The prospect of finding commercially viable oil and gas in Muzarabani is almost within reach as the company reported that it discovered the presence of moveable hydrocarbons at Mukuyu 2 exploration well.
Rudairo Mapuranga
According to Invictus Energy‘s Managing Director Scott MacMillan, the exploration team successfully recovered natural gas (predominantly methane and trace heavier hydrocarbons) to the surface from the Pebbly Arkose formation and continued pipe-conveyed logging operations due to challenging borehole conditions.
He said wireline logging data from gamma-ray, density-neutron and resistivity has identified multiple hydrocarbon bearing intervals in the Upper and Lower Angwa reservoir sands, subsequently reaffirming the moveable hydrocarbons observed during initial fluid sample cleanup which showed gas and liquid hydrocarbons flowing through the onboard compositional fluid analyser (CFA). “Prior to the fluid sampling in the Pebbly Arkose formation,” MacMillan said, “analysis of the wireline logs interpreted the presence of residual gas (low gas saturation below the net pay cutoff). The formation was targeted to acquire a water sample to assist the calibration of resistivity data and calculation of gas saturation in the below Upper and Lower Angwa formations.”
According to MacMillan the recovery of natural gas to the surface from a primarily water-bearing interval in the Pebbly Arkose confirms the presence of hydrocarbons coupled with the wireline log interpretation of hydrocarbon-bearing reservoirs in the Upper and Lower Angwa formations and most importantly signifies a potential discovery in the Mukuyu field (as per Society of Petroleum Engineers Petroleum Resource Management 2018 definition section 2.1.1.).
“Further evaluation results continue to reaffirm the presence of moveable hydrocarbons at Mukuyu2, evidenced by the recovery of natural gas from the Pebbly Arkose formation and further wireline logging data interpretations obtained from the Upper and Lower Angwa reservoirs.
“Due to compounding sampling challenges, borehole conditions and well control measures the Company, in conjunction with our service providers, have determined a simple vertical sidetrack will provide the strongest opportunity to achieve our remaining Upper and Lower Angwa evaluation objectives.
“The Company is currently funded to conduct and evaluate the planned sidetrack operations, with the completion allowing the well to be suspended for future flow testing. I thank our shareholders for their patience as we conduct the sidetrack well and finalise the evaluation program, I invite you to attend the webinar briefing to discuss the initial results and forward plan,” MacMillan said.
Subsequent evaluation of the Upper and Lower Angwa
Higher than anticipated pressure in the gas leg in the Lower Angwa beneath 3,400mMD where formation pressures exceed 5,000 psi which required an increase in the mud weight to maintain control of the wel and preserve well barriers whilst drilling.
Connection gases were observed during the drilling of this part of the hole section to a Total Depth of 3,718mMD together with high levels of trip gas resulting in the implementation of well control measures through the raising of the mud weight to ensure the safety of the drilling and logging operations and maintain well integrity.
The raising of the mud weight has subsequently led to high overbalance conditions in the shallower intervals of this hoe section which has resulted in fluid losses and formation invasion by the drilling fluid which is evidenced by the high pump-out volumes required to obtain fluid sample cleanup to obtain representative reservoir fluid sampes. High amounts of overpul are required to free the drill string and wireline tools from several points along the well bore resulting in tool damage, together with hold-ups and obstructions in the wellbore is typically indicative of hole instability/breakdown.
Subsequent attempts to complete the fluid sampling program on pipe-conveyed logging in the Upper and Lower Angwa reservoirs and the remaining data acquisition program have been hampered by too many failures. This is primarily related to the conditions, borehole deterioration and compounded by the duration this hole section has been exposed since drilling of this interval commenced.
Due to the limited availability of replacement fluid sampling tools and the risk of successfully completing the fluid sampling and remaining data acquisition program in the current borehole, the Company has carefully considered all options to achieve our objectives for the Mukuyu2 well.
A thorough assessment in conjunction with our service providers was conducted and determined that plugging back the existing 8 ½ inch wellbore section and conducting a simple vertical sidetrack from the 9 ⅝ inch shoe (at approximately 1,966mMD) would provide the Company with the strongest opportunity of acquiring vaid fluid samples from the well.
Forward plan
The Exao Rig 202 is preparing to plug back the existing 8 ½” wellbore section and commence re-drilling the 8 ½” hole section with more optimal parameters to approximately 3,400mMD above where the overpressure zone in the Lower Angwa commences. The Mukuyu-2 vertical sidetrack will be more conducive for conventional wireline logging operations including the fluid sampling to be conducted in the Upper Angwa and part of the Lower Angwa reservoirs, providing parameters for a more efficient and economic sidetrack operation in comparison to the Mukuyu-1 sidetrack well.
The completion of the sidetrack will also allow for the well to be suspended for future flow testing through running the 7 inch liner over this interval and retain the ability to drill, evaluate and test the remaining portion of the Lower Angwa in 6 inch hole in future operations.
Following the conclusion of the drilling of the 8 ½ inch hole section, the well will be logged including wireline formation testing and final results provided. The Company anticipates the remaining activities to conduct the sidetrack and wireline logging to take approximately 2128 days depending on drilling and logging conditions and is currently funded to complete these activities.
