Geochemical characterisation of Lower Maastrichtian Mamu Formation kerogens, Anambra Basin, Nigeria

Abstract

The source rock potential of kerogen isolated from shales, carbonaceous shales and sub-bituminous coals from the Lower Maastrichtian Mamu Formation in the Anambra Basin were determined using the total organic carbon (TOC) contents and Rock-Eval. analysis data. The TOC contents exhibit wide variations, ranging from 1.30 to 58.28 wt%. The hydrogen index (HI) and the genetic potential (GP) values ranged from 160 to 235 mg HC/g TOC and 32 to 133.11 mg HC/g rock, respectively. Plots from the Rock-Eval pyrolysis and elemental compositions classified the organic matter as mixture of Type II and III kerogens. The carbon isotopic values ranged from -28.12 to -26.49‰, supporting the mixed origin (Type II/III kerogen) although, the carbonaceous shale and coal samples are typically dominated by Type III kerogen. The Tmax values for the samples ranged from 417 to 422 °C . This study shows that the samples contain high quantity and good quality organic matter capable of generating oil and gas but are thermally immature within the intervals studied.

Mineralogical and pore structure of organic-rich deltaic shales and sub-bituminous coals from early Maastrichtian Mamu Formation, Anambra Basin, Nigeria

“…1) were collected from depths ranging from 7.65 to 50.5 m. The samples were taken from the Mamu Formation (Early Maastrichtian) in the Anambra Basin. The basic geochemical characteristics of the source rocks have been earlier described [17]. The TOC ranges from 1.30 to 7.37, 14.87 to 24.61 and 57.71 to 58.28% for shale, carbonaceous shale and sub-bituminous coal, respectively.…”

“…The Mamu Formation in the Anambra Basin contains organic matter with confirmed hydrocarbon generation potential [15][16][17]. The formation is composed of alternating shales, sandstones and coal seams [18].…”

“…The lower parts of the formation consist of several intervals of shale coexisting with coal, particularly in the middle section of the basin where its depth attains over 300 m [18], thereby positioning the formation as hot spot for possible unconventional shale gas generation. Studies on Mamu Formation have been limited to paleoenvironmental [16,[18][19][20][21] and hydrocarbons generative studies [15][16][17]22].…”

Hydrocarbon Generation Potential of the Campano-Maastrichtian Dark Mudstone Lithofacies, Benin Flank, South West Anambra Basin, Nigeria

“…At the core of this is the understanding of the basins' Cretaceous source rocks. The source rock properties of the mudstone (shale) and coal of Campano-Maastrichtian Mamu Formation, Anambra Basin have been evaluated mostly in the eastern segment using programmed pyrolysis (Akaegbobi et al, 2000;Ogala 2011;Akande et al, 2012;Olatinpo et al, 2016;Faboya et al, 2019), whereas only a few studies exist in the southwestern segment (Edegbai and Emofurieta, 2015;Ogbamikhumi et al, 2017 Maju-Oyovwikowhe andMalomi, 2019). Data from these findings have been used to characterize the Mamu Formation as having well to very good organic richness with thermally immature to early mature dominantly type III kerogen.…”

“…Data from these findings have been used to characterize the Mamu Formation as having well to very good organic richness with thermally immature to early mature dominantly type III kerogen. Interestingly, some of the data suggest the occurrence of marine and mixed marine kerogen (Olatinpo et al, 2016;Faboya et al, 2019), which is attractive to petroleum explorers. Hence, the need for kerogen / organic facies analysis to be undertaken on the dark mudstone.…”