Drilling systems under development will take significant costs out of the well construction process. From small coiled tubing (CT) drilling rigs for North Sea wells to microrigs for exploration wells in ultra-deepwater, development projects under way will radically cut the cost of exploratory holes.

US drilling expenditures hit a 13-year high of US $17.6 billion last year, spurred upward by the trend toward deepwater exploration, according to the American Petroleum Institute (API).
Offshore drilling accounted for $5.5 billion of that figure, which is 35% higher than the year before. The number of offshore development wells drilled rose 40%, and their costs rose 71% from 1997.
Both offshore and onshore, drillers targeted deeper objectives, leading to the highest-ever average cost per well and average cost per foot, $778,480 and $133.64 respectively.
Gas well drilling dominated, and an emphasis on deep to ultra-deep development objectives, mainly offshore, fueled similarly high drilling costs.
With all this in mind, the drilling technology trends that will advance in the next 5 years appear to be:
• low-cost offshore drilling systems;
• laser drilling systems;
• hydraulic jet drilling systems;
• equipment for offshore underbalanced drilling in deepwater; and
• extended-reach multilateral completions.
Environmental benefits come along with the new technology. Advanced technology has led to fewer dry holes, smaller drilling footprints, more productive wells and less waste. It takes 22,000 fewer wells annually to develop the same number of reserves as it did in 1985.
In the United States alone, operators produced 148 million bbl less drilling waste in 1998. Footprints were reduced as much as 70%. This is important in areas like Prudhoe Bay, Alaska. Horizontal wells can replace four or five vertical wells. Three or four extended-reach multilateral wells rather than 15 or 20 vertical wells will drain small offshore reservoirs.
An inexpensive offshore system
NeuRobot is a concept spearheaded by the Shell Expro group with the help of several suppliers and is designed to stimulate individual technology developments.
The goal is to develop a system to radically cut costs of drilling wells for small fields (500,000 to 40 million boe). This requires a change in construction costs.
The advanced subsea development system consists of three critical success factors:
• expandable solid tubulars that can be used to construct reeled monodiameter wells;
• an intelligent reeled drilling system incorporating advanced geosteering technology; and
• small, dynamically positioned, reeled-system drilling vessels.
The target date for completion of all of the technology goals is roughly 2004.
The work on reeled expandable solid tubulars is underway with joint ventures between Halliburton and Shell (Enventure) in the United States, and Shell and Baker Hughes (E2Tech) in Europe. Development on the intelligent reeled drillstring is progressing with one design for a 4½in. bottomhole assembly (BHA) with 5in. CT to drill hole sizes of 8in. OD with a variable gauge bit (6in. to 8in.). Slimhole BHAs sized to 31/8in. OD are in development. In the short term, this work would be beneficial for through-tubing sidetracks on existing North Sea platforms.
Composite CT will solve some of the problems with large diameter CT that are weight and fatigue-related. With less weight, better fatigue-resistant composite CT will provide a superior material. However the low density and low bending stiffness of composites reduces achievable bit weights. This can be overcome by use of drilling tractors, which are rapidly coming to market. The composite CT will incorporate the cables necessary for power and high-speed data transmission necessary for the intelligent BHA.
Variable-gauge bit designs being developed can be integrated into an existing 31/8in. steerable CT drilling BHA. The bit will expand from 3¾in. to 4½in.
As well, a CT drilling electric motor in development allows drive power to be provided independent of mud flow, thus avoiding motor stall, better controlling weight on bit and permitting more hydraulic power to be used for hole cleaning.
A seismic look-ahead/look-around tool incorporating a downhole sonic source and receivers as part of the BHA is under development with trials set for this year. The goal is to have a sonic range of about 200m with a resolution within 1m. Data transfer will occur with the cable embedded in the composite CT drillstring. This valuable
tool will aid in the better definition of casing points, avoidance of subsurface hazards and optimization of wellbore placement in the reservoir. Research is underway to better define tool specifications, improve seismic interpretation techniques and solve problems such as tube wave noise.
Reeled systems drilling vessel
A reeled systems vessel (NB-2) that constructs reeled monodiameter wells is the ultimate goal of the project. An interim goal is a light subsea well intervention and through-tubing CT drilling vessel. This system, NB-1, will include three features that enable faster subsea well intervention operations compared to traditional anchored semisubmersibles:
• dynamic positioning;
• fast transit speeds (about 12 knots); and
• wireline and CT intervention systems integrated and maintained as part of the vessel.
The project may be realized by 2001.

Subsea drilling rig
A step change in drilling technology will be required to economically drill beyond 4,000m due to the weight of the risers and the size of the drilling rig required.
Shell Deepwater International Services and Saipem have collaborated on a conceptual design for a subsea drilling rig that looks like a fully submersible jackup rig and would be controlled via an umbilical from a dedicated surface vessel (see picture , p59).
The overall cost estimate to develop and construct the first rig was $450 million, including a 10% contingency. It was deemed unlikely such a vessel would be built unless critical reserves could not be reached by any other means. However, this work spawned another concept for a subsea microrig for exploration drilling.

Cheap exploration drilling
Shell looked at designing a drilling system based on exploration failure - commonly 70%. It reasoned that if it could eliminate the high-cost parts of a well including coring, well testing, logging, re-entry and completion, a rig could be designed for minimal expense.
With the advent of slimhole logging-while-drilling (LWD) tool development, potential hole size can be reduced to around 3in. This would result in fewer cuttings, smaller and cheaper casings, no drill-in fluids, less cement, lighter equipment and reduced drilling time.
Enter the micro subsea rig concept proposed by the Center for Marine and Petroleum Technology (CMPT), Aberdeen, for the Drilling Independent of Depth (DIODE) project. Dick Winchester, former director of technology at CMPT, was responsible for developing the concept. He took over DIODE about a month ago and will be developing it through a new private company. The idea is to fund it using venture capital rather than trying to obtain funding from oil companies to develop a joint industry project.
The rig would be designed to drill a minimum size hole to gain a minimum amount of information using LWD. This data would then be used to make a decision on a full-size appraisal well. The rig would most likely use CT drilling, with some form of limited reeled casing system, which would enable a single string of casing to be set just above the reservoir.
Shell has shown internally that an exploration program based on the assumption of failure can lead to cost savings with this new concept, assuming a significant cost reduction of around 30% to 50% can be made with the failure-based drilling system.

Laser drilling project
"Achieving a technological breakthrough with laser drilling could generate the kind of radical change that occurred at the turn of the century when the rotary drill replaced cable tools. Rather than incremental improvements to already proven designs, laser technology has the potential to revolutionize gas drilling in the 21st century," said Richard Parker, GRI.
The GRI laser drilling contract will be finished by February. It has run low of funds, so GRI is focusing on capturing the results in a series of reports that will be published by that time or shortly thereafter. While interest in the project has remained high, GRI has not been able to gather a critical mass of companies willing to take a risk on this technology. While casting about for a laser lab, GRI discovered Argonne National Lab in Chicago has two lasers that would take them much further toward proof of concept.
"GRI became aware of an opportunity for funding through the Natural Gas and Oil Technology Partnership, which is a method to bring [US Department of Energy] money into the national labs with industry guidance. A proposal was submitted, made the short list and was slated for review. If approved, the proposal would give GRI funding for up to 3 years," said Parker.

High-pressure water jets
Laser drilling may become practical in the future, but a high-pressure fluid jetting system developed from proven military technology having comparable performance is here now.
For multiple laterals, San Francisco-based Petrolphysics Inc. has been using nothing but water or other liquids, a frac truck and a production rig with a CT drillstring to drill, re-enter and rework existing commercial wells with dramatic increases in production in light and heavy oil systems.
By attaching specialized nozzles at the end of a CT drillstring and employing pressures up to 15,000 psi, the jet drilling system creates fluid velocities of 700 to more than 1,000 ft/sec. Drilling action is caused by a stream of liquid and vapor microparticles that interact with rock, which produces rapid drilling rates. Rate of penetration in commercial reservoir rocks (sandstones and carbonates) is 1 to 5 ft/min (60 to 300 ft/hr) continuously. The shape of the nozzle controls the 2- to 4in. borehole diameter. Clean fluids cause hardly any wear on the nozzle.
The Petro Jet multilateral system is used to drill inexpensive multiple laterals (radials) in single or multiple layers from a vertical or deviated well. Three other drilling systems have been or are being developed by the company:
• Petro Jet vertical system;
• Petro Jet horizontal system, designed to produce 25,000ft horizontal wells near the surface and under the surfline; and
• Petro Jet vertical or extended-reach system, geared to drill vertically and then continue around a less-than-medium radius vertical to horizontal turn and extend horizontally for long distances.
Texaco has employed the inexpensive multilateral drilling system in light and heavy oil fields in Wyoming, and Unocal, Chevron and Sante Fe have used it in their California oil fields. Production enhancements of 160% to 1,000% have been achieved. Wells in California have typically been drilled for a cost of $125,000 to $150,000. For these wells, 10,000 psi pressures were used. Now the Petro Jet multilateral system is being extended to drilling with 15,000 psi fluid jets. Drilling rates have improved markedly at the higher pressure compared to 10,000 psi.
The multilateral approach is used to drill a minimum of four horizontal laterals at 90° from one another, all of which make a 1ft radius turn from vertical to horizontal. These laterals rest at least 100 to 200ft from the existing vertical cased hole. This creates stable channels of low-flow resistance through the near-wellbore zone. Essentially the holes are long perforations. Production has increased and stabilized over long periods of time.
This approach also helps bypass anisotropy or heterogeneity in the reservoir, particularly when these properties are not well-defined. At least some of the lateral holes will be in the optimum orientation to drain the well. Water coning has been controlled with this drilling technique in the Caddo-Pine field in Louisiana, where there is a strong natural water drive.
When Petro Jet multilaterals were placed in a typical well, the water cut was markedly reduced, and the oil production increased 400% to 800% on average. The production enhancement has reportedly continued without decline for more than 5 years.