Experimental Investigation of Emulsion Stability in Gas/Oil Separation Plants

SummaryThis paper presents an experimental study performed to charac-terize the stability of emulsion samples collected from different Gas/Oil Separation Plants (GOSPs). The first part of the study (Al-Ghamdi et al. 2007) focused on the analyses of separated phases. Many techniques (differential scanning calorimetry, Karl Fischer titration, rheology, optical microscopy, and cryo-scanning electron microscopy) were applied to analyze and characterize the separated phases: crude oil, emulsion, and free water. In the second part of this study, the stability of residual emulsions was investi-gated against several chemical demulsifiers by using bottle tests and an automated vertical-scan macroscopic analyzer (Turbiscan; Formulaction; Toulouse, France). This instrument is used to obtain kinetics of separation of concentrated and opaque dispersed sys-tems such as emulsions, suspensions, and foams. Interfacial ten-sion measurements were also made to obtain information about the interfacial behavior of samples including viscoelasticity properties of the film. The results of transient emulsion-separation experi-ments provide some useful insights into their behavior, stability, and tightness. The study highlights the main physicochemical parameters responsible for the varying tightness of these emulsions and should help provide recommendations to optimize their treat-ment costs and resolve emulsion issues in the GOSPs.IntroductionThe formation of stable water-in-crude-oil emulsions during oil production poses significant challenges during oil/water separa-tion in surface production facilities (Kokal 2006; Schramm 1992). These emulsions can be very stable because of the presence of rigid films formed by polar compounds, such as asphaltenes and resins, and other fine solids (Graham 1988; Papirer et al. 1982; Bridie et al. 1980; Ese et al. 1997; Jones et al. 1978; McLean and Kilpatrick 1997). Effective separation of crude oil and water is essential to ensure the quality of separated phases at the lowest cost. Crude-oil dehydration is generally accomplished by a combination of mechan-ical, electrical, thermal, and chemical methods. The addition of chemical additives is by far the most common method in emulsion breaking. The chemicals disrupt the interfacial film and enhance emulsion breaking (Schramm 1992; Lissant 1983).Earlier studies (Kokal and Al-Ghamdi 2007, 2008) have shown the importance of emulsion characteristics on the performance and optimization of oil/water separation. The present study was per-formed to carry out an in-depth analysis of the main physicochemi-cal properties of emulsions and the link to their behavior in the field. The main objective is to provide recommendations to reduce treatment costs and optimize oil/water separation in the field.In the first part of this study (Al-Ghamdi et al. 2007), a strict and rigorous method was applied to characterize the behavior and com-position of emulsion samples from several GOSPs. The samples first were separated to identify the amount of separated oil, water, and residual emulsion. Each phase then was analyzed separately. Bulk properties (viscosity, density) and chemical composition of crude oils were determined. Salinity and geochemical analysis of the separated water were made when possible or assessed by dif-ferential scanning calorimetry (DSC) in other cases. The residual emulsions were characterized using several techniques including Karl Fischer titration to determine the water content, DSC, optical microscopy or cryo-scanning electron microscopy (cryo-SEM) to assess the size and polydispersity of the dispersed droplets. The second part of this work addresses the stability of residual emulsions from selected samples using chemical demulsifiers. The efficiency of several chemical additives, including field demulsi-fiers, was determined using bottle tests and an automated vertical-scan macroscopic analyzer. Rheological behavior and fine-solids content of emulsions were also measured. Interfacial tension measurements were made to investigate the interfacial behavior of selected samples including viscoelasticity properties of the films.Materials and Methods