In April 2010, the worst oil spill ever recorded occurred when an explosion and
ID: 236731 • Letter: I
Question
In April 2010, the worst oil spill ever recorded occurred when an explosion and fire on the Deepwater Horizon offshore oil-drilling rig left 11 workers dead and began releasing oil into the Gulf of Mexico. One of the attempts to contain the spill involved pumping drilling mud into the well to balance the pressure of escaping oil against a column of fluid (the mud) having a density significantly higher than those of seawater and oil. In the following problems, you may assume that seawater has a specific gravity of 1.03 and that the subsea wellhead was 5053 ft below the surface of the Gulf. (a) Estimate the gauge pressure (psig) in the Gulf at a depth of 5053 ft. (b) Measurements indicate that the pressure inside the wellhead is 4400 psig. Suppose a pipe between the surface of the Gulf and the wellhead is filled with drilling mud and balances that pressure. Estimate the specific gravity of the drilling mud. (c) The drilling mud is a stagbhle slurry of seawater and barite (SG = 4.37). What is the mass fraction of barite in the slurry? (d) What would you expect to happen if the barite weight fraction were significantly less than that estimated in Part (c)? Explain your reasoning.
Explanation / Answer
A) pressure = Po + rho g h
= 10^5 + 1.03×1000×9.8×5053×0.305
= 15656519 Pa
= 2271 psig
B) P = Po + rho g h
4400 psig = Po + rho×9.8×5053×0.305 Pa
3.03 ×10^7 = 10^5 + rho× 9.8×5053×0.305
Rho = 3.03e7/(9.8×5053×0.305) =2006 kg/m3
SG = 2.006
C) Let the mass fraction be f,
1/ 2.006 = f/4.37 + (1-f)/1.03
0.5 = 0.23f + 0.97 - 0.97f
f = 0.47/0.74 =0.635
D) Then pressure will not balance because the overall SG of the drilling mud will be lesser than 2.006.