Water Wetting Study on Crude Oil Utilizing Model Oil Blend And Myristic Acid Mixture
Authors: Rayes Abdulaziz 
Published: May 2016

Water separation from crude oil inside oil transport pipelines causes the water to wet the inner steel surface of the pipe and leads to corrosion and leaks. Factors that affect the water settlement inside pipelines, interchangeably called as water-wetting phenomenon, are major areas of research. Previous studies focused on the physical properties of crude such as density, viscosity, interfacial tension and water-in-oil contact angle as factors affecting water wetting. In those studies, alteration of physical properties toward preventing water wetting inside crude pipelines was attributed to the presence of surface-active compounds in the crude oils, which promotes smaller water droplets, oil adsorption to the steel surface thus oil wetting; this was concluded through artificial mixing of selected surface active compounds with model oils. In the current paper, we will determine whether the natural presence of surface-active compounds in crude oils can only explain the alteration of the steel wettability of actual oils or not. To achieve that, a water-wetting study is conducted on a model oil blend mixture with 1% myristic acid, a carboxylic acid surface-active compounds, which mimics the PNA distribution and physical properties of an actual type of crude oil produced from a certain field. Using a doughnut cell wetting measurement apparatus, it was found that the model oil blend mixture with the myristic acid has reduced water wetting transition velocity by 60% compared to that of an actual crude of the similar physical properties. This indicates that the crude composition might have a higher impact on the water-wetting phenomena regardless of the natural presence of the surface-active compounds in the crude oil.

Introduction

Crude oil transport pipelines experience a significant increase in pipeline damage due to internal corrosion as oil fields mature. It is not coincidental that frequency of internal corrosion damage increases as the water-cut in the throughput continues to increase. In such situations, oil transport pipelines become oversized due to the low production rates which reduces the liquid velocities and allows free water to separate from the oil, thereby aggravating the corrosion environment in the pipeline.

Previous experiments were conducted and predication models were developed to calculate the velocities below which water dropout occurs. In these models, water wetting transition velocity is dependent on physical properties of the fluid that includes fluid density, viscosity, oil-water interfacial tension, pipe diameter (Hinze 1955, Brauner 2001 and Tang 2011) and water-in-oil contact angle (Tang 2011). According to these models, oil wetting is promoted by higher density, higher viscosity, lower interfacial tension and larger water-in-oil contact angle. Compared to actual crude oils, model oils have higher tendency toward water wetting, which was attributed to the natural presence of surface-active compounds in crude oils (Ayello 2013). The adsorption of surface-active compounds at the metal surface can create an organic protective film and its presence in the oil-water interface reduces the oil-water interfacial tension, which prevents water droplets from wetting the steel surface (Ayello 2013).