A revolutionary coiled tubing and well intervention system is about to change the way operators think about their assets. This advanced well construction system makes geological steering of complex, extended-reach wells - not previously achievable - a reality. Even more astonishing is that once rig up is complete, the well can be drilled via a laptop computer from anywhere in the world.

Big ideas are fragile things. But if one takes root, the results can transform an industry. "Statoil realized that they had to reduce the cost of drilling sidetracks in their watered-out mature North Sea fields. They had reached an honest understanding of their problems and decided to help develop radically new technology," said Jim Terry, director of the Anaconda project for Halliburton. "They had always been a leader in extended-reach drilling. We at Halliburton had an idea to develop a new approach to drilling using our reeled advanced composite tubing capabilities. Fields such as Statfjord and Gulfaks have opportunities for through-tubing work. To do this economically with current technology was becoming costly. The economics today won't support large equipment for marginal fields. Our two companies decided to co-fund the development of a radically new drilling system. Conceived in 1997, planning between our two companies began in April 1998 with design and safety teams fully engaged in August 1998. We had operational prototypes functional in June 1999, less than a year after the detailed design began."
Statoil and Halliburton personnel worked together over a 27-month period to design a fit-for-purpose advanced well construction system (AWCS) that met Norway's stringent health, safety and environment (HSE) requirements. The primary goals of the Anaconda project were to reduce drilling costs and optimize the position of wells in the reservoir. The team members challenged each other to avoid traditional thinking in the development of the new concept. The key technical challenges that had to be overcome were the dependence on steel tubulars for conveying downhole sensors, drilling tools and fluids, and the low bandwidth of conventional mud-pulse telemetry for transmitting downhole measurements.
Roy Marker, Statoil's Anaconda project manager, added, "Our goal with the first AWCS is to drill a through-tubing sidetrack for about US $2 million vs. $3 million-plus with current rig technology. We had to convince the asset managers that we were going to save them money drilling wells and be able to bring on new production. Historically, Statoil has had a portfolio of R&D projects, but they have been to develop
a lot of small pieces, never a complete system. We decided that to meet our cost targets,
we had to help fund the development of a new system.
The project vision consists of three evolving systems that each progressively build upon the technical achievements of the former. System I, in final testing, uses the 27/8in. advanced composite coiled tubing (ACCT) and a 31/8in. bottomhole assembly (BHA). This equipment will be used for through-tubing sidetracks that target bypassed hydrocarbon accumulations. It will be capable of all operations, from plug-and-abandonment of the mother well to perforation of the newly drilled sidetrack.
System II, which will use 4¼in. ACCT and a 4¾in. BHA, will include enhanced formation evaluation sensors and use the System I surface equipment with advanced spooling technology. It is intended for long-reach extensions and slimhole exploration.
System III will use 5½in. ACCT and a 6¾in. BHA to achieve measured depths of 45,000ft. Applications for this system will include minimizing the number of offshore structures and associated capital expenditures. It is the intention to use this system to drill geotechnical exploration wells in deepwater environments, subsea development wells and minimum diameter, high-rate production wells.
The challenges were in large part met by embedding power and telemetry wires within the ACCT umbilical. The composite tubing is much lighter than steel tubing. It becomes neutrally buoyant in mud weights typical of many North Sea fields, which results in reduced drag and enables longer reaches and extended steering than could be achieved with steel tubing.
The embedded conductors provide power, data telemetry and control of the downhole tools without the need for expensive batteries, downhole turbines, downhole memory, downhole processing or slow simplex mud-pulse telemetry. These conductors enable the downhole sensors to transmit all the raw data to the surface, where any number of computers can process it. The reeled composite pipe can be produced in lengths of 21,000ft, which minimizes the number of connectors. A special connector has been developed to join two or more sections of the reeled ACCT to ensure power and data integrity.
"The use of an openhole well tractor is
also a first. This tool will allow for very precise control of the drilling process by maintaining just the right amount of weight
on bit and help to significantly reduce downtime," Marker said.
A new way of working together
"Anaconda will change the way wells are drilled," said Dave Stegemeier, an Anaconda project manager. "The G&G (geology and geophysics) folks will play a much greater day-to-day role in drilling operations than ever before. Precise placement of the wellbore is now possible within a given zone. The amount of real-time data is enormous. Well control is improved, and hazardous conditions can now be avoided due to the amount of information coming back from the sensors, which enables better quality and more timely decisions. This technology will bring together coiled tubing specialists, formation evaluation experts, drilling engineers and the G&G people. Anaconda allows the driller to go in the hole and sniff out pockets of oil and gas
in real time instead of just steering geometrically from the surface. We can make the assembly almost turn on a dime. No one else can do that."
Marty Paulk, Anaconda formation evaluation and geosteering manager, said, "Anaconda provides real-time data that helps refine the earth model as drilling progresses. New geosteering applications present this data in both macroscopic and microscopic views. The macroscopic view shows the relative position of the well to the geological surfaces in a 3D view. The microscopic view is one in which the driller correlates expected model log responses to the measured log responses. The earth model is modified on the fly, and the relative stratigraphic position of the wellbore can be determined. Then the driller moves the targets in the 3D geology to maintain the optimum position in the reservoir.
"Equipment reliability and uptime should be greatly improved because most of the processing currently being carried out downhole is now performed at the surface. Software is programmed to minimize the need for human intervention. For example, the software takes action to reduce weight on bit before the mud motor stalls without any human intervention. With the fine level of control we have, drilling is more of a milling operation with bit bounce and whirl greatly reduced. The real-time pressure measurements help us optimize the hydraulics of the system, which results in highly improved hole cleaning and minimizes short trips. Drillers usually operate with a rule of thumb for short-tripping to clean the wellbore. This system takes the guesswork out of it so borehole condition is improved and the incidence of stuck pipe is reduced. When we build the Stage III system for deepwater, where time is very expensive, you'll know exactly when to circulate to avoid a problem."
Paulk added, "Anaconda creates a dynamic picture of the wellbore. You can see changes taking place. It's like a wireline run every trip in or out of the hole, giving us multiple passes over time. The high-speed telemetry and control capabilities provide everything we need to monitor and optimize the whole process. We can open circulation subs, bypassing the motor and bit during trips, which results in increased bit and motor life and reduces the potential for accidental sidetracks. We constantly monitor drilling dynamics through sensors, and can then manage and vastly reduce downhole vibration and shock, which contributes to improved reliability. You can see the harmonics while drilling. The surface system records everything in the entire drilling operation - from start to finish. So it can be reviewed for planning the next well or for training simulations and courses to qualify operators. It can be used in instant replay mode for detecting and analyzing problems. Because the system is digital, we can have experts anywhere in the world analyze and comment. The Anaconda system spans the field asset life cycle and opens up options for operators that they never had before."
The first applications
The Anaconda advanced well construction system is undergoing extensive testing at the Halliburton Research and Development Center in Duncan, Okla.. The ACCT endured more than 50 times the number of stress cycles usually considered acceptable for steel coiled tubing with an equivalent outside diameter. Some design improvements were made to BHA components, electronics and software as a result of the horizontal surface test program.
A test well was drilled and cased down to 1,800ft at the center. The Anaconda system will drill three extended horizontal sidetracks with multiple turn and build sections to test 3D steering capabilities, exercise the formation evaluation and directional sensors in a realistic environment, and perform real-time geosteering.
"The system has been extensively tested onshore. All the individual pieces have been thoroughly checked out both in the horizontal flow loop and in test wells in our Duncan facility. For example, we milled a window and ran the composite pipe back and forth many times to verify wear characteristics. The tests are currently under way with a 7,000ft test reel, and a 21,000ft reel is under construction for the next phase of testing," said Alan Coats, global technical consultant for AWCS.
"The first commercial deployment will most likely be for shallow gas applications in the Gulf of Mexico that were often uneconomical or out of reach until Anaconda was developed," said Terry. Statoil and Halliburton both agreed the first few commercial wells will be drilled in the United States to prove the system's components prior to going to Norway.
Added Marker, "The first Norwegian wells will be in either Statfjord or Gulfaks fields. They are older offshore fields both with three large platforms. All six platforms have 40 to 50 wells or slots each. What we want to do is use existing wells to drill through tubing to new targets that are more than 1,500m (4,922ft) away from the mother bore. We
will set a 3½in. or 4in. liner and use the existing completion equipment to produce. In these fields the target zones are becoming smaller and smaller, and the production declines are faster. We need to be able to drill faster and cheaper to keep the fields economically viable.
The way forward
Development of systems II and III will hinge on the success and ideas that evolve from the initial wells. "The second system might be funded in part by several other interested operators." Marker said, "There are applications beyond Statoil, and when we started out our management recognized that Anaconda had to be a good deal for the industry not just Statoil. We plan to put some percentage of our cost savings from System I into a technology fund for future work. For example, for the larger BHAs, we would like to have a gas sensor tool so that we can see the gas zones. Many of our fields have been water-flooded and also have gas reinjection. We want to be able to steer away from the gas and complete just the oil zones. We are talking about incorporating a sonic tool to look at borehole geometry. The sonic tool should also give us some seismic information and ideas about porosity and can help see gas."
Terry added, "We don't yet have visibility of all the innovative applications for the Anaconda system. Nor do we see all the benefits resulting from spinoff technologies that were born from this project. We feel confident this technology will change the way we exploit reserves, and help revise reserve estimates more accurately. The operators will need to change a lot of behavior in the way they complete wells such that they can take advantage of the Anaconda system to allow for through-tubing re-entry later in the field life.
"We feel one of our greatest future challenges will be to ramp up to deal with the business opportunities ahead of us. Initially, we plan to work very closely with just a few customers. In 2 to 3 years, we envision having about 20 or so units working around the world. One of the challenges in growing the business is attracting and training suitably qualified people," he said.
Anaconda represents the journey of drilling engineering into the new century. It takes advantage of everything information technology has brought to the table to optimize drilling the reservoir. n
References
l SPE Paper 60750, "Anaconda: Joint Development Project Leads to Digitally Controlled Composite Coiled Tubing Drilling System," Roy Marker et al. Presented at the ICoTA Coiled Tubing Roundtable, Houston, TX, April 5-6, 2000.
l SPE Paper 60757, "An overview of the Health, Safety, and Environmental Program for Advanced Well Construction Systems,"
E. Alan Coats, et al. Presented at the ICoTA Coiled Tubing Roundtable, Houston, TX, April 5-6, 2000.
l Acknowledgements
The author thanks Jim Terry, Dave Stegemeier, Marty Paulk and Alan Coats of Halliburton Energy Services and Roy Marker of Statoil.