Shale gas development involves aggressive hydraulic fracturing of a naturally fractured rock mass to generate an interconnected open fracture network with a large internal surface area for gas drainage. Conventional hydraulic fracture design software cannot cope adequately with fracture propagation in naturally fractured rock, and it is not clear what form a better design software environment will take, but activity in a number of directions is taking place. Several preliminary options are discussed herein, along with a review of shale gas occurrence and the geomechanical aspects of its development.
Decades ago, natural gas occurrence was noted during drilling through the naturally fractured black shales of Appalachia (Ohio Shale, Marcellus Shale, Utica Shale – Charpentier et al. 1995) and Texas. However, these fine-grained Naturally Fractured Rocks – NFRs – were considered poor prospects for economic production, despite considerable attention paid to them in the 1980's and 1990's by the United States Department of Energy and Gas Research Institute (e.g. Kruuskaa et al. 1998, Curtis 2002). Persistence in their development and the implementation of large volume propped Hydraulic Fracturing (HF) methods in vertical wells led to limited production of the gas in the Antrim Shale (Michigan Basin), Barnett Shale (Fort Worth Basin) and Ohio Shale (Appalachian Basin) during the 1990's and into the first part of the decade of the 2000's. Massive improvements in drill bit technology, top-drive drilling rigs, and down-hole steerable drilling motors made the emplacement of horizontal wells >1 km long economical by the late 1990's. This was followed by development of new well completion techniques – Multi-Stage Hydraulic Fracturing – MSHF – in the period 2000–2008.With these technologies, the "shale gas revolution" had arrived in the United States and Canada, but it was not until about 2010–2012 that the full economic impact was realized.