Production Forecasting And Economic Evaluation of Horizontal Wells Completed In Naturally Fractured Reservoirs
Authors: Evans R.D. 
Published: March 2010

Abstract
A systematic methodology which combines inflow performance analysis, production forecasting, and economic considerations is presented for optimum recovery of hydrocarbons from naturally fractured reservoirs using horizontal well technology. An analytical method for predicting the production performance of horizontal wells in a solution gas drive, naturally fractured reservoir is presented based on material balance analyses and linear approximations of reservoir fluid properties as functions of reservoir pressure. The effect of natural fracture characteristics on production performance is accounted for by use of inflow performance equations. A detailed economic evaluation model accounting for the time value of cash flow, including the effects of interest rate and inflation rate, is also presented and used in the analysis. Results are presented which demonstrate the methodology developed and its application to the optimum primary recovery from horizontal wells completed in naturally fractured reservoirs.

Introduction
Over the past two decades considerable interest has been focussed on the utilization of horizontal well technology to improve the recovery of hydrocarbons from naturally fractured reservoirs. This interest has resulted in the publication of numerous papers concerned with all aspects of drilling, completing and producing horizontal wells. However, an extensive literature review(1) indicated that systematic techniques have not been developed to optimize the recovery of hydrocarbons from such complex reservoirs utilizing horizontal well technology. The current industrial practice still relies primarily on the basic knowledge of fractured systems and on practical experiences for determining the orientation, length, and spacing of horizontal wells.
Guo and Evans(2 –7) have published several papers which focussed upon many important aspects of a horizontal well bore intersecting discrete and/or randomly distributed natural fractures. These papers have developed techniques for characterizing naturally fractured reservoirs, pressure transient testing, production forecasting, and economic evaluation. From this research a systematic methodology has evolved which can be used to maximize the recovery of hydrocarbons from a naturally fractured reservoir utilizing horizontal wellbores.
To maximize the recovery from naturally fractured reservoirs using horizontal well technology requires:a quantitative characterization of the natural fracture system so that the proposed horizontal wells can be drilled orthogonally intersecting the natural fractures;appropriate inflow performance equations for a horizontal well intersecting natural fractures to estimate the well productivity;a production forecasting technique to predict production performance of naturally fractured reservoirs; andan economic evaluation model for assessing the feasibility of exploiting naturally fractured reservoirs using horizontal well technology.

Characterization of Naturally Fractured Systems
An important first step in predicting the recovery of hydrocarbons from naturally fractured reservoirs is to adequately describe the fracture system. Techniques for deriving the permeability tensors for idealized fractured systems using geologic data are presented in Reference (2). The techniques developed are applicable for discrete fractures or random fractures. In a very recent paper by Quenes, Richardson and Weiss(8), a technique is presented for characterizing naturally fractured reservoirs using geomechanics and artificial intelligence via neuro-computing.