Kerogen analyses of sediments in the Lamu embayment Kenya

Abstract

Results of numerous wells drilled by BP-Shell Petroleum Development Company of Kenya between 1963 and 1971 within the Lamu Embayment, as confidential Geological Completion Reports indicate, gave hydrocarbon gas shows in Walu, Dodori and Pate wells. To investigate possible origin of these gases, the kerogen quality, quantity and maturation in these wells' samples were systematically evaluated. The study has shown that the percentage kerogen within the Lamu Embayment sediment is more than the minimum required to yield commercial accumulations on maturation. The results indicate that the quantity of kerogen within these sediments varies with age and the type of lithology. Calcareous mudstones and shales of lower Cretaceous together with bituminous mudstones and lignite interbeds within sandstones of upper Eocene constitute the organic ric6 sediments. The study also revealed the presence of two types of kerogen; the amorphous and the humic types which are the 011 and gas generating types, re~pectively. Kerogen colour and the percentage of fixed carbon ratio both show that some kerogenous matter within source sediments in the study area is mature. No attempt was made to establish whether hydrocarbons have migrated-from these source rocks. However,maturation boundaries have been located in the middle Eocene for Dodori and Pate wells at depth qreater than 2000 m , Further inland, at Walu, mature kerogen was noted within the cretaceous sediments from depths slightly more than 1500 m. With enouqh mature percentaqe keroqen within the Lamu Embayment, results of this work give a new dimension as regards the petroleum potentiality of the area.