ESD welcomes Maurice Dusseault, Ph.D. (Univ. of Waterloo)
Hydraulic fracturing (HF) has emerged as an important enabling technique in development of shale oil and shale gas, geothermal energy exploitation, and slurried solids disposal at depth. For example, the City of Los Angeles is injecting biosolids sludge on a trial basis into a depleted reservoir 1350 m deep under HF conditions as a means of treatment, with potential for harvesting generated methane.
The challenge facing the geomechanics community is development of a deep understanding and analysis methods for HF in naturally fractured (jointed) rock masses such as igneous rocks, petroliferous carbonates, and shale oil and shale gas reservoirs. Scale is critical: at the tip, local fabric dominates propagation; when fracture length is large, global propagation is dominated by the large-scale principal compressive stresses. Fluid density, viscosity and injection rate affect propagation, and in many cases, induced displacements can change the local principal stress values and lead to secondary fracture arms, an important factor in developing fracture networks.
Maurice will discuss what we can and cannot yet do in HF simulation and design. Changes of direction, stress alterations, buoyancy effects, and stress field variations in situ will be discussed. There are no easy answers, the goal of the talk will be to cast some clarity on the physical mechanisms involved in hydraulic fracturing in rock masses with strong fabric, and see what options are available for engineers to pursue in design and implementation of HF technologies.