American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.
This paper was prepared for the Rocky Mountain Regional Meeting of the Society of Petroleum Engineers of AIME, to be held in Billings, Montana, May 15–17, 1974. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is granted upon request to the Editor of the PETROLEUM ENGINEERS JOURNAL is granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made.
Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the SPE magazines.
A highly retarded acid emulsion has proven extremely effective in the stimulation of hot limestone and dolomite formations. The level of reaction rate retardation achieved with this acid is much greater than previously possible and is obtained through use of a unique surfactant system which both emulsifies the acid and forms a chemical barrier on the surface of the rock. Acid reaction rate studies performed in the laboratory under both static and flowing conditions demonstrate its high level of retardation.
In contrast to previous emulsified acids, which depend upon high viscosity for retardation, this emulsion has a viscosity of only 30 cps, thus greatly reducing pumping pressure and allowing increased injection rate. Due to its slow reaction rate and improved pumpability, acid penetration distance is greatly increased. Comparative well results clearly demonstrate the increased effectiveness of this type retarded acid.
Most acid treatments can generally be classified as either fracture or matrix acidizing. Matrix treatments are performed at pressures below that required to produce hydraulic fracturing and have as their main purpose the removal of formation damage in the area immediately around the wellbore. Acid fracturing treatments are performed at pressures above fracturing pressures, usually at greatly increased injection rates. pressures, usually at greatly increased injection rates. These treatments are designed primarily to improve the natural flow characteristics of the well by the creation of artificial flow channels deep into the formation. In contrast to ordinary hydraulic fracturing where fracture conductivity is produced by the placement of sand or other propping agents acid fracturing achieves conductivity by propping agents acid fracturing achieves conductivity by the non-uniform etching of the fracture faces.
