摘要
The hydrocarbon generation potential of the Campano-Maastrichtian to Paleogene shales from the Benin Flank(located in SW Nigeria)of the Anambra Basin,has been previously investigated mostly by studying outcrops and by relatively few subsurface data-based studies.Thus,it is expedient undertaking an assessment of the hydrocarbon generation potential of this frontier area from subsurface samples.Campano-Maastrichtian to Paleogene shale samples obtained from Egoli-1 borehole in the Benin Flank of the Anambra Basin are studied by means of HAWK programmed pyrolysis,organic petrography,and mineralogy(XRD),with the aim to explore the petroleum-generating potential and the thermal maturity.The obtained results display a significant variation of the TOC content ranging from very low(<0.5%)to significant(>5%),indicating poor to excellent oil potential based on S_(2)values under the condition,of course,the studied formations reached the oil window.The shales of the Nsukka and Imo Formations display lower petroleum-generating potential than these of the Mamu Formation.All the studied samples are dominated by gas-prone(type III)and inert(type IV)kerogens,with few displaying mixed II/III(oil-and gas-prone).The organic-petrography observations support partly the results of the HAWK programmed pyrolysis,as they reveal an organic-richer Mamu Formation in comparison to the Nsukka and Imo Formations;huminite/vitrinite particles(both indigenous and recycled)along with variable contents of liptinite(mostly alginite and bituminite)and inertinite macerals(mostly inertodetrinite)are hosted in the shales.The latter display a typical composition for fine-grained clastic sediments;mostly kaolinite,illite/montmorillonite,quartz,and subordinately,anatase.In terms of thermal maturity,huminite/vitrinite reflectance data points to immature stage;however,the occurrence of solid bitumens,displaying equivalent vitrinite reflectance values within the oil window,points to an active petroleum system in sequences deeper than the examined ones.
