Optimization of acid injection rate in high rate acidizing to enhance the production rate: An experimental study in Abteymour oil field, Iran

Abstract Matrix acidizing in which the injection pressure is maintained lower than fracturing limits of the formation, has long been known as a remedial stimulation technique to restore the well productivity. It is a must to determine the acidizing parameters such as injection rate and volume in a systematic way in order to achieve an optimum-efficient condition. Also, it is well known that low injection rates result in surface dissolution whereas high rates will create ramified wormholes. A single, dominant wormhole will be formed at an optimum intermediate rate. In this study, a series of low to high rate acid injection tests have been conducted on Abteymour oil field core samples at reservoir conditions. The experimental data was used to construct the acid efficiency curve from which the optimum injection rate can be determined. Then, the optimum injection rate up scaled from the core-scale to the field condition. Experimental data and CT scanning analysis show that the best wormholing efficiency was obtained at relatively high injection rates compared to other Iranian oil and gas fields. Also, the relationship between pore volumes to breakthrough and injection rate was found to be a polynomial function of order three rather than two.