Frac Gradient: 2016 #39

A frac with 8.5 lb/gal fluid, tubing pressure loss of 500 psia, and perforations centered at 5,000 TVD ft had negligible pressure losses in the prefs. ISIP = 1,525 psig.  The frac gradient (psi/ft) was most nearly: (A) 0.65 (B) 0.70 (C) 0.75 (D) 0.80. (Note: I've left out all the unneeded information, which makes the problem much harder).

Note this sort of equation is unlikely to be provided in the reference, but it is simple enough an engineer should know it. 

Solution by using equations on 7 PRD 2:
1) Find hydrostatic pressure at perfs: 0.052(8.5)5000 = 2210 psi.
2) Add the ISIP for total pressure at perfs: 2210 + 1525 = 3735 psi.
3) Calculate the gradient to perfs: 3735/5000 = 0.75 psi/ft or (C).