Effect of a Natural Fracture on Hydraulic Fracture Propagation

by
Naga Kiran Potluri, M.S.E

University of Texas at Austin, 2004
Supervisor: A. Daniel Hill

The effect of an existing fracture in a naturally fractured formation on the extension of a hydraulically induced natural fracture has been studied. Fracture interaction criterion was presented and a numerical model was developed to predict the dynamic fracture dimensions based on PKN²⁶ fracture mechanics. The numerical studies of induced fracture propagation in the presence of natural fractures show that natural fractures can have a substantial effect on the induced fracture propagation. Results from our model suggest that one of the main effects of the natural fractures is the width constriction that occurs when the induced fracture propagates into the natural fracture. This is because of the increased resistance to opening when the fracture goes non-planar. Due to the decrease in width the net pressure increases and in some cases the net pressure at the well bore can reach the maximum allowable treating pressure. In the case of induced fracture turning into the natural fracture the fracture penetration distance decreased with increase in differential stress. This is due to the ballooning of the induced fracture once it crosses the natural fracture.

A simple numerical model using PKN fracture mechanics has been presented to study the effect of the differential stress and angle of interaction on the geometry of induced fracture. It has been found that the induced fracture tends to cross the natural fracture at high angles of interaction and high differential stress. At low angles of interaction and low differential stress the induced fracture was diverted by the existing natural fracture.

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