Evaluation Method of CO2 Phase Change Fracturing Effect Based on Coalbed Methane Adsorption

Abstract

The application discloses a CO2 phase change fracturing effect evaluation method based on coalbed gas adsorption, relates to the technical field of coalbed gas exploration and development, and aims at the CO2 phase change fracturing coal mine area coalbed gas extraction condition, utilizes two parameters of a storage ratio alpha and a coalbed gas saturation beta to evaluate the CO2 phase change fracturing effect condition, effectively combines the CO2 phase change fracturing technology and the coalbed methane adsorption constant, and proposes a new CO2 phase change fracturing effect evaluation method based on coalbed gas adsorption, so that the CO2 phase change fracturing effect can be effectively evaluated. The application can serve the CO2 phase change fracturing effect evaluation of different coal mine area coalbed gas.

Description

Technical Field

[0001] This invention belongs to the field of coalbed methane exploration and development technology, specifically relating to a method for evaluating the effect of CO2 phase change-induced fracturing based on the adsorption properties of coalbed methane. Background Technology

[0002] CO2 phase change fracturing, a commonly used method for regulating low-permeability coal seams, utilizes liquid CO2 at certain pressures and temperatures. Through a heating pipe, liquid CO2 rapidly undergoes a phase change to gaseous CO2, resulting in an instantaneous volume expansion of 600 times, generating powerful fracturing pressure to fracture the coal seam and improve coalbed methane extraction in low-permeability coal seams. However, a mature and reasonable evaluation method for the effectiveness of CO2 phase change fracturing is currently lacking.

[0003] Therefore, this invention proposes a method for evaluating the effect of CO2 phase change fracturing on coalbed methane based on its adsorption properties, providing methodological support for evaluating the effect of CO2 phase change fracturing on coalbed methane and serving the efficient development of coalbed methane. Summary of the Invention

[0004] The present invention addresses the shortcomings of existing technologies by providing a method for evaluating the CO2 phase change fracturing effect based on the adsorption properties of coalbed methane. This method utilizes methane adsorption testing to ultimately evaluate the CO2 phase change fracturing effect on coalbed methane.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] A method for evaluating the CO2 phase change-induced fracturing effect based on coalbed methane adsorption includes the following steps:

[0007] Step 1: Determine the methane adsorption performance curve of the original coal seam in the coal mining area before CO2 phase transformation fracturing to obtain the methane adsorption constant of the original coal seam before CO2 phase transformation fracturing, mainly including the Langmuir volume V. L1 With Langmuir pressure P L1 ;

[0008] Step 2: Based on the coal seam reservoir pressure P measured on-site in the coal mining area m And the actual content of coalbed methane V m Based on the methane adsorption performance curves of the original coal seams in the coal mining area before CO2 phase change fracturing, the theoretical coalbed methane content V before CO2 phase change fracturing was calculated. t1 And the critical desorption pressure P of coalbed methane cd1 ;

[0009] Step 3: Utilize the critical desorption pressure P of coalbed methane before CO2 phase change fracturing cd1 Theoretical coalbed methane content V t1 The measured coal seam reservoir pressure P mAnd the actual content of coalbed methane V m Calculate the coal seam reserve ratio α1 and coalbed methane saturation β1 before CO2 phase change-induced fracturing, respectively;

[0010] Step 4: Determine the methane adsorption performance curve of the fractured coal seam in the coal mining area after CO2 phase transformation fracturing, and obtain the methane adsorption constant of the coal seam after CO2 phase transformation fracturing, mainly including the Langmuir volume V. L2 With Langmuir pressure P L2 ;

[0011] Step 5: Based on the coal seam reservoir pressure P measured on-site in the coal mining area m And the actual content of coalbed methane V m Based on the methane adsorption performance curve of the coal seam after CO2 phase change fracturing, the theoretical coalbed methane content V after CO2 phase change fracturing was calculated. t2 And the critical desorption pressure P of coalbed methane cd2 ;

[0012] Step Six: Utilize the critical desorption pressure P of the coalbed methane after CO2 phase change fracturing. cd2 Theoretical coalbed methane content V t2 The measured coal seam reservoir pressure P m And the actual content of coalbed methane V m Calculate the coal seam reserve ratio α2 and coalbed methane saturation β2 after CO2 phase change fracturing, respectively;

[0013] Step 7: Evaluate the effect of CO2 phase change fracturing based on the changes in the coal seam's reserve ratio α and coalbed methane saturation β before and after CO2 phase change fracturing.

[0014] To further optimize this invention patent, the following technical solutions may be preferred:

[0015] Preferably, before CO2 phase transformation-induced cracking in step one, the methane adsorption performance curve equation of the original coal seam in the coal mining area is as follows:

[0016]

[0017] Where V is the amount of adsorption at the adsorption equilibrium pressure P; V L1 Langmuir volume of the original coal seam in the coal mining area before CO2 phase transformation fracturing; P L1 Langmuir pressure of the original coal seam in the coal mining area before CO2 phase transformation-induced cracking.

[0018] Preferably, methane adsorption experiments are conducted on the original coal seams in the coal mining area to test the adsorption amount V corresponding to different adsorption equilibrium pressures P. The Langmuir volume V of the original coal seams in the coal mining area before CO2 phase transformation-induced cracking is obtained by fitting the above equation. L1With Langmuir pressure P L1 .

[0019] Preferably, the theoretical coalbed methane content V before CO2 phase change fracturing in step two is... t1 And the critical desorption pressure P of coalbed methane cd1 The calculation is performed as follows:

[0020] The coal seam reservoir pressure P measured on-site in the coal mining area m Substituting into the equation from step one, the theoretical coalbed methane content V before CO2 phase transformation cracking is calculated. t1 The calculation process is as follows:

[0021]

[0022] The actual coalbed methane content V measured on-site in the coal mining area m Substituting into the equation from step one, the critical desorption pressure P of the coalbed methane before CO2 phase transformation cracking is calculated. cd1 The calculation process is as follows:

[0023]

[0024]

[0025] Preferably, the coal seam reserve ratio α1 and coalbed methane saturation β1 before CO2 phase change fracturing in step three are achieved as follows:

[0026] The calculation process for the coal seam reserve ratio α1 before CO2 phase transformation fracturing is as follows:

[0027] α1=P cd1 / P m

[0028] The calculation process for coalbed methane saturation β1 before CO2 phase change-induced fracturing is as follows:

[0029] β1=(V m / V t1 )×100%.

[0030] After CO2 phase transformation fracturing in step four, the methane adsorption performance curve equation of the fracturing coal seam in the coal mining area is as follows:

[0031]

[0032] Where V is the amount of adsorption at the adsorption equilibrium pressure P; V L2 P represents the Langmuir volume of the fractured coal seam in the coal mining area after CO2 phase transformation fracturing. L2 Langmuir pressure in the fractured coal seam of the coal mining area after CO2 phase transformation fracturing.

[0033] Using methane adsorption experiments on fractured coal seams in coal mining areas, the adsorption capacity V corresponding to different adsorption equilibrium pressures P was measured. Combined with the above equation, the Langmuir volume V of the fractured coal seam after CO2 phase transition fracturing was obtained. L2 With Langmuir pressure P L2 .

[0034] Preferably, the theoretical coalbed methane content V after CO2 phase change fracturing in step five is... t2 And the critical desorption pressure P of coalbed methane cd2 The calculation is performed as follows:

[0035] Preferably, the coal seam reservoir pressure P measured on-site in the coal mining area is used. m Substituting into the equation from step five, the theoretical coalbed methane content V after CO2 phase transformation cracking is calculated. t2 The calculation process is as follows:

[0036]

[0037] The actual coalbed methane content V measured on-site in the coal mining area m Substituting into the equation in step (5), the critical desorption pressure P of the coalbed methane after CO2 phase transformation cracking is calculated. cd2 The calculation process is as follows:

[0038]

[0039]

[0040] Preferably, the coal seam reserve ratio α2 and coalbed methane saturation β2 after CO2 phase change fracturing in step six are achieved as follows:

[0041] The calculation process for the coal seam reserve ratio α2 after CO2 phase transformation fracturing is as follows:

[0042] α2=P cd2 / P m

[0043] The calculation process for coalbed methane saturation β2 after CO2 phase change fracturing is as follows:

[0044] β2=(V m / V t2 )×100%.

[0045] Preferably, the evaluation of the CO2 phase change fracturing effect in step seven, based on the changes in the coal seam's reserve ratio α and coalbed methane saturation β before and after CO2 phase change fracturing, is analyzed as follows:

[0046] If α2 is greater than α1 and β2 is greater than β1, it indicates that the coal seam reserve ratio increases after CO2 phase change fracturing, and the coalbed methane saturation increases. This indicates that the CO2 phase change fracturing effect is good, which is beneficial to the desorption and migration of coalbed methane and depressurization mining.

[0047] If α2 is less than α1 and β2 is less than β1, it reflects that the coal seam reserve ratio decreases after CO2 phase change fracturing and the coalbed methane saturation decreases. This indicates that the CO2 phase change fracturing effect is poor and is not conducive to the desorption and migration of coalbed methane and depressurization mining.

[0048] The present invention has the following technical effects:

[0049] 1. This invention provides a method for evaluating the effect of CO2 phase change fracturing based on the adsorption properties of coalbed methane. For coalbed methane extraction in CO2 phase change fracturing coal mining areas, the method uses two parameters, the temporary storage ratio α and the coalbed methane saturation β, to evaluate the effect of CO2 phase change fracturing. The evaluation method includes the following steps: (1) Determining the methane adsorption performance of the original coal seam in the coal mining area before CO2 phase change fracturing, and obtaining the methane adsorption constant of the original coal seam before CO2 phase change fracturing, mainly including the Langmuir volume V. L1 With Langmuir pressure P L1 (2) Based on the measured coal seam reservoir pressure P in the coal mining area m And the actual content of coalbed methane V m Based on the methane adsorption properties of the original coal seams in the coal mining area before CO2 phase change fracturing, the theoretical coalbed methane content V before CO2 phase change fracturing was calculated. t1 And the critical desorption pressure P of coalbed methane cd1 (3) Utilizing the critical desorption pressure P of coalbed methane before CO2 phase change-induced fracturing cd1 Theoretical coalbed methane content V t1 The measured coal seam reservoir pressure P m And the actual content of coalbed methane V m Calculate the coal seam reserve ratio α1 and coalbed methane saturation β1 before CO2 phase change fracturing; (4) Determine the methane adsorption performance of the fracturing coal seam in the coal mining area after CO2 phase change fracturing, and obtain the methane adsorption constant of the coal seam after CO2 phase change fracturing, mainly including Langmuir volume V L2 With Langmuir pressure P L2 (5) Based on the measured coal seam reservoir pressure P in the coal mining area m And the actual content of coalbed methane V m Based on the methane adsorption performance of the coal seam after CO2 phase change fracturing, the theoretical coalbed methane content V after CO2 phase change fracturing is calculated. t2 And the critical desorption pressure P of coalbed methane cd2 (6) Utilizing the critical desorption pressure P of coalbed methane after CO2 phase change fracturing cd2Theoretical coalbed methane content V t2 The measured coal seam reservoir pressure P m And the actual content of coalbed methane V m , calculate the coal seam reserve ratio α2 and coalbed methane saturation β2 after CO2 phase change fracturing respectively; (7) evaluate the CO2 phase change fracturing effect based on the changes in the coal seam reserve ratio α and coalbed methane saturation β before and after CO2 phase change fracturing; the present invention effectively combines CO2 phase change fracturing technology with coal seam methane adsorption constant, and proposes a new CO2 phase change fracturing effect evaluation method based on coalbed methane adsorption, which can effectively evaluate the CO2 phase change fracturing effect. The present invention can provide evaluation services for the CO2 phase change fracturing effect of coalbed methane in different coal mining areas, which is conducive to the efficient development of coalbed methane. Attached Figure Description

[0050] Figure 1 This is a flowchart illustrating the steps of this evaluation method;

[0051] Figure 2 The adsorption performance curves of coalbed methane before CO2 phase transformation cracking are shown.

[0052] Figure 3 The adsorption performance curves of coalbed methane after CO2 phase transformation cracking are shown.

[0053] Figure 4 V is the theoretical content of coalbed methane before CO2 phase transformation cracking. t1 and critical desorption pressure P cd1 Solve the diagram;

[0054] Figure 5 V is the theoretical content of coalbed methane after CO2 phase transformation cracking. t2 and critical desorption pressure P cd2 Solve the diagram. Detailed Implementation

[0055] The present invention will be further described below with reference to the accompanying drawings and embodiments, but it should not be construed that the scope of the present invention is limited to the following embodiments. Various substitutions and modifications made based on ordinary technical knowledge and common practice in the art without departing from the above-described technical concept of the present invention should be included within the scope of protection of the present invention.

[0056] A method for evaluating the CO2 phase change-induced fracturing effect based on coalbed methane adsorption includes the following steps:

[0057] Step 1: Determine the methane adsorption performance curve of the original coal seam in the coal mining area before CO2 phase transformation fracturing to obtain the methane adsorption constant of the original coal seam before CO2 phase transformation fracturing, mainly including the Langmuir volume V. L1 With Langmuir pressure P L1The equation for the methane adsorption performance curve of the original coal seam in the coal mining area before CO2 phase transformation cracking in step one is as follows:

[0058]

[0059] Where V is the amount of adsorption at the adsorption equilibrium pressure P; V L1 Langmuir volume of the original coal seam in the coal mining area before CO2 phase transformation fracturing; P L1 The Langmuir pressure of the original coal seam in the coal mining area before CO2 phase transition fracturing was determined. Using methane adsorption experiments on the original coal seam, the adsorption capacity V corresponding to different adsorption equilibrium pressures P was measured. The Langmuir volume V of the original coal seam in the coal mining area before CO2 phase transition fracturing was obtained by fitting the above equation. L1 With Langmuir pressure P L1 .

[0060] Step 2: Based on the coal seam reservoir pressure P measured on-site in the coal mining area m And the actual content of coalbed methane V m Based on the methane adsorption performance curves of the original coal seams in the coal mining area before CO2 phase change fracturing, the theoretical coalbed methane content V before CO2 phase change fracturing was calculated. t1 And the critical desorption pressure P of coalbed methane cd1 ;

[0061] The theoretical coalbed methane content V before CO2 phase change fracturing in step two. t1 And the critical desorption pressure P of coalbed methane cd1 The calculation is performed as follows:

[0062] The coal seam reservoir pressure P measured on-site in the coal mining area m Substituting into the equation from step one, the theoretical coalbed methane content V before CO2 phase transformation cracking is calculated. t1 The calculation process is as follows:

[0063]

[0064] The actual coalbed methane content V measured on-site in the coal mining area m Substituting into the equation from step one, the critical desorption pressure P of the coalbed methane before CO2 phase transformation cracking is calculated. cd1 The calculation process is as follows:

[0065]

[0066]

[0067] Step 3: Utilize the critical desorption pressure P of coalbed methane before CO2 phase change fracturing cd1 Theoretical coalbed methane content Vt1 The measured coal seam reservoir pressure P m And the actual content of coalbed methane V m The coal seam reserve ratio α1 and coalbed methane saturation β1 before CO2 phase change fracturing are calculated respectively. The calculation of the coal seam reserve ratio α1 and coalbed methane saturation β1 before CO2 phase change fracturing in step three is achieved as follows:

[0068] The calculation process for the coal seam reserve ratio α1 before CO2 phase transformation fracturing is as follows:

[0069] α1=P cd1 / P m

[0070] The calculation process for coalbed methane saturation β1 before CO2 phase change-induced fracturing is as follows:

[0071] β1=(V m / V t1 )×100%.

[0072] Step 4: Determine the methane adsorption performance curve of the fractured coal seam in the coal mining area after CO2 phase transformation fracturing, and obtain the methane adsorption constant of the coal seam after CO2 phase transformation fracturing, mainly including the Langmuir volume V. L2 With Langmuir pressure P L2 The following is the equation for the methane adsorption performance curve of the fractured coal seam in the coal mining area after CO2 phase transformation fracturing in step four:

[0073]

[0074] Where V is the amount of adsorption at the adsorption equilibrium pressure P; V L2 P represents the Langmuir volume of the fractured coal seam in the coal mining area after CO2 phase transformation fracturing. L2 Langmuir pressure in the fractured coal seam of the coal mining area after CO2 phase transformation fracturing.

[0075] Using methane adsorption experiments on fractured coal seams in coal mining areas, the adsorption capacity V corresponding to different adsorption equilibrium pressures P was measured. Combined with the above equation, the Langmuir volume V of the fractured coal seam after CO2 phase transition fracturing was obtained. L2 With Langmuir pressure P L2 .

[0076] Step 5: Based on the coal seam reservoir pressure P measured on-site in the coal mining area m And the actual content of coalbed methane V m Based on the methane adsorption performance curve of the coal seam after CO2 phase change fracturing, the theoretical coalbed methane content V after CO2 phase change fracturing was calculated. t2 And the critical desorption pressure P of coalbed methane cd2 ;

[0077] In step five, the theoretical coalbed methane content V after CO2 phase transformation fracturing... t2 And the critical desorption pressure P of coalbed methane cd2 The calculation is performed as follows:

[0078] The coal seam reservoir pressure P measured on-site in the coal mining area m Substituting into the equation from step five, the theoretical coalbed methane content V after CO2 phase transformation cracking is calculated. t2 The calculation process is as follows:

[0079]

[0080] The actual coalbed methane content V measured on-site in the coal mining area m Substituting into the equation in step (5), the critical desorption pressure P of the coalbed methane after CO2 phase transformation cracking is calculated. cd2 The calculation process is as follows:

[0081]

[0082]

[0083] Step Six: Utilize the critical desorption pressure P of the coalbed methane after CO2 phase change fracturing. cd2 Theoretical coalbed methane content V t2 The measured coal seam reservoir pressure P m And the actual content of coalbed methane V m The coal seam reserve ratio α2 and coalbed methane saturation β2 after CO2 phase change fracturing are calculated respectively; the coal seam reserve ratio α2 and coalbed methane saturation β2 after CO2 phase change fracturing in step six are implemented as follows:

[0084] The calculation process for the coal seam reserve ratio α2 after CO2 phase transformation fracturing is as follows:

[0085] α2=P cd2 / P m

[0086] The calculation process for coalbed methane saturation β2 after CO2 phase change fracturing is as follows:

[0087] β2=(V m / V t2 )×100%.

[0088] Step 7: Evaluate the effect of CO2 phase change fracturing based on the changes in the coal seam's reserve ratio α and coalbed methane saturation β before and after CO2 phase change fracturing.

[0089] The evaluation of the CO2 phase change fracturing effect in step seven, based on the changes in the coal seam's reserve ratio α and coalbed methane saturation β before and after CO2 phase change fracturing, is analyzed as follows:

[0090] If α2 is greater than α1 and β2 is greater than β1, it indicates that the coal seam reserve ratio increases after CO2 phase change fracturing, and the coalbed methane saturation increases. This indicates that the CO2 phase change fracturing effect is good, which is beneficial to the desorption and migration of coalbed methane and depressurization mining.

[0091] If α2 is less than α1 and β2 is less than β1, it reflects that the coal seam reserve ratio decreases after CO2 phase change fracturing and the coalbed methane saturation decreases. This indicates that the CO2 phase change fracturing effect is poor and is not conducive to the desorption and migration of coalbed methane and depressurization mining.

[0092] Example 1:

[0093] This invention innovatively proposes a method for evaluating the CO2 phase change fracturing effect based on coalbed methane adsorption. In a coal mining example, the methane adsorption performance curve of the original coal seam before CO2 phase change fracturing was first measured, as shown in the figure. Figure 2 - Methane adsorption performance curves of the original coal seam in a coal mining area example.

[0094] Figure 2 The methane adsorption performance equation of the original coal seam in the example coal mining area is shown in Equation 1.

[0095]

[0096] Using Formula 1, fit Figure 2 The methane adsorption performance curve of the original coal seam in a coal mining area before CO2 phase change-induced cracking is shown in Equation 2.

[0097]

[0098] Before CO2 phase transformation-induced fracturing, the Langmuir volume V of the original coal seam in this coal mining example was obtained through fitting. L1 =15.9331cm 3 / g, Langmuir pressure P L1 =1.2041MPa.

[0099] In this coal mining area example, the coal seam reservoir pressure P was measured on-site. m =1.89MPa and actual coalbed methane content V m =7.87cm 3 / g.

[0100] In this coal mining area example, the coal seam reservoir pressure P measured on-site was used. m Substituting 1.89 MPa into equation (2), the theoretical coalbed methane content V before CO2 phase transformation cracking in this example is calculated.t1 The calculation process is shown in Equation 3:

[0101]

[0102] In this coal mining area example, the actual coalbed methane content V measured on-site in the coal mining area is... m =7.87cm 3 Substituting / g into equation (2), the critical desorption pressure P of the coalbed methane before CO2 phase transformation cracking is calculated. cd1 The calculation process is shown in Equation 4-5:

[0103]

[0104]

[0105] In this coal mining example, the calculation process for the coal seam reserve ratio α1 before CO2 phase transformation fracturing is shown in Equation 6:

[0106] α1=P cd1 / P m =1.1753 / 1.89=0.6218 (6)

[0107] In this coal mining example, the calculation process for the coalbed methane saturation β1 before CO2 phase change-induced fracturing is shown in Equation 7:

[0108] β1=(V m / V t1 )×100%=(7.87 / 9.7326)×100%=80.8622% (7)

[0109] In this coal mining example, the methane adsorption performance curve of the fractured coal seam after CO2 phase change fracturing is shown in [reference needed]. Figure 3 .

[0110] Figure 3 Methane adsorption performance curve of fractured coal seams in coal mining area

[0111] Figure 3 The equation for the methane adsorption performance curve of the fractured coal seam in the coal mining area is shown in Equation 8.

[0112]

[0113] Using formula 8, fit Figure 3 The methane adsorption performance curve of the fractured coal seam in the coal mining area after CO2 phase change fracturing is shown in Equation 9.

[0114]

[0115] After fitting the data, the Langmuir volume V of the fractured coal seam in this coal mining example was obtained. L2=10.4001cm 3 / g, Langmuir pressure P L2 =0.7156MPa.

[0116] In this coal mining area example, the coal seam reservoir pressure P was measured on-site. m =1.89MPa and actual coalbed methane content V m =7.87cm 3 / g.

[0117] In this coal mining area example, the coal seam reservoir pressure P measured on-site was used. m Substituting 1.89 MPa into equation (9), the theoretical coalbed methane content V after CO2 phase transformation cracking in this example is calculated. t2 The calculation process is shown in Equation 10:

[0118]

[0119] In this coal mining area example, the actual coalbed methane content V measured on-site was used. m =7.87cm 3 Substituting / g into equation (9), the critical desorption pressure P of the coalbed methane after CO2 phase transformation cracking is calculated. cd2 The calculation process is shown in Equation 11-12:

[0120]

[0121]

[0122] In this coal mining example, the calculation process for the coal seam reserve ratio α2 after CO2 phase transformation fracturing is shown in Equation 13:

[0123] α2=P cd2 / P m =2.2259 / 1.89=1.1777 (13)

[0124] In this example coal mining area, the calculation process for the coalbed methane saturation β2 after CO2 phase change fracturing is shown in Equation 14:

[0125] β2=(V m / V t2 )×100%=(7.87 / 7.5438)×100%=104.3240% (14)

[0126] This study analyzes the changes in the coal seam's reserve ratio α and coalbed methane saturation β before and after CO2 phase change-induced fracturing in this coal mining area.

[0127] Table 1 shows the relationship between the coal seam's reserve ratio α and coalbed methane saturation β before and after CO2 phase transformation fracturing.

[0128]

[0129] As shown in Table 1, in this coal mining example, after CO2 phase change fracturing, α2 is greater than α1 and β2 is greater than β1, reflecting that the coal seam reserve ratio increases and the coalbed methane saturation increases after CO2 phase change fracturing. The CO2 phase change fracturing effect is good, which is conducive to the desorption and migration of coalbed methane and depressurization mining.

Claims

1. A method for evaluating the CO2 phase change-induced fracturing effect based on coalbed methane adsorption, characterized in that, Includes the following steps: Step 1: Determine the methane adsorption properties of the original coal seam in the coal mining area before CO2 phase transformation fracturing, and obtain the methane adsorption constant of the original coal seam before CO2 phase transformation fracturing, mainly including the Langmuir volume. V L1 With Langmuir pressure P L1 ; Step 2: Based on the coal seam reservoir pressure measured on-site in the coal mining area P m and actual coalbed methane content V m Based on the methane adsorption performance curves of the original coal seams in the coal mining area before CO2 phase change fracturing, the theoretical coalbed methane content before CO2 phase change fracturing was calculated. V t1 Critical desorption pressure of coalbed methane P cd1 ; Step 3: Utilizing the critical desorption pressure of coalbed methane before CO2 phase change fracturing P cd1 Theoretical content of coalbed methane V t1 Coal seam reservoir pressure measured on site P m and actual coalbed methane content V m Calculate the coal seam reserve ratio before CO2 phase transformation-induced fracturing. α 1 and coalbed methane saturation β 1; Step 4: Determine the methane adsorption performance of the fractured coal seam in the coal mining area after CO2 phase transition fracturing, and obtain the methane adsorption constant of the coal seam after CO2 phase transition fracturing, mainly including the Langmuir volume. V L2 With Langmuir pressure P L2 ; Step 5: Based on the coal seam reservoir pressure measured on-site in the coal mining area P m and actual coalbed methane content V m Based on the methane adsorption performance curve of the coal seam after CO2 phase change fracturing, the theoretical content of coalbed methane after CO2 phase change fracturing was calculated. V t2 Critical desorption pressure of coalbed methane P cd2 ; Step Six: Utilizing the critical desorption pressure of coalbed methane after CO2 phase change fracturing P cd2 Theoretical content of coalbed methane V t2 Coal seam reservoir pressure measured on site P m and actual coalbed methane content V m Calculate the coal seam reserve ratio after CO2 phase transformation fracturing. α 2 and coalbed methane saturation β 2; Step 7: Based on the reserve ratio of the coal seam before and after CO2 phase transformation fracturing α 1. α 2 and coalbed methane saturation β 1、 β The changes in 2 were used to evaluate the effect of CO2 phase transformation on cracking.

2. The method for evaluating the CO2 phase change-induced fracturing effect based on coalbed methane adsorption according to claim 1, characterized in that, Before CO2 phase transformation-induced cracking in step one, the methane adsorption curve equation of the original coal seam in the coal mining area is as follows: in, V For adsorption equilibrium pressure P The corresponding adsorption amount; V L1 Langmuir volume of the original coal seam in the coal mining area before CO2 phase transformation-induced fracturing; P L1 Langmuir pressure of the original coal seam in the coal mining area before CO2 phase transformation-induced fracturing; Methane adsorption experiments were conducted using original coal seams in a coal mining area to test different adsorption equilibrium pressures. P Corresponding adsorption amount V By fitting the above equations, the Langmuir volume of the original coal seam in the coal mining area before CO2 phase transformation fracturing was obtained. V L1 With Langmuir pressure P L1 .

3. The method for evaluating the CO2 phase change-induced fracturing effect based on coalbed methane adsorption according to claim 2, characterized in that, The theoretical coalbed methane content before CO2 phase change fracturing in step two. V t1 Critical desorption pressure of coalbed methane P cd1 The calculation is performed as follows: The coal seam reservoir pressure measured on-site in the coal mining area P m Substituting into the equation from step one, the theoretical coalbed methane content before CO2 phase transformation cracking is calculated. V t1 The calculation process is as follows: The actual coalbed methane content measured on-site in the coal mining area V m Substituting into the equation from step one, the critical desorption pressure of coalbed methane before CO2 phase transformation cracking is calculated. P cd1 The calculation process is as follows: 。 4. The method for evaluating the CO2 phase change-induced fracturing effect based on coalbed methane adsorption according to claim 3, characterized in that, The coal seam reserve ratio before CO2 phase transformation fracturing in step three α 1 and coalbed methane saturation β 1. This is how it is achieved: Coal seam reserve ratio before CO2 phase transformation fracturing α The calculation process is as follows: Coalbed methane saturation before CO2 phase change fracturing β The calculation process is as follows: 。 5. The method for evaluating the CO2 phase change-induced fracturing effect based on coalbed methane adsorption according to claim 4, characterized in that, After CO2 phase transformation fracturing in step four, the methane adsorption curve equation for the fracturing coal seam in the coal mining area is as follows: in, V For adsorption equilibrium pressure P The corresponding adsorption amount; V L2 The Langmuir volume of the fractured coal seam in the coal mining area after CO2 phase transformation fracturing; P L2 Langmuir pressure in the fractured coal seam of the coal mining area after CO2 phase transformation fracturing; Methane adsorption experiments were conducted on fractured coal seams in coal mining areas to test different adsorption equilibrium pressures. P Corresponding adsorption amount V By fitting the above equations, the Langmuir volume of the fractured coal seam in the coal mining area after CO2 phase transformation fracturing was obtained. V L2 With Langmuir pressure P L2 .

6. The method for evaluating the CO2 phase change-induced fracturing effect based on coalbed methane adsorption according to claim 5, characterized in that, The theoretical content of coalbed methane after CO2 phase change fracturing in step five. V t2 Critical desorption pressure of coalbed methane P cd2 The calculation is performed as follows: The coal seam reservoir pressure measured on-site in the coal mining area P m Substituting into the equation from step four, the theoretical coalbed methane content after CO2 phase transformation cracking is calculated. V t2 The calculation process is as follows: The actual coalbed methane content measured on-site in the coal mining area V m Substituting into the equation from step four, the critical desorption pressure of coalbed methane after CO2 phase transformation cracking is calculated. P cd2 The calculation process is as follows: 。 7. The method for evaluating the CO2 phase change-induced fracturing effect based on coalbed methane adsorption according to claim 6, characterized in that, The coal seam reserve ratio after CO2 phase transformation fracturing in step six α 2 and coalbed methane saturation β 2. This is how it is implemented: Coal seam reserve ratio after CO2 phase transformation fracturing α 2. The calculation process is as follows: Coalbed methane saturation after CO2 phase change fracturing β 2. The calculation process is as follows: 。 8. The method for evaluating the CO2 phase change-induced fracturing effect based on coalbed methane adsorption according to claim 7, characterized in that, The step seven involves the reserve ratio of the coal seam before and after CO2 phase transformation fracturing. α 1. α 2 and coalbed methane saturation β 1、 β The change in 2 is analyzed to evaluate the effect of CO2 phase transformation on cracking, as follows: like α 2 greater than α 1, and β 2 greater than β 1. It reflects that the coal seam reserve ratio increases and the coalbed methane saturation increases after CO2 phase change fracturing, which reflects the good effect of CO2 phase change fracturing and is conducive to the desorption and migration of coalbed methane and depressurization mining. like α 2 less than α 1, and β 2 less than β 1. This reflects the decrease in the coal seam reserve ratio and coalbed methane saturation after CO2 phase change fracturing, indicating a poor CO2 phase change fracturing effect, which is not conducive to the desorption and migration of coalbed methane and depressurization mining.

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