Effects of Biodegradation from the Producibility of Waxy Crude Oils

Michael Hsieh and Barry J. Katz
Chevron, Houston, TX

Biodegradation is perceived as a negative alteration process impacting physical and chemical properties of oils. Biological alteration of crude oils commonly results in decreased API gravities, increased viscosities, enrichment of asphaltenes and resins, increased sulfur content, the production of organic acids, resource reduction, higher production costs, and lower retail value. Thus, the potential for biodegradation and its impact on crude oil properties is a major concern for the exploration and exploitation of crude oil reserves. While studies on the effects of biodegradation often focus on the negative impacts, there are cases where biodegradation appears desirable. In cases where crude oils are high-wax, biodegradation has been demonstrated to improve their producibility by the removal of waxes, which reduces viscosity.

Crude oils from such areas as the South China Sea are characteristically waxy. Waxy crude oils may present a production challenge in deeper waters where temperatures are lower. An examination of oils from the Pearl River Mouth basin provides an example where biodegradation may be beneficial. In those cases where biodegradation has proceeded only sufficiently to remove low-molecular weight n-paraffins and long-chain waxes remain a very viscous oil is present. However, where biodegradation removed both low- and high-molecular weight n-paraffins, viscosity was significantly reduced due to the removal of the waxy components. While biodegradation can improve the producibility of some waxy oils, this improvement is not universal. In Central Sumatra, for example, the biodegradation of an originally waxy oil where both low- and high-molecular weight n-paraffins were removed was significantly more viscous than an oil where biodegradation did not remove the long-chain waxes. The cause for these different behaviors has not yet been established.

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