A Laboratory Investigation on the Effect of Different Acid Systems on Rock Solubility Rate of Bangestan Reservoir of Ahwaz Oil Field

In oil industry acidizing operation (matrix acidizing and acid fracturing) is performed to reduce or eliminate formation damage and increase permeability and productivity; also, acidizing is probably the most widely used work-over and stimulation practice in the oil industry. By dissolving acid-soluble components of rock formations, or removing material at the wellbore face, the rate of flow of oil or gas out of production wells or the rate of flow of oil-displacing fluids into injection wells may be increased. In this study, some laboratory work with different acid types was conducted on the carbonate rock samples of the Bangestan reservoir of Ahvaz oil field to find out the amount of the solubility of the carbonate rock samples in the acids. The effects of acid type, acid strength, and temperature on rock solubility were investigated. For this study, different acids such as HCl, acetic acid, hybrid acid, and emulsion acid at three different temperatures of 25 °C, 60 °C and 100 °C were used. The main goal of this study is to find out the optimum acid spot time at the formation to achieve the most productivity of the well without any formation damage creation and at the same time to select the most effective acid system for carbonate layer stimulation. The results show that 28% HCl acid has the most dissolving power between the tested acids in the experiments. In addition, the temperature has a direct effect on the solubility of the rocks in acids; i.e., the higher the temperature is the higher the solubility is. The laboratory results showed that the time needed for dissolving about 50% of Bangestan reservoir rock at 100 °C is 700, 25, and 30 minutes for organic acid (10% acetic acid), hybrid acid of 50:50 ratio of 10% acetic acid and 15% HCl, and hybrid acid of 80:20 ratio of 10% acetic acid and 15% HCl respectively. It is also found out that the hybrid acid system of 50:50 ratio of 10% acetic acid and 15% HCl has an effective role in dissolving formation core at high temperatures.