A new oil soluble resin mixture has proved extremely effective as a diverting agent for matrix acidizing treatments. The mixture has three major advantages which make it a more effective diverter than other agents currently in use:
1. It effectively equalizes flow into zones of varying permeability.
2. It is completely oil soluble and leaves no residual formation damage.
3. It can penetrate a gravel pack and divert in the formation behind the pack. It is the only diverter which is effective for this application at temperatures above 125degrees F.
One of the major factors controlling the success or failure of any sandstone matrix acidizing treatment is that of proper distribution of the treating acid over the entire producing interval. Unless an effective diverting agent is used, the largest portion of the acid may be expended on only a small part of the total zone.
A study was made of the various diverting agents presently used in matrix acidizing. These diverters were evaluated in terms of (1) their ability to equalize acid flow into zones of varying permeability, and (2) clean-up following the treatment without residual formation damage. Diverters evaluated included viscous gels, natural gums, emulsions, acid swellable polymers, solid organic acids and a new system employing a mixture of finely divided oil-soluble solids.
Of the materials tested, some were found to be totally ineffective while others produced extensive formation damage. Best diversion was obtained with the swellable polymers or the mixture of oil soluble resins.
This paper presents data comparing effectiveness of various matrix diverters. The diversion mechanism of the oil soluble resins is described and case histories are presented to show how better diversion improves production increases.
In recent years, renewed interest has been shown in the use of hydrochloric-hydrofluoric acid mixtures for the matrix treatment of sandstone formations.