Physical And Chemical Characterization Of Saudi Arabian Crude Oil Emulsions

Abstract

As watercuts increase, tight emulsions formed in the produced fluids from some wells in Saudi Arabian oilfields are causing problems at an increasing number of wet crude handling facilities. The processing of these fluids impacts operations in three major areas:–Inability to produce some wells, particularly during cooler weather.–Plant upsets due to grid trips and accumulation of sludge in vessels.–Increased chemical demulsifier demands. The overall effect is an increase in treatment costs and loss of revenue. In January 1995 a multi-disciplined emulsion study team was formed. As part of this study the Laboratory implemented the following stepwise investigation strategy:Develop an Index to compare emulsions for tightness.Perform tests for the physical and chemical characterization of the emulsions.Develop a model to correlate emulsion tightness with analytical data.Based on the above findings make recommendations for improved emulsion treatment. The paper discusses the development of an Emulsion Separation Index (ESI) through investigation of the effect of mechanical chokes on emulsion stability. Details of other tests - including droplet size, viscosity, TGA, organic and inorganic solids content, composition and particle size distribution are reported and related to emulsion stability. The emulsion formation mechanism developed from the above data is described. A model of organic and inorganic solids precipitation caused by shear and pressure drops during production is developed with reference to the literature. The paper concludes by using the model to make recommendations for solutions to the problems and for field trials and further laboratory work. Introduction Crude Production. Saudi Aramco is responsible for maintaining oil production throughout Saudi Arabia. Oil produced varies from Arab Heavy (API 27) through to Arab Super Light (API 51). This paper deals with emulsions encountered during the production of Arab Light (AL - API 31–33) The wet crude is processed through Wet Crude Handling Facilities (WCHF's) where demulsifier chemicals are added at the Production Header. The Company produces AL through around 20 WCHF's of up to 330MBD capacity. Since there are no fired heaters, problems with tight emulsions are typically encountered during the cooler months when demulsifier requirements increase from <5ppm in Summer to 10–20ppm in Winter. Compared to many parts of the world, peak demulsifier demands of 20ppm may seem to be a minor inconvenience. However, in view of the millions of barrels of AL produced, the potential for savings by reducing chemical use is considerable. Impact of Emulsion Problems. As the oilfields mature and watercuts become higher, oil/water emulsions are causing operational problems at an increasing number of (WCHFs). Processing of tight emulsions impacts operations in the following areas:–Inability to produce some wells, particularly in cooler weather. This results not only in loss of revenue, but also has a negative impact on long term Reservoir Management. - Upsets in WCHFs due to grid trips in vessels.–Accumulation of sludge in vessels, increasing downtime and decreasing residence times.–Increased demulsifier usage (and hence chemical costs) by a factor of five to ten times. The overall effect is a significant increase in treatment costs and loss of revenue. P. 675^

Properties of Crude Oil-in-Water and Water-in-Crude Oil Emulsions: A Critical Review

“…Asphaltenes and resins form a surface that adsorbs wax and other solids around the water droplets, as shown in Figure , allowing emulsion stability. In this schematic representation, the stabilizing effect of asphaltene, resins, and other solids was depicted portraying how these elements can bind together around water droplets to ensure emulsion stability.…”

“…46 Asphaltenes are also significant highly polar hydrocarbon components made up of condensed aromatic rings and naphthenic rings, which also contain heteroatom groups. 38 Asphaltenes and resins form a surface that adsorbs wax and other solids around the water droplets, 47 as shown in Figure 5, allowing emulsion stability. In this schematic representation, the stabilizing effect of asphaltene, resins, and other solids was depicted portraying how these elements can bind together around water droplets to ensure emulsion stability.…”

Emulsion Separation Index: From Laboratory to Field Case Studies

“…Qualitative data suggests that the amounts were higher in the untreated wells than in the treated wells. Solids have been linked to emulsion problems in another field in Saudi Arabia [3][4] .…”

“…This paper presents a method developed at Saudi Aramco for measuring the stability of an emulsion quantitatively 1,3,4 . It is referred to as the emulsion separation index, or ESI, to measure the tightness of an emulsion.…”

Snap‐off of a liquid drop immersed in another liquid flowing through a constricted capillary

“…Emulsion formation in oil production may take place inside the reservoir, in the two‐phase flow in production wells and in the flow through pipes and valves. According to Davies, Nilsen, and Gramme,8 and Sarbar and Wingrove,9 emulsions formed spontaneously in oil production may be stabilized by some components of the oil, typically heavy oil fractions, and suspended solids. Most crude oil in the World is in fact produced as water‐in‐oil (more commonly) or oil‐in‐water (generally at high watercut) emulsions.…”