Openhole expandable liner systems prevent loss of hole size in sidetracking operations.

The evolution of solid expandable tubular systems is reflected in technical enhancements and broadening use. The basic principle of solid expandable tubular technology is cold-drawing steel tubulars to the required size downhole. After the liner assembly is run in the hole, a dart is pumped through the drillpipe until it seats in the shoe of the assembly. Seating of the dart provides a pressure seal and enables the pipe to be expanded hydraulically or mechanically. An expansion cone mechanically deforms the pipe permanently. The cone moves through the tubular by a differential hydraulic pressure across the cone itself and/or by a direct mechanical pull or push force. The progress of the cone through the tubular deforms the steel past its elastic yield limit into its plastic deformation region, stopping short of its ultimate yield strength.
Solid expandable tubulars have been modified for corrosive well installation and introduced into deviated and horizontal wells.They have proven to be an advantageous asset when coupled with surface stack technology. In addition to applications that display the system's versatility, its adaptability was demonstrated with the successful expansion of solid tubulars through window exits and milled sections.
Conventional tubulars and tools used in sidetrack operations, executed either for corrective measures or for recompletion, result in the loss of an entire casing size. The loss of internal diameter (ID) in the production zone restricts the potential oil flow and decreases the well's economic viability. To mitigate the reduction of ID, a procedure was developed to expand casing off a whipstock through a window exit to deliver an optimized ID (Figure 1).
An expandable openhole liner system provided hole optimization and a cost-effective method to reactivate an offshore field from older platforms with no remaining template slots. Recompleting a deepwater well from a tension-leg platform through a riser was achieved by running an expandable system through a milled-casing window using a smaller production riser. Running this enabling technology through a whipstock window allows operators to use existing facilities
while still maintaining a larger ID for recompletion and stimulation.
This solution provides the means for turning a tubing-constrained completion into a big-bore
producer (Figure 2), whether the result of a re-entry or a new drill.
Operative conditions for sidetracking
The initial installations of solid expandable tubulars primarily consisted of casing remediation in vertical wells. Subsequent applications of the technology revealed its expansive functionality in a myriad of conditions and circumstances.
Each successful installation of solid expandable tubulars to retain hole size inevitably led to the conceptual consideration of using the systems in conjunction with whipstock technology. Developing a process to apply the technology in sidetracking operations required identifying
criteria that directly affect or have significant bearing on the equipment and conditions. Considerations identified included:
• Dogleg severity across the whipstock face and the openhole interval drilled past the whipstock window;
• Base casing size and connection;
• Type and size of whipstock;
• Length and configuration of the whipstock window;
• Quality of milled window; and
• Stiffness of the expansion assembly.
Running solid expandable tubulars through a whipstock window requires careful preparation. Because the configuration of the casing exit is critical for a successful application,
an additional milling run may be required to provide adequate window conditioning to finish dressing the window shape and facing and minimize damage to the system (Figure 3).
Equipment providers have whipstocks with extended blade lengths that reduce the dogleg severity at the whipstock window. The edges of the window should be smooth to minimize gouging on the outside of the solid expandable casing. A well plan with lower dogleg severity allows for easier expansion and less stress on the threaded connections of the expandable pipe. The process of identifying the criteria, formulating a process and successfully implementing expansion has contributed to the reliability of this technology and led to increased operator acceptance. Currently, 14 solid expandable tubular systems have been installed in sidetrack operations and three through milled sections.
Case history 1
A major operator in the Gulf of Mexico installed a 95/8-in. by 117/8-in. openhole liner system to isolate low-pressure zones below an 117/8-in. window at around 11,500 ft (3,507.5 m). A 105/8-in. by 12-in. bi-center bit was used to drill through depleted sand and prepare the window for the expansion system. After pulling through the window, subsequent trips back through the window showed little or no drag. The expandable liner system, about 3,000 ft (915 m) and consisting of 75 joints of pipe, was run in the hole. Using a tapered guide, the solid expandable liner started in the hole. As the launcher (at the bottom of the liner) went through the whipstock window in the 117/8-in. liner, no additional drag was recorded. There were no obstructions as the liner was run to bottom. A pickup weight of 495,000 lbs and slackoff weight of 350,000 lbs was recorded just off the bottom.
After cementing, the top drive was screwed in and displacement of the dart began. The dart was seated with 6 bbl/min and 1,800 psi. The pressure was held for about 1 minute and then released. Expansion was initiated with around 2,500 psi and proceeded smoothly. Stand number 31 marked the first stand expanded through the window. Expansion pressures ranged from 1,800 psi to 2,200 psi. The liner was pressure-tested to 1,450 psi for 30 minutes.
The successful installation of this system through a window enabled the operator to isolate the low-pressure zones and reach the target without compromising hole size. The well was completed as a successful producer.
Case history 2
An operator in the Middle East required a solution in a horizontal well to isolate a zone from overlying water-bearing formations. To prevent water influx into the wellbore, about 1,350 ft (411.75 m) of 51/2-in. by 7-in. openhole liner was installed to case off the angle-build section of this well.
A window was cut in the 7-in. liner, and an additional 15 ft (4.6 m) of new hole was drilled to prepare the hole for installation. A steerable assembly was run and kicked off the 8°/100 ft build section with a 6-in. by 7-in. bi-center bit. A near-bit reamer completed opening the 7-in. hole to about 7,400 ft (2,257 m). Two stacked string mills on a cleanout/dummy drift assembly were run in the hole and worked through the window until no torque was noted.
After making up the inner string to the expansion assembly, the solid expandable system was run in the hole on 31/2-in. drillpipe to about 7,400 ft. The running sequence for the openhole system consisted of the launcher with a 6 ft (18 m) pup joint,
32 joints of expandable pipe, an anchor hanger and a tapered guide. Once the expandable openhole liner was in position, the dart was dropped and was seated with 500 psi above the final circulating pressure. Expansion was initiated with 5,200 psi. The average expansion pressure measured 4,200 psi with about 4,600 psi expansion pressure through the connections and also through the elastomer sections of the anchor hanger.
The expandable liner was installed by expanding in the open hole across the 8 ft (24 m) window of the whipstock and finally anchoring in the 7-in. liner. The top of the liner was then successfully pressure-tested to 2,000 psi for 30 minutes. Following the liner installation, the shoe of the liner was drilled out, and the three laterals that had been drilled in the open hole past the end of the liner were opened for production.
Value proposition
Reaching a lower horizon with expandables through a sidetrack eliminates an extra string of pipe coming out of a window. Successfully expanding solid tubulars in sidetrack operations opens up the possibility of exploiting the resources of an entire field with fewer wells. These systems and the expansion process contribute value-added technology to drilling operations to the extent that they:
• Reduce well Authority for Expenditure cost by optimizing the rate of penetration (ROP). The ROP increases because expandables provide the ability to drill with larger, stronger, more competent drillpipe and accessories (bits, motors, measurements while drilling, etc.).
• Maximize reservoir potential by
- Ensuring target total depth is reached in optimal hole size for evaluation and testing or production.
- Accessing deeper reservoirs that are unreachable economically with other available technology.
• Maximize rate of investment via leveraging capitalized assets and infrastructure by preserving hole size in sidetracking programs and through milled sections.
Conclusion
The use of a whipstock to bypass obstacles or unstable formations creates a potential hole loss situation or well plan detour. The window exit capabilities of solid expandable tubular technology provide several benefits to the drilling process that include:
• The elimination of the need to cut and pull casing and re-drill the hole section;
• The elimination of section milling operations; and
• The ability to stay closer to the production zone.
For a proper window exit installation and expansion, certain tool configurations must be factored into the process. The main issues regarding tool configuration include the dogleg severity of the whipstock, the condition of the window and the absence of debris near the window. In most applications, an extended-length whipstock tool will provide an acceptable dogleg severity. An additional milling run may be required to provide adequate window conditioning to minimize damage to the solid expandable system.