A Comprehensive Monograph for Hydraulic Fracture Initiation From Deviated Wellbores Under Arbitrary Stress Regimes

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractHydraulic fracturing is a widely used stimulation technique in the petroleum industry for enhanced hydrocarbon recovery from low permeable reservoirs. Technological advancements in directional drilling have led the petroleum industry to drill arbitrarily deviated wellbores for development of reservoirs, which otherwise could not be economically produced. Efficient prediction of fracture initiation pressure from such deviated wellbores is therefore essential for petroleum industries to undertake effective hydraulic fracture stimulation tasks. This paper presents a generic model for prediction of hydraulic fracture initiation pressure and the orientation and location of fractures on the wellbore wall. The generic model is finally ramified to develop criteria for initiation of longitudinal, transverse and T-shaped or H-shaped fractures, with and without perforations. Final form of fracture initiation criteria for specified cases presented in the paper can be used by engineers for prediction of fracture initiation pressure. However, the estimation of fracture initiation pressure for deviated wellbores is cumbersome requiring numerical iterations. For such cases, results are presented graphically in terms of non-dimensional parameters to cover various stress regimes and wellbore deviations. Thus, the charts presented in this paper will be a useful tool for prediction of fracture initiation pressure for given in-situ stresses and help engineers to minimize computational efforts.Results of this study suggest that horizontal wellbores under the normal faulting stress condition requires less pressure for fracture initiation compared to vertical wellbores. In general, there is an optimum deviation that requires minimum fracture initiation pressure for a given set of in-situ stresses. Longitudinal fractures usually initiate from wellbores which are aligned with one of the in-situ stresses. Under some specific stress conditions, transverse fractures may also initiate directly from the wellbore wall. Without appropriate pressure control, longitudinal fractures also, however, initiate at some elevated pressure during the propagation of transverse fractures. This introduces the so-called T-shaped or H-shaped fractures. Perforations at appropriate alignment usually contribute in fracture initiation at lowe pressure.

A Finite Element Model to Predict Wellbore Fracture Pressure with Acid Damage

“…Huang and Xu (1986) presented a new model with inhomogeneous stress field. Hossain et al (1999) presented a generic model for prediction of hydraulic fracture initiation pressure, including the orientation and location of fractures in the wellbore wall. However, the accurate prediction of well bore fracture pressure requires an accurate prediction of the stress field in the vicinity of the crack tip for the given structural geometry, loading and boundary conditions, while the analytical solutions were only available in certain relatively simple cases due to the complicated boundary conditions associated with the governing equations.…”