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Abstract

The production and transportation of petroleum fluids could be severely affected by deposition of suspended particles (i.e. asphaltene, paraffin/wax, sand, and/or diamondoid) in the production wells and/or transfer pipelines. In many instances the amount of precipitation is rather large causing complete plugging of these conduits. Therefore, it is important to understand the behavior of suspended particles during flow conditions.

In this paper we present an analysis of the diffusional effects on the rate of solid particle deposition during turbulent flow conditions (crude oil production generally falls within this regime). The turbulent boundary layer theory and the concepts of mass transfer have been utilized to calculate the particle deposition rates on the walls of the flowing conduit. The developed model accounts for the eddy and Brownian diffusivities as well as for inertial effects.

The analysis presented in this paper shows that rates of solid-particle deposition (during crude oil production) on the walls of the flowing channel due solely to diffusional effects are small.

It is also shown that deposition rates decrease with increasing particle size. However, when the process is momentum controlled (large particle sizes) higher deposition rates are expected.

Introduction

Numerous experimental works have revealed the colloidal nature of the heavy asphaltene fraction of a crude oil. We consider the asphaltenes to exist in crude oil as both dissolved and suspended particles. Dispersed asphaltenes are sterically stabilized by neutral resins, they are electrically charged, and have a diameter of 30-40 A. The stability of these particles can be disrupted by addition of solvents (i.e. n-heptane), it could also be disrupted during flow conditions due to shear stresses, or by counterbalancing the weak asphaltene particle charge. The latter is an important phenomenon since during crude oil production a streaming potential is generated which is believed to cause asphaltene aggregation. When solvents are used to precipitate asphaltenes the resulting aggregates may have a diameter as large as 300. In addition to asphaltenes there may be other types of particles suspended in the crude oil as well. For instance, sand particles swept from the reservoir matrix, paraffin crystals if the temperature falls below the cloud point of the crude, and/or diamondoids.

Production and transportation of petroleum fluids could be severely affected by deposition of asphaltene (and other suspended particles). In many instances the amount of precipitation is rather large causing complete plugging of the flowing channel. Therefore, it is important to understand the behavior of the suspended particles (asphaltenes, sand, paraffin/wax, diamondoid etc.) during flow conditions.

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