Fracture Mode Analysis, Geomechanics, Petrophysics, and Fracture Characterization

Abstract

The rapidly decreasing reserves of conventional gas has forced oil and gas industries to conduct more exploration on unconventional resources, like shale gas. To produce gas from shales in economically viable manner, stimulation techniques like hydraulic fracturing are required. One important factor for a successful hydraulic fracturing is knowing the fracture characteristics such as the fracture mode occurrence. Unfortunately, the factors controlling the fracture mode occurrence are not known yet. This study tries to find out the factors controlling the fracture mode occurrence by investigating the relation between fracture angle, confining pressure, and several rock properties. The fracture mode analysis being developed in this study suggests that for low strength rock like Bad Bentheim sandstone (46.65 MPa) and Indiana limestone (36.5 MPa), fracture modes are not dependent to the confining pressure. Fractures are already at mode II at zero confining pressure, while stronger rocks like Belgium limestone and Granite (125 and 128 MPa respectively) show fracture mode I at zero confining pressure. The experiments convey that the strength of the rock, which is related to its porosity, is the dominant factor controlling the occurrence of fracture mode I and mode II. This study also evaluates the prospectivity of the Whitby mudstone formation in the United Kingdom, which is a depositionally- and time-equivalent shale to the Posidonia Shale Formation (PSF). The PSF is one of the potential resource rocks for shale gas exploration in the Netherlands. Brittleness indices and fraccability indices of WMF from various methods are also determined and analyzed in this study. The results of WMF characterization show that WMF has high heterogeneity, which could imply that it is less favorable for hydraulic fracturing. Comparing the results of WMF to other producing gas shale shows that the WMF has a low range in: porosity, Young’s modulus, and quartz content, and high range in: laminations, and clay contents, suggesting that WMF is less potential for the shale gas resource. However, based on its characteristics, if WMF is divided into four zones, our experiments show that several zones (top and bottom part of WMF) can be considered as the most favorable ones for hydraulic fracturing in the WMF formation.