A modified exponential decline method for shale gas reservoirs

Abstract

Compared with the conventional reservoir, the production rate in shale gas reservoir declines rather quickly during the early production period and conventional decline rate analysis becomes not suitable for shale gas production. In this article, we build a four parameter empirical decline model considering the varying decline exponent and terminal decline rate and propose a simple but efficient calculation method. By analyzing the sharp-to-shallow decline trend, a sophisticated decline rate form was assumed, which takes the initial decline rate, terminal decline rate and the curvature of the decline rate curve into consideration. For shale gas reservoirs with short production time and little production data, the early production data may not reflect the real terminal decline rate. A modification for such cases is also proposed. Field examples from a synthetic shale gas reservoir, Barnett shale gas, Haynesville shale gas and Fuling shale gas were used to test our newly proposed model. [Received: October 27, 2017; Accepted: January 30, 2018]