Cash Break Even (CBE): 2016 #80

An investment had net cash losses of $5 million and $12 million in the first and second years, respectively, but gained $4 million, $8 million, and $15 million in years three, four, and five, again respectively. The number of years required for cash flow breakeven was closest to:  (A) 4.6 (B) 4.5 (C) 4.4 (D) 4.3.

On this problem, NCF is calculated for each year until the accumulated amount is passes from negative to positive. One then iterates to find the exact time. To do this quickly, make a table (below):

Year 1 2 3 4 4.33 5
NCF (5) (12) 4 8 15
Cum (5) (17) (13) (5) 0 10
CBE yr 1 2 3 4 4.33 5

This problem is pretty easy since NCF is given directly and need not be calculated. Cumulative cash flow goes from (5) to 10 in years 4 and 5, respectively. So going 1/3 of the way between 4 and 5 gives about 4.33 This is closest to (D).

Waterflood: 2016 #70

A 2000 acre, 15 ft thick, 15% porosity waterflood reservoir with a Sgi of 20% and a producer/injector distance of 330 ft is started on injection.

How much water volume (barrels) must be injected until interference within a single 5-spot pattern?
Wii = [3.14159/(2*5.615)](330^2)15(0.15)(.2) = 13,710 bbl (B)

How much total volume to pattern's fill-up?
Wif = (2/5.615)](330^2)15(0.15)(.2) = 17,455 bbl (B)

Pipe Stress via Injection: 2016 #65

8.681 ID casing string rated for 437,000 lbf tension. 46% of the casing’s tension rating is applied. What is the maximum pumping pressure before the casing exceeds the tension rating?

Turn to 6 DTC 1 (casing, stress are the key words).
Find remaining tension allowed: (437,000)0.54 =  236,000 lbf
Find allowed pressure using 236,000 lbf = P(0.7854)D^2 lbf, or:
P = 3987 psi. (A)

This is a 3 minute problem if you know what you are doing. And it's realistic. And it's in TS 2. Know how to do problems like this quickly.

Reserves: 2018 #65

Problem 65: When estimating primary oil and gas reserves, the LEAST accurate statement is: 

(A) Drive mechanism is more important than well spacing for recovery efficiency. 
(B) A gas deviation factor estimated using empirical correlations...is acceptably accurate...
(C) The differential rather than flash formation volume factor should be used.
(D) ...capillary-pressure method...OWC...must be a robust correlation between porosity & perm. 

This solution (C) is found in the Guidebook 13 RES 13. Keep in mind, this sort of question you just have to understand each part, and the CBT forces you to know it. So read the Guidebook notes and learn them for the exam.

Also, read about this subject in detail in the HS5 P1509, P1509, P1512, and P1606. P1512 has a long discussion of the need for flash FVF use, well worth your time.