Thermal Maturity Evaluation of Albian Shales from Offshore Benin Basin (Benin - West Africa)

Abstract

The hydrocarbon maturity level of Albian shales intervals from four (04) wells drilled in the Offshore Benin Basin was assessed. The unnamed “Albian Formation” consists of marine sandstones and shales with some organic-rich black shales and minor limestone. The shale contains increase seaward and reaches 300m in deep water. For maturity assessment, traditional parameters such as Spore Coloration Index (SCI), Vitrinite Reflectance (Ro) and Rock-Eval pyrolysis Tmax data were appreciated. The kerogen identified in studied samples is of both types II/III and III. Spore Coloration Index (SCI) data range from 7.0 to 8.5 while Vitrinite Reflectance (Ro) data are comprise between 0.69 and 1.10. The Rock-Eval pyrolysis Tmax data show values in the range 434°C to 465°C. Obtained maturity data suggest that Albian shales are partially at the peak of oil generation zone (optimal mature) and partially within the lower part of the oil window (late mature). Moreover, the deepest shale interval (sequence 1) of R23, G20 and G21 wells have reached the upper part of the gas window. Similar maturity results were obtained after modeling burial history of the basin using Petrel software. To broaden the available thermal maturity information of Albian shales and attempt an oil-source rocks correlation, data from more wells and analyzes via GC-MS for a biomarker approach are require.