Abstract:
Hydraulic fracturing is widely employed for well stimulation. Different techniques have been utilized in practice to optimize fracking in the last five decades. However, it has some disadvantages including a lack of control over the direction of fracture propagation, the high treatment cost along with environmental issues. Producing multiple fractures by dynamic stimulation techniques seems to be more promising in naturally fractured reservoirs, since it is an effective way for connecting a pre-existing fracture network to a wellbore. In this study, applying high rate loadings we investigate fracturing in rocks due to explosives and propellants as two common methods for dynamic stimulation of a well. An interfacial damage model implemented in a Spacetime Discontinuous Galerkin finite element framework is utilized to simulate fracturing in rocks. A powerful dynamic mesh adaptivity scheme is implemented to track arbitrary crack paths and align them with element boundaries. High explosives produce shockwaves causing extreme compressive stresses, which results in crushing and compacting the rock around the wellbore. Propellants can generate a pressure pulse producing a fracturing behavior that loads the rock in tension. The main advantage of this later approach is to create multiple fractures and consequently prepare the well for an effective hydraulic fracturing with much lower cost as a re-fracturing solution.
Introduction
Stimulation treatments to enhance hydrocarbon recovery from shale and other tight formations as unconventional resources are mainly classified into fracturing based on hydraulic, thermal and dynamic loadings. There is no alternative to fracturing itself, since it is the only way to artificially fissure the source rock to provide sufficient permeability for oil and gas extraction cost-effectively. The technology of hydraulic fracturing which is also called fracking has been widely employed since 1949. It has been very common and popular in oil industry for decades owing to technological advances in practice. Horizontal drilling was a complement to this method since the late 1980. This technique was developed further in 1997 by the use of chemicals known as slickwater fracturing in which slickwater is water mixed with friction-reducing additives. Employing these advances along with the development of multi-well pads have made gas production from shales technically and economically feasible especially in North America in the last decade.
