ABSTRACT: Performance comparison of various injection schemes in enhanced recovery of coalbed methane

Manik, Julio¹and Turgay Ertekin²
(1) ICF Resources Inc, Fairfax, VA
(2) Penn State University, University Park, PA

Performance comparisons of nitrogen and carbon dioxide injections in enhanced coalbed methane recovery are presented. A compositional coalbed simulator was developed and utilized for the enhanced recovery study. Effects of injected gas mole fraction, delayed injection, and well spacing on the recovery performance are examined. Performances of cyclic injection/production and intermittent gas injection techniques are analyzed. Reservoir simulation study showed that both nitrogen and carbon dioxide injections are able to yield ultimate methane recovery of 100% in relatively short periods of time. Using the same operating condition, injection volume of nitrogen is less than that of carbon dioxide injection. Using the same condition, however, breakthrough time of carbon dioxide is more prolonged. Carbon dioxide as an additive in nitrogen injection does not improve the nitrogen breakthrough time. Nitrogen as an additive in carbon dioxide injections improves methane production to gas injection ratio. The effect of delayed injection to methane concentration in produced gas is more pronounced in the nitrogen injection. Well spacing reduction does not influence the peak of methane production to carbon dioxide injection ratio. The well spacing reduction, however, decreases methane production to nitrogen injection ratio significantly. Cyclic injection/production technique could lower methane recovery as the injected gas contaminates and lowers methane concentration in the gas production. Intermittent gas injection is able to approach the ultimate methane recovery of the continuous injection technique with less volume of gas injected.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia