Research and Application of Large Scale Multi-stage Fracturing Technology for Vertical Wells in Low Permeability Complex Fault Block Oilfield

In view of the unsatisfactory stimulation effect of the conventional fracturing technology in low-permeability complex fault block reservoirs, the exploratory large scale multi-stage fracturing pilot test with large displacement has been carried out to achieve the obvious stimulation effect and realize the breakthrough of oil production in single well. However, some problems of the conventional fracturing string, such as serious tool abrasion, frac string broken accident and heavy lifting workload after fracturing, were exposed during the frac operation with large displacement and large sand loading volume. The causes of the above problems were analyzed. The optimized design of core tools such as HPHT Y344 packer, pressure transmitting sand blaster with large-scale & wear-resistant function and hydraulic hold-down button with large inner diameter were verified by the test method. Meanwhile, the reasonable matching of choke diameter with operation displacement and scale was studied in depth. Three kinds of large scale multi-stage fracturing technologies, namely, fracturing the lower interval, dual-packer fracturing the target payzones by pulling up the string stage by stage and multi-stage fracturing without moving strings, have been developed, which meet the requirement of large-scale fracturing technology in vertical wells with flowback circulation rate of 8 m3/min, sand loading volume of 240 m3 rated up to differential pressure of 80 MPa at 150 °C. The technologies have been applied to 156 wells with favorable frac stimulation effect, which provide the vital reference to further enhance the operation displacement and scale of other fracturing technologies and indicate a step up for improving the technical adaptability and performance.