The evolution of expandable liners

Solid expandable liner technology involves the controlled expansion of solid-steel liners in the downhole environment for enhanced drilling, production, completion, and remedial operations. Usage of solid expandables in drilling applications of oil and gas wells has traditionally spanned drilling challenges such as covering up unstable formations due to pressure variations, isolate sections with losses or wellbore intrusions, maximising inner diameter (ID) of the liner at total depth (TD) for production optimisation.

As operators are looking to cut well costs, well designs are optimised with as few casing strings as possible to get to TD. Solid expandable liners have customarily been considered a contingency in case problems arise. The operational envelope of expandable liners has broadened over the years with the introduction of high torque eXpandable premium connections (XPC) and rotation-enabled expandable liners which allow the liners to be run in more complex scenarios and in increasingly challenging down hole applications. The expandable systems have been deployed in settings ranging from 30 – 7000 ft in length, through various wellbore configurations and in both onshore and offshore environments. The use of these expandable liners streamlines wellbore profiles, significantly cuts total development costs through the use of smaller, more cost-effective rigs, and ultimately enhances well longevity and estimated ultimate recoveries, maximising the return on investment for operators.

How expansion works

Expandable liner technology employs a cold-working process that radially expands the ID of liner. Expandable liners are made using proprietary grades and exceed API specifications. These systems feature a launcher with an expansion assembly, including a solid cone driven by hydraulic pressure, which moves upwards to radially expand the liner’s diameter. During the expansion process, the enlargement of the liner diameter causes the overall liner length to shorten from the top as a result of material balance. As the liner is expanded, its ID increases significantly, while the wall thickness decreases only slightly. This preserves the greatest post-expansion burst and collapse values possible. The process is completed when the expandable liner’s elastomer hangers seal against the original base casing or open hole wellbore, enabling precise well construction and reducing well tapering.

Expandable premium connection design features

The XPC is a semi-flush connection designed with swaged and stress-relieved pin and box ends to ensure uniform shoulder contact and robust torque transmission. XPC features a hooked thread design, that offers structural integrity and enhanced resistance to thread jump-out during running in hole and expansion operations. Additionally, the free-running tapered thread of the XPC enables it to withstand uniaxial, bending, combined loading, and high doglegs with ease. XPC connections use internal and/or external O-ring seals to provide the maximum pressure integrity before, during and after expansion. XPC connections are designed with a protective metal sleeve to prevent box connection from getting damaged during running in hole (RIH) operations.

XPC is available in a variety of sizes, including standard OCTG sizes and custom liner and casing sizes, ranging from 3 1/2 – 16 in. XPC’s feature O-ring seals, are designed to withstand pressures beyond connection yield, providing enhanced pressure-holding capabilities especially in withstanding high-pressure high-temperature (HPHT) and high deviation wells/high dogleg severity (DLS). The connection types are described in Figures 1 and 2.

Figure 1. XPC single O-Ring design.

Figure 2. XPC dual O-Ring design.

XPC Generation Hi-Torque: the XPC utilises a hooked thread form and incorporates a half dovetail groove on a flat cylindrical surface, enhancing the reliability of the O-ring during assembly and expansion. It is optimised to increase torque capacity, withstanding HPHT applications and accommodating high DLS. This design elevates the overall performance of the connection.

XPC Generation Hi-Collapse: this XPC is specifically designed to improve performance for high collapse conditions, in addition to Hi-torque, HPHT and High DLS. It is designed with an external half dovetail groove on the pin connection and optimised to use two identical O-rings, one for the pin and one for the box connection.

Expandable cone geometry effect on XPC

Standard cone: the standard cone, designed with a 10° angle, is engineered to support liner lengths exceeding 5000 ft without premature expansion during the RIH operation. It is optimised to provide overexpansion (post expanded ID slightly larger than cone OD), resulting in an improved ID for better drift post-expansion. Typically utilised in casing sizes of 6 in. and above. One of the disadvantages of the standard cone is that it exerts higher strain on the connection, resulting in noticeable spring-back in the pin nose. Radiused cone: the radius cone is designed to maintain contact with the connection as long as possible, especially below the pin nose. Through FEA, it has been demonstrated that a radiused cone effectively reduces strain on the connection, mitigating any spring-back effects on the pin nose. One drawback of a radiused cone is its tendency to under-expand by a few tenths of an inch below the cone’s diameter. This can be remedied by optimising the cone profile and adjusting its OD. A radiused cone is typically used in tubing sizes ≤ 5-1/2 in.

Figure 3. Connection expansion using a standard cone.

Figure 4. Connection expansion using a radiused cone.

Figure 5. Standard 10 Cone (right) vs dadiused cone (left) design. Both will deliver equivalent post expanded ID.

Applications and testing

As the applications for expandable premium connections continue to grow, the qualification testing for these connections is constantly being customised to meet the needs of operators. The testing of Enventure’s XPC connections follows the test programme as set out in API recommended practice API 5C5 & 5EX and consists of:

• Make and break testing.
• Pre-expansion testing.
• Expansion testing.
• Post-expansion testing load/pressure testing and limit load testing.

Make and break testing is used to determine the best make-up and break out practice for XPC, the galling sensitivity of XPC for different end finish options, the reliability of the O-rings staying intact, the torque retained in the connection for different thread compounds and the torque limits of the connection.

Pre and post-expansion testing is used to determine the limits of the connection before expansion for pure tension, pure compression, capped-end internal pressure, external pressure, and uni-axial bending. These limits are used to determine a combination of load and pressure points outlined by ISO 13679 used for pre and post-expansion combined load testing. The results of the combined load testing are used to generate the connection’s service load envelopes. The data obtained from the pre and post-expansion tests are then compared to analytical predictions which were used to determine service load envelopes for all connections.

Expansion tests are used to determine the structural soundness of the connection during expansion. Connections are expanded either mechanically or hydraulically using various cone sizes. Typically, the expansion ratios used for these tests are 20% (defined by % difference from pre-expanded ID to post expanded ID) which is greater than the most expansion ratios used commercially. Some operators may have special circumstances requesting a more robust expansion tests, such as expanding the liner and connection under fixed-fixed and fixed-free conditions through varying degrees of dogleg. Recent shifts in the economics of oil and gas production have driven operators to focus more attention on enhanced production techniques. Operators today are more commonly performing refracturing procedures to improve the return of investments of older wells. Re-fracking involves re-entering a well that has already been fracked and then deploying various methods to stimulate existing perforations, or isolate old perforations and then create new perforations. One common approach is mechanical isolation, whereby a new liner, or series of packers, is installed inside the previously fracked liner to isolate the existing perforations. New perforations can then be placed and staged for new re-fracking operations.

The use of solid expandable liners is more optimal for this type of isolation as the increased ID reduces the pressure loss when pumping and allows more power to be delivered into the reservoir during the re-fracturing operation. During an expandable liner isolation, the XPC are subjected to residual forces from expansion, ballooning forces due to frac pressure and tension forces due to piston forces and thermal cooling while fracking. In some applications, such as high reservoir temperatures (300+°F) high treatment pressures (12 000 psi) and high pumping rates (100 bbls/min.), careful consideration must me made the XPC design to prevent the sum of these forces exceeding the limitations of an expandable connection.

Considering the demanding conditions, a comprehensive testing programme was developed to evaluate XPC connections. The post expanded connections underwent testing, enduring a total of 120 frac cycles at combined loading (internal pressure + tension load) including connection yield and ultimate tensile loads to replicate the conditions experienced during fracking and re-fracking operations downhole. A total of three samples were tested and impressively, the XPC connections withstood all 120 cycles, with pipe body burst occurring only upon reaching failure, while the connection remained intact throughout testing on all 3 samples. Figure 6 depicts the 120 cyclic test results. Figure 7 illustrates the connection service load envelope (SLE) in quadrant 1 and the respective failure load points of the three samples. Figure 8 provides a pictorial representation of the pre and post-test samples.

Figure 6. Cyclic testing results.

Figure 7. Connection service load envelope and sample failure points (red dots).

Figure 8. Connection service pre and post cyclic test.

XPC Inspection (QA/QC)

XPC connections require meticulous attention and should undergo special end area (SEA) inspection on all machined surfaces to ensure quality and reliability. 100%-dimensional inspection of every feature of every single pin and box connection of all liners in inventory. Then, before the make-up on the rig floor, all threads are submitted to visual inspection. Liner should be on a rack allowing enough space for 360° revolution for inspection to assure that each connection is:

• Well cleaned.
• Free from rust due to a long and/or incorrect storage.
• Free from handling damage.
• Free from longitudinal cuts and scratches in the seal area.
• Free from burrs or wear.

Minor anomalies on thread and torque shoulder surfaces can sometimes be field repaired. Damage to seal surfaces, other than mild oxidation, is cause for rejection. After repairing, threads must be re-cleaned and dried. Exposed seal surfaces, such as pin nose areas, are particularly susceptible to handling damage. Special care is taken in inspection of these areas for dings, dents, and/or mashed ends.

Conclusion

The introduction of eXpandable premium connections (XPC) marks an advancement in solid expandable liner technology, revolutionising well construction, production, and intervention operations in the oil and gas industry. With reliability, versatility, and performance, XPC connections offer robust solutions to complex drilling challenges, including high-pressure, high-temperature, and high dogleg severity environments. Their larger inner diameter facilitates increased production rates and enables efficient refracturing procedures, enhancing the return on investment of older wells. Rigorous testing and meticulous inspection protocols ensure the quality and reliability of XPC connections, safeguarding well integrity and operational efficiency. As operators strive to optimise performance and maximise profitability, XPC connections stand as assets, driving innovation and efficiency in the exploration and production of oil and gas resources.

 

 

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