Effective liquid permeability is found in the lab by graphing gas permeability versus the reciprocal mean flowing pressure and extrapolating the reciprocal mean pressure to zero.
In this problem, a rock core filled with gas “A” has a permeability of 40 md with an average flowing pressure of 1.25 atm and has a permeability of 30 md when said mean flowing pressure is doubled.
If this same rock core is filled with gas “B” and then has a permeability of 40 md with a flowing pressure of 2.5 atm, the permeability (md) for gas “B” at a flowing pressure of 5 atm is closest to: A) 30 B) 25 C) 20 D) 15.
Where is the equation to solve for effective permeability in the reference manual? I thought the 2021 PE practice (CBT) problems are meant to be solved with Ali's manual reference. Thanks.
ReplyDeleteThanks for the question, it's a good one.
ReplyDeleteMany people think the test is somehow "bound" to Ali's reference manual. While nobody knows what will be on the exam each year, in my opinion, nothing could be further from the truth. Ali's manual is merely a summary of equations and table, and yes, you have to know how to use Ali's reference to solve many problems on the exam. But the exam can have anything found in any SPE book.
In this problem, referencing SPE HS5, it is tests one's knowledge of effective liquid perm from gas core samples, and it actually give you the equation you need in the opening line (Effective liquid permeability is found in the lab by graphing gas permeability versus the reciprocal mean flowing pressure and extrapolating the reciprocal mean pressure to zero). I highlight this in the Guidebook 12 WLT 1, because it's fairly confusing if you've never looked it over before. The last one I did casually I gave to my wife to check and sure enough she caught a mistake. The math can get tricky if you don't pay close attention because the graph uses the "reciprocal mean" which is not common.
Anyway, be careful to know Ali's book well, but never be a slave to it, because many people waste a lot of time looking in it for answers that just aren't there. The testers are trying to test understanding, not how fast you can look something up. Anyway, hope that helps!