Invictus recovers hydrocarbons in Mukuyu-2 well in Zimbabwe’s Cabora Bassa basin
(WO) — Invictus Energy Ltd. has reported significant progress in the drilling of the Mukuyu-2 well at its 80% owned and operated Cabora Bassa project in Zimbabwe.
The recovery of hydrocarbon gas from the Pebbly Arkose downhole sample and the identification of multiple hydrocarbon-bearing intervals in Upper and Lower Angwa reservoir sands, as revealed through wireline log interpretation, mark key milestones, according to Invictus.
Since the previous update, the exploration team has successfully recovered natural gas (predominantly methane and trace heavier hydrocarbons) to surface from the Pebbly Arkose formation and continued pipe conveyed logging operations due to challenging borehole conditions.
Additionally, 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 clean-up which showed gas and liquid hydrocarbons flowing through the onboard compositional fluid analyzer (CFA).
Prior to the fluid sampling in the Pebbly Arkose formation, 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.
The recovery of natural gas to surface from a primarily water bearing interval in the Pebbly Arkose provides confirmation of 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.
Subsequent evaluation of the Upper and Lower Angwa
Higher than anticipated pressure in the gas leg in the Lower Angwa beneath 3,400m (11,154 ft) MD where formation pressures exceed 5,000 psi which required an increase in the mud weight to maintain control of the well and preserve well barriers whilst drilling.
Connection gases were observed during the drilling of this part of the hole section to Total Depth at 3,718m (12,198 ft) MD together with high levels of trip gas resulted in the implementation of well control measures through 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 hole 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 samples. High amounts of overpull are required to free the drill string and wireline tools from several points along the wellbore resulting in tool damage, together with holdups 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 tool 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 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 its objectives for the Mukuyu-2 well.
A thorough assessment in conjunction with Invictus’ 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 1,966m MD) would provide the Company the strongest opportunity of acquiring valid fluid samples from the well.