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Unformatted text preview: y work with the shifted Horner line at early times, which has the following equation as derived in
step 5: In this equation the term represents the slope of the shifted Horner line. By measuring the slope and using the typically known core and fluid properties the permeability can be determined.
Providing the initial reservoir pressure is known, the only unknown in the above equation is R. Therefore
by choosing any point on the shifted Horner line, selecting the corresponding wellbore pressure and ∆t,
we can reduce the above and solve for R. The actual process of solving for R is difficult, since it is
included inside the exponential integral function. There are several ways to handle this, including a
software approach, graphical approach and a manual approach (using the ln assumption if possible, or
using a Newton Raphson numerical approach). My choice would be using trial and error with matlab,
then backing out the value or R. 8 If the initial reservoir pressure is not given, the second straight line in the late time region will have to be
used. This slope has twice the slope, which is the main indication of a nearby sealing fault. Using the
double slope line you could extrapolate the line to the Horner ratio value of 1 and determine the initial
(theoretical) reservoir pressure. Knowing this value you would solve as previously discussed.
Another approach was highlighted in class would be to look at the pressure difference between the two
lines at any point. Then, by taking the difference in the respective equations and evaluating at a point on
the plot R can be calculated. The equation in SI unit will be as follows: Again, R is still encompassed within the ei term, and therefore the solving procedure will be an involved
process. 9 Part 2
The next part of this case study deals with determining reservoir parameters from a buildup test. The
general data provided is as follows: Parameter
Value
Cum oil produced
Final flow rate
Buildup duration
Formation thickness
Porosity
Viscosity
Compressibility
Formation volume factor
Wellbore radius Units
5320 stb
3500 stb/d
29 hrs
25 ft
0.25
1 cp
1.70E05 psi^1
1.3 rb/stb
0.51 ft The...
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 Spring '12
 DrJohanssen

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