ABSTRACT:

Numerical simulations of hydraulic fracture (HF) propagation through layered rocks show the effects of rock layering and interfaces on fracture height growth. When the contrast in properties between adjacent rock layers is high and abrupt, the resulting interface between these layers is often weak, exhibiting low tensile strength, low friction coefficient, and high hydraulic conductivity. Thus, they easily detach (in tension) and slip (in shear), as the hydraulic fracture crosses them, creating localized obstacles for fracture propagation as well as localized zones of fluid loss. Numerical simulations were conducted using the newly-implemented pore pressure cohesive elements as certain predefined hydraulic fracture and interface opening paths in ABAQUS 2016. To validate the model and for comparison we conducted simulations on elastically-homogeneous and elastically-layered rocks and, for the latter, we used a range of tensile strength and fluid flow properties at the interfaces between layers, to understand their impact on vertical hydraulic fracture (height) growth. Our results show a systematic decrease in fracture height and fracturing fluid efficiency with increasing interface hydraulic conductivity. This relationship is important because of its potential impact on improving fracture diagnostics in the field. We also observe that the interface strength directly affects fracture height growth as well as fluid efficiency. These findings are important for a proper assessment of fracture height growth, a better assessment of the created fracture surface area, and better predictions of well production.

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