Behind-bit injector, neutral drillpipe extend drilling stepout distances

With deep and ultra-deepwater drilling pushing against the technical limits of steel pipe, Halliburton has announced a new drilling and intervention system that uses composite drillpipe to overcome many of the sticking points (literally) of current technology.

Drillpipe is very heavy and is moved downhole with the assistance of gravity. This method is very cheap going in (weight on bit), but expensive coming out (hookload, handling capacity). In addition, as step outs and horizontal sections exceed five miles, it becomes difficult to overcome the friction of the wellbore on the pipe.

Among several important technological advances, Jim Terry, Director of Anaconda for Halliburton, says the newly developed system (Anaconda) would use a spooled composite drill pipe that is neutrally buoyant in typical drilling fluids. This overcomes all of the problems faced with moving steel pipe in and out of the hole, and turning it when a stepout is in excess of five miles. In fact, turning the pipe is no longer a factor.

The Anaconda makes hole using a mud motor to turn the bit and an injector to drive the pipe. When the limits of these techniques are reached, new technology kicks in. A specially designed propulsion system integrated into the bottomhole assembly (BHA) draws the pipe further downhole.

The ability to not only move beyond the limits of conventional horizontal drilling, but accurately steer the bit, is due to the composite coiled tubing being pushed downhole from a point near the bit, rather than being pushed by the weight of the pipe. The downhole propulsion system can exert 6 tons of weight on the bit. The composite coiled tubing is coiled in lengths up to 20,000 ft on reels.

Downhole propulsion

The downhole propulsion unit on the Anaconda uses two expandable elements, similar in design to mechanical packers. These elements are spaced apart across a stroke length integral to the BHA.

• The first element is expanded to make mechanical contact with the borehole.
• The second element is 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 axial force to the bit. Drilling progresses until the full stroke of the unit is realized.
• The forward element is again expended, the second element contracts, and the process is repeated.

The propulsion system is capable of walking in or out of the hole, as required.

Bigger, not better

The typical ultra-deepwater drilling system is a variation on the standard technologies with bigger and heavier equipment. Once operations move offshore, heavy equals expensive. As the requirements of these wells push the conventional technology to its limits the returns on bigger and heavier equipment drop rapidly in relation to the costs.

By contrast, the composite drillstring at the heart of the Anaconda system is light, easy to handle, and thanks to the unique BHA, can be steered through an almost infinite number of angles and turns to optimize the well path and improve reservoir drainage.

Real-time data

In order to make the best use of this new system's capabilities, the driller needs to know two things, where the bit is and where he wants it to go. To accurately guide such a system will require real-time data on the bit and reservoir.

Current downhole data technology faces a number of challenges. Once the data is received at or near the bit, it must be processed. This means that expensive downhole processors with limited capabilities have to be included in the BHA. Because of the heat and stress, these units often fail.

The limitations of slow mud-pulse telemetry require that the data is processed downhole and only the answer is transmitted to the surface via mud pulses. While advancements in these capabilities continue to progress they can only move small batches of data at a time. In most cases the process is too slow to be considered real-time and much valuable data is not received at the surface. This data is stored in downhole memory and can only be reviewed after the fact on surface, when the tools are retrieved.

To give the driller an accurate real-time picture of the conditions downhole, a communications system had to be developed. Anaconda uses a product called SmartPipetrademark to achieve much faster data transmission than can be obtained by mud pulsing. This composite coiled tubing pipe has embedded conductors in the lining of the pipe that link the bottom hole assembly with automated processing equipment on the surface. Power is supplied from the surface to downhole.

The BHA is a new Halliburton design called the Advanced Drilling, Evaluation, and Propulsion Tool or ADEPT. Compared to conventional mud pulse technology, Terry explained that this BHA transmits enormous amounts of raw data to the surface 2,000 times faster mud pulsing. This provides the real-time data required to update the oil company's geologic earth model as the well is being drilled. The complex processing equipment that until now resided in the BHA has been moved to the surface where it takes advantage of high-speed data capabilities. This not only means a less expensive, more robust suite of technology, but less risk of down time due to processor, power, or mud pulse telemetry failure. If a problem does occur it can be remedied at the surface, without the time and expense of pulling the drillstring.

Remote control

Using these capabilities for steering and data transmission, the well path can be controlled from anywhere in the world. This means a team - drilling engineers, reservoir engineers, formation evaluation experts, geologists, and geophysicists - gathered at the oil company's visualization room or a Halliburton visualization center, can evaluate the incoming data and make decisions on how the well should proceed. Operations are so automated that the driller controls the project by mouse. In fact, routine drilling is fully automated.

Once the well path is chosen, the system drills on its own. The control center on deck is manned by a driller, called a pilot, a system engineer, and a navigator. Because there is so much automation built into the drilling routines, the people involved can focus on reading the downhole data, converting it to useful information, and using it to make decisions of how the bit should be steered.

In addition to the surface crew making decisions on the rig, the data can be transmitted back to the Halliburton center or to any remote location around the world for further collaboration. This saves the operator in terms of travel time, but more importantly allows the client to make the best use of top technical people.

Halliburton plans to drill the first offshore well using the Anaconda later this summer. The concept was developed with the support of Statoil with an eye to the North Sea, but the first offshore well will be drilled in the US Gulf of Mexico.

The initial system is a slimhole design for specific Statoil applications in through-tubing, sidetrack, and intervention work. Because of its light weight and compact size, the Anaconda system can be transported onto existing platforms to perform workover drilling as well as stimulation, testing, and completions work. The Anaconda system can be installed on a barge brought alongside for use on an offshore drilling unit.

C-BOP designed with Anaconda in mind

To accompany the numerous technological step changes brought forward by the Anaconda concept, Cameron has developed a new C BOP "Safety Head" specifically designed for use on this project.

Albert Kachich, Senior Product Design Engineer with Cameron's Drilling Products Engineering group said the shear rams on this unit (patent pending) were also of a special design. The safety head shear rams are required to perform a variety of special and complex cuts. For example the unit was tested to shear 10 pieces of 1-1/4-in. tubing.

Such cuts are difficult because multiple tubing strands randomly disperse along the cutting edges of the ram and flatten unevenly. The BOP was also required to cut through an extensive array of downhole tools such as sand screen assemblies and perforating guns. Jim Terry, director of the Anaconda Project for Halliburton said the "Safety Head" BOP must be able to shear anything that is being run through the hole if a gas kick occurs.

The most difficult cut required of this new unit, according to Kachich, was shearing 10 pieces of logging cable with zero tension. He explained that cutting cable is difficult because the strands of cable tend to fold instead of shear, so that most of the cable is cut, but a few strands remain connected. To overcome this a special patent pending shear ram design was developed.

The shears have a double edge along with a specific weld inlay for maximum hardness. The shear design is a press fit, meaning there is no clearance between the inner-locking shears. The lower blade is pinched against the upper blade producing a press fit that can cut cleanly through the cables.

Beyond the various shear requirements of the unit, size was also a prime consideration. The compact size of the new safety head design allows the unit to be deployed, in compliance with the strict health, safety, and environment guidelines in effect on Norwegian sector platforms and facilities.

To comply with these restrictions, Kachich said Cameron used a single large piston to provide strength for these difficult cuts. This is the largest piston of its kind to be used on a blowout preventer (BOP) this size, but Kachich said the alternative, using a second piston to act as a booster, would make the unit too large. "Cameron is pleased to be a partner in the development of this new technology for the Anaconda Project. Enhancements in the Model C BOP provide a major extension to shearing and sealing capabilities for workover and coil tubing applications." said Gilbert Nance, Vice President for Cameron's Drilling Business.