Effect of proppant distribution in hydraulic fractures on coalbed methane extraction

Abstract

Fracturing with proppants is often used to improve the permeability of coalbed methane (CBM) reservoir. The fracture is easy to close under the closure stress and the proppant distribution in fractures greatly influences the extraction efficiency of CBM. The past research mainly considered the impact of fracturing damage on the coalbed methane extraction but rarely investigated the influence of the proppant distribution forms on CBM extraction. Therefore, based on the theory of dual-porous media, this paper establishes a theoretical model of CBM extraction with different proppant distribution forms, which considers the proppant compaction, embedment, and fracture aperture change. The model is implemented numerically and is validated against field results of CBM production. The research results show that the extraction efficiency of CBM from high to low is the pulse proppant injection, continuous proppant injection, no proppant injection, no fracturing. The continuous proppant injection should ensure that the proppant placement rate is more than 60 %. The CBM extraction efficiency is the highest when the proppant column length is 0.2 m–0.3 m and the void area length is 0.5 m. The research results provide a theoretical basis for improving the extraction efficiency of coalbed methane using fracturing with sand injection.

Keywords

• Coal seam
• Hydraulic fractures
• Proppant embedment
• Continuous proppant injection
• Pulse proppant injection