Investigation of critical in situ and injection factors in multi-frac treatments: Guidelines for controlling fracture complexity
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Using a fully coupled (flow and mechanics) hydraulic fracture propagation model, we investigate the critical in situ and treatment factors controlling geometry in multi-frac horizontal wells. Fracture net pressure is calculated by considering continuity of flow rate and pressure equilibrium in the fracture and the wellbore between injection points. A two-dimensional displacement discontinuity method with correction for finite fracture height was used to calculate fracture aperture, accounting for mechanical interaction between multiple propagating fractures. Stress shadow effects change the local stress field in the surrounding rock, influencing fracture geometry. A sensitivity study is performed including fracture spacing, in-situ differential stress, pump rate and fluid viscosity. Simultaneous and sequential injection methods were examined. The results show that closely spaced hydraulic fractures can cause significant fracture width restriction, increasing the likelihood of premature screenout, but fracture propagation paths are generally pretty planar. Success in propagating simultaneous multiple fractures is greater for slickwater treatments than gel treatments because of the diminished mechanical interaction evident in the slickwater cases. Copyright 2013, Society of Petroleum Engineers.
