Calculate the equivalent density below the bottom joint of 6,000 ft of 11.75-in. casing (having an 11-in. ID) if the casing is being lowered at a rate of 1 ft/s in a 12.25-in. hole containing 10-lbm/gal fluid with a viscosity of 3 cp. Perform the calcula- tion assuming the flow pattem is laminar and the casing has a closed end. Answer: 12.8 lbm/gal.