Optimization of hydraulic fracture geometry

An optimized design for hydraulic fracturing is of great importance especially with the growing demand for this method as a means of production enhancement from tight gas reservoirs. The first optimum fracture design (OFD) approach, which maximizes well productivity for a given fracture volume, was introduced by Prats in 1960 for single-phase Darcy flow systems. This method, which was later modified and presented in the form of Unified Fractured Design (UFD) charts by other investigators, is widely used in the petroleum industry, even for gas condensate systems. Recently some methodologies have been proposed to modify UFD considering the two-phase region around the fracture as a damage zone with reduced permeability. These methods are generally oversimplified as they neglect the phase change and variation of relative permeability with interfacial tension (IFT) and velocity for these low IFT systems. They also require data that are not readily available, in particular the pressure profile (the two-phase boundary) around the wellbore. We introduce an explicit formulation and a more general methodology for OFD that includes the important gas condensate flow parameters in both matrix and fracture. The optimum fracture dimensions are obtained by maximizing the effective wellbore radius, using the recently developed correlation by Mahdiyar et al. (2009). This formulation accounts for the mechanical and flow skins based on quite readily available information at wellbore conditions. In this paper, the integrity of the introduced formulation has been verified for many different prevailing conditions, whilst highlighting the errors of using conventional approaches with some important practical guidelines. In this exercise, the maximum productivity calculated using the proposed formulation is compared with results of the literature or our in-house simulator. This program, using a fine grid approach, simulates gas condensate flow around a hydraulically fractured well for various fracture length-width ratios and identifies the optimum fracture dimensions, for a given fracture volume, providing maximum mass flow rate. Copyright 2009, Society of Petroleum Engineers.