Oil and gas reservoirs of low porosity and permeability will usually require drilling horizontal wells and conducting optimal hydraulic-fracturing treatments to attain commercial productivity. High production rates and long-term production sustainability are achieved by optimizing well placement (from setting well landing points and overall trajectory plans to reaching total depth), customizing completions design to fit reservoir and production conditions, and improving hydraulic fracturing to boost reservoir contact and flow capacity. Reservoirs of moderate to relatively higher permeability might also require high-rate matrix acidizing to clean up the near-wellbore region and connect the well to the reservoir.
Significant improvements to completions design and manufacturing have been made recently to accommodate long laterals and multiple fracturing or acidizing stages for different reservoir types, lithologies, and conditions. One such openhole completion is the controlled-injection and even-distribution ball-actuated limited-entry system where a long portion of the reservoir can be effectively isolated in one interval with hydraulically set mechanical packers. Multiple sleeves placed at intervals facing zones of interest are activated for stimulation with a single ball dropped from the surface. These multiple sleeves can be separated further by zonal-isolation packers to enhance stimulation efficacy through each sleeve.
One major challenge of multistage systems is to ensure that all stages are stimulated effectively. Surface pressure readings while pumping the job are necessary but not sufficient by themselves because they cannot always capture the subtle intricacy of fracturing-port openings because of many other pressure-change-related events occurring simultaneously. Newly initiated high-resolution acoustic-related measurements have been introduced and used that are compatible in openhole and cemented applications, effectively capturing sleeve opening and closing even in the absence of a pressure signature. A set of sensors placed on the wellhead measures acoustic events in real time.
At the stimulation-fluids front, a new single-phase retarded-acid system for high-temperature reservoirs has been developed and used for deeper penetration of live acid. The system has a low friction pressure, enabling higher pump rates, and does not require diesel as is needed for emulsified acid. The acid system is also used with engineered diversion mechanisms that are biodegradable and available in variable sizes, where the bigger blends are intercepted at the entrance of the fracture while small particles reduce permeability to create temporary isolation. The purpose of the diverters is to distribute fluids into several open intervals in a uniform fashion to create even stimulation treatment and simultaneously improve acid penetration. The diverters are held together with fibers that ensure the integrity of the blend during pumping and enhance the bridging effect.
Energized fracturing fluids with liquid carbon dioxide in different foam qualities also are proving successful in low-pressure, partially depleted areas, enhancing flowback and cleanup of the well and saving water. Many new technologies are evolving, upcoming, being tested, and being implemented in the completions-and-hydraulic-fracturing sector.
This Month's Technical Papers
Fracturing Volcanic Rock in India: Continuous Improvements Over 11 Years
Well-Placement Timing, Conductivity Loss Affect Production in Multiple-Fracture Wells
Pillar Fracturing a Sandstone Reservoir Shows Benefit Over Conventional Fracturing
Recommended Additional Reading
SPE 178963 Effect of Microproppant on Production in the SCOOP Woodford Shale: A Case History by James Calvin, Halliburton, et al.
SPE 183725 Optimizing Well Potential—Technologies That Affect Hydraulic-Fracturing Efficiency by Zillur Rahim, Saudi Aramco, et al.
SPE 187451 Proppants—What 30 Years of Study Has Taught Us by R.J. Duenckel, Stim-Lab, et al.
