Jets, mud-actuated hammers, water pulses and mini-lightning are boosting drilling speeds, while acoustic telemetry and embedded wire show promise in moving downhole data up the drill pipe faster.

Several revolutionary drilling methods that will dramatically increase rate of penetration (ROP) will be commercial in 3 to 5 years. Due to funding by the US Department of Energy (DOE), these research projects have come off the drawing board and are in various stages of field testing.
Jet-assisted CT drilling
Maurer Technology Inc., a division of Noble Drilling Corp., is developing a high-pressure, jet-assisted, coiled-tubing (CT) drilling system in conjunction with BJ Services, which is supplying the CT equipment.
Although the idea of using jet-assisted CT drilling to increase ROP in hard rock has been around for some time, the technology and equipment (10,000-psi pumps, CT, downhole motors and bits) only recently have matured to allow this system to be assembled, tested and commercialized. The high-pressure CT drilling system uses erosion jets to cut slots in the rock ahead of a PDC bit (Figure 1), increasing mechanical cutting efficiency and ROP. CT drilling is 25% less noisy than conventional drill pipe, and it uses 80% less fuel and emits 88% less SO2 compared to traditional drilling methods. CT requires no connections, so there is less chance of leakage when using high-pressure jet-assist.
Preliminary laboratory and bench-scale tests showed that this process is three to five times faster than current drilling rates (Figure 2). "We've achieved very, very high rates of penetration in the lab," said John Cohen, vice president at Maurer. "We've seen up to 1,000 ft/hour in the lab. Field results would be limited by how fast you can clean the hole." Maurer performed computer analyses to calculate the life and performance of the system and select the best candidate for the downhole drilling motor for the project. Software simulations with standard CT showed that the system would only last 12 to 13 cycles because of the high pressure and bending forces acting on the tubing as it goes over the gooseneck or drum. However, Maurer is working with Quality Tubing and BJ Services to test thicker-walled tubing, which computer simulations indicate should increase durability to 200 to 300 cycles, Cohen said.
DOE's National Energy Technology Laboratory is funding the deployment, field testing and commercialization of three CT systems, two for drilling and one for production enhancement and workovers. The US $3 million project is in the field testing and demonstration phase. The first shallow test - at 2,000 ft to 3,000 ft (610 m to 915 m) - will take place at the Catoosa facility in January 2002, and Maurer is looking for an operator willing to conduct a deep test - 8,500 ft to 10,000 ft (2,593 m to 3,050 m) - after that. The system should be commercial in about 3 years.
Mud-hammer drilling
Novatek of Provo, Utah, is investigating an integrated, steerable drilling system that uses a mud-actuated downhole hammer to cut through rock. A portion of the power from the circulating drilling fluid is converted into mechanical force that drives the drill bit into the formation. In addition to the diamond-hardened hammer invented by Novatek founder David Hall in 1974, the system has:
• a rotary vane motor to rotate the hammer drill;
• a high-pressure jet-assist for directional control;
• an integral electric engine to convert hydraulic power to electric power for downhole instruments;
• a casing-while-drilling system based on a diamond-hardened thrust bearing; and
• a seismic look-ahead system that uses hammer impacts as the seismic source.
The system is expected to cut drilling costs significantly in deep, hard formations by increasing ROP and bit life while decreasing down-time and weight-on-bit requirements. Laboratory tests with a prototype tool showed up to 70% improvement in ROP when drilling Carthage marble with 10 lb/gal mud. Novatek has completed a series of optimization tests that have improved tool energy output and efficiency and is working with BP and ExxonMobil to quantify operator benefits in the field.
Hydraulic pulse drilling
Tempress Technologies Inc. of Kent, Wash., has conducted theoretical and laboratory-scale research on the effectiveness of generating intense suction pulses around the bit to drill rock. The suction pressure pulse pulls the bit into the rock, allowing extended-reach and horizontal drilling with conventional rigs. Suction pulses with a magnitude of up to 21 MPa were generated at a rate of 50 Hz. Lab tests showed a fourfold to sixfold increase in ROP using 10 MPa pressure pulses to drill Mancos shale and Colton sandstone. These pulses also can provide a source of intense seismic energy for real-time measurement of pore pressures using seismic-while-drilling tools. A prototype HydroPulse water hammer subassembly has been constructed. The subassembly, mounted on a conventional drillstring and powered by mud hydraulics, is compact and compatible with downhole motors. To see how the tool works, visit www.tempresstech.com/hydropulse.htm.
Field tests of the prototype were carried out in February 2001 at the Baker Hughes Experimental Test Area. Results of these tests showed a 50% increase in ROP through hard rock. The high levels of seismic energy with tricone and PDC bits had sufficient amplitude and frequency to provide vertical seismic profiling with an accuracy of 49 ft (15 m), meeting DeepStar's requirements for look-ahead pore pressure prediction. Operating tests are continuing at the flow loop test facility. The goal is to use the method for drilling formations greater than 5,000 ft (1,525 m), where ROP is hampered by the high bottomhole pressures caused by the mud column.
Plasma-channel drilling
On the other side of the Atlantic Ocean, researchers at Strathclyde University's Department of Electronic and Electrical Engineering are working on a way to use high-voltage pulses - mini-lightning - to produce plasma-channel formation inside the rock ahead of the drill bit. The rapid expansion of this plasma channel, which occurs in less than a millionth of a second, causes the nearby rock to fracture and fragment, generating small holes 1 in. to 2 in. in diameter (Figure 3). Dr. Steven Turnbull of Strathclyde said the phenomenon is similar to how a tree ruptures when lightning strikes it. "A lightning strike would normally be a couple of miles long, but we have miniaturized it down to 1 cm to 2 cm, and it happens continuously 20 or 30 times a second so that the rock erodes through the repetitive action." The machinery needed to produce the high-voltage pulses is portable and more energy-efficient than conventional drilling rigs. And the small holes produced will generate far fewer cuttings that would require cleanup and disposal.
Dr. David McBeth, deputy director of the university's Department of Research and Consultancy, strongly supports commercial development of this new technology. "Many companies now recognize that small-diameter holes represent the preferred option for oil exploration and retrieval because of the resultant big reduction in drilling costs and in environmental impact. Clearly, plasma-channel drilling can provide this option and become the technology of the future for oil and gas exploration and recovery." Scottish Enterprise funded the plasma-channel drilling project in the amount of $212,000 (£146,000).
Data while drilling
Drilling faster requires faster methods of obtaining drilling data for analysis and decision making. Two new methods of moving downhole data to the surface faster are acoustic telemetry and embedding fiber- optic cable in the drill pipe.
Sandia National Laboratories has developed an effective alternative to mud-pulse telemetry. Rather than sending a sequence of pressure pulses in the mud flow, acoustic telemetry uses stress waves in the drillstring to communicate at much faster rates. Noncompressed mud-pulse data only travels at about 1 baud, which is orders of magnitude slower than the slowest modem, causing a data bottleneck for logging-while-drilling (LWD) and measurement-while-drilling (MWD) data. Because of this slow rate, mud-pulse telemetry is limited to directional drilling navigation, as opposed to more complex LWD and MWD tools.
Acoustic telemetry increases the communication rate by 10 to 100 times, which opens up more possibilities for real-time LWD. Acoustic telemetry employs piezoelectric transducers and power amplifiers, which are more reliable than mud-pulse devices because there are no moving parts. However, the digital electronics need to withstand high downhole temperatures. Acoustic systems transmit at frequencies that are unaffected by drilling noise, and they do not block the fluid flow path. Repeaters can be used to improve data transmission rates tenfold to depths of 15,000 ft (4,575 m), and two repeaters can be used for 25,000-ft (7,625-m) depths. Unlike mud-pulse telemetry, acoustic systems can be used for low mud circulation rates, air drilling and underbalanced drilling when nitrogen is injected into the mud.
A prototype has been tested in nondrilling applications, and a field test while drilling was conducted in September. "Drilling tools take a lot of abuse," said Douglas Drumheller, a distinguished member of the technical staff at Sandia National Laboratories in Albuquerque, N.M. Sandia continues to work on a drilling tool using this technology, while Baker Oil Tools has licensed the technology for completion and production operations. However, no commercial system has been released - yet.
Another project Novatek is working on, this time with Grant Prideco, is the development of high-speed data communications integrated right into the drill pipe, thereby doing away with the term "dumb iron." This recently was demonstrated at the Catoosa testing facility and is expected to become commercial in about 3 years.
The two-way data communication will enable drillers to collect data in real time at speeds equal to or greater than computer modem speeds (56K baud). This will be a boon for MWD tools, said David Pixton of Novatek. "We are integrating wireline in the pipe itself, bridging the gap between tool joints. It's made up like normal pipe," he said. The wired pipe will be particularly suitable for "deepwater wells and very deep onshore wells and any well where you need very good control," Pixton said.
"This system's success is highly dependent on how well the service companies accept the system and begin converting their tools to utilize it," said Bernadette Ward of the DOE's National Petroleum Technology Office. "This technology represents the next quantum leap in smart drilling, at least equal to the advent of mud-pulse telemetry."

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