A Prediction Model for Pressure Propagation and Production Boundary during Coalbed Methane Development

Abstract

In coalbed methane field development, an accurate understanding of dynamic propagation of reservoir pressure is crucial for predicting production potential, enhancing recovery, and engineering planning. Based on actual reservoir conditions and production data, a semi-analytical mathematical model that considers the self-regulating effects of coal reservoirs was established for both nonstimulated and hydraulically fractured vertical wells in undersaturated coal reservoirs. In the model, undersaturated coal seam is divided into the drainage area and desorption area. Material balance equations (MBE) are deduced based on the unique gas–water production mechanism of coal seams, and pressure profiles are expressed as continuous succession of steady state flow. The pressure propagation can be finally predicted by combining MBE and pressure profiles in different areas. Three hydraulically fractured vertical wells with different production characteristics in the Shizhuangnan Block, southern of Qinshui Basin are taken as examples to verify the applicability of the model. Results show that dynamic pressure propagation of a single well is accurately characterized in the early production stage, and the shape of the pressure propagation area translates from an ellipse into a circle during production; actual interference boundaries or damage boundaries are precisely predicted when interwell pressure interference is formed or a poor production strategy is adopted, respectively. Additionally, mechanism analysis under a mathematic model and orthogonal experiment evaluation are adopted to quantify the sensitivity of various parameters on the prediction results. Results show that coal reservoir physical properties, especially critical desorption pressure and porosity, mainly affect drainage radius expansion, whereas human factors and adsorption performance are the key factors influencing the desorption radius. The proposed model develops an accurate and efficient mathematical method for evaluating dynamic characteristics of pressure propagation in undersaturated coal reservoir and predicting production boundary and finally provides valuable guidance for the formulation of reasonable development plans.

Coalbed methane reservoir dynamic simulation comparisons using the actual steeply inclined model and ideal steeply inclined model

“…The drainage of CBM wells causes the formation of a pressure drop funnel, but the distribution of reservoir pressure is not uniform in space, and the pressure change also shows a nonlinear curve (Wang et al, 2012). In the process of studying reservoir pressure dynamics through numerical simulation, coal Frontiers in Earth Science frontiersin.org seams are usually assumed to be homogeneous (Yan et al, 2021). However, under special geological conditions, homogeneous coal reservoirs are no longer applicable.…”

Dewatering Optimization of Coal Seam Gas Production Wells: A Review and Future Perspectives

“…Further work by Yan et al divided the coal seam into drainage and desorption areas and extended their previous analytical model by including the hydraulic fracture in the dynamic pressure propagation during dewatering. Although the focus of that work was not on the optimization of depressurization, it emphasizes that desorption pressure and porosity are the main factors affecting drainage area, and Langmuir volume and hydraulic fracture length greatly influence the desorption area . The parametric study can provide valuable information when further optimizing the pressure-drop rate.…”

“…Although the focus of that work was not on the optimization of depressurization, it emphasizes that desorption pressure and porosity are the main factors affecting drainage area, and Langmuir volume and hydraulic fracture length greatly influence the desorption area. 256 The parametric study can provide valuable information when further optimizing the pressure-drop rate.…”

Primary studies on the effect of coal bio-gasification in situ in the Qinshui basin

“…Related researches such as increasing the reserves of coalbed methane (Wang et al 2014), improving the coal porosity (Xu et al 2017) have become the research focus of coal fluidized mining. Therefore, research involving coal gasification methods, gas drainage mechanisms, and applications, which serves to improve gas well productivity, has gradually deepened (Zhang et al 2020;Guo et al 2021;Yan et al 2021). Coal bio-gasification is a key technology, and related research started in the Dong Xiao and Enyuan Wang have contributed equally to this work and should be considered co-first authors.…”