Department of Earth and Environmental Sciences, University of Waterloo, Waterloo Ontario
Hydraulic Fracture Mechanics in Jointed Rock Masses: Searching for an Approach to Simulation
Thursday, January 9, 2014, 9:00 AM
102 Benedum Hall
Abstract: Shale gas development involves drilling a vertical well to depth, deviation to drill a long horizontal section, and multi-stage hydraulic fracturing (MSHF) of the naturally fractured reservoir to generate an interconnected open fracture network with a large internal surface area for gas drainage. Similar techniques are used to develop other energy resources such as shale oil, certain types of geothermal energy, tight gas sands, some coal bed methane fields, and there is reason to believe that the redevelopment of the rich fractured carbonates of the Persian Gulf will use similar technologies.
A key difference between MSHF and its predecessor technologies is the scale of the stimulation activity and the fact that it is done almost exclusively in rock masses that are naturally fractured in the ground. In terms of scale, more fluid is introduced more rapidly into a single fracturing point (among 15-30 for a single well) than was conventionally used for an entire vertical wellbore in the past. For example, in the Horn River Basin in British Columbia, a single 2.5 km long horizontal well may have 25 fracture stages, each accepting 3000 m3 of fluid at rates as high as 10-12 m3/min, for a total well stimulation volume of 75,000 m3 of fluid, executed over a period of 10-12 days.
The presentation will show the mechanics involved and how we came to understand that the stimulation of such large volumes of naturally fractured rock entailed mechanisms previously unconsidered. Commercial software for conventional fracturing is not adequate for designing MSHF cases, and there is a wide-spread search in the Rock Mechanics community for better approaches. Several approaches will be described, and a few simple results for 2-D simulations will be presented as examples. The link between microseismic activity and HF, including issues such as stress changes and energy, will be addressed briefly because there is a lack of linkage between the rock mechanics community and the geophysics community, and this linkage promises to have considerable value.
To place this research in a financial context, the Marcellus Shale alone (not including the underlying Utica Shale resource) will require perhaps 500,000 wells over the next 60-80 years of its exploitation, at an average cost of $8 million, or four trillion dollars. Fewer wells will be required for the Utica, perhaps 300,000, but at a higher cost. The known Canadian shale gas plays south of 60°N will require over 500,000 wells. If improved design methods can be developed for MSHF resulting only in the saving of 2% of the well costs, more than 200 billion dollars of value will be brought to the industry, and ultimately to the consumer, over the exploitation time.
Bio: Dr. Dusseault started teaching in Alberta in 1977 and came to Waterloo in 1982 as Professor of Geological Engineering, teaching rock mechanics, fossil fuel production methods, and related areas. He carries out research in geomechanics, oil production, and deep waste disposal. Current interests include sequestration, hydraulic fracturing, leaky wellbores, and THMC coupling issues. He publishes widely (500 full text articles) and works with industry as a professional instructor. Maurice currently serves on the Scientific Advisory Council of the New Brunswick Energy Institute, as science advisor to the Government of Alberta, and on the Shale Gas Environmental Impacts Panel of the Council of Canadian Academies.