Prediction method for peak gas production rate of deep coal bed gas fractured horizontal well

Abstract

The invention discloses a method for predicting the peak gas production rate of a deep coal bed gas fractured horizontal well, which comprises the following steps of: 1, data collection and arrangement: collecting actual drilling, well logging, fracturing and production data of the fractured horizontal well in a deep coal bed gas development target area; 2, starting from a known well, combining actual drilling, well logging, fracturing and production data, and comprehensively determining main factors influencing the peak gas production rate of the deep coal bed gas fractured horizontal well; main control factors of the peak yield of the deep coal bed gas fractured horizontal well are fully considered, the influence of the key index vitrinite reflectance on the peak yield is introduced and quantified, the method is suitable for deep coal bed gas fractured horizontal well development practice, key parameters are easy and convenient to obtain, field practicability is high, and the method is suitable for large-scale popularization and application. The method can quickly predict the peak gas production of the to-be-analyzed gas well.

Description

Technical Field

[0001] This invention relates to the field of coalbed methane development technology, specifically to a method for predicting peak gas production in deep coalbed methane fracturing horizontal wells. Background Technology

[0002] Currently, domestic coalbed methane (CBM) extraction is mainly concentrated in areas with a burial depth of over 1,500 meters, and the favorable areas for large-scale development are becoming increasingly scarce. Meanwhile, CBM resources below 1,500 meters account for more than 30% of the total national CBM resources, and remain largely unexplored. In recent years, domestic CBM exploration and development has gradually shifted "from shallow to deep layers," meaning that deeper CBM resources are being extracted to meet market demand.

[0003] Currently, peak gas production in fractured horizontal wells is a crucial indicator for evaluating well productivity during coalbed methane (CBM) extraction and a key factor determining the profitability of CBM well development. Domestic and international literature primarily focuses on predicting peak production in shallow and medium-depth CBM wells using methods such as the Weibu11 model, the generalized Weng's model, and the HCZ model (see "Research on Peak Production Fitting and Dynamic Prediction Methods for Coalbed Methane," Zhang Hairu, 2013). However, these productivity evaluation methods are based on the "drainage-depressurization-desorption" production mechanism of shallow and medium-depth CBMs. Deep CBM reservoirs contain free gas, which can be produced immediately after fracturing. Therefore, a peak gas production prediction method needs to be established specifically for deep CBMs.

[0004] While existing technologies address coalbed methane (CBM) production prediction—for example, Chinese patent CN1 158601 97A discloses a data-driven CBM production prediction method and system—this method utilizes static data such as post-fracturing permeability, initial gas content, geostress, and reservoir thickness, along with dynamic well production history data, to train a production prediction model for known wells using machine learning methods, guiding production prediction for wells to be predicted. However, the method provided by the aforementioned patent does not comprehensively consider the impact of reservoir thickness, vitrinite reflectivity, and fracturing fluid volume on peak gas production. Therefore, for deep CBM reservoirs, there is an urgent need to develop a targeted peak gas production prediction method. Summary of the Invention

[0005] The purpose of this invention is to provide a method for predicting the peak gas production of fracturing horizontal wells in deep coalbed methane, aiming to improve the problem of the inability to accurately evaluate and predict the peak gas production of fracturing horizontal wells in deep coalbed methane.

[0006] This invention is implemented as follows: a method for predicting peak gas production in horizontally fractured deep coalbed methane wells, comprising...

[0007] Step 1: Data collection and organization, collecting and studying the actual drilling, logging, fracturing and production data of fractured horizontal wells in the target area for deep coalbed methane development;

[0008] Step 2: Starting from known wells, and combining actual drilling, logging, fracturing, and production data, comprehensively determine the main factors affecting the peak gas production of deep coalbed methane fracturing horizontal wells as coal seam thickness, vitrinite reflectivity, horizontal section length, and total amount of fracturing fluid injected into the ground.

[0009] Step 3: Single-factor analysis of the relationship between influencing factors and peak gas production showed that coal seam thickness, vitrinite reflectance, horizontal section length, and total amount of fluid injected into the fracturing pit were all positively correlated with peak gas production.

[0010] Step 4: Based on Step 3, establish a prediction model for peak gas production of deep coalbed methane fracturing horizontal wells through linear multiple regression.

[0011] Step 5: Apply the peak gas production evaluation formula established in Step 4, and substitute these four factors—coal seam thickness, vitrinite reflectivity, horizontal section length, and total amount of fracturing fluid injected into the well—into the evaluation formula to predict the peak gas production of the well.

[0012] Preferably, the evaluation formula involved in step four is as follows:

[0013]

[0014] Q peak —Peak gas production, 10 4 m 3 / d;H coal — Coal seam thickness, m; R o —Vitreous reflectance, %; L hor - Horizontal segment length, m; V total -Total amount of fracturing fluid injected into the ground, 10 4 m 3 .

[0015] Preferably, the applicable range for coal seam thickness is H. coal ≥4.0n, the applicable range for vitrinite reflectance is 1.0% ≤R. o ≤4.0%.

[0016] Compared with existing technologies, the advantages of this invention are: This invention fully considers the main controlling factors of peak production in deep coalbed methane fracturing horizontal wells, introduces and quantifies the influence of the key indicator vitrinite reflectance on peak gas production, and is applicable to the development practice of deep coalbed methane fracturing horizontal wells. Key parameters are easy to obtain, it has strong field applicability, and can quickly predict peak gas production in the wells under analysis. This invention has been applied in mining practice, achieving a peak gas production prediction accuracy of 95.8%, and provides guidance for optimizing coalbed methane development schemes. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the steps of the present invention;

[0018] Figure 2 The graph shows the relationship between actual peak gas production and coal seam thickness, along with the fitted equation.

[0019] Figure 3 The graph shows the relationship between actual peak gas production and vitrinite reflectance, along with the fitted equation.

[0020] Figure 4 The graph shows the relationship between actual peak gas production and the length of the horizontal section, along with the fitted equation.

[0021] Figure 5 A graph showing the relationship between actual peak gas production and total amount of fracturing fluid injected into the ground, along with a fitted equation;

[0022] Figure 6 This is a dynamic production diagram of the XP1 gas well as an example.

[0023] Figure 7 This is a comparison chart showing the calculated peak gas production and the actual peak gas production during the verification process of this invention. Detailed Implementation

[0024] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0025] The following description, in conjunction with the accompanying drawings and specific embodiments, provides further details:

[0026] A method for predicting peak gas production in fracturing horizontal wells of deep coalbed methane, characterized by comprising:

[0027] Step 1: Data collection and organization, collecting and studying the actual drilling, logging, fracturing and production data of fractured horizontal wells in the target area for deep coalbed methane development.

[0028] Step 2: Starting from known wells, and combining actual drilling, logging, fracturing, and production data, comprehensively determine the main factors affecting the peak gas production of deep coalbed methane fracturing horizontal wells as coal seam thickness, vitrinite reflectivity, horizontal section length, and total amount of fracturing fluid injected into the ground.

[0029] Step 3: Single-factor analysis of the relationship between influencing factors and peak gas production showed that coal seam thickness, vitrinite reflectivity, horizontal section length, and total amount of fluid injected into the ground through fracturing were all positively correlated with peak gas production.

[0030] Step 4: Based on Step 3, establish a peak gas production prediction model for deep coalbed methane fracturing horizontal wells through linear multiple regression, and establish a peak gas production evaluation formula.

[0031] The evaluation formula is

[0032]

[0033] Q peak -Peak gas production, 10 4 m 3 / d;H coal — Coal seam thickness, m; R o —Vitreous reflectance, %; L hor — Horizontal segment length, m; V total —Total amount of fracturing fluid injected into the ground, 10 4 m 3 The applicable range for coal seam thickness is H. coal For surfaces ≥4.0m, the applicable range for vitrinite reflectance is 1.0% ≤R. o ≤4.0%.

[0034] Step 5: The four factors of coal seam thickness, vitrinite reflectivity, horizontal section length, and total amount of fracturing fluid injected into the well to be predicted should be substituted into the evaluation formula to predict the peak gas production of the well.

[0035] To verify the above method, the relationship between the actual peak production of parameters such as coal seam thickness, vitrinite reflectivity, horizontal section length, and total amount of fracturing fluid injected into the ground was analyzed.

[0036] Specifically, input the data for coal seam thicknesses between 6 and 11 meters into y = 2.2523e. 0.1937x In this process, a graph showing the relationship between coal seam thickness and peak production is generated.

[0037] Input the data for vitrinite reflectance ranging from 1% to 4% per meter into y = 6.8137x. 0.516 In this process, a graph showing the relationship between vitrinite reflectance and peak yield is generated.

[0038] Input the data with horizontal segment lengths ranging from 900 meters to 1400 meters into y = 0.0196x - 11.028 to generate a graph showing the relationship between horizontal segment length and peak output.

[0039] The accuracy of the prediction method was verified by conducting actual operations on wells XP1, XP2, XP3, XP4, XP5, XP6, XP7, XP8, XP9, XP10, XP11, XP12, XP13, and XP14.

[0040] Taking the XP1 well as an example, the embodiments of the present invention are described in detail below:

[0041] 1. Data preparation: Collect and calculate relevant data for well XP1, including coal seam thickness, vitrinite reflectivity, horizontal section length, and total amount of fracturing fluid injected into the ground;

[0042] 2. Substituting the coal seam thickness of 9.0m, vitrinite reflectance of 3.2%, horizontal section length of 1300m, and total fracturing fluid injection of 48,000 cubic meters into the peak gas production prediction formula, the predicted peak gas production of well XP1 is 142,000 cubic meters / day.

[0043]

[0044] 1. The actual peak gas production of well XP1 is 147,000 cubic meters per day. The relative error between the predicted and actual values ​​is 3.1%. The actual production dynamic curve of this well is shown in the attached figure.

[0045] The remaining wells can be operated in the same way as XP1 to obtain the results.

[0046] After making predictions using this method, the error between the predicted and actual results for each well is obtained, as detailed in the table below.

[0047] Table 1 Error Analysis Table Between Calculated Peak Gas Production and Actual Peak Gas Production in this Invention

[0048]

[0049] By systematically analyzing actual drilling, logging, fracturing, and production data of fractured horizontal wells, a method for predicting peak gas production in deep coalbed methane fractured horizontal wells was established using single-factor analysis combined with multi-regression. The prediction accuracy reached 95.8% in actual producing wells, enabling a faster and more accurate evaluation of the production capacity of deep coalbed methane fractured horizontal wells. This invention considers the influence of vitrinite reflectivity and the total amount of fracturing fluid injected into the formation on peak gas production, improving the accuracy and practicality of predicting peak gas production in deep coalbed methane horizontal wells, and has significant potential for widespread application.

[0050] The above are merely preferred embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for predicting peak gas production of a deep coalbed gas fracturing horizontal well, characterized in that, Comprising Step one: data collection and arrangement, collecting the real drilling, logging, fracturing and production data of the fracturing horizontal well in the deep coalbed methane development target area; Step two: starting from the known well, combining the real drilling, logging, fracturing and production data, and comprehensively determining the main factors affecting the peak gas production of the deep coalbed methane fracturing horizontal well; Step three: single factor analysis of the relationship between the influencing factors and the peak gas production, the coal seam thickness, vitrinite reflectance, horizontal section length and total fracturing liquid volume are positively correlated with the peak gas production; Step four: on the basis of step three, through linear multiple regression, a peak gas production prediction model of deep coalbed methane fracturing horizontal well is established. Step five: applying the peak gas production evaluation formula established in step three, according to the coal seam thickness, vitrinite reflectance, horizontal section length and total fracturing liquid volume of the well to be predicted, these four factors are substituted into the evaluation formula to realize the prediction of the peak gas production of the well.

2. The method for predicting peak gas production of deep coalbed gas fracturing horizontal wells according to claim 1, characterized in that, The evaluation formula involved in step four is 3. The method for predicting peak gas production of deep coalbed gas fracturing horizontal wells according to claim 2, characterized in that, Q peak - peak gas production, 10 4 m 3 / d; H coal - coal seam thickness, m; R o - vitrinite reflectance, %; L hor - horizontal section length, m; V total - total volume of fracturing fluid, 10 4 m 3 .

4. The method for predicting peak gas production of deep coalbed gas fracturing horizontal wells according to claim 3, characterized in that, The coal seam thickness suitable range is H coal ≥ 4.0 m, the vitrinite reflectance suitable range is 1.0% ≤ R o ≤ 4.0%.

5. The method for predicting peak gas production of deep coalbed gas fractured horizontal wells according to claim 1, wherein, The main factors described in step two are coal seam thickness, vitrinite reflectance, horizontal section length and total fracturing liquid volume.

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