Deep coalbed methane (DCBM), an unconventional gas reservoir, has undergone significant advancements in recent years, sparking a growing interest in assessing pore pressure dynamics within these reservoirs. While some production data analysis techniques have been adapted from conventional oil and gas wells, there remains a gap in the understanding of pore pressure generation and evolution, particularly in wells subjected to large-scale hydraulic fracturing. To address this gap, a novel technique called excess pore pressure analysis (EPPA) has been introduced to the coal seam gas industry for the first time to our knowledge, which employs dual-phase flow principles based on consolidation theory. This technique focuses on the generation and dissipation for excess pore-water pressure (EPWP) and excess pore-gas pressure (EPGP) in stimulated deep coal reservoirs. Equations have been developed respectively and numerical solutions have been provided using the finite element method (FEM). Application of this model to a representative field example reveals that excess pore pressure arises from rapid loading, with overburden weight transferred under undrained condition due to intense hydraulic fracturing, which significantly redistributes the weight-bearing role from the solid coal structure to the injected fluid and liberated gas within artificial pores over a brief timespan. Furthermore, field application indicates that the dissipation of EPWP and EPGP can be actually considered as the process of well production, where methane and water are extracted from deep coalbed methane wells, leading to consolidation for the artificial reservoirs. Moreover, history matching results demonstrate that the excess-pressure model established in this study provides a better explanation for the declining trends observed in both gas and water production curves, compared to conventional practices in coalbed methane reservoir engineering and petroleum engineering. This research not only enhances the understanding of DCBM reservoir behavior but also offers insights applicable to production analysis in other unconventional resources reliant on hydraulic fracturing.

中文翻译：

---

深层煤层气储层超孔隙水压力行为及演化


深层煤层气（DCBM）是一种非常规气藏，近年来取得了重大进展，引发了人们对评估这些储层内孔隙压力动态的日益浓厚的兴趣。虽然一些生产数据分析技术是从传统油气井中改编而来的，但对孔隙压力的产生和演变的理解仍然存在差距，特别是在经历大规模水力压裂的井中。为了解决这一差距，据我们所知，一种称为超孔隙压力分析（EPPA）的新技术首次被引入煤层气行业，该技术采用基于固结理论的双相流原理。该技术重点研究深层煤储层超孔隙水压力（EPWP）和超孔隙气体压力（EPGP）的产生和消散。分别建立了方程并使用有限元法（FEM）提供了数值解。将该模型应用于代表性的现场实例表明，超孔隙压力是由快速加载引起的，由于强烈的水力压裂，在不排水条件下覆盖层重量转移，这显着地将承重作用从固体煤结构重新分配到注入流体，并且在短时间内在人造孔隙内释放气体。此外，现场应用表明，EPWP和EPGP的消散实际上可以看作是井生产过程，从深层煤层气井中提取甲烷和水，导致人工储层固结。 此外，历史拟合结果表明，与煤层气藏工程和石油工程的常规实践相比，本研究建立的超压模型可以更好地解释产气和产水曲线中观察到的下降趋势。这项研究不仅增强了对 DCBM 储层行为的理解，而且还为依赖水力压裂的其他非常规资源的生产分析提供了见解。