Case Study 6 - Solutions

# My preferred approach would be to purely work with

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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 near-by 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 1.70E-05 psi^-1 1.3 rb/stb 0.51 ft The...
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