Fractured Devonian Shale Reservoir, Appalachian Basin: ABSTRACT

Abstract

Detailed structural analysis along the west flank of the Appalachian basin in Kentucky and West Virginia demonstrates the importance of detached and basement deformation in developing fracture permeability within Devonian shales. A porous fracture facies of regional extent within the organic-rich lower Huron Member of the Devonian shale partially relates to unique physical properties of the organic sediments, but an important factor for widespread gas production is fractures caused by differential shortening of sediments above a detachment surface in the lower Huron Member. Mineralized, uniquely oriented, and slickensided fractures, and increased fracture intensity within the organic lower Huron shales perpendicular to Alleghanian stress support this interpretation. The p rous fracture facies is most permeable (commercial) beyond the region of major tectonic transport where permeability is only local in extent. Linear trends of abnormally high final open flows in the producing area relate to trends of intensely fractured organic shale. These fracture zones seemingly reflect unique, complex, and perhaps more intense shear stress within organic shale found in flexures above basement faults. Gas migrated updip along open fractures placing the best wells slightly updip along the fracture trend or on the flank of adjacent low-relief flexures. This unique reservoir forms its own source and seal, and the lithologically restricted fracture facies imparts the permeability. Tailoring completion techniques which limit the vertical extent of induced fractures and whi h enhance recovery in the more common orthogonally fractured shale of the mid-continent region will be important for future development of this huge resource. End_of_Article - Last_Page 630------------