Abstract: Effects of Geologic Variables on Light Oil Co-Production from Coal Seam Gas Reservoirs
NELSON, CHARLES R., LI WENBAO, IULIA M. LAZAR, ABDUL MAKIK, and MILTON L. LEE
Upper Cretaceous coals in the U.S. Rocky Mountain region are an important exploration target for natural gas. Commercially significant amounts of light oils are co-produced with natural gas from some of these coal seam reservoirs. This phenomenon is indirect evidence that these reservoirs also contain significant light oil resources. At present little is known about the content or co-production potential of these light oils.
This paper presents results from analyses of the gross content and co-production trends of light oils from coal seam reservoirs in the U.S. Rocky Mountain region and elsewhere. Coals having similar thermal maturities generally contained similar gross light oil contents irrespective of their geologic age or the reservoir depth which suggests that mobility within the reservoir is the crucial factor effecting the observed light oil co-production volume trends. An empirical observation is that the reservoirs which co-produce light oils appear to exhibit two distinctive characteristics compared to those of other reservoirs. These characteristics are: (1 ) a produced gas stream that is CO-rich and (2) reservoir temperature and pressure conditions higher than the critical point values of C0. Laboratory test data reveal that the light oil solubility or co-produced volume will vary linearly with increasing reservoir pressure or depth when the produced gas is COrich. This depth-dependent solubility relationship is a practical tool for identifying areas with potential for commercially significant light oil co-production from coal seam reservoirs.
AAPG Search and Discovery Article #90946©1997 AAPG Rocky Mountain Section Meeting, Denver, Colorado