This paper presents an overview of the stimulation treatments performed on the Codell Sandstone Formation in the Denver-Julesburg (D-J) Basin northeast of Denver, Colorado. The Codell Formation, a recently-targeted oil and gas zone, provides a basis for much speculation and a variety of treatment designs.
Due to a high percentage of clays and an intense natural fractured network, considerable formation damage is encountered through conventional drilling operations. The Codell Sandstone will not economically produce without a stimulation treatment to bypass the damaged zone. Hydraulic fracturing is the best method to date to stimulate this formation.
Treatment fluids used on the Codell Sandstone are classified into two categories: aqueous and non-aqueous based fluids. The majority of field treatments producing the most satisfactory results thus far are the aqueous based fluids consisting of a gelling agent mixed in a potassium chloride (KCl) base. Sand concentrations as high as eight pounds of proppant per gallon of fluid have been hydraulically pumped into this low permeability formation with mixed results.
Recently, non-aqueous based fluids utilizing hydrocarbons or methanol as a treatment fluid base in either a gelled or foamed state have experienced some degree of popularity with some operators in the D-J Basin. This particular type of treatment is considered to be experimental with results currently indicating research is still needed before more extensive application is widely advocated.
Case histories on producing offset wells are presented.