Geological controls on coalbed methane accumulation and optimisation strategy for gas productivity: a case study in eastern Ordos Basin, China

Abstract

Drainage conditions can significantly affect the coalbed methane (CBM) production, which is accomplished by reducing the gas partial pressure in the coal seam. This can be achieved by pumping the formation water or gas injection. In this study, the Baode region is selected to study the drainage conditions and production characteristics on the early stage of CBM production. The temporal trends of water production, wellhead pressure and gas production have been analysed. Results show that the favourable burial depth for CBM accumulation between 500 and 700 m. Sandy mudstone and mudstone are beneficial to CBM preservation. The wellhead pressure should be maintained between 0.4 MPa and 1.0 MPa, and the optimal range of wellhead pressure lies between 0.5 and 0.8 MPa for stable production. The gas production increases with increased water production when the wellhead pressure has become progressively stable in the middle phase of early stage. [Received: September 9, 2018; Accepted: October 24, 2018]