Fracture stimulating horizontal wells is challenging using traditional workover methods. Running perforating guns in the horizontal well section, performing a fracture treatment, running a bridge plug, and then pulling or milling all the plugs has shown to be an extremely time consuming and expensive operation. An option using coiled tubing was proposed in China to improve on operational efficiencies.
Multiple zone completions using coiled tubing has traditionally used a straddle cup tool. This has proven effective for fracturing multiple zones in shallow environments. The drawback to this method is high pumping friction due to the small inside diameter of coiled tubing. With wells reaching ever greater depths and higher deviations, the multiple zone fracturing method using coiled tubing and straddle cup tools becomes unfeasible. A coiled tubing method using the larger area annulus was investigated and subsequently recommended for performing fracture treatments in deeper and/or horizontal wells.
The annular fracturing process involves first perforating by utilizing a coiled tubing sand jetting procedure and then pumping the fracture treatment through the coiled tubing by casing annulus. Following the fracture treatment, an ultra light weight proppant plug provides effective zonal isolation from the lower frac. The process is then repeated from the toe to the heel of the horizontal wellbore for the required number of fracture treatments. A sand cleanout at the end of the last fracture treatment removes sand isolation plugs. The method can quickly fracture stimulate a large number of sections in a horizontal wellbore with an easily removable isolation system.
Results to date have been improved well productivity and decreased workover time compared with traditional frac and plug methods in horizontal wells. A field wide case study is examined to discuss design criteria, job execution, improvements, procedures and results. As the world moves to deeper and more complex wellbore trajectories, this technique is a viable method for horizontal or deep well stimulation.