Unconventional Reservoir Geomechanics
In this course we address a range of topics that affect the recovery of hydrocarbons from extremely low-permeability unconventional oil and gas reservoirs. While there are multiple definitions of unconventional reservoirs, we consider in this course oil and gas-bearing formations with permeabilities so low that economically meaningful production can only be realized through horizontal drilling and multi-stage hydraulic fracturing. Despite this extraordinarily low permeability, the scale and impact of the production from unconventional oil and reservoirs over the past decade in the U.S. and Canada has been remarkable. In the first part of the course we consider topics that become progressively broader in scale, starting with laboratory studies on core samples that investigate the composition, microstructure and pore systems at the nanometer scale (the rocks matter) and conclude by discussing basin-scale stress fields, fracture and fault systems (which matter as well because they control hydraulic fracture propagation and the effectiveness of reservoir stimulation). In the second part of the course we address the process of stimulating production using horizontal drilling and multistage hydraulic fracturing. We briefly review several important engineering aspects of horizontal drilling and multi-stage hydraulic fracturing, the basics of microseismic monitoring, the importance of interactions among the state of stress, pre-existing fractures and faults and hydraulic fracturing which are critical to the production process and a unified overview of flow from nano-scale pores to hydraulic fractures via the fracture network stimulated during hydraulic fracturing. In the final part of the course we consider environmental impacts of unconventional oil and gas development, especially induced seismicity.
Dr. Mark D. Zoback, Benjamin M. Page Professor of Geophysics at Stanford University
Arjun H. Kohli, graduate teaching assistant, Department of Geophysics at Stanford, laboratory manager, Stress and Crustal Mechanics Laboratory