Petroleum is commonly extracted from pores in rock formations below the earth’s surface. Different kinds of rock have petroleum in their pores, but the petroleum is not part of the rock itself.
Kerogen, another hydrocarbon material, is a constituent material of a type of rock called oil shale. While oil shales can be burned directly as a fuel, it’s possible to extract a liquid substitute for petroleum from kerogen by heating the oil shale to a high temperature, thus producing a vapor, which is then cooled. Some of the cooled vapor remains gaseous (and is called “combustible oil-shale gas”), while the rest condenses into a liquid. So ordinary shale, or other sedimentary rock, may contain some petroleum in its pores, but oil shale can produce a petroleum substitute from the kerogen that it’s made of. The liquid condensed from the heated and cooled kerogen in oil shale is called “shale oil”.
The earth evidently contains enough oil shale—generally estimated as enough to produce a few hundred billion cubic meters of shale oil, which is on the order of a trillion barrels—to significantly augment the world petroleum supply. Roughly three fourths of this oil shale is in the US. Obstacles to its use include the expense of current shale-oil production technologies and their effects on our environment. Efforts to solve these problems continue to be made by researchers sponsored by the Department of Energy.
While US oil shale deposits are reported in both eastern and western states, “[w]estern oil shale represents the greatest potential for near-term development to help meet the Nation’s needs for liquid fuels.”[p. 1, DoE] The most recent research reports related to oil shales focus on extraction of shale oil from the Green River Formation in Colorado, Utah, and Wyoming.
While fuel can be (and has been) extracted from oil shale by mining it and then processing it, less environmental disruption in the form of waste piles aboveground may result if the fuel is extracted while the shale is still underground. Determining whether the disruption can be reduced while still obtaining a worthwhile amount of fuel requires an accurate mathematical model of the physical processes involved, as well as computer time to calculate what the model implies. To be practical, mathematical models need to be detailed enough to give useful information, but not so detailed that the information can’t be calculated in a reasonable amount of time.
Two recent reports by a group of researchers from Los Alamos National Laboratory and ExxonMobil Upstream Research Company describe how a mathematical model for one such in situ process was developed by adding new capabilities to the Finite Element Heat and Mass (or FEHM) model that Los Alamos has been using and improving over 30 years. FEHM was already used to analyze groundwater contaminant transport, geothermal energy extraction, nuclear waste isolation, methane hydrate production, and carbon dioxide sequestration by modeling their interacting mechanical, fluid, and thermal processes. By augmenting the FEHM software so it can also model flow-mechanics coupling, oil-gas-water flow, and physical properties of oil shales, it can now simulate what happens when oil shale is converted below ground.
The report “Development of Numerical Simulation Capabilities for In Situ Heating of Oil Shale”[SciTech Connect] briefly describes what key material properties and physical laws the mathematical model represents. The model is described in more detail in the slide presentation “Development of capabilities to simulate the coupled thermal-hydrological-mechanical-chemical (THMC) processes during in situ oil shale production”[SciTech Connect].
As the Los Alamos/ExxonMobil effort suggests, generic mathematical models like the original FEHM may not provide accurate information about a specific process if the process involves significant details that the generic model doesn’t account for. “Development of CFD-Based Simulation Tools for In-Situ Thermal Processing of Oil Shales/Sands”[SciTech Connect], a report prepared for the National Energy Technology Laboratory by the University of Utah’s Institute for Clean and Secure Energy, describes a similar augmentation of Computational Fluid Dynamic modeling tools to analyze a technology developed by Red Leaf Resources, Inc. Their EcoShale In-Capsule Technology is similar to in situ processing, but rather than heating the oil shale where it is found, the oil shale is mined, reburied in a clay-lined, closed-surface capsule, and then heated. Unlike the type of in situ processing represented by the aforementioned Los Alamos/ExxonMobil reports, which requires water to be pumped underground from the surface and also involves interaction with existing groundwater, the in-capsule fuel extraction process doesn’t use water. The capsule liner also protects groundwater, and since an overburden covers the capsule, the site can be reclaimed rapidly.
The kind of in situ fuel extraction modeled by Los Alamos’ modified FEHM software uses water for drilling down to the oil shale and for restoring the site after the fuel extraction is finished. Water is also produced from below ground while the site is under construction as well as during the retorting (i.e., the reaction-producing heating in an enclosed volume) that converts oil shale into usable fuel. Exactly how much water is used and produced, and its quality (salinity &c.), are important environmental and economic considerations in the American West, given the scarcity of water there.
Two reports from Idaho National Laboratory (INL), “Water Usage for In-Situ Oil Shale Retorting – A Systems Dynamics Model”[SciTech Connect] and “Documentation of INL’s In Situ Oil Shale Retorting Water Usage System Dynamics Model”[SciTech Connect], describe the workings of a mathematical model that focuses on how water is used and produced when oil shale is retorted in situ. While the second report simply documents the model itself, the first in addition presents some history of oil shale use as an energy source, a description of older and newer retorting methods for extracting shale oil, a comparison of the model’s predictions with actual experience from a field experiment by Shell, and the model’s application to a large-scale in situ retort. One conclusion from the model is that more water would be used than produced, with the greatest water use being for post-extraction site remediation. Remediation may involve flushing the retort zone with water multiple times to remove excess heat and mobile contaminants. In the model, water is assumed to be treated at the surface and reused for multiple flushes.
The importance of knowing industrial processes’ rates of water use at places where water is scarce is highlighted in two other reports prepared for the National Energy Technology Laboratory, both of which provide a great deal of background on water management in the West and describe its relevance to the development of oil shale and related industries.
“Conjunctive Surface and Groundwater Management in Utah: Implications for Oil Shale and Oil Sands Development”[SciTech Connect], from the University of Utah’s Institute for Clean and Secure Energy, describes how the originally unobvious interrelation of surface water and groundwater has gradually become recognized and accounted for in water management, and relates conjunctive management of surface and groundwater to the unconventional-fuel industry. The report states that conjunctive management holds promise for addressing “some of the West’s most intractable problems”, by more effectively capturing spring runoff and surplus water and integrating its use with groundwater withdrawls. Managed aquifer-recharge projects can integrate surface water and groundwater use even further. While conjunctive management “cannot resolve all problems or provide water where no unappropriated water exists”, integrated use can “maximize water storage and availability, while simultaneously minimizing evaporative loss, reservoir sedimentation, and surface use impacts. Any of these impacts, if left unresolved, could derail commercial-scale unconventional fuel development.”
“Water-related Issues Affecting Conventional Oil and Gas Recovery and Potential Oil-Shale Development in the Uinta Basin, Utah”[SciTech Connect], a report from the Utah Geological Survey, is an extensive report that addresses saline-water disposal from petroleum and natural-gas production. Regulators in Utah currently stipulate that “produced saline water must be disposed of into aquifers that already contain moderately saline water” that averages at least 10 grams per liter of dissolved solids. The Birds Nest aquifer has been identified by eastern Uinta Basin gas producers as the most promising saline-water disposal reservoir; it also lies in the immediate vicinity of oil shale deposits. The report describes the results of exploring the aquifer’s extent, water quality, and relation to the oil shale, thus informing decisions on how to manage the different water, petroleum, natural gas, and oil shale resources.
Shale oil is similar to petroleum, but it is not exactly the same.[Wikipedia] This affects its use as a petroleum substitute. Two recent reports from researchers at Oak Ridge National Laboratory's Fuels, Engines, and Emissions Research Center document ongoing experiments with engines using new fuels and combustion strategies. While both reports describe analyses of other fuels and the earlier one lists shale oil as one of the fuels to be studied later, each of them indicate the kinds of data being sought to inform the design of engines that can use non-petroleum-derived power sources. Such information can shorten cycles of product design and introduction.
As the report “DOE Project 18546, AOP Task 1.1, Fuel Effects on Advanced Combustion Engines”[SciTech Connect] describes, the Oak Ridge group’s main objective is to study how fuel formulation and emerging fuels can affect new combustion regimes and to exploit those properties for improved emissions and efficiency. In fiscal year 2011, the group, in partnership with the University of Wisconsin, improved both the accuracy and time-efficiency of a Computational Fluid Dynamics model by mathematically representing the fuels’ physical properties with larger, more complex molecules and their chemical properties with smaller molecules. They also evaluated a fuel-quality sensor from the French company sp3H and found it usable for predicting engine performance over a wide fuel range. Their evaluation of 20 biofuel blends for diesel engine performance showed that, compared to corresponding fuels derived from crude oil, the biofuels generally have lower hydrogen/carbon ratios, some remaining oxygen content, and improved emissions, but worse energy efficiency. The group also obtained several fuels from different labs and universities for evaluation in fiscal year 2012.
The group’s “Final Report for NFE-07-00912: Development of Model Fuels Experimental Engine Data Base & Kinetic Modeling Parameter Sets”[SciTech Connect] chronicles its work under a cooperative agreement with the Model Fuels Consortium, an industry group composed mainly of petroleum and automotive companies from several countries, and organized by Reaction Design, Inc., a supplier of software to model chemical processes. Although the consortium’s own products are proprietary, the Oak Ridge National Lab group’s contributions under the agreement were considered to be in the public domain and were widely published. These contributions consisted of experimental data related to engine performance with new fuels and new combustion strategies, along with interpretation and analysis of such data and consulting to Reaction Design, Inc. The data were used to develop or test mathematical models of engines and the chemical reactions that power them.
The history of progress toward making oil shales a common fuel source is long but intermittent, its active periods largely tracking times when petroleum threatened to become more expensive than shale oil. Checking SciTech Connect for report citations that contain the expression “oil shale” in either the list of report subjects, the title, or anywhere in the report’s full text (when the text is available in SciTech Connect) reveals something about the history of this progress, although the results are also influenced by the availability of different kinds of report information. For instance, many older reports are not yet available in electronic versions that SciTech Connect can examine, so full-text mentions of oil shales are underrepresented for earlier decades; also, the missions of the Energy Department’s predecessor agencies had narrower scope that didn’t generally include non-nuclear energy research except where it was closely associated with nuclear energy. But, even accounting for such influences on the content of SciTech Connect, its differing numbers of citations for each year suggest something of the ups and downs in efforts to advance the use of oil shales for energy.
Prepared by Dr. William N. Watson, Physicist
DoE Office of Scientific and Technical Information