Flow Regime Affects Erosion Prediction in Multiphase Flow
Authors: Carpenter Chris 
Published: October 2018

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 28360, “Investigation of Erosion Caused by Fine Particles in Multiphase Flow,” by Tran Nguyet Ngo, SPE, and Deng-Jr Peng, Intecsea, and William Pao, Hamdan Ya, and Rohaizad M. Norpiah, SPE, Petronas, prepared for the 2018 Offshore Technology Conference Asia, Kuala Lumpur, 20–23 March. The paper has not been peer reviewed. Copyright 2018 Offshore Technology Conference. Reproduced by permission.

Erosion caused by fine solid particles presents one of the greatest threats to oil and gas flow assurance, consequently affecting material selection and wall-thickness design. The authors of this paper conclude that the erosional effect caused by microsized particles is dependent on the flow patterns in the pipe, determined by superﬁcial velocities of each phase. The results of the proposed modeling using multiphase computational fluid dynamics (MCFD) are expected to benefit erosion-impact assessment in multiphase hydrocarbon-production and -piping systems.

Introduction

Understanding the effect of key parameters that regulate erosion mechanisms is essential. Studies addressing these issues have concluded that particles rebound and that the erosion profile is dependent on particle motion inside oilfield conduits. Researchers also have found that the direct-impingement (semiempirical) model agreed with results achieved with the discrete-phase model implemented in CFD, while the pure empirical model severely under-predicted the erosion, thus emphasizing the importance of flow-behavior modeling. Furthermore, the majority of available erosion-prediction models involve single-phase systems, not taking into account multiphase ﬂow patterns that address the characteristics of individual flow behaviors.

In other studies, the erosional effect caused by microsized particles in single-phase carrier fluid also has been reported. One hypothesis is that the presence of these microsized particles acts as an enabler, which produces homogeneous pits on the surface of metal, increasing significantly the contact surface area upon which chemical and mechanical interactions can take place.

The effect of multiphase flow and its interaction with sand particles, specifically fine solids, is often neglected. Hence, integrating both the erosion and fluid-flow models is essential in enhancing the accuracy of erosion evaluation.

MCFD Model for Erosion Prediction

In a pipeline system, the eroded spots caused by particles are detected typically at locations with restricted flow characteristics or radically changing flow directions, where the bend or elbow is identified as an erosion-susceptible area. Hence, in the present study, a 1-in. elbow is designed with a horizontal inlet and vertical upward outlet orientation. A length of 10 times the elbow internal diameter is placed upstream and down-stream of the 90° elbow.

The computational procedure for this work includes MCFD simulation, where an annular flow regime of air and water is modeled in the elbow, incorporated with the division of grids to represent predefined flow conditions (Step 1). By tracking particle impingement within the carrier fluids (Step 2), erosion rate is calculated and analyzed (Step 3).