The acid fracturing techniques developed for well stimulation purposes have been applied to maximize oil production while bypassing the near wellbore damage. Commonly used acids such as hydrochloric acid (HCl) and hydrofluoric acid (HF) damage equipment, are not environmentally friendly and, most importantly, they are harmful to oil field workers. Moreover, transportation of such fluids to the well-head and neutralization of the flow-back products is costly.
The Ultra Series FF-01 is an environmentally- and equipment-friendly alternative to the commercially available products. The Ultra Series FF-01 is very acidic, its pH is less than 1, and has a slower reaction rate compared to the HCl. It can work up to 72 times longer than hydrochloric acid. Most importantly, it is biodegradable and is non-corrosive to the field equipment.
Acid conductivity measurement tests were designed to simulate acid fracturing for comparing the performance of acid fracturing fluids. The main objectives of this study is to compare the ability of Ultra Series FF-01 samples in etching the surface of carbonate rocks by measuring the conductivity of the simulated etched fracture. The two acid fracturing fluids that are used in these experiments are the Ultra series FF-01 and a conventional 15% hydrochloric acid with the iron control agent, non-emulsifier, and corrosion inhibitors. The injection rate is at 100 mL/min and the total time of injection is 1 hr. Experiments were performed on carbonate rocks at 40° C and 70° C and the leak-off pressure was set to be 100 psi lower than the overall pressure. Then the conductivity was measured at different closure stress after the injection time is complete.
Conductivity after etching by the Ultra series FF-01 was significantly improved compared to that obtained with 15% hydrochloric acid with additives when the leak off was set at 100 psi lower than the system pressure for all values of closure stress. It was very evident from the difference in the etching patterns between the two fluids. The etching pattern that was created by the Ultra series FF-01 was in the shape of human veins, visible and connected. In contrast, the surface of the core samples that were etched by 15% hydrochloric acid with additive were bouncy but shallow, producing inferior conductivity. In addition, the performance of the Ultra series FF-01 was slightly better than 15% hydrochloric acid with additives when the leak off pressure was set at 50 psi lower than the system pressure for all closure stress pressure except for 1000 psi.