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Water 2018, 10(7), 929; https://doi.org/10.3390/w10070929

A Study on Optimization of CBM Water Drainage by Well-Test Deconvolution in the Early Development Stage

1
Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China
2
School of Engineering Science, University of Chinese Academy of Sciences, Beijing 100049, China
3
PetroChina Coalbed Methane Company Limited, Beijing 100028, China
4
Zhongshan Institute, University of Electronic Science and Technology of China, Zhongshan 528400, China
*
Authors to whom correspondence should be addressed.
Received: 29 May 2018 / Revised: 27 June 2018 / Accepted: 10 July 2018 / Published: 13 July 2018
(This article belongs to the Section Hydrology)
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Abstract

Different from the conventional gas reservoir, coalbed methane is developed mainly by water drainage, which leads methane desorption after reservoir pressure drop. Water drainage at a reasonable speed in the early development stage is the key for enhancing later gas performance. Therefore, the investigation radius, which reflects the pressure drop region scale, is studied by deconvolution well-test to find the reasonable water drainage speed in the early period. First, the early production data (well-bottom pressure and water rate) are processed by deconvolution algorithm, and then the pressure data under unit rate is obtained to invert the comprehensive reservoir permeability and investigation radius. This deconvolution method can save the cost of the conventional well-test, and avoid reservoir damage caused by frequent well shut-off. The feasibility of the deconvolution test method is verified by comparing its interpretation results with those of the conventional pressure drop/build-up test. For a field application, the 29 wells’ comprehensive permeability are inverted by the deconvolution well-test using early water production data of Hancheng block. Furthermore, their investigation radius and pressure drawdown gradient are calculated, and the performance optimization is determined by relationship analysis between working fluid level and steady gas production rate. We find that well-bottom pressure and reservoir pressure should decrease steadily in the early development stage, with the working fluid level declining less than 1 m/d (1 m per day) in wellbore, and the pressure drawdown gradient declining less than 2.8 MPa/100 m. View Full-Text
Keywords: coalbed methane wells; sustainable energy; deconvolution; comprehensive permeability; performance optimization; energy materials; CBM water coalbed methane wells; sustainable energy; deconvolution; comprehensive permeability; performance optimization; energy materials; CBM water
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Gao, D.; Liu, Y.; Guo, Z.; Han, J.; Lin, J.; Fang, H.; Ma, H.; Tsai, S.-B. A Study on Optimization of CBM Water Drainage by Well-Test Deconvolution in the Early Development Stage. Water 2018, 10, 929.

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