Swell packer technology is giving brownfield developments a new lease on life by changing the economic landscape for well construction costs. With 60% of the world's oil production coming from brownfields, they remain a significant source for fulfilling oil demand.

As operators pursue remaining pockets of oil from mature fields, they need wellbore construction techniques which reduce costs and allow more challenging and higher-risk projects to be tackled. Swell packer technology is delivering this need. With this well construction technique, there are no external setting operations, so installation and zonal isolation becomes a very low-risk operation. The use of swell packers has changed the economic landscape, allowing operators to simplify the construction of wells and tackle more challenging multilateral and re-entry projects.

Reducing construction costs

For example, during a brownfield development in Asia, an operator was challenged with the annular isolation of water and gas-bearing zones intermittently layered between oil sands. The complexity, cost and limited success of conventional cementing and perforating techniques required consideration of alternative completion designs to make future developments economical. Swell packers were run in conjunction with blank and perforated pipe, spaced out across individual zones. Using these special packers simplified the well construction process, eliminating the need to cement and perforate, and reduced total well costs. The packer not only provided superior zonal isolation, it contributed to reducing construction costs by 30% through savings in liner, cementing, clean-up, perforating and completion operations.

On through-tubing and re-entry work, an operator often drills slimhole sidetracks which pass through several zones before reaching target sands. Cementing or using mechanically set packers for isolation on these wells can be very complex and they can often fail, increasing the total risk profile for this type of work. In many cases, today's technology is simply unable able to meet the technical needs of brownfield wells, limiting the economic viability of some projects, and reducing the number of potential candidates.
In one instance in the Middle East, an operator had to isolate water-bearing zones on a slimhole sidetrack re-entry. To do this and cement a liner in place would have been technically impossible. Using swell technology in conjunction with blank pipe and slotted liner, the operator was able to isolate water zones and complete the well in a single trip. In another example a through-tubing, rotational drilling campaign was being undertaken by a major North Sea operator to secure low-cost development of marginal reserves with a sidetrack well drilled off an abandoned well. Although evaluated as technically feasible, the costs, complexity, and the risk of cementing and perforating the sidetrack with coiled tubing ruled out a conventional completion and rendered the project uneconomic.

Because the potential oil reserves were deemed a worthwhile prize, an alternative strategy was selected. Success would depend on accessing alternating low-pressure oil zones which were divided by water contact areas. Effective zonal isolation was critical if the project was to be an economic success.
Testing was done with a simulated washout program to exceed the 2,300 psi sealing requirement before rubber packers were chosen for the operation.

Annular isolation was achieved by running 12 packers to isolate alternating water-bearing zones and low-pressure sands with blank, perforated pipe, down to a total depth of 15,128 ft (4,612 m). The units were exposed to operating temperatures up to 110?C (230?F) and there were no reported installation problems since their use requires no direct vendor supervision. "The system is very simple, very easy to run and has very little risk associated with it," said Steve Kent, global marketing manager for Easywell. The final completion diameter was 27/8 in.

The well produced at a higher-than-predicted flow rate and with a lower water cut than offset, cemented wells.

On the Alaskan slope multilateral wells are often used to improve economics and increase recovery from mature reservoirs. But the extent and number of laterals that can be drilled off a single mother bore is sometimes limited by the inability to effectively isolate each lateral or to provide isolation along them. Conventional cementing and mechanical systems are too complex and increase the risk of conjunction to meet this challenge. In one case on the Alaskan Slope, an operator used swell packers to isolate each lateral at the entry point and also to provide isolation along individual laterals.

Even on simple openhole completions, swell packers continue to have a significant impact. In Africa, the North Sea, Asia and Oceania, these packers are becoming the default isolation device for operators to compartmentalize reservoirs and to isolate unwanted gas/water contact zones and shales, and they are also proving to be a much more reliable annular isolation technique compared to mechanically set and inflatable systems.

First used in Norway in 2001 on the Grane field, this type of packer can be made up as part of casing or completion strings. Rubber is bonded onto a base pipe and is run into a hole on a single trip. Upon contact with hydrocarbons - which can either come from the reservoir, oil based mud or a spotted fluid - the bonded rubber swells up to 200% of its original size to form a seal either inside casing or against the open hole. The process works by the introduction of hydrocarbon molecules into the molecular structure of the rubber, allowing it to swell and stretch. But the process is not instantaneous: "The swelling process does not take place overnight. You have a few days - you have time to run the packer into the well, allow it to swell and seal up against the formation face," said Kent. An outer rubber casing can also be applied to delay swelling of the packer for ocean-bottom mud environments. This allows operators to precisely locate the devices before they set. Furthermore, if the packer is breached, it will continue to swell in the presence of hydrocarbons, so the packers are effectively self-healing.

Simple in construction and easy to apply, the technology has no moving parts and requires no service tools or surface activation to set it. It is the simplicity of design and application that is providing a new lease of life to brownfield projects: Traditional well construction techniques relying on cementing or mechanical isolation systems as the primary zonal isolation technique often fail in brownfield developments. Or they are unable to fulfill requirements for zonal isolation across complex, multilayered formations which may contain depleted, over-pressurized fluids, or gas and water zones before the target oil sand.

"If you can improve the zonal isolation and improve production, you can open up the possibility to go after other reservoir targets," said Kent. "By improving the zonal isolation you have changed the economic landscape. You can change the economics of well construction, giving you the ability to adopt brownfield infield drilling. You can reduce the upfront construction costs for a 30% return. On top of that you are changing the risk of the operation. You are reducing the number of people involved - compared with conventional mechanical or inflatable isolation packers - and by improving the zonal isolation you are giving yourself the opportunity to target other pockets of oil."

The ability to deploy swell packers in a single trip and eliminate the mechanical setting process means that operators may deploy any number of packers to achieve true compartmentalization while still reducing the risk of the operation. Simplicity in deployment also means that the technology can be used to isolate unwanted sections that are only discovered during the drilling of the reservoir, avoiding costly sidetracks. "You can run as many of these as you want to along your completion string to give the zonal isolation that you require," Kent added.

Nominally the rubber can withstand a pressure differential of up to 3,000 psi in a 9-in. to 11-in. outside diameter hole, End rings fitted to each end of the packer limit the extent to which it can swell along the pipe. "But we can go a lot higher than 3,000 psi." Kent said. Applications are designed using a software simulator to ensure the downhole requirements for each application are met.

Service life of the packer is dependent on field conditions, but they are normally expected to last as long as the production string is in place - effectively a fit-and-forget solution for zonal isolation.

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