The Chiweta geothermal project is located in the Rumphi district (Northern Region of Malawi), 370 km north of Lilongwe. The site falls in the northern portion of the Malawi rift and is underlain by biotitic gneisses of the Basement Complex, covered by clastic sediments of the Karoo System and by a thin level of Quaternary deposits. The geoscientific investigations performed over the prospect, inclusive of geological, geochemical, gravimetric and geoelectrical surveys and allowed to elaborate the conceptual model of the field.
A volumetric estimate of the electric potential of the system indicates a likely value of 13.5 MW and a highly probable value of 10.5 MW, which was taken as a reference for selecting the capacity of the power plant. The initial step towards this goal consists of the implementation of a program of exploratory drilling, aimed at proving the existence of a geothermal system of commercial interest and at defining its thermodynamic, hydraulic and chemical features. For this purpose, it is proposed to drill three slim holes with final diameter of the slotted liner of 41/2” up to a vertical depth of 900 to 1,000 m (CW-01, CW-02 and CW-03). Two of these holes are easily accessible from highway M1, whereas the third is situated some 1.2 km to the west at elevation of 650 m a.s.l.
At completion of this exploratory stage, in case of favourable results, it will be possible to proceed with the development of the resources subject to the procurement of adequate financing. This development shall consist of four components, namely:
Drilling: In accordance with the required thermal input for the operation of the 10 MW power plant, it is foreseen to drill 9 production wells with final diameter of the slotted liner of 7” and vertical depth of 1,000 m. Wells will be located in three distinct pads (Pads A, B and C), out of which two are due to coincide with the pads utilized for drilling the slim holes of the previous stage. Four reinjection wells, all to be drilled from the same pad situated just beyond the southern limit of the probable zone (Pad D), are deemed to be necessary to dispose of the brine from the power plant.
A period of approximately 5.5 years is needed for completion of the above described program, out of which the first 2.5 years would be dedicated to the exploratory activities and the following 3 years to the development stage. Electric generation can accordingly start at the beginning of the year 2024. Costs for the implementation of the program have been estimated grouped into two major components, that is capital expenditures (CAPEX) and operation and maintenance (OPEX), as shown here after. CAPEX amounts to 76.2 MUSD, that is to 7,600 USD/kW.