Sonangol's Gimboa production is located in deepwater block 4 offshore Angola. Early in the life of the field and with the advent of water cut, it experienced solids production that fouled processing equipment and that were later identified as calcium naphthenates. The paper describes in detail Gimboa's calcium naphthenate deposition including its history and progression. Detailed characteristics of the crude and produced water are provided. The mechanisms of solids formation are elucidated and the remedial measures adopted to solve the problem are examined in detail. The impact of water cut and the role of system parameters like temperature and pressure in the resolution of the naphthenate problem are outlined and the use of field filtration and bottle testing methods in designing the eventual solution are highlighted. As with most oilfield problems calcium naphthenate deposition at Gimboa was brought under control through the conscientious efforts of Sonangol, Nalco Energy Services and Saipem personnel working as a team.Background "Calcium naphthenate" is the industry term for salts formed from naphthenic acids and alkali or alkali earth metals. The formation of naphthenate salts is an emerging problem and occurs in the production of crudes with significant amounts of naphthenic acids and produced waters with significant amounts of alkali or alkali earth metals. Calcium naphthenate problems span a whole spectrum ranging from naphthenate stabilized emulsions to interface sludge and solids deposition. Where one is on this spectrum depends on the presence in the crude of bicarbonate ions, inorganic scale and particulates, tetraprotic cyclic acids (known as 'ARN' acids) [1, 2] as well as several other factors.
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