Calibration of Brittleness to Elastic Rock Properties via Mineralogy Logs in Unconventional Reservoirs
Perez, Roderick1 and Marfurt, Kurt
To optimally stimulate an unconventional reservoir hydraulically, it is important to identify brittle regions based on knowledge of the geology, petrophysics, mineralogy, and rock mechanics of the area of study. This research reconciles some of the brittleness terminology in the literature and classifies the Barnett Shale in terms of its geomechanical properties, defining the more-brittle regions in Young's modulus and Poisson's ratio crossplots and λρ - μρ space. These geomechanical properties were defined, calibrated, and computed using specialized logging tools such as: mineralogy, density, and P- and S-wave sonic logs, and calibrated to previous core descriptions and laboratory measurements. With proper calibration these measurements provide a means to geomechanically characterize a reservoir. In the Barnett Shale, the combination of high concentrations of quartz and calcite gives rise to more brittle rocks, while ductility is controlled primarily by clay content. Contrary to the commonly held understanding, in the Barnett increased kerogen (TOC) does not make the rock more ductile. Further, microseismic event locations from a 3D seismic survey acquired after more than 400 wells have been drilled and hydraulically fractured in the area agree to the predicted brittle regions in the λρ - μρ crossplot, suggesting that hydraulically induced fractures preferentially populate brittle regions and consequently, produce more gas. Thus, these results are useful to calibrate 3D seismic attribute brittleness estimation.
AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013