Microseismic evidence for horizontal hydraulic fractures in the Marcellus Shale, southeastern West Virginia

Abstract

An integrated analysis of multistage hydraulic fracture stimulation done in three horizontal wells in the Marcellus Shale in southeastern West Virginia revealed that nearly half (14 out of 31) of the examined stages initiated horizontal hydraulic fractures. The study was performed in an area characterized by a transitional strike-slip/reverse faulting stress state where the maximum horizontal principal stress (SHmax) is oriented N55°E. The stages that produced horizontal hydraulic fractures were all within the organic-rich Lower Marcellus Shale. Two lines of evidence indicate horizontal hydraulic fracture propagation. The measured least principal stress of those stages was of similar magnitude to the vertical stress (SV), indicating that the vertical stress and microseismic events are limited to a narrow horizontal layer and do not propagate vertically out of the Lower Marcellus Shale. Both lines of argument indicate that the vertical stress is the least principal stress, perhaps due to viscoplastic stress relaxation in the clay- and kerogen-rich Lower Marcellus Shale. In the 17 stages where perforations were placed in the stiffer Onondaga and Cherry Valley formations, the measured least principal stresses were less than the magnitude of SV, indicating that Shmin was the least principal stress. The microseismic data indicate vertical hydraulic fracture propagation, principally upward outside the Marcellus Shale. Significant gas was produced from the two wells with horizontal fractures in the organic-rich Lower Marcellus Shale, perhaps because twice as much proppant was used as in stages characterized by vertical fracture propagation.

The Effect of Hydraulic Fracture Geometry on Well Productivity in Shale Oil Plays with High Pore Pressure

“…Horizontal bedding planes, mechanically weak owing to little cohesion, may be stimulated in shale plays in transitional strike-slip to reverse faulting stress regimes, in which S v and S hmin are close in magnitudes and similar to the least principal stress (i.e., S hmin ∼S v ∼S 3 ). Such stress conditions have been reported in some unconventional source rock plays (e.g., the Marcellus Shale in southern West Virginia and the Tuwaiq Mountain formation in the Jafurah Basin, Saudi Arabia [27,38,39]).…”

“…This last scenario may occur in shale plays characterized by severe overpressure and small differential stresses or by transitional strike-slip to reverse faulting stress regimes in which the least principal stress (S 3 ) is very close to the overburden (S v ). Such conditions are reported to exist, for example, in the Marcellus shale in southern West Virginia [27], and the Tuwaiq Mountain formation in the Jafurah Basin in Saudi Arabia [38,39]. The unique reservoir simulations discussed here enable us to understand the impact of varied hydraulic fracture and stimulated natural fracture geometries and bedding planes on hydrocarbon production.…”

“…Microseismic studies and field pilots have uncovered evidence of hydraulic fracture geometries that appear to deviate appreciably from an idealized geometry and include horizontal fracture components [27][28][29][30]. Such fracture geometries result in production volumes, and rates below customary forecasts [31].…”

Integrated Analysis of the Coupling Between Geomechanics and Operational Parameters to Optimize Hydraulic Fracture Propagation and Proppant Distribution

“…They also correlated the S hmin variations to stimulation performance. Alalli and Zoback (2018) attributed horizontal fractures in the organic rich lower Marcellus shale to increase in S hmin caused by viscoelastic stress relaxation.…”