GEOCHEMICAL CHARACTERIZATION OF OIL SEEPS FROM UPPER INDUS BASIN, PAKISTAN

Abstract

This research was carried out to delineate the geochemistry of selected samples of the oil seeps. Research is aimed to investigate the source input, thermal maturity, age, lithology and depositional environment of the source rock of these seeps, and to evaluate the extent of biodegradation of the seeps. Samples from four oil seeps from Upper Indus Basin were collected for the geochemical characterization. These four seepages were Jaba Seep, Golra Seep, Kundal Seep and Panoba Seep. Kundal Oil Seep occurs at the contact of Khatriara Sandstone with Siwalik Group. Seepages of Jaba occur in the upper 250 feet area of Sakesar Limestone. Golra Oil Seep lies along the northern boundary of Sakesar Limestone. The detailed geochemical analyses were carried out in the laboratories of Hydrocarbon Development Institutes of Pakistan, Islamabad. The samples were first de-asphalted followed by column chromatography for the separation of samples into saturated hydrocarbons, aromatic hydrocarbons and polar compounds. Gas chromatography flame ionized detector (GC-FID) was used to confirm the separation of mixture of organic compounds, in GC-FID hydrocarbons are separated into individual components on the base of their molecular size. For detailed analysis of saturated hydrocarbons and aromatics hydrocarbons gas chromatography mass spectrometry (GC-MS) was used which is one of the modern and sophisticated analytical techniques. Results show clear sign of biodegradation in almost all the studied samples. Marginal -highly maturity is noted for source rock of seeps being produced in different regions of Potwar. In Jaba Seep presence of Oleanane confirms Late Jurassic-Early Cretaceous age of source rock. Results show variation in depositional environment and source input. Kundal has anoxic depositional environment and carbonate lithology of the source rock. The source of Panoba was deposited in more of oxic environment that has received high deltaic input so high terrestrial input. The source rock of Jaba and Golra seeps appear to have moderate sub-oxic environment and shale lithology of the source rock.