Drilling and Excavation Technologies for the Future (1994)

Technology to drill holes and to excavate tunnels and openings in rock is vital for the economic, environmental, and scientific well-being of the United States. Drilling is a key technology in several applications of strategic or societal importance, including energy and mineral production, environmental protection, and infrastructure development. During this century, U.S. technology has dominated the worldwide drilling industry and much of the excavation and comminution industries. In the committee's view, this U.S. dominance is likely to erode without continued technological advances.

Although incremental improvements in the component processes in the present state of the art can continue to make drilling more productive, it is the basic conclusion of this committee that revolutionary advances are within reach through the introduction and concerted development of smart drilling systems. A smart drilling system is one that is capable of sensing and adapting to conditions around and ahead of the drill bit to reach desired targets. This system may be guided from the surface, or it may be self-guided, utilizing a remote guidance system that modifies the trajectory of the drill when the parameters measured by the sensing system deviate from expectations.

The smart drilling system does not currently exist, but it is presaged by recent dramatic advancements in directional drilling and measurement-while-drilling technologies. Rapid innovation in microelectronics and other fields of computer science and miniaturization technology holds the prospect for greater improvements—even revolutionary breakthroughs—in these systems.

The development of smart drilling systems has the potential to revolutionize drilling. Research in this area will have a significant impact

on drilling success and overall cost reduction. Such "smart" systems are increasingly needed to overcome the drilling challenges posed by small, elusive, easily damaged subsurface targets. This is particularly true in applications where identification of small or difficult-to-predict drilling targets and formation damage are key issues in drilling success.

In the development of smart drilling systems, the required improvements in the sensing elements of the system will have an impact on other processes such as rock breaking, debris removal, and borehole stabilization. Revolutionary advances in these fundamental processes might be possible as information about the subsurface environment becomes available in real time.

The development of a smart drilling system requires concerted technological advances in several areas, which include the following:

1. Development of precise connections between measurable properties and local drilling resistance: Such connections must be established based on the existing understanding of the connection between rock constitution and comminution mechanisms. Many physical and microstructural properties such as porosity, elastic properties, and wave attenuation can be measured locally. These must be associated more precisely with factors that govern the drilling resistance of rock through directed mechanistic studies and modeling to develop automated response characteristics of a smart system.

2. Development of sensors for the smart drilling system: The smart drilling system requires sensors that are capable of detecting and measuring the following:

   • Conditions at the drill bit: Sensors are needed for in situ measurement of pressure (including pore pressure), temperature, permeability, mineralogic and chemical composition of the rock and heterogeneities, borehole fluid composition (at the part-per-million level for environmental applications), stress state, and rock strength.  

   • Conditions ahead of the drill bit: Sensors are needed that measure rock properties (e.g., porosity, elastic properties, wave attenuation) ahead of the drill bit to adjust drilling parameters, such as the weight on the drill bit and the rotary speed, and to avoid potential problems (e.g., blowouts or loss of circulation) while drilling. 

• Spatial position of the drill bit: Sensors are needed that are capable of detecting the position of the drill bit in space as required, in order to steer the bit around undesirable zones and reach desired targets.

1. Development of control systems for accurate positioning and steering of the drill bit and for automatically adjusting drilling parameters (e.g., load and torque on the drill string, flow rates of drilling muds and fluids), according to local conditions, is necessary to optimize rock breakage and rock removal. This will require precise information at the bit-rock interface of the rock breaking mechanism, rock strength, pressure, temperature, and stress state.

2. Development of improved methods for steering the drill bit: A number of mechanical methods for steering are currently available, but large turning radii often preclude their application in a smart drilling system. To enhance steering capabilities, R&D is needed to develop downhole motors, flexible drill strings, and guidance techniques for smart drilling systems.

3. Continuous monitoring of the state of the entire drilling unit, including wear of tools, state of other mechanical components, flow of coolant, and the like, is required to anticipate the occurrence of possible discontinuities.

4. Development of improved telemetry methods for transmitting real-time borehole data to the surface: The use of advanced sensors for real-time downhole measurements will require significant improvements in data telemetry. Such telemetry is essential for monitoring the smart system from the surface. At present, the most advanced telemetry systems utilize mudpulse technology and are capable of transmitting data at only a few bits per second. Rates on the order of kilobits per second or higher will be required for advanced smart drilling systems. Telemetry is a rate-limiting step in present drilling systems, and it will become more so as smart drilling systems are developed.

5. Development of means for continuous and instantaneous support of the rock around the borehole: The support provided by the rock itself should be used, where possible, in lieu of casing the hole as a separate operation.

Although the principal thrust of the proposed R&D program should be on smart systems, the program should also facilitate incremental improvements in all consequential aspects of present drilling technology. This should result in more immediate attainment of greater efficiencies and cost savings, and will lend needed justification to continued long-term support for the program of smart system development. Such additional R&D should focus on the following problems:

• novel drilling technology, with a focus on the physics of rock removal to reduce energy requirements for drilling;

• improved cutter materials and bearings;

• improved bits for drilling in heterogeneous materials;

• development of environmentally benign drilling fluids; and

• development of durable, compact, high-power downhole motors for directional and extended reach drilling.

This R&D program should be a national effort. Both the public and the private sector should benefit; resources and guidance for the program should be shared, where appropriate. This program should have the following characteristics:

• Integration of industry, university, and government perspectives should be achieved.

• Federal support should serve primarily as a catalyst, with industry providing both technological and financial support. The percentage of R&D support from the federal government and industry could be project specific. The actual R&D should be done by the best-qualified institution whether in the private sector, universities, or government laboratories.

• Finally, a long-term commitment is needed to accomplish the objectives of the program.

The program should be structured with shared research objectives among the federal and industrial partners. Support of projects should be based on a peer-review process and assessment of how the results would contribute to overall program goals. Competition for research funds should be open to industry, national laboratories, and universities.

Attainment of the proposed enhanced drilling capabilities through both short-term and long-term R&D requires a long-range administra

tive structure that combines the discipline, mission orientation, and flexibility needed to nurture the required scientific and technological innovations. Although the committee discussed a number of possible administrative structures, it ultimately concluded that recommendations in this area were outside its task and expertise.