Sunil Kokal

Emulsion Separation Index: From Laboratory to Field Case Studies

Quantifying oil-water or emulsion separation has always been difficult. This is due, in part, to the numerous factors controlling oil-water separation. This paper describes a new method developed at Saudi Aramco for the quantification of oil-water separation process. It is designated as ESI or Emulsion Separation Index and it was developed to measure emulsion stability. This index has been used to select and screen demulsifiers and to quantify the effect of various factors that affect oil-water separation including temperature, shear, asphaltene content, watercut, demulsifier dosage and mixing different crudes. Its use has eliminated some of the `art-work associated with demulsifier selection and diagnosing emulsion treatment problems. This paper also describes three field case studies where the ESI was used to select the best demulsifier, diagnose, and ultimately solve emulsion related problems during oil production. The first field study is from the largest onshore oil field in the world. The emulsions from this field were being stabilized by inorganic scales and organic asphaltenes. The paper describes how the ESI was used to diagnose and resolve the problem. The second field study is from the second largest offshore field in the world. Here extremely tight emulsions were forming and plugging the separation equipment offshore. These emulsions contained 70-90% water and were very viscous. Their deposition in the separation equipment was resolved by using recommended demulsifiers and performing ESI tests in the field. The demulsifier dosage was also optimized using these tests. The third field case study is from another large offshore field that produces from seven different reservoirs. The properties of the crudes from the seven reservoirs vary significantly. These properties provide an interesting case of operational problems in oil-water separation including increased incidents of arcing/shorting in the separator, tripping of equipment and increased demulsifier consumption. The factors affecting oil-water separation were quantified using ESI. The results show a strong correlation of asphaltene content in the crude oil with ESI or emulsion tightness. Recommendations were made for reducing and optimizing demulsifier dosage by adding chemical additives. Many lessons learnt in these field studies are applicable to any crude oil treating facilities.

Quantification of Various Factors Affecting Emulsion Stability: Watercut, Temperature, Shear, Asphaltene Content, Demulsifier Dosage and Mixing Different Crudes

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.

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

Phase behavior of gas condensate/water system

Gas condensate reservoirs are an essential part of Saudi Arabias hydrocarbon resources. A good understanding of the effect of water on the phase behavior properties of these hydrocarbons is essential for carrying out accurate forecasts of the performance of these reservoirs using numerical simulators. In addition, the scaling and corrosion tendencies of the produced water are strongly influenced by mass transfer with the hydrocarbon phase. This paper presents unique experimental phase behavior data for a typical Saudi Arab gas condensate three-phase (water/condensate/gas) system. The objective of this work is to quantify the effect of water on gas condensate fluid properties. The results show that appreciable amount of carbon dioxide and methane partition from the gas condensate phase into the aqueous phase. Another important observation was the mass transfer of water into the condensate phase. The mass transfer between the condensate and aqueous phases results in a decrease in the gas/condensate ratio. The carbon dioxide in solution makes the brine acidic, and can dissolve carbonate minerals from the formation, for example, calcium carbonate. In addition, the acidic or sour brine will be quite corrosive. The experimental results are compared with equation-of-state and other correlations published in the literature.

Experimental Investigation of Emulsions Stability in GOSPs - Part I: Analyses of Separated Phases

This paper presents the first part of an experimental study performed jointly by IFP and Saudi Aramco to characterize the stability of emulsion samples collected from different Saudi Aramco Gas/Oil Separation Plants (GOSP). Earlier studies 1-2 have shown the importance of emulsion characteristics on the performance and optimization of oil-water separation at Saudi Aramco GOSPs. A strict and rigorous methodology was applied to understand the characteristics, behaviour and composition of these systems. Samples were first separated by simple gravity sedimentation in order to identify the amount of separated water, oil and residual emulsion. Each separated phase was then analyzed separately. This included the chemical composition and bulk properties of crude oil and the salinity of the separated water phase. Residual emulsions were characterized using several techniques including Karl Fisher analysis for water content, as well as optical microscopy, DSC (Differential Scanning Calorimetry) and cryo-SEM to assess the size and polydispersity of the dispersed droplets. The objective of the study is to highlight the main physicochemical parameters responsible for the varying tightness of these emulsions, and provide insights to optimize their treatment costs and resolve emulsion issues in the GOSPs. The second part of this study still under progress will investigate the stability of residual emulsions in terms of chemical demulsification and interfacial properties.

Cost Effective Design of Scale Inhibitor Squeeze Treatments Using a Mathematical Model

Scale formation and deposition in production facilities is a challenging problem faced by the oil industry. Their deposition leads to operational problems, safety hazards, and an overall decrease in production efficiency. Downhole scale-inhibitor squeeze treatments provide the most common and effective means of preventing the formation of oilfield scale deposits. This paper presents an analysis and design study of field-inhibitor squeeze treatments. A mathematical model was used to simulate inhibitor-squeeze return data from several Saudi Aramco wells. A wide range of sensitivities in squeeze treatments were investigated, including inhibitor concentration, inhibitor volume, overflush size, and shut-in time. An optimization of the squeeze injection parameters was carried out with the numerical simulator. This optimization was based on squeeze performance as well as on economic criteria. The results indicate that the optimized treatment strategy is very well-specific and depends on the water production rates and operational parameters, like the scale-inhibitor concentration and volume and the amount of overflush. Recommendations are made for optimizing (in terms of cost effectiveness) the squeeze-treatment design.

Oil/Water Separation Experience From a Large Oil Field

The full-length paper discusses challenges related to emulsions in a large Saudi Arabian field. The field produces from several different reservoirs with a range of fluid properties. These properties provide an interesting case of operational challenges in oil/water separation including increased incidents of shorting in the separator and tripping of equipment and increased demulsifier consumption. The paper presents the results of a comprehensive study to understand the main causes of emulsion formation and ways to optimize oil/water separation.

Cost Effective Design of Corrosion Inhibitor Squeeze Treatments for Water Supply Wells

Water for pressure maintenance in oil producing reservoirs is often obtained from wells that are drilled in water aquifers. Aquifer brine is corrosive and leads to the corrosion of well tubing, manifolds and water injection system. Downhole squeeze treatments with corrosion inhibitors provide an effective means of controlling the corrosion problem in supply wells and injection system. Filming amine type corrosion inhibitors are squeezed into the aquifer and the chemical returned with the produced water provides the necessary protection. This paper presents an analysis and design study of corrosion inhibitor squeeze treatments for aquifer water supply wells. Laboratory and field data are presented for optimizing chemical usage and squeeze strategies. Corefloods conducted at reservoir conditions show that adsorption/desorption is the dominant mechanism of corrosion inhibitor retention and release from the formation. Squeeze treatments were simulated in the laboratory to determine the effect of important variables on squeeze life. These variables included the amount and concentration of inhibitor, volume of formation to contact, amount of overflush and the shut-in time. Laboratory testing and field trials have insured corrosion control at reduced operational costs. This has been attributed to the teamwork between laboratory personnel and operation engineers. Recommendations are made for optimizing future squeeze treatments.

Experimental Investigation of Emulsion Stability in GOSPs, Part II: Emulsion Behavior

This paper presents an experimental study performed jointly by IFP and Saudi Aramco to characterize the stability of emulsion samples collected from different Saudi Aramco Gas Oil Separation Plants (GOSPs). The first part of the study 1 (SPE 106128) focused on the analyses of separated phases. Many techniques (differential scanning calorimeter, Karl Fisher coulometer, rheology, optical microscopy, cryoscanning electron microscope) 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 investigated against several chemical demulsifiers by using classical bottle tests and an automated, vertical-scan, macroscopic analyzer (Turbiscan). This instrument is used to obtain kinetics of separation of concentrated and opaque dispersed systems such as emulsions, suspensions and foams. Interfacial tension 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 experiments 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 provides recommendations to optimize their treatment costs and resolve emulsion issues in the GOSPs.