INVESTIGATION OF PARAFFIN DEPOSITION IN MULTIPHASE SYSTEMS

Abstract

As oil and gas production extends to severe environments and deep waters to meet the increasing energy demand, several issues have been encountered. Thus, it is a challenge to ensure the flow of products safely and profitably, a topic known as flow assurance. Some of the flow assurance elements are paraffin deposition, hydrate formation, asphaltene precipitation, and severe slugging. Paraffin deposition occurs when normal alkanes ranging from C17 to C60 precipitate from the solution and deposit at pipe walls restricting the flow and in worse cases blocking it completely. Therefore, understanding the mechanisms of, developing models for predicting, and finding methods to prevent/mitigate paraffin deposition is of major interest. To improve the accuracy and reliability of these prediction models, a better understanding of the wax precipitation and deposition mechanisms is needed. Currently, the available wax precipitation models still have some errors that might have been propagated from the input parameters. Thus, part of this work targeted the measurements and correlations validation of temperature and enthalpy of fusion, and temperature and enthalpy of solid-solid transition to reduce the uncertainty in wax precipitation models input parameters. New correlations were proposed wherever the accuracy of the existing ones was too low. Additionally, an investigation of wax deposition in pipelines is to be conducted. While most of the work has been done in single-phase flow, oil and gas production lines may carry multiphase flow thus proper understanding of the effect of multiphase flow on paraffin deposition is crucial to ensure the flow. As a first step, a thorough investigation of wax deposition characteristics on a single phase was conducted to study the effect of Reynolds Number and time on wax deposition hardness, amount, and characteristics. This will ensure the reliability of the new flow loop and testing model oil and provide a baseline for multiphase studies. Finally, this work investigated paraffin deposition in multiphase oil and gas systems in stratified and slug flow patterns. An in-house model oil was prepared to mimic the wax properties of crude oil will be used. By using a flow loop capable of operating at stratified, and intermittent flow patterns, a comprehensive set of data for paraffin deposition and temperature profile was obtained. The effect of gas superficial velocity and flow pattern were investigated. In wax deposition in stratified flow, the deposition profile was dependent on the waviness of the flow. Thus, a new, three-stage deposition process was proposed. On the other hand, wax deposition in slug flow exhibits different characteristics between the top and the bottom of the pipe circumference validating that flow pattern needs to be considered to propose effective mitigation strategies whether it is thermal, mechanical, or chemical treatment.