Understanding the Implications of Changes in Shale Geomechanical Properties With Fracturing Fluid

Abstract

During hydraulic fracturing in shale plays, it is found that only 10% to 50% of fracturing fluids is recovered and up to 90% of the injected fluid may remain in the shale. The reasons for low water recovery are still highly controversial; however the major mechanism responsible for water retention and low water recovery is believed to be capillary invasion followed by spontaneous imbibition of fracturing fluid in shale formation. Imbibition is inversely proportional to the saturation of the wetting phase; hence increasing the water saturation reduces the imbibition potential. The effect of the remaining fracturing fluid on production is a concern. Matrix relative permeability to gas decreases by increasing the water saturation in the media. The field production however, does not necessarily show a reduction in production by increasing the shut-in time. This could be attributed in interactions between fracturing fluid and the rock that alleviates the pore plugging effect of water encroachment. This study aims to investigate the role of fracturing fluid and shale interaction on rock strength, fracture complexity and production before and during shut-in period as a function of water saturation. In this way, a geomechanical coupled numerical modeling approach has been applied to account for the rock strength change as the fracturing fluid is invading into the shale formation and changing the water saturation. Based on the results, it is observed that capillary invasion takes place before and within shut-in period which increases the water saturation in the media. In addition, as the water saturation rises possibility of failure increases since the geomechanical properties of the shale is altered by the fracturing fluid. The results imply that reduction in compressive strength and elastic modulus as well as generation of internal stresses can significantly decrease the shale strength and increase the possibility of microfractures generation. The results of this study enable us to understand the mechanisms of interactions between the fracturing fluid and the shale formation and how it may affect the fracture complexity and productivity.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016