Chapter 17 - Coalbed Methane Evaluation and Development: An Example from Qinshui Basin in China

Abstract

It is estimated that the original in-place coalbed methane resources in China above a depth of 2000m are approximately 36.81×1012 m3. The Qinshui Basin, situated in Central China, is the most mature basin for coalbed methane exploration and development in China, with estimated original in-place resources of 3.85×1012m3 in Pennsylvanian–Permian coalbeds. This basin has experienced a number of tectonic activities after the deposition of coals. Gas generation reached its first peak before the late Triassic period and its second peak during the late Jurassic to early Cretaceous periods due to a tectonic thermal event, which raised the coal rank to low volatile bituminous-anthracite over most of the basin. The Pennsylvanian–Permian coals in the Qinshui Basin are in a high rank, with a high methane content and low permeability. Low permeability and effective stress-dependent coal reservoirs lead to challenges for coalbed methane development, including: (1) selection of well completion types; (2) selection of site/interval for fracturing operations; (3) new technology for permeability enhancement operations and fracturing volume design; and (4) dewatering and production management. In this chapter, we present the results of our study, including: (1) on the selection of well completion types, one major direction is cased single-lateral wells with staged fracturing for enhancing the permeability of coals; (2) cross-sections showing lithological assemblages overlying and underlying the target coals are good methods for the selection of site/interval for fracturing operations; (3) fracturing–acidizing operations are proposed in the face of the cleats filled with calcite; and (4) early dewatering control is necessary to prevent the fast permeability decrease caused by increasing effective stress.