Numerical analysis of drainage rate for multilayer drainage coalbed methane well group in Southern Qinshui basin

Qiujia Hu,Chonghao Mao,Huihuang Fang,Shiqi Liu,Shuxun Sang,Ashutosh Tripathy,Ling Yan,Mengfu Qin

doi:10.1177/0144598720946494

Qiujia Hu, Chonghao Mao + Show 6 more

Open Access

https://doi.org/10.1177/0144598720946494

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Abstract

Multilayer drainage is one of the important technologies for coalbed methane (CBM) production in China. In this study, a multi-field fully coupled mathematical model for CBM production was established to analyze the multilayer drainage of CBM well group in southern Qinshui basin. Based on the numerical simulation results, the characteristics of CBM well production under different drainage rates and key factors influencing the CBM production were further discussed. The results show that the effect of an increased drainage rate on gas production of CBM wells and CBM recovery of No.3 coal seam is not significant. However, it significantly improved the gas production of CBM wells and CBM recovery of No.15 coal seam. After a long period of production, the CBM content in No.3 coal seam has reduced to a low level and the pressure drop potential of No.3 coal seam is insignificant, which are important reasons for the insignificant increase of CBM production even under a drainage rate of 2 to 7 times. Conversely, No.15 coal seam has larger residual CBM content and increasing the drainage rate can significantly improve the pressure drop and superimposed well interference of No.15 coal seam, which means No.15 coal seam has greater production potential than No.3 coal seam. Therefore, it is recommended to improve the gas production and CBM recovery in No.15 coal seam by increasing the drainage rate, and the average hydraulic pressure drop should be 0.018–0.031 MPa/day. The influence of effective stress is weak in No.3 and No.15 coal seam, and the coal seam permeability is largely influenced by the shrinkage of coal matrix caused by CBM desorption. This indicates the feasibility of increase in gas production from CBM wells by increasing the drainage rate.

Highlights

The international energy agency (IEA) estimates that there are 2.638 Â 1014 m3 of coalbed methane (CBM) in the world, and the exploitation and utilization of CBM has been carried out in more than 30 countries (Lau et al, 2017; Li et al, 2018)
An increase in drainage rate can effectively increase the daily production of CBM wells (Figure 3)
Except FZ-10, the differences in increase of daily gas production and cumulative daily gas production of CBM wells under 5 times and 7 times drainage rates are relatively small, which are around 1–2% (Table 5)

Summary

Introduction

The international energy agency (IEA) estimates that there are 2.638 Â 1014 m3 of coalbed methane (CBM) in the world, and the exploitation and utilization of CBM has been carried out in more than 30 countries (Lau et al, 2017; Li et al, 2018). The 5 new multilayer drainage wells have a shorter production time of only 1750 days, and the CBM recovery in No.15 coal seam is only 10–20% in a small area around the wellbore (Figure 4).

Results

Conclusion