Malawi’s Geological Survey Department (GSD) says investigations continue to unveil increased potential for the discovery of hydrocarbons in Lake Malawi and the lower Shire valley.
GSD director Leonard Kalindekafe says: “Our geological investigations have unearthed . . . considerable potential for the discovery of hydrocarbons, so there is need for us to team up with international investors or institutions to do detailed oil and gas exploration at these sites.”
In addition to the encouraging data collected by the department, various research and oil exploration companies have also confirmed the existence of sedimentary rock on the lake bed that could be hydrocarbon bearing.
Kalindekafe says detailed seismic studies and, eventually, the sinking of an exploratory drill hole would be required to determine the presence of hydrocarbons under Lake Malawi.
“Siting the exploratory well offshore would be the most cost-effective way of acquiring this missing information. “Of course, the use of other techniques, such as satellite data and microbial anomalies in surface soil samples [will also be employed].”
Kalindekafe explains that the geology of the lake bed has mainly been revealed by seismic reflection data and core and grab samples that were collected by different entities.
For instance, in 1981, a scientific expedition from Duke University, in North Carolina, US, carried out a seismic survey in Lake Malawi with the aim of finding a site to obtain a core of mud from the lakebed from which to decipher climatic changes in Southern Africa.
“As a by-product of this work, it was demon-strated that very thick sedimentary rock sequences exist in some parts of the lakebed, and that structures necessary to trap oil are present in these rocks,” says Kalindekafe.
He also says other work carried out demon-strated that very thick sedimentary rock sequences and structures that trap oil are present in parts of the lakebed.
Kalindekafe explains that the results indi- cated that there are three places in the northern part of the lake which have sedimentary sequences over 2 000 m in thickness; thick-nesses of over 1 600 m were identified in the lower Shire valley.
In 1981, the Cenozoic Environments and Geodynamics of African Lakes project revealed two sedimentary units underlying the lake, which were named the Lake Nyasa and Lake Malawi groups. The Lake Nyasa Group has thicknesses of up to 600 m and there are indications that it may contain shale and mudstone. The Lake Malawi Group rests ‘uncom-formably’ on the Lake Nyasa Group and consists of richly diatomaceous clay and organic debris with hard ground bands.
The seismic reflection data collected during Project PROBE, from 1985 to 1987, revealed four sedimentary sequences in the lake strati- graphy rather than two sequences. The sequences are generally thin towards the south, with local discontinuities in the lower sequences.
Kalindekafe says: “An interesting feature of the sediments is their proximity to the Karoo sediments in the north of the lake, which might mean that they could be reservoirs for hydrocarbons emigrating from Karoo coals.
“The available information raises the potential of Lake Malawi as a target for hydrocarbon exploration. Further geophysical work and the sinking of a stratigraphic well to establish the nature of the rocks, the thick- ness of the sedimentary sequence and the occurrence of hydrocarbons are highly recom-mended.”
The Malawi government has awarded an exploration licence to British firm Surestream Petroleum to carry out oil prospecting activities in one of the potential areas in Lake Malawi but has yet to award licences for the other potential areas in the lake and in the Shire valley.