Pulsed Online Acidizing Augmented Injection to Sandstone Reservoirs

Water injection is a key technique for long and efficient development of oil. In recent years, more and more wells in some blocks of the Huaqing oilfield are faced with increasing injection pressure resulted from the physical properties of the reservoir and the quality of injected water. Presently increasing injection rate is done by acidizing, but there are several challenges for this technique, for example, the time for this technique to work effectively is short, the injection efficiency is low after many times of acidizing, the execution of the technique lasts a too long, the equipment required for executing the technique is difficult to move, and finally, the operation cost is not acceptable. In laboratory study, a lot of experiments have been done to resolve these problems based on the study on the characteristics of the reservoirs in Huaqing. It was fount that by changing the commonly used hexadentate amino carboxylic acid chelating agent to octadentate chelating agent, the ability of the chelating agent to capture, chelate and wrap metal ions is enhanced. By mixing the chelating agent and acid, a new acid suitable for acidizing job was formulated. Meanwhile, the equipment used for water injection was also improved and optimized. A long-distance operational system was added to the equipment to improve the accuracy of the operation. Using a surface pulsed piston pump, a pulsed online acidizing augmented injection technology was formed. This technology has till now been applied 4 times, water injection pressure was reduced by an average of 9.0 MPa, volume of water injected per day per well was increased by 14.0 m³, and the average time for the stimulation measure to remain effective was 182 d. Other problems previously met, such as long time of operation, difficulty in moving the equipment required etc. have all been resolved. It is worth spreading this new and easy technology in water injection job.