RE: Malcy Positive Comment1 Oct 2022 11:24
Excellent informed answer which I felt worth copying on here.
Part 1
The drilling over the last 20 years at Saltfleetby, once the early exploration was past, was not especially difficult or unsuccessful. Nor is it true that the reservoir presents greater hazards than any other gas reservoir. It should be noted that the drilling strategy of the previous operators in the early years was to drill a pilot hole first and then side track horizontally it to increase the chances of hitting a productive layer. Very often the pilot well itself was deliberately “hockey-sticked” to verify productivity of a previously encountered layer.
SF01, actually originally spudded back in 1986, was a pilot well. This was sidetracked no less than six times between 1996 and 1998 when the field was poorly understood and just being explored. The final side track SF01U was actually the most productive well on the field.
Thereafter the record was excellent until previous operators attempted to address the southern lobe of the reservoir. SF02 did not require a side track at all and was a good producer. SF03 required one sidetrack and was a good producer. SF04 likewise a good producer, no side track required. SF05 again no side track but a less impressive but reasonable producer.
Later drilling on the field, in particular exploratory drilling aimed at the southern satellite structure (via SF06 and SF08) did encounter both less productive zones and these boreholes did require no less than five side tracks betwen them (much as the original SF01 had) and had limited but not negligible success. However with our side track we are actually addressing the better understood main reservoir again and not that southern lobe; we are also aiming at an area within the main reservoir which we know with exceedingly high levels of confidence to have been both greatly productive and not exhausted by previous boreholes.
SF07, something of a special case, was originally drilled in 2003 and had four side tracks: the first two encountered low permeability whilst the latter two, SF07X and SF07W were drilled in 2016 and were beset with operational difficulties which may be the source of the rumour that side-tracking in this field was particularly difficult.
The problems involved loss of part of the downhole assembly due, inter alia, to differential sticking (note we are taking great care to avoid sticking and are supported by specialist and respected managed pressure drilling consultants as appropriate for a partially depleted reservoir) whilst the other issue involved hole collapse in a coal rich seam (prone to instability) just above the target Westphalian layer: we are aware of this and we have adjusted the angle of approach accordingly. It should be noted that the drilling manager at the time proceeded against the explicit advice of the drilling company and indeed the company’s own consultant engineer.
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