Over the last 10 years, the number of horizontal wells completed with lateral lengths exceeding 3,000 m (or 10,000 ft) in unconventional plays across North America has grown significantly—and longer laterals mean more stages. This combination has pushed the development of improved drilling and completion techniques. Operators are consistently pumping stimulation treatments with higher fluid volumes at higher rates, with higher proppant loads and tighter stage spacing.
Operators choose open-hole ball drop systems, because they can offer higher production rates and quicker frac stimulations while using less water. While these improved completion programs have contributed to better operational efficiency and higher production, these items come at greater risk.
Longer laterals and more stages mean higher pressure, more sand and multiple pressure cycles. High frac rates and large tonnage can cause erosion, while multiple high-pressure cycles can cause liner or tool failures, resulting in expensive remedial solutions, lower production, or potentially both. This impact can be seen in both plug-and-perf completions and ball-activated sliding sleeve systems.
In plug-and-perf completions, proppant eroding and enlarging perforations cause the first cluster to accept most of the fluid, while others in the same interval receive minimal or no treatment. This inefficient use of proppant leads to lower-than-expected production and lower return on investment.
In ball-activated sliding sleeve systems, the turbulence of fluid flow through a ball seat causes a slight pressure increase. This is inconsequential for one seat, but a completion string of 50 or more sliding sleeves can add thousands of pounds of pressure in additional friction, which is a source of operational concern.
Advanced completion technology. Fortunately, Packers Plus ball-activated sliding sleeves were re-engineered to overcome these challenges. StackFRAC HD-X builds on revolutionary ball-activated completion technology that has been used in more than 250,000 stages worldwide, Fig. 1. The latest evolution of the system was developed, using computational fluid dynamics simulation to reshape the internal fluid path, reducing pressure drop (and thus fluid friction) by over 60%. This step change in design enables the successful deployment of ball seat increments as small as 1/64-in. and the ability to run open-hole ball drop systems with more than 100 stages.
Fig. 1. The StackFRAC HD-X multi-stage completion system provides high-intensity stimulation in unconventional tight oil and gas formations. An advanced seat and port activation design, along with anti-erosion coating, enables smaller ball and seat increments to be used for increased stage count
In addition to increasing the number of stages in long laterals, the smaller ball seat increments of StackFRAC HD-X provide a larger inside diameter (ID) throughout the length of the wellbore to allow for:
- Higher stimulation rates
- Better coil tubing access
- Prevention of production blockages.
Critically, the smaller increments are protected against erosion during stimulation, using Inner Armor erosion coating (Fig. 2) on select ball seats in the completion system. With this added protection, producers can deliver a high tonnage per stage while maintaining the integrity of the downhole equipment. While The StackFRAC HD-X system has allowed operators to achieve their stimulation goals, other challenges drilling and completing long laterals still persist.
Fig. 2. Inner Armor erosion coating ensures completion equipment integrity during high-rate/tonnage stimulation
Every phase of well development can take longer to complete with extended-reach laterals and higher stage counts, including system installation and well clean-up post-stimulation. Finding ways to reduce time spent on any phase of operation and improving efficiency becomes important in controlling overall well costs. Packers Plus has introduced multiple solutions to complement the StackFRAC HD-X ball-activated completion system to improve operational efficiency and system reliability. These key technologies are listed below:
Installation
- STAT floatation subs (drill pipe or casing)
- Hydraulic-Set StackFRAC liner hanger packer (single trip)
- StackFRAC liner hanger packer with annular release running tool
- StackFRAC liner hanger packer with torque lock running tool for liner rotation
- Stage tools equipped with built-in casing patches.
Stimulation
- ePLUS Retina well monitoring system.
Post-stimulation
- Ports can be milled out
- Closable ports available for production control.
Reliability
- Automated assembly and pressure testing ensures every tool is assembled properly.
The weight of the longer tool string creates increased drag during installation, requiring more weight to reach total depth (TD) and risk of damaging downhole tools during installation. The AeroSTAT glass floatation sub is designed to improve operations for completion system installation by facilitating casing flotation to planned depth, Fig. 3. A glass disc in the sub acts as a barrier that isolates fluid weight above the sub and creates an air chamber that lightens the completion string in the lateral, enabling the system to float as it is run in hole.
Fig. 3. The AeroSTAT glass barrier sub improves operations for completion system installation by facilitating casing flotation to planned depth. A glass disc in the sub acts as a barrier that isolates fluid weight above the sub and creates an air chamber that lightens the completion string in the lateral, enabling the system to float as it is run in hole.
Liner hangers and stage tools. Packers Plus introduced the hydraulic-set StackFRAC liner hanger packer specifically to reduce rig time, operational risk, and cost, Fig. 4. The single trip liner hanger is installed, using a polished bore receptacle run on the tie-back casing, providing the advantage of being tied back into the completion string immediately after setting operations. The polished bore receptacle can be disconnected with a quarter turn, which is important when working at high angles.
In extreme cases, where rotation cannot be achieved, the StackFRAC liner hanger packer can be run on drill pipe with the annular release running tool. This allows the liner to be set, and drill pipe can be disconnected without the need to rotate. Pipe rotation can help break friction to get a string to bottom with high torque premium casing and the torque lock running tool on the liner hanger.
Fig. 4. The hydraulic-set liner hanger packer does not require a setting tool, reducing operational time. The tool is set by applying hydraulic tubing pressure to create a mechanical setting force, causing the slips to expand and the element to extrude securing the packer in the casing.
To reduce risk, stage tools are equipped with a built-in casing patch. If a leak were to occur, the patch has shifting ability, leaving the operator with full well integrity, with no ID loss. Without this feature, if a casing patch was used, it would result in a loss in ID, making it impossible to stimulate certain stages.
Stimulation day. The Packers Plus ePLUS Retina well monitoring system is an innovative solution that verifies surface and downhole events, Fig. 5. It can shave hours (hr) off operations, as it is designed to detect multi-stage completion system operations and their effects on the reservoir. The Retina system provides a cost-effective way for operators to visualize their multi-stage completions, enabling on-the-fly operational adjustments to ensure a successful stimulation. After stimulation, ball-activated sliding sleeves give operators the flexibility to start the treatment process faster. When paired with SF903 Dissolvable Balls in the completion, they eliminate the need to flow balls back prior to production, reducing operational risk.
Fig. 5. The ePLUS Retina monitoring system verifies downhole events and completion operations independently from other measurements. The system enables operators to quickly identify problems with accurate information.
Summary. Ball-activated sleeves revolutionized well completions through continuous pumping operations to reduce completion time and improve operational efficiency. The latest design enhancements to the ball seats in the StackFRAC HD-X system, combined with Packers Plus Inner Armor erosion coating, now brings that operational efficiency to laterals with greater than 50 stages and the ability to ensure completion equipment integrity during high-rate and high tonnage stimulation.
CASE STUDIES
Reliable delivery of high stage count stimulations in long laterals has attracted several operators in different formations to deploy StackFRAC HD-X over other sliding sleeve (coil frac) systems or plug-and-perf operations.
70-stage completion in the Montney formation. By deploying the latest advancements in multi-stage completion technology, a Montney producer was able to significantly increase the length of its laterals, while maintaining optimal stage spacing to ensure full stimulation coverage across the reservoir. The company has deployed several 70-stage open-hole ball drop completion systems in laterals of more than 2,900 m. The smallest ball seat size in the system is typically 1.960-in., which enabled higher frac rates at the toe of the well and allowed for coiled tubing access for clean-out, as well as a larger ID for production flow area. Some of the key technologies deployed as part of the Montney producer’s 70-stage completion system included:
- StackFRAC HD-X with ball seat increments smaller than 1/40-in.
- Packers Plus Inner Armor erosion coating
- SF903 dissolvable balls
- AeroSTAT glass barrier sub
- SF cementor stage tools
- Dual external hydraulic: toe port with redundant sleeve.
The completion program was designed to deliver 70 tonnes of proppant per stage at 12 m3/min with fluid volumes up to 600 m.3 All 70 stages were successfully completed in a total of 58 hr and 6 min.
51-stage completion in the Montney formation. An operator working in the Montney formation ran the frac string and liner for its 51-stage open-hole ball drop completion in one run, saving cost on running drill pipe and reducing the overall cost of developing a sour gas well.
The producer installed a 51-stage StackFRAC HD-X completion system in the well that had a measured depth (MD) of more than 5,800 m and a lateral length of more than 3,000 m. The smallest ball seat size in the system was 2.125-in., which enabled higher frac rates at the toe of the well and allowed for coiled tubing access for clean-out, as well as a larger ID for production flow area. Some of the key technologies deployed as part of the Montney producer’s 51-stage completion system included:
- StackFRAC HD-X
- Packers Plus Inner Armor erosion coating
- SF903 dissolvable balls
- AeroSTAT glass floatation
- Hydraulic-Set StackFRAC liner hanger packer with polished bore receptacle.
The completion program was designed to deliver approximately 12 tonnes of proppant per stage at rates of 5.5 m3/min with fluid volumes up to 104.5 m3. Each stage of the well was successfully completed in a total of 15 hr and 14 min.
65-stage completion in the Dunvegan formation. A Dunvegan producer was able to significantly increase the length of its laterals, while maintaining optimal stage spacing to ensure full stimulation coverage across the reservoir. One of the recent wells in the company’s completion program included a 65-stage open-hole ball drop completion. The smallest ball seat size in the system was 2.026-in., which enabled higher frac rates at the toe of the well and allowed for coiled tubing access for clean-out, as well as a larger ID for production flow area. Some of the key technologies deployed as part of the Dunvegan producer’s 65-stage completion system included:
- StackFRAC HD-X
- Packers Plus Inner Armor erosion coating
- SF903 dissolvable balls
- AeroSTAT glass barrier sub
- ePLUS Retina well monitoring system.
The Retina system uses an array of sensors that collects and analyzes signals from multiple locations on the wellsite, independently from the data van. At data sampling rates of 10,000 times per second, Retina can capture events that may be missed or could be ambiguous, due to the conventional sampling rate of once per second, such as balls launching and sliding sleeves shifting open. All 65 stages were successfully completed at a rate of 10 m3/min for the entire wellbore.
40-stage completion in the Falher formation (reduced water requirement). An operator working in the Falher formation evolved their completion program, so they would stimulate during the day and flow the well back at night. Frac fluid recovered at night was then used again the next day to complete up hole stages. Their typical well includes a 40-stage open-hole ball-drop completion with measured depths greater than 5,700 m and laterals of more than 2,800 m. The smallest ball seat size in the system was 2.3-in., which enabled higher frac rates at the toe of the well and allowed for coiled tubing access for clean-out, as well as a larger ID for production flow area. Some of the key technologies deployed as part of the Falher producer’s 40-stage completion system included:
- StackFRAC HD
- Packers Plus Inner Armor erosion coating
- SF903 dissolvable balls
- ePLUS Retina well monitoring system.
The completion program was designed to deliver 50 tonnes of proppant per stage at rates of 9 - 12 m3/min with fluid volumes up to 329 m3. Stages 1-12 were completed on the first day, stages 13-33 were completed on the second day, and stages 34-40 were completed on the third day. Each stage of the well was successfully completed in a total of 17 hr and 14 min.
CONCLUSION
During the past two decades, as operators continued to develop new fields, maximize recovery, and increase stage counts and treatment sizes, completion technology has evolved continuously to meet the needs of operators.
Sliding sleeve technology helped transform the completions industry nearly two decades ago, and innovation has continued steadily throughout the years to help maximize efficiency. The latest evolution of open-hole ball-activated completion systems was developed, using computational fluid dynamics simulation to reshape the internal fluid path, reducing pressure drop (and thus fluid friction) by over 60%. This step change in design enables the successful deployment of ball seat increments smaller than 1/16-in. and the ability to run open hole ball drop systems with more than 100 stages, Fig. 6.
Fig. 6. Subsurface representation of a multiple-stage horizontal completion.
Critically, the smaller increments are protected against erosion during stimulation, using Inner Armor erosion coating on select ball seats in the completion system. With this added protection, producers can deliver high tonnage per stage while maintaining the integrity of the downhole equipment.
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About the Authors
Mike Kenyon
Packers Plus Energy Services
Mike Kenyon is regional sales manager of Canadian Operations for Packers Plus Energy Services. He has 25 years of oil and gas experience and has been involved in running and designing open-hole multi-stage systems since their inception. Over his career, Mr. Kenyon has also worked in various operational and sales roles.
