The need to estimate an apparent skin factor, which is usually not known, is the biggest limitation of this method. Pressure buildup tests run in other wells in the same reservoir often provide a good estimate of typical skin factors. Low permeability wells are generally broken down and balled out after completion and prior to testing; in these wells, a skin factor of –1 to –2 is often a reasonable assumption. If a well has been damaged by [[drilling fluid]]s and the perforations have not been broken down, a skin factor of +2 to +5 (or more) is appropriate (see [[Fundamentals of fluid flow]]). | The need to estimate an apparent skin factor, which is usually not known, is the biggest limitation of this method. Pressure buildup tests run in other wells in the same reservoir often provide a good estimate of typical skin factors. Low permeability wells are generally broken down and balled out after completion and prior to testing; in these wells, a skin factor of –1 to –2 is often a reasonable assumption. If a well has been damaged by [[drilling fluid]]s and the perforations have not been broken down, a skin factor of +2 to +5 (or more) is appropriate (see [[Fundamentals of fluid flow]]). |