Geochemistry of Petroleum Gases and Liquids from the Inhassoro, Pande and Temane Fields Onshore Mozambique

Markus Loegering,Alexei Milkov

doi:10.3390/geosciences7020033

Abstract

Although the first petroleum fields in the Mozambique basin were discovered more than 60 years ago, the composition and origin of petroleum fluids in this basin are largely unknown. We studied the geochemical composition of petroleum gases and liquids from the Inhassoro, Pande and Temane fields located onshore Mozambique. The gases are relatively dry (methane-dominated, average C1/(C1–C5) ratio is ~0.96), have pure thermogenic origin, originate predominantly from marine shale source organofacies and show no evidence of primary microbial gas or biodegradation. Most condensates have relatively high API gravity up to 76 degrees, are very mature and contain only traces of biomarkers, likely from migration contamination. However, biomarkers in the light oil from the Inhassoro field indicate that the oil derived from sub-oxic marine shales of the Late Cretaceous age. We suggest that the Aptian-Coniacian Domo Shale is the likely source rock for petroleum gases and liquids in the studied fields. Our geochemical data, including gas isotopes, as well as source-specific and age-specific biomarkers, exclude coals in the Late Carboniferous—Early Jurassic Karoo Supergroup as effective source rocks for the studied fields.

Highlights

We suggest that the Aptian-Coniacian Domo Shale is the likely source rock for petroleum gases and liquids in the studied fields
The Mozambique basin encompasses over 300,000 km2 onshore and offshore Mozambique and is the largest sub-equatorial sedimentary basin in Africa [1,2]
The geochemical data presented above suggests that petroleum gases and liquids in the Inhassoro, Pande and Temane fields have a thermogenic origin (Figures 2, 3 and 6)

Summary

Introduction

The Mozambique basin encompasses over 300,000 km onshore and offshore Mozambique and is the largest sub-equatorial sedimentary basin in Africa [1,2]. The Mozambique basin was formed in the oceanic void created by the rifting of the African and Antarctic plates during the Gondwana break-up in the Late Jurassic period [3]. The upper part of the sedimentary fill is divided into the Cretaceous “Limpopo” and the Tertiary “Zambezi” deltaic super-cycles [5]. Petroleum exploration in the Mozambique basin started in 1904 [6], and 85 onshore exploration wells have been drilled to date. These wells penetrated the Tertiary and Cretaceous section and resulted in the discovery of four fields (Pande, Temane, Inhassoro and Buzi). Exploration success is relatively low, as only 10% of exploration wells resulted in petroleum discoveries. There are several onshore oil and gas seeps reported in the basin [6,7]

Methods

Discussion

Conclusion