Abstract: Possibility of Abnormally High Fluid Pressures During Folding and Faulting in Eastern West Virginia

William J. Perry, Jr.

The abundance of calcite- and quartz-filled extension fractures (veins) in brittle rocks below the thick Middle to Upper Devonian shale sequence indicates that abnormally high fluid pressures, sufficient to fracture hydraulically Lower Devonian and older rocks or to open preexisting fractures, may have existed during folding and faulting in eastern West Virginia. The geometry and orientation of the fractures indicate formation by tectonic stresses. Geologic field relations indicate a depth of burial greater than 2,500 m for the intensely fractured Lower Devonian and older sandstones and limestones during tectonism. On the basis of the work of D. T. Secor, such fracturing (in an entirely compressive stress field) is symptomatic of natural hydraulic fracturing.

Abnormally high fluid pressures in Lower Devonian and older rocks during tectonism would be responsible for the locally high degree of fracture porosity in the Lower Devonian and older sandstone reservoirs in the area, but also may have affected the petroleum potential of the more deeply buried rock sequence.

Localized extension fractures, adjacent to thrust faults in rocks as young as Mississippian, suggest that the faults were conduits for fluids and that abnormal fluid pressures may have existed locally adjacent to the thrust faults during formation of the faults.

AAPG Search and Discovery Article #90972©1976 AAPG-SEPM Annual Convention and Exhibition, New Orleans, LA