Physicochemical Analysis and Biomarker Distributions in Waxy Crude Oils from the Lower Indus Basin, Pakistan

Abstract

Lower Indus Basin, Sindh Province Pakistan, produces many small to medium petroleum reservoirs. The petroleum hydrocarbons mainly contain two types of oils, condensates (light crude oils) and waxy crude oils (higher wax contents). Condensates are highly thermal mature form of crude oils and do not contain enough molecular information for determination of biological origin. In this study only high wax contents containing crude oils were used for physicochemical analysis and biomarker were analyzed in wax fraction of crude oils. Physicochemical properties such as specific gravity, American Petroleum Institute (API) gravity, sulfur contents and pour points were analyzed from set of four crude oils. Asphaltenes were removed from crude oils and wax fraction was separated from maltenes fraction. The wax fractions were analyzed by high temperature gas chromatography-flame ionization detector (HT-GC- FID). High molecular weight hydrocarbons have been reported in these wax samples up to C₆₀ n-alkanes. A cross plot of API gravity vs %wax content shows a decrease in API gravity with increase in wax content. Biomarkers distribution indicates clearly a significant contribution of terrestrial organic matter in sediments producing these oils.