Abstract

Paraffin deposition is a very complex phenomenon. Whenever a paraffinic oil gets in contact with a cold pipe wall which is below the Wax Appearance Temperature (WAT) of the oil, solid paraffin crystals can precipitate and deposit on the pipe surface. This may significantly reduce or even block the area open to flow.

Most oil fields produce water along with the oil, and the deposition process is not well understood for oil-water flow conditions. Very few studies have been conducted to investigate the effect of water on the deposition process.

The objective of this study is to investigate paraffin deposition under different oil-water conditions. The tests were conducted using a cold finger device and a crude oil from the Gulf of Mexico. Emulsions were created with both fresh water and brine. A simple oil-water wax deposition model was developed by modifying the current University of Tulsa single phase deposition model for solubility and physical properties of the mixture as a function of water content.

Introduction

Transportation of paraffinic oil in an environment which is below its Wax Appearance Temperature (WAT) or cloud point can result in deposition of solid wax particles on the pipe wall. The deposit will decrease the area of the pipe open to flow or even block it completely. It is essential to have a better understanding of the paraffin precipitation and deposition processes, since problems related to deposition of paraffin during production and transportation of crude oil can cause significant financial losses through prevention and remediation costs, which increase as oil production moves into deeper water.

Most oil fields produce water along with the oil. The paraffin deposition process is not well understood for oil-water flow conditions. Very few studies have been conducted to investigate the effect of fresh water or brine on the deposition process. This is due to the higher complexity of the problem with the addition of the water phase and the difficulty in obtaining consistent results with oil-water mixtures. Hsu et. al1 conducted high pressure flow loop experiments with waxy crude oils to study the effect of water on paraffin deposition under turbulent flow conditions. The results showed that wax deposition was significantly reduced with the addition of water. Cole and Jessen2 conducted a series of laboratory experiments in laminar conditions using a deposition cell consisting of a cold plate through which the oil-water solution could flow and where the paraffin deposition would occur. The study included the effect of wettability characteristics of the pipe wall on paraffin deposition. The wettability of the deposition surface was altered through the use of different substances. The results showed that, with the presence of water, paraffin deposition on the more water wet surface was significantly reduced, while no difference in deposition was found for the oil-wet surfaces.

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