A method for determining the productivity of a coalbed methane well without shutting in

Abstract

This invention discloses a method for determining the production capacity of a coalbed methane (CBM) well without shutting it in. The method includes: acquiring basic data of the CBM well; determining a relationship table between pressure and CBM deviation factor, and a relationship table between pressure and apparent pressure, based on CBM PVT experimental data; recording the daily gas production, bottom hole pressure, and cumulative gas production of the CBM well at each stable flowing pressure test moment during three or more different production stages; determining the formation pressure corresponding to each stable flowing pressure test moment using a mass balance equation; determining the coefficients of the CBM well's production capacity equation based on the formation pressure, bottom hole pressure, and production at each stable flowing pressure test moment, thereby obtaining the CBM well's production capacity equation; and substituting the formation pressure and bottom hole pressure values ​​into the production capacity equation and solving for the corresponding CBM well production capacity. This invention effectively overcomes the shortcomings of traditional well testing methods that require shutting in the well to test formation pressure, and avoids the problem that the applicable conditions of existing non-shutdown methods for determining gas well production capacity equations are difficult to meet.

Description

Technical Field

[0001] This invention belongs to the field of coalbed methane development research, and specifically relates to a method for determining the production capacity of a coalbed methane well without shutting it in. Background Technology

[0002] Determining the production capacity equation and production capacity of coalbed methane wells is a crucial routine task in dynamic analysis, serving as a fundamental basis for predicting well production patterns, analyzing production potential, and optimizing operating procedures. To determine well production capacity, the production capacity equation must first be established. Currently, this is primarily achieved through well testing. However, well testing requires shutting down the well for pressure recovery testing. Shutting down a well impacts production, and because the fracturing scale of current coalbed methane wells is very large, often exceeding tens of thousands of cubic meters of fluid, sometimes even reaching 50,000 cubic meters, water flooding is easily encountered after shutting down, making production recovery difficult. There are very few literature reports on determining the production capacity equation without shutting down the well; fewer than five articles have been found. The reported methods for determining the production capacity equation without shutting down the well require two conditions: first, the formation pressure must remain essentially constant during different stable bottomhole flowing pressure tests; second, the well must maintain a stable seepage state during bottomhole flowing pressure tests under various constant production conditions. Determining the production capacity equation often requires conducting stable bottomhole flowing pressure tests under three different production conditions. Coal seams generally have a permeability of less than 0.1 mD, resulting in poor permeability. This means that after a change in coalbed methane well production, it typically takes a long time to return to a stable flow state. Consequently, the formation pressure at each stable bottomhole flowing pressure test time varies significantly and is difficult to maintain a relatively constant level. Therefore, the well productivity equation determination method without shutting in the well, as reported in the literature, is difficult to apply to coalbed methane wells due to its unmet application conditions. A brief introduction to the relevant knowledge follows.

[0003] Verification of the applicability conditions of existing gas well productivity equation non-shutdown determination methods.

[0004] According to literature reports, the time required for a gas well to return to a stable seepage state after changing its operating conditions (i.e., changing its production rate) can be calculated using formula (1).

[0005]

[0006] In the formula, t: the time required for stable seepage in the gas well, in hours; Gas layer porosity, decimal; S g Gas saturation, decimal; Gas viscosity, mPa·s; r: vent radius, m; K: gas layer permeability, mD; P r : Formation pressure, MPa.

[0007] The following example, using parameters from a typical deep coalbed methane horizontal well in a certain block, illustrates that the existing well productivity equation's non-shutdown determination method is difficult to apply to coalbed methane wells. The corresponding average reservoir porosity of a certain coalbed methane well... Gas saturation S g =0.7; Gas viscosity under formation conditions The gas well's vent radius r = 160 m; the effective formation permeability K = 0.1 mD; and the formation pressure P. r =28MPa. Based on the above parameters, it can be calculated using formula (1) that after the gas well changes its working system, it will take 475.14 hours, or about 19.8 days, to reach a stable seepage state again. If continuous stable flow pressure tests are conducted under three different production conditions (45,000 cubic meters / day, 30,000 cubic meters / day, and 15,000 cubic meters / day), it will take about 59.4 days. During this period, the cumulative gas production of the gas well is 4.5*19.8+3*19.8+1.5*19.8=1,782,000 cubic meters. The average dynamic reserves of deep coalbed methane horizontal wells in this area are approximately 55 million cubic meters. According to the material balance equation, after producing 1.782 million cubic meters of gas, the formation pressure will change by approximately 1.782 / 5500*28 = 0.9072 MPa. The formation pressure will change significantly. Therefore, for coalbed methane wells, the prerequisite that "the formation pressure remains basically unchanged during the well flow pressure test" required by the existing gas well production capacity equation and the no-shutdown method is difficult to meet. Summary of the Invention

[0008] The purpose of this invention is to provide a method for determining the production capacity of coalbed methane wells without shutting them in, aiming to solve the problem that the applicable conditions of the existing gas well production capacity determination method without shutting in are difficult to meet.

[0009] To achieve the above objectives, the present invention provides a method for determining the production capacity of a coalbed methane well without shutting it in, the steps of which are as follows:

[0010] Step 1: Collect basic data of the target coalbed methane well, including PVT experimental data of coalbed methane and the original formation pressure P. Ri Bottom-hole flowing pressure data P of coalbed methane wells during production process wf and daily production data q sc ;

[0011] Step 2: Based on the coalbed methane PVT experimental data obtained in Step 1, determine the relationship table between pressure P and coalbed methane deviation factor Z, and further determine the relationship between pressure P and apparent pressure P. s A table showing the relationships between P and P. s =P / Z;

[0012] Step 3: Conduct a stable bottom hole flowing pressure test under constant production conditions at each of the three or more different production stages of the coalbed methane well, and record the daily gas production q of the coalbed methane well at each stable flowing pressure test time. sc(1) q sc(2) ,…,q sc(n) Bottom-hole flowing pressure P wf(1) P wf(2) ,…,P wf(n) and cumulative gas production GP (1) ,GP (2) ,…,GP (n) ;

[0013] Step 4: Set the initial iterative assumption value G0 for the dynamic reserves of the gas well, and combine it with the cumulative gas production GP at each stable flowing pressure test time in different production stages. (1) ,GP (2) ,…,GP (n) Based on the mass balance equation, the formation pressure P corresponding to each steady-state pressure test moment was determined. Rm(1) P Rm(2) ,…,P Rm(n) ;

[0014] Step 5: Based on the formation pressure P corresponding to each steady-state pressure test moment determined by the mass balance equation. Rm(1) P Rm(2) , ..., P Rm(n) Bottom-hole flowing pressure P wf(1) ,P wf(2) ,…,P wf(n) and output q sc(1) q sc(2) ,…,q sc(n) The binomial productivity equation for coalbed methane wells was determined. The coefficients A and B in the formula, where P R For formation pressure, P wf q represents the bottom hole flowing pressure of a coalbed methane well. sc This represents the daily production of coalbed methane wells.

[0015] Step 6: Based on the coalbed methane well productivity equation determined in Step 5 Combined with the bottom hole flowing pressure P obtained in step 3 at different steady-state flowing pressure test times wf(1) P wf(2) , ..., P wf(n) and daily gas production q sc(1) q sc(2) ,…,q sc(n) use Determine the formation pressure P corresponding to different steady-state flow pressure test times. Rp(1) ,P Rp(2) ,…,P Rp(n)That is, the formation pressure P obtained based on the productivity equation. Rp(1) ,P Rp(2) ,…,P Rp(n) ;

[0016] Step 7: Obtain the formation pressure P based on the material balance equation at different steady-state pressure test times. Rm(1) ,P Rm(2) ,…,P Rm(n) and formation pressure P obtained based on gas well productivity equation Rp(1) ,P Rp(2) ,…,P Rp(n) An error check is performed. If the error between the formation pressures calculated by the two methods does not meet the preset accuracy requirements, steps 4-6 are repeated to continue iterating until the preset accuracy is met. The production capacity equation determined when the accuracy requirements are met is the production capacity equation of the coalbed methane well. Substituting the formation pressure and bottom hole flowing pressure values ​​into the production capacity equation of the coalbed methane well and solving it yields the production capacity of the coalbed methane well under the corresponding formation pressure and bottom hole flowing pressure conditions.

[0017] Furthermore, the steps in step 4 for determining the formation pressure corresponding to each steady-state pressure test moment are as follows:

[0018] First, the formation apparent pressure P corresponding to each steady-state pressure test moment is determined based on the material balance equation based on apparent pressure. Rs(1) ,P Rs(2) , ..., P Rs(n) Then, based on pressure P and apparent pressure P s The relationship table is used to calculate and determine the corresponding formation pressure P using interpolation or function fitting methods. Rm(1) P Rm(2) ,…,P Rm(n) .

[0019] Furthermore, the steps in step 5 to determine the coefficients A and B of the binomial productivity equation for coalbed methane wells are as follows:

[0020] make x (i) =q sc(i) i = 1, 2, ..., n, based on the production rate q corresponding to each stable flowing pressure test moment in different production stages of the coalbed methane well. sc(1) q sc(2) ,…,q sc(n) and the corresponding stable bottom hole flowing pressure test data P wf(1) ,P wf(2) ,…,P wf(n) A series of observation points (y) were obtained. (i) ,x (i) If a linear fit is performed on the observation point data, then A is equal to the intercept of the fitted line equation, and B is equal to the slope of the fitted line equation.

[0021] Beneficial effects:

[0022] (1) The method proposed in this invention effectively overcomes the shortcomings of the traditional well test method in determining the gas well production capacity equation, which requires shutting in the well and affects the production output. It also avoids the problem that the existing gas well production capacity equation determination method without shutting in the well is difficult to meet the applicable conditions, and fills the gap in "determining the coalbed methane well production capacity without shutting in the well".

[0023] (2) Determining the production capacity equation and production capacity of coalbed methane wells is an essential task in daily production dynamic analysis. It is an important foundation for predicting gas well production patterns, analyzing production potential, and optimizing work systems, and therefore has very important practical value in the mine.

[0024] (3) The method of the present invention is simple, easy to understand and implement, highly operable, effective and practical, and has great value for promotion and use. Attached Figure Description

[0025] Figure 1 This is a schematic flowchart of an embodiment of a method for determining the production capacity of a coalbed methane well without shutting it in, according to the present invention.

[0026] Figure 2 It is a graph showing the functional relationship between pressure and apparent pressure.

[0027] Figure 3 It is a linear fit graph of the observation points. Detailed Implementation

[0028] Reference Figure 1 This invention provides a flowchart illustrating an embodiment of a method for determining the production capacity of a coalbed methane well without shutting it in. The specific implementation method is as follows:

[0029] Step 1: Collect basic data from the target coalbed methane well. This basic data includes PVT experimental data for coalbed methane and the original formation pressure P. Ri Bottom-hole flowing pressure data P of coalbed methane wells during production process wf and daily production data q sc .

[0030] Step 2: Based on the PVT experimental data of coalbed methane obtained in Step 1, determine the relationship table between pressure P and coalbed methane deviation factor Z. Generally, the relationship table between pressure P and coalbed methane deviation factor Z can be obtained directly from the PVT experimental data. Furthermore, determine the relationship between pressure P and apparent pressure P. s A table showing the relationships between P and P. s =P / Z.

[0031] Step 3: Conduct a stable bottom hole flowing pressure test under constant production conditions at three or more different production stages of the coalbed methane well, and record the daily gas production q of the coalbed methane well at each stable flowing pressure test time. sc(1) q sc(2) ,…,q sc(n) Bottom-hole flowing pressure P wf(1) ,P wf(2) ,…,P wf(n) and cumulative gas production GP (1) ,GP (2) ,…,GP (n) ;

[0032] Step 4 sets the initial iterative assumption value G0 for the dynamic reserves of the gas well, and combines it with the cumulative gas production GP at each stable flowing pressure test time in different production stages. (1) ,GP (2) ,…,GP (n) The formation apparent pressure P at each steady-state flow pressure test time was determined using the apparent pressure material balance equation. Rs(1) ,P Rs(2) ,…,P Rs(n) Then, based on pressure P and apparent pressure P s (P s The relationship table between P and Z is used to calculate and determine the corresponding formation pressure P based on the material balance equation using interpolation or function fitting methods. Rm(1) P Rm(2) , ..., P Rm(n) ;

[0033] Step 5: Based on the formation pressure P at each steady-state pressure test moment determined by the mass balance equation, Rm(1) P Rm(2) , ..., P Rm(n) Bottom-hole flowing pressure P wf(1) P wf(2) , ..., P wf(n) and output q sc(1) q sc(2) ,…,q sc(n) ,make x (i) =q sc(i) If i = 1, 2, ..., n, then a series of observation points (y) are obtained. (i) ,x (i) By performing linear fitting on the observation point data, the binomial productivity equation for coalbed methane wells can be determined. In the equation, coefficients A and B are used, where A is equal to the intercept of the fitted linear equation and B is equal to the slope of the fitted linear equation.

[0034] Step 6 is based on the coalbed methane well productivity equation determined in Step 5. Combined with the bottom hole flowing pressure P obtained in step 3 at different steady-state flowing pressure test times wf(1) ,P wf(2) ,…,P wf(n) and daily gas production q sc(1) q sc(2) ,…,q sc(n) ,use Determine the formation pressure P corresponding to different steady-state flow pressure test times. Rp(1) ,P Rp(2) ,…,P Rp(n) That is, the formation pressure P obtained based on the productivity equation. Rp(1) ,P Rp(2) , ..., P Rp(n) ;

[0035] Step 7: The formation pressure P obtained based on the mass balance equation at different steady-state pressure test times. Rm(1) P Rm(2) , ..., P Rm(n) and formation pressure P obtained based on gas well productivity equation Rp(1) ,P Rp(2) ,…,P Rp(n) An error check is performed. If the error between the formation pressures calculated by the two methods does not meet the preset accuracy requirements, steps 4-6 are repeated to continue iteratively solving until the preset accuracy is met. The production capacity equation determined when the accuracy requirements are met is the production capacity equation of the coalbed methane well. Substituting the formation pressure and bottom hole flowing pressure values ​​into the production capacity equation of the coalbed methane well and solving it, the production capacity of the coalbed methane well under the corresponding formation pressure and bottom hole flowing pressure conditions can be obtained.

[0036] Explanation of symbol meanings:

[0037] P Ri Original formation pressure, MPa; P wf Bottom hole flowing pressure, MPa; q sc Gas well production, 10,000 cubic meters / day; P: Pressure, MPa; Z: Gas deviation factor, dimensionless, decimal; P s (P s =P / Z): Apparent pressure, MPa; q sc(i) : Daily gas production corresponding to the i-th stable flow pressure test point, 10,000 cubic meters / day; P wf(i) : based on output q sc(i) The stable bottom hole flowing pressure corresponding to fixed production; GP (i) The cumulative gas production corresponding to the i-th stable flow pressure test point, in ten thousand cubic meters; P Rm(i) : Formation pressure corresponding to the i-th steady-state flow pressure test point, calculated based on the mass balance equation; P Rp(i): Formation pressure corresponding to the i-th steady-state pressure test point obtained based on the productivity equation; i is the steady-state pressure test point number, i = 1, 2, ..., n; P R G0: Formation pressure, MPa; G0: Dynamic reserves of coalbed methane well, 10,000 cubic meters;

[0038] Furthermore, based on the apparent pressure-based material balance equation used in step 4, the following is... The specific derivation process is as follows:

[0039] The expression for the generalized mass balance equation is:

[0040]

[0041] In the formula, P R Z represents the formation pressure, and P represents the formation pressure. R The corresponding gas deviation factor, G P G0 represents cumulative gas production, and P represents dynamic reserves. Ri Z represents the original formation pressure. i The original formation pressure P Ri Deviation factor under certain conditions.

[0042] Formation pressure P R The ratio of its corresponding deviation factor Z is defined as the apparent pressure P. Rs Original formation pressure P Ri Its corresponding deviation factor Z i The ratio is defined as the apparent pressure P. Rsi Right now

[0043]

[0044]

[0045] Then, from equations (2), (3), and (4), we can obtain the mass balance equation based on apparent pressure:

[0046]

[0047] Equation (5) is the material balance equation based on apparent pressure used in this invention. If the original formation pressure P has been determined... Ri visual pressure P Rsi Cumulative production G of gas wells P Given the dynamic reserves G0, the corresponding formation pressure P can be determined using equation (5). R visual pressure P Rs Then, based on the relationship table between pressure and apparent pressure, and the apparent pressure of the formation, the corresponding formation pressure can be determined using interpolation or function fitting methods.

[0048] Furthermore, based on the determination of constant coefficients in the coalbed methane well productivity equation in step 5, the details are as follows:

[0049] The binomial productivity equation for a gas well is:

[0050]

[0051] Divide both sides of equation (6) by q. sc We can obtain:

[0052]

[0053] Since the coefficients A and B in the binomial productivity equation are constants related to formation characteristics, the coefficients A and B in the gas well productivity equation can be obtained by linear fitting based on the bottom hole flowing pressure and corresponding formation pressure under different production conditions.

[0054] make

[0055] x (i) =q sc(i) (9)

[0056] In the formula, i is the steady-state pressure test point number, i = 1, 2, ..., n; P R(i) The formation pressure corresponding to the i-th steady-state flow pressure test point; P wf(i) To produce q sc(i) The stable bottom hole flowing pressure corresponding to fixed-production; q sc(i) Let be the daily gas production corresponding to the i-th stable flow pressure test point. Based on the daily gas production q of the coalbed methane well at each stable flow pressure test moment during different production periods. sc(1) q sc(2) ,…,q sc(n) and bottom hole flowing pressure P wf(1) P wf(2) , ..., P wf(n) A series of observation points (y) can be obtained from equations (8) and (9). (i) ,x (i) ); Linear fitting is performed on the above observation point data. According to equation (7), A is equal to the intercept of the fitted linear equation, and B is equal to the slope of the fitted linear equation.

[0057] In this embodiment, basic data of coalbed methane wells are acquired, and a relationship table between pressure and coalbed methane deviation factor is determined based on coalbed methane PVT experimental data. Furthermore, a relationship table between pressure and apparent pressure (apparent pressure equals pressure divided by the deviation factor) is further determined. Stable bottomhole flowing pressure tests are conducted under constant production conditions at three or more different production stages of the coalbed methane well, recording the daily gas production, bottomhole flowing pressure, and cumulative gas production at each stable flowing pressure test moment. Initial iterative assumptions for the dynamic reserves of the gas well are given. Combined with the cumulative gas production at each stable flowing pressure test moment in different production stages, the formation pressure corresponding to each stable flowing pressure test moment is determined using the material balance equation. Based on the formation pressure corresponding to each stable flowing pressure test moment... The production capacity equation coefficients of a coalbed methane well are determined by considering the pressure, bottom hole flowing pressure, and production rate. Using this determined production capacity equation, and combining it with the bottom hole flowing pressure and daily gas production at different stable flowing pressure test times, the formation pressure at each test time is determined. The formation pressures calculated using the material balance equation and the well production capacity equation at different stable flowing pressure test times are checked for errors. If the error between the two methods does not meet the accuracy requirements, the solution is iterated until the accuracy is met. The production capacity equation determined when the accuracy requirements are met is the production capacity equation for the coalbed methane well. Substituting the formation pressure and bottom hole flowing pressure values ​​into this production capacity equation and solving it yields the coalbed methane well production capacity under the corresponding formation pressure and bottom hole flowing pressure conditions. This invention effectively overcomes the shortcomings of traditional well testing methods that require shutting in the well to test formation pressure, and avoids the problem that existing methods for determining production capacity equations without shutting in the well cannot meet the applicable conditions. It fills the gap in "determining coalbed methane well production capacity without shutting in the well." Furthermore, the method is simple, highly operable, effective, and practical, possessing significant value for widespread application.

[0058] Furthermore, the technical solutions of the present invention will be illustrated below with specific examples, but the scope of protection of the present invention is not limited thereto.

[0059] Verification example:

[0060] A coalbed methane well has a vertical depth of 2880m in the middle of the formation, an original formation pressure of 28MPa, and a formation temperature of 81.3℃.

[0061] The method for determining the non-shutdown well production capacity equation of coalbed methane wells according to this embodiment:

[0062] (1) The basic data of the target coalbed methane well collected are as follows: original formation pressure P Ri =28MPa. The relationship between the deviation factor in the PVT parameters and the pressure is shown in Table 1.

[0063] Table 1. Relationship between pressure, deviation factor, and visual pressure.

[0064]

[0065] (2) Based on the experimental data on the relationship between coalbed methane pressure and deviation factor obtained in step (1), the pressure P in the table can be divided by the corresponding deviation factor Z to obtain the pressure P and apparent pressure P. s (P s The relationship between P and Z (see Table 1) is based on the pressure P and apparent pressure P. s (P s The relationship data between P and Z was used for function fitting (see...). Figure 2 The functional relationship between the two is Ps = 1.127P + 0.1596.

[0066] (3) During the production period, the well used three different production rates q in three different production stages. sc(1) =8.3 cubic meters / day, q sc(2) =75,000 cubic meters / day, q sc(3) =72,000 cubic meters / day for stable production, the stable bottom hole flowing pressure values ​​under the three production conditions are P wf(1) =8.8MPa,P wf(2) =8.7MPa,P wf(3) =7.1MPa; the cumulative gas production at the three steady-state pressure test times are respectively GP (1) =1,735,700 cubic meters, GP (2) =8,520,700 cubic meters, GP (3) =11,992,100 cubic meters.

[0067] (4) Using the functional relationship between the pressure P and apparent pressure Ps obtained in step (2), Ps = 1.127P + 0.1596, the original formation pressure P is determined. Ri =28MPa corresponds to the apparent pressure P Rsi =31.7156MPa; using G0 (iter+1) =G0 (iter) The dynamic reserve iteration mode is *(1+0.021), meaning the dynamic reserve assumption value at the (iter+1)th iteration is 1.021 times the dynamic reserve assumption value at the iterth iteration. Simultaneously, the initial iteration assumption value G0 for the gas well's dynamic reserves is set to 30 million cubic meters. When iterating to the 46th iteration, the iteration assumption value for dynamic reserves is G0 = 78,037,867 million cubic meters. This is combined with the cumulative gas production GP at each stable flow pressure test time during different production stages. (1) =1,735,700 cubic meters, GP (2) =8,520,700 cubic meters, GP (3) =11,992,100 cubic meters, using a material balance equation based on apparent pressure. Determine the formation apparent pressure P at each steady-state flow pressure test time. Rs(1)=31.0102MPa, P Rs(2) =28.2527MPa, P Rs(3) =26.8419MPa; then, by using the functional relationship between the pressure P and apparent pressure Ps obtained in step (2) Ps = 1.127P + 0.1596, the corresponding formation pressure P based on the material balance equation can be determined. Rm(1) =27.3741MPa, P Rm(2) =24.9273MPa, P Rm(3) =23.6755MPa;

[0068] (5) Based on the formation pressure P corresponding to each steady-state pressure test time based on the mass balance equation. Rm(1) =27.3741MPa, P Rm(2) =24.9273MPa, P Rm(3) =23.6755MPa, bottom hole flowing pressure P wf(1) =8.8MPa, P wf(2) =8.7MPa, P wf(3) =7.1MPa and output q sc(1) =8.3 cubic meters / day, q sc(2) =75,000 cubic meters / day, q sc(3) = 72,000 cubic meters / day, making x (i) =q sc(i) If i = 1, 2, 3, then a series of observation points (y) are obtained. (i) ,x (i) (See Table 2); Perform linear fitting on the observation point data (see...) Figure 3 Then the binomial productivity equation for coalbed methane wells can be determined. The coefficients A = 2.7698 and B = 9.4022 in the equation.

[0069] Table 2 Data table for constructing observation points

[0070]

[0071] (6) Based on the coalbed methane well productivity equation determined in step (5) Combined with the bottom hole flowing pressure P at different steady-state flowing pressure test times wf(1) =8.8MPa, P wf(2) =8.7MPa, P wf(3) =7.1MPa and daily gas production q sc(1) =8.3 cubic meters / day, q sc(2) =75,000 cubic meters / day, q sc(3) =72,000 cubic meters / day, using Determine the formation pressure P corresponding to different steady-state flowing pressure test times, obtained based on the gas well productivity equation. Rp(1) =27.3523MPa, P Rp(2) =25.0067MPa, P Rp(3) =23.6170 MPa;

[0072] (7) For different steady-flow pressure test times, the formation pressure P obtained in step (4) based on the material balance equation is used. Rm(1) =27.3741MPa, P Rm(2) =24.9273MPa, P Rm(3) =23.6755 MPa and the formation pressure P obtained in step (6) based on the gas well productivity equation Rp(1) =27.3523MPa, P Rp(2) =25.0067MPa, P Rp(3) =23.6170MPa was used for error verification, and the relative error between the two was expressed by the formula Err(i) = abs(P Rm(i) -P Rp(i) ) / P Rm(i) The calculations show that the relative errors between the two formation pressures corresponding to the three stable flowing pressure test points are Err(1) = 0.000797, Err(2) = 0.003187, and Err(3) = 0.002471, respectively. Clearly, the relative errors between the two are all less than 0.5%, meeting the accuracy requirements for mine applications. In this iterative solution that meets the accuracy requirements, the obtained gas well productivity equation coefficients are A = 2.7698 and B = 9.4022. Therefore, the binomial productivity equation for the gas well in this embodiment is... When the ground pressure P R =21MPa, P wf When the pressure is 7 MPa, the gas well productivity equation is: Solving this production capacity equation yields q. sc = 63,113 cubic meters / day; therefore, when the formation pressure is 21 MPa and the bottom hole flowing pressure is 7 MPa, the production capacity of this gas well is 63,113 cubic meters / day.

[0073] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes made without departing from the present invention should be considered as equivalent substitutions and are included within the protection scope of the present invention.

Claims

1. A method for determining the production capacity of a coalbed methane well without shutting it in, characterized in that, The steps of the method are as follows: Step 1: Collect basic data of the target coalbed methane well, including PVT experimental data of coalbed methane and the original formation pressure P. Ri Bottom-hole flowing pressure data P of coalbed methane wells during production process wf and daily production data q sc ; Step 2: Based on the coalbed methane PVT experimental data obtained in Step 1, determine the relationship table between pressure P and coalbed methane deviation factor Z, and further determine the relationship between pressure P and apparent pressure P. s A table showing the relationships between P and P. s =P / Z; Step 3: Conduct a stable bottom hole flowing pressure test under constant production conditions at each of the three or more different production stages of the coalbed methane well, and record the daily gas production q of the coalbed methane well at each stable flowing pressure test time. sc(1) q sc(2) ,…,q sc(n) Bottom-hole flowing pressure P wf(1) ,P wf(2) ,…,P wf(n) and cumulative gas production GP (1) GP (2) ,…,GP (n) ; Step 4: Set the initial iterative assumption value G0 for the dynamic reserves of the gas well, and combine it with the cumulative gas production GP at each stable flow pressure test time in different production stages. (1) ,GP (2) ,…,GP (n) Based on the mass balance equation, the formation pressure P corresponding to each steady-state pressure test moment was determined. Rm(1) P Rm(2) ,…,P Rm(n) ; Step 5: Based on the formation pressure P corresponding to each steady-state pressure test moment determined by the mass balance equation. Rm(1) ,P Rm(2) ,…,P Rm(n) Bottom-hole flowing pressure P wf(1) ,P wf(2) , ..., P wf(n) and output q sc(1) q sc(2) ,…,q sc(n) The binomial productivity equation for coalbed methane wells was determined. The coefficients A and B in the formula, where P R For formation pressure, P wf q represents the bottom hole flowing pressure of a coalbed methane well. sc This represents the daily production of coalbed methane wells. Step 6: Based on the coalbed methane well productivity equation determined in Step 5 Combined with the bottom hole flowing pressure P obtained in step 3 at different steady-state flowing pressure test times wf(1) ,P wf(2) , ..., P wf(n) and daily gas production q sc(1) q sc(2) ,…,q sc(n) use Determine the formation pressure P corresponding to different steady-state flow pressure test times. Rp(1) P Rp(2) ,…,P Rp(n) That is, the formation pressure P obtained based on the productivity equation. Rp(1) P Rp(2) , ..., P Rp(n) ; Step 7: Obtain the formation pressure P based on the material balance equation at different steady-state pressure test times. Rm(1) P Rm(2) , ..., P Rm(n) and formation pressure P obtained based on gas well productivity equation Rp(1) P Rp(2) ,…,P Rp(n) An error check is performed. If the error between the formation pressures calculated by the two methods does not meet the preset accuracy requirements, steps 4-6 are repeated to continue iterating until the preset accuracy is met. The production capacity equation determined when the accuracy requirements are met is the production capacity equation of the coalbed methane well. Substituting the formation pressure and bottom hole flowing pressure values ​​into the production capacity equation of the coalbed methane well and solving it yields the production capacity of the coalbed methane well under the corresponding formation pressure and bottom hole flowing pressure conditions.

2. The method for determining coalbed methane well productivity without shutting down the well according to claim 1, characterized in that, The steps for determining the formation pressure at each steady-state pressure test moment in step 4 are as follows: First, the formation apparent pressure P corresponding to each steady-state pressure test moment is determined based on the material balance equation based on apparent pressure. Rs(1) ,P Rs(2) , ..., P Rs(n) Then, based on the pressure P and the apparent pressure P s The relationship table is used to calculate and determine the corresponding formation pressure P using interpolation or function fitting methods. Rm(1) ,P Rm(2) ,…,P Rm(n) .

3. The method for determining coalbed methane well productivity without shutting down the well according to claim 1, characterized in that, The steps for determining the coefficients A and B of the binomial productivity equation for coalbed methane wells in step 5 are as follows: make x (i) =q sc(i) i = 1, 2, ..., n, based on the production rate q corresponding to each stable flowing pressure test time in different production stages of the coalbed methane well. sc(1) q sc(2) ,…,q sc(n) and the corresponding stable bottom hole flowing pressure test data P wf(1) ,P wf(2) ,…,P wf(n) A series of observation points (y) were obtained. (i) ,x (i) ); If a linear fit is performed on the observation point data, then A is equal to the intercept of the fitted line equation, and B is equal to the slope of the fitted line equation.

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