A Four-Component, Two-Phase Flow Model for CO2 Storage and Enhanced CoalbedMethane Recovery

摘要

Injection of CO2 into deep unminable coal seams is an optionrnfor geological storage of CO2. Moreover, injection of CO2rnmay enhance the recovery CH4 in these systems making coalrnreservoirs interesting candidates for sequestration.rnNew analytical solutions are presented for two-phase,rnthree- and four-component flow with volume change onrnmixing in adsorbing systems. We analyze the simultaneousrnflow of water and gas containing multiple adsorbingrncomponents. The displacement problem is solved by thernmethod of characteristics. Mixtures of N2, CH4, CO2 and H2Ornare used to represent enhanced coal bed methane recoveryrnprocesses. The displacement behavior is demonstrated to bernstrongly dependent on the relative adsorption strength of therngas components.rnIn ternary systems, two types of solutions result. When arngas rich in CO2 displaces a less strongly adsorbing gas (likernCH4), a shock solution results. As the injected gas propagatesrnthrough the system, CO2 is removed from the mobile phase byrnadsorption, while desorbed gas propagates ahead of the CO2rnfront. The adsorption of CO2 reduces the flow velocity of therninjected gas, delaying breakthrough and allowing for morernCO2 to be sequestered per volume of CH4 produced. Forrninjection gases rich in N2, a decrease in partial pressure isrnrequired to displace the preferentially adsorbed CH4, and arnrarefaction solution results.rnIn quaternary displacements with injection gas mixtures ofrnCO2 and N2, the relative adsorption strength of therncomponents result in solutions that exhibit features of both thernN2-rich and CO2-rich ternary displacements.rnAnalytical solutions for enhanced coal bed methanern(ECBM) recovery processes provide insight into the complexrninterplay of adsorption, phase behavior and convection.rnImproved understanding of the physics of these displacementsrnwill aid in developing more efficient and physically accuratetechniques for predicting the fate of injected CO2 in thernsubsurface.