Integrated Geosciences for Optimal Hydraulic Fracturing of Shale Reservoirs

Tran, Minh H.; Abousleiman, Younane N.

The integration of sequence stratigraphy and geomechanics characterization to evaluate shale reservoir fracability has been introduced by Slatt & Abousleiman (2011) and applied to characterize the Woodford shale formation (Tran et al., 2012). It is wellknown that some shale shrink and swell drastically when exposed to aqueous solutions. This chemically behavior of shale can significantly alter the formation characteristic and affect the hydraulic fracturing efficiency. In this work, the shale formation geochemical properties such as Cation Exchange Capacity (CEC) and pore fluid salinity are incorporated into the poroelastic Mandel's problem to better optimize the hydraulic fracture job.

The Mandel's problem has been used by geomechanicians to describe the responses of reservoir during steam flooding and production. Regarding hydraulic fracturing in shale, the Mandel's problem mimics a shale formation section formed by two often closely spaced parallel natural fractures that reopen and propagate during hydraulic fracturing. In this work, the solutions are used to investigate the effects of fracturing fluid chemistry and formation clay content on the fracture deformation and the stresses distributions inside the shale formation.

The analyses show that the presence of reactive clay can induce additional fracturing fluid loss into the formation and create a tensile damage zone near the fracture surface. In particular, shale with higher CEC values will result in more severe fluid loss and a larger the damage zone near the fracture face. The damaged formation shall become weaker and deform more easily under application of hydraulic pressure, leading to a wider fracture aperture and a shorter fracture length. Similarly, a large amount of fluid loss will significantly reduce the pressure acting on the fracture wall necessary for the fracture propagation. Thus, the results explain why intervals with high content of reactive clay such as smectite are often observed to be more ductile than the lower and less reactive clay intervals. The results also show that a fracturing fluid with higher salinity than the native pore fluid can reduce the fracturing fluid loss and, thus, works for the advantages of the fracturing job.

The outcomes of this work will allow, for the first time, the integration of shale geochemical properties into the aforementioned geological-geomechanics framework for shale reservoirs fracability evaluation and hydraulic fracturing optimization.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013