Abstract
The coalbed methane (CBM) resources in the Qinshui Basin are abundant with exceptional production potential. Coalbed methane wells usually need to be hydraulically fractured to build economical production. However, the exploration and production experiences have shown that the penetration distances of hydraulic fractures in the vertical direction of coal seams are uncertain, which may lead to fracture communication of the layers above and beneath aquifer layers, resulting in divergent production dynamics among coalbed methane producers. It has been observed that some of the CBM wells in Block M produced significantly more water than other wells in the surrounding area. It is suspected that the hydraulic fracturing among these producers may have communicated to the sandstone aquifers. To address the above challenge, this study investigated the geological characteristics of the aforementioned aquifer and coalbed layers, established a three-dimensional geological model, applied numerical simulation to quantify the influence of the aquifer on the production of the CBM wells, and developed a method to improve the history matching of CBM production simulation with the influence of the aquifer considered. This method has significantly improved the accuracy of the history matching performance and the reliability of the remaining gas study. The results from this study laid the foundation for the subsequent development strategy optimization.
Highlights
The coalbed methane resources in the Qinshui Basin are abundant and have good production potential
Based on the hypothesis that it is possible that the producing wells fractured the top sandstone water layer during the fracturing process, resulting in some of the gas wells producing significantly more water than the average producing wells, and this study focuses on the effect of the water-bearing layer in the coal seam on the gas production effect of coalbed methane (CBM)
The coalbed methane content in the Qinshui Basin is high, with most of the coalbed methane in the Shanxi Group #3 coal seam ranging from 7 m3/t to 32 m3/t, with the highest measured being 36 m3/t, and most of the coalbed methane in the Taiyuan Group #15 coal seam ranging from 6 m3/t to 21 m3/t, with the highest measured being 27 m3/t
Summary
The coalbed methane resources in the Qinshui Basin are abundant and have good production potential. Coal reservoirs are characterized by loose texture, strong adsorption, cutting development, a large surface area, and fracture development, and they tend to be low-porosity, low-permeability, and low-pressure reservoirs with poor overall physical properties (Qin et al, 2012; Guo and Zhang, 2017; Zhu et al, 2017; Lai, 2020; Cui et al, 2021; Taboada Jose and Diaz-Casas VicenteYu, 2021) They usually need to be developed by hydraulic fracturing of gas wells, drainage, reduction of formation pressure, coalbed methane desorption, and gas percolation (Ma, 2003; Zhang et al, 2017; Zhu et al, 2018; Zhu et al, 2019a; Hu et al, 2021; Zhang, 2021). Based on the hypothesis that it is possible that the producing wells fractured the top sandstone water layer during the fracturing process, resulting in some of the gas wells producing significantly more water than the average producing wells, and this study focuses on the effect of the water-bearing layer in the coal seam on the gas production effect of CBM
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