Evaluation of CO2 Injection in Shale Gas Reservoirs Based on Numerical Simulation

Abstract

Shale gas is natural gas that is found trapped within a typical sedimentary rock derived from clastic sources which is known as shale. The combination of two advanced technologies (horizontal drilling and hydraulic fracturing) has helped to access to a large volumes of shale gas that was previously not producible. In this paper, the performance of CO2 injection and CH4  recovery in shale gas reservoirs is evaluated. The study reveals that it is a complex function a several parameters such as CO2 injection time, soaking time, injection volume, reservoir permeability, reservoir porosity, and thickness. Numerical simulation is performed to model CO2 huff-n-puff process and multicomponent Langmuir isotherms in the Barnett Shale formation; two horizontal wells are performed for this case. Results show that CO2-EGR is very efficient for shale gas and a recovery factor of 82.6% can be obtained by this process. Besides, an analytical study is done in order to facilitate the estimation of recovery factor based on critical parameters obtained from simulation. A comparison study of the observed data from simulation and the estimated date from some production decline models such as LGA (Logistic Growth Analysis) model, and Ali model is also performed in this study.