Mitchell Plummer | Idaho National Laboratory (original) (raw)
Papers by Mitchell Plummer
Journal of Nuclear Materials, 2022
This file contains the first set of tracer data for the EGS Collab testbed. The first set of trac... more This file contains the first set of tracer data for the EGS Collab testbed. The first set of tracer tests were conducted during October-November, 2018. We have included tracer data for C-dots, chloride, fluorescein, and rhodamine-B. The details about the tracer test can be found in Background and Methods of Tracer Tests (Mattson et al. (2019)) (also included in this package). References Mattson, E.D., Neupane, G., Plummer, M.A., Hawkins, A., Zhang, Y. and the EGS Collab Team 2019. Preliminary Collab fracture characterization results from flow and tracer testing efforts. In Proceedings 44th Workshop on Geothermal Reservoir Engineering, edited, Stanford University, Stanford, California.
The injection well stimulation project at the Raft River geothermal field tests the effect of lon... more The injection well stimulation project at the Raft River geothermal field tests the effect of long-term cold water injection and high pressure injection on well injectivity, improvements to which could reduce operating costs. The primary data for analysis and interpretation of the injection test are step-rate flow tests run before each new phase of the injection. These tests were analyzed using a combination of standard pump-test analytical solution methods and methods developed expressly for the observed conditions. The stepped rate injection tests, combined with long-term flow and pressure response data suggest that the well is located within a fractured formation of low transmissivity but high storativity. These calculated parameters appeared to increase with pressure during the first injection test and the higher values were reproduced during the second stepped rate test. Calculated transmissivity and storativity are on the order of 4E-5 m cm and 1E-4 m Pa, respectively. The app...
The EGS Collab project is developing ~10-20 m-scale field sites where fracture stimulation and fl... more The EGS Collab project is developing ~10-20 m-scale field sites where fracture stimulation and flow models can be validated against controlled, small-scale, in-situ experiments. The first multi-well experimental site was established at the 4850 level in the Homestake Mine, where hydraulic fractures were created at an injection well drilled sub-horizontal from the drift. Ten tracer tests were conducted to characterize fracture flow pathways during the second hydraulic characterization test for 164’ Notch (October 24 to November 14, 2018) during steady state injection of 400 ml/min at the injection well. Injected tracers include DNA, C-dots (fluorescein nano particles), fluorescein, rhodamine-b, sodium chloride, lithium bromide and cesium iodine. The tracers have been detected in three flowing wells located about 7.5 to 9 meters away from the injection interval. The tracer breakthrough curves from these locations have been adjusted to account for the residence time in the injection an...
The Eastern Snake River Plain (ESRP) in southern Idaho is a region with significant potential as ... more The Eastern Snake River Plain (ESRP) in southern Idaho is a region with significant potential as a geothermal energy resource. Deep boreholes in the region suggest generally high geothermal heat flux, of approximately 100 mW m, with a slight eastward increase across the plain (Blackwell 1989). Evidence of that vertical heat flux, however, is largely masked by the rapid flow of cold groundwater that originates in the Yellowstone Plateau and transports heat horizontally through the highly permeable basalts making up the aquifer. This masking means that spatial distribution of temperature and heat flux below the aquifer is only poorly known and that, in turn, reduces confidence in identification of areas most suitable for geothermal development. To improve understanding of temperature distribution below the aquifer and advance the general understanding of heat flux in the ESRP, we conducted groundwater heat transport simulations and compared results to mapped groundwater temperatures. ...
Typically, high-temperature geothermal systems are found in regions of high geothermal gradients ... more Typically, high-temperature geothermal systems are found in regions of high geothermal gradients and strain rates that are host to an adequate and accessible groundwater supply to be used as a medium for heat exchange with the surrounding rock matrix. In some regions such as older collapsed calderas, there are reservoirs with extensive amounts of heat resources that lack either the permeability and hydraulic connectivity or the deep circulating waters necessary for traditional geothermal power production. The Snake River Plain is one such area with high geothermal gradients that was unfavorable in the past due to limitations in in-situ groundwater and proper circulation. As more attention is focused on the region with the advancement of Engineered Geothermal Systems (EGS), the high heat flow beneath the extensive Snake River Plain Aquifer can be reassessed in terms of potential thermal energy available. While enhancement of the reservoir is likely to increase the efficiency of the g...
Silicon carbide (SiC) monitors provide a means of measuring peak irradiation temperature of exper... more Silicon carbide (SiC) monitors provide a means of measuring peak irradiation temperature of experiment capsules in nuclear irradiation experiments. Neutron irradiation of a SiC monitor causes permanent lattice changes that are removed by annealing via heating to a temperature that exceeds the peak irradiation temperature. The annealing process results in changes to SiC physical characteristics that can be observed during the annealing process. This paper presents results of a method aimed at using electrical resistance, measured during a two-pass heating-cooling cycle as a means of recovering the irradiation temperature of a SiC monitor. Results indicate that the relationship between resistance and temperature of a SiC monitor shows a significant change in slope when the peak irradiation temperature is reached. This demonstrates the potential for this method to replace the current manual, and lengthy, process of post irradiation examination used to extract the peak irradiation temperature from irradiated SiC monitors.
Rock Mechanics and Rock Engineering, 2017
The Raft River geothermal field, located in southern Idaho, roughly 100 miles northwest of Salt L... more The Raft River geothermal field, located in southern Idaho, roughly 100 miles northwest of Salt Lake City, is the site of a Department of Energy Enhanced Geothermal System project designed to develop new techniques for enhancing the permeability of geothermal wells. RRG-9 ST1, the target stimulation well, was drilled to a measured depth of 5962 ft. and cased to 5551 ft. The open-hole section of the well penetrates Precambrian quartzite and quartz monzonite. The well encountered a temperature of 282 °F at its base. Thermal and hydraulic stimulation was initiated in June 2013. Several injection strategies have been employed. These strategies have included the continuous injection of water at temperatures ranging from 53 to 115 °F at wellhead pressures of approximately 275 psi and three short-term hydraulic stimulations at pressures up to approximately 1150 psi. Flow rates, wellhead and line pressures and fluid temperatures are measured continuously. These data are being utilized to assess the effectiveness of the stimulation program. As of August 2014, nearly 90 million gallons have been injected. A modified Hall plot has been used to characterize the relationships between the bottom-hole flowing pressure and the cumulative injection fluid volume. The data indicate that the skin factor is decreased, and/or the permeability around the wellbore has increased since the stimulation program was initiated. The injectivity index also indicates a positive improvement with values ranging from 0.15 gal/min psi in July 2013 to 1.73 gal/min psi in February 2015. Absolute flow rates have increased from approximately 20 to 475 gpm by February 2 2015. Geologic, downhole temperature and seismic data suggest the injected fluid enters a fracture zone at 5650 ft and then travels upward to a permeable horizon at the contact between the Precambrian rocks and the overlying Tertiary sedimentary and volcanic deposits. The reservoir simulation program FALCON developed at the Idaho National Laboratory is being used to simulate and visualize the effects of the injection. The simulation model uses a discrete fracture network generated for RRG-9 using acoustic borehole imaging and analysis of microseismic activity. By adjusting the permeability of the fractures, a pressure history match for the first part of the stimulation program was obtained. The results of this model indicate that hydraulic fracturing is the dominant mechanism for permeability improvement for this part of the stimulation program.
Geological Society of America Abstracts with Programs, 2016
The Holocene glacial history of the North Cascades is poorly understood, in part because most exi... more The Holocene glacial history of the North Cascades is poorly understood, in part because most existing records rely on moraine remnants and are therefore discontinuous. To develop a more complete record of Holocene fluctuations of North Cascades glaciers, we collected and analyzed glaciolacustrine sediments (i.e., rock flour) deposited over the past ~7800 years in Lyman Lake by the upstream Lyman Glacier. We combined these results with equilibrium-line altitude (ELA) reconstructions and glacier-climate modeling to quantify the climatic conditions that drove these fluctuations. Finally, we compared the Lyman Glacier's continuous fluctuation record to existing glacier and climate records of the North Cascades. Our results indicate that the Lyman Glacier was absent in the early Holocene, from before 7.8 ka until ~4.9 ka, when it experienced an early Neoglacial advance that persisted until at least ~3.8 ka. Following an extended non-glacial interval, the glacier experienced significant advances between ~2.6-2.25 ka, ~1.8-1.3 ka and ~1.1-0.9 ka. An advance starting ~ 0.8 ka (1150 CE) culminated at the glacier's maximum Holocene extent between ~0.6-0.5 ka (~1350-1450 CE), from which it retreated and disappeared entirely by ~0.35 ka (~1600 CE). After ~200 years with no significant glacier presence in the cirque, the glacier reformed and rapidly advanced to its maximum Holocene extent (~1800-1900 CE). Following this event, the glacier retreated steadily throughout the 20 th and early 21 st centuries and as of 2014, has approached its minimum viable extent. Paleo-ELA reconstructions of the glacier's maximum Holocene extents suggest that summers were ~2.6 °C cooler than modern (l981-2010 CE); alternatively, glacier-climate modeling indicates that annual temperatures ~1.5 °C cooler than modern would result in maximum glacier extents. v Combining these new results with existing North Cascades glacial records indicates that: 1) the earliest Neoglacial advances in the region (starting ~6 ka) occurred asynchronously, with higher latitude and more maritime sites experiencing earlier advances; 2) Neoglacial advances remained small, infrequent and asynchronous until the last millennium; 3) Beginning at ~1.0 ka, glaciers throughout the North Cascades advanced synchronously, signaling the onset of the Little Ice Age (LIA); 4) North Cascades glaciers reached their maximum Holocene extents during the 15 th and early 16 th centuries (~0.55-0.45 ka), followed by apparent regional retreat and a final smaller 19 th century (~0.15-0.05 ka) readvance. The asynchronous early-to-mid Neoglacial fluctuations followed by synchronous LIA behavior suggests that local climate factors drove glacier fluctuations until the regional climate signal became strong enough to induce synchrony ca. 1.0 ka. Although the inferred regional retreat remains uncertain, the disappearance of the Lyman Glacier in the mid-LIA (~0.45-0.15 ka) is consistent with the precipitation record at Castor Lake (~100 km to the east), which indicates unusually dry winter conditions between ~1450-1850 CE (~0.5-0.1 ka). vi Acknowledgements As science advances by the collaboration of dedicated individuals, so this project came to completion by the outstanding efforts of many, many people. I am deeply grateful to everyone who lent their valuable time and effort to this endeavor. A small army of field assistants served as human mules, hauling hundreds of pounds of coring equipment and ancient mud over Spider Gap in the quest for a glacial history book. Thanks, Tien Devin
Geological Society of America Special Papers
Geothermal energy depends on high subsurface temperature, adequate permeability and fracture volu... more Geothermal energy depends on high subsurface temperature, adequate permeability and fracture volume, and accessible groundwater supply to support heat exchange with surrounding rock. Some regions may have adequate thermal resources but lack the necessary permeability or deep circulating water. Exploitation of such areas for geothermal energy could occur if permeability can be enhanced enough to provide the necessary heat exchange. These improvements to the geothermal reservoir would produce what is termed an "enhanced geothermal system" (EGS). The Snake River Plain (SRP) in southern Idaho is a geological region with high heat fl ux (~110 mW/m 2) that has been recommended as an EGS target. In this study, we consider how the geologic and thermal history of the SRP might infl uence its EGS potential. We describe the fracture distribution (mean = 28.63 fractures/10 m) in a welded tuff core recovered from one of the few deep boreholes located on the SRP and provide a preliminary discussion of the likely geomechanical behavior under in situ stress. Spatial autocorrelation of fracture features is defi ned with geostatistical techniques and used in a stochastic simulation of possible structures in other welded tuff reservoirs. Autocorrelation scales for the continuous date are on the order of 70 meters with high subsample scale variability (56 m). Results should aid in designing criteria for a hydraulic fracturing plan that would augment the permeability and connectivity of an SRP reservoir's preexisting fracture network.
Drying Technology, 2016
ABSTRACT Pretreatment and densification of biomass can increase the viability of bioenergy produc... more ABSTRACT Pretreatment and densification of biomass can increase the viability of bioenergy production by providing a feedstock that is readily hydrolyzed and able to be transported over greater distances. Ammonia fiber expansion (AFEX™) is one such method targeted for use at distributed depots to create a value-added and densified feedstock for bioenergy use. However, the pretreatment process results in a high-moisture material that must be dried, further size reduced, and pelletized, all of which are energy-intensive processes. This work quantifies the energy consumption required to dry, grind, and densify AFEX-pretreated corn stover compared to non-pretreated stover and explores the potential of reduced drying as a means to conserve energy. The purpose of this work is to understand whether material property changes resulting from AFEX pretreatment influence the material performance in downstream formatting operations. Material properties, heat balance equations, and a rotary drum dryer model were used to model a commercial-scale rotary drum dryer for AFEX-pretreated corn stover, showing the potential to reduce dryer energy consumption by up to 36% compared to non-pretreated corn stover. Laboratory-measured grinding and pelleting energies were both very sensitive to material moisture content. Overall, the total energy required for drying, grinding, and pelleting amounts to a savings of up to 23 kWh/dry Mg for the AFEX-pretreated material when dried to a low moisture content, equating to up to 0.61 $/Mg savings for gas and electricity. Grinding and pelleting of high-moisture AFEX-pretreated stover was shown to be more costlier than the savings collected through reduced drying. Although the energy and cost savings shown here are modest, the results help to highlight operational challenges and opportunities for continued improvement.
Tracers provide an important means of interrogating the subsurface to provide critical informatio... more Tracers provide an important means of interrogating the subsurface to provide critical information about hydraulic characteristics of the reservoir. In a geothermal reservoir, reactive tracers may add information about the thermal state of the reservoir. Tracer test analysis methods vary, but generally involve curve fitting to a simple model of the system or a moment analysis approach. The Idaho National Laboratory is currently developing an analysis tool that provides a variety of commonly used approaches in a single program, and which extends to analysis of reactive tracers. To provide a reactive tracer test analysis method that can be easily implemented without extensive knowledge of the reservoir geometry, we include an approach that relies on a simplified model of the subsurface. The approach involves (1) fitting a simplified reservoir model geometry to a combination of conservative and reactive tracer data (2) using the assumed geometry to interpret changes in reactive tracer concentrations (from tests conducted at different times) and (3) examining the sensitivity of inferences about thermal evolution to the assumptions about geometry. Sensitivity of such an analysis depends on the sensitivity of a reactive tracer to changes in its temperature-time history. We illustrate sensitivity differences between several possible reaction combinations.
Reactive tracers have long been considered a possible means of measuring thermal drawdown in a ge... more Reactive tracers have long been considered a possible means of measuring thermal drawdown in a geothermal system, before significant cooling occurs at the extraction well. Here, we examine the sensitivity of the proposed method to evaluate reservoir cooling and demonstrate that while the sensitivity of the method as generally proposed is low, it may be practical under certain conditions.
16. Discontinuities in the depth-age distribution of OL90-2 indicate a sediment hiatus between-15... more 16. Discontinuities in the depth-age distribution of OL90-2 indicate a sediment hiatus between-15,500 and 13,700 14C years B.P. Sediments at the base of the hiatus are characterized by features that indicate desiccation, including a 1-to 3-mmthick lag deposit of frosted quartz grains. Removal of sediments by wave reworking or deflation implies that the 15,500-year age represents a maximum estimate of the initiation of desiccation. 17. S. P. Lund, unpublished data. 18. The presence of greigite and the absence of magnetite in high-x intervals were inferred from thermomagnetic measurements of magnetic mineral blocking temperatures.
Journal of Nuclear Materials, 2022
This file contains the first set of tracer data for the EGS Collab testbed. The first set of trac... more This file contains the first set of tracer data for the EGS Collab testbed. The first set of tracer tests were conducted during October-November, 2018. We have included tracer data for C-dots, chloride, fluorescein, and rhodamine-B. The details about the tracer test can be found in Background and Methods of Tracer Tests (Mattson et al. (2019)) (also included in this package). References Mattson, E.D., Neupane, G., Plummer, M.A., Hawkins, A., Zhang, Y. and the EGS Collab Team 2019. Preliminary Collab fracture characterization results from flow and tracer testing efforts. In Proceedings 44th Workshop on Geothermal Reservoir Engineering, edited, Stanford University, Stanford, California.
The injection well stimulation project at the Raft River geothermal field tests the effect of lon... more The injection well stimulation project at the Raft River geothermal field tests the effect of long-term cold water injection and high pressure injection on well injectivity, improvements to which could reduce operating costs. The primary data for analysis and interpretation of the injection test are step-rate flow tests run before each new phase of the injection. These tests were analyzed using a combination of standard pump-test analytical solution methods and methods developed expressly for the observed conditions. The stepped rate injection tests, combined with long-term flow and pressure response data suggest that the well is located within a fractured formation of low transmissivity but high storativity. These calculated parameters appeared to increase with pressure during the first injection test and the higher values were reproduced during the second stepped rate test. Calculated transmissivity and storativity are on the order of 4E-5 m cm and 1E-4 m Pa, respectively. The app...
The EGS Collab project is developing ~10-20 m-scale field sites where fracture stimulation and fl... more The EGS Collab project is developing ~10-20 m-scale field sites where fracture stimulation and flow models can be validated against controlled, small-scale, in-situ experiments. The first multi-well experimental site was established at the 4850 level in the Homestake Mine, where hydraulic fractures were created at an injection well drilled sub-horizontal from the drift. Ten tracer tests were conducted to characterize fracture flow pathways during the second hydraulic characterization test for 164’ Notch (October 24 to November 14, 2018) during steady state injection of 400 ml/min at the injection well. Injected tracers include DNA, C-dots (fluorescein nano particles), fluorescein, rhodamine-b, sodium chloride, lithium bromide and cesium iodine. The tracers have been detected in three flowing wells located about 7.5 to 9 meters away from the injection interval. The tracer breakthrough curves from these locations have been adjusted to account for the residence time in the injection an...
The Eastern Snake River Plain (ESRP) in southern Idaho is a region with significant potential as ... more The Eastern Snake River Plain (ESRP) in southern Idaho is a region with significant potential as a geothermal energy resource. Deep boreholes in the region suggest generally high geothermal heat flux, of approximately 100 mW m, with a slight eastward increase across the plain (Blackwell 1989). Evidence of that vertical heat flux, however, is largely masked by the rapid flow of cold groundwater that originates in the Yellowstone Plateau and transports heat horizontally through the highly permeable basalts making up the aquifer. This masking means that spatial distribution of temperature and heat flux below the aquifer is only poorly known and that, in turn, reduces confidence in identification of areas most suitable for geothermal development. To improve understanding of temperature distribution below the aquifer and advance the general understanding of heat flux in the ESRP, we conducted groundwater heat transport simulations and compared results to mapped groundwater temperatures. ...
Typically, high-temperature geothermal systems are found in regions of high geothermal gradients ... more Typically, high-temperature geothermal systems are found in regions of high geothermal gradients and strain rates that are host to an adequate and accessible groundwater supply to be used as a medium for heat exchange with the surrounding rock matrix. In some regions such as older collapsed calderas, there are reservoirs with extensive amounts of heat resources that lack either the permeability and hydraulic connectivity or the deep circulating waters necessary for traditional geothermal power production. The Snake River Plain is one such area with high geothermal gradients that was unfavorable in the past due to limitations in in-situ groundwater and proper circulation. As more attention is focused on the region with the advancement of Engineered Geothermal Systems (EGS), the high heat flow beneath the extensive Snake River Plain Aquifer can be reassessed in terms of potential thermal energy available. While enhancement of the reservoir is likely to increase the efficiency of the g...
Silicon carbide (SiC) monitors provide a means of measuring peak irradiation temperature of exper... more Silicon carbide (SiC) monitors provide a means of measuring peak irradiation temperature of experiment capsules in nuclear irradiation experiments. Neutron irradiation of a SiC monitor causes permanent lattice changes that are removed by annealing via heating to a temperature that exceeds the peak irradiation temperature. The annealing process results in changes to SiC physical characteristics that can be observed during the annealing process. This paper presents results of a method aimed at using electrical resistance, measured during a two-pass heating-cooling cycle as a means of recovering the irradiation temperature of a SiC monitor. Results indicate that the relationship between resistance and temperature of a SiC monitor shows a significant change in slope when the peak irradiation temperature is reached. This demonstrates the potential for this method to replace the current manual, and lengthy, process of post irradiation examination used to extract the peak irradiation temperature from irradiated SiC monitors.
Rock Mechanics and Rock Engineering, 2017
The Raft River geothermal field, located in southern Idaho, roughly 100 miles northwest of Salt L... more The Raft River geothermal field, located in southern Idaho, roughly 100 miles northwest of Salt Lake City, is the site of a Department of Energy Enhanced Geothermal System project designed to develop new techniques for enhancing the permeability of geothermal wells. RRG-9 ST1, the target stimulation well, was drilled to a measured depth of 5962 ft. and cased to 5551 ft. The open-hole section of the well penetrates Precambrian quartzite and quartz monzonite. The well encountered a temperature of 282 °F at its base. Thermal and hydraulic stimulation was initiated in June 2013. Several injection strategies have been employed. These strategies have included the continuous injection of water at temperatures ranging from 53 to 115 °F at wellhead pressures of approximately 275 psi and three short-term hydraulic stimulations at pressures up to approximately 1150 psi. Flow rates, wellhead and line pressures and fluid temperatures are measured continuously. These data are being utilized to assess the effectiveness of the stimulation program. As of August 2014, nearly 90 million gallons have been injected. A modified Hall plot has been used to characterize the relationships between the bottom-hole flowing pressure and the cumulative injection fluid volume. The data indicate that the skin factor is decreased, and/or the permeability around the wellbore has increased since the stimulation program was initiated. The injectivity index also indicates a positive improvement with values ranging from 0.15 gal/min psi in July 2013 to 1.73 gal/min psi in February 2015. Absolute flow rates have increased from approximately 20 to 475 gpm by February 2 2015. Geologic, downhole temperature and seismic data suggest the injected fluid enters a fracture zone at 5650 ft and then travels upward to a permeable horizon at the contact between the Precambrian rocks and the overlying Tertiary sedimentary and volcanic deposits. The reservoir simulation program FALCON developed at the Idaho National Laboratory is being used to simulate and visualize the effects of the injection. The simulation model uses a discrete fracture network generated for RRG-9 using acoustic borehole imaging and analysis of microseismic activity. By adjusting the permeability of the fractures, a pressure history match for the first part of the stimulation program was obtained. The results of this model indicate that hydraulic fracturing is the dominant mechanism for permeability improvement for this part of the stimulation program.
Geological Society of America Abstracts with Programs, 2016
The Holocene glacial history of the North Cascades is poorly understood, in part because most exi... more The Holocene glacial history of the North Cascades is poorly understood, in part because most existing records rely on moraine remnants and are therefore discontinuous. To develop a more complete record of Holocene fluctuations of North Cascades glaciers, we collected and analyzed glaciolacustrine sediments (i.e., rock flour) deposited over the past ~7800 years in Lyman Lake by the upstream Lyman Glacier. We combined these results with equilibrium-line altitude (ELA) reconstructions and glacier-climate modeling to quantify the climatic conditions that drove these fluctuations. Finally, we compared the Lyman Glacier's continuous fluctuation record to existing glacier and climate records of the North Cascades. Our results indicate that the Lyman Glacier was absent in the early Holocene, from before 7.8 ka until ~4.9 ka, when it experienced an early Neoglacial advance that persisted until at least ~3.8 ka. Following an extended non-glacial interval, the glacier experienced significant advances between ~2.6-2.25 ka, ~1.8-1.3 ka and ~1.1-0.9 ka. An advance starting ~ 0.8 ka (1150 CE) culminated at the glacier's maximum Holocene extent between ~0.6-0.5 ka (~1350-1450 CE), from which it retreated and disappeared entirely by ~0.35 ka (~1600 CE). After ~200 years with no significant glacier presence in the cirque, the glacier reformed and rapidly advanced to its maximum Holocene extent (~1800-1900 CE). Following this event, the glacier retreated steadily throughout the 20 th and early 21 st centuries and as of 2014, has approached its minimum viable extent. Paleo-ELA reconstructions of the glacier's maximum Holocene extents suggest that summers were ~2.6 °C cooler than modern (l981-2010 CE); alternatively, glacier-climate modeling indicates that annual temperatures ~1.5 °C cooler than modern would result in maximum glacier extents. v Combining these new results with existing North Cascades glacial records indicates that: 1) the earliest Neoglacial advances in the region (starting ~6 ka) occurred asynchronously, with higher latitude and more maritime sites experiencing earlier advances; 2) Neoglacial advances remained small, infrequent and asynchronous until the last millennium; 3) Beginning at ~1.0 ka, glaciers throughout the North Cascades advanced synchronously, signaling the onset of the Little Ice Age (LIA); 4) North Cascades glaciers reached their maximum Holocene extents during the 15 th and early 16 th centuries (~0.55-0.45 ka), followed by apparent regional retreat and a final smaller 19 th century (~0.15-0.05 ka) readvance. The asynchronous early-to-mid Neoglacial fluctuations followed by synchronous LIA behavior suggests that local climate factors drove glacier fluctuations until the regional climate signal became strong enough to induce synchrony ca. 1.0 ka. Although the inferred regional retreat remains uncertain, the disappearance of the Lyman Glacier in the mid-LIA (~0.45-0.15 ka) is consistent with the precipitation record at Castor Lake (~100 km to the east), which indicates unusually dry winter conditions between ~1450-1850 CE (~0.5-0.1 ka). vi Acknowledgements As science advances by the collaboration of dedicated individuals, so this project came to completion by the outstanding efforts of many, many people. I am deeply grateful to everyone who lent their valuable time and effort to this endeavor. A small army of field assistants served as human mules, hauling hundreds of pounds of coring equipment and ancient mud over Spider Gap in the quest for a glacial history book. Thanks, Tien Devin
Geological Society of America Special Papers
Geothermal energy depends on high subsurface temperature, adequate permeability and fracture volu... more Geothermal energy depends on high subsurface temperature, adequate permeability and fracture volume, and accessible groundwater supply to support heat exchange with surrounding rock. Some regions may have adequate thermal resources but lack the necessary permeability or deep circulating water. Exploitation of such areas for geothermal energy could occur if permeability can be enhanced enough to provide the necessary heat exchange. These improvements to the geothermal reservoir would produce what is termed an "enhanced geothermal system" (EGS). The Snake River Plain (SRP) in southern Idaho is a geological region with high heat fl ux (~110 mW/m 2) that has been recommended as an EGS target. In this study, we consider how the geologic and thermal history of the SRP might infl uence its EGS potential. We describe the fracture distribution (mean = 28.63 fractures/10 m) in a welded tuff core recovered from one of the few deep boreholes located on the SRP and provide a preliminary discussion of the likely geomechanical behavior under in situ stress. Spatial autocorrelation of fracture features is defi ned with geostatistical techniques and used in a stochastic simulation of possible structures in other welded tuff reservoirs. Autocorrelation scales for the continuous date are on the order of 70 meters with high subsample scale variability (56 m). Results should aid in designing criteria for a hydraulic fracturing plan that would augment the permeability and connectivity of an SRP reservoir's preexisting fracture network.
Drying Technology, 2016
ABSTRACT Pretreatment and densification of biomass can increase the viability of bioenergy produc... more ABSTRACT Pretreatment and densification of biomass can increase the viability of bioenergy production by providing a feedstock that is readily hydrolyzed and able to be transported over greater distances. Ammonia fiber expansion (AFEX™) is one such method targeted for use at distributed depots to create a value-added and densified feedstock for bioenergy use. However, the pretreatment process results in a high-moisture material that must be dried, further size reduced, and pelletized, all of which are energy-intensive processes. This work quantifies the energy consumption required to dry, grind, and densify AFEX-pretreated corn stover compared to non-pretreated stover and explores the potential of reduced drying as a means to conserve energy. The purpose of this work is to understand whether material property changes resulting from AFEX pretreatment influence the material performance in downstream formatting operations. Material properties, heat balance equations, and a rotary drum dryer model were used to model a commercial-scale rotary drum dryer for AFEX-pretreated corn stover, showing the potential to reduce dryer energy consumption by up to 36% compared to non-pretreated corn stover. Laboratory-measured grinding and pelleting energies were both very sensitive to material moisture content. Overall, the total energy required for drying, grinding, and pelleting amounts to a savings of up to 23 kWh/dry Mg for the AFEX-pretreated material when dried to a low moisture content, equating to up to 0.61 $/Mg savings for gas and electricity. Grinding and pelleting of high-moisture AFEX-pretreated stover was shown to be more costlier than the savings collected through reduced drying. Although the energy and cost savings shown here are modest, the results help to highlight operational challenges and opportunities for continued improvement.
Tracers provide an important means of interrogating the subsurface to provide critical informatio... more Tracers provide an important means of interrogating the subsurface to provide critical information about hydraulic characteristics of the reservoir. In a geothermal reservoir, reactive tracers may add information about the thermal state of the reservoir. Tracer test analysis methods vary, but generally involve curve fitting to a simple model of the system or a moment analysis approach. The Idaho National Laboratory is currently developing an analysis tool that provides a variety of commonly used approaches in a single program, and which extends to analysis of reactive tracers. To provide a reactive tracer test analysis method that can be easily implemented without extensive knowledge of the reservoir geometry, we include an approach that relies on a simplified model of the subsurface. The approach involves (1) fitting a simplified reservoir model geometry to a combination of conservative and reactive tracer data (2) using the assumed geometry to interpret changes in reactive tracer concentrations (from tests conducted at different times) and (3) examining the sensitivity of inferences about thermal evolution to the assumptions about geometry. Sensitivity of such an analysis depends on the sensitivity of a reactive tracer to changes in its temperature-time history. We illustrate sensitivity differences between several possible reaction combinations.
Reactive tracers have long been considered a possible means of measuring thermal drawdown in a ge... more Reactive tracers have long been considered a possible means of measuring thermal drawdown in a geothermal system, before significant cooling occurs at the extraction well. Here, we examine the sensitivity of the proposed method to evaluate reservoir cooling and demonstrate that while the sensitivity of the method as generally proposed is low, it may be practical under certain conditions.
16. Discontinuities in the depth-age distribution of OL90-2 indicate a sediment hiatus between-15... more 16. Discontinuities in the depth-age distribution of OL90-2 indicate a sediment hiatus between-15,500 and 13,700 14C years B.P. Sediments at the base of the hiatus are characterized by features that indicate desiccation, including a 1-to 3-mmthick lag deposit of frosted quartz grains. Removal of sediments by wave reworking or deflation implies that the 15,500-year age represents a maximum estimate of the initiation of desiccation. 17. S. P. Lund, unpublished data. 18. The presence of greigite and the absence of magnetite in high-x intervals were inferred from thermomagnetic measurements of magnetic mineral blocking temperatures.