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Developing a Hydrocarbon Exploration Tool in a Foreland Basin: Arkoma Basin, Oklahoma and Arkansas, USA


The Arkoma Foreland basin of the Pennsylvania Ouachita fold -thrust belt in Oklahoma and Arkansas contains over 4 TCF of undiscovered natural gas. Since the mid-1990's, my colleagues, graduate students, and I have constructed over 20 balanced structural cross-sections and plotted different sandstone sedimentary facies on the cross-sections to locate the extent of the porous zones likely to have hydrocarbon reservoir. By the turn of the millennia, our work evolved into compartmentalization and fault sealing studies. The thrust faults in the horses of the duplex structures are overpressured and thrust faults act as permeability barriers. Later, 3D seismic data gave us a chance to refine our structural cross-sections. We found out that duplexes in the basin do not only contain break-forward hinterland dipping thrust faults but also contain foreland dipping backthrusts which cause structural thickening and provide much thicker reservoir intervals in many wells, previously attributed to sedimentary facies changes. Recently, we have been using seismic attributes to define the relationship between reservoir porosity and seismic impedance. The areas of tighter anticlinal folds correlated reasonably well with the lower acoustic impedance values in thick sandstone reservoir intervals. Our research in the Arkoma Basin indicates that a successful gas well in the Arkoma Basin should be drilled into the hanging wall of folded sandstone reservoirs in the duplex structure where porosity is controlled by sedimentary facies and faulting serves as the hydrocarbon seal. Backthrusts in the horses may cause structural thickening and thus can enhance reservoir thickness. Seismic impedance values can also be used to determine the porous zones if the sandstone reservoir is recognizable by the tuning thickness intervals.