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

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.

Effect of CO2 injection on Coalbed Permeability Based on a Thermal–Hydraulic–Mechanical Coupling Model

“…Field data for the Qinshui Basin shown in the plots are taken from Hu et al Adapted from ref . Available under a CC-BY 4.0 license.…”

“…It has the characteristics of uniform thickness, high gas content, shallow burial depth, etc. The study by Hu et al59 presents time-dependent data on daily methane production from producing wells in the Zhengzhuang block of the southern Qinshui Basin. In the numerical simulation, we set up a 100 m × 100 m coal seam with the CO 2 injection borehole at the lower left and the production borehole at the upper right.…”

Research on deep gas geological laws and gas prediction: a case study of the Lvjiatuo coal mine

“…In the same geological unit, the law of gas accumulation is often dominated by one geological factor, while other geological factors cause the uneven distribution of gas in that geological unit. (Cai et al 2011;Yan et al 2014;Zhang et al 2017;Li et al 2018;Zhang et al 2019;Li et al 2020;Hu et al 2020;Esen et al 2020;).…”

Drainage Type Classification and Key Controlling Factors of Productivity for CBM Wells in the Zheng Zhuang Area, Southern Qinshui Basin, North China

“…The CBM productivity of a well is controlled by many complicated geological and engineering factors. The geological factors reflect the reservoir properties, strata permeability, and desorption and adsorption characteristics of the coal reservoir, including gas content, porosity, thickness of the coal seam, permeability, burial depth, coal structure, in situ stress, hydrogeological conditions, and geological structures. ,− The engineering factors are mainly concerned with drilling and completion methods, reservoir reconstruction techniques, well pattern deployment methods, drainage system, and stimulation measures …”