Chemical Treatments Offer Alternative to Acidification for Sheen Control
Authors: Carpenter Chris 
Published: December 2024

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This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 218979, “Evaluating New Chemical Treatments To Decrease Water-Soluble Organic Content From Produced-Water Discharge,” by Fabrício Venancio, SPE, Antonio P. Oliveira, and Sérgio C. Silva, Clariant, et al. The paper has not been peer reviewed.

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During the offshore disposal of produced water, an oil sheen is sometimes visible at the surface, even when the oil content is within acceptable limits. Water-soluble organics (WSO) are known as one of the main causes of the appearance of sheen. A common approach to inhibiting sheening is the acidification of oil, in which some organic acid is added before the oil-treatment system. However, high acid volumes (3–5 tons/day at 500 ppm) raise asset-integrity concerns. This work investigates a cost-effective and sustainable alternative to acidification for sheen control.

Introduction

This paper presents a proposal to inhibit the appearance of sheen as an alternative method to acidification. Two products are described, one an emulsion breaker with WSO-removal properties, called Product A, and the other a flocculant with WSO-removal properties, called Product B. Product A can be applied as a replacement to a regular emulsion breaker, while Product B can be used as a replacement to a flocculant agent. The application of this technology does not result in any setup alternation in offshore platforms except for the beneficial elimination of acid injection.

Materials and Methods

Samples.

The crude oil sample used in this work had 52% basic sediment and water (BS&W) and a density of 0.889 g/mL. The oil was acquired from an offshore platform and collected before entering the separator system. The produced water was collected at the beginning of the produced-water-treatment system before the hydrocyclone.

The products used to treat the crude oil were a reference emulsion breaker (Reference EB) and Product A. The products used to treat the produced water were a reference flocculant (Reference F) and Product B. A detailed description of both bottle-test and jar-test analyses is provided in the complete paper.

Qualitative Sheen-Appearance Test.

This test aims to simulate the disposal of produced water into the sea and to evaluate the appearance of sheen.

A brine consisting of a solution of 3.5% sodium chloride in water was prepared, and 90 mL was added to a beaker. A syringe or pipette with its tip 0.5 cm below the water surface was used to add 10.0 mL of the water sample. The beaker was monitored in a black chamber with ultraviolet illumination for 1 hour. A negative result in which the sheen was detected was found when the presence of blank dots appeared; otherwise, a positive result occurred when no blank dots were detected during the observed period.

Total Oil Content (TOC) and WSO Content.

Concentrated hydrochloric acid (37%) was used to acidify 500 mL of a produced water sample until its pH reached 2.0. The sample was extracted with 60.0 mL of n-hexane, which was divided into three portions of 20.0 mL. The organic phase with the extracted oil was collected in a weighed glass balloon through an 8.0-µm cellulose filter. After evaporation, the balloon was weighed again. The TOC was calculated from the difference in the balloon’s mass before and after evaporation.