Adsorption of pure carbon dioxide and methane on dry coal from Sulcis coal Province (SW Sardinia, Italy).

Abstract

When coal seams are formed by compaction of plants, gases including methane are generated and accumulated into the coal cleats or adsorbed into the coal micropores. Such coalbed methane is normally recovered by means of reservoir-pressure depletion, i.e. by pumping out water and degassing the reservoir. A more attractive process with higher yields is the so-called Enhanced Coal Bed Methane recovery (ECBM), whereby carbon dioxide is pumped into the coal seam to displace methane thanks to higher CO2 adsorptivity. Injecting CO2 in unminable coal seams leads not only to methane recovery but also to CO2 sequestration. The factors still limiting the implementation of ECBM recovery are economical, i.e. lack of penalties for CO2 emissions, as well as technological and scientific, i.e. limited understanding of fundamental issues related to ECBM. Therefore, the goal of this study is to combine experimental measurements and modelling to characterize pure and multicomponent competitive adsorption of CO2 and CH4 on coal and study the coalbed dynamics using breakthrough experiments, including the effect of the injection of CO2 on matrix swelling and permeability. Since December 2004, a feasibility study throughout the Sulcis Coal Province in Sardinia [Quattrocchi, 2004] is in progress and one of its objectives is to correlate the results of the mentioned experiments with the compositional patterns of the coal, considering its role in the CBM-ECBM exploitation.