Pulse Fracturing in Shale Reservoirs: Geomechanical Aspects, Ductile/Brittle Transition, and Field Implications

Abstract

Summary This paper presents a brief review of misconceptions on industry-standard brittleness/ductility definitions; geomechanical aspects and numerical evaluation of pulse fracturing by use of an advanced constitutive model implemented within the ANSYS® Autodyn® (ANSYS 2014); and fracture-network patterns because of pulse loading in shale that show ductile/brittle transition. In shale gas, one of the primary goals is to create extensive fracture networks that can remain open during production. Field experience has shown that not all shale formations respond to hydraulic fracturing effectively. It is important to identify and accurately design alternative fracturing techniques that would overcome some of the limitations. Pulse-fracturing rates and peak loads can be customized to lie between hydraulic and explosive fracturing. This technique has the potential to shatter shale, in particular by triggering a ductile/brittle transition at an optimized pulse rate. To date, operational considerations of pulse fracturing for success remain qualitative. Recent advances in computational geomechanics help us quantify the effect of key operational parameters for field applications. Further to this, advanced constitutive models implemented for these analyses have the benefit of simulating ductile/brittle transition, if the stress state and loading conditions dictate that the material should. This study on pulse fracturing shows that for a certain combination of reservoir, geomechanical, and pulse-loading parameters, induced fractures can propagate in multiple directions. This phenomenon might promote a self-propping mechanism for a network of fractures. At the end of this paper, favorable conditions when the pulse-fracturing technique would work and key parameters that trigger ductile/brittle transition are summarized and presented.