The clay filled low permeability sandstone of the Codell formation of Colorado has historically been a difficult formation to stimulate. In the past, conventional methods of stimulation have been used in the Codell sandstone with results below expectations.

Codell sandstone core samples were taken from several wells in the Denver-Julesberg Basin of Colorado, over a three county area, and were from various depths of approximately 1554.50m (5100 ft.) to 2438.40m (8000 ft.)

The object of this paper is to characterize the Codell sandstone cores by use of Scanning Electron Microscopy and Energy Dispersive Spectrometry (SEM/EDS) to evaluate the mineralogy and lithology of the formation. The samples were then subjected to experimental and conventional treatment fluids by use of a Gas/Liquid Reference Core Flow Apparatus to determine the least damaging stimulation treatment.

Treatment fluids evaluated in this study were: 100% methanol, low pH methanol with specific additives, KCl water/methanol blends, KCl water and various weak acid blends. One of the low pH methanol systems described in this paper has shown positive gains in permeability during core flow testing and can be an effective enhancement of conventional water based systems used for stimulating other low permeability reservoirs. The most effective method of application of such a system has been as a prepad ahead of conventional water base treatments.

The concept of low pH (4.0) methanol combined with a special silt suspension and clay control chemical additives is suspected to partially dissolve and/or reduce the size of the various clay components in the immediate wellbore vicinity where maximum leak-off/spurt-loss damage usually occurs.

Case histories from treatments done in the DJ Basin will be discussed and evaluated.

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