Abstract

With the recent rebirth of horizontal well technology comes a need to understand the flow of multiphase fluids within the horizontal wellbore. This understanding is required by both the production and reservoir engineer in their attempts to optimize reservoir exploitation. In Canada, a number of horizontal wells have been drilled in heavy oil areas, which are prone to sand production because of the unconsolidated nature of the reservoir. This poses an additional problem as it potentially adds an extra flowing phase and further complicates the flow regime as the sand settles and forms dunes. As a first approach to investigating sand transport in horizontal wells, a pipeline flow model was used to simulate the axial component of emulsion/sand flow.

Although non-Newtonian behaviour may occur, crude oil emulsions are often nearly Newtonian, with viscosities up to 100 times that of the continuous phase. Pipeline flow of these emulsions may be either laminar or turbulent, Of interest are the frictional headlosses and delivered concentrations for sand transport by these mixtures.

Predictions of pipeline performance can be made using existing experimental measurements for deposit free sand transport by Newtonian fluids of viscosity ranging between 5.8 mPa.s and 38 mPa.s, These tests included both laminar and turbulent flow of a 190-jJm diameter sand. Unfortunately delivered sand concentrations were not measured in these tests. The test results have been extrapolated using models that recognize which concentration variation is likely to occur. It is concluded that turbulent flow is much more effective than laminar flow for sand transport.

Introduction

Horizontal wells were first used for oil recovery over fifty years ago. Over the years they had limited success until recent developments in drilling and completion made them more feasible. These technological developments have resulted in a phenomenal increase in the number of horizontal wells drilled. In Canada, horizontal wells are employed in a variety of reservoir settings and resource types. A common use of horizontal wells is in the heavy oil areas where productivity is low due to the high viscosity of the crude oil, and recoveries are marginal because of the influence of a bottomwater zone.

One area of concern when producing from a heavy oil unconsolidated formation is the flow of oil/water emulsions and sand in the horizontal well. If a stationary deposit of sand is formed, the resultant partial obstruction will increase the pressure drop and energy consumption for a given volumetric flow rate. Unfortunately this flow regime has not been studied systematically for wide ranges of deposit thicknesses and fluid viscosities so that mechanistic models for them have yet to be produced.

For deposit-free flow, which requires higher flow rates, rather more is known. This is especially true for mixtures whose flow is turbulent. Much less is known about laminar flow of a slurry type system where the sand particles can settle. In this communication we attempt to illustrate the present state of knowledge as it would apply to horizontal well and pipeline flow.

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