Optimization of hydraulic fracture geometry in gas condensate reservoirs

Abstract

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 unconventional 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 was then further developed and presented in the form of Unified Fractured Design (UFD) charts by Valko et al. (1998), which is applicable to Pseudo-steady state conditions. Later on, some methodologies have been proposed to make UFD applicable to gas condensate systems assuming the distribution of the condensate phase around the fracture as a rectangular damage zone with constant thickness and reduced permeability. These latter methods are generally oversimplified as they neglect different possible shapes of the two phase region around the fracture and the 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 (required to identify the two-phase boundary) around the wellbore.In this paper, we introduce an explicit formulation and a more general methodology for OFD that is applicable to both Steady state and Pseudo-steady state single-phase gas and two-phase gas condensate flow systems and includes the important flow parameters in both the matrix and fracture. The optimum fracture dimensions are obtained by maximizing the effective wellbore radius, using the recently developed correlation by Mahdiyar et al. (2011). This formulation accounts for the mechanical and flow skins based on quite readily available information at wellbore conditions.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.