Australian minnow, Invictus Energy, has moved from citing "encouraging signs of hydrocarbon", in its drilling campaign in Zimbabwe, to formally declaring a hydrocarbon discovery.

The company is on the sidetrack to the Mukuyu-2 well, (Mikuyu-2STK), its fourth hole on the Mukuyu prospect, in the Caborra Basa project, onshore Zimbabwe.

"We are delighted to declare a gas discovery from the Mukuyu-2 sidetrack well in the Upper Angwa formation", Scott Macmillian, Invictus' Managing Director, declared in a statement. "The discovery represents one of the most significant developments in the onshore Southern Africa oil and gas industry for decades".

Invictus explains that the decision to call a discovery was made after an intermediate wireline logging was run with the primary objective of obtaining hydrocarbon samples from Upper Angwa reservoirs located close to the base of the Upper Angwa formation following indications from real-time logging while drilling and mudgas.

"A limited suite of wireline logging data was acquired over the interval from 1,969metre Measured Depth (MD) to 2,975mMD in the Basal Pebbly Arkose and Upper Angwa formations which identified multiple hydrocarbon bearing reservoirs in the Upper Angwa. A total of four hydrocarbon samples were recovered to surface from two separate zones in the Upper Angwa using the wireline formation testing tool. A further two formation water samples were recovered from the Basal Pebbly Arkose formation".

Wireline log interpretation calculates a preliminary net pay estimate of 13.9metres for the Upper Angwa, "however, this estimate is still subject to further calibration of the logs with core and fluid data to determine appropriate net cutoffs and subsequent pay estimates", Invictus explains. "Significant additional gross sands were intersected within the Upper Angwa gas leg but are below the current net reservoir cutoff. These intervals may have better reservoir development elsewhere in the Mukuyu field and along with the refinement to the net pay criteria represents additional upside. Further appraisal and technical evaluation of log, core, seismic and well test data is required to determine the full extent of the resource size.

Prior to the Mukuyu-2 Sidetrack, Invictus had earlier drilled Mukuyu-1, Mukuyu 1 Sidetrack as well as Mukuyu 2. In all cases it filled the media with upbeat reports of "elevated mud gas and fluorescence were encountered and strong gas shows".

Now "the Mukuyu-2 discovery, seven kilometres away and 450 metres updip of the Mukuyu-1 well, which can subsequently be classified as a discovery, provides confirmation of the large potential of the Mukuyu field which has a structural closure of over 200km2 ", Macmillian says. "With additional hydrocarbon bearing reservoirs ahead, the focus now is to complete the drilling and evaluation program and obtain further wireline data including fluid samples to declare an additional discovery from the Lower Angwa formation."

Gas and fluid properties from the recovered samples will be confirmed following laboratory testing once the sample bottles are dispatched from the rig for analysis. No additional fluid samples were captured in order to preserve the wireline formation sampling tool and remaining sample chambers for use in the interpreted Lower Angwa hydrocarbon-bearing zones where thicker sandstone units were penetrated in Mukuyu-2.

The Exalo Rig 202 is drilling ahead "towards the total depth at approximately 3,400mMD sidetrack section through the remaining Upper and Lower Angwa reservoirs where multiple hydrocarbon bearing zones were intersected in Mukuyu-2.", Invictus notes in that report.