The Sunday Mail
Golden Sibanda
INVICTUS ENERGY, the Australian company searching for oil and gas in the north of Zimbabwe, says preliminary analysis of data from the ongoing exploration drilling programme supports the presence of a viable petroleum system.
A working petroleum system encompasses a pod of active source rock and all genetically related oil and gas accumulations. It includes all the geologic elements and processes that are essential if an oil and gas accumulation is to exist.
Invictus is currently drilling its second exploration well at the Mukuyu-2 site in Mbire district, Mashonaland Central province. The firm said it was on course to complete the test well drilling, to a depth of 3 750 metres, within the targeted period of 50 days to 60 days.
Earlier exploration well drilling in September last year similarly produced encouraging results confirming the presence of a working hydrocarbons (petroleum) system in the firm’s prospective area — Zimbabwe’s Cabora Bassa Basin. However, technical challenges encountered during the drilling did not allow the company to recover a fluid sample as required by regulators in Australia, where the firm is listed, for the firm to declare commercial discovery.
Sample recovery is the process of taking a small portion of an object such that key stakeholders can be able to determine if the consistency of the portion will be truly representative of the entire property of the object under assessment.
Commercial discovery of oil and gas in Zimbabwe would usher in energy security for a country long plagued by crippling power shortages, create jobs and new industries, as well as drive export revenues, among other benefits.
Officiating at a function for the signing of an agreement on the development framework for the oil and gas project in March 2021, President Mnangagwa said potential benefits of the oil and gas discovery in Zimbabwe included electricity generation, as well as production of liquid petroleum, liquefied petroleum gas, fertiliser and petrochemicals.
Beyond driving investment in the sector, President Mnangagwa also said “the prospect of oil discovery is exciting”, as this was also expected to inevitably positively impact local communities and the national economy at large.
Invictus said the total background gas at Mukuyu-2 was higher than that observed at Mukuyu-1, while heavier hydrocarbons (petroleum features) have also been detected, providing further evidence of an active petroleum system in the basin.
Invictus’ Mukuyu conventional gas-condensate prospect is the largest undrilled prospect onshore Africa, with an independently estimated 20 trillion cubic feet + 845 million barrels (gross mean unrisked basis) of conventional gas-condensate in a stacked target.
“We have encouraging signs in our Upper Angwa (geological formation) primary target, which has shown elevated gas readings, including heavier hydrocarbons and elevated LWD (log while drilling) resistivity across the zones of interest,” Invictus said.
Resistivity logs are acquired by logging (measurement) tools, usually conveyed either by electric wireline or LWD equipment.
Resistivity can be interpreted as a measurement of a formation’s fluid saturation as it is a function of the (oil/gas) formation’s rock type, porosity, fluid type and fluid volume used to identify permeable areas, estimate the porosity of a formation and estimate fluid saturation.
“The presence of elevated mud gas readings combined with elevated LWD resistivity and increasing background gas with depth is a positive sign as we progress through the Upper Angwa Alternations Member,” Invictus said.
Gas readings are monitored by a complex system, which provides real-time continuous measurements of the concentration of formation gases from very light components such as methane to heavy components such as C6, C7 and C8 hydrocarbon species.
Scientifically tested evidence of formation gas is considered the first indication of a reservoir’s fluid characterisation and reflects the extent of the potential productivity of the well.
Resistivity can be interpreted as a measurement of a formation’s fluid saturation as it is a function of the formation’s rock type, porosity, fluid type and fluid volume. Consequently, resistivity is used to identify permeable areas, estimate the porosity of a formation and estimate fluid saturation.
“Following a drill bit change, we are preparing to drill a further 1 000 metres to our planned total depth of 3 750 metres through the remaining Upper Angwa and into the additional potential in the untested Lower Angwa.
“Once total depth is reached a comprehensive wireline logging programme to evaluate results will follow, with the aim of confirming the presence of moveable hydrocarbons in multiple zones.
“The well remains on track to be completed in the forecast 50 to 60 days.”
While drilling through a reservoir, a lot of valuable information can be obtained from mud logging to support formation evaluation. Field data will help well site geologists, petrophysicists and reservoir engineers to predict reservoir quality, fluid contacts and reservoir permeability based on formation gases detected while drilling.
