RE: Rocket31 Jan 2023 21:11
The sidetrack drilled before Christmas into the top of the reservoir encountered in January a very small fracture system which had not been captured by our seismic study. This would not have been an issue had we not been working in small bore, or so-called skinny drill pipe, as a consequence of laying 5.5? liner to secure the coal and marine band zone behind us. The use of this smaller liner, rather than 7? casing, was driven by the nature of the formation we had passed through and in turn this required us to use this lighter drill pipe.
Rather than try to clear or work around the fractured zone, as our predecessors had spent a fruitless month trying to do back in 1998, a decision was made to back up about 100 metres, mill a new window in the 7? casing, set a second whipstock and re-enter the reservoir via 6? open hole and more robust drill pipe and bits. This was also the successful solution arrived at by Candecca in 1998. This we have done and as of 31st Jan we are drilling forward in earnest along the timetable given in RNS.
In addition we are increasing the mud weight to secure each of these vulnerable zones, but using calcium carbonate throughout which will act as a bridging agent inside the Westphalian and prevent mud and drilling tools being displaced into the reservoir away from the borehole (differential sticking). In short we have more room for maneouvre and even if we are forced to use 5.5? inch liner again, we have more mitigations in terms of equipment selection and mud weight.