Abstract

The performance of horizontal wells in bounded anisotropic reservoirs has been investigated using the statistical analysis. New statistical models for calculating the fraction of horizontal well length contributing to unrestricted production, and horizontal well shape factor, are presented.

To predict the productivity index of horizontal wells requires the determination of the pressure drop due to formation damage around such wells. Long duration of formation exposure to drilling fluids and difficulties in designing a truly non-damaging drilling fluid may be the main reason for the unexpected failure of some horizontal wells drilled in favorable reservoirs.

The concept that the performance of horizontal well of half-length Xf1 with mechanical skin can be replaced by the performance of an equivalent horizontal well of half-length Xf2 with no mechanical skin is used. The statistical analysis showed that for a given reservoir shape and well asymmetry, the horizontal well shape factor can be directly correlated with three dimensionless parameters, XLD, rw/h, and LD, which are functions of reservoir and well parameters. These statistical correlations can easily be used to predict the performance of a damaged and/or stimulated horizontal well without the need to use complex numerical and/or analytical solutions which require extensive computer use.

Introduction

The growing interest in field development using horizontal well drilling necessitates development of new concepts for improved performance prediction of these wells.

The combined effect of the formation damage and the presence of impermeable barriers and low permeability regions in the vicinity of some sections of the horizontal wellbore will manifest itself as mechanical skin damage in well test analysis if the total drilled (or perforated) length of the horizontal section is used in the calculations. The total skin factor obtained from a well test is the summation of the mechanical skin factor and pseudo skin factor. New analytical equations for calculating pseudo skin factor and mechanical skin factor for horizontal wells during the unsteady state and pseudo steady state flow period have been presented recently. These new equations can be used to determine:

  1. the fraction of horizontal well length contributing to unrestricted production,

  2. horizontal well shape factor and

  3. horizontal well productivity index based on the equivalent non-damaged length of the horizontal wellbore The purpose of this paper is to present statistical model for the horizontal well shape factor and the fraction of horizontal well length contributing to unrestricted production.

The model developed in this study can be used to evaluate the performance of horizontal wells without the need to use complex numerical and/or analytical solutions.

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