Modeling and prediction for gas production during coalbed methane drainage based on two indirect reservoir parameters

Abstract

Two indirect parameters influencing coalbed methane (CBM) drainage performances are proposed in this paper, which are effective desorption radius and difference between reservoir pressure and critical desorption pressure (DRPCDP). Variations of the two parameters during CBM drainage are investigated, which shows that they have a linear relationship. By using formula derivations, a theoretical model for gas production prediction is built. It suggests that the cumulative gas production is a product of square of effective desorption radius with DRPCDP, and there is also a cubic polynomial relationship between cumulative gas production and linear average DRPCDP. Furthermore, well PM01 located at southern Qinshui basin of China is selected as a case, and a commercial software is adopted to predict the gas production. Compared with the simulated and modeled cumulative gas productions, the simulated data match well with the modeled data, which indicates that the model has a good accuracy.

Fracturing curve and its corresponding gas productivity of coalbed methane wells in the Zhengzhuang block, southern Qinshui Basin, North China

“…The production of CBM has a process of gas and water complex flow (Li et al., 2017). First, the coal reservoir pressure should be reduced below the critical desorption pressure by extracting the formation water, then CBM desorbs and diffuses from matrix pores to fractures/cleats with the decrease of concentration and pressure, and finally flows into the wellbore through the fracture system (Pan and Da, 2015; Zou et al., 2018). Normally, high rank coals have particular performance of low porosity, low permeability, low reservoir pressure, and high gas saturation (Cai et al., 2018; Singh et al., 2015; Yao et al., 2019).…”