Technology Update: Tool Enables Boost in Brownfield Production

Traditional well-construction techniques relying on cementing or mechanical isolation systems for primary zonal isolation can often fail in brownfield developments. Or, they are unable to fulfill requirements for zonal isolation across complex, multilayered formations that may contain depleted, overpressurized fluids or gas/water zones lying ahead of the target oil sand.

Swell packers are an enabling technology that is allowing production from wells that otherwise would not have been feasible either technically or economically. Easy Well’s packer technology consists of a standard oilfield tubular with an elastomer bonded along its length. The packer uses hydrocarbon to swell the elastomer downhole. The packer has no moving parts and requires no service tools, dropping of balls, hydraulic actuation, or surface/downhole manipulation to set it. Any number of packers are simply made up in the completion or casing string and deployed in a single trip into the well.

On contact with hydrocarbons—from the reservoir, oil-based mud (OBM), or a spotted fluid—the bonded rubber swells to form a seal either inside the casing or against the open hole (Fig. 1). The process works by the thermodynamic absorption of hydrocarbon molecules into the molecular structure of the rubber, allowing it to swell and stretch.

Fig. 1—Swell packer for oil-based mud

Fig. 1—Swell packer for oil-based mud.

Zonal Isolation Without Cement
The first application of this tool in the U.K. sector of the North Sea was on Shell’s North Cormorant asset in 2004 (Fig. 2). The challenge of assuring future production was for the asset’s well engineers to find ways of drilling cheaper wells to exploit smaller pockets of reserves. After reviewing the portfolio of work, it was decided that, by introducing a series of technologies over a six-well program, a 25% reduction in drilling costs could be made. The key leading technology was through-tubing rotary drilling over the six-well campaign.

Fig. 2—Swell-packer deployment in the North Sea

Fig. 2—Swell-packer deployment in the North Sea.

Project engineers devised a strategy that first addressed the least challenging wells. New technology was introduced in an orderly manner, allowing opportunity to see the challenges in advance and to tackle the necessary learning curve. Nevertheless, the first well (CN24s2) was unsuccessful. The bottomhole assembly from the coiled-tubing cleanout string became stuck and was not recoverable. Solids debris from the cementing operation coupled with low annular clearances, not normally associated with conventional wells, caused the problem. The second well also ended up at a higher cost than anticipated as a result of cementing issues.

At this point, the team rethought its zonal-isolation strategy. Needing to find a technology that would simplify the well construction and dramatically reduce the risk profile, swell-packer technology was considered as a way to avoid the necessity of cementation.

Shell already had some experience with the technology in approximately 20 wells around the world, including some wells drilled by Shell Malaysia, but not in the small-diameter, high-pressure conditions being drilled on the North Cormorant. The team decided to try the packers because they showed the potential for better zonal isolation in a small hole size, with a concomitant increase in oil production.

Bench testing on the packer sizes that were to be run helped to determine their applicability and ensure that they could be run successfully. They were then used in Well 5, where they worked exceptionally well. All cementing was completely eliminated, as was cement cleanup and perforating.

The North Cormorant team believed that a phased introduction of the packers was made possible through active service-provider cooperation. As a result of that support, drilling came down from 40 days for the first well to 20 days for the last well. It is thought that there is significant potential to reduce this even further, with 12-day wells now a serious possibility, with the ability to reduce costs to U.K. £1.5 million per well, and as a consequence, to access oil that otherwise would have been economically unviable.

Shell’s experience with the swell packer has now expanded to more-conventional hole sizes and to completing wells that otherwise might have been lost. Well CN39s3 was one of a pair in which swell-packer technology was to be used in conjunction with a formation-isolation valve (FIV) to deliver a cost-effective completion—saving as much as U.K. £1 million per well. When the first well of the pair was drilled, a pressure kick was experienced that was greater than the pressure prognosis and therefore outside the design criteria for the well. The mud-weight gradient required to kill the well was almost equivalent to the rock strength.

The fluid dynamics involved in a conventional cementation would have resulted in total loss of fluid returns and, consequently, nonisolation of the high-pressure water interval. Water flow would have completely dominated production. The production liner was redesigned, and swell-packer technology was used to isolate the high-pressure water zone—recovering U.K. £5 million in reserves. The partner well (CN10) was drilled according to plan.

BP used the Easywell Swell Packer on its Andrew field in the North Sea. The challenge was an extensive water zone in the middle of the field. In addition to drilling two sidetrack wells, this water zone needed to be isolated from the heel and toe of the reservoir. Conventional cementing and perforating were rejected as too expensive.

On the first of the two wells, producing 100% dry oil from the start of production, a predrilled liner was used in the pay zones with five 5.6-in. packers built on 4.5-in. base pipe to isolate the water zone. The liner was run in OBM with an FIV to isolate the packers as they set (the swelling process does not take place immediately). For use in OBM, there is a packer specifically designed for that environment that has a three-layered construction that delays the swelling of the packers so they can be deployed before being set. If the packer is breached, it will continue to swell in the presence of hydrocarbons, so the packers are effectively self-healing.

A critical part of the operation was verification, based on observation of any losses into the formation (a condition occurring when the water zone is not properly isolated). The first well has been producing under capacity at 10,000 B/D of dry oil thanks to a 300- to 400-psi differential pressure between the water zone and pay zones and has been producing virtually no water.