Gas Condensate Flow Around Hydraulically Fractured Wells

Abstract

Fracturing is one of the most common well-stimulation techniques especially for tight gas-condensate reservoirs. Considerable efforts have been devoted to this subject albeit mainly for single-phase or conventional gas oil systems. Gas condensate flow around hydraulically fractured wells (HFWs) is different from that in conventional gas oil systems. Previous studies (Danesh et al. in Gas Condensate Recovery Studies, 1994; Jamiolahmady in Transp Porous Media 41(1): 2000) have shown that at low to moderate velocities, the relative permeability of these low interfacial tension systems increases as velocity increases and/or interfacial tension decreases. At very high velocity values, on the other hand, the inertial effect becomes dominant, reducing the relative permeability as velocity increases (Forchheimer in Hydraulik, Chap 15, Teubner, Leipzik, 1914). Description of HFWs in gas condensate reservoirs using the existing reservoir simulators requires the use of very fine grids to capture the abrupt changes in flow and rock parameters for these systems. This task is very cumbersome, time consuming and impractical. In this work, a two-dimensional mathematical simulator has been developed, based on finite-difference methods. The simulator accounts for phase change, condensate drop out, coupling and inertial effects. This single-well model has been used to investigate the impact of important geometrical and flow parameters on the performance of a HFW. Based on this investigation new formulae have been developed for fracture skin factor and effective wellbore radius. The developed formula for effective wellbore radius, which is applicable under both steady state and pseudo-steady state conditions, can be used in an equivalent open-hole system replicating flow around HFWs. The approach is similar to that followed for single phase systems albeit with a modified formula for the fracture conductivity term as developed here. Another important application of these formulae is in the optimization of fracture dimensions for a given fracture volume, in gas condensate reservoirs.