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Zimbabwe: Mukuyu-1 encounters additional elevated gas shows and fluorescence in primary target Upper Angwa formation

23 Nov 2022

Photo - see caption


  • Mukuyu-1 successfully deepened to 3,923 metres Measured Depth ('mMD'), encountering additional elevated gas shows and fluorescence through to total depth
  • Results prove up potential of the Upper Angwa formation over a 900m gross interval
  • Upper Angwa formation thicker than pre-drill estimates, boding well for future prospectivity in the Cabora Bassa Basin
  • Mukuyu-1 to be sidetracked to complete evaluation
  • Shareholder briefing to discuss preliminary well results and forward operations

Invictus Energy has provided an update on the Mukuyu-1 well that is currently being drilled in its 80% owned SG 4571 licence in Zimbabwe’s Cabora Bassa Basin.

Comments from Managing Director Scott Macmillan:

'The existing Mukuyu-1 wellbore was successfully deepened to 3,923mMD and continued to encounter multiple reservoir units with elevated gas shows and fluorescence until total depth (TD), proving up the potential of the Upper Angwa formation over a 900m gross interval.

'Our primary Upper Angwa target formation is thicker than anticipated from pre-drill estimates, which bodes well for future prospectivity in the basin.

'After reaching TD, the borehole was prepared to run wireline logs, however, due to a deterioration in borehole conditions, the tools were unable to pass below a depth of approximately 3,030mMD where the primary fluid sampling targets are located.

'Current borehole conditions make logging the existing hole section extremely risky with an increased likelihood of losing tools and not meeting the objectives of the well.

'As a result, the decision has been made to sidetrack* the Mukuyu-1 well in order to complete our evaluation and obtain a fluid sample.

'Results to date have been extremely encouraging and we plan to suspend the sidetrack well for future testing.

'We anticipate the remaining activities will require a further 12 to 18 days and we look forward to providing further updates in coming weeks.'

*Sidetracking is a regularly used oilfield practice where a secondary wellbore is drilled away from the original wellbore to bypass an unusable section of the well or explore a geological feature nearby. In the bypass case, the secondary wellbore is usually drilled substantially parallel to the original well. Mukuyu-1 ST-1 planned well path is shown below in Figure 1.

Photo - see caption
Figure 1 - Mukuyu-1 and proposed Mukuyu-1 sidetrack well trajectories

Progress and current operations

Since the last update, the Mukuyu-1 well was successfully deepened to 3,923mMD where TD was called.

The well encountered additional reservoir zones displaying elevated gas shows and fluorescence to TD.

This proves up the potential over an approx. 900m gross interval within the Upper Angwa, which is thicker than pre-drill estimates.

Following TD, the borehole was prepared for wireline logging, however the logging tools were unable to pass beyond a depth of 3,030mMD following several attempts. In addition, substantial amounts of overpull were required to free the tool from several points along the wellbore which is typically indicative of wellbore instability/breakdown.

Analysis shows borehole conditions have deteriorated over the last few days while waiting for the wireline formation testing tool to arrive. Further attempts to log the existing hole section is deemed to carry elevated risk of losing wireline tools and not fulfilling the objectives of the evaluation program to obtain a fluid sample.

Deterioration is likely due to heavy water-based mud utilised as a precaution during drilling, previous remedial action taken to stem the losses experienced in the Pebbly Arkose formation and the substantial length of time the current 8½” hole section has been open, which now exceeds 25 days.

An assessment determined plugging back the existing 8½” wellbore section and conducting a sidetrack from the 9? casing shoe (at approx. 2,020mMD) would provide the Company the best opportunity of acquiring a valid fluid sample and the ability to suspend the well for future flow testing.

Forward plan

Exalo Rig 202 is preparing to plug back the existing 8½” wellbore section to seal off hydrocarbon zones and leave the well in a safe state prior to and commencing the re-drill of the upper 8½” hole section to approx. 3,500mMD. This will provide sufficient
information to calibrate the deeper sections of the original Mukuyu-1 wellbore.

The sidetrack well (Mukuyu-1 ST-1) will be drilled to a slight updip location to the north of Mukuyu-1, with a lower mud weight and solids content mud system (approx. 1,500psi reduction in overbalance), which will improve the logging conditions and chances of successfully obtaining a fluid sample.

Following conclusion of sidetrack drilling, the well will be logged, including wireline formation testing, with final results to be provided.

The Mukuyu-1 ST-1 well will then be suspended for potential future testing.

Original article link

Source: Invictus Energy

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