Occurrence of naphthenate deposition in crude oil production field offshore Niger Delta
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SHORT COMMUNICATION-PRODUCTION GEOLOGY
Occurrence of naphthenate deposition in crude oil production field offshore Niger Delta Opeyemi Lawal1 · Solomon A. Adekola1 · Akinsehinwa Akinlua2 Received: 16 July 2020 / Accepted: 20 October 2020 © The Author(s) 2020
Abstract Crude oil and produced water samples obtained from ten wells in an offshore field, Niger Delta, were analyzed, in order to determine the occurrence of naphthenates deposition in the field. Total acid number (TAN) and °API of the crude oil samples, pH and metal ions concentrations of the produced water samples were determined. The results revealed that TAN values ranged from 0.47 to 1.01 mgKOH/g with pH of 6.9–8.9, which were above established threshold. The metal ions concentrations especially for Ca++ and Na+ were relatively high. These imply a high possibility of metal-naphthenate precipitation in the oil production facilities in this field. Keywords Naphthenate · Crude oil · Produced water · Metal ions · Niger delta
Introduction Naphthenate deposit or scale is presently one of the production chemistry challenges in the upstream crude oil sector with occurrence in different sites, both onshore and offshore, across the globe (Igwebueze et al. 2013). In recent years, there has been a worldwide increase in the production of acidic crudes that are rich in naphthenic acids (NAs) (Oliveira et al. 2013). Geochemical methods have proven useful in determining the presence of these acids in crude oil, which when present implies high potential or possibility of two major problems that are significant in process control as well as flow assurance in crude processing plants; naphthenic acid corrosion (NAC), and formation of naphthenates (naphthenic acid salts) which can either precipitate and form organic deposits (which block process lines and vessels thereby immensely contributing to flow assurance difficulties) or form interfacial active salts (soaps) that are prone to stabilized emulsions (Oliveira et al. 2013). Therefore, determining the presence of naphthenic acids in crude oil is the first step in detecting a portending deposit nucleation * Akinsehinwa Akinlua [email protected]; [email protected] 1
Department of Geology, Obafemi Awolowo University, Ile‑Ife, Nigeria
Fossil Fuels and Environmental Geochemistry, Department of Chemistry, Obafemi Awolowo University, Ile‑Ife, Nigeria
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sequence and tackling these two aforementioned problems. For example, deposition of calcium naphthenate (CaN) occurs when tetraprotic acids (tetra-acids with molecular weight above 1200 Da) are present in crude oil (Igwebueze et al. 2013). Meanwhile, it is a known fact that the naphthenic acid phase behavior is a function of produced water composition and pH. Both the tetraprotic acids and other naphthenic acids present in crude oil may react with the cations present in produced water at certain pH values and some specific set of conditions. For example, if there is sufficient calcium and the pH of produced water increases above pH 6 (due to depressurizat
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