«Geology, geophysics and development of oil and gas fields»

Mozambique and Tanzania – new gas bearing countries at the western continental margins of the Indian Ocean

UDC: 553.98(679+678)
DOI: -

Authors:

¹ Institute of Oceanology named after P.P. Shirshov Russian Academy of Sciences, Moscow, Russia

Keywords: oil, gas, hydrocarbons, continental margin, basin, sub-basin, gas content, oil content

Annotation:

Sedimentary basins and subbasins extended along the whole continental margin of the East Africa from Mozambique till Somali are actively exploited for prospecting hydrocarbons. Hydrocarbons have been prospected here for more than 70 years with some intervals, however the researches haven’t brought desirable results. Large scale research–exploration works for oil and gas began in 2010 when large gas fields were discovered in the deep water areas of the north-eastern part of Mozambique such as Lagosta, Mamba-North, Mamba-South, Mamba-North-East and others and in 2008 at the south-east of Tanzania also in the offshore limits large gas fields such as Songo Songo, Mnazi Bay, Kilivani North-1 and other ones were discovered. Today summary reserves of gas in Mozambique and Tanzania are estimated up to 10…15 trillion m3, three fourths of which are concentrated in Mozambique and one fourth – in Tanzania. These reserves are mainly concentrated in Rovuma basin, which is a part of widened eastern African frontier basin, including the north-eastern part of Mozambique as well as parts of inshore plains and continental margins of the south-eastern Tanzania and Kenya. The largest basins at the continental margin of these countries are the following ones: Mozambiquian, Rovuma and Tanzanian. Within the limits of Mozambique basin the following sub-basins: Angoch in the north and Delta Zambezi in the central part are revealed. In Tanzanian basin in the direction from the north to the south there exist the following sub-basins: Tanga, Pemba Zanzibar, Latam, Rufiji, Mafia and Mandava. The sedimentary cover of the basins is very similar and is presented by Phanerozoic deposits of 7…10 km thickness. This thickness is lying on the Precambrian fundament. The structure of the basins is complicated and relatively similar, that is caused by some stages of rifting with different directions of tension. There exist three stages of these sedimentary basins evolution at the continental margin of this region: the first stage is pre-rifting development, the second stage is rifting and third stage is post-rifting. The analysis of more of 50 gas fields on the continental margin of Mozambique and Tanzania reveals the following fact: nearly all gas fields are located in the deep-water regions of the Indian Ocean that is on the continental slope, mainly in the Rovuma basin. The depths of their location are different. It should be noted, that the deeper the similar age deposits are buried under the mass of water the bigger are the hydrocarbons reserves. While moving in the northern direction, in Tanzania the amount and the reserves of the discovered gas fields decrease while at the north of the country there is no gas accumulations at all, but there is evidence of oil accumulation.

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