Once the 9â…” has been run and is cemented and you drill out the shoe and drill the 8"” section it would be interesting if your drilling BHA has the capability on the way out of the hole to log over the whipstock area to confirm the actual DLS over the whip area.
At this point however it´s too late to do anything about it but it´s all good learning´s for the future operations.
I´m assuming the 10deg/30m DLS has been quoted to you from the whipstock supplier. However as they will also tell you the whipstock is not 30m long and so the DLS is calculated in various ways making some assumptions.
I´ve had this conversation several times when constructing multilateral wells and there are other factors to take into account such as the length of the window milled, the size of the liner you run over the whipstock and how the drilling BHA behaves out in the open hole once departed from the whipstock.
The reality is that once you have milled the window and drilled the lateral section you will more than likely run a liner over the whip and out into the open hole. This liner wants to be straight and it will at the point where it passes over the whipstock want to be straight. This will mean that the liner will contact the upper portion of the window and the lower portion of the window and will reduce the ”œcalculated” DLS significantly. I´ve run whipstocks with a calculated 12 degree/30m and once the liner has been run and cemented logged the liner at the whipstock and the DLS is actually less than 5degree/30m.
Sit down with your casing exit company and get them to draw out in CAD or similar the liner passed over the whipstock. The longer the window you mill and the smaller the liner you run the less the DLS will be.
Are you constrained with only one whipstock vendor?Ken Horne.............