Investigating the Effect of an Emulsified Acid Retarder on Bangestan Carbonate Rock

Acidizing is one of the methods used for the stimulation of carbonate reservoirs to improve oil production. Hydrochloric acid (HCl) is the most common acid for acidizing these reservoirs. Since fast reaction of this acid with calcite components of carbonate formations damages them, the effect of HCl should be retarded by acid retarders. This gives the acid the ability to penetrate more deeply into the formation, which will enhance well performance. In this research, a Bangestan core was taken from south of Iran and an evaluation system was designed based on the weight loss of rock samples. Experiments were carried out under dynamic conditions at 25 and 58°C using a commercial and a designed acid retarder in the presence of 15 and 28 wt% HCl emulsified acid respectively, and the effect of acid concentration and temperature were investigated. The results show that increasing temperature inversely affects the retarding characteristics of the above two retarders. The high dissolution of rock samples (14.5-16.5%) in 28% HCl emulsified acid shows that such a concentration as well as higher ones is a critical condition for carbonate reservoirs and damage them. Comparison of the amounts of rocks weight loss also shows that 15% HCl is normally preferred over 28% HCl in matrix acidizing of carbonate reservoirs.