GAS INJECTION AND BREAKTHROUGH TRENDS AS OBSERVED IN ECBM SEQUESTRATION PILOT PROJECTS AND FIELD DEMONSTRATIONS

摘要

Enhanced coalbed methane(ECBM)recovery is of growing interest primarily because its' synergistic application with carbon sequestration(in the case of carbon dioxide(CO2)injection),and the potential to unlock coalbed methane(CBM)resources that are sub-economic to produce via conventional means(in the case of nitrogen(N2)injection).However there is limited field experience with ECBM technology,and the experience that does exist suggests that the reservoir dynamics at play with ECBM are more complex than those under primary CBM production.While laboratory studies provide a valuable foundation upon which to base working hypotheses for understanding reservoir behavior,reconciling these hypotheses to field observations is an important element of the learning process.Based upon the experiences at three ECBM/sequestration pilots projects and field demonstrations-the Allison CO2-ECBM pilot in the San Juan basin,the Tiffany N2-ECBM pilot,also in the San Juan basin,and the RECOPOL CO2-sequestration demonstration in Poland-trends regarding gas injection and breakthrough are emerging,most generally consistent with current understanding of reservoir behavior,but some not.Specifically,as predicted by laboratory experiments,coal permeability(i.e.,injectivity)is reduced with CO2 injection due to swelling,and is enhanced by N2 injection.Rapid breakthrough of N2 also occurs,as one would expect based on relative sorption capacities.However,an apparently "disperse" flood front at the Allison Unit,and rapid CO2 breakthrough at the RECOPOL project,was unexpected.While a number of possible mechanisms have been put forth to explain these observations,primarily based upon reservoir simulation studies,uncertainty remains.The experience gained from these pilots and demonstrations suggests that while a sound fundamental understanding of the ECBM/sequestration process is believed to exist,there is still much to learn,particularly regarding how CO2 and coal interact.