Prediction method for original geological reserves and recovery ratio of coal bed gas in undersaturated gas reservoir

Abstract

The invention discloses a method for predicting original geological reserves and recovery rates of coalbed methane in an undersaturated gas reservoir, which comprises the following steps of: determining Langmuir pressure of the coalbed methane, determining average formation pressure and accumulated gas production rate under at least two production dates, establishing a prediction fitting model based on a material balance principle of the undersaturated coalbed methane reservoir, and predicting the original geological reserves and recovery rates of the coalbed methane in the undersaturated gas reservoir. The prediction fitting model is set to be a linear fitting model with the accumulative gas production as the horizontal axis and the ratio of the Langmuir pressure to the sum of the Langmuir pressure and the average formation pressure as the longitudinal axis, and the original geological reserves are determined according to the slope and the longitudinal axis intercept of the prediction fitting model. The given exhaust gas pressure serves as the average formation pressure and is substituted into the prediction fitting model to obtain the recoverable gas storage capacity, the recovery efficiency is determined according to the original geological reserves and the recoverable gas storage capacity, the calculation process can be simple and convenient, needed parameters are few, a large amount of time and energy are saved, the calculation efficiency is improved, and the recovery efficiency is improved. And the adsorption gas does not need to be equivalent to the property of free gas, so that the calculation precision is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of coalbed methane development, and in particular relates to a method for predicting the original geological reserves and recovery rate of coalbed methane in an undersaturated gas reservoir. Background Art

[0002] Coalbed methane, commonly known as "gas", is an unconventional natural gas that is stored in coal seams in an adsorbed state and is associated with coal. The original geological reserves are the material basis for the development of coalbed methane, and the recovery rate is the ultimate goal of coalbed methane development. Accurately evaluating the original geological reserves of coalbed methane and predicting the recovery rate are of great theoretical and practical significance to the efficient development of coalbed methane.

[0003] At present, the original geological reserve evaluation method and recovery rate prediction method of undersaturated coalbed methane reservoirs are based on the material balance principle of coalbed methane and water phase, taking into account the changes in porosity and saturation, and applying the pseudo-deviation coefficient Z* to equate the adsorbed gas to free gas so that it has the properties of free gas. Although this method is feasible, it requires many parameters and the calculation process is complicated. Small errors in parameter values ​​may lead to large errors in the original geological reserve evaluation results and recovery rate prediction results. Summary of the invention

[0004] In view of the above-mentioned defects or shortcomings of the prior art, the present invention provides a method for predicting the original geological reserves and recovery rate of coalbed methane in undersaturated gas reservoirs, aiming to solve at least one of the above-mentioned technical problems.

[0005] In order to achieve the above object, the present invention provides a method for predicting the original geological reserves and recovery rate of coalbed methane in an undersaturated gas reservoir, wherein the prediction method comprises:

[0006] Determine the Langmuir pressure of coal seam gas;

[0007] Determine the average formation pressure and cumulative gas production for at least two production dates;

[0008] A prediction fitting model is established based on the material balance principle of undersaturated coalbed methane reservoirs, wherein the prediction fitting model is set as a linear fitting model with cumulative gas production as the horizontal axis and the ratio of Langmuir pressure to the sum of Langmuir pressure and average formation pressure as the vertical axis;

[0009] The original geological reserves of coalbed methane are determined based on the slope and vertical intercept of the predicted fitting model;

[0010] Substitute the given exhaust gas pressure as the average formation pressure into the prediction fitting model to obtain the recoverable gas storage volume of coalbed methane;

[0011] The recovery rate of coalbed methane is determined based on its original geological reserves and recoverable gas reserves.

[0012] In one embodiment of the present invention, the calculation formula of the prediction fitting model is:

[0013]

[0014] In the formula, G p is the cumulative gas production, 10 6 m 3 ;p L is the Langmuir pressure, MPa; p is the average formation pressure, MPa; m is the slope of the predicted fitting model, and b is the vertical intercept of the prediction fitting model, and

[0015] In one embodiment of the present invention, determining the original geological reserves of coalbed methane according to the slope and the vertical axis intercept of the prediction fitting model includes:

[0016] The actual calculation formula of the original geological reserves of coalbed methane is constructed as a prediction calculation formula calculated by the slope and vertical intercept of the prediction fitting model, wherein the prediction calculation formula of the original geological reserves is:

[0017]

[0018] Where G is the original geological reserves of coalbed methane, 10 6 m 3 ; m is the slope of the prediction fitting model; b is the vertical intercept of the prediction fitting model;

[0019] The slope and vertical axis intercept of the prediction fitting model are substituted into the prediction calculation formula of the original geological reserves to calculate the original geological reserves of coalbed methane.

[0020] In one embodiment of the present invention, the actual calculation formula of the original geological reserves of coalbed methane is constructed as a prediction calculation formula calculated by the slope and the vertical axis intercept of the prediction fitting model, including:

[0021] The actual calculation formula for determining the original geological reserves of coalbed methane is:

[0022]

[0023] Where G is the original geological reserves of coalbed methane, 10 6 m 3 ; A is the controlled area of ​​coalbed methane reservoir, km 2 ; h is the thickness of the coal reservoir, m; ρ c is the density of coal rock, t / m 3 ; V L is the Langmuir volume, m 3 / t;p L is the Langmuir pressure, MPa; p d is the critical desorption pressure, MPa;

[0024] The intermediate derivation calculation formula is obtained according to the actual calculation formula of the original geological reserves, among which the intermediate derivation calculation formula is:

[0025]

[0026] In the intermediate derivation calculation formula, let The prediction calculation formula of original geological reserves is obtained by conversion.

[0027] In one embodiment of the present invention, establishing a prediction fitting model based on the material balance principle of an undersaturated coalbed methane reservoir includes:

[0028] The material balance equation is established based on the material balance principle of undersaturated coalbed methane reservoirs, where the material balance equation is:

[0029] G p =GG r

[0030] In the formula, G p is the cumulative gas production, 10 6 m 3 ; G is the original geological reserves of coalbed methane, 10 6 m 3 ; G r The remaining geological reserves of coalbed methane are 10 6 m 3 ;

[0031] Substitute the actual calculation formulas of original geological reserves and remaining geological reserves into the material balance equation to obtain the calculation formula for the cumulative gas production of coalbed methane:

[0032]

[0033] In the formula, G p is the cumulative gas production, 10 6 m 3 ; A is the controlled area of ​​coalbed methane reservoir, km 2 ; h is the thickness of the coal reservoir, m; ρ c is the density of coal rock, t / m 3 ; V L is the Langmuir volume, m 3 / t;p L is the Langmuir pressure, MPa; p d is the critical desorption pressure, MPa; p is the average formation pressure, MPa;

[0034] The third derived calculation formula is obtained according to the calculation formula of the cumulative gas production, where the third derived calculation formula is:

[0035]

[0036] In the third derived calculation formula, let The calculation formula of the prediction fitting model is obtained by transformation.

[0037] In one embodiment of the present invention, the third derived calculation formula is obtained according to the calculation formula of the cumulative gas production, including:

[0038] The first derived calculation formula is obtained according to the calculation formula of the cumulative gas production, wherein the first derived calculation formula is:

[0039]

[0040] The second derivation calculation formula is obtained according to the first derivation calculation formula, wherein the second derivation calculation formula is:

[0041]

[0042] The third derivation calculation formula is obtained by sorting out the second derivation calculation formula.

[0043] In one embodiment of the present invention, substituting a given exhaust gas pressure as the average formation pressure into the prediction fitting model to obtain the recoverable gas storage volume of the coalbed methane includes:

[0044] Substitute the given exhaust gas pressure as the average formation pressure into the calculation formula of the prediction fitting model, and obtain the calculation formula of the recoverable gas storage volume of coalbed methane. The calculation formula of the recoverable gas storage volume is:

[0045]

[0046] In the formula, G pa For a given waste pressure p a The cumulative gas production under the condition of 10 6 m 3 ;p L is the Langmuir pressure, MPa; p a is the given abandoned pressure, MPa; m is the slope of the prediction fitting model; b is the vertical intercept of the prediction fitting model;

[0047] The recoverable gas storage volume of coalbed methane is calculated according to the calculation formula of recoverable gas storage volume.

[0048] In one embodiment of the present invention, determining the recovery rate of coalbed methane according to the original geological reserves and recoverable gas reserves of coalbed methane includes:

[0049] Substitute the original geological reserves and recoverable gas reserves of coalbed methane into the calculation formula of recovery rate to calculate the recovery rate of coalbed methane, where the calculation formula of recovery rate is:

[0050]

[0051] Where, R is the recovery rate of coalbed methane; G pa is the recoverable gas storage volume of coalbed methane, (10 6 m 3 ); G is the original geological reserves of coalbed methane, (10 6 m 3 ).

[0052] In one embodiment of the present invention, determining the Langmuir pressure of coalbed methane includes:

[0053] The Langmuir pressure is determined by fitting the isothermal adsorption and desorption experimental data of coalbed methane.

[0054] In one embodiment of the present invention, the given exhaust gas pressure is set to be less than or equal to 3 MPa.

[0055] Through the above technical solution, the method for predicting the original geological reserves and recovery rate of coalbed methane in undersaturated gas reservoirs provided by the embodiment of the present invention has the following beneficial effects:

[0056] In the above technical scheme, the Langmuir pressure of coalbed methane, the average formation pressure and the cumulative gas production under at least two production dates are first determined, and then a prediction fitting model is established based on the material balance principle of undersaturated coalbed methane reservoirs, and the prediction fitting model is set as a linear fitting model with the cumulative gas production as the horizontal axis and the ratio of the Langmuir pressure to the sum of the Langmuir pressure and the average formation pressure as the vertical axis, so that the original geological reserves of coalbed methane can be determined according to the slope and the vertical intercept of the prediction fitting model, and the recoverable gas reserves of coalbed methane can be obtained by substituting the given exhaust gas pressure as the average formation pressure into the prediction fitting model. Finally, the recovery rate of coalbed methane can be determined according to the original geological reserves and recoverable gas reserves of coalbed methane, so that the whole calculation process is simple, fewer parameters are required, a lot of time and energy are saved, and the calculation efficiency is improved. There is no need to equate the adsorbed gas with the properties of free gas, and the material balance principle based on the properties of adsorbed gas is directly adopted to establish the prediction fitting model, which is conducive to improving the calculation accuracy and facilitating large-scale promotion and application.

[0057] Other features and advantages of the embodiments of the present invention will be described in detail in the subsequent detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The accompanying drawings are used to provide a further understanding of the embodiments of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the embodiments of the present invention, but do not constitute a limitation on the embodiments of the present invention. In the accompanying drawings:

[0059] Figure 1 is a flow chart of a method for predicting the original geological reserves and recovery rate of coalbed methane in an undersaturated gas reservoir according to an embodiment of the present invention;

[0060] Figure 2 is a model diagram of a prediction fitting model according to an embodiment of the present invention. DETAILED DESCRIPTION

[0061] The specific implementation of the embodiment of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the embodiment of the present invention, and is not used to limit the embodiment of the present invention.

[0062] It should be noted that if the implementation methods of the present application involve directional indications (such as up, down, left, right, front, back...), such directional indications are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0063] In addition, if there are descriptions involving "first", "second", etc. in the implementation methods of this application, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or suggesting their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various implementation methods can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0064] Figure 1 The flowchart of the method for predicting the original geological reserves and recovery rate of coalbed methane in an undersaturated gas reservoir according to an embodiment of the present invention is schematically shown. Figure 1 As shown, the present invention provides a method for predicting the original geological reserves and recovery rate of coalbed methane in an undersaturated gas reservoir, wherein the prediction method comprises the following steps:

[0065] Step S100, determining the Langmuir pressure of coalbed methane.

[0066] Specifically, Langmuir pressure refers to the adsorption constant in the Langmuir equation that describes the adsorption isotherm of coal to methane. Langmuir pressure is a parameter that affects the shape of the coal adsorption isotherm curve. The smaller the Langmuir pressure, the greater the curvature of the adsorption curve; conversely, the smaller the curvature.

[0067] In one embodiment of the present invention, step S100, determining the Langmuir pressure of coalbed methane includes:

[0068] The Langmuir pressure is determined by fitting the isothermal adsorption and desorption experimental data of coalbed methane.

[0069] Step S200, determining the average formation pressure and cumulative gas production under at least two production dates.

[0070] Furthermore, the average formation pressure and cumulative gas production under at least two production dates are sorted and counted according to the production dates.

[0071] Step S300, establishing a prediction fitting model based on the material balance principle of the undersaturated coalbed methane reservoir, wherein the prediction fitting model is set as a linear fitting model with the cumulative gas production as the horizontal axis and the ratio of the Langmuir pressure to the sum of the Langmuir pressure and the average formation pressure as the vertical axis.

[0072] In fact, for undersaturated coalbed methane reservoirs, there is only adsorbed gas and no free gas. The production process is only the property of the adsorbed gas. There is no need to equate the adsorbed gas with the properties of the free gas. A prediction fitting model is established directly based on the material balance principle of the adsorbed gas, and the prediction fitting model is set as a linear fitting model with the cumulative gas production as the horizontal axis and the ratio of the Langmuir pressure to the sum of the Langmuir pressure and the average formation pressure as the vertical axis. In this way, only the Langmuir pressure and at least two pressure measurement data (average formation pressure) during the production process and the corresponding cumulative gas production data are required to obtain the prediction fitting model, especially the slope and vertical intercept of the prediction fitting model.

[0073] In one embodiment of the present invention, step S300, establishing a prediction fitting model based on the material balance principle of an undersaturated coalbed methane reservoir includes:

[0074] Step S310, establishing a material balance equation based on the material balance principle of an undersaturated coalbed methane reservoir, wherein the material balance equation is:

[0075] G p =GG r

[0076] In the formula, G p is the cumulative gas production, 10 6 m 3 ; G is the original geological reserves of coalbed methane, 10 6m 3 ; G r The remaining geological reserves of coalbed methane are 10 6 m 3 .

[0077] Step S320, the actual calculation formulas of the original geological reserves and the remaining geological reserves are respectively substituted into the material balance equation to obtain the calculation formula of the cumulative gas production of the coalbed methane:

[0078]

[0079] In the formula, G p is the cumulative gas production, 10 6 m 3 ; A is the controlled area of ​​coalbed methane reservoir, km 2 ; h is the thickness of the coal reservoir, m; ρ c is the density of coal rock, t / m 3 ; V L is the Langmuir volume, m 3 / t;p L is the Langmuir pressure, MPa; p d is the critical desorption pressure, MPa; p is the average formation pressure, MPa.

[0080] Specifically, the actual calculation formula for the original geological reserves is:

[0081]

[0082] And the actual calculation formula for the remaining geological reserves is:

[0083]

[0084] Step S330, a third derivation calculation formula is obtained according to the calculation formula of the cumulative gas production, wherein the third derivation calculation formula is:

[0085] In one embodiment of the present invention, in step S330, the third derived calculation formula is obtained according to the calculation formula of the cumulative gas production, including:

[0086] Step S331, a first derivation calculation formula is obtained according to the calculation formula of the cumulative gas production, wherein the first derivation calculation formula is:

[0087]

[0088] Step S332, obtaining a second derivation formula according to the first derivation formula, wherein the second derivation formula is:

[0089]

[0090] Step S333, obtaining a third derivation formula according to the second derivation formula.

[0091] Step S340, in the third derivation calculation formula, let The calculation formula of the prediction fitting model is obtained by transformation.

[0092] It can be understood that, through multiple steps of rearranging the calculation formula of cumulative gas production, a linear fitting model with cumulative gas production as the horizontal axis and the ratio of Langmuir pressure to the sum of Langmuir pressure and average formation pressure as the vertical axis is obtained.

[0093] Specifically, the calculation formula of the prediction fitting model is:

[0094]

[0095] In the formula, G p is the cumulative gas production, 10 6 m 3 ;p L is the Langmuir pressure, MPa; p is the average formation pressure, MPa; m is the slope of the predicted fitting model, and b is the vertical intercept of the prediction fitting model, and

[0096] More specifically, the cumulative gas production G under at least two production dates is p The horizontal axis is the ratio of the Langmuir pressure to the sum of the Langmuir pressure and the average formation pressure. L / (p L +p) as the vertical axis, make a scatter plot in the rectangular coordinate graph, apply a linear function to fit these data points to obtain the model diagram of the prediction fitting model, and obtain the slope m of the straight line fitting model (unit: (10 6 m 3 ) -1 ) and the ordinate intercept b (in dimensionless units).

[0097] Step S400, determining the original geological reserves of coalbed methane according to the slope and vertical axis intercept of the prediction fitting model.

[0098] In one embodiment of the present invention, step S400, determining the original geological reserves of coalbed methane according to the slope and the vertical axis intercept of the prediction fitting model includes:

[0099] Step S410, constructing the actual calculation formula of the original geological reserves of coalbed methane into a prediction calculation formula calculated by the slope and the vertical axis intercept of the prediction fitting model, wherein the prediction calculation formula of the original geological reserves is:

[0100]

[0101] Where G is the original geological reserves of coalbed methane, 10 6 m 3 ; m is the slope of the predicted fitting model; b is the vertical intercept of the predicted fitting model.

[0102] In one embodiment of the present invention, step S410, constructing the actual calculation formula of the original geological reserves of coalbed methane into a prediction calculation formula calculated by the slope and the vertical axis intercept of the prediction fitting model includes:

[0103] Step S411, determining the actual calculation formula of the original geological reserves of coalbed methane, wherein the actual calculation formula of the original geological reserves is:

[0104]

[0105] Where G is the original geological reserves of coalbed methane, 10 6 m 3 ; A is the controlled area of ​​coalbed methane reservoir, km 2 ; h is the thickness of the coal reservoir, m; ρ c is the density of coal rock, t / m 3 ; V L is the Langmuir volume, m 3 / t;p L is the Langmuir pressure, MPa; p d is the critical desorption pressure, MPa.

[0106] Step S412, an intermediate derivation calculation formula is obtained according to the actual calculation formula of the original geological reserves, wherein the intermediate derivation calculation formula is:

[0107]

[0108] Step S413, in the intermediate derivation calculation formula, let The prediction calculation formula of original geological reserves is obtained by conversion.

[0109] Step S420, substituting the slope and the vertical axis intercept of the prediction fitting model into the prediction calculation formula of the original geological reserves to calculate the original geological reserves of the coalbed methane.

[0110] It can be understood that by converting the parameters in the actual calculation formula of the original geological reserves into the slope and intercept in the prediction fitting model, the original geological reserves of coalbed methane can be cleverly obtained.

[0111] Step S500, substituting the given exhaust gas pressure as the average formation pressure into the prediction fitting model to obtain the recoverable gas storage volume of the coalbed methane.

[0112] In one embodiment of the present invention, step S500, substituting a given exhaust gas pressure as an average formation pressure into a prediction fitting model to obtain the recoverable gas storage volume of coalbed methane includes:

[0113] Step S510, substituting the given exhaust gas pressure as the average formation pressure into the calculation formula of the prediction fitting model, and sorting out the calculation formula of the recoverable gas storage volume of the coalbed methane, wherein the calculation formula of the recoverable gas storage volume is:

[0114]

[0115] In the formula, G pa For a given waste pressure p a The cumulative gas production under the condition of 10 6 m 3 ;p L is the Langmuir pressure, MPa; p a is the given waste pressure, MPa; m is the slope of the prediction fitting model; b is the vertical intercept of the prediction fitting model.

[0116] Step S520, calculating the recoverable gas storage volume of the coalbed methane according to the calculation formula of the recoverable gas storage volume.

[0117] Step S600, determining the recovery rate of coalbed methane according to the original geological reserves and recoverable gas reserves of the coalbed methane.

[0118] Specifically, step S600, determining the recovery rate of coalbed methane according to the original geological reserves and recoverable gas reserves of coalbed methane includes:

[0119] Substitute the original geological reserves and recoverable gas reserves of coalbed methane into the calculation formula of recovery rate to calculate the recovery rate of coalbed methane, where the calculation formula of recovery rate is:

[0120]

[0121] Where R is the recovery rate of coalbed methane; G pa is the recoverable gas storage volume of coalbed methane, (10 6 m 3 ); G is the original geological reserves of coalbed methane, (10 6 m 3 ).

[0122] In one embodiment of the present invention, the given exhaust gas pressure may be set to be less than or equal to 3 MPa, preferably 2 MPa.

[0123] In the above technical scheme, the Langmuir pressure of coalbed methane, the average formation pressure and the cumulative gas production under at least two production dates are first determined, and then a prediction fitting model is established based on the material balance principle of undersaturated coalbed methane reservoirs, and the prediction fitting model is set as a linear fitting model with the cumulative gas production as the horizontal axis and the ratio of the Langmuir pressure to the sum of the Langmuir pressure and the average formation pressure as the vertical axis, so that the original geological reserves of coalbed methane can be determined according to the slope and the vertical intercept of the prediction fitting model, and the recoverable gas reserves of coalbed methane can be obtained by substituting the given exhaust gas pressure as the average formation pressure into the prediction fitting model. Finally, the recovery rate of coalbed methane can be determined according to the original geological reserves and recoverable gas reserves of coalbed methane, so that the whole calculation process is simple, fewer parameters are required, a lot of time and energy are saved, and the calculation efficiency is improved. There is no need to equate the adsorbed gas with the properties of free gas, and the material balance principle based on the properties of adsorbed gas is directly adopted to establish the prediction fitting model, which is conducive to improving the calculation accuracy and facilitating large-scale promotion and application.

[0124] Example 1: Drainage and depressurization of an undersaturated coalbed methane reservoir, with a known Langmuir pressure p L The original geological reserves of CBM in the undersaturated CBM reservoir are evaluated by using the values ​​of several measured average formation pressures and the corresponding cumulative gas production, and the abandoned pressure p is predicted. a It is the recovery rate of coalbed methane at 2MPa.

[0125] 1. Determine the Langmuir pressure p of undersaturated coalbed methane reservoirs L

[0126] According to the experimental data of coalbed methane isothermal adsorption and desorption, the Langmuir pressure p is determined by fitting. L It is 2.7MPa.

[0127] 2. Compile and count the measured average formation pressure and corresponding cumulative production of coalbed methane reservoirs

[0128] The average formation pressure and corresponding cumulative gas production measured each time during the production process of the coalbed methane reservoir are sorted and counted, see Table 1.

[0129] Table 1 The measured average formation pressure and the corresponding cumulative gas production data during the production process of coalbed methane reservoirs

[0130] Production date / day Average formation pressure / MPa <![CDATA[Cumulative gas production / (10 6 m 3 )]]> 371 8.13 0.171222 613 7.7 0.387476 842 7.42 0.536367 1127 7.08 0.730805 1515 6.61 1.024925 3503 5.11 2.189225

[0131] 3. Establish a prediction fitting model based on the material balance principle of undersaturated coalbed methane reservoirs

[0132] The cumulative gas production G in Table 1 p The horizontal axis is the ratio of the Langmuir pressure to the sum of the Langmuir pressure and the average formation pressure.L / (p L +p) as the vertical axis, and make a scatter plot in the rectangular coordinate graph, such as Figure 2 As shown, a linear function is applied to fit these data points to obtain a model diagram of the prediction fitting model, and the slope of the straight line fitting model can be obtained as m = 0.047763 (unit: (10 6 m 3 ) -1 ), the vertical axis intercept b = 0.241132, that is, the calculation formula of the prediction fitting model is:

[0133]

[0134] 4. Calculate the original geological reserves of coalbed methane in undersaturated coalbed methane reservoirs

[0135] Using the calculation formula of original geological reserves, the original geological reserves G of the undersaturated coalbed methane reservoir are calculated to be 15.8882 (10 6 m 3 ).

[0136]

[0137] 5. Calculate the recoverable gas reserves of coalbed methane in coalbed methane reservoirs

[0138] Apply the calculation formula of recoverable gas storage volume to calculate the given waste pressure p a = Cumulative gas production under 2MPa (i.e. recoverable reserves of coalbed methane) G pa is 6.97896(10 6 m 3 ).

[0139]

[0140] 6. Predicting the recovery rate of coalbed methane in undersaturated coalbed methane reservoirs

[0141] The calculated given waste pressure p a = Cumulative gas production under 2MPa (i.e. recoverable reserves of coalbed methane) G pa =6.97896(10 6 m 3 ) and the calculated original geological reserves of coalbed methane in the undersaturated coalbed methane reservoir G = 15.8882 (10 6 m 3 ) is substituted into the recovery rate calculation formula, and the coalbed methane recovery rate R under a given abandonment pressure is obtained to be 0.4393.

[0142]

[0143] In addition, another embodiment of the present invention provides a processor configured to execute the method for predicting the original geological reserves and recovery rate of coalbed methane in undersaturated gas reservoirs as described above.

[0144] In addition, another embodiment of the present invention provides a machine-readable storage medium, on which instructions are stored. When the instructions are executed by a processor, a method for predicting the original geological reserves and recovery rate of coalbed methane in undersaturated gas reservoirs as described above is implemented.

[0145] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0146] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0147] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0148] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0149] In a typical configuration, a computing device includes one or more processors (CPU), input / output interfaces, network interfaces, and memory.

[0150] The memory may include non-permanent memory in a computer-readable medium, random access memory (RAM) and / or non-volatile memory in the form of read-only memory (ROM) or flash RAM. The memory is an example of a computer-readable medium.

[0151] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0152] The above are only embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included within the scope of the claims of the present application.

Claims

1. A method for predicting the original geological reserves and recovery rate of coalbed methane in an undersaturated gas reservoir, characterized in that: The prediction method comprises: Determine the Langmuir pressure of coal seam gas; Determine the average formation pressure and cumulative gas production for at least two production dates; A prediction fitting model is established based on the material balance principle of undersaturated coalbed methane reservoirs, wherein the prediction fitting model is set as a linear fitting model with cumulative gas production as the horizontal axis and the ratio of Langmuir pressure to the sum of Langmuir pressure and average formation pressure as the vertical axis; The original geological reserves of coalbed methane are determined based on the slope and vertical intercept of the predicted fitting model; Substitute the given exhaust gas pressure as the average formation pressure into the prediction fitting model to obtain the recoverable gas storage volume of coalbed methane; The recovery rate of coalbed methane is determined based on its original geological reserves and recoverable gas reserves.

2. The method for predicting the original geological reserves and recovery rate of coalbed methane in undersaturated gas reservoirs according to claim 1, characterized in that: The calculation formula of the prediction fitting model is: In the formula, G p is the cumulative gas production, 10 6 m 3 ;p L is the Langmuir pressure, MPa; p is the average formation pressure, MPa; m is the slope of the predicted fitting model, and b is the vertical intercept of the prediction fitting model, and 3. The method for predicting the original geological reserves and recovery rate of coalbed methane in undersaturated gas reservoirs according to claim 2, characterized in that: Determining the original geological reserves of coalbed methane according to the slope and ordinate intercept of the prediction fitting model includes: The actual calculation formula of the original geological reserves of coalbed methane is constructed as a prediction calculation formula calculated by the slope and vertical intercept of the prediction fitting model, wherein the prediction calculation formula of the original geological reserves is: Where G is the original geological reserves of coalbed methane, 10 6 m 3 ; m is the slope of the prediction fitting model; b is the vertical intercept of the prediction fitting model; The slope and vertical intercept of the prediction fitting model are substituted into the prediction calculation formula of the original geological reserves to calculate the original geological reserves of coalbed methane.

4. The method for predicting the original geological reserves and recovery rate of coalbed methane in undersaturated gas reservoirs according to claim 3, characterized in that: The actual calculation formula for the original geological reserves of coalbed methane is constructed as a prediction calculation formula calculated by the slope and the vertical axis intercept of the prediction fitting model, including: The actual calculation formula for determining the original geological reserves of coalbed methane is: Where G is the original geological reserves of coalbed methane, 10 6 m 3 ; A is the controlled area of ​​coalbed methane reservoir, km 2 ; h is the thickness of the coal reservoir, m; ρ c is the density of coal rock, t / m 3 ; V L is the Langmuir volume, m 3 / t;p L is the Langmuir pressure, MPa; p d is the critical desorption pressure, MPa; The intermediate derivation calculation formula is obtained according to the actual calculation formula of the original geological reserves, among which the intermediate derivation calculation formula is: In the intermediate derivation calculation formula, let The prediction calculation formula of original geological reserves is obtained by conversion.

5. The method for predicting the original geological reserves and recovery rate of coalbed methane in undersaturated gas reservoirs according to claim 1, characterized in that: The prediction fitting model established based on the material balance principle of undersaturated coalbed methane reservoirs includes: The material balance equation is established based on the material balance principle of undersaturated coalbed methane reservoirs, where the material balance equation is: G p =GG r In the formula, G p is the cumulative gas production, 10 6 m 3 ; G is the original geological reserves of coalbed methane, 10 6 m 3 ; G r The remaining geological reserves of coalbed methane are 10 6 m 3 ; Substitute the actual calculation formulas of original geological reserves and remaining geological reserves into the material balance equation to obtain the calculation formula for the cumulative gas production of coalbed methane: In the formula, G p is the cumulative gas production, 10 6 m 3 ; A is the controlled area of ​​coalbed methane reservoir, km 2 ; h is the thickness of the coal reservoir, m; ρ c is the density of coal rock, t / m 3 ; V L is the Langmuir volume, m 3 / t;p L is the Langmuir pressure, MPa; p d is the critical desorption pressure, MPa; p is the average formation pressure, MPa; The third derived calculation formula is obtained according to the calculation formula of the cumulative gas production, wherein the third derived calculation formula is: In the third derived calculation formula, let The calculation formula of the prediction fitting model is obtained by transformation.

6. The method for predicting the original geological reserves and recovery rate of coalbed methane in undersaturated gas reservoirs according to claim 5, characterized in that: The third derived calculation formula obtained by arranging the calculation formula of the cumulative gas production includes: The first derived calculation formula is obtained according to the calculation formula of the cumulative gas production, wherein the first derived calculation formula is: The second derivation calculation formula is obtained according to the first derivation calculation formula, wherein the second derivation calculation formula is: The third derivation calculation formula is obtained by sorting out the second derivation calculation formula.

7. The method for predicting the original geological reserves and recovery rate of coalbed methane in undersaturated gas reservoirs according to claim 2, characterized in that: Substituting the given exhaust gas pressure as the average formation pressure into the prediction fitting model to obtain the recoverable gas storage volume of the coalbed methane includes: Substitute the given exhaust gas pressure as the average formation pressure into the calculation formula of the prediction fitting model, and obtain the calculation formula of the recoverable gas storage volume of coalbed methane. The calculation formula of the recoverable gas storage volume is: In the formula, G pa For a given waste pressure p a The cumulative gas production under the condition of 10 6 m 3 ;p L is the Langmuir pressure, MPa; p a is the given abandoned pressure, MPa; m is the slope of the prediction fitting model; b is the vertical intercept of the prediction fitting model; The recoverable gas storage volume of coalbed methane is calculated according to the calculation formula of recoverable gas storage volume.

8. The method for predicting the original geological reserves and recovery rate of coalbed methane in undersaturated gas reservoirs according to any one of claims 1 to 7, characterized in that: The recovery rate of coalbed methane determined based on the original geological reserves and recoverable gas reserves of coalbed methane includes: Substitute the original geological reserves and recoverable gas reserves of coalbed methane into the calculation formula of recovery rate to calculate the recovery rate of coalbed methane, where the calculation formula of recovery rate is: Where R is the recovery rate of coalbed methane; G pa is the recoverable gas storage volume of coalbed methane, (10 6 m 3 ); G is the original geological reserves of coalbed methane, (10 6 m 3 ).

9. The method for predicting the original geological reserves and recovery rate of coalbed methane in undersaturated gas reservoirs according to any one of claims 1 to 7, characterized in that: Determining the Langmuir pressure of coalbed methane includes: The Langmuir pressure is determined by fitting the isothermal adsorption and desorption experimental data of coalbed methane.

10. The method for predicting the original geological reserves and recovery rate of coalbed methane in undersaturated gas reservoirs according to any one of claims 1 to 7, characterized in that: The given exhaust gas pressure is set to be less than or equal to 3 MPa.

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