modeling and fracturing engineering parameters.

[0067] In a specific embodiment, the geological model includes average porosity, permeability, gas saturation, adsorbed gas volume, well type, well coordinates and well trajectory; the geostress model includes maximum principal stress, minimum principal stress, Young's modulus and Poisson's ratio; the fracturing engineering parameters include fracturing construction fluid volume, construction process pressure and reservoir fracture pressure; the parameters required for geological modeling include well logging interpretation results, seismic interpretation layer results, core description, sedimentary phase interpretation results and gas content; the parameters required for geostress modeling include well logging stress interpretation results, seismic rock mechanics parameters and small pressure test results.

[0068] It should be noted that in the above embodiment, the small pressure test results are used to obtain the fracture pressure of the coal rock and the roof and floor plates. If there are no small pressure test results, the fracture pressure can also be calculated using a formula based on rock mechanical parameters and ground stress.

[0069] In a specific embodiment, the numerical model is as follows Figure 1 As shown, in Figure 1 In the figure, the upper rock layer and the lower rock layer are both 50m. It should be noted that the 50m in this embodiment refers to the upper 50m and the lower 50m except the roof and the floor, excluding the thickness of the surrounding rock. In addition, the value set here is to include the hydraulic fracture. According to the existing hydraulic fracture scale and fracture height, coal rock + roof and floor + upper and lower 100m is enough to include the hydraulic fracture. A smaller thickness will affect the calculation results, and a larger thickness will affect the calculation efficiency. The specific value can be set according to the actual working conditions.

[0070] S2: setting average parameters of multiple groups of fracturing conditions and performing numerical simulation of fracture expansion in the numerical model, and completing history matching research to obtain average fracture height and production intensity corresponding to the average parameters of each fracturing condition.

[0071] In a specific embodiment, the average parameters of the fracturing conditions include the amount of fracturing fluid, the total amount of sand, the average displacement, the maximum pump pressure and the viscosity of the fracturing fluid. When setting multiple groups of the average parameters of the fracturing conditions, they are grouped according to 85%, 90%, 95%, 100%, 105%, 110% and 115% of each average parameter to obtain a total of 7 5 The average parameters of the group fracturing conditions.

[0072] It should be noted that when setting the average parameters of multiple groups of the fracturing conditions, other interval percentages can also be used for setting, such as 2%, 3%, etc. The smaller the interval, the more accurate the result, but the greater the amount of calculation. In addition, in addition to setting 7 groups of intervals, more groups can be divided, which will also improve the accuracy, but this requires more simulation calculations.

[0073] In a specific embodiment, when performing numerical simulation of fracture expansion, the bottom hole flow pressure is set to 0.1 MPa, and the numerical simulation is performed on a daily basis;

[0074] When the typical well is a horizontal well, the production intensity is calculated by the following formula:

[0075]

[0076] Where: C h is the production intensity of horizontal wells, cubic meters per day per hundred meters; Q h0 is the initial production capacity of the horizontal well, cubic meters per day; L his the length of the horizontal well, hundred meters;

[0077] When the typical well is a vertical well, the production intensity is calculated by the following formula:

[0078]

[0079] Where: C v is the production intensity of vertical wells, cubic meters per day per ten meters; Q v0 is the initial production capacity of the vertical well, cubic meters per day; D v is the thickness of the vertical well, ten meters;

[0080] The initial production capacity of the horizontal well and the initial production capacity of the vertical well are both the average daily production in the first two months of the numerical simulation of the typical well.

[0081] In the above embodiment, the bottom hole pressure of 0.1MPa is used to meet the requirement of unobstructed flow, and the daily average output of the first two months is taken as the initial production capacity, which can provide technical support for obtaining more accurate production effect evaluation charts. It should be noted that because the lengths of horizontal wells are different, it is difficult to directly compare the production capacity. The same problem exists in vertical wells, and the thickness of coal seams is different. Therefore, in the above embodiment, the production capacity intensity of horizontal wells uses 100-meter production capacity, and the production capacity intensity of vertical wells uses 10-meter thickness production capacity; if there are other methods that can accurately represent the production capacity intensity of each well, they can also be applied to the present invention.

[0082] S3: Establish an initial calculation model for the fracturing energy index and energy focusing index of deep coalbed methane, and calculate the fracturing energy index and energy focusing index of deep coalbed methane based on the initial calculation model; calculate the evaluation parameters of the focusing effect of the top and bottom plates on coal seam cracks.

[0083] In a specific embodiment, the calculation model of the fracturing energy index is:

[0084]

[0085] Where: FE is the fracturing energy index, dimensionless; p max is the maximum pump pressure during fracturing, MPa; is the average fracture pressure of the coal seam, MPa; μ L is the average viscosity of the fracturing fluid, mPas; Q max is the maximum displacement during fracturing, m 3 / min; σ c is the average minimum in-situ stress in the horizontal well section of the coal rock, MPa; is the porosity of coal rock, dimensionless; h c is the average thickness of coal rock, m; L is the length of the well section, km; x f is the average crack half length, m; α1 and α 2 All are weight coefficients and are dimensionless;

[0086] The calculation model of the energy focusing index is:

[0087]

[0088] Where: EF is the energy focusing index, dimensionless; h tba is the average thickness of the top and bottom plates, m; σ tba is the average minimum in-situ stress of the top and bottom plates, MPa; is the average rupture pressure of the top and bottom plates, MPa; is the average fracture pressure of coal rock and roof and floor, MPa; β 1 , β 2 and β 3 All are weight coefficients and are dimensionless;

[0089] When the weight coefficients in the calculation model are all 1, the corresponding model is the initial calculation model;

[0090] The evaluation parameters of the focusing effect of the roof and floor plates on the coal seam fractures are calculated by the following formula:

[0091]

[0092] Where: λ is the evaluation parameter of the focusing effect of the roof and floor plates on the coal seam fractures, dimensionless; h b is the average thickness of the bottom plate below the horizontal section, m; h t is the average thickness of the top plate above the horizontal section, m; h f is the average fracture height of the hydraulic fracture, m.

[0093] In a specific embodiment, the average thickness of the top and bottom plates is calculated by the following formula:

[0094]

[0095] The average minimum ground stress of the top and bottom plates is calculated by the following formula:

[0096]

[0097] Where: b is the average minimum principal stress of the bottom plate below the horizontal section, MPa; σ t is the average minimum principal stress in the top plate above the horizontal section, MPa;

[0098] The average fracture pressure of the coal rock and the roof and floor is calculated by the following formula:

[0099]

[0100] The average bursting pressure of the top and bottom plates is calculated by the following formula:

[0101]

[0102] Where: p fb is the average rupture pressure of the bottom plate below the horizontal section, MPa; p ft is the average rupture pressure of the top plate above the horizontal section, MPa.

[0103] It should be noted that the parameter calculation methods in the above embodiment are only preferred methods in this embodiment, and other methods for obtaining the parameters in the prior art may also be applicable to the present invention. For example, the fracture pressure can be calculated by the collected data (ground stress, pore pressure, Young's modulus, Poisson's ratio), or obtained by a small pressure test.

[0104] S4: Adjust the weight coefficients in the initial calculation model so that the fracturing energy index, energy focusing index, focusing effect evaluation parameters and production capacity intensity corresponding to the average parameters of each fracturing condition form four quadrants to obtain a production effect evaluation chart.

[0105] In a specific embodiment, Figure 2 As shown, with the energy focusing index and the focusing effect evaluation parameter as the abscissa, and the fracturing energy index and the production capacity intensity as the ordinate, the limit value of the focusing effect evaluation parameter is 1, and the limit value of the production capacity intensity is 5000 cubic meters / day / 10 meters (vertical well) or 5000 cubic meters / day / 100 meters (horizontal well), the production effect evaluation chart is formed as follows:

[0106] The first quadrant represents good sealing effect of roof and floor, sufficient fracturing scale, energy is limited to the coal seam, and the coal seam development effect is good;

[0107] The second quadrant represents poor sealing effect of roof and floor plates, sufficient fracturing scale, a large number of fractures penetrating the layers, and poor coal seam development effect;

[0108] The third quadrant represents that the sealing effect of the roof and floor is not good, but the scale of fracturing is insufficient; in the coalbed methane chain model; the energy is not focused on the coal seam, the cracks penetrate the layer; the coal seam development effect is not good;

[0109] The fourth quadrant represents that the sealing effect of the roof and floor is good, but the scale of fracturing is insufficient; in the coal layer gas chain model; the matrix mass transfer efficiency has not increased significantly; and the coal seam development effect is not good.

[0110] In a specific embodiment, the weight coefficient is adjusted within a range of -2 to 5. It should be noted that this range is only an adjustment range of a specific embodiment of the present invention. When applying the present invention, it is also feasible to adjust within other ranges, mainly by adjusting the weight coefficient so that the four parameters can form four quadrants to obtain the production effect evaluation chart.

[0111] S5: Determine the weight coefficient at this time according to the production effect evaluation chart, and establish the final calculation model of the fracturing energy index and energy focusing index of deep coalbed methane with the weight coefficient at this time.

[0112] S6: Calculate the fracturing energy index and energy focusing index of the target well in the target area according to the final calculation model, determine the production effect quadrant to which the target well belongs in combination with the production effect evaluation chart, and obtain the recoverability evaluation result of the target well.

[0113] In a specific embodiment, taking the Ordos Basin as an example, the deep coalbed methane recoverability evaluation method based on surrounding rock focusing effect of the present invention is used to evaluate the deep coalbed methane recoverability of a target well in the basin, specifically comprising the following steps:

[0114] (1) Taking the deep No. 8 coal in the Daningji County area of ​​the study area as a typical well, its numerical model is established.

[0115] In this embodiment, based on the results of well logging, seismic and geological basic research, the geological engineering parameters of the target area are collected, including average porosity, permeability, adsorption and desorption parameters, gas saturation, fluid PVT parameters, production history data, fracturing construction data and microseismic data, etc., to establish the wellbore structure and three-dimensional geological model of the coalbed methane well. Figure 3 shown.

[0116] After collecting the physical parameters, the following parameters can be calculated through theoretical calculation or on-site fracturing parameter testing: the fracture pressure of coal rock, the fracture pressure of the roof, and the fracture pressure of the floor.

[0117] According to the geological characteristic parameters of the target block, a numerical model is established, including the attribute distribution of the porosity, permeability, ground stress and mechanical characteristic parameters of the coal seam and the roof and floor. At the same time, the numerical model should not only include coal rock and the roof and floor, but also all the strata within 50m above the roof and 50m below the floor for geological modeling. The benchmark parameters of the numerical model are shown in the following table:

[0118] Table 1 Coal matrix physical properties parameters

[0119] Coal seam thickness, m Coal rock porosity Permeability, mD Ground stress, MPa Burst pressure, MPa 10 0.03 0.1 40 48

[0120] Table 2 Physical parameters of the matrix of the top and bottom plates

[0121] Average thickness, m Average ground stress, MPa Average bursting pressure, MPa Young's modulus, MPa Poisson's ratio 5 42 57.77741193 3500 0.27

[0122] Table 3 Fracturing construction parameters

[0123] Maximum pressure, MPa <![CDATA[Average displacement, m 3 / min]]> Liquid viscosity, mPa·s Horizontal well length, m Horizontal well control radius 50 16 70 800 120

[0124] (2) Setting the average parameters of multiple groups of fracturing conditions and conducting numerical simulation of fracture expansion.

[0125] In this embodiment, the expansion simulation of the fracture is carried out according to the average parameters of the fracturing conditions (fracturing fluid dosage, total sand volume, average displacement, maximum pump pressure and fracturing fluid viscosity). At the same time, the grouping setting is carried out according to 85%, 90%, 95%, 100%, 105%, 110% and 115% of each parameter, and a total of 7 5 The average fracture height and production capacity intensity of each group are obtained by numerical simulation of fracture expansion of each group. In this embodiment, the average daily production capacity of the first two months obtained by simulation is divided by 8 to obtain the production capacity intensity of the horizontal well. Figure 4 As shown in the figure, the history matching study of the numerical simulation is completed as Figure 5 shown.

[0126] (3) Based on the initial calculation model (a 1 、a 2 , β 1 , β 2 and β 3 Both are 1) Calculate the fracturing energy index and energy focusing index of deep coalbed methane; Calculate the evaluation parameters of the focusing effect of the top and bottom plates on the coal seam cracks.

[0127] In this embodiment, the scatter plot of each group of calculation results is as follows: Figure 6 As shown. Figure 6 It can be seen that the attribute distribution of each scattered point is rather chaotic, without obvious regional distribution.

[0128] (4) Adjust the weight coefficient α 1 , α 2 , β 1 , β 2 and β 3 , forming four quadrants and obtaining the production effect evaluation chart.

[0129] In this embodiment, α 1 , α 2 , β 1 , β 2 and β 3 After adjusting to 0.55, 0.65, 0.85, 1.15 and 1.05 respectively, the scattered points clearly appear in four quadrants. The results are as follows Figure 7 shown.

[0130] (5) Calculate the fracturing energy index and energy focusing index of the target well using the calculation model after adjusting the weight coefficient, and Figure 7 The production effect evaluation chart shown evaluates the deep coalbed methane recoverability of the target well.

[0131] In this embodiment, the evaluation results of the target wells in the Daningji County area and the Shenfu area are as follows: Figure 8 As shown. Figure 8 It can be seen that the development effect of the coal seams in the target wells in Ji County, Daning is good, while the development effect of the coal seams in the target wells in Shenfu area is not good.

[0132] On-site production dynamics show that the mineability in the Ji County area of ​​Daning is good, and the fracturing energy in the Shenfu area is sufficient, but a large number of cracks penetrate the layers, causing the coal seams in the area to still be in a poor mineability range.

[0133] It can be seen from this that the present invention can accurately determine the recoverability of deep coalbed methane in each target well.

[0134] In summary, the present invention can accurately evaluate the recoverability of deep coalbed methane. Compared with the prior art, the present invention has significant progress.

[0135] The above description is only a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A method for evaluating the recoverability of deep coalbed methane based on surrounding rock focusing effect, characterized in that: The following steps are involved: S1: Establishing a numerical model of a typical well in the target area, wherein the numerical model includes upper rock formation, roof, coal rock, floor, and lower rock formation from top to bottom; S2: setting average parameters of multiple groups of fracturing conditions and performing numerical simulation of fracture extension in the numerical model, and completing history matching research to obtain average fracture height and production intensity corresponding to the average parameters of each fracturing condition; S3: establishing an initial calculation model for the fracturing energy index and energy focusing index of deep coalbed methane, and calculating the fracturing energy index and energy focusing index of deep coalbed methane according to the initial calculation model; Calculate the evaluation parameters of the focusing effect of the roof and floor plates on the coal seam fractures; The calculation model of the fracturing energy index is: （3） Where: is the fracturing energy index, dimensionless; is the maximum pump pressure during fracturing, MPa; is the average fracture pressure of the coal seam, MPa; is the average viscosity of the fracturing fluid, mPas; is the maximum displacement during fracturing, m 3 / min; is the average minimum in-situ stress in the horizontal well section of the coal rock, MPa; is the porosity of coal rock, dimensionless; is the average thickness of coal rock, m; is the well section length, km; is the average crack half-length, m; and All are weight coefficients and are dimensionless; The calculation model of the energy focusing index is: （4） Where: is the energy focusing index, dimensionless; is the average thickness of the top and bottom plates, m; is the average minimum in-situ stress of the top and bottom plates, MPa; is the average rupture pressure of the top and bottom plates, MPa; is the average fracture pressure of coal rock and roof and floor, MPa; , and All are weight coefficients and are dimensionless; When the weight coefficients in the calculation model are all 1, the corresponding model is the initial calculation model; The evaluation parameters of the focusing effect of the roof and floor plates on the coal seam fractures are calculated by the following formula: （5） Where: It is the evaluation parameter of the focusing effect of roof and floor plates on coal seam fractures, dimensionless; is the average thickness of the bottom plate below the horizontal section, m; is the average thickness of the top plate above the horizontal section, m; is the average fracture height of the hydraulic fracture, m; S4: adjusting the weight coefficient in the initial calculation model so that the fracturing energy index, energy focusing index, focusing effect evaluation parameter and production capacity intensity corresponding to the average parameters of each fracturing condition form four quadrants to obtain a production effect evaluation chart; S5: determining the weight coefficient at this time according to the production effect evaluation chart, and establishing a final calculation model of the fracturing energy index and energy focusing index of deep coalbed methane with the weight coefficient at this time; S6: Calculate the fracturing energy index and energy focusing index of the target well in the target area according to the final calculation model, determine the production effect quadrant to which the target well belongs in combination with the production effect evaluation chart, and obtain the recoverability evaluation result of the target well.

2. The deep coalbed methane recoverability evaluation method based on surrounding rock focusing effect according to claim 1 is characterized in that: In step S1, the numerical model is established by collecting geological models, geostress models and fracturing engineering parameters; Alternatively, the numerical model is established by collecting parameters required for geological modeling, parameters required for geostress modeling, and fracturing engineering parameters.

3. The deep coalbed methane recoverability evaluation method based on surrounding rock focusing effect according to claim 2 is characterized in that: The geological model includes average porosity, permeability, gas saturation, adsorbed gas volume, well type, well coordinates and well trajectory; The geostress model includes maximum principal stress, minimum principal stress, Young's modulus and Poisson's ratio; The fracturing engineering parameters include fracturing fluid volume, construction process pressure and reservoir fracture pressure; The parameters required for geological modeling include well logging interpretation results, seismic interpretation layer results, core description, sedimentary facies interpretation results and gas content; The parameters required for the geostress modeling include logging stress interpretation results, seismic rock mechanics parameters and small pressure test results.

4. The deep coalbed methane recoverability evaluation method based on surrounding rock focusing effect according to claim 1 is characterized in that: In step S1, the upper rock layer and the lower rock layer are both 50 m.

5. The deep coalbed methane recoverability evaluation method based on surrounding rock focusing effect according to claim 1 is characterized in that: In step S2, the average parameters of the fracturing conditions include the amount of fracturing fluid, the total amount of sand, the average displacement, the maximum pump pressure and the viscosity of the fracturing fluid. When setting multiple groups of the average parameters of the fracturing conditions, they are grouped according to 85%, 90%, 95%, 100%, 105%, 110% and 115% of each average parameter to obtain a total of 7 5 The average parameters of the group fracturing conditions.

6. The deep coalbed methane recoverability evaluation method based on surrounding rock focusing effect according to claim 1 is characterized in that: In step S2, when performing the numerical simulation of fracture expansion, the bottom hole flow pressure is set to 0.1 MPa, and the numerical simulation is performed on a daily basis; When the typical well is a horizontal well, the production intensity is calculated by the following formula: （1） Where: is the production intensity of horizontal wells, cubic meters per day per hundred meters; is the initial production capacity of the horizontal well, cubic meters per day; is the length of the horizontal well, hundred meters; When the typical well is a vertical well, the production intensity is calculated by the following formula: （2） Where: is the production intensity of vertical wells, cubic meters per day per ten meters; is the initial production capacity of the vertical well, cubic meters per day; is the thickness of the vertical well, ten meters; The initial production capacity of the horizontal well and the initial production capacity of the vertical well are both the average daily production in the first two months of the numerical simulation of the typical well.

7. The deep coalbed methane recoverability evaluation method based on surrounding rock focusing effect according to claim 1 is characterized in that: The average thickness of the top and bottom plates is calculated by the following formula: （6） The average minimum ground stress of the top and bottom plates is calculated by the following formula: （7） Where: is the average minimum principal stress of the bottom plate below the horizontal section, MPa; is the average minimum principal stress in the top plate above the horizontal section, MPa; The average fracture pressure of the coal rock and the roof and floor is calculated by the following formula: （8） The average bursting pressure of the top and bottom plates is calculated by the following formula: （9） Where: is the average rupture pressure of the bottom plate below the horizontal section, MPa; is the average rupture pressure of the top plate above the horizontal section, MPa.

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