In the central Appalachian basin, sandstones of the Catskill-Pocono delta have produced commercial oil and gas for over a century. In northern West Virginia, spatial and temporal relationships in this sequence (Chemung, Hampshire, and Pocono Formations) are poorly defined and understood.
Correlation using base-lined (relative method) gamma-ray logs, supplemented by lithologic logs and outcrop study, elucidates detailed lithostratigraphic and chronostratigraphic interrelationships including: (1) development of a stratigraphic and sedimentologic “framework” for these strata, (2) illustration of “true” thickness variations of subsurface rock units, (3) determination of distribution and position of “clean” sandstone and red-bed lithofacies, (4) identification of persistent sandstone trends through time, (5) positioning of time lines, which pass through apexes of maximum onlap and offlap, and (6) recognition of an angular unconformity as the upper sequence boundary.
Resultant cross sections illustrate subtle stratigraphic relationships including intertonguing lithofacies, updip and downdip pinch-outs of shallow marine sandstones, and probable cross-slope channel and lobe deposits of turbiditic origin. In addition, subsurface-to-outcrop correlation resulted in identification and description of various gas-bearing sandstones on outcrop, and in correlation of subsurface lithostratigraphic units to outcrop lithofacies.
A similar methodology is recommended for subsequent studies to determine “true” and/or net thickness of a particular facies (i.e., organic-rich shale, “clean” sandstone, or “tight” sandstone). The same approach may be used in other basins where: (1) adequate numbers of gamma-ray logs are available, (2) a consistent shale base line may be determined, and (3) a “clean” sandstone lithofacies or uniform carbonate section is present for determination of a clean sandstone or minimum deflection base line.