Casing Design: 2017 #54

A well’s production casing will be set at a TD of 16,000 ft in 10.2 lb/gal mud. Which statement is most FALSE? 

(A) Production casing design should start at 16,000 ft and move uphole. 
(B) Casing collapse resistance must be reduced for tension if below 13,500 ft. 
(C) Casing collapse resistance needn’t be reduced for tension if below 14,500 ft. 
(D) Casing collapse resistance must be reduced for tension for casing above 12,500 ft. 

This problem has a lot of garbage you don't need (I don't include it here). (A) is clearly true (csg design starts on bottom and moves uphole; look up as needed). (B) through (D), however, are really the same question regarding collapse in relation to depth.

Solution: See Guidebook 6 DTC 9 that covers casing design and the neutral plane. Next, look up the 10.2 ppg buoyancy factor to calculate the hole section's neutral plane (16M*0.844 = 13,500 ft). The rest is academic; as TS 12 puts it on P430: Collapse performance properties will require derating for tension above the neutral plane. So (B) is false. 

But watch the wording on these types of problems like a hawk. You might work 5 minutes then mess up the answer due to some double-negative in the wording, confusion over "above" versus "below" the NP, or if the text is actually "true" or "false", even if you understand the problem fully. For this reason I always save 30 seconds for a check/re-read of each problem. Paranoia here is your friend.