Abstract

Transportation and handling of the weathered crude oils in Kuwaiti oil lakes have long been of great interest. Various methods have been suggested to transport these highly viscous fluids via pipelines by heating or blending with light crudes or petroleum products to reduce their viscosities. The present paper proposes the emulsification of heavy crude oil in water as an alternative method.

This work investigates the rheological characteristics of the weathered crude oil and their emulsions. Crude oil samples collected from the major Kuwaiti oil lakes were tested. Emulsion preparation involved using either a nonionic surfactant or alkali, as well as both alkali and fatty acid to convert the high viscosity oils to low viscosity oil-in-water emulsions. Emulsion characterization was determined by measuring the droplet size distribution of the dispersed phase using optical microscopy. Emulsion stability was also examined in terms of the system breakdown. The rheological properties were measured using a concentric cylinder rotary rheometer. The emulsion rheological behavior has been studied as a function of composition, temperature, and shear rate. A rheological model was developed to characterize the pseudoplastic behavior of the crude oil and emulsion systems. The model fitted well the experimental results with a correlation coefficient higher than 95%. Associated with the pseudoplastic behavior, viscoelastic behavior has been observed with emulsions and some oils at high shear rates.

Results indicated that the examined crude oils can be transported through pipelines as emulsions of up to 80 vol.% oil concentration. The proposed method of treatment with NaOH and oleic acid offers several advantages over the surfactant treatment. This method exhibited comparable rheological behavior at lower cost and less mixing energy. It also provided higher emulsion stability, which favors oil transportation for longer distances.

Introduction

One of the major consequences of the Gulf war in 1991 was the spillage of huge quantities of crude oil which accumulated in the lower ground forming oil lakes. More than 300 oil lakes covered an area of about 50 km2 of the state of Kuwait. Although some 21 million barrels of relatively light oils have been recovered from these oil lakes, large quantities are still remaining in the form of weathered crude oils (WCO) including heavy oils, emulsions or mousses and sludges. According to the latest survey in June 1994, over 22.5 million barrels of crude oil are accumulating in the oil lakes. This oil was subjected, for more than 5 years, to severe weathering conditions and evaporation of the volatile components leaving low gravity oils as low as 5 API. Emulsions were formed from the oil and water used during fire extinguishing operations and rainfall. The presence of some materials such as asphaltenes waxes, and fine solids assisted the stabilization of emulsions. Existence of these types of fluids threatens the environment in Kuwait and presents a source of income that can be exploited through treatment. Transportation of the weathered crude oils, with viscosity more than 100,000 cp [mPa.s], through pipelines presents a major field problem. Various methods have been proposed for reducing oil viscosity or conditioning such oils for pipeline transportation and processing. These methods include:

  1. reduction of viscosity by heating,

  2. blending with lighter crude oils or petroleum products,

  3. lubrication by introducing a water layer between the crude oil and pipeline material, and

  4. oil-in-water emulsification.

Selection of an appropriate method depends basically on the particular oil lake location and size, oil physical properties, flow rate, pipeline length and size, etc.

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