This is the exact problem found on 12 WLT 4. The skin calculates to 3.0.
It's pretty simple; I include it to show a few testing tricks:
1. FVF is given as "shrinkage factor" (STB/bbl); merely invert for 1.2 bbl/STB.
2. The answer 3.0 splits the difference between options (A) 3.2 & (B) 2.7; the closest answer is "A".
This, as I said, is simple. But these tricks can unsettle anyone under stress, so they are ideal to practice on "plug-and-chug" problems like this.
Here's a comment from another thread about this problem: "I used 12 WLT 12 to find m, and then rearranged pressure drop using skin for s=delta p/(.869*m) Is that the way to go about it? I'm getting 2.98 though for skin". This is another clever way to use the GB to solve it so I wanted to include it here. You've got a myriad of choices in 12 WLT to solve well testing problems, so know the chapter well.
ReplyDeleteThe only caveat to your statement above is that the legend on 12WLT12 has q as STB/hr, which will give you the wrong answer if you convert the given 20 bbl/day to bbl/hr.
ReplyDeleteIf it is not mentioned in the question, should we simply assume pseudo steady state? Assuming steady state gives a skin of ~2.2
ReplyDeleteNo, never assume, the problem will always give you the clues you need, which help direct (you have to move so fast on this exam, the problem info is clues where to go). On this question I think it says, "A PBU is performed after the well is brought on line". Since just BOL you can use psudo steady. Does this check out?
DeleteQuestion does not mention that, it says "Produced fluid turns out to be 20bbl/d with viscosity....."
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DeleteOK, I see, I was looking at #28. Here's what I have on #29:
DeleteProblem 29. A 12-inch internal diameter completion penetrates a 25 ft thick, 1,800 ft diameter reservoir. The permeability is 18 md. Produced fluid turns out to be 20 barrels per day with a viscosity of 1.6 cp and a shrinkage factor of 0.833 STB/bbl. If the drawdown is 117 psi, and the pressure drop due to skin is 36 psi, the skin is closest to:
So the clue is "produced fluid turns out to be", which means it's a new completion, so pseudo. Check?
That makes sense, thanks!
ReplyDeleteUsing 2020 reference guide. pg 15. Psuedosteady-state radial flow of slightly compressible fluids equation. Solve for s. (careful with the radius, shrinkage factor). Skin pressure drop isnt used.
ReplyDelete