Purpose

The trial was to demonstrate cost effective separation and recovery of weathered crude oil from sand that was heavily contaminated with oil spills eighteen years ago. It successfully used small quantities (1% to 2% by weight of material to be treated) of surfactant blends with cold salt water to achieve separation of the crude oil from the sand.

Overview

A number of tests were carried out to determine the most effective combination of chemicals/surfactants and minimum effective concentrations to achieve the best result.

The starting point to recover the crude oil from the sand was a surfactant system to wash oil well drill cuttings heavily contaminated with crude oil hydrocarbons. This uses suitably designed mechanical washing plant which utilises cavitation scrubbing and a solution of a formulated surfactant system in fresh or salt water to release the hydrocarbon oils from drill cuttings. The hydrocarbons separate from the drill cuttings into the wash solution without a stable emulsion being formed and coalesce into drops, which float to the surface enabling the hydrocarbons to be recovered in an oil/water separator.

A method to separate the weathered crude oil from the sand ex Kuwait was developed, which uses two surfactant formulations with differing properties that interact during washing to rapidly release the crude oil from the sand grains. The two surfactant formulations are:

• Viscosity Modifier DC881A is a formulation which rapidly penetrates and substantially reduces viscosities of heavy/weathered crude oil hydrocarbons. This formulation is mixed into the weathered crude oil/sand mixture at a rate of between 1% and 2% by weight causing it to effectively liquefy.
• Hydrocarbon Release Agent DC881B is a salt water-soluble surfactant formulation. This is mixed with sea water to make up a process solution that contains 0.25% and 0.5% of the formulation by weight. The process solution is used to wash and separate the crude oil after it has been mixed with Viscosity Modifier DC881A. During washing, surfactants in DC881B interact across oil-water boundaries with surfactants in DC881A dissolved in crude oil facilitating its removal from the sand into the process solution, without forming a stable emulsion. The released crude oil rapidly coalesces and floats to the surface of the process solution, where it collects and may be recovered.

Demonstration

The following section describes the method used to wash the crude oil out from the sand and the results obtained.

Approximately 300g of the weathered crude oil contaminated sand ex Kuwait containing approximately 20% of crude oil by weight, was available for the development and tests.

Method

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Conclusion

The weathered crude oil from the sample (ex Kuwait) was successfully recovered using a small amount of formulated surfactants (1% to 2% by weight of weathered crude oil/sand to be treated) with cold, salt water.