The influence of bedding-parallel fractures in hydraulic fracture containment

Abstract

The Middle Devonian Marcellus Shale Formation in the Appalachian Basin, which encompasses more than 3.3 trillion tonnes of organic matter, has low permeability (0.1 to 10 μd) and requires extensive fracture stimulation before the reservoir will yield gas in commercial volumes (de Witt, 1986). Since 2004, the application of horizontal drilling, combined with multi-staged hydraulic fracturing to create permeable flow paths from the shale units into wellbores, has resulted in a drilling boom for the Marcellus Formation (Engelder et al., 2009). These lateral wells are usually completed from the toe to the heel over a number of stages using a plug-and-perf method, or if a multiple well pad is being stimulated, after a zipper-frac style (Baig, et al., 2012). Effective hydraulic fracturing in unconventional shale reservoirs requires an understanding of the pre-existing discontinuities (impermeable/not effectively connected natural fractures) state and an assessment of whether at any point of the stimulation it is energetically favourable to move fluids within the reservoir. The dynamic nature of the local stress regime owing to hydraulic fracturing leads to stimulation of different fracture sets which could include bedding-parallel fractures and bedding planes. Describing the progression of the fracturing into the formation and ancillary issues of how far into the reservoir the rock has been stimulated and the stimulation containment provides the opportunity for operators to potentially control fracture behaviour and improve completion designs.