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Unformatted text preview: 10 and field units becomes: This equation can be applied at the end of each flow period. This can be broken out into: And This results in a linear equation of the form: ’m’ is the slope, given as: And the slope may be found utilizing: Here it is clear that m is the slope, while ‘
’ represents the intercept of the straight line. Using these equations and the data provided, the skin and permeability can be determined. It is important to note that the formula is evaluated for each flow period individually; meaning the value ‘n’ represents the last value for the current step. Also, the assumption of infinitely acting must apply over the entire duration of the test. 2 The calculated values for the given data are provided in the table below: Flow Period Flow Oil Pwf time Rate (psi) (hrs) (stb/d) t0 t1 0 3 0 500 6 1000 3000 2892 t2 2778 t3 9 1500 2660 t4 12 2000 2538 The values can now be plotted to determine permeability and skin, since the equation a straight line with slope m and intercept m
provided: is . The plot is shown below, with the best fit equation Case Study 4 ‐ Multi‐Rate Well Test ‐ Assumed IAR
0.22 Γn 0.215
0.21 Series1 0.205 Linear (Series1) 0.2 y = 0.0431x + 0.1952
R² = 0.9974 0.195
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Ψn 3 The best fit straight line equation is: Therefore to find permeability: 4 And to find skin: The value of skin is negative, indicating stimulation (increased permeability) in the near wellbore region. 5...
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- Spring '12