The Geomechanics Of A Shale Play: What Makes A Shale Prospective

Many shale plays are being successfully developed throughout North America. These shale plays are being evaluated based on a number of criteria, but primarily through typical unconventional and tight formation gas reservoir characteristics. Prospective shale plays share several interesting characteristics such as mineralogy, rock mechanics, and geomechanics. It is the intent of this paper to highlight and demonstrate the interrelationship of these characteristics, and to show their importance on completion and stimulation design and more importantly to the very prospectivity of an unconventional shale play. This paper will first show, through an analysis of the mineralogy, that shale plays are made up of mostly silica and carbonate material and have few clay constituents. In other words, the prospective shales are actually fine-grained clastics and not shale!Second, prospective shales tend to be brittle, with the static Young’s Modulus generally in excess of 3.5 x 10 6 psi. Of course, this brittleness is related to the lack of clay constituents that make up these rocks. In addition, prospective shales tend to satisfy clastic correlations of dynamic to static Young’s Modulus. They do not behave like typical shales, but more like finegrained isotropic (on a core scale) clastics! Finally, gas can flow through induced fractures or natural fissures under effective stress conditions in these shale plays. As a result, water-frac treatments are the stimulation of choice! However, proppant is still necessary in at least the near wellbore vicinity to provide a conductive pathway to the wellbore.This paper focuses on three key elements (mineralogy, rock mechanics, and geomechanics) of prospective shale plays and benefits the petroleum industry by: 1. Integrating the laboratory core work with multi-disciplinary data to develop a shale and unconventional reservoir prospectivity evaluation tool, 2. Illustrating how this multi-disciplinary dataset influences completion and stimulation design, execution, and well performance, and 3. Demonstrating how this multi-discipline dataset can be used to identify and mitigate well completion and stimulation risks in these unconventional reservoirs.