Method for determining productivity of deep coalbed methane well considering fracturing fluid and water production effects

Abstract

The application discloses a method for determining the productivity of a deep coalbed methane well by considering the influence of fracturing fluid and water production, and the method comprises the following steps: determining a relationship table of pressure and a coalbed methane deviation factor and relevant process parameters according to coalbed methane PVT experimental data; recording the daily gas production of the coalbed methane well, the bottom hole flowing pressure, the cumulative gas production and the cumulative water production at each stable flow pressure testing time; determining the formation pressure corresponding to each stable flow pressure testing time by using a coalbed methane material balance equation considering the influence of fracturing fluid and water production; determining the productivity equation coefficient of the coalbed methane well according to the formation pressure corresponding to each stable flow pressure testing time, the bottom hole flowing pressure and the daily gas production, and then obtaining the productivity equation of the coalbed methane well; and substituting the formation pressure and the bottom hole flowing pressure into the productivity equation and solving to obtain the corresponding coalbed methane well productivity. Compared with the method without considering the influence of fracturing fluid and water production, the coalbed methane well production evaluation and prediction result obtained by using the method is more consistent with the actual production data of a mine.

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 deep coalbed methane wells considering the influence of fracturing fluid and water production. 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 operational procedures. Deep coalbed methane wells often involve very large-scale fracturing operations, typically using over 30,000 cubic meters of fracturing fluid, sometimes exceeding 50,000 cubic meters. Furthermore, significant amounts of water are produced during extraction. Current technologies do not disclose how to account for the impact of fracturing fluid and water production on deep coalbed methane production capacity. Therefore, there is an urgent need to develop a method for determining the production capacity of deep coalbed methane wells that considers the influence of fracturing fluid and water production. Summary of the Invention

[0003] The purpose of this invention is to provide a method for determining the production capacity of deep coalbed methane wells that takes into account the effects of fracturing fluid and water production, thereby solving the technical problem that existing methods for determining the production capacity of deep coalbed methane wells cannot take into account the effects of fracturing fluid and water production.

[0004] To achieve the above objectives, the present invention provides a method for determining the productivity of deep coalbed methane wells considering the effects of fracturing fluid and water production. The steps of the method are as follows:

[0005] Step 1: Collect basic data of the target coalbed methane well, including PVT experimental data of coalbed methane and original formation pressure. Formation temperature Standard pressure conditions Standard temperature conditions The amount of fracturing fluid used during the fracturing process Langevin pressure The original free gas content measured in the laboratory and the original adsorbed gas content Bottom-hole flowing pressure data of coalbed methane wells during production process Daily gas production data ;

[0006] Step 2: Based on the coalbed methane PVT experimental data obtained in Step 1, determine the pressure. Deviation factor with coalbed methane Based on the relationship table, the relationship with the original formation pressure is determined. Corresponding coalbed methane deviation factor And combined with the original formation pressure obtained in step 1 Formation temperature Standard pressure conditions and standard temperature conditions Parameters, calculation process parameters ,in, ;

[0007] 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 of the coalbed methane well at each stable flowing pressure test time. Bottom hole flowing pressure Cumulative gas production and cumulative water production ;

[0008] 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 at each stable flowing pressure test time in different production stages. and cumulative water production Based on the coalbed methane material balance equation that takes into account the effects of fracturing fluid and water production, the formation pressure corresponding to each steady-state pressure test moment was determined. ;

[0009] Step 5: Based on the formation pressure corresponding to each steady-state pressure test moment obtained in Step 4. Bottom hole flowing pressure and output The binomial productivity equation for coalbed methane wells was determined. The coefficients A and B in the formula are... For formation pressure, This refers to the bottom-hole flowing pressure of a coalbed methane well. This represents the daily production of coalbed methane wells.

[0010] Step 6: Based on the binomial productivity equation of the coalbed methane well determined in Step 5. Combined with the bottom hole flowing pressures obtained in step 3 at different stable flowing pressure test times and daily gas production ,use Determine the formation pressure corresponding to different steady-state flow pressure test times. That is, the formation pressure obtained based on the productivity equation. ;

[0011] Step 7: Analyze the formation pressure obtained from the mass balance equation at different steady-state pressure test times. and formation pressure obtained based on gas well productivity equation 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.

[0012] Furthermore, the steps in step 4 for determining the formation pressure corresponding to each steady-state pressure test moment are as follows:

[0013] First, based on the original formation pressure Combined with pressure Deviation factor with coalbed methane The relationship table determines the deviation factor under the original stratigraphic conditions. ;

[0014] Then, the original formation pressure Deviation factor under original formation pressure Formation temperature Dynamic reserves G0 and Random pressure of coalbed methane wells Original free gas content Original adsorbed gas content Fracturing fluid usage in gas wells and the cumulative gas production at the corresponding test time Cumulative water production and the process parameters obtained in step 2 Substituting into the coalbed methane material balance equation that considers the effects of fracturing fluid and water production... This yields a nonlinear equation related to the formation pressure P;

[0015] Finally, by using an iterative method to solve the nonlinear equation, the formation pressure corresponding to the cumulative gas production (GP) at each test time can be obtained.

[0016] Furthermore, the coalbed methane material balance equation considering the effects of fracturing fluid and water production in step 4 is as follows: ,in, .

[0017] Beneficial effects

[0018] (1) The method of the present invention can effectively consider the influence of fracturing fluid and water production on the determination of coalbed methane production capacity equation. The coalbed methane production capacity equation determined by the method of the present invention is more consistent with the actual mine.

[0019] (2) 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

[0020] Figure 1 This is a schematic flowchart of an embodiment of the method for determining the production capacity of deep coalbed methane wells, taking into account the effects of fracturing fluid and water production according to the present invention.

[0021] Figure 2 It is a linear fit graph of the observation points. Detailed Implementation Reference Figure 1 This invention provides a flowchart illustrating an embodiment of a method for determining the productivity of deep coalbed methane wells, taking into account the effects of fracturing fluid and water production. The specific implementation method is as follows:

[0022] Step 1: Collect basic data of the target coalbed methane well. The basic data includes PVT experimental data of coalbed methane and original formation pressure. Formation temperature Standard pressure conditions Standard temperature conditions Fracturing fluid usage during fracturing process Langevin pressure The original free gas content measured in the laboratory and the original adsorbed gas content Bottom-hole flowing pressure data of coalbed methane wells during production process Daily gas production data .

[0023] Step 2: Based on the coalbed methane PVT experimental data obtained in Step 1, determine the pressure. Deviation factor with coalbed methane A relationship table was used to determine the relationship with the original formation pressure. Corresponding coalbed methane deviation factor And combined with the original formation pressure obtained in step 1 Formation temperature Standard pressure conditions and standard temperature conditions Parameters, calculation process parameters , here .

[0024] 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 of the coalbed methane well at each stable flowing pressure test time. , ,…, Bottom hole flowing pressure Cumulative gas production and cumulative water production .

[0025] Step 4: First, set the initial iterative assumption value G0 for the dynamic reserves of the gas well, and then base it on the original formation pressure. Combined with pressure Deviation factor with coalbed methane The relationship table determines the deviation factor under the original stratigraphic conditions. ;

[0026] Then, the original formation pressure Deviation factor under original formation pressure Formation temperature Dynamic reserves G0 and Random pressure of coalbed methane wells Original free gas content Original adsorbed gas content Fracturing fluid usage in gas wells and the cumulative gas production at the corresponding test time Cumulative water production and the process parameters obtained in step 2 Substituting into the coalbed methane material balance equation that considers the effects of fracturing fluid and water production... This yields a nonlinear equation related to the formation pressure P;

[0027] Finally, by using an iterative method to solve the nonlinear equation, the formation pressure corresponding to the cumulative gas production (GP) at each test time can be obtained.

[0028] Step 5: Determine the formation pressure at each steady-state pressure test moment based on the mass balance equation. Bottom hole flowing pressure and output ,make This yields a series of observation points. By performing linear fitting on the observation point data, the binomial productivity equation of the coalbed methane well can be determined. In the equation, coefficients A and B are used. A is equal to the intercept of the fitted linear equation, and B is equal to the slope of the fitted linear equation.

[0029] Step 6: Based on the binomial productivity equation of the coalbed methane well determined in Step 5. Combined with the bottom hole flowing pressures obtained in step 3 at different stable flowing pressure test times and daily gas production ,use Determine the formation pressure corresponding to different steady-state flow pressure test times. That is, the formation pressure obtained based on the productivity equation. .

[0030] Step 7: Analyze the formation pressure obtained from the mass balance equation at different steady-state pressure test times. and formation pressure obtained based on gas well productivity equation 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.

[0031] Explanation of symbol meanings:

[0032] Original formation pressure, MPa; Bottom hole flowing pressure, MPa; Gas well production, 10,000 cubic meters / day; Pressure, MPa; Gas deviation factor, dimensionless, decimal; : Approximate pressure, MPa; : No. The daily gas production corresponding to each stable flow pressure test point is 10,000 cubic meters / day. Based on output The stable bottom-hole flowing pressure corresponding to a fixed production rate; No. The cumulative gas production corresponding to each stable flow pressure test point, in ten thousand cubic meters; The first result obtained based on the mass balance equation Formation pressure corresponding to each stable flow pressure test point; The first result obtained based on the production capacity equation Formation pressure corresponding to each stable flow pressure test point; Stable flow pressure test point numbering ; Formation pressure, MPa; Dynamic reserves of coalbed methane wells, in tens of thousands of cubic meters; Formation temperature, K; Standard pressure, MPa; Standard temperature, K; : Volume coefficient of water, decimal; Fracturing fluid usage, in ten thousand cubic meters; Cumulative water production, in ten thousand cubic meters; Free gas content under original formation pressure and temperature conditions, m3 / t; Adsorbed gas content under original formation pressure and temperature conditions. Wanfang; Process parameters, decimals, dimensionless. ;

[0033] Furthermore, based on the coalbed methane material balance equation considering the effects of fracturing fluid and water production used in step 4, the following equation is derived: The specific derivation process is as follows:

[0034] Based on the isothermal adsorption equation for coalbed methane, the original formation pressure can be obtained. Adsorbed gas content per unit mass of coal and rock under the following conditions :

[0035] (1)

[0036] Under any formation pressure P, the adsorbed gas content per unit mass of coal and rock is: Therefore, under formation pressure Cumulative production of adsorbed gas per unit mass of coal rock for:

[0037] (2)

[0038] So, the formation pressure Corresponding degree of adsorbed gas extraction for:

[0039] (3)

[0040] From equations (1), (2), and (3), we can obtain:

[0041] (4)

[0042] Let the adsorbed gas reserves under the original formation pressure and temperature conditions be: So, according to pressure Corresponding degree of adsorbed gas extraction The cumulative yield of the adsorbed gas can be obtained. for: (5)

[0043] From equations (4) and (5), we can obtain

[0044] (6)

[0045] The amount of fracturing fluid injected into the formation during the fracturing process of coalbed methane wells Converted to stratigraphic volume Subsequently, it is used as the "water intrusion" in water-driven gas reservoirs. Therefore, based on the water drive material balance equation for a gas reservoir under normal pressure, the free gas material balance equation considering the effects of fracturing fluid and produced water can be obtained as follows:

[0046] (7)

[0047] In the formula, (8)

[0048] From equation (7), the yield of free gas is:

[0049] (9)

[0050] From equations (6) and (9), the total output of free gas and adsorbed gas under pressure P can be obtained. for: (10)

[0051] Let the original free gas content in the coal and rock be The original adsorbed gas content was The original reserves of the coalbed methane well were So, what is the free gas reserve under the original formation pressure and temperature conditions? for:

[0052] (11)

[0053] Similarly, the adsorbed gas reserves under the original formation pressure and temperature conditions for:

[0054] (12)

[0055] From equations (10), (11) and (12), we can obtain

[0056] (13)

[0057] Equation (13) is the coalbed methane material balance equation that takes into account the effects of fracturing fluid, water production and adsorbed gas.

[0058] Furthermore, the specific method for determining the constant coefficients A and B in the binomial productivity equation of the coalbed methane well in step 5 is as follows: The binomial productivity equation of the gas well is: (14).

[0059] Divide both sides of equation (14) by We can obtain:

[0060] (15)

[0061] 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.

[0062] make (16)

[0063] (17)

[0064] In the formula, Number the stable flow pressure test points. ; No. Formation pressure corresponding to each stable flow pressure test point; To produce The stable bottom-hole flowing pressure corresponding to a fixed production rate; For the first The daily gas production corresponding to each stable flow pressure test point. Based on the daily gas production of the coalbed methane well at each stable flow pressure test moment during different production periods. , ,…, and bottom hole flowing pressure A series of observation points can be obtained from equations (16) and (17). Linear fitting is performed on the above observation point data. According to equation (15), A is equal to the intercept of the fitted linear equation, and B is equal to the slope of the fitted linear equation.

[0065] This invention collects basic data from coalbed methane (CBM) wells, determines the relationship between pressure and CBM deviation factors, and identifies relevant process parameters based on CBM PVT experimental data. It records the daily gas production, bottom hole flowing pressure, cumulative gas production, and cumulative water production at each stable flowing pressure test moment during three or more different production stages of the CBM well. The invention uses a CBM material balance equation that considers the effects of fracturing fluid and water production to determine the formation pressure corresponding to each stable flowing pressure test moment. Based on the formation pressure, bottom hole flowing pressure, and daily gas production at each stable flowing pressure test moment, the coefficients of the CBM well's production capacity equation are determined, leading to a binomial production capacity equation. Substituting the formation pressure and bottom hole flowing pressure values ​​into this production capacity equation and solving for the corresponding CBM well production capacity yields the results. Compared to methods that do not consider the effects of fracturing fluid and water production, the CBM well production evaluation and prediction results obtained using this invention are more consistent with actual mine production data. Furthermore, the method is simple, highly operable, effective, and practical, possessing significant value for widespread application.

[0066] Furthermore, the technical solution of the present invention will be illustrated by the following specific examples, but the scope of protection of the present invention is not limited thereto.

[0067] Verification example:

[0068] 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℃.

[0069] The method for determining the productivity of deep coalbed methane wells, taking into account the effects of fracturing fluid and water production, as described in this embodiment:

[0070] (1) The original formation pressure of a coalbed methane well Formation temperature Standard pressure conditions Standard temperature The amount of fracturing fluid used during the fracturing process Wanfang, Lan's pressure The original free gas content measured in the laboratory The volume index of water, Bw = 1.01, and the initial adsorbed gas content... .

[0071] (2) The relationship between pressure and deviation factor obtained from PVT sampling experimental data is shown in Table 1; according to this table, the original formation pressure can be obtained. Corresponding coalbed methane deviation factor And combined with the original formation pressure obtained in step 1 Formation temperature Standard pressure conditions and standard temperature conditions Process parameters are calculated from parameters such as [other parameters]. .

[0072] Table 1. Relationship between pressure and deviation factor.

[0073]

[0074] (3) During the production period, the well adopted three different production rates in three different production stages. 10,000 cubic meters / day 10,000 cubic meters / day For stable production at 10,000 cubic meters per day, the stable bottom hole flowing pressure values ​​under three production conditions are as follows: ; Wanfang Wanfang The cumulative gas production at the three stable flow pressure test moments of Wanfang were as follows; the cumulative water production at the three stable flow pressure test moments were as follows. Wanfang Wanfang Wanfang.

[0075] (4) Adopt The dynamic reserve iteration mode, namely the first The dynamic storage assumption value at the next iteration is the first The dynamic reserve assumption value was 1.02 times the initial value of the dynamic reserve assumption value at the time of the 55th iteration. Meanwhile, the initial iterative assumption value G0 for the dynamic reserve of the gas well was set to 30 million cubic meters. Wanfang; will the original formation pressure Deviation factor under original formation pressure Formation temperature Dynamic reserves of coalbed methane wells Wanfang, Lan's pressure Original adsorbed gas content Fracturing fluid usage in gas wells 10,000 cubic meters and the cumulative gas production at the corresponding test time. 10,000 cubic meters, cumulative water production and the process parameters obtained in step 2 Substituting into the coalbed methane material balance equation that considers the effects of fracturing fluid and water production... This yields a nonlinear equation related to the formation pressure P: The formation pressure based on the mass balance equation at the corresponding flow pressure test time was obtained by using an iterative method. Similarly, the formation pressures based on the mass balance equation at the other two steady-state pressure test moments can be obtained using the same method. .

[0076] (5) Formation pressure at each steady-state pressure test time determined based on the mass balance equation. Bottom hole flowing pressure and output 10,000 cubic meters / day 10,000 cubic meters / day 10,000 square meters / day, order This yields a series of observation points. (See Table 2); Linear fitting was performed on the observation point data (see Table 2). Figure 2 Then the binomial productivity equation for coalbed methane wells can be determined. coefficients in and .

[0077] Table 2 Data table for constructing observation points

[0078]

[0079] (6) Based on the binomial productivity equation of coalbed methane wells determined in step 5 Combined with the bottom hole flowing pressure at different steady-state flowing pressure test times and daily gas production 10,000 cubic meters / day 10,000 cubic meters / day 10,000 cubic meters / day, using Determine the formation pressure obtained from the gas well productivity equation at different steady-state pressure test times. .

[0080] (7) For different steady-flow pressure test times, the formation pressure obtained in step (4) based on the material balance equation is used. and the formation pressure obtained in step (6) based on the gas well productivity equation To perform error verification, the relative error between the two is expressed as follows: The calculations show that the relative errors between the two formation pressures corresponding to the three steady-state pressure test points are as follows: Clearly, the relative errors between the two are both less than 5%, meeting the accuracy requirements for mining applications. In this iterative solution that meets the accuracy requirements, the obtained gas well productivity equation coefficients are: and Therefore, the binomial productivity equation for the gas well in this embodiment is: When the stratum pressure At that time, the production capacity equation of the gas well is: Solving this capacity equation yields... 10,000 cubic meters / day; therefore, the ground pressure is When the bottom pressure is 8.71 MPa, the production capacity of the gas well is 70,798 cubic meters per day.

[0081] If the effects of fracturing fluid and water production are not considered, the determined gas well productivity equation is as follows: When the stratum pressure At that time, the production capacity equation of the gas well is: Solving this capacity equation yields... 10,000 cubic meters / day; Since the well was put into production by fracturing, when the bottom hole pressure is around 8.7 MPa, the daily production of the gas well has never exceeded 110,000 cubic meters / day, but has been between 68,000 and 85,000 cubic meters / day. Therefore, the gas well production capacity determined without considering the influence of fracturing fluid and water production differs greatly from the actual production situation. The gas well production capacity determined after considering the influence of fracturing fluid and water production is more consistent with the actual production situation.

[0082] 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 productivity of deep coalbed methane wells considering the effects of fracturing fluid and water production, 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 original formation pressure. Formation temperature Standard pressure conditions Standard temperature conditions Fracturing fluid usage during fracturing process Langevin pressure The original free gas content measured in the laboratory and the original adsorbed gas content Bottom-hole flowing pressure data of coalbed methane wells during production process Daily gas production data ; Step 2: Determine the pressure based on the coalbed methane PVT experimental data obtained in Step 1. Deviation factor with coalbed methane A relationship table was used to determine the relationship with the original formation pressure. Corresponding coalbed methane deviation factor And combined with the original formation pressure obtained in step 1 Formation temperature Standard pressure conditions and standard temperature conditions Calculation process parameters ,in, ; 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 data of the coalbed methane well at each stable flowing pressure test time. , ,…, Bottom hole flowing pressure data Cumulative gas production and cumulative water production ; 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 at each stable flowing pressure test time in different production stages. and cumulative water production Based on the coalbed methane material balance equation that takes into account the effects of fracturing fluid and water production, the formation pressure corresponding to each steady-state pressure test moment was determined. ; Step 5: Based on the formation pressure corresponding to each steady-state pressure test moment obtained in Step 4. Bottom hole flowing pressure data Daily gas production data of coalbed methane wells , ,…, Determine the binomial productivity equation for coalbed methane wells The coefficients A and B in the formula are... For formation pressure, For bottom hole flowing pressure data, This refers to the daily gas production data of coalbed methane wells. Step 6: Based on the binomial productivity equation of the coalbed methane well determined in Step 5. Combined with the bottom hole flowing pressures obtained in step 3 at different stable flowing pressure test times Daily gas production data of coalbed methane wells , ,…, use Determine the formation pressure corresponding to different steady-state flow pressure test times. That is, the formation pressure obtained based on the productivity equation. ; Step 7: Analyze the formation pressure obtained from the mass balance equation at different steady-state pressure test times. and formation pressure obtained based on gas well productivity equation 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. The formation pressure and bottom hole flowing pressure values ​​are substituted into the production capacity equation of the coalbed methane well and solved to obtain the production capacity of the coalbed methane well under the corresponding formation pressure and bottom hole flowing pressure conditions.

2. The method for determining the productivity of deep coalbed methane wells considering the influence of fracturing fluid and water production according to claim 1, characterized in that, Step 4, which determines the formation pressure corresponding to each steady-state pressure test moment, includes the following steps: First, based on the original formation pressure and pressure Deviation factor with coalbed methane The relationship table determines the deviation factor under the original stratigraphic conditions. ; Then, the original formation pressure Deviation factor under original formation pressure Formation temperature Dynamic reserves G0 and Random pressure of coalbed methane wells Original free gas content Original adsorbed gas content Fracturing fluid usage in gas wells and the cumulative gas production at the corresponding test time Cumulative water production and the process parameters obtained in step 2 Substituting the coalbed methane material balance equation that takes into account the effects of fracturing fluid and water production, we obtain a nonlinear equation related to the formation pressure P. Finally, by solving the nonlinear equation using an iterative method, the formation pressure corresponding to the cumulative gas production (GP) at each test time can be obtained.

3. The method for determining the productivity of deep coalbed methane wells considering the influence of fracturing fluid and water production according to claim 1, characterized in that, The coalbed methane material balance equation considering the effects of fracturing fluid and water production in step 4 is as follows: ,in .

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