Because of the diversity of this type of accumulation, they are poorly understood, hindering recognition and development of effective exploration strategies. Reservoirs may be single and isolated or vertically stacked reservoirs several 1000 meters thick. Gas saturated reservoirs Gas of thermal origin Water most often present as irreducible water Thick regionally pervasive accumulations commonly contain interbedded water-bearing reservoirs. Looking beyond common attributes, BCGS can be further divided into two distinct types direct and indirect.
Direct types have gas-prone source rock.
Because direct type reservoirs are not limited structurally and stratigrapically, reconstruction of their thermal history is, the most important factor in formulating an exploration strategy. Lance Formation, Fox Hills. Indirect types of BCGS have oil-prone source rock and are confined within basinal stratigraphic units so it is critically important to understand the time relationships among hydrocarbon generation expulsion, migration and trap formation. See Page 4 for a summary of on-going and future research directed at the Lewis Shale in the Greater Green River Basin. The screening is part of a current re-evaluation of the resource potential of BCGA in the U.S., prompted by such changing geologic perceptions about BCGA as sweet spots produced by subtle structures and by the availability of new data.