Hydraulic Fracturing Optimization for Woodford Shale through Integration of Geological Characterization and Coupled Anisotropic Thermo-Hydro-Geomechanics
Abousleiman, Younane N.; Hoang, Son; Liu, Chao
A newly-derived fully-coupled thermo-hydro-geomechanics one-dimensional simulation is used to study the time-dependent evolution of the fracture aperture during hydraulic fracturing of the anisotropic Woodford Shale. The study aims at quantifying the effects of the spacing of natural fractures and the temperature gradient between the hotter reservoir rock and the colder fracturing fluid on the efficiency of the frac job. The results can then be used to optimize hydraulic fracturing design for the shale reservoir.
It has been observed during geological characterization that many natural fractures exist in the Woodford Shale and they are roughly vertical. During the hydraulic fracturing operation, they may reactivate and join to form fractures with almost parallel branches. Due to the large vertical and lateral extent of the hydraulic fracture, a section sufficiently far from the wellbore, fracture tips, and fracture joints can be modeled using the 1D solution.
It was found that with an average natural fracture spacing of 1.2m, a fracturing fluid with the same temperature as the reservoir rock will create a nominal fracture aperture of 0.84mm. Furthermore, this fracture will gradually closes due to shale swelling from the fracturing fluid invasion into the formation so proppant transport will gradually degrade. On the other hand, with a fracturing fluid 60°C colder than the rock formation, the fracture will gradually widen due to shale contraction as the cold front penetrates into the formation. At the end of the pumping, the aperture with the colder fracturing fluid is approximately 70% larger than that created with the hotter fluid. It was also found that the fracture aperture monotonically increases with increasing natural fracture spacing.
It is noted that while a wider fracture aperture promotes proppant transport, it requires more fracturing fluid volume to fill the same fracture length. Alternatively, the same pumped fluid volume will create a shorter hydraulic fracture and the impression of a less brittle formation. Therefore, it is crucial that the natural fracture spacing is taken as an input in the design of hydraulic fracturing jobs. Furthermore, based on the proppant size and transport characteristics, the temperature of the fracturing fluid must be controlled to optimize both proppant transport and fracturing efficiency.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013