A 6.125-in. hole is being drilled through a 100- ft depleted gas sand. The pressure in the wellbore is 2,000 psi greater than the formation pressure of the depleted sand. The mud cake has a thickness of 0.5 in. and a coefficient of friction of 0.10. If the 4.75-in. collars become differentially stuck over the entire sand in- terval, what force would be required to pull the collars free? Answer: 1,129,000 lbf.