The energy needs of the world likely will continue to evolve at rates similar to those recently experienced by the world. The United States is both a major consumer of geologically based energy resources from around the world and a developer of energy resources. To deliberate its recommendations regarding a future strategy for the Energy Resources Program (ERP), the committee formulated a systematic framework for considering how ERP products (e.g., data, research, assessments) meet the energy research challenges identified in Chapter 2. As described in Chapter 1, the committee considered how the ERP portfolio, processes, and products might evolve to address the nation’s evolving energy needs. Previous chapters focused on current energy challenges and the ERP response to them. The committee presented conclusions about some near-term ERP strategies, given the current tools and technologies (Chapter 4). This chapter provides the committee’s perspective on some of the nation’s future energy challenges and the ERP’s role in addressing them.
Existing and potential energy domains and their related issues considered by the committee included coal, uranium, conventional and continuous (unconventional) oil and gas, renewables, hydrates, the energy-water nexus, and energy storage. Current and potential ERP products considered by the committee ranged from resource assessments and databases to economic recovery assessments, basic research, and evaluation of environmental impacts of resource development. The committee identified program-wide strategies to improve relevance of both the ERP portfolio and its products. This chapter first addresses program-wide strategies (i.e., related to resource assessments, the energy-water nexus, and data and information management) and then addresses strategies for individual program areas.
The service the ERP provides through its resource assessments is appropriate and relevant, and its relevance will continue, with variable emphasis depending on the resource. National-scale assessments of recoverable resources are still required for continuous (unconventional) oil and gas, geothermal, and uranium ores. Rock property information provided in those assessments might serve purposes other than for development assessment (for example, as input for assessments of the energy storage capability of those rock units) if data are captured and presented in meaningful ways. As development of a resource type becomes more mature (e.g., coal or conventional oil and gas), the ERP needs to transition from providing national-scale assessments of overall resource recoverability to providing more focused products. The ERP might target, for example, assessment of coal resources suitable for metallurgical applications, or if revisiting an assessment of conventional oil and gas volumes, they might focus their efforts on previously unidentified resource in a
region. Assessments are of lower priority for resources such as methane hydrates, for which there is still a need for basic research on technical recoverability.
The ERP may continue to receive requests from outside the program to apply its oil and gas assessment methodologies to non-geologic resources, similar to its efforts on the impacts of wind turbines on wildlife (Diffendorfer et al., 2015; see Chapter 3 of this report). Responding to requests to identify new applications for ERP assessment methodologies and build databases to support those new applications is an appropriate use of ERP expertise, as long as the ERP transfers responsibility for maintenance of those products to the responsible agency (e.g., the Department of Energy [DOE] in the case of wind).
The next sections describe priorities for ERP resource assessments that are common to most or all ERP research areas.
Alignment with Consumer Needs
It is possible to better align ERP assessments with stakeholder needs without sacrificing the scientific integrity of current approaches or review processes. Better alignment is necessary if the ERP wants to provide the most relevant information for resource management decisions and policy. Future actions by the ERP could include improvements in product timeliness and in the amount and types of data released. More information regarding how methodologies are applied in analyses would also be helpful, and the release of more raw data would improve consumer confidence in and reproducibility of assessment results. Assessments will have greater relevance if complete reports are released soon after the release of the technical summaries (released as U.S. Geological Survey [USGS] fact sheets). It now is common for there to be a lag time of years between release of those products. Assessments will also be of greater value if they are updated more frequently in response to new data, technology advances that increase resource recoverability, and depletion of a resource as a result of development.
Given that ERP assessments often are informed by proprietary data, certain details about the data may not be made public. Delivering more useful assessment products, however, is still possible. For example, if individual well locations cannot be released, the ERP could release derived products such as maps of reservoir porosity and thicknesses used as input parameters in the assessments. Releasing such derived products simultaneously with the assessments would allow ERP product consumers to evaluate the spatial variation in the density of input data as well as to evaluate the numerical values for individual geologic variables (e.g., reservoir porosity) within an assessment unit. This would increase confidence in assessed resource volumes and their uncertainties. Such maps will have greater spatial resolution of geologic heterogeneities than current products and might allow consumers to pursue their own analyses, such as analysis of high resource density (“sweet spots”) relative to sensitive environmental areas or existing infrastructure. Broader use of ERP assessments is a likely result. Areas of development might be prioritized with more confidence, or potential environmental consequences given specific development scenarios might be predicted. Incorporating derived product data into validated databases will be important as science and industry progress into technologies such as automated learning.
Moving Toward Full Lifecycle Assessments
Future assessment utility will increase if the ERP moves beyond providing just estimates of resource supply if the program also incorporates information that will allow analysis of full costs and impacts associated with energy extraction, transportation, waste production and disposal, and reclamation of developed lands. Energy development of any kind uses resources such as land and water, produces waste, and leaves a legacy (see Box 5.1). Decisions regarding which energy resources are developed and where they are developed need also to include consideration of competing demands for resources and various kinds of risk (e.g., economic and environmental). Recognition of these facts has led to increased interest in lifecycle analysis and development in consideration of impacts on people, wildlife, and the natural environment.
Lifecycle analysis provides a thorough accounting of the resources used and the waste produced for the full lifecycle of a product. The lifecycle of geologic resource development begins with exploration and includes the cleanup and retirement of the energy site. Any lifecycle analysis has to be bound. For the goals of the ERP, those boundaries could be drawn to include the well sites or mines, and possibly transport infrastructure (pipes, roads, or trucks). Importantly, a recent USGS Science Strategy review (Ferrero et al., 2013) advocated that the USGS develop its scientific capacity for lifecycle analyses for energy and mineral resources in general. This science strategy review recommended an energy and mineral lifecycle analysis that included “use,” as depicted in Figure 5.1. Combining lifecycle analyses with analyses of competing resource demands and environmental risks allows consideration of such questions as: “Given the need for a certain amount of natural gas, where should wells be placed to minimize conflicts with other priorities (e.g., endangered species and financial risk)?” and “Which extraction technologies might mitigate environmental impacts?” ERP assessments and basic research need to be designed and conducted in consideration of the planning necessary to best utilize energy reserves in consideration of competing interests and in the nation’s best interest.
The ERP is uniquely positioned to support lifecycle analyses for the resources it assesses because lifecycle outcomes vary with geology and extraction techniques—which the USGS understands and about which it has data. Several studies have shown the value of combining lifecycle impacts with standard assessments. For example, Wolaver and others (2018) combine shale gas production outlooks with data on expected well density and land impacts to forecast threats to endangered species in Texas. Liden and others (2017) map areas anticipated to experience large increases in oil and gas production using high-water-volume hydraulic fracturing, then they couple this to waste management needs and the water cycle. This information then leads to recommendations for investments in cost-effective recycling technologies. Going forward, the ERP will need to examine its own personnel, budget, and other resources to determine how it may incorporate lifecycle data and routine elements of its assessments so that its consumers might more easily combine resource availability with environmental impacts. Decision makers and society can better understand choices, potential future energy portfolios, and the geography of risk (Oakleaf et al., 2017).
Technological Advances and Economic Viability
Current ERP oil and gas assessments describe technically recoverable resources extractable using existing technologies. They do not include projected advances in technology or the economic factors that may inform the viability of production. Future ERP assessments could incorporate factors such as locations or availability of infrastructure, areas where recovery might be enhanced given technology advances (e.g., via cyclic gas injection for oil and gas recovery), or price forecasts for a given commodity. The ERP
might collaborate with the DOE, for example, to obtain some of this information. Economic recoverability information might be overlaid with maps of biodiversity, endangered species habitat, and other environmental variables so that the cost and benefits of development might be more fully considered.
The ERP could assess both technically and economically recoverable oil and gas using a variety of approaches: it might apply similar approaches to those it applies in its coal assessments,1 to approaches used by the USGS Energy and Mineral Resources mission area (e.g., Meinert et al., 2016), or to approaches applied by the oil and gas industry. The Texas Bureau of Economic Geology has developed a comprehensive approach to assessments of unconventional oil and gas resources that includes geophysical well log analysis, petrophysical analysis, and three dimensional geologic modeling to develop projections of technically and economically recoverable resources in consideration of advances in technology (Fu et al., 2015; Ikonnikova et al., 2017). The program will need to decide which assessment method is appropriately rigorous and meets the needs of its product consumers. To prioritize the technologic and economic variables that are most important for ERP product consumers, the ERP could collaborate with organizations such as the Energy Information Administration. Providing information to facilitate the development of resource supply curves (see Box 3.2) by policy makers and land managers, for example, is an appropriate role for the ERP and will allow evaluation of resources by ERP product consumers that is available at different costs.
When incorporating estimates of economic viability, consumers need to be able to evaluate what is and is not included in ERP estimates relative to industry and U.S. Security and Exchange Commission standards. Multiple references are available to the ERP to assist with this effort. Frameworks have been developed for reporting resources including the Petroleum Resources Management System (PRMS)2 originally developed by Society of Petroleum Engineers, the Society of Petroleum Evaluation Engineers, the American Association of Petroleum Geologists, the Society of Exploration Geophysicists, and the
World Petroleum Council in 2001. A 2017 update of the PRMS was made open for public comment, but has not yet been released.
Next-Generation Assessment Approaches
Effective ERP resource assessments of the near future will need to be dynamic and flexible so that the growing volume of new data becoming available may be quickly incorporated and accounted for. They need to accommodate systems approaches to management by including the information about water resources, waste disposal, environmental factors, factors affecting production viability, and lifecycle assessments. All of this is particularly important, given the accelerated pace of domestic drilling and production. The ERP needs to present that information in its products using formats that are accessible, usable, and informative for ERP product consumers. The ERP needs to position itself to explore, identify, and apply new data analytics and machine learning tools to its assessments. For example, ERP resource assessments now include basic information about variables that influence the probability an undrilled well interval will add resource (see Appendix B). The spatial distribution of those variables is reported as large regional assessment polygons that are input into geographic information systems. No accompanying information about geologic heterogeneities and their uncertainties is provided. The ERP needs to investigate advanced data analytics tools that might allow it both to incorporate and to report higher-resolution geologic heterogeneities as part of the assessment. Not only would the spatial resolution be increased as desired by ERP product consumers—especially if assessments are continuously updated with available data—but it would allow more efficient, reliable, and varied use of the assessments as well. Providing the algorithms used to perform the various analyses would increase transparency, allow product consumers to reproduce the results, and result in better trust of ERP products.
Data management and custodianship will grow in importance as more data are collected and the impacts of more and more complex energy-related decisions need to be made. Subsurface characterization is required to support realistic and useful conceptual energy resource models, reduce exploration risk, manage potential environmental impacts, and support effective decision making for resource development. Subsurface characterization, however, is dependent on access to appropriate geoscientific and geospatial datasets (i.e., geochemical, geological, geophysical, engineering, and hydrological).
The ERP maintains geologic energy resource-related databases of rock and fluid geochemistry analyses from sedimentary basins and geologic provinces within the United States and the world. These are, effectively, the only publicly accessible, national-scale archives for those types of data. The ERP’s capabilities to generate these data, the databases, and the products for using these data (e.g., mapping applications) are valuable and unique. Congress and other organizations routinely use ERP data and data products to
support internal decision making. As described in Chapter 4 and in this chapter, however, the ERP product line could better inform decision making by including more resource assessment input data and data related to the environmental impacts of resource development; increasing the ease of access to existing data (e.g., turn legacy nondigital core and log data into more accessible information); identifying, acquiring, and archiving new types of data (e.g., geomechanics data); and evaluating and integrating new data management and analysis tools into ERP practices. There is also a need for improved custodianship and dissemination of such national-scale geoscientific data sets. Challenges associated with data management include:
- designing appropriate database structures to store information (database architecture);
- migrating and merging existing data into new databases;
- managing and incorporating proprietary data sets used by the ERP with permission;
- maintaining data quality assurance and control (QA/QC);
- updating and maintenance of databases (populating with new data; software management); and
- designing systems that allow rapid, effective dissemination of data to external stakeholders.
Developing a national geoscience data repository is a formidable task that would require a substantial investment in resources. As of the writing of this report, advanced data science and analytics are beginning to transform the ways in which organizations collect, analyze, and manage their data (e.g., Bean, 2017). New tools for managing and evaluating data might be necessary and they might enhance the ability of the ERP to address the above challenges. Exploring these tools and applications, however, is best undertaken by the ERP with input from product consumers and external experts in data information and management.
The next sections address future priorities specific to the different ERP priorities. These include for assessments and products related to coal, oil and gas, wind, uranium, energy storage, and methane hydrates.
Oil and Gas
Oil and gas companies will continue to create their own resource assessments to better understand the global hydrocarbon endowment and to meet Securities and Exchange Commission requirements for publicly traded companies. Their assessments are based on data collected with state-of-the-art technologies and use resources often not available to the public sector. Because the data and analyses are generally proprietary, they are not
available to support policy decisions. Given that oil and gas will remain important parts of the U.S. energy mix over the next 10-15 years, the United States will continue to need independent, unbiased, and robust assessments of domestic and international oil and gas inventories to inform policy and energy strategies at all levels. As such, the ERP needs to continue to produce its oil and gas assessments. To better align its assessments and data products with the needs of ERP product consumers, and to better serve both USGS and U.S. priorities, the ERP will need to take some specific steps: (1) Increase the transparency of its assessment approaches by adding to the raw data and intermediate data products that are released with assessments, and (2) Ensure that assessments can be seamlessly updated when new production information; any updated geologic mapping; petrophysical analyses, or rock-fluid analyses conducted by the ERP and elsewhere in the USGS; new data analytic technologies; advances of production technologies; or new economic forces make previously unrecoverable resources economically feasible to recover.
Initial resource assessments are based largely on basic geologic interpretation and interpolation of data in areas where data are scant. As resources are developed, production and other data become available and can be used to refine initial resource assessments and reduce uncertainties. By the time complete assessments are released, however, they can be out of date, and they still may not include useful levels of data and background information. This practice limits the utility of ERP products because users cannot trust that they represent the best available science. Several suggestions for types of useful data the ERP might release are provided in Chapters 3 and 4. Access to intermediate data products derived from the assessments will allow product users to better understand the reliability and uncertainty of the estimated resource volumes as well as to reproduce those assessments as needed to ensure that decisions made using them are based on the best available information. The pace of development of continuous (unconventional) resources implies that the ERP needs the capacity to quickly publish updates to its assessments. Current ERP reporting strategies, however, make this difficult.
Raw and Derived Data
Raw and derived data products associated with oil and gas assessments need to be available publicly in a timely manner for ERP product consumers so that consumers may better understand the reliability of both the ERP’s resource assessments and any independent assessments that may have been conducted. The private sector will always have access to more subsurface seismic and well production data than public agencies do, but raw data generated by the ERP in support of its assessments (e.g., geochemical analyses of rocks and fluids) are an ERP commodity. The USGS has significant strengths in basic rock and fluid characterization, and the ERP might expand the existing datasets to include detailed petrophysical and geomechanical analyses of cores as well as additional geochemical and fluid properties studies on oils, gases, and waters. These types of data and analyses lead to an enhanced understanding of how different rock-fluid property combinations perform under production and thus improve assessments of ultimate resource recovery. Such studies are routinely conducted by the private sector for the regions in which they have producing assets. Those studies are generally proprietary and responsive
to private sector needs. The ERP has the opportunity to perform analyses across multiple regions and sedimentary basins, with variable rock and fluid types. In the process, the ERP might broaden overall knowledge of U.S. resource endowment. Public-sector decision makers and land managers need access to publicly available, scientifically sound, unbiased, and trusted sources of information for all regions and basins.
The ERP does not assess some oil and gas resources—for example, residual oil zones (ROZs)—because of a lack of economically viable strategies for producing them. ROZs consist of immobile oil beneath the oil/water contact of some reservoirs and are the result of modification of an original oil accumulation by natural subsurface hydraulic processes (e.g., Aleidan et al., 2016). They are typically classified as part of the underlying aquifer rather than the overlying oil accumulation. They may, however, contain billions of barrels of oil that could increase the U.S. domestic endowment (DOE, 2012; Petzet, 2012). Recent studies suggest that such enhanced recovery mechanisms as carbon dioxide (CO2) injection or stepwise pressure reduction, coupled with the drive to increase subsurface storage of CO2, may make it feasible to produce ROZs (e.g., Jamali et al., 2017; Rotelli et al., 2017). Management of the additional produced water that would result will be critical to consider in the development. Through basic research on the geologic controls on their distribution, producibility, and potential environmental impacts related to production, the ERP might take the lead to quantify the extent to which these and other unassessed resources might contribute to U.S. and global endowments.
Economic and Environmental Challenges
The ERP is qualified, especially in collaboration with other USGS mission areas, to address the geologic characterization and assessment of resources as well as the environmental impacts of their development, such as land use, water contamination, and induced seismicity. Different resource production strategies to develop continuous (unconventional) resources, for example, are likely to have different environmental impacts. Today, such wells can be drilled horizontally, beginning miles from their target reservoirs. Such extended-reach wells previously targeted difficult to access conventional offshore resources, but they are increasingly used onshore and improve economic recoverability of those resources. This style of production may decrease the footprint of drilling pads but it increases the per-well volumes of water used for hydraulic fracturing and extracted during production. The overall environmental impacts have yet to be evaluated fully. The ERP might collaborate with the USGS Water Resources mission area to evaluate the impacts of specific high-water-volume hydraulic fracturing development strategies on water resource depletion and potential groundwater contamination.
Despite the major decrease in demand precipitated by low natural gas prices, more than 728 million tons of coal were produced in 2016 (EIA, 2017b), and coal remains a critical part of the domestic energy mix. And although the decline in coal consumption is expected to continue in the United States and abroad, it is not clear how pricing and supply for natural gas and coal will change. Lowered demand and the move away from coal for power generation suggests that the ERP can place less emphasis on its coal program, but it is essential that the ERP maintain a program robust enough to react to changing coal markets and to address coal resources with respect to utility. Hence, assessment should remain part of the ERP coal program. To maintain relevance and to even expand the stakeholder base of the coal research area, the ERP might migrate from high-level assessments of technically recoverable resources and toward more focused assessments of metallurgical coal as well as coal by-products and constituents like rare-earth elements. Other coal assessments could include the quantities of resources suitable for coal-to-liquids processes and in situ coal gasification, which would provide vital data and products related to energy security.
The bulk of the nation’s coal endowment has been explored and assessed in most basins. Some efforts are underway at the DOE to characterize advanced coal properties and utility, but the ERP and USGS are uniquely positioned to develop focused and comprehensive geologically based resource assessments at the basin and national scales. The ERP coal research area will be most relevant by enhancing or developing databases to address the future utility of coal. Database development has long been an imperative for the ERP coal program, as exemplified by the National Coal Resources Data System (NCRDS) database.3 The core NCRDS database, which includes basic data on coal occurrence (e.g, depth, thickness) can remain an important resource if it is expanded greatly in areas of coalbed methane development. Other databases, such as the USGS coal quality database (COALQUAL)4—which contains proximate, ultimate, and trace element data—will become a higher priority and might be expanded because of their importance for identifying coal quality and utility. Additional databases of coal petrology (i.e., maceral composition and mineralogy) will also improve knowledge of coal quality and utility. Characterizing fluids and microbiota in coal—vital for coalbed methane exploration—has significance for understanding how coal-borne water can be disposed of or utilized. This is another area for database development.
There are issues related to coal that are worthy of basic research, such as understanding the distribution and occurrence of rare-earth elements in coal-bearing strata. Because much of the nation’s coal resource base has been characterized, however, basic research for exploration and development, particularly from the standpoint of mining, needs to be a lesser priority for the ERP. Similarly, the need for basic research on coalbed methane resources currently lacks immediacy: coalbed methane development is mature but has been hampered by competition from other parts of the gas industry that employ high-water-volume hydraulic fracturing. Data generated by the coalbed methane industry is useful, however, for continued quantification of the coal resource base.
The ERP has the basic data and expertise related to potential impacts and remedial actions associated with the tangible environmental impacts of coal mining, coal utilization, and coalbed methane development needed by most stakeholders. The ERP databases, such as COALQUAL, are vital for predicting and understanding environmental impacts associated with coal resource development and can be used to inform strategies for prevention and mitigation. Moreover, these databases are useful for understanding legacy impacts, such as acid mine drainage, as well as predicting impacts of activities that may become important in the future, such as extraction of rare-earth elements from coal-bearing strata.
As described in previous chapters, because the ERP focuses on geologically based energy resources, its efforts related to renewable energy resources has been limited to geothermal resources and wind.
Geothermal resources quality in the United States varies dramatically as a result of natural permeability and geothermal gradient. National-scale estimates of geothermal resource potential for conventional and engineered geothermal systems (EGS) will be needed to support development of U.S. energy strategy and policies and to guide future research priorities. As for the oil and gas assessments described above, the ERP needs to revise and update geothermal resource estimates as new data and technology advancements become available as well as when assessment methodologies are updated. Making the fundamental data sets used in the geothermal assessments publicly available would support wider use of the resource estimates due to the greater transparency and increased confidence in the results. Incorporating information about economic recoverability would add to the value and utility of these estimates for stakeholders who use these products.
Evaluating the location and quality of water sources near potential EGS targets is also warranted: EGS reservoirs will gradually lose water with long-term operation of EGS plants. Additional water will likely need to be injected. It may be appropriate for the ERP to partner with the USGS Water Resources mission areas and with other agencies to evaluate potential water resources. There may be opportunities to leverage synergistic ERP activities involving the characterization of produced water volumes and compositions associated with oil and gas development, although areas of high-temperature geothermal potential often are not located in oil and gas provinces.
Continued basic research on geothermal resources will allow the ERP to maintain a reputation of excellence, innovation, and leadership, and, most importantly, to contribute to higher-quality resource assessments. This will contribute to sustained demand (and potential funding) for ERP research and products. Such research could leverage new and existing collaborative relationships with other research groups within the United States, including complementary geothermal programs such as those initiated by the Geothermal
Technologies Office at the DOE. Examples of potential research directions include projects to evaluate resource exploration techniques, development and production strategies (e.g., via acquiring specific monitoring data sets at productive sites), and developing new data mining and machine learning approaches to improve resource prediction.
Basic research on the impacts of wind energy development on wildlife, to which the ERP has contributed, fills a critical gap. The ERP has developed a methodology by which national, regional, and locality-specific assessments can be designed and implemented by other entities. Limited ERP contributions to such efforts are appropriate, but the actual conduct of assessments of the impact of turbines on wildlife, for example, is best left for the organization with ultimate responsibility. The ERP’s expertise is better utilized for assessments of geologically based energy resources.
ERP uranium research was initiated to inform policy makers when a resurgence in low-carbon electricity generation by nuclear power was anticipated (NRC, 1999). Although prospects for nuclear capacity growth have faded, updated assessments of domestic uranium potential remain important. About 90% of U.S. uranium requirements are currently met by imports from a number of countries, supplemented by domestic production. Concerns about this heavy reliance on imported uranium, and about the associated vulnerabilities associated with that reliance, have been raised recently (WNN, 2018), stimulating interest from the Senate Environment Committee (Volcovici, 2018). New policies aimed at increasing reliance on domestic uranum production would significantly increase interest in the undiscovered uranium resource inventory being updated by the ERP. Thus, the ERP needs to remain ready to provide current information by maintaining capacity in this area.
Given the expected retirement of aging U.S. reactors, U.S. uranium requirements are projected to decline (NEA, 2017). The operator of the North Anna and Surry nuclear power plants (three reactors in total), however, intends to apply for a second 20-year life extension, for a total of 80 years of lifetime operation (NEI, 2017b). Should these licenses be approved and other utilities apply for and receive license extensions, U.S. uranium requirements would extend the period of heavy import reliance. Advanced and small modular reactor designs are under development in the United States (DOE, 2017) and, if successfully commercialized, would increase national uranium requirements.
Updated estimates of domestic uranium support current and future U.S. activities in civil nuclear power. Cutting-edge ERP estimates of undiscovered uranium resources add valuable, unbiased information on the national endowment of this strategic metal. Should market conditions change or new policies be introduced to increase domestic supply of uranium for U.S. requirements, this ERP work will kick-start exploration and mine development activities. High-quality research on the groundwater impacts of solution
mining provide information to government, industry, regulators, and the interested public on current mining operations. These efforts also help guide the remediation of legacy mines.
Water Use, Disposal, and the Energy-Water Nexus
The complexity of the relationship between water and energy has increased with the expansion of high-water-volume hydraulic fracturing in oil and gas production. The volume of water resources needed to support energy development is increasing, as is the energy required to treat and dispose of waters used for hydraulic fracturing. Water volumes required for hydraulic fracturing already have increased by a factor of 10, and they are anticipated to increase further (Scanlon et al., 2016, 2017; Haines et al., 2017a). Disposal options for produced water are likely to be increasingly limited, driving interest in reuse of produced water for oil and gas production. Basic water resource studies related to high-water-volume hydraulic fracturing are in their early stages (see Chapter 2), and identifying those research efforts that will best support near-term policy decisions regarding water management is imperative. The USGS has conducted several studies on the volumes of water used for hydraulic fracturing (e.g., Gallegos et al., 2015). Priorities for including water volumes in assessments are described in the preceding sections of this chapter. The following sections summarize two high-priority areas in which the ERP could help address gaps in current understanding of water chemistry and disposal.
Geochemical Characterization of Produced Water
Produced water can be viewed as a waste product or a resource depending on one’s perspective. Whether it is treated as waste or a resource depends on an understanding of its composition; the toxicity of its constituents; geologic constraints on its disposal (to avoid, for example, induced seismicity); the cost of managing it relative to the cost of resource production; and specific strategies for industrial or agricultural reuse of the water. Robust water geochemistry data are critical, but those data are limited. Only a few analytical results are in the public domain, relatively few constituents have been measured, and the majority of the existing analyses come from conventional oil and gas reservoirs.
The ERP and USGS Water Resources Mission areas collect raw water samples and conduct detailed, high-quality analyses of major and trace elements and isotopes to better understand the source and quality of produced waters. This information is stored in the produced water database.5 The ERP needs strategies to update and expand that database by incorporating a greater number of basic water chemistry analyses, coupled with detailed analyses for trace elements, transition metals, natural radioactive and organic constituents, and other constituents that may contribute to toxicity, particularly those from the oil and gas reservoirs. Such analyses will provide preliminary information on amounts and
distribution of potentially harmful constituents in produced waters and inform decisions about treatment and disposal options. New analytical approaches will need to be developed, however, to identify constituents in produced waters not yet identified (Oetjen et al., 2017) so that the potential health and safety effects of produced waters may be better understood.
To supplement its own database, the ERP might also begin to incorporate analyses of produced waters from the oil and gas industry. Industry typically collects a limited suite of analytes, but their databases will have many samples with a broad geographic distribution and provide additional information about spatial heterogeneities in those fluids. This will help scientists determine where to concentrate efforts on more advanced analyses of potentially toxic constituents. Heightened interest in reuse of produced water for industrial and agricultural applications also provides an opportunity for the ERP and Water Resources mission areas to collaborate with external groups on new analytical approaches for water samples with complex matrices, thereby identifying previously unrecognized constituents of produced waters that may influence treatment and reuse decisions. The combination of chemistry data with produced water volumes data (described in the previous section) can be used by other USGS researches investigating aquifer contamination.
Once an improved water geochemistry database is designed and created, a follow-on priority for the ERP will be to begin identifying patterns in produced water composition relative to the formations where the waters originated. Coupling produced water chemistries to the subsurface geology and mineral chemistry of the formations that produced those waters is a start. The ERP has already begun to collect detailed geochemical and mineralogic information from continuous (unconventional) oil and gas reservoirs in conjunction with field studies in key producing regions (e.g., Engle and Rowan, 2014; Enomoto et al., 2015; Engle et al., 2016). If rock observations are coupled to fluid chemistry observations from a single reservoir, and those data are collected for multiple reservoirs over many regions, basin types, and reservoir lithologies, then the ERP might begin to predict produced water chemistry in those undrilled areas where policy makers need to develop strategies for water management with very limited information.
Produced Water Disposal and Reuse
Waters produced during oil and gas extraction are typically managed through surface disposal or surface discharge after chemical treatment to remove harmful constituents. In conventional reservoirs, waters can be reinjected into the producing formation to enhance oil and gas recovery, but this approach is not possible for some reservoirs due to their low permeabilities and concerns that geochemical reactions may damage the formation’s ability to produce oil and gas. Current disposal practices face increasing challenges, however, including higher cost of water handling in semiarid regions and greater constraints on subsurface disposal, as described in Chapter 2. These challenges are driving research on alternative strategies for disposal and reuse of produced waters, including evaluation of reuse of produced waters for hydraulic fracturing fluids (e.g., Haghshenas and Nasr-El-Din, 2014; Esmaeilirad et al., 2016; Scanlon et al., 2017). During the early phase of continuous (unconventional) resource development, freshwater with various additives was
used for hydraulic fracturing. More recently, however, industry has recognized that it can use produced water with little treatment (i.e., “clean brine” for hydraulic fracturing [McMahon et al., 2015; Nichols et al., 2017]). There is a general need for information on water volumes and chemistry that are linked to temperature, pressure, and mineral composition and chemistry data for the rocks in the producing reservoirs. This would also support improved understanding of the potential negative water-rock interactions that might occur during development of EGS. With databases of produced water volumes and chemistry coupled to rock observations in key study areas, as described in the preceding section, the ERP would be well positioned to partner with other agencies and academic groups that are pursuing experimental studies of water-rock interaction (e.g., National Energy Technology Laboratory, DOE, and academia), companies responsible for implementing the hydraulic fracturing process (e.g., service companies), and companies that produce unconventional resources (including EGS) to advance efforts to identify new and more efficient options for reuse of produced waters.
The expertise in the ERP methane hydrates research area is sought by research programs in China, India, and Japan. Developing methods to produce natural gas from methane hydrates will continue to be a focus of the international methane hydrate research community in the coming years. Critical needs in hydrate development include
- resource identification: ERP methods to predict the thickness and saturation of hydrate deposits (Haines et al., 2017c) based on seismic data are used extensively to identify likely productive hydrate deposits. Until further data are collected on the technical recoverability of gas hydrates from onshore deposits, however, resource assessments will not likely be a priority. Lack of production and exploration data for onshore gas hydrate resources in the United States demonstrates no ongoing need to maintain hydrate resources databases until more data are acquired;
- development and verification of production methods. Limited, short-term production tests onshore in Canada and on the Alaska North Slope and offshore in the Nankai Trough off Japan, in the East China Sea, and in the Indian Ocean have been performed. The ERP is involved in the design and development of a long-term production test program in collaboration with the DOE, the State of Alaska Department of Natural Resources, and the Japan Oil, Gas and Metals National Corporation; and
- evaluation of the environmental issues associated with both hydrate production and the natural release of gases in situ given rising ambient temperatures (e.g., warming arctic temperatures). Research on methane hydrate as a widespread constituent of the shallow geosphere in arctic and marine settings is needed.
The level of priority now placed on hydrates research with the ERP is appropriate given the potential of methane hydrates as a resource. ERP collaboration with the DOE on
demonstration projects for the recovery of natural gas from hydrate deposits leading to the current estimates for economic recovery of natural gas hydrates will continue as new data are collected. This basic research and the evaluation of the environmental impacts need to continue as the highest priority for the ERP hydrate research area. Given the uncertainties of the contributions of methane hydrates to the future energy mix, emphasis placed on methane hydrates research by the ERP in the next 10-15 years will need to reflect progress (or lack thereof) toward development of viable technologies for natural gas production from hydrates as well as on the information needs of ERP product consumers.
Geologic Carbon Dioxide Sequestration
Geologic CO2 sequestration will remain promising means to permanently store CO2. The use of injected CO2 to first enhance oil recovery, then permanently store CO2 in the subsurface looks to be a way to accomplish two important energy-related goals. The ERP’s subsurface expertise will remain an important resource as technologies in these areas are developed. There remain concerns regarding the associated issues of leakage and groundwater contamination and subsurface mineralization that ERP expertise might help address. The ERP could contribute toward improved understanding of associated induced seismicity (Zoback and Gorelick, 2012). As for future assessments conducted in its other research areas, the ERP may need to prepare geologic carbon sequestration resource assessments that support full-lifecycle and full-system approaches. The program may need to incorporate data in its assessments that support determination of the economic viability of sequestration technologies.
Diversification of energy generation and changing demand patterns places a greater interest on use of the subsurface both for disposal of energy-related waste products and for short- and long-term storage of energy-related resources. With an increase in non-baseload renewable energy power generation, there is an increasing need for energy storage options to moderate the variability, to increase system flexibility, and to support dispatchable, high-ramping power generators on today’s electricity grid. Various energy storage options exist including compressed air energy storage (CAES), pumped hydroelectric energy storage, and underground natural gas storage. Individually, these storage options may not contribute greatly to the energy mix, but combined, they have the potential to be important. Geologic and land-use expertise is necessary to understand the characteristics of these storage options, and basic research is required to forecast long-term performance and effects. Subsurface energy storage involves coupled hydro/chemical/thermal/mechanical processes that can be difficult to anticipate. There is a practical focus on understanding the impacts on capacity and round-trip efficiencies,6 but there are also temporal issues to consider.
6 The ratio of the energy consumed to put energy into storage to that consumed to retrieve it from storage.
CAES and natural gas storage, for example, have rapid cycles. The long-term impacts—including environmental—associated with the interactions between the engineered and natural systems also need to be understood. Reversible extraction of fluids and other materials from storage all require better data and assessment of the storage reservoirs and environmental implications of their use. With the ERP’s deep geologic expertise, assessing the storage potential for various basins would be an important contribution it could make, potentially in collaboration with the DOE and its partners.
Pumped-storage hydroelectricity (PSH) plants pump water from a reservoir at a lower elevation to one at a higher elevation, often doing so when there is low power or energy demand and electricity may be available at lower cost. Power is generated by releasing water from the upper reservoir when power demand is high. Siting of PSH plants requires elevation and water and can raise environmental, aesthetic, and other concerns. Installation of some plants has been proposed in depleted mines or underground reservoirs. Given an increasing interest in PSH, the ERP could leverage its unique expertise in geology and land use with USGS water resource expertise to assess opportunities to repower existing dams or develop new paired reservoirs for this purpose. Such efforts could be designed to support interests of multiple agencies (e.g., the U.S. Army Corps of Engineers, the Department of the Interior, and the DOE).
Compressed Air Energy Storage (CAES)
CAES systems are similar to PSH systems in terms of their applications, output, and storage capacities. CAES plants compress ambient air (rather than water) and store it under pressure in underground caverns. The pressurized air is heated and expanded in an expansion turbine to drive a generator for power.7 Since air compression creates heat and air expansion removes heat, different approaches (e.g., adiabatic, diabatic, or isothermal) have been developed to address the thermal considerations, each with different efficiencies. A key aspect affecting the commercial viability of such systems is the location and character of the geologic storage reservoir; this is an emerging need that the ERP could address.
Underground Natural Gas Storage
Given the growth of natural gas production and the nation’s increasing dependence on natural gas, availability is becoming more reliant on pipelines and storage options. Natural gas is commonly stored underground and under pressure in depleted oil or natural gas
fields, aquifers, and salt cavern formations.8 The suitability of a particular underground formation for a particular use will be related to the formation’s physical characteristics (e.g., porosity, permeability, and retention capability) and factors such as the costs of site preparation and maintenance, how quickly gas can be retrieved from storage (i.e., its deliverability rate), and cycling capability. Failure of underground natural storage systems in California has been estimated at approximately four times a year in California, largely as a result of loss of well integrity, but also as a result of loss of containment within the underground storage reservoir (CCST, 2018). Loss of containment can result in the explosive release of natural gas that threatens safety, and the nonexplosive release of gas that may have long-term environmental impacts. The ERP might provide national or regional-level assessments of the location and character of geologic storage options for natural gas.