Abstract:

In the oil and gas industry, vertical growth/containment of fractures during hydraulic fracturing is of pivotal importance to the success of well stimulations. Experimental work have improved our understanding of the topic, but it is sometimes difficult to explore, in isolation, some of the multiple parameters involved in the problem. Analytical models cannot account for the whole complexity of the problem, and although numerical models are an alternative, they also come with their own benefits and drawbacks. Oversimplification, limitations on the size of the treatable systems, and erroneous/doubtful assumptions are sometimes drawbacks of numerical approaches. In this work, an effort is made to overcome some of these issues and present a numerical model which incorporates the physics of fracture growth and does not rely on prescribed constitute laws or continuum equations. The approach is based on the discrete element method (DEM) and accounts for the physics of fracture growth from basic principles. The model has the benefit of being a hybrid model that includes the fine-details of tip mechanics plus the large-scale effects of an arbitrarily large surrounding medium. This approach was used to study, in isolation, the influence of toughness contrast on the propagation mode of a fracture through an interface separating two formations. The model captured the local scale effects of the interaction of the tip of a vertical fracture approaching a horizontal fracture while still being computationally efficient. The results obtained indicate that when varying the single parameter of toughness contrast, four main propagation modes were observed for Mode I fractures: straight crossing across the interface between layers, arrest at the interface, propagation across the interface but with a T-shaped fracture, and reinitiation of the fracture with an offset (jog).

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