3
NATIONAL IMPORTANCE OF DRILLING

Introduction

Drilling is a key technology in several applications of strategic or societal importance, including

  • exploration for and extraction of oil, gas, geothermal, and mineral resources;

  • environmental monitoring and remediation;

  • underground excavation and infrastructure development; and

  • scientific studies of the Earth's subsurface. 

Drilling is the primary tool for extracting petroleum from rocks in the subsurface. Improvements in drilling technology that lower drilling costs and increase the rate of success in finding and extracting petroleum will have a direct benefit to the United States in terms of higher energy reserves, stable energy costs, and improved economic competitiveness in the drilling and service industries, which are increasingly global in character. Drilling is also the primary tool for extracting geothermal energy (hot water and steam) from the subsurface for heat and electricity production. At present, geothermal energy is more expensive than fossil fuel energy, owing in part to the high cost of drilling. The reduction in drilling costs through the introduction of improved technologies will allow more of this clean, domestic energy source to be utilized.

Drilling is becoming an increasingly important tool for environmental protection and remediation. Drilling is a relatively noninvasive method for investigating and removing chemical and radioactive wastes from the subsurface, and for placing barriers in the subsurface to halt the spread of contamination. Improvements in drilling technology will improve the efficiency of waste extraction and thereby lower the cost of cleanup efforts.



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3 NATIONAL IMPORTANCE OF DRILLING Introduction Drilling is a key technology in several applications of strategic or societal importance, including exploration for and extraction of oil, gas, geothermal, and mineral resources; environmental monitoring and remediation; underground excavation and infrastructure development; and scientific studies of the Earth's subsurface.  Drilling is the primary tool for extracting petroleum from rocks in the subsurface. Improvements in drilling technology that lower drilling costs and increase the rate of success in finding and extracting petroleum will have a direct benefit to the United States in terms of higher energy reserves, stable energy costs, and improved economic competitiveness in the drilling and service industries, which are increasingly global in character. Drilling is also the primary tool for extracting geothermal energy (hot water and steam) from the subsurface for heat and electricity production. At present, geothermal energy is more expensive than fossil fuel energy, owing in part to the high cost of drilling. The reduction in drilling costs through the introduction of improved technologies will allow more of this clean, domestic energy source to be utilized. Drilling is becoming an increasingly important tool for environmental protection and remediation. Drilling is a relatively noninvasive method for investigating and removing chemical and radioactive wastes from the subsurface, and for placing barriers in the subsurface to halt the spread of contamination. Improvements in drilling technology will improve the efficiency of waste extraction and thereby lower the cost of cleanup efforts.

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Drilling technology, including tunneling technology, is finding increased application in the development of urban infrastructure (utilities, transportation, and communications facilities), much of which is located underground. A significant fraction of this development is supported directly or indirectly by taxpayers. Improvements in drilling technology will lower costs and could allow more infrastructure to be located underground, thereby increasing aboveground living space in urban areas. Oil Drilling The U.S. petroleum industry maintains a high level of drilling and spending for drilling-related goods and services in the continental United States, despite the oil price collapse in 1986. This substantial level of activity should continue in the foreseeable future. In 1990, total petroleum industry exploration and production was $45.2 billion (American Petroleum Institute [API], 1991). Expenditures for drilling comprised about $10.9 billion of this total and were concentrated mostly in exploration and development well drilling. Although the U.S. petroleum industry continues to maintain a considerable level of domestic drilling activity, the character of the companies drilling domestic petroleum wells is changing. Major petroleum companies are redirecting their exploration and production budgets for work abroad, and drilling activity by these companies in the lower 48 states has reached historically low levels. An increasingly large number of domestic wells are now drilled by small- to moderate-sized companies (independents) rather than major companies. Independents drill about 85% of domestic exploratory petroleum wells in the United States (Bode, 1992). Many independent companies occupy niches in certain geographic or technological areas in order to reduce costs and increase success rates. In the future, domestic oil and gas development will probably be dominated by these technically oriented, small- to moderate-sized companies or by major companies that have decentralized activities (Fisher, 1993). This change in the character of the industry reflects in part the changed character of the remaining resource base. Statistics compiled by the API (Table 3.1) indicate the magnitude of the domestic petroleum oil and gas industry drilling effort. In 1992, the U.S. petroleum industry drilled 124, 148, 449 ft in 23,998 wells (World Oil, 1993). Oil well drilling continues to slightly outpace gas well drilling.

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TABLE 3.1 Estimated Wells and Footages Drilled by the Petroleum Industry in 1992 (World Oil, 1993) CONTINENT OIL GAS DRY OTHER TOTAL FOOTAGE North America 10,981 8,887 7,875 902 28,745 144,436,169 United States 8,596 7,929 6,610 863 23,998 124,148,449 South America 1,462 62 274 192 1,990 12,477,671 West Europe 256 189 170 216 831 7,534,692 East Europe 9,965 786 860 88 11,699 84,797,571 Africa 408 36 99 66 609 5,670,955 Middle East 256 23 63 51 1,033 7,096,678 Far East 7,323 235 250 2,265a 11,149 61,530,591 South Pacific 61 41 94 11 207 1,465,770 World 30,712 10,259 9,685 3,891 56,263 325,010,097 a Mostly mainland China.

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In 1992, the number of gas wells drilled was 7,929, compared to 8,596 oil wells. Drilling between depths of 1,250 and 9,999 ft accounted for most oil well drilling in 1992; the average depth for all wells in 1992 was 5,444 ft. The number of wells drilled by the petroleum industry in the United States amounted to about 43% of wells drilled worldwide in 1992, and U.S. drilling accounted for about 68% of all dry holes drilled worldwide in 1992 (Table 3.1). This reflects the increasingly complex and elusive nature of potential reservoirs, as well as limitations of current methods for locating hydrocarbon deposits. The proportion of wells drilled and the total drilled footage outside North America should increase as additional areas around the world are explored and developed. Complex geological conditions and difficult geographic circumstances in many of these areas will require the capability to remotely sense conditions in the subsurface and to drill holes in different orientations. In 1990, the average cost for "conventional wells" (i.e., vertical wells drilled by using standard equipment) was about $75/ft (API, 1991). Drilling costs reflect the depth, type, and location of wells and the costs of drilling-related services. A comparison of wells drilled to similar depths at similar locations indicates an actual decrease in drilling costs for conventional wells since 1984 (API, 1991). This likely reflects, in part, improved drilling efficiencies and lowered costs resulting from advances in technology. Petroleum well drilling in the United States is essential to ensure a stable domestic supply of energy. Recent estimates of the volume of recoverable resources suggest that operators should be able to improve their ability to add more reserves per unit of effort through improved technology (Fisher, 1993). In 1992, a panel of oil resource analysts convened at the request of the U.S. Department of Energy concluded that there is a substantial remaining, recoverable volume of crude oil in the United States, on the order of 99 to 204 billion barrels (Oil Resources Panel, 1992). The range in estimates reflects different assumptions of price and technology. This recoverable resource is the target of drilling for oil resource development (Fisher, 1987; U.S. Department of the Interior, 1989).

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Although the undiscovered oil resource base is substantial in the aggregate, it is different from what has been pursued historically. The nature of the typical oil drilling target is changing from large reservoirs to smaller, less readily detectable reservoirs (Fisher, 1988). The fields being developed today generally are more geologically complex; consequently, their development requires reserve growth drilling.1 In summary, the potential oil resource accessible by drilling is significant, and U.S. oil and gas drilling for this resource will continue at or near current levels for at least the foreseeable future. The potential oil resource accessible by drilling is significant. However, reservoirs are increasingly smaller in size and are located in more geologically complex settings. Advances in drilling technology are especially important for accessing these targets and reducing overall development costs. Natural Gas Drilling Natural gas, which is composed mostly of methane, is a relatively clean and domestically abundant fuel that provides more than one-fifth of the primary energy used in the United States. Natural gas is particularly important in the residential sector, where it supplies nearly half of the energy consumed in U.S. homes (Energy Information Administration, 1993). It can also be liquefied for use in transportation as compressed natural gas. There is potential for growth in the use of this fuel for transportation and for generation of electricity, given the large size of gas reserves in the United States and the availability of sophisticated natural gas production and delivery systems. The use of natural gas to generate electricity is projected to increase from 2.8 trillion cubic feet (Tcf) in 1992 to 5.5 Tcf by the year 2005 (U.S. Department of Energy, 1992), primarily due to the relatively clean-burning nature of natural gas compared to other fossil fuels. At present, most natural gas is produced in the lower 48 states from conventional sources (Table 3.2). In 1991, about 20.5 Tcf of gas were 1   Such as infill drilling, intrapool recompletions, or horizontal drilling.

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TABLE 3.2 Current and Projected U.S. Gas Supply (Tcf or quads, see footnote 2)—Prices (1992$ per 106 Btu) are shown in square brackets (Woods, 1993) AREA 1991 2000 2010 Lower-48 states 18.0 [$1.52] 19.4 [$2.26] 21.0 [$3.14] Alaskaa 0.4 0.4 0.5 Importsb 1.8 [$1.78] 2.8 [$2.43] 3.8 [$3.27] Nonconventional 0.2 [$3.44] 0.1 [$3.54] 0.1 [$4.15] Totals 20.5 [$1.56] 22.7 [$2.29] 25.4 [$3.16] a Prices were not developed for gas production consumed in Alaska or exported. b Imports have a higher price because they often enter the transmission system downstream from the wellhead. consumed domestically at an average price of about $1.56 per 106 Btu.2 Gas consumption is expected to increase to about 25.4 Tcf per year by 2010 at an average price of $3.16 (in 1992 dollars) per 106 But. The majority of this supply (21.5 Tcf) is expected to be produced in the lower 48 states and Alaska. Recent domestic supply projections indicate that a substantial resource of about 1,300 Tcf exists in the lower 48 states (National Petroleum Council, 1992; Enron Corporation, 1993). At present rates of U.S. gas consumption (approximately 20 Tcf/yr), this amounts to a supply of about 65 years. This resource includes 160 Tcf of proved reserves, 616 Tcf of conventional resources, and 519 Tcf of unconventional resources (National Petroleum Council, 1992). Major unconventional sources include 2   1 Tcf of dry gas has the energy equivalent of 1 × 1015 British thermal units (Btu), or 1 quad (1 quad = 1 × 1015 Btu).

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low-permeability (tight) gas in shale and sandstone, and gas found in coal seams (coalbed methane). For these sources, technological advances may be particularly critical to efficient exploration and development because reservoirs are difficult to detect and access. This is also true for conventional gas resources located at depths greater than 15,000 ft (deep gas). Of the more than 2 million wells drilled to date in the United States, only about 16,000 reached depths of 15,000 ft or greater. Tight gas and deep gas are likely targets for targeted drilling, directional and horizontal drilling, and smart drilling technology. Geothermal Drilling Geothermal energy, including steam, hydrothermal, hot dry rock, and magma resources, constitutes a large and relatively untapped source of energy in the United States. The U.S. Geological Survey estimates total geothermal resources in the upper 10 km of the Earth's crust in the United States to be between 210,000 and 1,100,000 quads (Table 3.3), which is several orders of magnitude large than current annual rates of domestic energy consumption.3 Rex and Howell (1973) estimate that geothermal energy in the United States could supply 400,000 megawatts (MW) of power for a projected life of 100 years.4 The U.S. Department of Energy (1991) estimates that geothermal energy output will rise from 20 billion kilowatthours (kWh) in 1990 to 184 billion kWh in 2030 and will account for about 3% of all U.S. electricity generation. Geothermal energy is used in the vicinity of the production site for heating purposes (e.g., space heating and chemical processing) or is converted to electricity for long-distance transport, in which case it competes directly with oil, gas, coal, and nuclear energy. The cost of geothermally produced electricity exceeds that for most other energy 3   The current annual rate of domestic energy consumption is approximately 82 quads (Energy Information Administration, 1993). 4   In 1993, the United States had 2,725 MW of installed capacity of geothermal energy from plants in California, Hawaii, Nevada, and Utah (U.S. Department of Energy, 1993). For comparison purposes, U.S. electrical generating capacity (i.e., net summer capability) in 1992 was approximately 695,000 MW (Energy Information Administration, 1993).

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sources. For example, current electricity prices are $0.025 to $0.060 per kWh in California (Kito, 1993), compared to Standard Offer 4 prices for geothermally produced electricity of $0.10 to $0.11/kWh. 5 In allowing for geothermal power plant costs, which are about $0.03 to $0.04/kWh, steam must be delivered to the power plant for less than $0.03/kWh to be directly competitive at current prices, compared to $0.07/kWh under Standard Offer 4 prices. At current electricity prices in California, it is not economical to build a geothermal power plant or to purchase geothermal energy. TABLE 3.3 Estimated Geothermal Resources in the Upper 10 km of the Earth's Crust in the United States (Muffler, 1979) SOURCE ESTIMATED RESOURCE (quads) Hydrothermal 110,000 Hot dry rock 50,000-500,000 Magma 50,000-500,000 Total 210,000-1,100,000 Geothermal energy is more costly than oil and gas at current prices, owing to the relatively low energy capacity of geothermal water and steam. In general, high numbers of large-diameter wells must be drilled in order to obtain sufficient water and steam for heating or electrical production. Geothermal reservoirs are frequently found in mixed hard and soft volcanic rocks, which makes drilling difficult and costly. Only a small portion of known geothermal resources can be exploited at current energy prices. Exploitable resources are usually found at shallow depths (generally less than 4,000 ft) and have extremely high productive capacities. 5   Standard Offer prices are established by the California Public Utilities Commission for the purchase of electricity from qualifying facilities.

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There is considerable room for improvement in technology for geothermal drilling. Improvements are needed to increase penetration rates and tool life in the mixed (hard-soft) volcanic rocks that form many geothermal reservoirs. Improvements are also needed to reduce the number of ''discontinuities," such as lost circulation and stuck pipe, that typically occur while drilling in geothermal reservoirs. These improvements will allow deeper or less productive geothermal resources to be exploited. Environmental Drilling The cost of cleaning up hazardous wastes in the United States may exceed $1.2 trillion to be spent over the next 30 years, with a "best guess" value of $750 billion. Of this, about one-third ($240 billion) will be spent on the government's weapons complexes (Nuclear Waste News [NWN], 1991). The market for environmental consulting may grow at a rate of 20% per year from its 1991 value of $8.2 billion (NWN, 1992a), and simultaneously, the market for environmental remediation work will grow from about $2.5 billion in 1992 to more than $5 billion in 1995 (NWN, 1992b). There are approximately 45,000 sites across the United States that are in some way contaminated by radioactivity; half of these are owned by the government (NWN, 1992c). Perhaps the best-known of these is Hanford (Washington), where there are 149 single-shell and 28 double-shell storage tanks for radioactive waste ranging in size from 55,000 to 1 million gallons (NWN, 1992d). Other sites at Hanford contain smaller amounts of radioactive material, as well as nonradioactive pollutants such as chlorinated hydrocarbons. The number of U.S. sites at which hazardous but nonradioactive pollution occurs is not known with certainty, but it is probably at least as large as the number of radioactive sites. In a majority of cases, pollution is in the form of solid or liquid wastes that have escaped into the subsurface. Depths of penetration range from the immediate surface to at most a couple of hundred feet. Cleanup will involve two stages, namely, site characterization followed by remediation. No techniques are yet available that allow the extent of subsurface pollution to be estimated noninvasively. Further, remediation will always require access to the polluted zone. Drilling is probably the least disruptive method presently available for examining the subsurface. Remediation methods that operate through one

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or more boreholes will certainly be preferable to, for example, excavating the entire site and removing the polluted ground for treatment elsewhere. The fraction of total remediation costs attributable to drilling is not easily estimated. The difficulty of access, the type of pollutant, and the nature and time of treatment will influence the total cost. In petroleum operations, drilling costs typically account for 50 to 80% of exploration finding costs, and about 30 to 80% of subsequent field development costs (Vincken, 1987). Typical costs for shallow hydrocarbon wells (up to 1,250-ft depth) drilled in the United States are about $27/ft (Anderson and others, 1991). Whether this figure applies to typical environmental projects is not clear, but the sequence of operations—namely, identification of the zone of interest, test drilling, "production" drilling, and pumping operations to "produce" fluids—is of similar relative importance. The boreholes required for environmental remediation will be shallow, so it might be expected that they will cost in the range of $20 to $30/ft, similar to shallow petroleum wells. However, special circumstances may increase these costs substantially. If the drilled solids contain toxic or radioactive substances, the cost of drilling may increase dramatically because of the need to collect, document, and dispose of the cuttings and to decontaminate drilling equipment. At the Hanford site, for example, typical drilling rates (cable tool) are about 8 ft/day, at a cost of $800 to $1,000/ft (Volk, 1992). Alternative drilling methods are under investigation at the Hanford site, including the use of resonant sonic drilling methods (Volk, 1992; Volk and others, 1993) and the cone penetrometer (NWN, 1992e). The former has about twice the rate of penetration and is similar in cost to the cable tool method (Volk, 1992). Cost estimates for the cone penetrometer are as low as $50/ft (NWN, 1992e). The cleanup of small-scale, nonradioactive subsurface contamination (e.g., local gasoline spills) will probably be more straightforward, and it is expected that drilling costs will be much lower. In the absence of any estimate of the relative numbers of wells that will be drilled in "difficult" and "easy" circumstances, a very approximate estimate can be obtained by assuming that the fraction of the environmental budget spent on drilling will be the same as the fraction of a petroleum operations budget spent on drilling. If this estimate is correct, then by using the figures given previously, the total value of the environmental drilling market ranges from $225 billion to $960 billion, with $72 billion to $192 billion to be spent on the government's weapons facilities. In any case, it is clear that

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there is a substantial opportunity for drilling research to develop techniques for drilling in contaminated ground, with a major issue being the handling of contaminated cuttings. Once a contaminated site is characterized, remediation wells have to be drilled to place barriers, to inject or pump out subsurface fluids ("pump and treat"), or to use air sparging and other remediation activities. Many of these wells will have to be directionally drilled. At the Department of Energy Savannah River Site, several directional and horizontal wells have been drilled (Kaback and others, 1989a, b; Westinghouse Savannah River Co., 1992). Early work was carried out by using conventional oil field directional drilling technologies, but subsequent holes have been drilled with purpose-built equipment or with drilling techniques adapted from river-crossing and service placement technologies. The use of horizontal wells to remove contaminants from the Savannah River Site saved $125 million compared to a conventional pump-and-treat program (NWN, 1992f). Once the hole has been drilled, it is not always easy to keep it open, particularly in very soft, sandy ground. Various consolidation techniques are available from the oil industry and from civil engineering practice, but many rely on the use of grouts6 that themselves introduce undesirable additional pollution. One promising technique that is under investigation (Simon and Cooper, 1994) is to freeze the ground around the borehole, thus preventing collapse until a protective casing can be set. An application of particular importance in the field of environmental characterization is the need to sample subsurface solids and fluids accurately. In the case of solids, issues concern the requirement to recover undisturbed cores so as to identify chemical species that are present and also to measure strength, porosity, and permeability. In the case of the fluids, the nature of the fluids, dissolved solids concentration, and saturation are important parameters. In taking a longer perspective, there is an obvious need for directional drilling instrumentation and steering techniques that will be able to monitor and react to the surroundings as the hole is drilled. This would allow the detection and avoidance of undesirable obstacles such as pipelines, tanks, or contaminated regions. It would also allow the drilling assembly to be 6   Cement slurries that are injected into the subsurface, usually through boreholes, to seal fractures and other openings.

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steered to follow a desired direction, for example, to stay at or near the water table or to follow permeable layers. In summary, there is a large market for "environmental drilling." It is characterized by a need for minimally invasive vertical (investigation and monitoring) to horizontal (remediation) drilling at relatively shallow depths (maximum, 300 ft). Penetration of loose ground is probably the most difficult problem, because of poor hole stability, particularly if the ground contains a mix of hard and soft material (e.g., sand and boulders). Although existing drilling technologies may work under some conditions, there is no universally applicable technique. For some applications, there is no acceptable method available at all. Service Companies U.S. service companies have historically been leaders in drilling technology related to the oil, gas, mining, and tunneling industries. This leadership is being threatened by economic problems and the fact that mining and oil companies are moving overseas. Data from the Bureau of Labor Statistics (Fletcher, 1992) show that from the peak drilling activity in 1981, the oil and gas industry has lost more than 369,000 jobs. Total annual oil and gas exploration and production expenditures paid to service companies decreased from $36.7 billion in 1981 to $10.6 billion in 1990 (Independent Petroleum Association of America, 1991). Job losses in the oil and gas service companies include many of the technical leaders in this field. Service company technical leadership was established and has been maintained for several reasons. Until recently, there has been a large domestic market for these companies, because of the large number of holes drilled for oil and gas in the United States. The profitability of the service industry was high, which allowed it to make large expenditures for R&D. This industry also had the benefit of an excellent U.S. educational system, which turned out large numbers of trained engineers, as well as excellent technical resources, including universities and national laboratories. The world leadership of U.S. service companies has been diminished by several recent developments. First, and foremost, is the reduction in the exploration and production of domestic mineral resources, due mainly to a reduction in market prices for petroleum and certain mineral commodities, as well as environmental restrictions. There has been a concomitant

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reduction in profitability of the major petroleum, mining, and service companies. These companies have slashed their budgets and pared their staffs, and many have significantly reduced or eliminated their spending for R&D. Overseas operations of domestic service companies have also been affected by foreign laws and policies that exclude them from certain markets. The leadership of U.S. service companies is also being challenged by foreign government-subsidized projects to develop advanced drilling tools. Examples of such projects include (1) extended reach offshore drilling tools (6 to 8 miles) to drain entire offshore fields from single platforms (BP and Statoil—North Sea); (2) slim-hole drilling systems to significantly reduce drilling costs in remote areas (BP and Shell); (3) deep-water offshore oil production systems (Petrobas—Brazil); (4) hard-rock geothermal drilling systems (Komatsu—Japan); and (5) advanced deep-well guidance systems (KTB—Germany). U.S. service companies do not presently have the resources to undertake these types of long-term development projects. In the committee's view, development of advanced drilling systems is needed to keep U.S. service companies competitive. These advanced systems will require the integration of advanced mechanical, computer, hydraulic, electronic, and rock destruction technologies. U.S. service companies are specialized and therefore do not have the in-house capabilities to develop all components of these systems. Infrastructure, Underground Excavation, and Mining Infrastructure and underground excavation include facilities such as water and sewers, railroads, highways, mass transit, and communications. Demands for new facilities are increasing at an accelerated rate due to the increase in urban populations. In addition, there is a high demand for replacement facilities because many existing facilities have exceeded their design lives. Until recently, most of these facilities have been located on or near the surface. However, with increased urban crowding, there is increased interest in building these replacement facilities underground. Recent estimates suggest that over 200 miles of tunnels, 5 ft and larger in diameter, will be built in the United States by the end of the century (American Underground Space Association, 1993). In addition,

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approximately 1,000 to 3,000 miles of microtunnels, tunnels between 1 and 5 ft in diameter, and perhaps another 10,000 miles of tunnels less than 1 ft in diameter, are expected to be built in the same time period (Kramer and others, 1992; Boyce, 1993; Iseley, 1993). This represents a capital expenditure of $7 billion to $10 billion for driving the tunnels alone. In contrast to drillholes discussed earlier, these tunnels are one to two orders of magnitude greater in diameter, they are generally horizontal, and they must be lined to provide a service life of 50 to 100 years. Additionally, these tunnels must be driven through a variety of geologic materials from soft, water-bearing silts and clays to very hard bedrock, and very often they must be driven in crowded and environmentally sensitive urban areas. The owners and users of infrastructure and underground facilities generally are the taxpayers, through federal, state, and local governments. In some instances (e.g., communications and some utilities) the immediate owners are regulated or quasi-governmental entities, but the ultimate users are taxpayers. In the past, the federal government often provided the majority of funding (up to 90%) for construction of these facilities. However, the current and continuing trend is toward greater financial participation of local governments through taxation, bonds, or user fees. In the privately owned mining industry, much of the exploratory drilling is similar to that described previously for the oil and gas industries. In addition, the mining industry uses boring machines to gain access to ore bodies and to drive operations connections between various areas of mines. These machines are similar to, or use technology similar to, tunnel boring machines (TBMs) used for infrastructure and underground excavation. The mining industry also uses smaller machines to drive smaller connecting tunnels and shafts, and to provide communications and utility connections between various areas of mines. These machines are similar to, or use technology similar to, microtunneling machines. Estimates for the lengths of TBM- and microtunneling-like excavations in mining operations are not available. Discussions with Professor L. Ozdimir, Colorado School of Mines, have led to the rough estimate that by the end of the century, these might total 100 miles of mining tunnels greater than 5 ft in diameter and 500 miles of microtunnels (Ozdimir, 1993). In the past, improvements in tunneling technology have followed an evolutionary path, owing to gradual changes in machine design by TBM manufacturers and general contractors. When TBMs were introduced some 35 years ago, tunneling rates were measured in feet per day at best; tunneling rates of modern machines under ideal conditions are measured

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in hundreds of feet per day. Advances in U.S. TBM technology have slowed, mainly because domestic manufacturers are leaving the business or are being acquired by foreign firms. In the committee's view, the ability of U.S. industry to build next-generation TBMs will be difficult without a coordinated domestic effort. A coordinated effort is needed for TBMs because although some components can be tested individually, the machine itself must be tested by prototype. Only stable, well-capitalized companies can handle the risk associated with the development of new technology, given the expense of prototype design, construction, and testing. Continued improvement is expected in tunnel construction technology, but it is also expected that, left to the continuing historical evolutionary process, advances will continue at an average rate of only a few percent per year. A coordinated development program would greatly accelerate this rate of improvement by concentrating resources and expertise. Drilling for Scientific Purposes Drilling provides a vital operational avenue to satisfy a multitude of scientific purposes, both on the continents and in the oceans. Although drilling and exploration for resource recovery remain important purposes, the overall objectives of scientific drilling are far broader and include the following (National Research Council [NRC], 1979, 1988, 1992): structure and chemical constitution of continental crust; distribution of mineral resources; thermal regime of the crust and crustal heat flow; state of stress in the Earth's crust and crustal response to stress, including properties of fault zones for purposes of understanding earthquake phenomena; and nature and age of the ocean floor with particular reference to seafloor spreading. A considerable amount of scientific drilling is supported by federal agencies in order to address several societally important issues, such as supplies of energy, water resources, mineral resources, environmental management, disposal or storage of hazardous wastes, siting of dams, and location of nuclear power stations. In 1978, federal expenditures for continental drilling amounted to $500 million/yr (NRC, 1979). Although

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the portion of this total designated purely for scientific purposes was much smaller, scientific investigations of various magnitudes were associated with nearly all such drilling activity. In more recent times, for example, from 1985 to 1992, the extent of scientific drilling in the continental United States involved a total of 31 holes to an average depth of 425 m, with one reaching a depth of 3,250 m and a temperature of 350°C. The purposes of these programs included activities such as the study of crustal structure (5 holes), volcanology (4), geothermal processes (21), and fault tectonics (1). The present (1992-1993) scientific drilling activity in the United States involves about 20 projects reaching an average depth of 902 m for rather similar purposes such as the study of sedimentary basins (7 holes), geothermal processes (4), volcanology (4), mineral deposits (2), and meteorite impacts (3). In addition to these, the United States is an important collaborator in several large international scientific drilling programs such as the Lake Baikal, Kola Peninsula, and KTB deep drilling programs (MacGregor, 1993). In distinction to the continental drilling programs, the Ocean Drilling Program of recent years involves an outlay of roughly $40 million/yr but is devoted to almost exclusively to scientific purposes (NRC, 1992). There are well-established organizational means of exploiting most drilling opportunities for scientific purposes. Several recent NRC studies of both continental drilling (NRC, 1979, 1988) and ocean drilling (NRC, 1992) have assessed the goals, potentials, and successes of these programs and have recommended well-thought-out, long-range operational procedures for nurturing, selecting, and funding them. These studies have concluded that in a number of important areas, key improvements in the state of the art of drilling could markedly improve the attainment of scientific objectives (NRC, 1979, 1988). These objectives include drilling to greater depths (∼ 10 km), drilling through harder rock at higher temperature (∼ 500°C), and sample collecting from these environments, which often have higher reactivity. Other recommendations include development of long-term fluid-flow measurement techniques; techniques for slim-hole drilling with continuous casing capability; better techniques to determine the in situ state of stress in the crust; and development of means for making reliable long-term incremental stress measurements in such adverse environments. In areas more specifically related to hydrocarbon resource recovery, recommendations have included improved a priori reservoir evaluation to increase the fraction of available resources that can potentially be

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recovered (the average present recoverable fraction in most oil fields is no better than one-third, with the remainder being declared nonrecoverable [NRC, 1988]). This requires the development of better predrilling geophysical assessment of potential reservoirs. Even with the above provisos, however, the long-range objectives associated with scientific drilling are generally being met with present technology. In many areas, the demands of scientific drilling programs in terms of (1) precision and depth in hard rock, as in the KTB Scientific Bore Hole program (Zoback and others, 1993a); (2) required sophistication for core recovery, as in the projected San Andreas Fault Drilling Project (Zoback, 1993b); and (3) overall complexity in undersea drilling at high pressures and temperatures into hard rock (NRC, 1992) both act as stimulus for radical improvements in drilling technology and provide the opportunity for such developments. Because the cost of drilling is usually the major part of any scientific drilling program, such programs require careful planning to utilize all available opportunities, both nationally and internationally. Therefore, the scientific drilling community must be well organized and fully cognizant of developments in commercial drilling. Alternatively, in any long-range development plan for radical improvements in drilling for resource recovery, full liaison with the scientific drilling community is essential. Summary and Recommendations Drilling is a key technology in several applications of strategic or societal significance, including: exploration for and extraction of oil, gas, geothermal, and mineral resources; environmental monitoring and remediation;  underground excavation and infrastructure development; and scientific studies of the Earth's subsurface.  All of these applications would benefit from improvements in the basic drilling system that breaks rocks and removes debris from boreholes and excavations. Such advances should include the following:

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increasing rates of penetration and tool life through improvements in cutter technology and materials; improving capabilities to sense conditions at and ahead of the tool in order to locate targets or avoid obstacles in the subsurface; and improving the ability to steer the bit and to drill directional, or horizontal holes to reach desired targets or target zones.  The objective of these improvements is to enhance the ability to locate and reach targets in the subsurface and to reduce the overall costs of doing so. Indeed, these improvements in drilling technology will enhance the competitive position of U.S. companies in several sectors of the economy, most notably in the areas of resource exploration and extraction, environmental remediation, and infrastructure development. The committee believes that improvements in drilling technology can best be achieved through a national R&D effort that integrates industry, university, and government perspectives. Federal support for this effort should be used primarily as a catalyst, with industry providing both technological and financial support. The actual R&D should be done by the best-qualified institutions, whether in the private sector, universities, or government laboratories, with the percentage of R&D support from the federal government and industry being project specific. The committee also believes that the program should be structured with shared research objectives between 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- and long-term R&D requires a long-range administrative structure that combines the needed discipline, mission orientation, and flexibility to nurture the required scientific and technological innovations. The committee discussed a number of possible administrative structures, but it ultimately concluded that recommendations in this area were outside its task and expertise.

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