A Practical Method for Theoretically Determining the Productivity of Multi-fractured Horizontal Wells

Abstract

Abstract This work investigates the productivity of different configurations offractured horizontal wells by means of numerical simulation. Model results havebeen compared to a number of analytical solutions available for estimating theproductivity of unfractured horizontal wells under various boundary conditions.The simulation model was expanded to include varying lengths of one, three, five, and seven infinite conductivity, vertical hydraulic fractureconfigurations. In this work, infinite (high) fracture conductivity was used, although the model can also be used to investigate the effect of finiteconductivity. Based on the numerical results, a third order polynomialcorrection to the linear flow equation was developed to yield more accurateproductivity index predictions without the limitations of analyticalsolutions. The empirical formula, generated from this work, can be used easily foraccurate predictions of multi-fractured horizontal well productivity andproject economics, under a variety of reservoir and boundary conditions. Introduction The productivity and hydrocarbon recovery benefits of horizontal wells, compared to their vertical counterparts are, by now, well established concepts.The unstimulated horizontal well can generate production rates of two to fivetimes that of an unstimulated vertical well at similar pressure drawdowns(1).In addition, horizontal wells that intersect natural fractures dramaticallyincrease reservoir contact area and, consequently, further increase theproductivity and drainage efficiency(1,2). Historically, horizontal wells havebeen less effective in thicker reservoirs (with thicknesses in the order of 500ft. or more), reservoirs with low vertical permeability (relative to horizontalpermeability), and in stratified reservoirs with impermeable shale barriers.The improvement of well completion and stimulation technology, however, isrenewing enthusiasm for horizontal well applications in areas that werepreviously considered unqualified. The use of hydraulic fractures to enhance horizontal well productivity wasforeseen already in early works by Giger et al(1) and Giger(2). With the advent of fractured horizontal wells (or unstimulated horizontalwells, for that matter) has come a host of analytical solutions, developed topredict the productivity of these wells, although too few includefractures.