A Method for Evaluating Coalbed Methane Reservoir Productivity Considering Drilling Fluid Damage

Chen Li (), Lichun Sun, Zhigang Zhao, Jian Zhang, Yong Li, Yanjun Meng and Lei Wang
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Chen Li: CNOOC Research Institute Ltd., CNOOC Building, Yard 6, Taiyanggong South Street, Chaoyang District, Beijing 100028, China
Lichun Sun: CNOOC Research Institute Ltd., CNOOC Building, Yard 6, Taiyanggong South Street, Chaoyang District, Beijing 100028, China
Zhigang Zhao: CNOOC Research Institute Ltd., CNOOC Building, Yard 6, Taiyanggong South Street, Chaoyang District, Beijing 100028, China
Jian Zhang: CNOOC Research Institute Ltd., CNOOC Building, Yard 6, Taiyanggong South Street, Chaoyang District, Beijing 100028, China
Yong Li: College of Geosciences and Surveying Engineering, China University of Mining & Technology, No. 11, Xueyuan Road, Haidian District, Beijing 100083, China
Yanjun Meng: College of Mining Engineering, Taiyuan University of Technology, No. 79 Yingze Xi Street, Wanbolin District, Taiyuan 030002, China
Lei Wang: School of Earth Resources, China University of Geosciences Wuhan, 388 Lumo Road, Wuhan 430074, China

Energies, 2024, vol. 17, issue 7, 1-16

Abstract: In the process of coalbed methane development, drilling fluid and fracturing fluid cannot achieve absolute compatibility with formation. The incompatibility between the working fluid and reservoir will lead to the intrusion of working fluid into the reservoir and cause reservoir pollution. This is a very common phenomenon. There is a large amount of pulverized coal in the coal seam, and the intrusion of working liquid will be combined with the pulverized coal to form cement to block the seepage space in the reservoir. Since pressure relief and fracturing fluid backflow will be performed at the first time after fracturing, the intrusion range of the working fluid is small, generally reaching 10 m to 50 m. Compared with a conventional gas reservoir or shale gas reservoir, the working fluid loss during CBM development will seriously affect the subsequent production project and even make the gas well lose production capacity. On the other hand, in order to avoid this phenomenon, measures such as acidification or volumetric fracturing are sometimes used to improve the seepage environment near the well and near the fracture. The purpose of this study is to quantitatively evaluate the impacts of working fluid filtration and reservoir reconstruction on production. In this study, a single well productivity evaluation model and sensitivity analysis method considering drilling fluid filtration loss, fracturing fluid filtration loss, reservoir reconstruction and other processes is proposed. The formation mechanism of fluid loss during drilling and fracturing is described, and the productivity evaluation model considering fluid loss is combined with the Langmuir isothermal adsorption equation, steady-state diffusion law, Darcy’s seepage law and Duhamel convolution formation. Combined with the distribution of actual gas reservoir flow characteristics, the sensitivity of single well productivity to gas reservoir porosity, gas reservoir permeability, coal seam adsorption coefficient, working fluid filtration loss and reservoir reconstruction measures are analyzed. Through the analysis and fitting of the actual production data on site, the relationship curve can better fit the field production data, and the evaluation results are in line with the drilling and fracturing conditions at that time and the subsequent production conditions, with small errors. The obtained method is suitable for predicting the productivity of fractured vertical wells in different working conditions and provides a basis for the development and productivity prediction of CBM reservoirs in China and in international cooperation.

Keywords: coal bed methane; drilling fluid filtration; fracturing fluid filtration; reservoir reconstruction; productivity evaluation (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2024
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