In - plane and anti - plane investigations of the hydraulic fracture propagation from a cased and cemented wellbore, have been pursued in this communication. The problem has been reduced to the solution of a system of integral equations and a propagation criterion of maximum tensile stress ahead of the crack tip has been implemented. Results indicate that the preferable plane for fracture initiation depends on the material properties of the rock. Far from the well the fracture reorients itself perpendicularly to the plane of the minimum earths stress. The effect of the casing and the cement on the crack opening displacements, is more evident when the elasticity modulus of the rock is relatively small.
Deviated wells are increasingly used in oil recovery. Multidirectional drilling can thus be pursued from a single platform and also particular reservoirs and rocks, whose geometry and properties are highly orientation dependent, can be treated more efficiently. Hydraulic fracturing is however often problematic when initiated from an inclined wellbore. In that case the state of stresses near the well changes and the prediction of the fracture surface is not immediately attainable. The turning and twisting of the crack is often coupled with the generation of multiple fractures. The fracturing fluid advance can thus be severely impeded and this may lead to an early screen out. Yew and Li (1987) and Yew et. al (1989) have applied 3D elasticity theory in order to study hydraulically induced fractures from inclined wellbores. The growth and link up of mini - cracks initiated at the perforations of a cased wellbore, are investigated by Yew et. al (1993). A 3D analysis of the fracturing process from an inclined well, via the use of a numerical simulator, has been presented by Morales and Brady (1993). The initiation, interaction and propagation of fractures from a deviated well have been studied by Weng (1993). The effect of casing on the hydraulic fracture have been considered by Carter et. al (1994). Romero et. al (1994) have investigated several near wellbore effects like fracture reorientation, perforation phasing misalignment, perforation pressure drop etc. Atkinson and Thiercelin (1993) have studied the interaction between an open hole and pressure induced fractures of mode I. In this study, the crack propagation from a cased, cemented and inclined wellbore is considered by using 2D in - plane and anti - plane elasticity analysis. Thus, all the three modes of crack opening displacements (COD's), i.e tensile, in - plane shear and out of - plane shear, are incorporated. Perfect bond is assumed along the steel/cement and the cement/rock interfaces and the pressure is kept constant along the crack. The path of the crack is determined by the maximum tensile stress criterion. For the sake of simplicity, we consider that the crack lies in an infinite medium, loaded by the stresses calculated by Atkinson and Eftaxiopoulos (1996). A numerical method is used for the solution of the system of integral equations at each propagation step.
