A full system test is conducted in the horizontal well at the Bridge of Don test well facility in Aberdeen, Scotland. (Image courtesy of Caledus)

Slimming down oil and gas well geometry to reduce the cost of well construction has long been a goal of operators. To achieve the desired size of pipe across the zone of interest while slimming down the rest of the well construction geometry and still enabling the desired size and configuration of the completion to be installed are the main challenges. In an ongoing effort to meet these challenges, Caledus has designed, tested, and conducted field trials of a system that is practical to deploy.

The company has installed the first SlimWELL liner in an onshore development well in Alberta, Canada. The Talisman Energy (UK)-sponsored trial was extremely successful.

“Talisman UK evaluated the potential benefits of SlimWELL across a number of North Sea well types.?The study indicated that successful deployment of the technology on a full scale would lower well construction costs and even increase production in some scenarios. The study also recognized the value of the system being able to provide another casing size as a contingency in different scenarios. Sufficient interest was generated to sponsor a field trial of the existing 51?2-in. by 7-in. SlimWELL system,” a Talisman representative said.

SlimWELL technology

SlimWELL technology is an evolutionary well construction technique based on a design of close-clearance, flushed jointed liners. The system slims down the well profile resulting in the optimum pipe size across the zone of interest, while maintaining well integrity and intervention ability.

It is suitable for partial or full well construction.

The technology aims to reduce well construction costs by more than 50% when compared to conventional practices. It could rival expandable tubular and drilling with casing technology in this respect.

The technology achieves the desired size of tubular at the reservoir by use of an innovative deployment tool arrangement and novel liner hanging system. The system enables a sequence of reduced clearance cased liner strings to be run, avoiding all the associated problems such as high swab and surge and increased ECD during the cementing operation.

The benefits of reducing the casing sizes from top to bottom while maintaining the optimum size across the zones of interest are significant:

Economic. Fewer consumables such as casing, drilling fluids and cement, faster overall drilling, lower logistics and reduced rig costs;

Environmental. Fewer cuttings and less drilling fluid to dispose of; Reduced risk. Fewer big casing operations, reduced risk during transportation and handling. Wells may be developed faster, with increased safety;Contingency. Additional casing strings may be run without affecting the final hole size. Additional liners may be spaced over troublesome zones;Bottom-up design. Allows the well to be designed for the required production casing and completion tubular without excessively large top-hole sizes;

Abandonment. Simplifies the well abandonment process due to the lack of overlapping casing strings and potential leak paths at the top of the well;

Well integrity. The ability to use standard API casing and normal cementing techniques means integrity is straightforward to engineer and plan, coupled with the high-pressure, metal-to-metal seal incorporated in the system;

Technical. Constructing wells from close clearance liners partially or fully reduces the telescoping effect in wells when compared to conventional techniques; and

Practical. No rig modifications or special training of rig crews is required. Accepted drilling, casing running and cementing procedures apply.

Applications

SlimWELL is believed to be suitable in most oil and gas well applications currently being constructed using conventional technology, from the most complex ERD, high-pressure/high-temperature or deepwater wells, through exploration/appraisal wells, to in-fill (side tracks) drilling for small accumulations, to low-cost or remote locations.

The system should allow more complex wells to be drilled with smaller, earlier-generation rigs, reduce variable decks loads, reduce mud pit volumes, allow slender risers to be used, reduce the horsepower requirements on land rigs from above 2,000 hp to below 1,500 hp, use splitter wellhead technology, but in all circumstances deliver the same well performance for less, while enhancing safety and reducing environmental impact.

The field trial

The Alberta Kaybob field well is a 6,562 ft (2,000 m) vertical well, with 7-in., 26 ppf L80 LTC connection casing run and set with an upper (backup) and lower (primary) set of SlimWELL dedicated locator and cementing-anchoring-sealing joints above the normal 7-in. shoetrack. The 7-in. was run and cemented 656 ft (200 m) off bottom of an 83?4-in. open hole to facilitate the trial of the 51?2-in. (53?4-in.) by 7-in. SlimWELL system. The 83?4-in. open hole was drilled on rotary with an insert rock bit. The mud was a 10 ppg water-based fluid. The 7-in. was drilled out with a 6-in. insert rock bit after cementation. A precautionary 7-in. scraper run and re-tagging of total depth was performed as part of the trial.

The SlimWELL liner was 918 ft (280 m) long of 51?2-in., 15.5 ppf L80 Hydril 511 casing run and set 1 m off bottom with a 262 ft (80 m) overlap and was run, located, cemented, anchored, and sealed into the lower (primary) set of dedicated joints prior to the running tools being hydraulically released and pulled out of the hole. The system was run in the hole on 4-in. DSTJ drill pipe.

The trial objectives were met, and the first ever SlimWELL liner was successfully set and cemented in the well. A number of lessons were learned, and improvements were made related to debris tolerance and the seal arrangement. Caledus has since conducted a significant debris tolerance and reaming down through cuttings beds test in the Bridge of Don facility in Aberdeen Scotland, in advance of building new equipment for BP in the United Kingdom. These tests where extremely successful.

Progress report

It was decided that an early commercial size that could be used in in-fill drilling (side-tracks) was required, a size that later could also figure in full well construction. Caledus believed this size should be 51?2-in. by 7-in., allowing a 51?2-in. flush-jointed liner to be run through, cemented into the open hole below, set, anchored, and sealed inside 7-in. casing. It is important to note that the system has no inside diameter restriction throughout and incorporates a high pressure liner lap seal, in addition to swab/surge and ECD reduction features.

A successful test of the first size was conducted, and all the critical items in the system were proved out. One of many successful tasks in the trial was the actual picking up, screwing together, handling and running of the system in a safe and efficient manner. It was important to ensure this was accomplished using industry standard equipment and techniques before it goes to a live well site, where it would be expected to be safe and straightforward to deploy, without the need for special training of the rig crews.

Because BP was interested in possible North Sea installations they decided to sponsor the development of the next size of SlimWELL that would be useful to use in in-fill drilling opportunities in the North Sea. This has allowed Caledus to make significant progress with developing the 4-in. by 51?2-in.
system that would be run inside the existing system. The second size was completed in December 2007.