A method for determining the recovery factor of a deep coalbed methane well

Abstract

The application discloses a kind of deep coalbed methane well recovery factor determination methods.The method includes: obtaining the original formation pressure and PVT experimental data of coalbed methane well, establish the corresponding relationship table between pressure and deviation factor;Obtain the isothermal adsorption experimental data for deep coal rock, original adsorbed gas content experimental data and original free gas content experimental data;According to the isothermal adsorption experimental data of coal rock, determine the Langmuir pressure and Langmuir volume;Determine the abandoned formation pressure of coalbed methane well exploitation;Determine the deviation factor corresponding to original formation pressure and the deviation factor corresponding to abandoned formation pressure;Based on the above obtained original formation pressure, original adsorbed gas content and original free gas content, Langmuir pressure, abandoned formation pressure and the deviation factor corresponding to original formation pressure and the deviation factor corresponding to abandoned formation pressure determine the recovery factor of coalbed methane well.The present application method is simple, easy to understand, and has good popularization and use value.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field development research, and specifically relates to a method for determining the recovery rate of deep coalbed methane wells. Background Technology

[0002] In recent years, breakthroughs have been made in deep coalbed methane (CBM) development technology, making it an important energy resource alongside conventional natural gas. Practice shows that deep CBM contains both free gas and adsorbed gas. Currently, methods for predicting CBM recovery rates mainly include analogy, desorption, isothermal adsorption curve methods, and reservoir numerical simulation. Among these, the analogy method is somewhat arbitrary and relatively unreliable, primarily used in the early development stages where basic data is scarce. Desorption and isothermal adsorption curve methods are widely used in shallow CBM development, but these methods can only determine the recovery rate of adsorbed gas and cannot account for the impact of free gas on CBM recovery, thus they are unsuitable for evaluating the recovery rate of deep CBM where both free and adsorbed gas coexist. Reservoir numerical simulation can comprehensively consider the influence of heterogeneous geological characteristics and seepage characteristics of coal seams, but this method requires the collection of large amounts of data, the research process is complex, and its application is difficult. Furthermore, the reliability of the simulation results is greatly affected by the researcher's understanding of the geological conditions of the target area and their experience and technical skill. Therefore, there is an urgent need to propose a new method for determining the recovery rate of coalbed methane wells. Summary of the Invention

[0003] The purpose of this invention is to provide a method for determining the recovery rate of deep coalbed methane wells. This aims to address the problem that existing recovery methods do not consider the influence of the presence of free gas on coalbed methane recovery, making them unsuitable for determining the recovery rate of deep coalbed methane where both free and adsorbed gas coexist.

[0004] To achieve the above objectives, the present invention provides a method for determining the recovery rate of deep coalbed methane wells, the steps of which are as follows:

[0005] Step 1: Collect the original formation pressure P of the coalbed methane well. i By analyzing the data from PVT sampling experiments, we obtained the deviation factors corresponding to different pressures under coalbed methane formation temperature conditions and established a table showing the relationship between pressure and deviation factors.

[0006] Step 2: Obtain isothermal adsorption experimental data for deep coal and rock formations, and the adsorbed gas content G under the original formation pressure and temperature conditions. 0ad Experimental data and free gas content G 0f Experimental data;

[0007] Step 3: Determine the Rankine pressure P based on the isothermal adsorption experimental data of coal and rock. L and Langevin volume V L ;

[0008] Step 4: Determine the formation pressure P in the abandoned coalbed methane well based on the coal seam burial depth. ab ;

[0009] Step 5: Based on the pressure and deviation factor relationship table established in Step 1, obtain the original formation pressure P. i The corresponding deviation factor Z i and abandoned formation pressure P ab The corresponding deviation factor Z ab ;

[0010] Step 6, based on the original formation pressure P obtained in Step 1 i The adsorbed gas content G obtained in step 2 under the original formation pressure and temperature conditions. 0ad With free gas content G 0f The Langmuir pressure P obtained in step 3 L The abandoned formation pressure P obtained in step 4 ab and the original formation pressure P obtained in step 5 i The corresponding deviation factor Z i and abandoned formation pressure P ab The corresponding deviation factor Z ab Based on model Calculate the recovery rate corresponding to coalbed methane development.

[0011] Further, in step 3, the Randolph pressure P is determined. L and Langevin volume V L The steps are as follows:

[0012] make Based on the different pressures P of coalbed methane under formation temperature conditions (1) P (2) ...,P (n) The corresponding adsorption gas volume V g(1) V g(2) ,…,V g(n) A series of observation points (y) were obtained. (i) ,x (i) ); By performing a linear fit on the observation point data, the Langevin volume V L Equal to the reciprocal of the intercept of the fitted linear equation, the Randuin pressure P L It equals the slope of the fitted line equation divided by the intercept of the fitted line equation.

[0013] Furthermore, in step 4, the formation pressure P of the abandoned coalbed methane well is determined based on the coal seam burial depth of the coalbed methane well. ab The steps are as follows:

[0014] The pressure of abandoned formations in coalbed methane wells can be determined using analogy or empirical formulas.

[0015] Further, in step 5, the original formation pressure P is obtained. i The corresponding deviation factor Z i and abandoned formation pressure P ab The corresponding deviation factor Z ab The steps are as follows:

[0016] Based on the relationship table between pressure and deviation factor, the deviation factor Z is obtained using an interpolation method. i Sum of deviation factors Z ab Alternatively, based on the relationship table between pressure and deviation factor, a fitting function relationship Z = f(P) can be established between the deviation factor and pressure, with the deviation factor as the dependent variable and pressure as the independent variable. Then, this function relationship can be used to calculate the relationship with the original formation pressure P. i The corresponding deviation factor Z i =f(P i ) and abandoned formation pressure P ab The corresponding deviation factor Z ab =f(P ab ).

[0017] Beneficial effects:

[0018] (1) Based on PVT experimental data and isothermal adsorption experimental data of coalbed methane, this invention proposes a new method for determining the recovery rate of deep coalbed methane wells. It effectively overcomes the shortcomings of analogy method, desorption method, isothermal adsorption curve method and gas reservoir numerical simulation method. It can consider the influence of free gas and adsorbed gas mining on coalbed methane recovery rate, and can also avoid the application difficulty of gas reservoir numerical simulation. It is simple and convenient to apply, easy to understand and implement, highly operable, effective and practical, and has great value for promotion and use.

[0019] (2) Recovery rate is an essential development indicator for coalbed methane development plan preparation, development benefit evaluation and development feasibility demonstration. Therefore, the determination of recovery rate has very important practical value in the mine. Attached Figure Description

[0020] Figure 1 This is a flowchart of an embodiment of a method for determining the recovery rate of deep coalbed methane wells according to the present invention.

[0021] Figure 2 It is a linear fit plot of the observation point data during the process of determining the Langmuir pressure and Langmuir volume. Detailed Implementation

[0022] Reference Figure 1 This invention provides a flowchart of an embodiment of a method for determining the recovery rate of deep coalbed methane wells. The specific implementation details are as follows:

[0023] Step 1: Collect the original formation pressure P of the coalbed methane well. i By analyzing the data from PVT sampling experiments, we obtained the deviation factors corresponding to different pressures under coalbed methane formation temperature conditions and established a table showing the relationship between pressure and deviation factors.

[0024] Step 2: Obtain isothermal adsorption experimental data for deep coal and rock formations, and the adsorbed gas content G under the original formation pressure and temperature conditions. 0ad Experimental data and free gas content G 0f Experimental data;

[0025] Step 3: Determine the Rankine pressure P based on the isothermal adsorption experimental data of coal and rock. L and Langevin volume V L .

[0026] Specifically, according to the isothermal adsorption equation for coalbed methane:

[0027]

[0028] Taking the reciprocal of both sides of equation (1), we get:

[0029]

[0030] From equation (2), we can obtain:

[0031]

[0032] make

[0033]

[0034] In the formula, i is the data point number of the isothermal adsorption experiment, i = 1, 2, ..., n, V g(i) The adsorbed gas volume m corresponding to the i-th experimental data point 3 / t;P (i) The pressure corresponding to the i-th experimental data point, in MPa; V L The volume is the Langevin volume, m³ / t; P L : Langmuir pressure, MPa.

[0035] Based on isothermal adsorption experimental data, coalbed methane under different pressures P at formation temperature conditions... (1) P (2) ...,P (n) The corresponding adsorbed gas volume V g(1) V g(2) ,…,V g(n) A series of observation points (y) can be obtained from equations (4) and (5). (i) ,x (i)Linear fitting is performed on the observation point data, and according to equation (3), the Langevin volume V L Equal to the reciprocal of the intercept of the fitted linear equation, the Randuin pressure P L It equals the slope of the fitted line equation divided by the intercept of the fitted line equation.

[0036] Step 4: Determine the formation pressure P in the abandoned coalbed methane well based on the coal seam burial depth. ab Specifically, the formation pressure in abandoned coalbed methane wells is determined using either analogy or empirical formulas. Preferably, the Makeke empirical formula P is used. ab =2.149×10 -3 D calculates the abandoned formation pressure of the gas well; where P is... ab : Abandoned formation pressure, MPa; D: Coal seam burial depth, m.

[0037] Step 5: Based on the pressure-deviation factor relationship table established in Step 1, obtain the deviation factor Z using an interpolation method. i Sum of deviation factors Z ab Alternatively, based on the relationship table between pressure and deviation factor, a fitting function relationship Z = f(P) can be established between the deviation factor and pressure, with the deviation factor as the dependent variable and pressure as the independent variable. Then, this function relationship can be used to calculate the relationship with the original formation pressure P. i The corresponding deviation factor Z i =f(P i ) and abandoned formation pressure P ab The corresponding deviation factor Z ab =f(P ab );

[0038] (6) Step 6, based on the original formation pressure P obtained in step 1 i The adsorbed gas content G obtained in step (2) under the original formation pressure and temperature conditions 0ad With free gas content G 0f The Langmuir pressure P obtained in step (3) L The abandoned formation pressure P obtained in step (4) ab and the original formation pressure P obtained in step 5 i The corresponding deviation factor Z i and abandoned formation pressure P ab The corresponding deviation factor Z ab Using the model Calculate the recovery rate corresponding to coalbed methane development.

[0039] Specifically, the process of determining the expression for calculating coalbed methane recovery rate is as follows:

[0040] According to the isothermal adsorption equation of coalbed methane (1), the original formation pressure P can be obtained. i Adsorbed gas volume V under certain conditions gi :

[0041]

[0042] In the abandoned formation pressure P ab The amount of adsorbed gas under the given conditions is Therefore, in the abandoned formation pressure P ab Cumulative production of adsorbed gas G under the conditions pa for:

[0043]

[0044] So the pressure P in the abandoned formation ab The corresponding adsorbed gas recovery rate R a for:

[0045] R a =G pa / V gi (8)

[0046] From equations (6), (7), and (8), we can obtain:

[0047]

[0048] Equation (9) is given when the pressure of the abandoned formation is P. ab A model for calculating the recovery rate of adsorbed gas at that time.

[0049] The mass balance equation for free gas is:

[0050]

[0051] From equation (10), we can obtain the pressure P in the abandoned formation. ab Free gas recovery rate R under the conditions f :

[0052]

[0053] Let the free gas content G under the original formation pressure and temperature conditions be... 0f Then, according to the abandoned formation pressure P ab The corresponding free gas recovery rate R f It can be obtained that the amount of free gas produced at the time of disposal is G. pf for:

[0054] G pf =G 0f *R f (12)

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

[0056]

[0057] Let the adsorbed gas content under the original formation pressure and temperature conditions be G. 0ad Then, according to the abandoned formation pressure P ab The corresponding adsorbed gas recovery rate R a It can be obtained that the amount of adsorbed gas produced at the time of disposal is G. pa for:

[0058] G pa =G 0ad *R a (14)

[0059] From equations (9) and (14), we can obtain

[0060]

[0061] From equations (13) and (15), we can obtain the pressure P in the abandoned formation. ab The total yield G of free gas and adsorbed gas under the corresponding conditions p for:

[0062]

[0063] Then, under the pressure P of the abandoned formation ab The coalbed methane recovery rate R is:

[0064]

[0065] Equation (17) is the abandoned formation pressure P. ab The expression for calculating coalbed methane recovery rate.

[0066] In the formula: P i Original formation pressure, MPa; V gi Original formation pressure P i Adsorbed gas quantity under the given conditions, m 3 / t;P ab P: Formation pressure, MPa; V: Formation pressure, MPa; g Adsorbed gas volume (m) at formation pressure P 3 / t;G pa Cumulative adsorbed gas yield at the time of disposal, m 3 / t;R a The recovery rate of adsorbed gas at the time of disposal, decimal; G pf Cumulative free gas production at the time of disposal, m 3 / t;R f: Free gas recovery rate at the time of abandonment, decimal; z: Gas deviation factor corresponding to formation pressure P, decimal; Z i : Gas deviation factor corresponding to the original formation pressure, decimal; Z ab : Abandoned formation pressure P ab The corresponding gas deviation factor, a decimal; G P Cumulative natural gas production, m 3 G0: Original reserves of natural gas, m 3 G 0f Free gas content under original formation pressure and temperature conditions, m 3 / t;G 0a Adsorbed gas content under original formation pressure and temperature conditions, m 3 / t; R: Abandoned Formation Pressure P ab Coalbed methane recovery rate, decimal; V L The volume is the Langevin volume, m³ / t; P L : Langmuir pressure, MPa.

[0067] In this embodiment, by collecting the original formation pressure and PVT experimental data of coalbed methane wells, a correspondence table between pressure and deviation factors is established; isothermal adsorption experimental data, original adsorbed gas content experimental data, and original free gas content experimental data of deep coal and rock are collected; based on the isothermal adsorption experimental data of coal and rock, the Langmuir pressure and Langmuir volume are determined; the abandoned formation pressure of the coalbed methane well is determined; the deviation factors corresponding to the original formation pressure and the abandoned formation pressure are determined; based on the original formation pressure, original adsorbed gas content, original free gas content, Langmuir pressure, abandoned formation pressure, and the deviation factors corresponding to the original formation pressure and the abandoned formation pressure obtained above, the recovery rate of the coalbed methane well is calculated and determined. This invention is simple, easy to understand, highly operable, effective, and practical, and has great potential for widespread application.

[0068] 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.

[0069] Example 1

[0070] (1) The basic data of the coalbed methane well collected are as follows: original formation pressure P i =28MPa. The relationship between the deviation factor in the PVT parameters and the pressure is shown in Table 1.

[0071] Table 1. Relationship between pressure, deviation factor, and visual pressure.

[0072]

[0073]

[0074] (2) The collected deep coalbed methane isothermal adsorption experimental data are shown in Table 2. The adsorbed gas content G under the original formation pressure and temperature conditions is shown in Table 2. 0ad =18.34m 3 / t and free gas content G 0f =7.66m 3 / t.

[0075] Table 2. Experimental and observational data of isothermal adsorption of deep coalbed methane.

[0076]

[0077] (3) Based on the different pressures P of coalbed methane under formation temperature conditions (1) P (2) ...,P (n) The corresponding adsorption gas volume V g(1) V g(2) ,…,V g(n) ,make A series of observation points (y) were obtained. (i) ,x (i) (See Table 2); Perform linear fitting on the observation point data (see...) Figure 2 If the Langevin volume V is given, then V is the volume of the Langevin volume. L It is equal to the reciprocal of the intercept of the fitted linear equation, that is... Langevin pressure P L It equals the slope of the fitted line equation divided by the intercept of the fitted line equation, i.e.

[0078] (4) Determine the formation pressure in abandoned coalbed methane wells using analogy or empirical formulas; use the Meck empirical formula P ab =2.149×10 -3 D calculates the abandoned formation pressure of the gas well; where P is... ab D: Abandoned formation pressure, MPa; D: Coal seam depth, m; The coalbed methane well is approximately 2850 m deep, therefore the abandoned formation pressure P is... ab =2.149×10 -3 D = 2.149 × 10 -3 ×2850=6.1246MPa.

[0079] (5) Based on the pressure and deviation factor relationship table established in step (1), the original formation pressure P is obtained by linear interpolation. i =28MPa corresponding to the gas deviation factor Z i =0.8805, the abandoned formation pressure P was obtained using linear interpolation. ab =6.1246MPa corresponds to the gas deviation factor Z ab =0.9035.

[0080] (6) Based on the original formation pressure P obtained in step (1) i =28MPa, the adsorbed gas content G under the original formation pressure and temperature conditions obtained in step (2) 0ad =18.34m 3 / t and free gas content G 0f =7.66m 3 / t, the Langevin pressure P obtained in step (3) L =3.1347 MPa, the abandoned formation pressure P obtained in step (4) ab = 6.1246 MPa and the original formation pressure P obtained in step (5) i The corresponding deviation factor Z i =0.8805 and abandoned formation pressure P ab The corresponding deviation factor Z ab =0.9035, using the model The recovery rate corresponding to coalbed methane development is calculated, i.e.

[0081]

[0082]

[0083] R = 0.4183

[0084] Therefore, the recovery rate of the coalbed methane well in this Example 1 is 41.83%.

[0085] 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 that do not depart from the present invention should be considered equivalent substitutions and are included within the protection scope of the present invention.

Claims

1. A method for determining the recovery rate of deep coalbed methane wells, characterized in that, The steps of the method are as follows: Step 1: Collect the original formation pressure P of the coalbed methane well. i By analyzing the data from PVT sampling experiments, we obtained the deviation factors corresponding to different pressures under coalbed methane formation temperature conditions and established a table showing the relationship between pressure and deviation factors. Step 2: Obtain isothermal adsorption experimental data for deep coal and rock formations, and the adsorbed gas content G under the original formation pressure and temperature conditions. 0ad Experimental data and free gas content G 0f Experimental data; Step 3: Determine the Rankine pressure P based on the isothermal adsorption experimental data of coal and rock. L and Langevin volume V L ; Step 4: Determine the formation pressure P in the abandoned coalbed methane well based on the coal seam burial depth. ab ; Step 5: Based on the pressure and deviation factor relationship table established in Step 1, obtain the original formation pressure P. i The corresponding deviation factor Z i and abandoned formation pressure P ab The corresponding deviation factor Z ab ; Step 6, based on the original formation pressure P obtained in Step 1 i The adsorbed gas content G obtained in step 2 under the original formation pressure and temperature conditions. 0ad With free gas content G 0f The Langmuir pressure P obtained in step 3 L The abandoned formation pressure P obtained in step 4 ab and the original formation pressure P obtained in step 5 i The corresponding deviation factor Z i and abandoned formation pressure P ab The corresponding deviation factor Z ab Based on model Calculate the recovery rate corresponding to coalbed methane development.

2. The method for determining the recovery rate of deep coalbed methane wells according to claim 1, characterized in that, In step 3, the Randolph pressure P is determined. L and Langevin volume V L The steps are as follows: make Based on the different pressures P of coalbed methane under formation temperature conditions (1) P (2) ...,P (n) The corresponding adsorption gas volume V g(1) V g(2) ,…,V g(n) A series of observation points (y) were obtained. (i) ,x (i) ); By performing a linear fit on the observation point data, the Langevin volume V L Equal to the reciprocal of the intercept of the fitted linear equation, the Randuin pressure P L It equals the slope of the fitted line equation divided by the intercept of the fitted line equation.

3. The method for determining the recovery rate of deep coalbed methane wells according to claim 1, characterized in that, In step 4, the formation pressure P of the abandoned coalbed methane well is determined based on the coal seam burial depth. ab The steps are as follows: The pressure of abandoned formations in coalbed methane wells can be determined by analogy or empirical formulas.

4. The method for determining the recovery rate of deep coalbed methane wells according to claim 1, characterized in that, In step 5, the original formation pressure P is obtained. i The corresponding deviation factor Z i and abandoned formation pressure P ab The corresponding deviation factor Z ab The steps are as follows: Based on the relationship table between pressure and deviation factor, an interpolation method is used to obtain the original formation pressure P. i The corresponding deviation factor Z i and the pressure P of abandoned formation ab The corresponding deviation factor Z ab ; Alternatively, based on the relationship table between pressure and deviation factor, a fitting function relationship Z = f(P) can be established between the deviation factor and pressure, with the deviation factor as the dependent variable and pressure as the independent variable. Then, this function relationship can be used to calculate the original formation pressure P. i The corresponding deviation factor Z i =f(P i ) and the pressure P of abandoned formations ab The corresponding deviation factor Z ab =f(P ab ).

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