Summary

In this paper we study the flow in a perforated pipe where fluid enters the pipe through the perforations. The focus of the paper is to describe and understand the evolution of the pressure field inside the pipe as a result of the radially inflowing fluid. Details of extensive single-phase experimental measurements are reported. A first-generation model which describes trends observed in the experiments is presented.

Introduction

While oil production by means of horizontal wells has many advantages over conventional oil recovery techniques, there are many specific complications in applying horizontal-well technology to produce oil. One of the main complications is related to the length of the well. Although the perforated pipe section may be up to a few kilometres long, the pressure drop in the pipe can severely limit the actual production length of the pipe. Namely, it will be clear that frictional effects will lead to a significant drop in the pressure between the heel and the toe of the well. The result is that the pressure difference between the well and the reservoir may reduce significantly as one moves from the heel toward the toe of the well. This leads to a corresponding reduction in the oil production per unit length of the well. It is clear that for high permeability reservoirs where the drawdown is small, one of the central questions in horizontal-well production technology concerns the pressure drop in a well liner.

The prediction of the pressure drop is complicated for various reasons. First of all, the horizontal-well problem is not one which deals with a fully developed turbulent pipe flow. It is, in fact, quite the opposite. Liquid (and/or gas) enters the well bore through perforations along the length of the well so that the volume flux inside the perforated pipe increases toward the heel of the well. It follows that a fully developed flow is unlikely to exist in any section of significant length. Furthermore, the distortion of the pipe flow as a result of many thousands of radial inflow points is highly nontrivial, and the pressure drop in such perforated pipes is not readily calculated. Additional complications occur because, for a variety of reasons not only oil, but also gas, water, or sand may enter the pipe. Furthermore, the name "horizontal well" is misleading because the well bore is, in fact, unlikely to be truly horizontal along most of its length. The result of this is that the horizontal-well problem is one in which we have to deal with the problem of multiphase flow through inclined, perforated pipes. A detailed outline of difficulties that may be encountered in horizontal-well operations is given by Tehrani and Peden.

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