Joint sets that enhance production from Middle and Upper Devonian gas shales of the Appalachian Basin

Abstract

A B S T R A C TThe marine Middle and Upper Devonian section of the Appalachian Basin includes several black shale units that carry two regional joint sets (J 1 and J 2 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 J 1 joints are crosscut by later J 2 joints. In outcrops of black shale on the foreland (northwest) side of the Appalachian Basin, the eastnortheast-trending J 1 set is more closely spaced than the northwest-striking J 2 set. However, J 2 joints are far more pervasive throughout the exposed Devonian marine clastic section on both sides of the basin. By geological coincidence, the J 1 set is nearly parallel the maximum compressive normal stress of the contemporary tectonic stress field (S Hmax ). 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 J 2 joints. Horizontal drilling and subsequent stimulation benefit from both joint sets. By drilling in the north-northwestsouth-southeast directions, horizontal wells cross and drain J 1 joints, whenever present. Then, staged hydraulic fracture stimulations, if necessary, run east-northeast (i.e., parallel to the J 1 set) under the influence of the contemporary tectonic stress field thereby crosscutting and draining J 2 joints.

Geochemical evidence for possible natural migration of Marcellus Formation brine to shallow aquifers in Pennsylvania

“…In the Michigan Basin, upward migration of saline fluid into the overlying glacial sediments (34,35) was interpreted to reflect isostatic rebound following the retreat of glaciers, leading to fracture intensification and increased permeability (34). Alternatively, vertical migration of over-pressured hydrocarbons has been proposed for the Appalachian Basin in response to tectonic deformation and catagensis (i.e., natural gas induced fracturing) during the Alleghenian Orogeny (38)(39)(40). This deformation resulted in joints that cut across formations (J 2 ) in Middle and Upper Devonian formations (39).…”

Well water contamination in a rural community in southwestern Pennsylvania near unconventional shale gas extraction

“…The laterals follow a north-north west or south-south-east drilling direction to take advantage of the enhanced permeability of the J 1 joint of the Marcellus shale, maximizing yields. [59] The large volumes of fluids and proppant used in the slick water hydraulic fracturing of the new wells (on average 3.2 million gal. and 3 million lbs, respectively) ( Table 6) could also affect the local hydrology and contribute to subsurface disturbance resulting in well water contamination.…”

Seismic sensitivity to variations of rock properties in the productive zone of the Marcellus Shale, WV

“…Two sets of regional joints (J1 and J2) from outcrops and geophysical well logs in different parts of the Appalachian basin have been documented and analysed by numerous authors. It is postulated that 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 (Engelder et al, 2009). The overall trend of J1 joint is east-northeast while the J2 joint trends northwest.…”