Policy Paper

Evolving Technologies for Future Deep Geological Repositories: A Closer Look

Technology advancement in drilling industrial oil and gas wells might have potential application for future geological repositories of spent nuclear fuel

The nuclear fuel cycle in the 21st century has been leaning toward the back-end of the fuel cycle. Recognizing that existing stockpiles of nuclear waste are continuing to grow, this study aims to advance the debate on back-end fuel cycle options to enhance the opportunity for the successful disposal of radioactive waste. Using an interdisciplinary approach, we recognize that current advancement in borehole drilling technology used intensively and extensively in the oil and gas industry might have potential application for deep geological repositories (DGRs) of spent fuel. The study, therefore, identifies several promising innovative drilling technologies that might be used in constructing and monitoring DGRs, provides some safeguards considerations for permanent disposal at DGRs and highlights technical issues to be considered.

Abstract

The nuclear fuel cycle in the 21st century has been leaning toward the back-end of the fuel cycle. Recognizing that existing stockpiles of nuclear waste are continuing to grow, this study aims to advance the debate on back-end fuel cycle options to enhance the opportunity for the successful disposal of radioactive waste. Using an interdisciplinary approach, we recognize that current advancement in borehole drilling technology used intensively and extensively in the oil and gas industry might have potential application for deep geological repositories (DGRs). The study, therefore, identifies several promising innovative drilling technologies that might be used in constructing and monitoring DGRs, provides some safeguards considerations for permanent disposal at DGRs and highlights technical issues to be considered.

Introduction

The nuclear waste industry is considering a range of technologies as they design and construct deep geological repositories for the permanent disposal of spent nuclear fuel (SNF) and other high-level waste (HLW). Designs for DGRs typically have a depth greater than 1,000 feet (305 m) however depths can vary based on host environmental characteristics, design and utilization purposes in each country. For example, the DGR in Olkiluoto, Finland goes 1500 ft. (455 m) down in the granite bedrock, the Waste Isolation Pilot Plant (WIPP) in New Mexico, USA has been constructed in an ancient salt bed at a depth of 2150 ft. (655 m), and a DGR in Canada anticipates being at a depth of about 1640 ft. (500 m), depending on rock characteristics at the site. ¹ No matter how deep DGRs are, rock excavation and drilling would be primary methods used for construction.

For many decades, drilling methods have been used intensively and extensively in the oil and gas industry. Advances in technology resulted in reduced drilling and completion times, lower average well drilling and completion costs by 25-30% in the 2012-2015 period and increased well performance.² Historical success and experience in the oil and gas industry may have a potential application in designing, constructing and monitoring the next generation of DGRs. Therefore, it is worth examining some of the innovative drilling technologies and exploring how changes in technology side might affect the future geological repositories for SNF and other HLW and their potential impact on nuclear safeguards implementation.

Technology Revolution and Implications

The oil and gas industry revolution has resulted from the need for more petroleum resources and innovative drilling technology. Since the early 20th century, unconventional resources such as shale oil and gas, tight sandstone oil and gas, coal-bed methane, and natural gas hydrates have been gradually exploited due to exhausted conventional resources and advances in directional drilling.³ Deep drilling in-ground can reach reserves at 15,000 ft. (4500 m) while ultra-deep drilling can go as far as 25,000 ft. (7500 m). Drilling under the seabed is more challenging; yet, industry records show that operators can reach reserves in deep water at 1,000 ft. (300 meters) and ultra-deep water at 11,156 feet (3,400 meters). ⁴, ⁵ To exploit ultra-deep petroleum resources, vertical drilling is needed, mainly due to the ability to reduce down-hole accidents. Unconventional petroleum resources, on the other hand, are exploited by mostly non-vertical wells, such as directional wells, horizontal wells, multilateral wells, and extended reach wells. ⁶ In terms of geological disposal of spent nuclear fuel (SNF), both vertical and non-vertical boreholes drilling methods can be useful. By studying industrial use cases, we identify relevant technologies and make recommendations for underground geological disposal. SNF disposal in deep water is not considered in this study.

Vertical drilling for conventional boreholes

Vertical boreholes are wells aimed at a target directly below its surface location. Vertical drilling is typically less than 20° deviation between the hole and the vertical, so the boreholes are almost straight down. In 1895, the first vertical well was drilled by the percussion drilling method or cable-tool drilling method to a depth of 65 ft. (20 m) at Titusville in the United States. It is still in use, particularly for shallow oil or gas wells in the Appalachian Basin. ⁷ , ⁸ In this method, the rock formation is cracked by repeated strikes from a heavy steel bit which is lifted and dropped using a cable. This drilling operation has to be paused after a while to remove the rock fragments, and then resume until a hole is formed at designed width and depth. However, the cable-tool drilling is not suitable for soft formations of the southern United States, i.e. sedimentary rocks such as sandstones, limestones, clays in Texas. Hence, a new approach was needed.

Starting mid-20th century, operators improved the operation efficiency by applying rotary drilling to penetrate different types of rock formations. This method features a rotating long steel pipe (drill-string) with a sharp bit on the end to cut through underground formations. In contrast to the cable-tool drilling, rock fragments are lifted from the downhole by the drilling fluid circulation system. ⁹ Rotary drilling has demonstrated its efficiency among many technologies applied in the petroleum industry. As an example, after Shell ¹⁰ started applying rotary drilling in the Gulf of Mexico in 1907, other oil and gas companies followed suit, such as Standard Oil of California ¹¹ to drill the hard formations of California. For an economic point of view, innovative rotary drilling started the bloom of oil and gas production with annual production exceeding one billion barrels in 1925 and two billion barrels in 1940. By the 1990s, global supplies recorded 20 billion barrels annually. ¹²

Directional drilling of unconventional boreholes

Directional drilling is the method of drilling a borehole along a projected and controlled, non-vertical route to a favoured target. This method has transformed the oil and gas industry since the 1920s because of its efficiency in unfavourable surface configurations such as buildings, trees, groundwater above, or a steeply inclined rock fault zone. * In geology, a fault is a planar fracture or discontinuity in a volume of rock, across which there has been significant displacement as a result of rock-mass movement. * Several models of directional drilling include horizontal, multilateral, extended reach, which will be investigated in the next sections. These enable natural gas and oil businesses to work more expeditiously, to diminish waste, and to reach more reserves. Directional drilling also has non-petroleum uses such as a potential application in building DGRs for permanent disposal of spent nuclear fuel. Deep Isolation – a US-based nuclear waste company – proposes to drill horizontal boreholes allowing countries to dispose of nuclear waste more quickly, at a much lower cost, and with a smaller footprint than traditional disposal approaches. ¹³

Directional drilling coupled with advanced drilling techniques ¹⁴ such as mud motors, rotary steerable systems (RSS), measurement-while-drilling (MWD) sensing and logging-while-drilling (LWD) has brought two-fold benefits: 1) overcoming prior disadvantages in slower rate of penetration and higher frequency of checking in the devices; and 2) increasing dramatically natural gas and oil production which helps balance the demand-supply relationship.

Mud motors and Rotary Steerable Systems

Mud motors and RSS are helping directional drilling advance rapidly due to greater ease in changing the drill bit’s directions. In using mud motors, drilling fluid (or mud) is pumped through, making the drill bit rotate continuously. This mud pressure pushes the bit into a different angle. On the other hand, RSS is 3-D controlled from the surface using advanced communication techniques such as downlink drilling control system. ¹⁵Therefore, RSS tools can either push the bit or point the bit in the required direction in real time. Mud motors, specifically high-performance motors, are more popular than RSS because they can result in daily cost savings of 50% or more, significantly low lost-in-hole cost ($168,000 versus $1 million) and well suit all bit types and sizes. ¹⁶ Yet, RSS can perform faster, deeper, and more precise. Mud motors and RSS offer petroleum operators with more drilling options, depending on target zones, precision, and time constraint. For future geological disposal, directional drilling coupled with RSS and mud motor can help construct DGRs in a faster, more secure, convenient and economical way, as compared with the traditional tunnelling method.

LWD/MWD

Logging-while-drilling (LWD) and measure-while-drilling (MWD) are well logging systems ¹⁷ used to acquire and collect wellbore information and transmit data to the surface in real time. While MWD is a type of LWD, they are not interchangeable due to their specific functions. LWD helps operators study composition, chemical and physical characteristics of the rocks. On the other hands, MWD records drilling mechanics data such as drill-bit position, direction and downhole pressure.

In the construction of a DGR, the use of LWD could give operators up-to-the-minute updates to monitor canister placement and avoid potential hazards. In the same manner, MWD could allow operators to obtain real-time data about the direction and drill steering for a more accurate construction of the wellbore. For current and future DGRs, newest MWD sensors offer higher quality and accuracy data of the boreholes such as trajectory, rock properties, temperature, and pressure.

Directional Drilling Techniques for Future DGRs

Directional drilling techniques have been used for almost 100 years now. Thanks to technological advancements, engineering has achieved astounding angles, turns, and underground distances covered. Featuring techniques such as horizontal, multilateral, and extended reach drilling have proven their efficiency in enhancing the recovery of oil and gas. Therefore, these techniques can offer certain benefits to the exploration and construction of future DGRs.

Horizontal drilling

Since 1929, horizontal drilling has showcased its advancement and become one of the most successful techniques of directional drilling. The technique was quickly being applied across the United States, China and former Soviet Union countries.¹⁸ Based on a U.S. patented concept labelled as US459152 of non-straight line, relatively short-radius drilling, horizontal drilling distinguishes itself from traditional vertical drilling by deviating the wells until they orient horizontally.¹⁹ Once a target oil or gas resource is located, a well is first drilled vertically from the surface then bends its way just above the target along a curve to reach the reservoir in the horizontal direction. If using vertical drilling, operators can only contact a certain amount of oil and gas within a specific hydrocarbon-bearing shale formation of about 200 ft. (61 m) thick. ²⁰ However, horizontal drilling now allows these same operators to drill and contact for more than 5,000 ft. (1,500 m) in the formation. Thanks to the advancement and exactness of the technology, drillers today can approach a target with a drill string running 10,000 ft. (3,000 m) vertically, a mile-long horizontally, and is a few inches in diameter. For countries considering DGRs, the horizontal drilling technique can offer an alternative solution to lower footprints of their underground repositories while increasing the amount of disposed spent fuel along the horizontal section.

There are three popular patterns for horizontal drilling called short, medium and long. They can be distinguished using the angle-build rate, turn radius and horizontal extension. Table 1 shows the differences between these patterns.

Pattern name	Short	Medium	Long
Build rate	95–300 (°/100 ft.)	7.2–19.1 (°/100 ft.)	1.2–5.7 (°/100 ft.)
Turn radius	2–60 ft.	300–800 ft.	1000–3000 ft.
Horizontal extension	100–800 ft.	1500–3000 ft.	2000–5000 ft.

Table 1. Horizontal pattern classifications ²¹

Canister specifications, including thickness, length and material may help determine the most effective drilling pattern. A typical DGR may benefit from the medium and long patterns of horizontal drilling because of the turn radius, horizontal extension, operational style, and cost. Larger turn radius helps avoid canisters from getting jammed; longer horizontal extension allows operators to emplace more spent fuels into the repository; conventional operation reduces man-hours on training and operating special devices; the cost is lower as the equipment and replacement parts are cheaper.

Constructing DGRs using horizontal drilling technique can also reduce the risk of a surface site having environmental sensitive or operational difficulty. It can also reduce the cost when drilling multiple boreholes in different horizontal directions from one location. For the environment, this means less land impact and society disturbance during the construction period.

Multilateral drilling

A multilateral borehole is a single borehole with one or more wellbore branches radiating from the main borehole. These types of boreholes serve several purposes such as exploration, inﬁll development, or re-entry into an existing wellbore. Depending on the geological conditions of the drill zone, operators will make a decision on multilateral configurations. ²² In general, these boreholes represent two basic types: vertically staggered laterals and horizontally spread laterals in fan, spine-and-rib or dual-opposing T shapes, as shown in Figure 1 and 2.

For DGRs, multilateral boreholes may yield advantages in storing more waste canisters. However, there is always a certain risk ranging from borehole instability, problems with too-close-distance between branches, stuck pipe and problems with over-pressured zones to the casing, cementing and branching problems. ²³

Extended Reach Drilling (ERD)

In the oil and gas industry, ERD allows operators to reach oil and natural gas deposits further away from the rig and under unfavoured areas for vertical drilling. To date, the longest measured ERD well is 50,000 ft (15 km) from the Orlan platform at the Chaivo field (Rosneft, Russia).²⁴ To reach great distances, the motor must be directed in a particular direction while drilling follows the designed path. Current technology advancement in Rotary Steerable System (RSS) allows operators to steer a hole continuously along a horizontal section of the wellbore. This technology has proven to be an asset for all directional drilling models. For DGRs, this ERD technique allows operators to construct a horizontal section as long as the social and geological situation is permitted. It not only maximizes the use of drilling tools for the boreholes and emplacing tools for waste canisters, but also avoids the need to drill multiple vertical and/or horizontal sections in unfavourable surface configuration areas.

Horizontal, multilateral and extended reach drilling techniques have shown their ability to support the construction of future DGRs. However, there are further considerations raised by nuclear waste experts when it comes to technology applications to a DGR for SNF permanent disposal. Modern onshore drilling tools can construct a wellbore up to 16-20 inches wide. ²⁵ However, emplacing a spent fuel canister will require a wider borehole. Fuel assemblies from popular pressurized water reactors (PWRs) and boiling water reactors (BWRs) have dimensions of 6 to 13 inches in diameter by 12 to 14 feet long. ²⁶Taking into account the thickness of canisters, casings, and space for emplacing tools, a drilled borehole needs to be at least 22 inches wide. Therefore, drilling deep boreholes using current drilling tools and techniques from the oil and gas industry may require a sufficient upgrade.

The host rock environment should also be considered thoroughly as oil and gas wells are drilled in soft rock which can be soluble in mild acid such as rainwater when exposed. A DGR is expected to last for thousands of years so a hard rock environment is preferable in the siting process. The natural differences between soft and hard rock pose a question about the sustainability of current drilling tools and techniques in the construction of a future DGR.

The oil and gas industry is moving toward the automation era. According to oil and gas operators, automated drilling will be applied at over 40 percent of wells in the next 5 years. Therefore, the development of future DGRs should adapt well to this fast-changing environment. Moreover, the scale of DGRs needs to be considered to possibly accommodate all spent nuclear fuel in a country. As a rough estimation, one will need 4 boreholes of 30-inch diameter and 2 km horizontal extension to dispose of 9000 metric tons of waste.

Safeguards

The IAEA considers all spent nuclear fuel as practically retrievable, even after emplacement and enclosure of a DGR and therefore, safeguards remain in perpetuity so long as the Safeguards Agreement is in force. ²⁷ The IAEA also emphasizes that safeguards measures must be flexible enough to respond to changing technological developments and to changing needs of current as well as future generations.²⁸ For example, new technologies or new economic conditions may lead part of the waste, particularly SNF, to be considered a useful resource; or the DGR does not perform according to its expectations; or new technologies may be developed which can make the SNF less dangerous or even harmless. All possible social, economic, political and environmental changes might demand recovery of SNF from the repository sometime in the future.

From a safeguards perspective, a DGR poses several challenges. In terms of international safeguards, the design of nuclear facilities subject to a safeguards agreement must be verified by the IAEA. Therefore, IAEA inspectors perform Design Information Verification (DIV) which consists of activities at a facility to confirm that the design information provided by the State is correct and complete. DIV is undertaken periodically during the lifetime of the facility until it has been decommissioned. If a future DGR is constructed by directional borehole method, inspectors may not be able to physically count and weigh waste canisters emplaced underground. It is important that the State and the IAEA have an early consultation starting at the preliminary design stage. Therefore, a future DGR design should consider the use of containment and surveillance (C/S) measures such as cameras and remote instrumentation to transmit data to the IAEA. A recent study of design verification of deep boreholes addressed this challenge by evaluating LWD and MWD for a potential application to DIV inspections of DGRs. ²⁹ The study indicated that sharing some technologies and tools between oil and gas industry and nuclear waste industry might not only leverage use of technologies but also help the Agency maintain Continuity of Knowledge (CoK) of the entire borehole development process. IAEA-dedicated inspection tools coupled with drilling equipment enable inspectors to a broader spectrum of repository visualization without restrictions from ambient borehole environment (air or fluid).

SNF retrievability has been also studied from an industrial standpoint. In industrial drilling, well retrieval, or ‘fishing’, is a technique used to remove or recover a tool lost down a borehole or detached from the drill string. These obstructions are called ‘fish’. Special tools are lowered into the borehole to retrieve specific types of ‘fish’, in which the fish can be speared, grasped, crushed into smaller pieces, or destroyed using explosives. Fishing can be used all the way to 6000 meters (20,000 feet) and probably beyond. ³⁰, ³¹ Big oil and gas companies such as Schlumberger, Weatherford, Haliburton all sell fishing tools and services, making the technique price-competitive and accessible to customers. Therefore, modern technology has the capability to support the retrieval of anything down the holes. On January 2019, Deep Isolation demonstrated the ability to use wireline and fishing tools to successfully emplace and retrieve a prototype waste canister from a horizontal extension of an existing oil and gas borehole in Texas. ³² This is marked as the very first real-life application of oil and gas drilling technologies to nuclear waste disposal – as well as highlighting how nuclear materials, even if buried deep underground, can be retrieved.

One aspect of a DGR worth considering is how to monitor and control activities thoroughly before and after repository closure. Long-term monitoring is highly recommended as a State moves forward with geological disposal. Countries may adopt various monitoring approaches for their repositories. For example, the Finnish baseline monitoring program includes the monitoring of the biosphere and bedrock conditions post-closure even though the Finnish Government has stated that “spent fuel disposal shall be planned so that no monitoring of the disposal site is required for ensuring long-term safety so that retrievability of the waste canister is maintained to provide for such development”. ³³

In our study of well-logging tools, even though they are advanced and efficient, current logging operations are limited to downhole tools with a diameter of 3.75 inches or less. Running tools at a bigger diameter as in the case of deep boreholes for SNF may push the instrumentation tolerances to unsafe limits. ³⁴ Engineering tolerance is an allowable amount above (upper limit) and below (lower limit) a nominal value, that makes measurement acceptable. For maintaining CoK of a DGR using the advanced well-logging system, perhaps, the nuclear waste industry should first consider how to define reasonable tolerance limits for both monitoring instrumentation and borehole design. Proper tolerance limits will increase the liability of performing the safeguards measurements correctly and therefore, diminish discrepancies from subsequent inspections. Using tolerance limits appropriately will save time spent coordinating with the inspectors, circumvent design issues, and reduce unnecessary costs.

Given access to materials is impossible after enclosure of a DGR, monitoring activities will have to be completed by containment and surveillance techniques. Seismic monitoring tracks the movement of the ground from seismic waves created by earthquakes or any violent disturbance of the ground. ³⁵ This monitoring technology can pint-point the location, time, and magnitude of an event, which can be useful to detect any suspected excavations around the DGR area. To document underground openings in case of undeclared premises, there are several technology candidates such as 3D laser imaging, photographs of the rock surface, and/or geologic mapping. ³⁶ 3D laser imaging or scanning digitally captures the image of underground tunnels by using laser light. By measuring many points on the external surfaces of objects, this device represents exact details of size and shape of the tunnel on the computer. Geologic mapping, on the other hand, can look deeper into the composition and structure of the bedrock surrounding the DGR. ³⁷ Field observations, including sketches, measurements and narratives, together with the Geographic Information System (GIS) software, make a complete field interpretation. These technologies could be adapted to site specific requirements and could assist safeguards implementation by creating a profile of undeclared borehole activities which might identify proliferation pathways. This profile might indicate evidence for any intention to retrieve spent fuel or any other material from the DGR, intention to access the sealed DGR after final closure, any tunneling, mining or blasting activities in the vicinity of the repository. The IAEA, upon assistance from member States, then has timely access to investigate these activities, determine if they are unauthorized and/or show early signs of diversion, and impose immediate actions to prevent any further damages. This profile may be an essential resource as States develop acquisition path analysis to deter and prevent proliferation.

The IAEA has indicated a long-term need to strengthen instrumentation capabilities for monitoring and verification in a project on “Develop the Next Generation Surveillance Review software (NGSR)” and the continuity of Modernization of SG IT (MOSAIC) project. ³⁸ As commercial technologies have been rapidly developed, there should be more research projects on the applications of commercial off-the-shelf (COTS) monitoring devices to safeguards verification activities.

To further our study on the applications of advance technology on the safeguards system as well as the impact of geological repositories on existing nuclear cooperation agreements (NCAs), the Stimson Center organized a closed roundtable on “Borehole to Blockchain: Evolving Technologies and Geological Disposal” in May 2019. Key takeaways from the roundtable conversation included perspectives on technology applications for drilling such as tunnelling and hydraulic fracturing to the use of distributed ledger technology (DLT) for safeguards data and long-term information management. From a safeguards implication perspective, there will be a need to ensure that the functioning of a DGR is consistent with the requirements arising from international treaties, agreements, conventions, guidelines and national policy. The safeguards requirements arising from an existing safeguards agreement with the IAEA may not be deemed to be sufficient from a public perspective for a DGR. However, it is possible that a DGR could be created in such a way so as to minimize these concerns and adapt to the future global political landscape and its nuclear risks. For the time being, the IAEA has not considered the deep borehole disposal concept yet. It will be a long distance from studying the DGR concept based on borehole technology to the IAEA’s acceptance and safeguards implementation, but it is better to prepare for the date to come.

Acknowledgements

This research is made possible by the generous financial and logistical support of the John D. and Catherine T. MacArthur Foundation to the Stimson Center’s Back-end to the Future project.

Keywords

safeguards; repository; geological disposal; emerging technology; spent nuclear fuel

Notes

1
* Noronha J. 2016. Deep Geological Repository Conceptual Design Report, Crystalline/Sedimentary Rock Environment; APM-REP-00440-0015 R001, Nuclear Waste Management Organization. *
2
* U.S. Department of Energy, Energy Information Administration. 2016. Trends in U.S. Oil and Natural Gas Upstream Costs. *
3
* Zou C. 2017. Unconventional Petroleum Geology 2nd ed; ISBN-9780128122341, Elsevier, p 49-95. *
4
* OMV Group. 2017. Horizontal Drilling: Lateral Approach to Straight Lines. *
5
* Schuler M. 2016. Maersk Drillship Spuds World’s Deepest Well, gCaptain. *
6
* Ma T, Chen P, and Zhao J. 2016. Overview on vertical and directional drilling technologies for the exploration and exploitation of deep petroleum resources; Volume 2, Issue 4, Geomechanics and Geophysics for Geo-Energy and Geo-Resources, p 365-395. *
7
* See previous*
8
* Pees S. 2004. Cable-tool Drilling, Oil History. *
9
* Term explanation: The circulation system is responsible for cooling and lubricating the drill bit to keep it at its optimal performance. *
10
* Shell Oil Company is the United States-based wholly owned subsidiary of Royal Dutch Shell, which is amongst the largest oil companies in the world. The U.S. headquarters are in Houston, Texas. *
11
* Standard Oil of California was part of the United States-based Standard Oil Corporation. Standard Oil of California acquired Standard Oil of Kentucky in 1961 and was renamed Chevron Corporation in 1984. *
12
* Caudle B. 2010. Petroleum Production, Encyclopedia Britannica. *
13
* Muller R, Finsterle S, Grimsich J, Baltzer R, Muller E, Rector J, Payer J, and Apps J. 2019. Disposal of High-Level Nuclear Waste in Deep Horizontal Drillholes, Energies. *
14
* Kinematicsmfg. 2017. Advanced Drilling Techniques for Directional Drilling, Blog. *
15
* Wang D, and Finke M. 2003. The New, Downlink Drilling ControlTM System that Changes Conventional Drilling Operations, AADE-03-NTCE-47, American Association of Drilling Engineers Technical Conference. *
16
* Drilling Contractor. 2012. Reservoir Drives Choice of RSS vs Mud Motors. *
17
* Wikipedia. Well Logging Definition. *
18
* Ma T, Chen P, and Zhao J. 2016. Overview on vertical and directional drilling technologies for the exploration and exploitation of deep petroleum resources; Volume 2, Issue 4. Geomechanics and Geophysics for Geo-Energy and Geo-Resources, p 365-395. *
19
* Campbell J. 1891. Flexible Driving-Shaft or Cable in Dental Engines, U.S. Patent and Trademark Office, Patent number 459152A. *
20
* U.S. Department of Energy. 2013. Shale Gas Glossary. Penn State University, Marcellus Center for Outreach and Research; Maps and Graphics – Thickness of Marcellus Shale. *
21
* Ma T, Chen P, and Zhao J. 2016. Overview on vertical and directional drilling technologies for the exploration and exploitation of deep petroleum resources; Volume 2, Issue 4. Geomechanics and Geophysics for Geo-Energy and Geo-Resources, p 365-395. *
22
* Term explanation: Multilateral configurations include multi-branched wells, forked wells, wells with several laterals branching from one horizontal main wellbore, wells with several laterals branching from one vertical main wellbore, wells with stacked laterals, and wells with dual-opposing laterals. *
23
* Bosworth S, El-Sayed H, Ismail G, Ohmer H, Stracke M, West C, and Retnanto A. 1998. Key Issues in Multilateral Technology, Oilfield Review, Schlumberger. *
24
* Rosneft. 2017. The world’s longest well was drilled in Sakhalin, https://www.rosneft.com/press/news/item/188679/ *
25
* https://naturalgas.org/naturalgas/well-completion/, published September 5, 2013. *
26
* Muller R, Finsterle S, Grimsich J, Baltzer R, Muller E, Rector J, Payer J, and Apps J. 2019. Disposal of High-Level Nuclear Waste in Deep Horizontal Drillholes, Energies. *
27
* IAEA. 2004. Developing multinational radioactive waste repositories: Infrastructural framework and scenarios of cooperation, IAEA-TECDOC-1413. *
28
* IAEA. 1999. Retrievability of high level waste and spent nuclear fuel. Proceedings of an international seminar organized by the Swedish National Council for Nuclear Waste and the IAEA. IAEA-TECHDOC-1187. *
29
* Finch R, Smart H, and Haddal R. 2017. Design Verification of Deep Boreholes – A Scoping Study, SAND2017-10586, Sandia National Laboratories Report. *
30
* Douglas C. Fishing Techniques for Drilling Operations, Cearley Technology. *
31
* Rigzone. How Does Fishing Work? *
32
* Deep Isolation. 2019. Technology Demonstration. *
33
* IAEA. 2009. Geological Disposal of Radioactive Waste: Technological Implications for Retrievability. No. NW-T-1.19, p 31. *
34
* Lamont-Doherty Earth Observatory. 2004. ODP Logging Manual. *
35
* CTBTO. Verification Regime. https://www.ctbto.org/verification-regime/monitoring-technologies-how-they-work/seismic-monitoring/ *
36
* Posiva. 2018. Safeguards planning and implementation in the geological repository project. *
37
* Soller D. 2004. Introduction to Geologic Mapping. McGraw-Hill Yearbook of Science & Technology, p 128-130. *
38
* IAEA. 2018. Enhancing Capabilities for Nuclear Verification. Department of Safeguards R&D Plan. *

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