New formula for acid fracturing in low permeability gas reservoirs: Experimental study and field application

One of the main stimulation techniques to enhance gas production in low permeability reservoirs is acid fracturing. Controlling the leak-off of reactive fluids is the key to a successful acid fracturing. In this study, new chemicals and techniques have been developed to control the leak-off by increasing the viscosity of the fluid systems after the acid fracturing fluids were injected into formations. The initial viscosity of the acid fluids was low. The viscosity increased with the increase in the amount of acid injected. Experiments have been conducted in laboratory to prove the efficiency of leak-off control using the new chemicals. The experimental results showed that the new fluid systems reduced the leak-off significantly compared to the gelled and normal acids. The leak-off rate of the new fluid systems was close to that of non-reactive fluids. Because the targeted reservoirs had a high temperature, the thermal stability was also tested and the results showed that the new chemical fluids were stable at 120 °C. Because of the remarkable experimental results, acid fracturing stimulations have been conducted using the new chemical fluid systems in 26 wells in Changqing gas field. The production performance has been evaluated after acid fracturing using the new chemicals. The field test results showed that the gas production was increased remarkably using the new chemical fluids and techniques, compared to the routine gelled acid fracturing. A plan has been embarked to apply the proposed techniques in Changqing gas field widely because of the satisfactory pilot field test results and the low cost of the chemicals.