Expandable technology steps to the fore in Gulf of Mexico extreme HP/HT project planning
Jay Nylund, Sarah Flaming, Kristaq Mitrushi - Enventure
Enventure’s recent record-setting installation of solid expandable tubulars in ultra deep Gulf of Mexico (GoM) waters establishes a new era for technology once contained to contingency applications. Today, expandable tubulars are increasingly seen as an opportunity to reach oil and gas resources in reservoirs of extreme depth, pressure, and temperature.
While shelf drilling continues to produce considerable reserves from deeper and more challenging environments, ventures into deep and ultra deepwater also are becoming more common. The discoveries at Keathley Canyon and Walker Ridge are examples of how the industry has evolved technically and procedurally to reach previously unattainable and unknown resources.
The range of challenges in the GoM is extensive, and includes salt and subsalt zones, narrow pore pressure/frac gradient windows, over-pressured and depleted sands, and extreme water and target depths. These complexities require a fresh look at drilling and production challenges, since increased depths require larger equipment and greater hoisting and mud-circulating capacities, implying a reduction in efficiency, reliability, and, ultimately, the economic feasibility of the project.
Consequently, oil and gas operators meet these challenges with a range of solutions such as refinement in sensing and modeling technologies, better chemistry for muds and cements, and tools such as swellable elastomers and solid expandable tubulars that can facilitate longer and more stable wellbores at extreme depths and pressures. One of the advantages of expandables is their use in very deep and complex wells – even if those wells are through existing infrastructure.
These new considerations for front-end planning have meant incorporating expandable tubulars as part of project planning.
Expandable tubing comes of age
The installation in the GoM of a 6,935 ft (2,114 m) solid expandable liner set a record and established the role of an expandable system as a key element in the project strategy. The operator had identified deep exploratory targets on 3D seismic surveys that indicated potential pay intervals below an existing field development. The existing infrastructure provided access to the deep shelf target zones by sidetracking through the 13 5/8-in. and 11 7/8-in. casing, but the subsequent 9 5/8-in. extended shoe needed an uncompromised leak-off test (LOT). To further complicate the situation, the new wellbore section had a bottomhole static temperature (BHST) of 327º F (164º C) and pore pressure of ~19,000 psi.
The planned-in approach of using solid expandable tubulars allowed the operator to incorporate a customized design and to maintain more control of the downhole environment. The design optimized elastomer technology, using swellable seals to ensure isolation of an inconsistent wellbore. In addition, the expandable system used in conjunction with the swellable elastomers eliminated wait time, enabled proper compression and attained greater sealing capability.
A 7 5/8- x 9 5/8-in. 53.5 lb/ft openhole expandable system with a pre-expansion length of 6,935 ft (~2,115 m) was installed from ~14,000 to ~21,000 ft (~4,270 to ~6,400 m) and anchored back to the 9-5/8 in. casing. The openhole liner featured an expandable shoe with swellable elastomers (to ensure a successful LOT). The liner was made-up at an average of about 16 joints per hour and run to depth. After cementing as planned, the dart was displaced, landed, and expansion was initiated. Once installed in the 8 3/4-in. hole, the liner was expanded at about 700 ft (214 m) per hour. Water-activated swellable elastomer seals rated to 360° F (182° C) were on the expandable anchor directly above the shoe and achieved immediate compression against the formation as the liner expanded. The shoe was drilled out in five hours and a successful LOT was performed with 1,189 psi at surface with 17.9 ppg mud in the well.
Planning a solid expandable system as part of the wellbore architecture optimized the use of pre-existing infrastructure, providing savings and facilitating discovery of a ~150 ft (~45 m) deep gas pay zone. The swellable solution ensured a successful LOT without a remedial shoe squeeze (a savings of some $1 million). This approach ultimately maximized the hole size for continued drilling to the target, for proper evaluation of the pay zone and for future completions.
Streamlining operations
This same operator used a similar-sized expandable system in a different GoM prospect to extend the shoe of the 9 3/8-in. casing through a window exit. In addition to extending the shoe, swellable elastomers were mounted just above the shoe on the solid expandable system. After running the system through the window to depth, the well was circulated, cement was pumped, and the dart was displaced and landed as calculated. The liner was successfully tested with 2,350 psi for 30 minutes after which the shoe of the liner was drilled out in two hours. A fully successful LOT was performed with 19 lb/gal results. As with the previous well, the operator realized savings by using swellable elastomers deployed on a solid expandable liner in lieu of a cement shoe squeeze.
Another major GoM operator realized similar benefits using solid expandable tubulars to extend the 11 3/4-in. casing shoe and cover a depleted zone. The application consisted of installing a 9 5/8- x 11 3/4-in. openhole liner in a directional well with a 2º/100 ft dogleg severity (DLS). This system included 22 joints of expandable liner banded with swellable elastomers. After reaching setting depth at more than 18,500 ft (~5,640 m), expansion was initiated. The liner was successfully pressure tested to 1,500 psi for 30 minutes. The operator maintained the planned casing points, covered the trouble zone, and streamlined operations by eliminating the cement shoe squeeze.
Cost-effective re-entry
The previous record length for a solid expandable system, also in the GoM, was installed as part of a re-entry program to sidetrack out of the 9 7/8-in. production casing at ~15,000 ft (4,570 m), and drill an 8 1/2-in. hole below ~23,000 ft (7,010 m) across depleted pay sands. During the drilling operations, higher-than-expected pore pressures (up to 15.6 ppg) were encountered at ~21,000 ft (6,400 m) and resulted in the loss of the original wellbore due to lost returns in the depleted sands. To isolate the depleted sands and to preserve hole size for the 7 in. production casing, a 7 5/8-in. x 9 5/8-in. solid expandable liner (over 6,865 ft [2,092 m]) was installed as an intermediate drilling liner for re-drill operations.
Approximately 190 joints of expandable pipe were run slowly into position to mitigate surge pressures, and had to be washed through a tight spot ~980 ft (300 m) above the final total depth in the openhole section. The dart landed as calculated and expansion was initiated. Once the liner was expanded at a rate of ~700 ft/hour (213 m/hr), it was pressure tested successfully before drilling out the float equipment. Following drillout of the shoe, the operator drilled to the targeted depth, and moved forward with production of the desired zone. Preserving hole size with the solid expandable system reduced the mechanical risks associated with a smaller completion, and prevented a significant decrease in production by completion with 5 1/2-in. hole.
Reducing NPT
In another example, a separate GoM operator leveraged offset well data to identify possible and probable challenges in its deep shelf operations. The referenced data revealed two deep pressure regression zones where low fracture gradients resulted in high non-productive time (NPT), due to lost circulation and hole stability in the offset wells. To meet this challenge, two solid expandable systems were planned into the well design to isolate these zones – a 9 5/8- x 11 7/8-in. solid expandable openhole liner and a 7 5/8- x 9 3/8-in. solid expandable openhole liner.
Fifteen barrels of cement slurry were pumped as planned, after running the 9 5/8- x 11 7/8-in. system to depth. The dart was displaced out of the cement head and landed as planned with ~300 bbl of mud. After expansion, the liner top was tested successfully to 2,840 psi. With the 11 7/8-in. casing shoe extended across the first regression zone, drilling continued. The 7 5/8-x 9 3/8-in. expandable liner was run when the 9 3/8-in. casing shoe needed to be extended beyond 12,000 ft (~3,650 m). This second system was run in the hole slowly to mitigate surge pressures.
With the liner on bottom, cementing proceeded with 25 bbl of 17.8 ppg spacer, and 29 bbl of 18.5 ppg cement, followed by 5 bbl of 17.8 ppg spacer. After the successful expansion, the liner top was pressure-tested to 500 psi for five minutes. Following drill out of the liner shoe, a successful LOT was achieved with an estimated mud weight (EMW) of 18.4 ppg, eliminating the need for a squeeze job to drill the next casing point.
As a result, the operator saved ~$24 million by reducing NPT and drilling risks. This dual-system solution enabled completion of several high production rate wells at the targeted depths with a larger completion size to maximize production rates. The success of this strategy to minimize NPT set a precedent for reducing costs and mitigating drilling challenges in future development wells.
Avoiding differential sticking
Part of the broadening application envelope is the expandable system’s ability to integrate with other enabling technologies. An operator in the North Sea, for example, implemented a redevelopment project by sidetracking from an abandoned well to gain access to a new reservoir section. Optimal reservoir access required 6 5/8-in. sand screens. To prevent a loss of hole size and to avoid differential sticking in the build and horizontal sections, injection-molded composite standoff blades were fitted to the outside diameter of an openhole solid expandable system. Three spiral blades per joint were bonded directly to the pipe surface. The 1,991 ft (607 m) 8 5/8- x 10 3/4-in. solid expandable system was deployed and expanded at a setting depth of 17,480 ft to 15,574 ft (5,328 m to 4,747 m). This configuration kept the pipe centered, ensuring a better cement job and preserving optimal hole size.
A prior GoM installation of an expandable system fitted with the same type of composite blades also mitigated a differential sticking problem. In this case, a standard 8 5/8- x 10 3/4-in. openhole liner got stuck during a run in a deviated hole with depleted sands. To preserve the hole size and prevent a repeat of the sticking issue, a 7 5/8- x 8 5/8-in. solid expandable liner fitted with the composite standoff blades was run and expanded through a whipstock window set in the previously expanded 8 5/8-in. liner. This system “nested” in the 8 5/8-in. liner and prevented differential sticking, improved cement quality, and extended the shoe of the previous expandable liner. After the shoe was drilled out, an acceptable LOT was obtained.
Conclusions
Solid expandable tubulars have advanced beyond their first commercial applications in the shallow waters of the Gulf in 1999. Today, they continue to extend their reach and application realm to greater depths in the hostile conditions of frontier oil and gas exploration offshore. The recent emphasis on the use of expandable technology as a planned element of project strategy rather than on contingency applications has made it possible to set new records for depth. It has also resulted in reduced NPT, streamlined operations and greater project feasibility across the spectrum of downhole applications from drilling and completion to production.
