Stimulation of natural cleats for gas production from coal beds by graded proppant injection

Abstract

Graded injection of proppant particles with increasing size and decreasing concentration, proposed in the previous paper results in deep percolation of proppant into the natural fracture system, expansion of the stimulated zone and enhanced well productivity index. The mathematical model developed describes the proppant-free water injection stage, the capture kinetics of proppant particles in the natural fractures and the change in well index due to graded proppant injection. Computational fluid dynamics and classical Hertz theory have been used to determine the hydraulic resistance due to proppant plugging in the fracture system and the deformation of fractures during the production stage. An optimal injection schedule, i.e. the timely dependence of the injected proppant size and concentration that avoids fracture closure during production stage and provides minimum hydraulic resistance in the system of fractures plugged by proppant particles has been developed. The model is used to predict the change in well productivity index allowing estimating the feasibility of the graded particle injection for well stimulation in natural fractured systems. The aim of the current paper is to analyse the feasibility of application of the proposed graded proppant injection method for stimulation of the natural fracture system in 3 field cases of large coal bed methane reservoirs.