Posted 02.11.2018 12:17 by Magnus Tvedt
Klaff is an exploration well in the game of thin, hot sands with uncertain oil quality. With the eyes of a driller, this is a race track. Read on to follow our 5 minute well review of the soon-to-be-drilled exploration well by Equinor.
Johan Sverdrup is the latest giant developed on NCS, the reservoir is slightly shallower than 2000m, the overburden is a walk in the park, and the temperature is electronics and fluids friendly. Klaff seems to be an appraisal well where the goal is the same Viking Group, Draupne sands as in the Johan Sverdrup field.
There are 6 other exploration wells in block 16/5, and they show a strong confidence in the overburden, with the exception of some shallow gas pilot holes which add some extra costs to the operations. In fact all of these wells seems to have been drilled with a simplified casing design, either dropping the 26" or 17 1/2" sections. Elf set that standard already in 1971.
In many of the 16/5 wells there has been a 9 7/8" pilot hole because of shallow gas warnings. With no reported gas, these has been expensive operations. If our money was on the line, we would invest some more in shallow gas examinations up front, maybe follow Spirit Energy's brilliant Coiled Tubing drilling for gas pilot. The drilling team could easily argue for skipping the shallow gas costs over on a project budget and drill with seawater in the top hole at full speed.
As mentioned above, the table is all set for skipping a casing level, but the requirements of a 18 5/8" well head is set by rig BOP and contracts agreements. If the commercial team got pumped up on this well, they could have argued for a 13 3/8" well head and a slimmer rig. The dual ram rig Transocean Spitsbergen can be fast if the well is planned by a strong team, but the rig is built to carry significantly more riser and equipment than this 100m water depth well, and comes with a huge, 18 5/8" riser and BOP.
Probably they are going with a 30" conductor, then we'll see how brave they are. Will they skip the 20" and go directly for the 17 1/2" section and run a 13 3/8" x 20" surface casing, or will they safe it and run a deep 26" section with a 20" casing? We haven't looked at the load cases for the 13 3/8" casing running, but at these depths, it shouldn't be a problem.
Since the area is very well developed with exploration and production wells, this is like the race track of the NCS. The rig team should really show off how efficiently they can run the new and brilliant Transocean Spitsbergen.
Drilling was faster in the '70s
In terms of speed, Lundin made a show of ROP's in the Utsira area, other than that, the ROP has been conservative in all the neighboring wells. Maybe one can say that after spending all the courage on a simplified casing design, they became more risk-averse in the drilling. Let's see how Equinor does it in the coming well.
ROP and formation in neighbor well
In terms of pressures, the well will probably be drilled with 1.4 sg mud from top to bottom, just as all the other wells in the block. That provides margins for shallow gas, and is in a safe distance of the 1.6 LOT taken just over the reservoir. Will they go bold and drill with water based mud? They history has proven that water based fluids goes well, although some glycol has been added, probably to prevent hydrates in the 120m riser.
As already mentioned, the risk of shallow gas seems present in the area, but should be able to eliminate with use of new measures. By reducing the risk of shallow gas, they can drill with dirt-cheap seawater from surface and down to bottom of Utsira, where pressure starts building up.
As a summary, this well should be plain chewing, if they want to show off new technology or drilling management, this is a safe well to exercise in. The risk seems to lie in the oil quality, thickness of reservoir formation and presence of a water contact. Maybe we will hear of some new world records in drilling data management or drilling performance?
We look forward to this well, and expect a drilling time of about 16 days. Based on our models, that is twice the time for a perfect (robot) well, but not bad for a manual crew.
Best of luck!
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