NEW METHOD DETERMINES WELL BORE DAMAGE

I.M. Kutasov MultiSpectrum Technologies Santa Monica, Calif. A new, simple method has been developed for determining a well's skin factor for wells producing against constant bottom hole pressure. The flowing time and cumulative production are the only, two variables required.
Jan. 3, 1994
2 min read
I.M. Kutasov
MultiSpectrum Technologies
Santa Monica, Calif.

A new, simple method has been developed for determining a well's skin factor for wells producing against constant bottom hole pressure. The flowing time and cumulative production are the only, two variables required.

The effective well bore radius concept can be used for wells producing against a constant pressure from an infinite acting reservoir.1 In this case, the cumulative produced volume, Q, in oil field units is defined by Equation 1.2 Dimensionless cumulative production, QD, may be estimated from Equation 2. Equation 3 is derived from Equation 2 for damaged wells with tD 200.

Equation 4 is obtained by substituting QD, TD, and rwa into Equation 1.

Table 1 shows data from an oil well test. Dimensionless cumulative produced volumes, QD = f(TD), were obtained from the paper by Van Everdingen and Hurst.4 A skin factor of 1.50 is assumed first.

Other parameters are:

  • B = 1.08 bbl/st tk bbl

  • rw = 0.33 ft

  • h = 41.6 ft

  • k = 20 md

  • Pi = 2,500 psi

  • Pwf = 2,000 psi

  • 0/ = 0.10

  • u = 1.0 cp

  • c = 19.455 X 10 6 1/psi.

From these parameters A and C are calculated as 115.1 and 5.06, respectively. The calculated skin values tabulated in Table 1, all agree well with the assumed value of 1.50.

For reservoirs where the pressure distribution around the well bore is not constant before the test, Slider's method for analyzing transient test should be used.5 In this case the corrected value of initial reservoir pressure (Pi) is used in Equations 1 and 4. To calculate the skin factor, the shut in pressure just before starting the test rather than Pi is usually used.

REFERENCES

  1. Uraiet, A.A., and Raghavan, R., "Unsteady Flow to a Well Producing at Constant Pressure," JPT, October 1980, pp. 1803 12.

  2. Lee, J., Well Testing, SPE Monograph Series, 1982.

  3. Edwardson, M.J., Girner, H.M., Parkinson, H.R., Williams, C.D., and Matthews, C.S., "Calculation of Formation Temperature Disturbances Caused by Mud Circulation," JPT, April 1962, pp. 416 26.

  4. Van Everdingen, A.F., and Hurst, W., "The Application of the Laplace Transformation to flow Problems in Reservoirs," AIME Transactions, Vol. 186, 1949, pp, 305 24.

  5. Earlougher, R.C., Jr., Advances in Well Test Analysis, SPE Monograph Series, 1977.

Copyright 1994 Oil & Gas Journal. All Rights Reserved.

Sign up for Oil & Gas Journal Newsletters