Identification of high-molecular weight naphthenic acids in crude oil and methods of management of their calcium salts depositson Sakhalin-2 project assets

UDK: 622.276.8
DOI: 10.24887/0028-2448-2023-3-89-94
Key words: high-molecular weight naphthenic acids, high-performance liquid chromatography, mass spectrometry, salt deposits, emulsion, biocide, tetrakis (hydroxymethyl) phosphonium sulfate (THPS), field trials
Authors: R.U. Kunaev (Sakhalin Energy LLC, RF, Yuzhno-Sakhalinsk), I.O. Glukhova (Sakhalin Energy LLC, RF, Yuzhno-Sakhalinsk), M.G. Patrushev (Institute of Chemistry, Far-East Branch of the RAS, Russia, RF, Vladivostok), S.V. Sukhoverkhov (Institute of Chemistry, Far-East Branch of the RAS, Russia, RF, Vladivostok)

Since the early 2000s in the world practice of offshore oil and gas production, the problem of deposits of high-molecular naphthenic acids calcium salts in process facilities of offshore platforms has become known. The rapid formation and accumulation of naphthenic acids calcium salts in oil treatment units (separators, coalescers) can cause disruption of oil production at offshore fields of the Russian Federation and in the production of heavy biodegradable oil onshore. At the Sakhalin-2 project facilities, such deposits were discovered in 2015 and unambiguously identified in 2020. The emulsions discovered in 2015 significantly worsened the oil preparation process and required increased demulsifier consumption. The deposits blocked process units (separators and coalescers) and reduced their throughput; this is led to a long-term annual shutdown of equipment for its purification. It has been proposed that the recovered deposits were products of undesirable interaction of produced oil and drilling fluids components or reaction products in the use of polymeric scale inhibitors. In 2019-2020 a deep analysis of the component composition of the formed sediments and, in particular, the search for "atypical" components was carried out. Obtained data showed that one of the likely causes of sediment formation may be naphthenic acids calcium salts. The composition of sediments from process units on the Piltun-Astokhskaya-B platform of Sakhalin Energy LLC has been investigated via several modern instrumental analytical methods. In addition, identification and semi-quantitative determination of high-molecular naphthenic acids by IR spectroscopy and HPLC/MS in oil were performed. The field trial of a reagent based on tetrakis (hydroxymethyl) phosphonium sulfate (THPS) as an inhibitor of naphthenate deposits finished, the reagent confirmed its effectiveness, and a program for its use was developed.


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