Solid expandables take operators to previously unreachable deepwater reserves
Kevin Waddell
Jerry Fritsch
Mark Holland
Enventure
More than 1,100 installations worldwide in myriad conditions – including over 115 in deepwater – demonstrate the effectiveness of solid expandable systems in offshore programs. Expandable systems can be an advantage in challenging wells where lack of offset data and unknown formations can disrupt the planned drilling program. When these conditions necessitate setting casing higher than planned, expandable technology may mitigate wellbore diameter reduction and enable the operator to return to the original casing program to complete the well, meeting hole size and depth objectives.
The continuing evolution of expandable applications has increased the frequency of planning expandable systems into a wellbore design. Successful applications demonstrate that solid expandable systems can reduce non productive time, provide larger hole size for maximum completion/evaluation flexibility, or extend casing programs.
The current deepwater records for solid expandable systems are represented by three installations: deepest use at about 28,750 ft (8,763 m), the longest liner at 6,867 ft (2,083 m), and an installation in more than 7,800 ft (2,377 m) water depth. These are not the limit for expandable tubulars, simply the milestones to-date. The technology has room for additional upside to meet the ever-escalating description of “extreme well conditions.”
The following offshore case histories demonstrate the application of expandable systems to deepwater applications.
Record-setting liner
The 95⁄8-in. base casing was at about 15,000 ft (4,572 m), and the well needed to be drilled below about 23,000 ft (7,010 m). The interval to be drilled included depleted sands with a narrow pore pressure/fracture gradient.
Multiple attempts to drill and side track the section to reach the target zone were foiled and running a conventional casing string would impact the production liner size. The operator decided to use a solid expandable system. In a new side track, a window was carefully prepared in the existing 95⁄8-in. casing, and the section for the expandable liner was drilled to about 20,650 ft (6,294 m) with an 8½-in. bit and opened up to 9½-in. with an underreamer. The 6,867-ft (2,093-m) 75⁄8 x 95⁄8-in. solid expandable open hole liner was installed and expanded. The operator achieved zone isolation and maintained wellbore diameter. Because of the expandable, total depth was reached with a hole size large enough to complete with a 7-in. flush liner versus the conventional option of a 5½-in. production liner. The larger size increased productivity, accelerated recovery of the investment, and avoided mechanical risks associated with drilling and evaluating a smaller diameter hole.
Staying on track in ultra deepwater
The challenges of this ultra-deep deepwater, high-pressure well were complicated by a narrow pore pressure/fracture gradient window and multiple salt sutures that constrained the mud weight changes. While drilling the 8½-in. section, lost circulation was encountered and multiple lost circulation material (LCM) squeezes did not succeed. At this point, the operator was faced with a compromised completion size because the use of conventional 75⁄8-in. casing carried the penalty of losing a hole size, which would threaten the original well objectives.
To ensure reaching total depth with the desired ID, the operator installed a 1,900-ft (579-m), 75⁄8 x 95⁄8-in. solid expandable open hole liner to isolate the higher pressure. Once isolated, the mud weight could be reduced to manage the lower-pressure zones, which were causing the lost circulation. As an additional benefit, the larger hole size provided by the expandable, created enough clearance to drill an underreamed 8½-in. hole from the expandable liner shoe to TD of about 30,000 ft (9,144 m). This strategy produced sufficient clearances to allow another contingency casing size to be run, if needed.
Expandables in brownfields
As offshore developments mature and infrastructure ages, production wanes. To maximize the value of capitalized assets, operators target deeper or stranded reserves by using enhanced oil recovery techniques. In a North Sea well, the operator was side-tracking for an injection well. To optimize the wellbore trajectory and reduce risk in the side tracking operation, the operator exited from 14-in. casing. However, there was an unstable clay zone near the kickoff point that had to be isolated.
Side tracking from the existing infrastructure constrained the hole size. To maximize hole diameter and complete the well with the desired 7-in. injection string, a 11¾ x 14 in. solid expandable liner was installed as the intermediate string. The expandable liner conserved hole size to allow the optimized completion size for more effective water injection and enhanced production. Additionally, the ability to isolate the trouble zone enabled side-tracking at an optimal depth, improving well trajectory, and reducing risk associated with drilling through known geologically challenging zones.
Higher performance systems
As operators target deeper formations in more complex environments, expandable technology adapts and evolves. New systems with greater yield and collapse ratings were designed and developed specifically to address more-demanding operations. The first high-performance system was a 75⁄8 x 95⁄8-in. liner for an operator drilling in the UK sector of the North Sea. The system was about 79% more collapse-resistant with a collapse strength of about 4,750 psi (32.75 MPa), versus the previous systems’ collapse strength of 2,550 psi (18.27 MPa) in 47 lb/ft base casing.
The initial application went as follows: The target reservoir was below a high-pressure cap rock of questionable shale stability. Uncertainty surrounding shale stability necessitated careful progression through this section to minimize stimulating movement or collapse. The operator needed an expandable liner capable of passing through the 97⁄8-in. casing and into the 8¾-in. underreamed hole. The objectives required the system to expand and isolate across the cap rock with a post-installation collapse rating of about 4,000 psi while still allowing the planned 5½-in. completion. Isolating the cap rock by the conventional casing off the section would have resulted in telescoping the wellbore, thereby reducing valuable production volume and compromising commercial viability.
11¾-in. high-performance expandable liner inside 133⁄8-in. 72 ppf casing (with elastomeric seal compressed between) covered existing wear and provided the wear resistance to side-track to the desired total depth and meet completion objectives.
This first application of the high-collapse 75⁄8 x 97⁄8-in. solid expandable system successfully cased the trouble interval, which facilitated drilling the next hole section with a lower mud weight. By isolating the high-pressure zone while maximizing hole diameter, the operator could drill to the planned total depth of a heavily depleted reservoir and case it with a conventional-size liner.
The second high-performance system developed is 11¾ x 133⁄8-in. It has over 200% more collapse-resistance than previous systems (3,800 psi vs 1,220 psi) in 72 lb/ft base casing.
The first installation of a 11¾ x 133⁄8-in. high-performance liner was in the GoM – in an innovative fashion. An operator side-tracking from an existing wellbore had significant wear in the 133⁄8-in. casing. To continue drilling, a substantial increase in casing integrity was required. The 11¾-in. solid expandable system installation enabled the operator to clad over the worn area in the 133⁄8-in. casing and continue drilling to target depth.
Offshore drilling raises new, more difficult challenges every day. Technology is required to meet these challenges safely, while lowering risk and increasing productivity efficiently and reliably. These case histories not only demonstrate how solid expandable technology can adapt to address challenging drilling issues in deepwater, but also show operators’ willingness to apply a proven technology.
