Mechanisms for Controlling Sand-Induced Corrosion in Horizontal Pipe Flow of Sand, Crude Oil and Water

Abstract

Background: The presence of sand particles and associated water in crude oil calls for serious concern when the flow conditions leading to flow stratification in an upstream petroleum pipeline become significant. At such conditions, problems such as sand deposition and water containment on the pipe wall may result in consequences such as sand-induced corrosion, mechanical failure, pipe fatigue, reduced flow area, loss of production and pipe blockage which are still currently unresolved by conventional and current models. Objective: A modelling approach was adopted to control the conditions leading to sand-induced corrosion and other related problems caused by flow stratification in the upstream petroleum sector since conventional methods adopted to screen sand, only contribute to the problem. Also, to date, mechanisms and models exist for other corrosion types such as CO2, H2S, acid-induced corrosion, etc. but none currently exists for sand-induced corrosion. However, the concept of force-competition or dimensionless numbers was adopted using a modelling approach to resolve the problem. Method: This research work resolves the situation by means of a three-phase model which incorporates sand, crude oil and water phases in its mass and momentum balance equations while taking into cognisance, the effect of eddies. The three-layer model established in this work, has its origin in a two-phase sand-crude oil system and, based on current literature, a modelling approach that considers the flow of sand, crude oil and water has never been adopted to tackle the problem of sand-induced corrosion caused by associated water as a stimulant for corrosion. Conclusion: The established model gave an accuracy of 99% when results from the model were compared with sand and crude oil production data obtained from the field. Based on the model’s reliability, flow mechanisms/dimensionless numbers were used to ascertain critical flow conditions in order to be able to avoid situations leading to sand deposition, sand-induced corrosion and other related problems. Based on the results obtained, the estimated Euler numbers revealed that the 18 m point of the pipe is at risk due to the impact of the sand-deposit-drag-force on the pipe wall. Also, the estimated Froude numbers were indicative of the 12-18 m points as deposit/corrosion prone areas.