Transp Porous Med (2008) 75:35–54 DOI 10.1007/s11242-008-9209-9 Competitive Methane Desorption by Supercritical CO 2 Injection in Coal Ji-Quan Shi · Saikat Mazumder · Karl-Heinz Wolf · Sevket Durucan Received: 22 May 2006 / Accepted: 21 January 2008 / Published online: 13 February 2008 © Springer Science+Business Media B.V. 2008 Abstract A large diameter (∼70mm) dry coal sample was used to study the competitive displacement of CH 4 by injection of supercritical CO 2 , and CO 2 –CH 4 counter-diffusion in coal matrix. During the test, a staged loading procedure, which allows the calibration of the key reservoir modelling parameters in a sequential and progressive manner, was employed. The core-flooding test was history matched using an Enhanced Coalbed Methane (ECBM) simulator, in which Fick’s Law for mixed gas diffusion and the extended Langmuir equations are implemented. The system pressure rise during the two loading stages and the CO 2 break- through time in the final production stage were matched by using the pair of constant sorption times (9 and 3.2 days) for CH 4 and CO 2 , respectively. The corresponding diffusion coeffi- cients for CH 4 and CO 2 were estimated to be 1.6 × 10 -12 and 4.6 × 10 -12 m 2 /s, respectively. Comparison was made with published gas diffusion coefficients for dry ground samples (ranging from <0.063 to ∼3 mm) of the same coal at relatively low pressures (<4 MPa). The CO 2 /CH 4 gas diffusion coefficient ratio was well within the reported range (2–3), whereas the CH 4 diffusion coefficient obtained from history matching of the core-flooding test is approx- imately 15 times smaller than that arrived by curve-fitting the measured sorption uptake rate using a unipore diffusion model. The calibrated model prediction of the effluent gas compo- sition was in good agreement with the test data for CO 2 mole fraction of up to 20%. Keywords CO 2 storage · Enhanced methane recovery · Coal · Supercritical CO 2 · Competitive desorption · Numerical simulation J.-Q. Shi (B ) · S. Durucan Imperial College, London, UK e-mail: j.q.shi@imperial.ac.uk S. Mazumder · K.-H. Wolf Technical University of Delft, Delft, The Netherlands Present Address: S. Mazumder Shell International Exploration and Production B.V., The Hague, The Netherlands 123