in the wellbore so as to isolate lower permeability zone or interval 20 from those above once the pre pad has conditioned and cooled moderate permeability interval 18 and high permeability interval 16 a pad of a viscous gel is injected into moderate and high permeability zones so as to effectively make them resistive to fluid flow from the wellbore if desired the viscous gel may contain a gel breaker if it is desired to open moderate and high permeability intervals to fluid flow after acidizing the lower permeability zone or interval the size of the viscous gel utilized may be determined from surveys of intervals or by use of a spinner survey for example to determine their permeabilities also core samples obtained during the drilling of the wellbore may be utilized the viscous gel that is injected into the intervals is injected at rates greater than 5 bpm while monitoring surface pressures as used herein the purpose of the viscous gel pad is to equalize a subsequent injection of acid into these intervals the injection rate of the pad is such as to hold an existing fracture or a created fracture open although it is not essential to the practice of this invention a fracture may be created during the injection of the pad into the formation after the pad of viscous gel has been injected in an amount sufficient to equalize a subsequent injection of acid and hold the fracture open acid is then injected into the formation by holding the fracture open acid injected at a rate greater than 5 bpm is allowed to contact and circulate around clay damage in the formation and thereby remove it.