This April, Enventure Global Technology for the first time ran and expanded three successive liners with a uniform internal diameter (ID). A field appraisal well proved the technology for field installation of successive, single-diameter liners.

The expandable system provides multiple casing points without loss of ID and maximizes hole size in the producing zone. Reduced friction and drag are among key benefits adding longer lateral capabilities to extended-reach drilling (ERD) applications. The single-diameter wellbore liner system also achieves higher production rates by retaining larger hole diameters. And by mitigating well uncertainties without sacrificing hole size, the system helps ensure design objectives are met.

Appraisal well
The conventionally drilled and cemented field appraisal well in Oklahoma confirmed the

Figure 1. The modularity of Enventure’s MonoDiameter technology development was demonstrated in the field appraisal well. The well design was based on recom-
mendations by operators drilling extended reach wells and proved the adaptability of the technology. (Images courtesy of Enventure)
company’s ability to run three consecutive MonoDiameter liners in a variety of common wellbore conditions. It was drilled in a real-world environment using a conventional, unmodified drilling rig in a typical drilling scenario.

The project was recently completed without a single safety incident — a tribute to the skill of the crews as well as the easy integration of the expandable liner-running technology with regular drilling operations.

The drilling program, with Enventure as the operator, was based on several key considerations developed with oil and gas company engineers. The well design included three different hole angles, used an oil-based mud system and called for cementing the last liner through the liner string.

The interests of extended reach operators were addressed by directionally drilling the well bore at multiple angles. Oil-based mud also provided a common point with conditions in many ERD applications.

The objective of the program was to install three successive 95¼8 in. expandable liners and expand them to a uniform 10.4-in. ID over 1,750 ft (533.75 m) of hole.

Technology suite
Running the liner program involved a series of steps executed with a very adaptable system of specialized components. This technology suite is assembled by component according
to the application, which enables many downhole tasks to be easily accomplished with a single tool system.

The modular technology suite consists of six main components:
• The anchor, which supports
the load during mechanical expansion;
• A force multiplier, which provides the force to mechanically expand the casing;
• An extender, which deploys the cones below the liner to initiate expansion;
• Two retractable expansion cones (10.95-in. and 10.40-in. diameter);
• A drillable packer and setting tool assembly to provide pressure integrity for hydraulic expansion and cementing capability; and
• A cutter to remove excess casing following liner expansion.

Liner running
The first liner was set below 11 3/4-in. and 20 in. surface casing. When the well bore caused an unplanned sidetrack while under-reaming in a soft formation, the section was cased higher in the hole than planned but the unanticipated casing point did not result in a loss of hole size in the following liner section. Once the section was cased off, the second liner was added to extend the casing maintaining the same 10.4-in. ID.

For the first section, an expandable 9 5/8-in. liner was run 250 ft (76.25 m) into the 10° hole. Once the liner was in position, the 10.95-in. cone was used to expand the bottom of the liner into a widened, bell-shaped section. This end configuration forms the union with the liner to follow.

After the bell was formed, the second 10.40-in. diameter cone was used to expand the remaining 9 5/8 in. liner 10.4 in. ID. Inside the 113¼4-in. casing, the force of expanding the liner clad it to the inside of the larger pipe, forming a metal-to-metal, liner-to-casing seal.
The second liner was run 500 ft (152.5 m) at a 20° angle to the next casing point. This time, a different approach to joining the liners was applied. The 10.95-in. bell shape was not formed at the end of the liner until installation of the third liner.

The entire liner was expanded with the 10.4-in. cone to create the 10.4-in. ID. When the
Figure 2. The April 2007 field appraisal well was the culmination of seven years of research and development for the MonoDiameter technology suite.
expansion reached the bell-shaped end of the first liner, the liner was expanded against the bell to form a metal-to-metal seal. This left excess liner above the overlap in the bell section. To remove it, a special cutter assembly was run, and the liner above the 10.95-in. diameter of the bell was cut off. The resulting interface, smooth enough to be unnoticeable on a caliper log, leaves no liner top to impede tool access.

The third 9 5/8-in. liner was run 1,000 ft (305 m) at a 55° angle. When expanded to 10.4 in., the connection between liner three and liner two (where the bell-forming step had previously been eliminated) was formed by expanding into the previous liner. The cutter assembly was used again to cut off the pipe up-hole of the overlap and finish the metal-to-metal seal. During this liner installation, 500 ft (152.5 m) of cement was pumped into the annulus of the third liner through the tool string.

This process could have been repeated indefinitely. In fact, if it was necessary to deepen the well at a later date, the same expandable single-diameter system would allow the casing program to be continued while maintaining the same ID.

Extended-reach applications
Coupling single-diameter technology with extended reach drilling mitigates many critical factors that limit reach, including casing openhole size versus drill string size, and ultimately torque and drag. The combined technologies provide the foundation for a significant increase in lateral length in many extended-reach well bores. Because extended reach laterals can be cased with successive liners at no loss of ID, shorter lengths can be run with no penalty to reduce friction and drag.

The friction reduction resulting from solid-expandable, single-diameter technology could extend the current ERD envelope up to 50%, according to a study done for a major North Sea operator. The study assessed the relative merits of applying conventional drilling technology vs. expandable tubular technology and its effect on lateral reach, capital efficiency and potential field development.

The study determined that added reach achieved by reduced friction would lower the number of wells, raise production per well, increase reservoir contact and reserve access and improve capital efficiency and field development economics. As a result, new field development plans would be optimized, sub-economic or marginal fields would be revitalized and efficient access to currently unreachable and uneconomic satellite fields would be improved by reduced infrastructure requirements.

Complementary drilling performance and cost studies have also indicated that well costs and time expenditures in the same North Sea study area can be reduced by up to 30 to 50% of the current drilling cost and time, using solid expandable tubulars and single-diameter technology.

Preserving the desired completion size using an expandable tubular system or single- diameter technology, the operator concluded, would eliminate planned subsea templates and associated infrastructure and satellite tie-ins from their field developments.

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