DRILLING TECHNOLOGY: Re-entry in US Gulf first offshore test well for Anaconda system

North Sea ultimate destination

Producers will have a better opportunity to evaluate the Anaconda drilling system as Halliburton gears up to drill its first offshore well using the revolutionary equipment. While the proposed three-well drilling program for BP in Eugene Island Block 322 of the Gulf of Mexico is the first offshore application, Jim Terry, Director of Advanced Well Construction Systems for Halliburton says the system has a total of six test wells under its belt.

The drilling system uses lightweight composite coiled tubing and a bottom hole assembly that can, when required, pull the pipe into the hole. This is accomplished using two expandable elements, similar in design to mechanical packers. These elements are spaced apart across a stroke length integral to the bottom hole assembly (BHA).

Downhole, the first element is expanded to make mechanical contact with the borehole. The second element is then brought forward in a stroking motion, set and expanded. At this point the first element is released. As this element moves forward, under hydraulic force, it applies weight on bit. Drilling progresses until the full stroke of the unit is realized, then the forward element is again expended, the latter contracts and the process is repeated.

The propulsion system is capable of walking in or out of the hole, as required. The flexibility of the light-weight composite tubing, combined with the unique propulsion system, allows for extremely precise directional drilling. In addition, the Anaconda drillstring is made up of what Hallibur-ton calls "Smart Pipe." The pipe is hard wired to allow for high bandwidth, real-time data from the wellbore. Combining this real-time well data and the flexibility of the drilling system Anaconda is able to drill very precise horizontal wells.

BP re-entry

These features and the small footprint make the Anaconda system ideal for reentry work such as the one BP has targeted. Terry said the system can drill very accurate stepouts that optimize returns from a reservoir.

Often when a pay zone is encountered and a stepout drilled, the bit has trouble staying within the zone. If it punches through or encounters a point where the zone is fractured, there can be a delay before the problem is identified and remedied.

During this time, there is always the danger of lost circulation into the formation or water invasion. The Anaconda system moves readings from the drill bit in real time, and of sufficient density to make a quick determination of the action needed. As part of the package, Halliburton says it will have experts available onshore in Houston to monitor and advise on the progress of wells, receiving the data through a satellite link.

In preparation for this first offshore operation, Halliburton used the Anaconda system to drill a sixth test well, T6, which has the same horizontal profile as the most difficult of the wells planned for BP. Before green-lighting the Anaconda for this project, BP conducted a peer review of the entire operation. During the review, BP called on its internal experts from all over the world. BP evaluated the equipment, techniques, and procedures Halliburton has planned for this project.

BP was interested in contingency plans and in clarifying questions that still remain concerning the system. Terry said Halliburton developed action plans to address BP's concerns, revised the schedule accordingly, and moved forward with the project. The Anaconda system has been working in Duncan, Okla. for the past 18 months, drilling increasingly complex wells leading up to the T6.

The team in charge of breaking down and assembling the Anaconda in Galveston will be the same team in charge of the system offshore. Terry said an experienced crew capable of a rapid rig up helps Halliburton focus on the wells rather than the preliminary processes. "We don't want to deal with anything that is not a technology issue," Terry said. The BP project will consist initially of two wells, with the possibility of a third.

Reservoir exploitation

Anaconda's biggest advantage over a traditional drilling system is its real-time telemetry. This data allows the driller to steer expertly through the reservoir. It is suited for a sidetracking project into an undeveloped reservoir, such as the one being performed for BP.

The unit can identify and reach a target zone that might not otherwise be accessible from an existing wellbore, and stay in that zone longer that a conventional system, Terry said. The third target for BP is bypassed reserves, where the trick is to avoid water. Drilling offset wells using conventional reentry tools in a fractured reservoir requires the driller to use lithology based on logs of these existing wells. The "sweet spot" may be obvious, but it is difficult to steer through it without real-time data.

If the driller punches through the bottom of the zone, he runs the risk of watering out the well. This is particularly true in a fractured zone in which the driller can't know if the pay is above or below where he has been drilling.

Geosteering using resistivity logs, even with the latest technology and modern tools is difficult, Terry said. The real-time data from Anaconda allows the driller to determine quickly where to go. Feedback from experts back onshore also contributes to the accuracy of these decisions. "We can collaborate on the geosteering process," Terry said. The system is versatile enough that if a punch out occurs, all the data is available to determine quickly which direction to go. The Anaconda can change direction to gather more data with a second pass through an area, or to get back into the pay zone.

Future applications

Norwegian-owned Statoil jointly funded the development of Anaconda, although its first application will be in the Gulf of Mexico. Terry said Statoil is interested in using the system to re-enter wells in the North Sea. Because the unit was developed and tested at Halliburton's Duncan facility, it made sense that the first offshore application would be in the Gulf of Mexico.

In the case where a problem developed system experts on the system would be near by. Also, once the project is complete the unit could be broken down and returned to Duncan for evaluation and refit. Assuming everything goes well it will then be transported to the North Sea to work on the Statfjord field for Statoil.

Assuming the BP project will be a success, Terry said different versions of this Anaconda could be developed with the Gulf of Mexico in mind. While Statoil has the first right of refusal on newbuild units, a smaller version of the Anaconda would appeal to shelf operators in the Gulf of Mexico where high gas prices have made re-entry drilling a hot market.

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