Horizontal wells are a proven and acknowledged technology to enhance well productivity through an increase in reservoir contact compared to that of vertical wells under the same conditions. In the last three decades, a considerable effort has been directed by many investigators to study flow around horizontal wells. In gas condensate reservoirs, in addition to the three dimensional (3D) nature of the flow geometry, the flow behaviour is further complicated by the phase change and the variation of relative permeability (kr) due to the coupling (increase in kr by an increase in velocity or decrease in IFT) and inertia (a decrease in kr by an increase in velocity) effects. Therefore, simulating such a complex 3D flow using commercial numerical simulators requires a 3D fine grid compositional approach which is very impractical, cumbersome and sometimes triggers convergence problems due to numerical instability. So far, none of these studies propose a method to deal with the complex multiphase behaviour of gas condensate flow around the horizontal well. Consequently, the introduction of a quick and reliable tool for long term productivity calculation in such a system is much needed. This paper presents a technique which was developed through a comprehensive study of the flow behaviour around horizontal wells in gas condensate reservoirs involving the creation of many in-house mathematical models using finite element and finite difference methods. An in-house simulator was developed to accurately model the multiphase flow of gas and condensate around horizontal wells. A large data bank was then generated covering the impact of a wide range of pertinent geometric and flow parameters on well performance including: well and reservoir geometries, reservoir and bottom-hole pressure, fluid velocity, gas oil ratio and fluid composition.Based on the results of the simulation, a new method has been proposed to predict the productivity of horizontal wells for the case of multiphase flow of gas and condensate. In this approach, the flow behaviour of gas and condensate around the well is quantified in terms of the effective wellbore radius of an equivalent open hole that replicates flow around the actual 3D system. The effective wellbore radius varies with fluid properties, velocity and interfacial tension (IFT), reservoir and wellbore conditions. The integrity of the new methodology has also been verified for various fluids and flow conditions.With this approach, a simple spreadsheet, without recourse to complex numerical simulation, can predict the horizontal well performance, significantly facilitating engineering and management decisions on the application of costly horizontal well technologies.

Fracturing is one of the most common well stimulation techniques especially for tight gas-condensate reservoirs. Gas condensate flow around hydraulically fractured wells (HFWs) is different from conventional gas oil systems. This is mainly due to phase change, condensate drop out and coupling (i.e., the increase of relative permeability as velocity increases and/or interfacial tension decreases) and inertial (i.e., the reduction of relative permeability as velocity increases) effects. Description of HFWs in gas condensate reservoirs using the existing reservoir simulators requires the use of very fine grids to capture the significant changes of flow and rock properties occurring in and around the fracture. This tasks it very cumbersome, time consuming and impractical. In this work a two dimensional mathematical simulator has been developed, which is based on finite-difference methods and accounts for the combined effects of coupling and inertia using our recently developed generalized correlation. This single-well model, which simulates the steady-state flow of gas and condensate around HFWs, also allows for phase change in these low interfacial tension systems. A series of sensitivity studies were carried out using this simulator. The results were used to develop a general method for estimation of flow skin factor based on the definition of dimensionless effective fracture conductivity. In the proposed method the skin factor expressing the impact of pertinent parameters are then converted to an effective well bore radius, which can be used by a reservoir engineer to conduct a realistic open-hole simulation of flow around HFWs. Introduction Hydraulic fracturing is a well known and common practice to improve the well productivity especially in tight gas condensate reservoirs. A hydraulic farcture reduces the flow resistance around a well bore, decreasing the pressure drawdown hence, reducing the negative impact of the condensate banking. Because of the importance and wide applications of hydraulic fracturing, productivity calculations in such systems has been the subject of interest by many investigators [e.g., McGuire and Sikora (1960), Cinco-ley et al (1977, 1978), Valko et al (2003), Meyer and Jacot (2005), Mahdiyar et al. (2007)]. These studies were aimed at the determination of improvement in well productivity or optimum fracture design. In these studies the flow behavior and pressure distribution around the fracture at steady state or pseudo steady-state conditions have been investigated. Results of theses works are in the form of charts or correlations for calculating the well productivity, skin factor or effective well-bore radius. In a Hydraulically Fractured Well (HFW) system, the thickness of the fracture is usually less than 1 inch, requiring fine grids for the fracture cells to accurately simulate fluid flow in these systems. Furthermore, fine grids are required around the fracture to capture the abrupt changes in flow parameters in this region. Accurate skin factors, on the other hand, can help reservoir engineers to forecast the well productivity without using fine grid, which is time consuming and cumbersome. Skin factor, or effective well bore radius, is a useful tool for comparing the performance of a real system, which is often complex and difficult to replicate, with that of an open-hole system. Most of the available methods in the literature for estimation of fracture skin or effective well bore radius of a Hydraulically Fractured Well (HFW) were developed for single phase Darcy flow systems [McGuire and Sikora (1960), Prats (1961), Cinco-ley et al (1977, 1978), Valko et al. (2003), Meyer and Jacot (2005), Mahdiyar et al. (2007)].