When Can a Stock-Tank Oil be a Condensate?

Abstract Database plots of the distribution of C7+ to C40+ fractions, as well as plus fraction density and molecular weight, show that there is a clear statistical difference - with minor overlap - between stabilized hydrocarbon liquids from reservoir gas (condensate) and reservoir oil. In most cases, the origin of a stock-tank oil sample can be interpreted on basis of composition, density, molecular weight and reservoir pressure. Typically, hydrocarbon liquid with density higher than 0.85 g/cm3 and C7+ molecular weight > 250 g/mol origins from reservoir oil, while hydrocarbon liquid with density lower than 0.8 g/cm3 and C7+ molecular weight < 170 g/mol origins from reservoir gas. A main purpose of the present paper is to identify cases where composition, molecular weight and density show that a hydrocarbon liquid sample cannot origin from a reservoir gas at a given reservoir pressure. In addition to statistics from a large PVT database, a PVT simulation procedure is proposed, giving additional proof for such cases.