Physical Simulations of Gas Production Mechanism in Constant-Rate Co-production from Multiple Coal Reservoirs
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Original Paper
Physical Simulations of Gas Production Mechanism in Constant-Rate Co-production from Multiple Coal Reservoirs Qixian Li ,1,2 Jiang Xu,1,2 Shoujian Peng,1,2,3 Fazhi Yan,1,2,3 Bin Zhou,1,2 Ende Han,1,2 and Cheng Jiang1,2 Received 24 August 2020; accepted 15 November 2020
Coalbed methane co-production is an efficient technique for producing gas from multiple coal reservoirs. In this study, four large-scale specimens were connected in parallel to model a system of coalbed methane production. The results revealed that a low-pressure coal reservoir is disrupted owing to the pressure equilibrium, causing the cross-formational flow of gas through the wellbore. The production and productivity contribution rates were positively correlated with the initial reservoir pressure over a stable production period, forming a ‘‘dynamic supply’’ state among the coal reservoirs. The intensity of the interlayer interference was negatively correlated with reservoir pressure such that with significant interlayer interference, reverse gas flow or a halt in production could occur in the low-pressure coal reservoir. The constant-rate production value and the effect of interlayer interference had an inverse relationship in terms of production; the smaller the former, the greater was the latter. Increasing the constant-rate value can restrict large-scale production from the high-pressure coal reservoir and improve the productivity recovery rate and production distribution of the low-pressure coal reservoir. KEY WORDS: Coalbed methane (CBM), Multiple coal reservoirs, Co-production, Reverse gas flow.
INTRODUCTION Coalbed methane (CBM) is an important unconventional natural gas resource, and it has attracted considerable attention because it is a cleaner energy source than conventional fossil fuels (Yan et al. 2019, 2020; Liu et al. 2020). CBM has been economically produced from coal seams in several basins such as the Powder River and Black Warrior 1
State Key Laboratory of Coal Mine Disaster Dynamics and Control, College of Resources and Environmental Science, Chongqing University, Chongqing 400044, China. 2 State and Local Joint Engineering Laboratory of Methane Drainage in Complex Coal Gas Seam, School of Resources and Safety Engineering, Chongqing University, Chongqing 400044, China. 3 To whom correspondence should be addressed; e-mail: [email protected], [email protected]
Basin in the USA (Wicks et al. 1986; U.S. Department of Energy 2003), Alberta Basin in Canada (Beaton et al. 2006; Bustin and Bustin 2016), SuratBowen Basin in Australia (Li et al. 2014; Towler et al. 2016), and Qinshui and Ordos Basins in China (Li et al. 2016, 2019a). China is one of the highest energy consumers worldwide and it is estimated to have CBM reserves of 29.8 trillion m3 at depths shallower than 2000 m, ranking third in the world (Ni et al. 2018; Wang et al. 2020). The overall CBM yield of ground exploitation in 2019 was 5.46 billion m3 (Ministry of Natural Resources of the Peoples Republic of China 2020); this is considerably lower than the t
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