A field study on simulation of CO2 injection-ECBM production and prediction of CO2 storage capacity in un-mineable coal seam

Abstract

Studies have shown that, coal seam, an un-conventional reservoir, is considered as a promising option for CO2 sequestration because of its large CO2 sequestration capacity, long time CO2 trapping and extra enhanced coal-bed methane (ECBM) production benefits. However, unlike conventional reservoirs, gas flow in the coal seam can cause the cleat permeability and porosity change during the injection/production process. In other words, for example, once gas is injected and adsorbed on coal matrix, the matrix will swell, and the cleat permeability and porosity will decrease correspondently. Because of its special features and the nature of gas retention in CBM reservoirs, simulating the production and injection will have more complexity compared to conventional resources. In this paper, a real project is studied and is used to simulate the primary and secondary coal bed methane production and CO2 injection. The key geological and reservoir parameters that are germane to driving ECBM and sequestration processes, including cleat permeability, cleat porosity, CH4 adsorption time, CO 2 adsorption time, CH4 Langmuir Isotherm, CO2 Langmuir Isotherm, Palmer and Mansoori parameters, have been analyzed and varied within a reasonable range consistent with typical coal seam performance through sensitivity analysis. The final simulation results of the CBM/ECBM production and CO2 injection show a perfect match with the actual data. The history matched model is selected thereafter to predict total CO2 sequestration capacity in this field, which gives a very good approximation of the initial calculation by the company based on experimental results. Some predictive scenarios for CO2 injection have been performed and the results are shown in the following sections in order to evaluate how much CO2 can be injected in the next few years or, when the required CO2 injection amount can be fulfilled. In the end, a suggestive simplified workflow for CO2 sequestration-ECBM simulation is addressed.