Dalan and Kangan formations are the most important host gas reservoirs in Iran. These geological formations are extended to other regions, and they are famous as Khuff formation in the Middle East. They are mainly composed of limestone and dolomite with some inter-beds of shale. So far many reservoirs in Iran are hosted by Asmari carbonate formation. However, acidizing in other hydrocarbon formations (Asmari formation) is accomplished similarly. Conventional acidizing operations were performed on Dalan and Kangan formations in one of the gas fields in south of Iran. Substantial reduction of produced gas was observed over a short period of time. For this reason a comprehensive engineering geological site investigation was accomplished to explain the symptoms and avoid possible further deterioration. Connate water samples from the well while production, showed some unexpected results. Different chokes were tested to see if the amount of impurities in the sample would change. To reduce the amount of water accompanied with produced gas, a different choke was selected; but the result was not satisfactory enough based on refinery report.

Therefore, the geological features of the well were gathered based on well sketch and logging data. The phase equilibrium of the reservoir rock before and after acidizing was simulated using a software. The results of chemical lab were analyzed to check the kind of the salts in the well. Laboratory chemical experiments were accomplished to explore produced salts in the well. Further investigation revealed that the choke size was not suitable, and inappropriate acidizing could deteriorate the situation. Based on this research, a number of recommendations were suggested to improve the circumstances of production rate. The authors suggested more carefully designed techniques of acidizing to be applied. The results of this research may be used to prevent geomechanical destabilization around the wellbore in similar cases.

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