Theoretical Critical WOB: 2018 #47

Problem 47. A BHA has 200 ft of 7 ½ in. by 2 ½ in. steel DC and a 12 ¼ in. bit w/an offset of 3 degrees. The entire hole section has a steady 9-degree inclination and is filled with 12 lbm/gal mud. Once the DC are in full compression, the additional WOB (Mlbm) required to reach the theoretical critical WOB is closest to: (A) 83 (B) 81 (C) 79 (D) 77.

This problem can be solved using 2 DRL 6 or TS 12 (P593-594). In fact, the problem is similar to the TS12 problem but it has a 5-degrees inclination. Using the calculated 104,790 with a buoyant 108.6 lb/ft(cos9)200ft = 21,453 we can find the delta: 83,266 lbm or (A).

UPDATE: Note for this problem you need to calculate I, w_bp, and m. These calculations are shown on TS12 P593. Two points: 1) have TS12 and be able to navigate it; 2) maybe 80% of what you need from TS12 is in the GB...but TS12 is 700 pages so to be at the top of your game you should have TS12 and know it well.  Also anticipate test-writers to "piggy-back" on existing TS problems like this where you can save time if you have seen it before. That's why I wrote this problem the way I did. The real exam is NOT easy; anticipate this level of difficulty (at times). I would expect to lose >3/4 of engineers on this one.