Saudi Aramco Unconventional Production Engineering Division currently performs multistage propped fracturing operations using cemented plug and perf completions, to target tight gas reservoirs requiring stimulation. To improve operational efficiency, eliminate wireline intervention and coil tubing milling operations, the decision was made to test an openhole multistage fracture system (OH MSF). This came with the challenge of ensuring adequate reservoir contact, comparable to the cemented plug and perf operations, where 21 perforation clusters, in average, are targeted.
The OH MSF technology chosen consists of multiple frac ports per stage with high pressure mechanical packers to isolate each stage and slip-on oil swell packers, to isolate the individual frac port within a stage. This new method of diversion within the compartment itself helps to ensure that small variances in pressure between nozzle ports are isolated preventing the fracture operation within a stage from consolidating to a single-entry point. Like standard ball drop sleeve systems, the OH multiple entry frac sleeve system uses progressively increasing diameter balls to open each stage. One single ball will open all the ports in one stage simulating multiple clusters per stage. This allows for an increase in reservoir contact when stimulating large openhole lengths.
Case Study Well-A was completed with six multi-entry stages, three entry points per stage, and one toe stage utilizing a hydraulic port resulting in a total of seven stages and 19 frac sleeves. The isolation plan for this well consisted of mechanical packers between the main nine stages and slip-on constrictors between the individual ports within each stage. Each fracture port was engineered with three jets of 0.563 in. hole diameter as part of the limited entry design. All the fracture stages were performed as per design. The initial production response was better than offset wells completed with plug and perf technique. A production log suggests contribution from 75% of each individual jet, indicating the proper diversion was achieved. Using a seven-stage openhole system yielded to 17 effective fractures contributing to production. By utilizing OH Multiple Entry MSF system technology for limited entry fracturing, Saudi Aramco has improved reservoir productivity and operation efficiency.
This is the first time an openhole multistage fracturing system combining mechanical and constrictor swell packers has been deployed to promote limited entry diversion. This qualified and field-tested novel completion methodology ensures proper fracturing diversion between frac-ports located within the same stage. The benefits of this technology include improved reservoir contact, operation efficiency, cost reduction and placement improvement.