A drilling mud additive influencing geochemical hydrocarbon interpretation in the northern North Sea ///

Oil-based mud additives are used frequently during drilling for various purposes. The chemical compositions of additives may overprint or interfere with the chemical composition of hydrocarbon shows in the well and, therefore, complicate geochemical interpretations. This is likely to be an increasing problem as discovering hydrocarbons becomes more difficult and subtle. Geochemists must compile a list of all additives used during drilling and also must obtain a sample of the pre-drill oil-based mud additives used during each project. Then, confirming the influence or possible contamination of additives on the discovered hydrocarbon is possible using detailed geochemical analyses performed post-drilling. In this article, a frequently used, oil-based mud additive is shown to have overprinted the hopane signature of an oil-slick sample in Well 35/1-1 in the northern North Sea. However, the sterane biomarkers used for facies interpretation are shown to be unaffected by the mud additive, and an accurate age and facies determination was formed from the steranes.

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