Laboratory Experiments of Hydraulic Fracturing Help Investigating Conditions for Fracture Branching and Fracture Containment
Suarez-Rivera, Roberto, Chaitanya Deenadayalu, David
Handwerger, and Sid Green
TerraTek, a Schlumberger company, Salt Lake City, UT
Economic production of gas from micro- to nano-darcy permeability tight rocks, requires the generation of large surface area during hydraulic fracturing. Large surface area can be created by increasing the fracture geometry (height and length), or by increasing the fracture complexity (branching). Micro seismic monitoring during hydraulic fracturing in tight gas shales indicates narrow and often broad spread of microseismic events along the plane of fracture propagation. These results allow us to interpret the degree of fracture complexity. The overall resulting structure with single or multiple branches propagating in the direction of the maximum horizontal stress and often, smaller, cross cutting, branches propagating orthogonal to the former is referred to as the stimulation fairway. Given that branching significantly increases surface area during hydraulic fracturing, understanding the causes and consequences of branching, and most importantly, understanding whether these structures can be affected during pumping is of great technical relevance and economic importance for the unconventional gas industry. In this paper we present results of laboratory experiments of hydraulic fracturing on small- to large- scale samples to evaluate the sources of fracture branching. Experimental results suggest that interfaces and deviatoric stresses are required for branching. Under stress free conditions, once encountering the interface the fractures are either arrested, or turn to propagate along the direction of the interface. Under strong stress contrast, the fracture steps-over laterally to cross the interface. This process often results in multiple branches.
AAPG Search and Discovery Article #90071 © 2007 AAPG Rocky Mountain Meeting, Snowbird, Utah