Problem 35. A well produces 100 MSCF of gas with a SG of 0.8 along with 200 STB of 30 API oil. The oil FVF is 1.4 RB/STB. The 200 dF reservoir has a fluid gradient closest to: (A) 0.28;
(B) 0.30;
(C) 0.32;
(D) There is not enough information given to solve the problem.
This is the example problem in the Guidebook on 13 RES 9 in the latest edition, and solves to (B). It's good to think about all the different ways this problem can be written so you won't be blindsided.
In this problem, solve for unitless Rs (use 5.615 SCF/STB constant) to find the density of both the oil & gas (from the given API & SGg) using lbm/SCF. Then find Bo from Standing's equation. I don't think the provided Reference includes Standing's equation or the API/SG conversion, but don't let that lull you into complacency; the exam could just provide the equation with a bunch of other stuff to confuse you. Note that SPE TS8 by Towler has this sort of problem, so it's absolutely fair game.
The constant needed for this problem, however, is in the new Reference Guide (provided on the exam) on page 190 of chapter 7 under volume, but you probably have this conversion memorized.
IMO this multi-step problem is kinda amazing inasmuch as some guy using oil/gas from the separator can calculate his reservoir gradient 10,000 ft below his feet with just the FVF.
Question - you are given Bo, which is the step where you need reservoir pressure. So, if you jump to the Density of oil and gas combined equation with that Bo, you can get to the gradient without reservoir temp. That is the answer that you have in that test book (0.30 psi/ft). I do not see where you need Res temp when you are given Bo.
ReplyDeleteSure; it's not uncommon to have extra info given to confuse.
DeleteI've gone back and forth adding in the Bo calculation depending on how long people are saying the test takes them, which is why I like to keep T so I won't forget it if I add the Bo calc.
What do you think about this practice problem timing? Should I add the Bo calc back in?
It is pretty quick once you get to the right set of equations. But, that being said, this is probably a 4 mins with Bo given and could be 7 mins without due to calculator interaction. You would know better what they will do in testing, but it goes from a question that is on quicker end to one that is a bit long with a lot more chance for calculation errors. Maybe add it in for practice to show how it is done?
DeleteI agree with you, but most will need to leave 2 minutes to read/understand the problem gotta factor that in...
DeleteCould you post your solution for the fluid gradient problem you have in the 2018 PM practice exam. Solution says D is the answer, however I am calculating .37
ReplyDeleteSolution says B (.3 psi/ft).
DeleteWhat number?
Delete#45. I might be missing something. Thanks!
Deletewhere in the guidebook is the example?
ReplyDeleteJust scan the cover by subject for "Reservoir" then scan down the list, you can see it on 13 RES 9 for "Res Density". On that page is the problem type. This type of problem is given in SPE TS #8.
Deletehow would you suggest this problem be worked on the 2019 CBT exam?
ReplyDeleteYou wouldn't have this problem in the same format. Rather, it could be a word problem, or the needed equations would be given.
DeleteThe main thing, IMO, is to understand how it all works and get familiar with the concepts. This exact problem is in SPE TS #8, so it's clearly fair game. It's a perfect question style for the PE exam. Were I writing the exam, I would ask: "What information do you need to calculate the reservoir gradient?" and list a bunch of options making it seem you need a lot, when all you need is res T, gas & oil production, & FVF.