Petroleum Geochemistry of the Varicolored Shale of the Nubian Formation in Wells R8-82, R9-82, and R10-82, Sirte Basin, North Central Libya

Abstract

A mineralogical and geochemical evaluation of the Varicolored Shale of the Nubian Formation (Early Cretaceous) was carried out in wells R8-82, R9-82, and R10-82, Sirte Basin, north central Libya. Regarding mineral composition, the studied shale in well R8-82 mainly consists of clay minerals with smaller amounts of quartz, carbonates (calcite and dolomite), and potassium feldspar. The shale is classified into three lithofacies: (1) Argillaceous shale (CM); (2) Silica rich-argillaceous shale (CM-1); and (3) Mixed argillaceous shale (CM-2). Regarding source rock evaluation, there are four categories of organic richness in the shale: poor, fair, good, and very good. The shale is dominated by hydrogen-poor kerogens (II–III, III, and IV). The degree of thermal maturity varies from immature to late mature. The shale mainly contains indigenous hydrocarbons with lesser amount of nonindigenous hydrocarbons. The shale is principally a source of oil. The shale is deemed inappropriate for the extraction of shale oil. Regarding shale oil evaluation, mature oil predominates in the shale. There are two oil families; the first family is derived from carbonate or evaporite, while the shale or clay-rich rock is the source of the second family. The majority of these families are marine in origin.