Evidence of Strong Fracture Height Containment Based on Complex Shear Failure and Formation Anisotropy

Abstract

For years, uncontrolled fracture heights have been modeled for layered reservoirs using Mode-I tensile failure driven threedimensional (3D) and pseudo-three-dimensional (P3D) fracture geometry models. In these models stress contrast between layers has been assumed to provide the dominant height containment mechanism. Meanwhile, many of the completion diagnostic tools were revealing more contained fracture heights and were thus being discounted. As more diagnostic tools have been employed, it has become apparent that the frac models may have been incorrectly over-predicting fracture heights in many cases. Mine-backs and post-frac coring revealed more contained fracture heights, as did radioactive tracer logs, treating pressure profiles, fall-off data, production modeling, and the absence of perforated interval communication. This paper will present some of the diagnostic data that support more contained fracture height development. These will include case histories from tight gas sands and shales in which restricted fracture height observations are supported by diagnostic observations. It will also go one-step further, by proposing mechanisms which contribute to fracture height containment. These include poroelasticity, abnormally high "trapped" pore pressure, and complex shear in layered or anisotropic media. It will present some modeling methodologies that place more emphasis on poroelasticity and Mode-II shear failure than current conventional fracture models. The need for investigation, and adoption, of these methodologies will be corroborated by diagnostic data.

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

“…In hydraulic fracturing design, typical hydraulic fracture geometry is assumed to be elliptical, vertical with symmetrical bi-wings, and a propagation direction perpendicular to the least principal stress (S 3 ) assumed to be the minimum principal horizontal stress (S hmin ) [3,4]. However, a growing body of evidence suggests that hydraulic fracture geometries are often far more complex [5][6][7][8].…”

Hydraulic Fracture Height Containment by Weak Horizontal Interfaces

“…It has also been recognized that fracture propagation terminates at layer interfaces that are cohesionally weaker than the surrounding rock (Van Eekelen 1982;Teufel and Clark 1984;Boyer et al 1986;Warpinski et al 1998, Miskimins andBarree 2003; Barree et al 2010). This mechanism used to be invoked only for shallow depths or overpressurized reservoirs, where the frictional shear stress at bedding interfaces is small.…”