Example 4.6. A well is being drilled at a vertical depth of 10,000 ft while circulating a 9.6-Ibm/gal mud at a rate of 8.5 bbl/min when the well begins to flow. Twenty bar- rels of mud are gained in the pit over a 3-minute period before the pump is stopped and the blowout preventers are closed. After the pressures stabilized, an initial drillpipe pressure of 520 psig and an initial casing pressure of 720 psig are recorded. The annular capacity of the casing opposite the drillpipe is 12.9 ft/bbl. The an- nular capacity opposite the 900 ft of drill collars is 28.6 ft/bbl. Compute the density of the kick fluid. The total capacity of the drillstring is 130 bbl