Water washing: a major hydrocarbon alteration process. Part 1—geochemistry

Abstract

This paper presents the geochemistry portion of a larger study attempting to better predict hydrocarbon type prior to drilling. The geochemistry indicates that condensate-gas or gas-oil ratios have a predictable relationship with gasoline-range hydrocarbon solubility. The study shows that soluble gasoline-range aromatic compounds such as toluene are significantly depleted in oils compared with gases, whereas more insoluble compounds such as methylcyclohexane are enriched.

The review indicates that water-washing in the reservoir is a major alteration process affecting hydrocarbon type and, in extreme cases, can convert a major gas accumulation into a smaller oil accumulation. Source type and maturity have a relationship with the volume of liquids produced, but are not the primary control on the hydrocarbon phase in the reservoir.

The water-washing process will also affect carbon dioxide geosequestration projects, particularly where injection into abandoned low GOR oilfields is proposed.