Blasingame (log-log)

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These questions apply to Blasingame (log-log):

Does the normalized rate continuously decline?

  • The log-log plot of normalized rate (q/App) versus material balance time (Gp/q) should have a declining trend.
  • A step change in rate will cause a sudden deviation from the declining trend, but if the data is consistent, it will revert to the original declining trend.

Reasons for inconsistencies:

  • An increasing trend indicates non-reservoir effects, such as near wellbore cleanup, improving skin, wellbore liquid unloading (if pressures have been calculated from wellhead data).

Does the Blasingame plot have a single continuous stem?

  • Changes in rate or pressure are accounted for in the Blasingame plot, and should not cause it to develop multiple stems.
  • In the case of multiple stems, the stem that represents the correct reservoir model should be used for analysis.

Reasons for inconsistencies:

  • The reservoir model has changed (e.g., workover, recompletion, refrac, etc.).
  • The wellhead pressures measurement location may have changed (tubing, casing, before / after valve), or there may have been a change of flow path or tubulars.

Are outliers being misinterpreted as boundary-dominated flow?

  • Outliers often appear on a unit slope on the Blasingame plot. This can lead to an incorrect diagnosis of reservoir depletion or boundary-dominated flow (BDF).

Reasons for inconsistencies:

  • Outliers have been included in the analyses. Apply the median filter to remove the outliers.