Comprehensive evaluation method for coal bed gas fracturing effect

Abstract

The invention discloses a coal bed gas fracturing effect comprehensive evaluation method which comprises the following steps: (1) collecting basic parameters, establishing a numerical simulation model, and comparing and fitting a calculation result of the numerical simulation model with on-site fracturing construction data to obtain coal bed gas fracturing fracture network parameters; (2) monitoring flow-back stage data, obtaining liquid production capacity regularized pressure and material balance time, drawing a characteristic curve, obtaining intermediate parameters, and calculating effective volume and fracture forming efficiency through the intermediate parameters; and (3) classifying the fractured wells according to the fracture form coefficient, the fracture forming efficiency and the post-fracturing yield data, and performing field application according to the classification result of the fractured wells. According to the method, a coal bed gas fracturing effect full-chain evaluation system from construction formation to flowback response to production expression is constructed, the one-sidedness and hysteresis of an existing single evaluation method are overcome, and a brand new technical path is provided for achieving accurate and prospective evaluation of the fracturing effect.

Description

Technical Field

[0001] This invention relates to the field of coalbed methane hydraulic fracturing technology, specifically a comprehensive evaluation method for coalbed methane fracturing effect. Background Technology

[0002] Coalbed methane (CBM), as an important unconventional natural gas resource, relies heavily on the successful application of hydraulic fracturing technology for its commercial development. However, coal seam reservoirs typically possess low permeability, soft coal rock mechanical properties, and complex natural fracture systems. These geological characteristics result in extremely complex fracture morphologies formed during hydraulic fracturing, making accurate prediction and control difficult. Traditional methods for evaluating the effectiveness of hydraulic fracturing often rely on indirect construction data inversion or single production dynamic analysis, which have significant limitations. For example, while the pump shutdown pressure drop inversion method can indirectly estimate fracture parameters, it is based on a simplified theoretical model and cannot accurately reflect the three-dimensional spatial distribution of complex fracture networks. Direct production data evaluation, on the other hand, suffers from severe lag and cannot provide timely feedback for real-time optimization of fracturing operations. These shortcomings lead to inaccurate judgments of fracturing effectiveness and an inability to systematically reveal the dominant factors influencing fracturing results, thus restricting targeted optimization of fracturing processes and further improvement of coalbed methane well productivity.

[0003] Existing evaluation methods either rely on indirect means such as pump shutdown pressure drop inversion or rely solely on direct phenomena such as backflow data and production curves for single-dimensional evaluation, lacking multi-scale and multi-stage coupled analysis. Summary of the Invention

[0004] In view of the above-mentioned defects or deficiencies in the prior art, it is desirable to provide a comprehensive evaluation method for coalbed methane fracturing effect to solve the problems mentioned in the background art and provide a solution that is significantly different from the prior art.

[0005] This application provides a comprehensive evaluation method for the effect of coalbed methane fracturing, including the following steps: (1) Collect basic parameters, establish a numerical simulation model, compare and fit the calculation results of the numerical simulation model with the field fracturing construction data, and obtain the parameters of the coalbed methane fracturing network. (2) Monitor the data during the backflow stage, obtain the normalization pressure of the produced liquid and the material balance time, draw the characteristic curve and obtain the intermediate parameters, and calculate the effective volume and the slit-making efficiency through the intermediate parameters. (3) Classify fractured wells according to fracture morphology coefficient, fracture efficiency and post-fracture production data, and apply the classification results in the field.

[0006] Furthermore, step (1) involves comparing and fitting the calculation results of the numerical simulation model with the field fracturing construction data, and also includes: Furthermore, the calculated construction pressure curve from the numerical simulation model is compared with the on-site fracturing construction pressure curve. The fitting parameters are adjusted, and the numerical model is iteratively optimized to achieve the best match between the calculated construction pressure curve and the on-site fracturing construction pressure curve.

[0007] Further adjustments to the fitting parameters include: adjusting the filtering coefficient.

[0008] Furthermore, the parameters of the pressure fracture network are fracture morphology coefficients, which are the ratio of the width to the length of the fracture network expansion.

[0009] Furthermore, the characteristic curve mentioned in step (2) is a double logarithmic curve of the normalized pressure derivative of the liquid production as a function of the material equilibrium time.

[0010] Furthermore, the method for obtaining the intermediate parameters is as follows: determine the time point corresponding to the straight line segment with a slope of 1 on the characteristic curve, record the value corresponding to that time point, and calculate the intermediate parameters. , .

[0011] Furthermore, the effective volume and joint formation efficiency are calculated using intermediate parameters, including: ; In the formula, —Total effective volume of fracture pore space ; —The volume coefficient of water; —Comprehensive rock compression coefficient; —Total liquid volume ; —Seam-making efficiency,%.

[0012] Furthermore, step (3) also includes: If the efficiency of seam making If the well produces high output after fracturing, then the fracturing well is classified as a Class I well, which is a high-efficiency production well. If the efficiency of seam making If the well produces high output after fracturing, then the fracturing well is classified as a Class II well, which is an inefficient production type. If crack morphology coefficient If the production output after fracturing is low and stable, then the fracturing well is a Class III well, which is a type of well with unreleased potential. If the crack morphology coefficient satisfies Post-pressure production is low-yield stable well; or fracture efficiency If the well only produces water and not gas after fracturing, it is classified as a Class IV well, which is a geologically constrained well. If the efficiency of seam making If the well only produces water and not gas after fracturing, it is classified as a Class V well, which is considered a failed fracturing well.

[0013] Furthermore, for Class I wells, this also includes: If the crack morphology coefficient satisfies This indicates that the fractured well has formed a complex fracture network system, with a large volume of workpieces, achieving the desired workpiece effect. If the crack morphology coefficient satisfies This indicates that the fractured well is mainly characterized by the extension of the main fracture, with a relatively limited communication range, but it has a high fracture creation efficiency and can still achieve high production.

[0014] Furthermore, for Class I wells, the construction parameters for Class I wells will be promoted throughout the relevant blocks; For Class II wells, the optimization directions are to optimize the fracturing fluid system, add filtration loss reducers, or adopt temporary plugging and diversion technology. For Class III wells, the optimization direction is to optimize the drainage and production system, accelerate the drainage and pressure reduction speed, and release production capacity; For Class IV wells, the optimization direction is geological sweet spot prediction and drilling trajectory optimization; For Class V wells, the optimization direction is to review the construction process or repeat fracturing.

[0015] Compared with the prior art, the beneficial effects of the present invention are: (1) This invention introduces numerical simulation software to simulate the actual fracture network of hydraulic fracturing, and uses the ratio of the width to the length of the fracture network as the core evaluation index, thereby achieving a quantitative characterization of the fracture geometry. By comparing the fitting of construction curves, the error of parameter assumptions in traditional inversion methods is avoided. By organically combining the fracture morphology parameters obtained from numerical simulation with the fracture formation efficiency in the flowback stage and the dynamic response in the production stage, a full-chain evaluation system from "construction formation - flowback response - production performance" is constructed, overcoming the one-sidedness and lag of single-method evaluation, and providing a new technical path for achieving accurate and forward-looking evaluation of fracturing effects.

[0016] (2) This invention achieves a comprehensive and accurate diagnosis of the fracturing effect of coalbed methane by synergistic analysis of fracture morphology coefficient, fracturing efficiency and post-fracturing production and discharge data, and formulates corresponding fine classification methods for fracturing wells and optimization directions for each classification well. It can provide a scientific basis for the dynamic analysis and continued development of post-fracturing coalbed methane. Attached Figure Description

[0017] Figure 1 This is a flowchart of the method of the present invention; Figure 2 This is a fitting graph of construction pressure. Figure 3 For characteristic curve plot; Figure 4Production curve diagram for Class I production wells; Figure 5 Production curve diagram for Class II production wells; Figure 6 Production curve diagram for Class III production wells; Figure 7 This is a production curve diagram of well A in an embodiment of the present invention; Figure 8 This is a characteristic curve diagram of well A in an embodiment of the present invention. Detailed Implementation

[0018] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0019] like Figure 1 As shown, this application provides a comprehensive evaluation method for coalbed methane fracturing effect, including the following steps: (1) Collect basic parameters, establish a numerical simulation model, compare and fit the calculation results of the numerical simulation model with the field fracturing construction data, and obtain the parameters of the coalbed methane fracturing network. In step (1), it is first necessary to collect basic parameters such as fracturing operation data and geological data. The fracturing operation data includes complete operation data of the target fracturing well section, including fracturing point data (such as parameters that change over time, such as displacement, pressure, sand volume, and fluid volume). The geological data includes static geological and rock mechanics parameters of the target block, as well as key data such as well trajectory, formation depth, and formation thickness. The static geological and rock mechanics parameters are integrated into numerical simulation software to construct a numerical simulation model that can accurately reflect the actual geomechanical background.

[0020] In the simulation module of the numerical simulation software, a numerical simulation model that can reflect the hydraulic fracturing process is established based on the integrated geological model. This includes defining the initial conditions (such as initial formation pressure) and boundary conditions (such as geostress field) of the model, and inputting the rock mechanics parameters collected in step (1) and the preset filtration coefficient.

[0021] After setting the model parameters, a preliminary numerical simulation model is run. The calculated construction pressure curve is then compared with the construction pressure curve collected on-site to verify the basic rationality of the model. Next, by adjusting key parameters such as the filtration coefficient, the numerical model is iteratively optimized to achieve the best match between the calculated construction pressure curve and the on-site fracturing construction pressure curve. Figure 2 As shown, this indicates that the simulated fracture morphology parameters can characterize the actual fracture morphology formed in the coal seam.

[0022] After the construction pressure history fitting meets the requirements, the simulated crack morphology is exported and analyzed, and the crack morphology coefficient is obtained. Crack morphology coefficient Defined as the ratio of the width to the length of the fracture network expansion. Referring to fracture morphology evaluation criteria established through extensive simulation studies, the complexity of the fracture network formed by hydraulic fracturing is quantitatively assessed, thereby determining the fracturing effect of hydraulic fracturing.

[0023] when At that time, the crack morphology was simple; when At that time, the crack morphology was more complex; when At that time, the crack morphology was highly complex.

[0024] (2) Monitor the data during the backflow stage, obtain the normalization pressure of the produced liquid and the material balance time, draw the characteristic curve and obtain the intermediate parameters, and calculate the effective volume and the slit-making efficiency through the intermediate parameters. In step (2), based on the flowback data, the wellhead pressure is first converted to the bottom hole pressure, and then the normalized pressure for the production volume is calculated. ) and material equilibrium time ( ).

[0025] The calculation method is as follows: Bottom hole pressure: ; Normalization pressure for product output: ; Material equilibrium time: ; In the formula, — Bottom hole pressure, MPa; —Wellhead pressure, MPa; —Density of water, kg / m³ 3 ; —Acceleration due to gravity ; —Horizontal well vertical depth ; —Original formation pressure, MPa; —Daily liquid (water) production, ; —Cumulative water production, ; Based on the parameters calculated above, a characteristic curve is plotted, as follows: Figure 3 The figure shows the normalized pressure of the production flow (P0). ) and its derivative ( ) with the time of material equilibrium ( The curves represent the changes in the double logarithmic curves, where the characteristic curve is the normalized derivative of the product yield ( ). ) with the time of material equilibrium ( For a changing double logarithmic curve, identify the time point corresponding to the straight line segment with a slope of 1 on the characteristic curve, and record the value corresponding to that time point as an intermediate parameter. , .

[0026] The effective volume and joint formation efficiency are calculated using the intermediate parameter m. The calculation method is as follows: ; In the formula, —Total effective volume of fracture pore space ; —The volume coefficient of water; —Comprehensive rock compression coefficient; —Total liquid volume ; —Seam-making efficiency,%.

[0027] (3) Classify fractured wells according to fracture morphology coefficient, fracture creation efficiency, and post-fracture production data, and apply the classification results in the field; plot production dynamic curves based on collected gas production, water production, and bottom hole pressure data, and classify wells into three categories according to gas production characteristics: High-yield wells: daily gas production exceeding 1000 m³ 3 Production begins to decline after the peak production stage or peak production period, such as... Figure 4 As shown; Low-production stable wells: low gas production (e.g., about 100m³) 3 (Approximately / d), gas production is relatively stable, still in the drainage and pressure reduction stage, such as Figure 5 As shown; Water-producing wells (not gas-producing wells): These wells are in the drainage and pressure reduction stage, producing only water and no gas. Figure 6 As shown.

[0028] A comprehensive evaluation system encompassing the entire chain of "construction formation - flowback response - production performance" is used to classify fractured wells based on fracture morphology coefficient, fracture creation efficiency, and post-fracture production data. The classification criteria are as follows: If the efficiency of seam making If the well produces high output after fracturing, then the fracturing well is classified as a Class I well, which is a high-efficiency production well. If the efficiency of seam making If the well produces high output after fracturing, then the fracturing well is classified as a Class II well, which is an inefficient production type. If crack morphology coefficient If the production output after fracturing is low and stable, then the fracturing well is a Class III well, which is a type of well with unreleased potential. If the crack morphology coefficient satisfies Post-pressure production is low-yield stable well; or fracture efficiency If the well only produces water and not gas after fracturing, it is classified as a Class IV well, which is a geologically constrained well. If the efficiency of seam making If the well only produces water and not gas after fracturing, it is classified as a Class V well, which is considered a failed fracturing well.

[0029] For Class I wells: If the crack morphology coefficient satisfies This indicates that the fractured well has formed a complex fracture network system, with a large volume of workpieces, achieving the desired workpiece effect. If the crack morphology coefficient satisfies This indicates that the fractured well is mainly characterized by the extension of the main fracture, with a relatively limited communication range, but it has a high fracture creation efficiency and can still achieve high production.

[0030] The field application of the above-mentioned fracturing well classification results includes the following steps: For Class I wells, which indicate excellent stimulation effects, they should be used as the optimization template for the block, and their construction parameters (such as displacement, sand ratio, and liquid volume) should be promoted and standardized.

[0031] For Class II wells, the main problem is low construction efficiency and severe fracturing fluid loss. The optimization direction is to optimize the fracturing fluid system, add fluid loss reducers, or adopt temporary plugging and diversion technology.

[0032] For Class III wells, the reservoir potential has been effectively utilized through fracturing, but the production system is mismatched. The optimization direction is to optimize the drainage and production system, accelerate the drainage and depressurization speed, and release production capacity.

[0033] For Class IV wells, the main limiting factors are the geological conditions (such as geostress and coal structure) or wellbore quality, and the optimization direction is the prediction of geological sweet spots and the optimization of drilling trajectory.

[0034] For Class V wells, which indicate fracturing failure or extremely poor reservoir properties, the optimization direction is to review the fracturing process or repeat fracturing.

[0035] To facilitate a better understanding of the technical solution of this invention by technical personnel, a comprehensive application was carried out using Well A as a practical example.

[0036] First, the crack morphology is evaluated using the method in step (1), and the numerical simulation results are as follows ( Figure 2 The data shows a good fit to the historical construction pressure. The calculated average effective half-length of the main fracture in the well is 136.5 meters, and the fracture network width is 72.3 meters. The fracture morphology coefficient was also calculated. The value is 0.26 (which is considered a relatively complex crack).

[0037] Then, based on the monitoring data in step (2), the effective volume after compression was calculated to be 8287 m³. 3The seam-making efficiency was 63.93% (which is relatively high).

[0038] Finally, following the steps in step (3), monitor the well's production dynamics curve, such as... Figure 7 As shown, its gas production is stable at approximately 10,000 m³ / s. 3 / d, with excellent results, the well produced high output after pressure, and its flowback data was plotted in a double logarithmic chart ( Figure 8 The early appearance of boundary flow features with a slope of 1 also indicates an effective fracture system.

[0039] According to the post-compression well classification criteria provided in this application, well A has high fracture creation efficiency ( Well A is classified as a Class I well because its post-pressurization production is high. (Fracturation morphology of well A) This result indicates that the well section is dominated by the extension of the main fracture, with a relatively limited communication range, but high production is achieved thanks to the high fracture creation efficiency.

[0040] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. A method for comprehensive evaluation of coalbed methane fracturing effect, characterized in that, The method comprises the following steps: (1) collecting basic parameters, establishing a numerical simulation model, comparing and fitting the calculation results of the numerical simulation model with the field fracturing operation data, and obtaining the coalbed methane fracture network parameters; (2) monitoring the data in the flowback stage, obtaining the normalized pressure of liquid production and the material balance time, drawing a characteristic curve and obtaining intermediate parameters, and calculating the effective volume and fracture creation efficiency through the intermediate parameters; (3) classifying the fracturing wells according to the fracture morphology coefficient, fracture creation efficiency and post-fracturing production data, and applying the classification results to the field.

2. The coalbed methane fracturing effect comprehensive evaluation method according to claim 1, wherein in step (1), the comparison and fitting of the calculation results of the numerical simulation model with the field fracturing operation data further comprises: comparing the calculation construction pressure curve of the numerical simulation model with the field fracturing construction pressure curve, adjusting the fitting parameters, iteratively optimizing the numerical model, and realizing the best matching of the calculation construction pressure curve and the field fracturing construction pressure curve.

3. The coalbed gas fracturing effect comprehensive evaluation method according to claim 2, adjusting the fitting parameters comprises: adjusting the filtration coefficient.

4. The coalbed methane fracturing effect comprehensive evaluation method according to claim 1, wherein the fracture network parameters are the fracture morphology coefficient, and the fracture morphology coefficient is the ratio of the width to the length of the fracture network expansion.

5. The coalbed methane fracturing effect comprehensive evaluation method according to claim 1, wherein in step (2), the characteristic curve is a double-logarithmic curve of the derivative of the normalized pressure of liquid production with respect to the material balance time.

6. The coal bed gas fracturing effect comprehensive evaluation method according to claim 1, wherein the intermediate parameter acquisition method is: determining a time point corresponding to a straight line segment with a slope of 1 on a characteristic curve, recording a value corresponding to the time point, and calculating an intermediate parameter , ， wherein For the liquid production to normalize the pressure, For the material balance time.

7. The coalbed methane fracturing effect comprehensive evaluation method according to claim 1, wherein the effective volume and fracture creation efficiency are calculated through the intermediate parameters, and the method comprises: ； wherein Total fracture pore space effective volume, ; — Volume factor of water; — Rock compressibility; — Total liquid volume, ; — Fracture efficiency, %.

8. The coalbed methane fracturing effect comprehensive evaluation method according to claim 1, wherein step (3) further comprises: If the efficiency of the fracture is high , the post-frac production is high, then the fractured well is a Class I well, which is a high-efficiency production type; If the efficiency of the fracture is high , the post-frac production is high, then the fractured well is a Class II well, which is a low-efficiency production type; If the fracture morphology coefficient If the post-fracturing production is low and stable, the fractured well is a type III well, which is a potential unreleased type. If the crack morphology coefficient satisfies , the post-fracturing production is low and stable; or the fracture efficiency , only water is produced after fracturing, and the fracturing well is a type IV well, which is a geology-constrained type. If the efficiency of creating fractures is If only water is produced after the fracturing, the well is classified as type V, which is a failure of the reconstruction.

9. The coalbed methane fracturing effect comprehensive evaluation method according to claim 1, wherein for the type I well, the method further comprises: If the fracture morphology coefficient satisfies , it indicates that the fractured well has formed a complex fracture network system, the volume of the reformation is large, and the ideal reformation effect is achieved. If the fracture morphology coefficient satisfies It indicates that the main fracture extends mainly in the fractured well, the communication range is relatively limited, but the fracture efficiency is high, and high production can still be achieved.

10. The coalbed methane fracturing effect comprehensive evaluation method according to claim 1, wherein the method further comprises: for the type I well, promoting the construction parameters of the type I well in the block; for the type II well, the optimization direction is to optimize the fracturing fluid system, add a filtration reducer or use a temporary plugging and diverting technology; for the type III well, the optimization direction is to optimize the drainage and production system, speed up the drainage and depressurization speed, and liberate the production capacity; for the type IV well, the optimization direction is to predict the geological sweet spot area and optimize the drilling trajectory; for the type V well, the optimization direction is to review the construction process or repeat fracturing.

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