Leaves in turbidite sands:The main source of oil and gas in the deep-water Kutei Basin,Indonesia

摘要

More than 6 tcf of gas and 200 million bbl of oil and condensate have been discovered in upper Miocene sandstones in the* deep-water Kutei Basin,offshore East Kalimantan,Indonesia.Chemical analyses of oil,gas,and condensate indicate derivation from land-plant source material.Conventional cores and cuttings of deep-water strata show that the best source rocks are sandstones,not shales.Organic material in deep-water sandstones includes lami-nar coaly fragments,pieces of wood,resinite,and other coaly de-bris.Laminar coaly fragments are dominant,and their size,shape,and cuticle structure indicate that they were leaf fragments.Fossil leaf fragments occur in all deep-water sandstone packages from the upper slope to the basin floor.Fossil leaf fragments were ap-parently carried into deep water by turbidity currents during low-stands of sea level.Within turbidite sandstones,fossil leaf fragments are concentrated in layers with up to 50 wt.% total organic carbon (TOC).Kerogen that was separated from these layers has hydrogen index values of 200-500 mg hydrocarbon/gTOC.Kutei Basin deep-water shales contain mainly silt-size vitrinite grains with poor genera-tive qualities.Microscale sealed vessel pyrolysis and kinetic and generation modeling indicate that land-plant kerogens occurring in quantities similar to the upper Miocene sandstones are capable of generating the gas and oil found in deep-water fields.Hence,leaf fragments in turbidite sandstones are interpreted as the main source for deep-water oil and gas.Liquids derived from leaves have caused production problems that include high pour points because of high wax contents and emulsions formed when fatty acids combined with water.