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The exploration of predicting CBM content by geophysical logging data: A case study based on slope correlation random forest method |
GUO Jian-Hong1,2( ), ZHANG Zhan-Song1,2( ), ZHANG Chao-Mo1,2, ZHOU Xue-Qing1,2, XIAO Hang1,2, QIN Rui-Bao3, YU Jie3 |
1. College of Physics and Petroleum Resources, Yangtze University, Wuhan 430100, China 2. Key Laboratory of Exploration Technologies for Oil and Gas Resources, Ministry of Education, Yangtze University, Wuhan 430100, China 3. CNOOC Research Institute, Beijing 100027, China |
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Abstract Coalbed methane content is one of the key parameters in coal seam exploration and development research. Due to the influence of many factors on coalbed methane content, it is very important to predict coalbed methane content effectively. In this paper, slope correlation degree method and random forest algorithm are combined to predict coalbed methane content based on geophysical logging data. Firstly, the improved slope correlation degree method is used to obtain the favorable geophysical logging curves for CBM content prediction, and then the cross validation method is used to explore the appropriate number of random forest decision trees, and the random forest algorithm is used to predict the coalbed methane content for the logging curve sequence with positive correlation. With the No.3 seam in Shizhuang north area of Qinshui coalfield as an example, the block was evaluated and predicted with the results compared with the results of multiple regression model, and the anti-interference ability of the model was studied and analyzed. The results show that the application of slope correlation method to analyzing and calculating the geophysical logging curve and coalbed methane content can accurately and effectively find the logging curve that can be used to predict the content of coalbed methane, the model trained by random forest algorithm is accurate in predicting the content of coalbed methane in the non-gangue section, and the calculation result has high reliability, but the prediction ability is weak in the gangue section. The results obtained by the authors are of guiding significance to the exploration and development of coalbed methane and have practical application value.
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Received: 08 November 2020
Published: 01 March 2021
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Corresponding Authors:
ZHANG Zhan-Song
E-mail: 87942024@qq.com;Zhangzhs@yangtzeu.edu.cn
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Relationship between coalbed methane content and logging parameters
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参数 | 测试气量/ (m3·t-1) | 自然伽马/ API | 自然电位/ mV | 补偿密度/ (g·cm-3) | 声波时差/ (μs·m-1) | 补偿中子/ (V·V-1) | 深电阻率/ (Ω·m) | 浅电阻率/ (Ω·m) | 范围 | 5.91~26.07 | 30.4~109.4 | 26~134 | 1.19~1.89 | 384~489 | 0.41~0.56 | 165~33766 | 470~18355 | 平均值 | 18.83 | 55.3 | 82 | 1.39 | 419 | 0.49 | 4845 | 4428 |
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Logging response range of No.3 Coal Seam
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样号 | 测试气量/ (m3·t-1) | 深度曲线/ m | 自然伽马/ API | 自然电位/ mV | 补偿密度/ (g·cm-3) | 声波时差/ (μs·m-1) | 补偿中子/ (V·V-1) | 深电阻率/ (Ω·m) | 浅电阻率/ (Ω·m) | A1-1 | 17.32 | 972.94 | 52.96 | 134.34 | 1.21 | 395.9 | 0.47 | 11946 | 9024 | A1-2 | 18.93 | 975.28 | 59.63 | 41.22 | 1.27 | 418.5 | 0.44 | 5121 | 3892 | A1-3 | 15.90 | 976.00 | 45.51 | 42.10 | 1.20 | 415.1 | 0.46 | 5224 | 4563 | ? | | | | ? | | | | | | A9-2 | 7.81 | 956.55 | 77.90 | 25.93 | 1.38 | 411.0 | 0.44 | 1514 | 88 |
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Calculation sample of slope correlation degree of No.3 Coal Seam
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| γ(x0,x1) 深度曲线 | γ(x0,x2) 自然伽马 | γ(x0,x3) 自然电位 | γ(x0,x4) 声波时差 | γ(x0,x5) 补偿密度 | γ(x0,x6) 补偿中子 | γ(x0,x7) 深电阻率 | γ(x0,x8) 浅电阻率 | 关联度 | 0.134 | 0.056 | -0.049 | 0.163 | 0.183 | 0.168 | 0.196 | -0.076 | 关联序 | 5 | 6 | 7 | 4 | 2 | 3 | 1 | 8 |
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Calculation results of slope correlation degree of No.3 coal seam
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Results of random forest out of bag error before and after slope correlation calculation
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Cross validation to explore decision tree range results
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Out of bag error when the number of decision trees is 500
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Slope correlation degree-prediction of coalbed methane content by random forest
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| 测试气量/(m3·t-1) | 预测气量/(m3·t-1) | 绝对误差/(m3·t-1) | 相对误差/% | A1-2 | 18.93 | 16.67 | 2.26 | 0.12 | A7-5 | 23.53 | 18.93 | 4.60 | 0.20 | A7-3 | 18.83 | 19.90 | 1.07 | 0.06 | A7-2 | 18.91 | 19.19 | 0.28 | 0.01 | A2-6 | 19.07 | 17.66 | 1.41 | 0.07 | A8-5 | 22.44 | 20.79 | 1.65 | 0.07 | A6-2 | 15.14 | 17.77 | 2.63 | 0.17 | A4-2 | 17.76 | 19.08 | 1.32 | 0.07 | A3-1 | 15.96 | 20.59 | 4.63 | 0.29 | A4-3 | 18.77 | 18.10 | 0.67 | 0.04 | 平均值 | | | 2.05 | 11.10 |
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Prediction results of No.3 coal seam test set
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Prediction results of No.3 coalbed methane content in A7 well
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Response and experimental value analysis of No.3 coal seam in well A3
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