"And they may also be prioritising a flow test of the over pressured zone in this well and saving a crack at setting a depth record for the next appraisal well."
I came across an interesting paper on the well casing design required for safely drilling deep(water) over-pressured reservoirs......"Because of over-pressure and the small drilling mud window between the fracturing pressure and the pore pressure, the wellbore structure in deep wells is usually very complex since multiple layers of casing have been used in order to drill to the total depth of the design....for example, up to 9 layers of casings and liners were used in the Macondo well in order to drill to the planned TD." by Xingru Wu, 2018, A Special Focus on Formation Damage in Offshore and Deepwater Reservoirs. Sorry I can't provide a link to this Science Direct paper.
Although the above paper is focused on deepwater over-pressure formations, I am sure that at least 6 casing/liners would be required for future Mukuyu wells in order to TD as deep as possible. Invictus has stated that there will be well design optimisation in the future, but for M-2 maybe the best way of drilling as deep as possible would be to drill 6" hole as deep as the drilling mud window will allow, run and cement 4.5" liner, then drill as deep as possible with a 4" or a 3.5" bit.....hopefully down to at least 4300m MD.
The casing sizes referred to in the paper were 36", 28", 22", 18", 16", 13.5/8", 11.7/8", 9.7/8", and 7". However, the casing string sizes/grades in a typical Mukuyu well would need to be safe for encountering hydrocarbons in the Dande, Forest, Pebbly Arkose and the Upper and Lower Angwa.....perhaps 20", 13.5/8", 11.7/8", 9.7/8", 7", and 4.5" ?
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