AAPG Bulletin; July 2009; v. 93; no. 7;
p. 857-889; DOI: 10.1306/03230908032
© 2009 American Association of Petroleum Geologists (AAPG)
Joint sets that enhance production from Middle and Upper Devonian gas shales of the Appalachian Basin
Terry Engelder1,
Gary G. Lash2 and
Redescal S. Uzcátegui3
1 Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802; jte2{at}psu.edu
2 Department of Geosciences, State University of New York, College at Fredonia, Fredonia, New York 14063
3 Departamento de Ciencias de la Tierra, Simón Bolívar, Caracas, Venezuela; present address: Intevep, S.A., Apartado Postal 76343, Caracas 1070A, Venezuela
Terry Engelder, a leading authority on the recent Marcellus gas shale play, received his B.S. degree from Pennsylvania State University (1968), his M.S. degree from Yale University (1972), and his Ph.D. from Texas A&M University (1973). He is currently a professor of geosciences at Penn State and has previously served on the staff of the U.S. Geological Survey, Texaco, and Lamont-Doherty Earth Observatory. He has written 150 research papers, many focused on fracture in Devonian rocks of the Appalachian Basin, and a book, Stress Regimes in the Lithosphere.
Gary Lash, an authority on various aspects of the Middle and Upper Devonian shale succession of western New York, received his B.S. degree from Kutztown State University (1976) and his M.S. degree and Ph.D. from Lehigh University (1978 and 1980, respectively). Before working in western New York, Lash was involved in stratigraphic and structural investigations of thrusted Cambrian–Ordovician deposits of the central Appalachians.
Redescal Uzcátegui is a professor of structural geology at the Universidad Simón Bolívar and an I&D (Instruction & Development) associated professional in tectonics and structural geology at Petroleos de Venezuela, S.A. (PDVSA)-Intevep. He received his B.A. degree in geology at the Universidad Central de Venezuela and his Ph.D. in geosciences from the Pennsylvania State University. His current focus of research is the geometry and evolution of structures and fractures in the Perijá and Andes de Mérida foothills, and the Maracaibo Basin in Venezuela.
ABSTRACT
The marine Middle and Upper Devonian section of the Appalachian Basin includes several black shale units that carry two regional joint sets (J1 and J2 sets) as observed in outcrop, core, and borehole images. These joints formed close to or at peak burial depth as natural hydraulic fractures induced by abnormal fluid pressures generated during thermal maturation of organic matter. When present together, earlier J1 joints are crosscut by later J2 joints. In outcrops of black shale on the foreland (northwest) side of the Appalachian Basin, the east-northeast–trending J1 set is more closely spaced than the northwest-striking J2 set. However, J2 joints are far more pervasive throughout the exposed Devonian marine clastic section on both sides of the basin. By geological coincidence, the J1 set is nearly parallel the maximum compressive normal stress of the contemporary tectonic stress field (SHmax). Because the contemporary tectonic stress field favors the propagation of hydraulic fracture completions to the east-northeast, fracture stimulation from vertical wells intersects and drains J2 joints. Horizontal drilling and subsequent stimulation benefit from both joint sets. By drilling in the north-northwest–south-southeast directions, horizontal wells cross and drain J1 joints, whenever present. Then, staged hydraulic fracture stimulations, if necessary, run east-northeast (i.e., parallel to the J1 set) under the influence of the contemporary tectonic stress field thereby crosscutting and draining J2 joints.
Copyright © 2009 by American Association of Petroleum Geologists (AAPG)
