Problem 55: A saturated 2,200 psi sandstone reservoir has 13 producing wells yielding 18 MBOPD. One of these wells produces 400 BOPD with a flowing bottom hole pressure of 1800 psig; this well has a SSSV at 1,000 ft TVD with a 3-inch ID.
Oil viscosity, the formation volume factor, oil saturation, and permeability are 3.1 cp, 1.2 bbl/STB, 0.77, and 0.82 millidarcies, respectively.
Simulations predict the reservoir pressure will fall 400 psi in 3 years and remain saturated; oil viscosity, FVF, saturation, and permeability should remain roughly the same. The maximum oil rate (STB/day) for this well after 3 years will be closest to: (A) 1010; (B) 1060; (C) 1090; (D) 1120
Guidebook 7 PRD 1. Saturated? Think Vogel.
qo max = qo current/(1-0.2*(pwf/pr)-0.8*(pwf/pr)^2) = STB/day
qo max = 400/(1-0.2*(1800/2200)-0.8*(1800/2200)^2) = 1330 STB/day
qo max future = qo max(pr f/pr p) = 1330/(1800/2200) = 1088 STB/day
Update: this is a "future" well performance problem. First do the
Vogel calculation for "current" qo max (using current qo, pf, & pr).
Second find the "future" qo max based on future pr. Note this is a
simple, linear relationship only if oil fluid properties &
permeabilities "remain roughly the same". For more details,
see the Guidebook's references on 7 PRD 1.
How do we consider the pressure drop of 400psi? It seems like the solution requires the original reservoir pressure of 2200 psi even though the question asks for the maximum rate after 3 years when the pressure would be lower...i.e. since the flowing bottom hole pressure (pwf) is 1800, wouldn't pwf/pr be equal to 1 after 3 years?
ReplyDeleteGood questions. 7 PRD 1 points you to PO, RE, HS4 as references I'm pretty sure all 3 discuss Standing's "future" well performance method. If memory serves with "fixed" fluid properties qo_max future/now ratio = pr future/now ratio.
DeleteProblem 2-9 of the PO reference has a good example (but in this one Beggs calcs the fluid property change and I just assume it constant to make it easy). But it's just a qomaxfut = qomax(prfut/pr).
Does this make sense? Do you have Beggs Prod Opt using Nodal Analysis (prob 2-9) or TS4 P23? In both, they talk about calculating future IPR from current. Let me know if you see something wrong since I whipped this one out pretty fast. Older Guidebook versions had better explanations and I might try adding some more.
I forgot to say: not only is the fluid required to be unchanged but perm too.
DeleteHi mdavid,
ReplyDeleteSaturated reservoir means that there are gas in the reservoir (Pb > Pres).
My understanding is that Vogel should be used mainly for undersaturated reservoirs (Pres > Pb).
Or maybe I am missing something?