New Correlations for Optimizing Horizontal Wells Completions
Authors: Al-Qahtani Abdullah M. , Menouar Habib 
Published: December 2007

Due to the large exposure to the reservoir, horizontal wells may be several times more productive than vertical wells drilled in the same formation. Hence, longer horizontal wells are expected to be more productive than shorter wells. However, that may not be always the case. The major uncertainty is whether the productivity of a horizontal well will increase with increasing well length and perforation percentage of the horizontal section. Field experience with horizontal wells has shown that the productivity of a horizontal well may be severely restricted by frictional losses obtained in longer horizontal sections. Wells suffering from this are those drilled in high permeability reservoirs where frictional losses in the horizontal section may be comparable to the pressure drawdown across formation.

This paper is a companion paper to a paper presented in reference 1 where the effect of horizontal well length as well as the length and distribution of perforated intervals on horizontal well performance has been studied. A computer program based on analytical solution of the flow performance in the case of partially horizontal wells has been developed and tested against field data. After conducting an extensive number of computer runs to study the influence of the main parameters affecting the performance of horizontal wells such as the length, the perforated length fraction, the reservoir permeability and the fluid viscosity, a correlation has been developed to describe the performance of partially perforated horizontal wells by comparison to openhole well. The results are presented in the form of a relation between the production loss due to partial perforation and friction forces and various well parameters.

Another correlation to estimate the optimum horizontal well length beyond which the contribution of horizontal wellbore to the production rate is negligible is also presented.

Introduction

In the last decade, horizontal wells drilling has gained wide acceptance due to the wide range of advantages they offer. The principal applications of horizontal wells is to increase the well productivity via increased contact with the reservoir rock. Increasing the area of contact with the reservoir will result in an increase in the productivity index of the well. Economics aside, these facts imply that longer horizontal wells are more productive and horizontal wells should be drilled as long as possible. However, increasing the well length will increase the frictional losses in the horizontal wellbore which in turn will increase the back pressure at the reservoir rendering some portion of that wellbore unproductive.

As the technology matures, the issue of the effect of frictional losses on the performance of horizontal wells becomes more conceived. As more wells are being drilled and more experience with horizontal wells is gained, the fact of the frictional losses having the potential of seriously impairing the productivity of horizontal wells has been established. Nowadays, it is a common practice to consider wellbore hydraulics in planning development of oil field utilizing horizontal drilling.

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