Prospectivity Analysis and Resource Assessment of the Unlicensed Angoche Basin

Barlass, D.; Zibane, M.; Samuel, Cherian; Langa, H.; Tembe, C.

doi:10.3997/2214-4609.201702396

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“…In the Rovuma and Angoche basins (south of Rovuma) a Jurassic source rock has been suggested, with Upper Jurassic to Cretaceous reservoirs of submarine turbidity fan and channel affinity. This is comparable to what has been described from other offshore Mozambique sites farther south, and in Tanzania and Kenya in the north (Mahanjane et al 2014;Barlass et al 2017;Davison & Steel 2018, see Fig. 1).…”

Section: Accepted Manuscriptsupporting

confidence: 90%

Petroleum geochemical aspects of the Mandawa Basin, coastal Tanzania: the origin of migrated oil occurring today as partly biodegraded bitumen

Abay

Fossum

Karlsen

et al. 2019

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The shallow-marine Upper Jurassic–Lower Cretaceous sedimentary successions of the Mandawa Basin, coastal Tanzania, are located about 80 km away from the offshore gas discoveries of Block 2, Tanzania. In this paper we present petroleum geochemical data, including bitumen extracted from outcrop samples which are relevant to the understanding of the onshore ‘Petroleum System’ and possibly also to the offshore basin. Despite some biodegradation and weathering, common to all outcrop samples, most bitumen samples analysed contain mature migrated oil. The maturity span of geomarkers (C13–C15 range) covers the entire oil and condensate/wet gas window (Rc = 0.7–2% Rc, where Rc is the calculated vitrinite reflectance), with the biomarkers generally indicating the oil window (Rc = 0.7–1.3% Rc). This suggests that the bitumen extracts represent several phases of migrated oil and condensate, which shows that the samples are part of an active or recently active migration regime or ‘Petroleum System’. The source-rock facies inferred for the bitumen is Type II/III kerogen of siliciclastic to carbonate facies. This is oil-prone kerogen, typical for a marine depositional system with an influx of proximal-derived terrigenous material blended in with in situ marine algal organic matter (OM). Application of age-specific biomarkers such as the C28/C29-steranes, extended tricyclic terpane ratio (ETR), nordiacholestanes and the aromatic steroids suggest that more than one source rock have contributed to the bitumen. Possible ages are limited to the Mesozoic (i.e. excluding the Late Paleozoic), with the most likely source rock belonging to the Early Jurassic. More geochemical and geological studies should be undertaken to further develop the general understanding of the petroleum system of the Mandawa Basin and its implications to the ‘Petroleum Systems’ both offshore and onshore. This paper also presents a reinterpretation of published gas composition and isotope data on the Pande, Temane and Inhassoro gas fields (Mozambique) with implications for possible oil discoveries in the gas-dominated region.

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Section: Accepted Manuscriptsupporting

confidence: 90%