Impact of Sorption Isotherms On the Simulation of CO2-Enhanced Gas Recovery and Storage Process in Marcellus Shale

Continuous, low-permeability, fractured, organic-rich gas shale units are widespread and are possible geologic storage targets .The Marcellus could act as a storage reservoir for captured CO₂. In this scenario, Marcellus could provide favorable CO₂ adsorption as well as available pore space from massive hydraulic fracture treatment.

One of the key components of a CO₂-Enhanced Gas Recovery and Storage (CO₂-EGR&S) process is considering the impact of sorption isotherms. The isotherm represents the thermodynamic limit of how much carbon dioxide or methane can be stored in shale at a given pressure.

In this paper, a shale gas simulation model is developed and history matching process is performed for multi stage/clusters hydraulically fractured horizontal wells in Marcellus shale. Before starting the injection process, both wells that are already history matched are continuing their production to reach to the point that one of the production wells, which is going to be converted to an injection well, produces 75% of its accessible gas.

The history matched and depleted simulation model is then used to perform the sensitivity analysis in order to identify the impact of both methane and carbon dioxide sorption isotherms on cumulative methane production, total injected CO₂ and CO₂ breakthrough time and molar density of methane and CO₂ changes in both producer and injector and also a monitoring well in between. In order to express the relative adsorption capacities of CH₄ and CO₂, the separation factor or CO₂-CH₄ competitive adsorption capacity are defined.