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This paper discusses problems related to emulsions that have been encountered in a large Saudi Arabian field. This is a unique field lying both onshore and offshore and is producing from seven different reservoirs. These oils range in viscosities from 2 cP to over 10 cP (@ 22°C) and API gravities range from 28 to 40. The n-pentane asphaltene content varies from 0.2% to over 7% and watercut for producing wells ranges from dry wells (0% watercut) to over 70%. These properties provide an interesting case of operational problems in oil-water separation. The problems include increased incidents of shorting in the separator, tripping of equipment and increased demulsifier consumption. This paper presents the results of a comprehensive study that was initiated to understand the main causes of emulsion formation in the field. The factors investigated were watercut, temperature, shear, asphaltene content, demulsifier dosage and mixing different crudes. These factors were quantified with a new water-oil separation index that was developed to measure emulsion stability. The results show a strong correlation of asphaltene content in the crude oil with the water-oil separation index or emulsion tightness. Photomicrographs of high asphaltenic crude oil also shows the presence of organic particulate and a generally lower water drop size. These emulsions were videotaped at high magnification using a novel flow-through cell and the visual information has helped our understanding of how emulsions are stabilized by the organic films or "skin" on the water droplets. Recommendations are made for reducing and optimizing demulsifier dosage by adding chemical additives. Many lessons learned are applicable to any crude oil treating facilities. |
