A well’s surface section is drilled to 8,000 ft TVD where the pore pressure is 3,000 psig and the fracture pressure is 6,000 psig. At 4,000 TVD the pore/fracture pressures are 1,500/4,000 psig, and 5,000/8,000 psig at 10,000 ft TVD.
Assuming a trip margin of 200 psi and a kick margin of 500 psi, and a future intention to drill to 10,000 ft TVD once the surface casing is set, the maximum mud weight allowed to drill the surface section is closest to:
(A) 14.1 lb/gal
(B) 13.2 lb/gal
(C) 13.5 lb/gal
(D) 13.8 lb/gal
This is pretty simple once you've read through all the details. See 6 DTC 6 (csg set depth) and it has the single needed equation: Max MW=(Pff - KM)/0.052(TVDshoe) = (5,000-500)/(0.052*8,000) = 13.2 or (B). The GB has the exact problem as an example.
The answer reads 5,000 - 500. When working the equation out with that the answer becomes 10.8 ppg. Only when you use 5,000 + 500 does the math work out to 13.2 ppg.
ReplyDeleteThis question is misleading. that math works out to be the MINIMUM allowable MW to drill the hole section since you used pore pressure of 5,000 psi at 10,000' TVD. Furthermore it is not uncommon to weight up or weight down after setting casing. It would be more clear to say "assuming that you do not change MW from the surface hole section..."
Sorry for the delay in reply (fishing). Thanks for the comment. I'll look this over in the next few weeks.
DeleteSurface Section Fracture Pressure = 6,000 psi.
DeleteIntermediate Pore Pressure = 5,000 psi
500 psi kick margin minus fracture pressure of surface casing = 5,500 psi
5500 is still high enough to cover pore pressure of 10,000' TVD & trip margin of intermediate section and wont fracture formation at 4,000
8000 / 0.052 / 5500 = 13.2 ppg
Hey David, since, the question is asking for surface csg which it says is set at 8000 ft with the pore pressure of 3000 psi and frac of 6000 psi, would we not be using 6000 psi instead of 5000 as its asking for the maximum allowable pressure?
DeleteCould you please clarify? Thanks for your help.