With a decade of installations, expandable systems have logged great success in well construction and remediation to mitigate common problems. Expandables are no longer regarded only as a last-resort solution. One of the next hurdles facing expandable providers came in the guise of transitioning the technology to the production phase in oil and gas

Figure 1. On this Middle Eastern project, the openhole expandable systems provided the operator with the flexibility to drill as many as four sidetracks from the expandable liner. Smart-well completion systems (shown here) were then deployed to provide isolation between open hole completed legs so that each could be controlled independently. (Images courtesy of Weatherford
recovery.

Expandable production liner

Key issues that needed addressing if expandable systems were to be qualified for production application included taking into consideration the environment in which the expandable liners were to be subjected, and ensuring that system components were fit for the wells’ operating envelope. The producing well bores were to be horizontal and many would be drilled through 7-in. casing windows. These sidetracks would typically contain laterals and well trajectories with large dogleg severity (DLS) angles. The characteristics of these horizontal well bores push the solid expandable liner’s performance envelope by creating fixed-fixed conditions during the expansion of the casing.

In a fixed-fixed condition casing cannot move in the well bore as it is being expanded. A breach in the casing or casing connections could result in the loss of expansion pressure and in the ability to continue expansion of the liner.

These wells harbored some of the most difficult conditions in which to successfully install solid expandable liners. Rather than using electrode resistant welded tubulars, seamless 50 ksi expandable tubulars were deemed more conducive to expansion due to better corrosion resistance. They also eliminating risk associated with weld failure. A collapsible expansion cone was designed to add an operational contingency that provides a means of “closing” the cone to allow the end user to retrieve it through unexpanded casing if required. Also, casing connections with metal-to-metal seals that had been fully qualified in “fixed-fixed” conditions were developed to attain and maintain sealing capability even after radial plastic deformation.
Figure 2. The monobore openhole liner system helps operators gain an extra string of casing with no loss of hole size. It also allows for drill out with the same size bit and gives operators the ability to remediate drilling hazards such as lost circulation and overpressured zones.


Fundamental process improvements were reassessed to keep best practices current and ensure that procedures correlated with technical enhancements. Pressurizing the expandable casing ahead of the expansion cone proved successful in lowering expansion pressures and further reducing associated operational risks. Sealing the expandable casing with a simple gate valve rather than a dart eliminated problems related with attaining a dart pressure seal, which commonly resulted in a poor cement job through the over-displacement of the cement and the creation of a wet shoe.

Hole preparation and conditioning is still a factor in successful installation. Operators have taken advantage of rotary-steerable tools and near-bit reamers to improve conditions not just for conventional wellbore construction but for expandable applications as
well with straighter holes, improved cleanout operations, and reduced
wellbore friction.

Maximizing reservoir contact

An operator embarked on a workover campaign that called for drilling multilaterals from the originally completed single-lateral well bores. The approach relied on a congruous integration of solid expandable systems and smart-well technology to optimize the existing infrastructure and maximize reservoir contact. A large gas cap and a relatively weak aquifer necessitated horizontal completions to mitigate gas coning challenges, which minimized the potential of water breakthrough when the field was first put into production in the late 1990s.

The company’s 51⁄2-in. MetalSkin Open-Hole Liners were used to either extend or sidetrack the 7-in. casing to form part of the wells’ production string from which the multiple laterals could be drilled. The openhole liners were cemented prior to expansion, facilitating the necessary zonal isolation in the single-lateral well bore. Once the expandable production conduit was installed with adequate hole size via the openhole liners, low-angle whipstocks were set and multiple laterals were drilled off the expanded liner. The openhole expandable systems provided the operator with the flexibility to drill as many as four sidetracks from the expandable liner. Smart-well completion systems were then deployed to provide isolation between openhole completed legs so that each could be controlled independently. Interval control valves and isolation packers inside the expanded 51⁄2-in. liners now enable the operator to control the flow from each lateral and shut off water production if necessary. This workover program maximized reservoir contact and increased production from as little as zero production to as much as 10,000 b/d in some wells.

Extend casing size up hole

Of interest to the industry is a single-diameter or monobore system for shoe extensions of the intermediate string where too often high pressure, low pressure, or unstable formations cost casing points. The company collaborated with operators to focus on a solution further up hole, which resulted in reconsidering the idea of “force fitting” solid expandable solutions to every trouble zone. A more practical approach began with the well basis of design (BoD) to “extend” casing size up hole and address trouble zones with high-strength conventional casing further down hole where they add the highest value. The company upsized its smaller systems to create a monobore 113⁄4-in. by 133⁄8-in. system. This 133⁄8-in. monobore openhole liner system, with lower expansion pressure requirements, allowed for the use of thicker-wall casing (0.582 in. versus typical 0.375 in.) and created a large expandable casing with relative high collapse characteristics. An expanded 113⁄4-in. casing with a post expanded drift of 121⁄4-in. and a collapse rating of ~2,500 lb provides a more reliable system when compared to a smaller conventional single-diameter expandable system with ~1,000 lb collapse rating. Using the 135⁄8-in. monobore system to extend the 133⁄8-in./135⁄8-in. casing string preserves hole size initially and enables the operator to address trouble zones while maintaining the original BoD. This system can also enable a conduit for a larger completion by capitalizing on thicker-wall expandable casing in the top-hole sections.

The monobore system features a special-sized, flush-joint conventional casing run on the bottom of the 133⁄8-in. conventional casing string, forming an oversized tieback shoe that creates a “receptacle” for the top of the expanded 113⁄4-in. liner. The tieback shoe outside diameter is similar to that of the 133⁄8-in. collars, with an inside diameter large enough to accommodate the system’s expanded 113⁄4-in. casing and still allow the monobore liner to have an expanded drift of 121⁄4-in. An expansion cone that travels in a collapsed mode and does not require an oversized launcher to house the bottomhore assembly helps with equivalent circulating density challenges during run-in of the expandable liner. This cone has the ability to create its own launcher downhole when it is assembled or expanded.
Addressing trouble zones

A monobore openhole cladding system can be installed against the well bore to isolate trouble zones as they are encountered in the 81⁄2-in. hole section so that drilling can continue without sacrificing hole size. The 81⁄2-in. system selectively mitigates the risks of drilling problem formations and eliminates the need to case off the entire well bore. The trouble zone is minimally underreamed (1.0 in.), and the clad system is expanded into it without losing any hole size. After the clad is expanded to cover the zone, another clad can be passed through it (clad-thru-clad capability) to treat the next trouble zone, again without losing hole size. The clad allows full-bore access and drilling may continue without having to downsize the bit. These liners are typically short (less than 164 ft or 50 m) and are covered up with the next full casing string after the hole section has been drilled.

The practical monobore well

The most practical path to the monobore well is by leveraging existing and proven solid expandable technology. Empirical evidence and results from actual applications confirm that improved mechanics have taken single-diameter technology from an idealistic concept to a feasible reality. The company has collaborated with end users to combine the monobore open-hole clad and monobore open-hole liner to create a monobore well system. Using the 133⁄8-in. oversized tieback shoe followed by the 113⁄4-in. by 133⁄8-in. monobore liner creates the initial monobore extension. Subsequent installations of 133⁄8-in. monobore liners and 131⁄2-in. monobore openhole clads combine to extend the 133⁄8-in. liners to depths that are within the systems’ operating envelope.

Although this well system can be made up of many monobore extensions, working with operators has shown that some of the most complex drilling challenges can be effectively addressed by simply extending the 133⁄8-in. casing string once or twice.