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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Investigation of Error Patterns in Geographical Databases

The objective of the research conducted in this project is to develop a methodology to investigate the accuracy of Airport Safety Modeling Data (ASMD) using statistical, visualization, and Artificial Neural Network (ANN) techniques. Such a methodology can contribute to answering the following research questions: Over a representative sampling of ASMD databases, can statistical error analysis techniques be accurately learned and replicated by ANN modeling techniques? This representative ASMD sample should include numerous airports and a variety of terrain characterizations. Is it possible to identify and automate the recognition of patterns of error related to geographical features? Do such patterns of error relate to specific geographical features, such as elevation or terrain slope? Is it possible to combine the errors in small regions into an error prediction for a larger region? What are the data density reduction implications of this work? ASMD may be used as the source of terrain data for a synthetic visual system to be used in the cockpit of aircraft when visual reference to ground features is not possible during conditions of marginal weather or reduced visibility. In this research, United States Geologic Survey (USGS) digital elevation model (DEM) data has been selected as the benchmark. Artificial Neural Networks (ANNS) have been used and tested as alternate methods in place of the statistical methods in similar problems. They often perform better in pattern recognition, prediction and classification and categorization problems. Many studies show that when the data is complex and noisy, the accuracy of ANN models is generally higher than those of comparable traditional methods.

Dryer, David↗
DOE OSTI2023

An adjoint-based optimization method for jointly inverting heterogeneous material properties and fault slip from earthquake surface deformation data

SUMMARY Analysis of tectonic and earthquake-cycle associated deformation of the crust can provide valuable insights into the underlying deformation processes including fault slip. How those processes are expressed at the surface depends on the lateral and depth variations of rock properties. The effect of such variations is often tested by forward models based on a priori geological or geophysical information. Here, we first develop a novel technique based on an open-source finite-element computational framework to invert geodetic constraints directly for heterogeneous media properties. We focus on the elastic, coseismic problem and seek to constrain variations in shear modulus and Poisson’s ratio, proxies for the effects of lithology and/or temperature and porous flow, respectively. The corresponding nonlinear inversion is implemented using adjoint-based optimization that efficiently reduces the cost function that includes the misfit between the calculated and observed displacements and a penalty term. We then extend our theoretical and numerical framework to simultaneously infer both heterogeneous Earth’s structure and fault slip from surface deformation. Based on a range of 2-D synthetic cases, we find that both model parameters can be satisfactorily estimated for the megathrust setting-inspired test problems considered. Within limits, this is the case even in the presence of noise and if the fault geometry is not perfectly known. Our method lays the foundation for a future reassessment of the information contained in increasingly data-rich settings, for example, geodetic GNSS constraints for large earthquakes such as the 2011 Tohoku-oki M9 event, or distributed deformation along plate boundaries as constrained from InSAR.

Geochemistry & Geophysics↗
DOE OSTI2024

GDSA Repository Systems Analysis Investigations in FY 2024

The Disposal Research and Development (R&D) Program of the US Department of Energy (DOE) office of Nuclear Energy (NE-8) Spent Fuel and Waste Science and Technology (SFWST) Campaign is to conduct R&D on disposal of spent nuclear fuel (SNF) and high-level waste (HLW). The goal of the Geologic Disposal Safety Assessment (GDSA) within this project is to develop a disposal system modeling and analysis capability that supports the integrated modeling of coupled processes controlling disposal system performance of deep geologic repositories, including uncertainty. This report describes specific activities in the Fiscal Year (FY) 2024 associated with the GDSA Repository Systems Analysis (RSA) work package. The overall objective of the GDSA RSA work package is to develop generic deep geologic repository concepts and repository system performance models in crystalline, argillite, salt, and unsaturated alluvium potential host-rock environments, and to simulate and analyze these generic repository concepts and models using GDSA Framework toolkit, and other tools as needed.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2015

Nevada national security site environmental remediation Large-Scale Multi-Well Aquifer Tests Used to Define Flow Systems - 15589

Over the past 5 years, 10 new groundwater wells have been drilled and hydraulically tested on Pahute Mesa Corrective Action Unit (CAU) under the Underground Test Area (UGTA) Activity at the Nevada National Security Site (NNSS). The new wells were drilled as part of a Phase II Corrective Action Investigation to gain a better understanding of the geology and hydrology of the system and to support development of a groundwater flow and transport model used for forecasting contaminant boundaries. Multi-well aquifer testing provides the most integrated assessment of hydraulic properties and connectivity within complex geologic systems. By providing hydraulic connectivity, these tests can be used to generate insight on potential contaminant flow paths and provide constraint on overall groundwater flow pathways. Drawdown in observation wells provides direct evidence of a hydraulic connection. During well drilling and testing activities, a total of 20 aquifer tests were conducted with as many as 36 individual completion zones. A signal-processing method developed by the U.S. Geological Survey was used to improve pumping drawdown detection. Using this approach, drawdown as far away as 3-4 kilometers has been detected. In addition to the typical analysis for hydraulic property values, the observed hydraulic connectivity are qualitatively and quantitatively used to inform the hydrogeologic framework model which is updated using other permissible geologic interpretations, when necessary, to incorporate the aquifer-testing results. These results will be used for developing and building confidence in the conceptual and numerical models for the Pahute Mesa CAU. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2017

Heterogeneity, pore pressure, and injectate chemistry: Control measures for geologic carbon storage

Desirable outcomes for geologic carbon storage include maximizing storage efficiency, preserving injectivity, and avoiding unwanted consequences such as caprock or wellbore leakage or induced seismicity during and post injection. Here, to achieve these outcomes, three control measures are evident including pore pressure, injectate chemistry, and knowledge and prudent use of geologic heterogeneity. Field, experimental, and modeling examples are presented that demonstrate controllable GCS via these three measures. Observed changes in reservoir response accompanying CO 2 injection at the Cranfield (Mississippi, USA) site, along with lab testing, show potential for use of injectate chemistry as a means to alter fracture permeability (with concomitant improvements for sweep and storage efficiency). Further control of reservoir sweep attends brine extraction from reservoirs, with benefit for pressure control, mitigation of reservoir and wellbore damage, and water use. State-of-the-art validated models predict the extent of damage and deformation associated with pore pressure hazards in reservoirs, timing and location of networks of fractures, and development of localized leakage pathways. Experimentally validated geomechanics models show where wellbore failure is likely to occur during injection, and efficiency of repair methods. Use of heterogeneity as a control measure includes where best to inject, and where to avoid attempts at storage. Lastly, an example is use of waste zones or leaky seals to both reduce pore pressure hazards and enhance residual CO 2 trapping.

58 GEOSCIENCES↗
NASA NTRS1983

Two-dimensional Finite Element Modeling for Modeling Tectonic Stress and Strain

Techniques of finite element analysis in two dimensional plane strain were applied to problems of geophysics and tectonics. More specifically, the flexibility of the finite element method was employed to address problems involving geological complexity and fault interactions. The modeling of effective anisotropy in material elastic properties proved useful in describing the deformation of faulted crustal blocks. The applications of this modeling work to problems of actual tectonics in southern California was explored. Preliminary models show encouraging agreement with measured tectonic strain in this region, and modeling work was done to gain an understanding of the stress state in a locked fault region with future seismic potential.

Lyzenga, G. A.↗
DOE OSTI2015

Experimental Investigation of Two-Phase Flow in Consolidating and Intact Salt: Analysis of Capillary Pressure Measurements from Core Labs

Two-phase flow of brine and air through very low permeability porous media is the dominant fluid flow state in and around geologic repositories for nuclear waste disposal. Constitutive models developed for other subsurface media (shale, sandstone, limestone, etc.) have been adopted but never experimentally parameterized for geologic salt. This report summarizes results of scoping capillary pressure and brine saturation measurements on reconsolidated run-of-mine salt and intact geologic salt samples. These measurements were obtained using mercury injection tests and yielded values of threshold pressure, pore-size distribution, and mercury saturation. The brine capillary pressure curve was then inferred from the raw mercury capillary pressure data. This report also summarizes estimates of the constitutive model parameters from the brine saturation and capillary pressure data (Brooks and Corey, 1964; van Genuchten, 1980). The results suggests that the model of van Genuchten (1980) is better suited for brine-air-salt systems. Additional testing is needed for the low brine saturation range of the capillary pressure curve where the present suite of tests did not yield sufficient data.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2017

Geothermal Play-Fairway Analysis of Washington State Prospects: Phase 2 Results

An investment of $0.7M from the Geothermal Technology Office for Phase 2 of Play Fairway Analysis in Washington State improved existing favorability models and increased model confidence. The new 1:24,000-scale geological mapping, 15 detailed geophysical surveys, 2 passive seismic surveys, and geochronology collected during this phase are coupled with updated and detailed structural modeling and have significantly improved the conceptual models of three potential blind geothermal systems/plays in Washington State: the St. Helens Shear Zone, Mount Baker, and Wind River Valley. Results of this analysis reveal the presence of commercially viable undiscovered geothermal resources in all three study areas. The analysis additionally provides a clear definition of the geothermal prospects in terms of the essential elements of a functioning geothermal system, the confidence in these assessments, and associated potential and risk of development. As a result, several groups have recently approached our organization about opportunities for large-capital moderate- to high-temperature geothermal development and are very interested in the results of Phase 3 drilling. Here, our updated models, coupled with development interest, provides a compelling basis for investment in future validation activities.

exploration risk↗
DOE OSTI2020

LLNL Kimberlina 1.2 NUFT Simulations June 2018 (v2)

This dataset contains the output 6,000, 3-dimensional reactive multi-phase flow and transport aquifer simulations of brine and CO2 leakage into a protective aquiver in California’s San Joaquin Valley and input data files detailing the geologic mesh, aquifer physical properties and CO2 and brine injection rates. This data set was generated as an ongoing effort with the US DOE National Risk Assessment Partnership (NRAP) to evaluate the effectiveness of monitoring techniques to detect brine and CO2 leakage from legacy wells into underground sources of drinking water overlaying a CO2 storage reservoir. Each simulation contains a unique set of input parameters, generated stochastically. The outputs consist of these upper three geologic layers (from top): the Etchegoin, Macoma-Chanac, Santa Margarita-McLure formations. These simulations span the several distances (1, 3 and 6 km or wells W31-0.2, W31-0.5 and W31-1.0, respectively) from the CO2 injector, initiated from bottom hole pressure and saturation to calculate wellbore leakage from the storage reservoir, with low and high regional groundwater gradients and wellbore leakage into 5 leaky nodes. The dataset includes 1,000 unique simulations for each distance, which each contain a unique aquifer heterogeneity, aquifer and caprock permeability, and two model generations are included with a high permeability (prod07) and hybrid permeability (prod09). The range of permeability distributions is listed in Table 1. Each model generation consists of 3,000 simulations. Included in the dataset are the leakage rates determined from 2D wellbore models which utilize the pressure and CO2 saturation from LBL's reservoir simulations, NUFT mesh files with distributed lithology, NUFT rocktab files which describe the material properties for the geologic layers and the NUFT input files and post-processed output 'ntab' files. Each ntab file contains spatial (rows) and temporal (columns) model output tables for each model cell, the locations (x,y,z) and dimensions for each cells (dx, dy, dz). Table 1. Permeability distribution ranges for prod07 and prod09 model generations Geologic Layer: Permeability Range (log10 m^2) prod07 prod09 Etchegoin -12.92 to -10.92 -13.70 to -11.44 Macoma-Chanac -12.72 to -10.72 -13.50 to -11.24 Santa Margarita-McLure -12.70 to -10.70 -13.48 to -11.22 The input files used to generate the model include which are included in the dataset are: Time series of CO2 leakage input into the model (ex: Q_brn.W31-0.2.sim1000.layers123.tab) Time series of CO2 leakage input into the model (ex: Q_CO2.W31-0.2.sim1000.layers123.tab) Physical properties of the aquifer materials detailing the aquifer porosity, solid density, partitioning coefficients, permeabilities and van-Genuchten parameters detailed in a NUFT rocktab file: (ex: sim1000.usnt.rocktab) Numerical mesh and geologic data assigned to each model cell detailed in a NUFT genmsh format (ex: sim1000.mesh_k16.prod07.trans.genmsh) The primary output parameters are: pH (use absolute value) Change in TDS (mg/kg) Change in Pressure (Pa) Change CO2 gas saturation (fraction range 0.0-1.0) for example, the directory /p/lscratchh/mansoor1/nrap/kimberlina/prod09/mainfiles/sim1000/W31- 0.2 contains: sim1000.W31-0.2.trans.pH.red.ntab sim1000.W31-0.2.no_bg.trans.TDS.red.ntab sim1000.W31-0.2.usnt.P.deltabg.red.ntab sim1000.W31-0.2.usnt.CO2_sat.deltabg.red.ntab Each row in the NTAB files consist of model output per numerical grid cell. Each output file contains 33 columns (variables), including the information of numerical records, geologic location and sizes and the simulated parameter values over time. The first 13 variables are about numerical records and relative geologic information for a simulation grid: 1. index: simulation index 2. i: the ith grid of x-axis 3. j: the ith grid of y-axis 4. k: the ith grid of z-axis 5. element_ref: element reference 6. nuft_ind: nuft index 7. x: grid location in the x axis direction 8. y: grid location in the y axis direction 9. z: grid location in the z axis direction 10. dx: grid length in the x axis direction 11. dy: grid length in the y axis direction 12. dz: grid length in the z axis direction 13. volume: volume of the simulation grid The remainder (14, 15, 16...) variables are the simulated parameter values over time, take Pressure as an example, are: 14. 0.0y: initial pressure per cell. 15. 10.0y: simulated pressure at the end of the 10th year. 16. 20.0y: simulated pressure at the end of the 20th year. ... (repeated for every 10 years until 200 years)... The model extends 10,000 m, 5,000 m and 1,411 m in the x,y and z dimensions, respectively. The mesh consists of 164,832 cells with mesh dimensions of 101 x 51 x 32 (nx, ny, nz), with cell dimensions ranging from 100 m laterally (along x and y-axis) and model layers are as designated in the z-axis: Layer 1: atmosphere (1e-30 m thick) Layer 2: upper caprock (10 m thick) Layers 3-13: Etchegoin (536.23 m thck) Layers 14-27: Macoma-Chanac (679.04 m thick) Layers 28-32: Santa Margarita-McLure (185.94 m thick) The wellbore is placed along node i=51, j=26, and extends vertically along 5 nodes from the top to the bottom of the model. Special instructions when extracting files: Each Gzip archive (ex: prod07.sim1000-sim00099.tar.gz) contains 100 simulations. Gzip archives should be transferred into base directories (ie. In Linux: mkdir prod07; mv prod07.*.tar.gz prod07/.) before extracting, or files will be overwritten. Each sub-simulation tree should have the following file structure pattern (using the linux 'tree' command): |-- prod07 | |-- sim0001 | |-- W31-0.2 | | |-- Q_brn.W31-0.2.sim0001.layers123.tab | | |-- Q_co2.W31-0.2.sim0001.layers123.tab | | |-- sim0001.W31-0.2.no_bg.trans.TDS.red.ntab | | |-- sim0001.W31-0.2.trans.pH.red.ntab | | |-- sim0001.W31-0.2.usnt.CO2_sat.deltabg.red.ntab | | |-- sim0001.W31-0.2.usnt.P.deltabg.red.ntab | |-- W31-0.5 | | |-- Q_brn.W31-0.5.sim0001.layers123.tab | | |-- Q_co2.W31-0.5.sim0001.layers123.tab | | |-- sim0001.W31-0.5.no_bg.trans.TDS.red.ntab | | |-- sim0001.W31-0.5.trans.pH.red.ntab | | |-- sim0001.W31-0.5.usnt.CO2_sat.deltabg.red.ntab | | |-- sim0001.W31-0.5.usnt.P.deltabg.red.ntab | |-- W31-1.0 | | |-- Q_brn.W31-1.0.sim0001.layers123.tab | | |-- Q_co2.W31-1.0.sim0001.layers123.tab | | |-- sim0001.W31-1.0.no_bg.trans.TDS.red.ntab | | |-- sim0001.W31-1.0.trans.pH.red.ntab | | |-- sim0001.W31-1.0.usnt.CO2_sat.deltabg.red.ntab | | |-- sim0001.W31-1.0.usnt.P.deltabg.red.ntab | |-- sim0001.mesh_k16.prod07.trans.genmsh Disclaimer This document was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor Lawrence Livermore National Security, LLC, nor any of their employees makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or Lawrence Livermore National Security, LLC. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or Lawrence Livermore National Security, LLC, and shall not be used for advertising or product endorsement purposes. Lawrence Livermore National Laboratory is operated by Lawrence Livermore National Security, LLC, for the U.S. Department of Energy, National Nuclear Security Administration under Contract DE-AC52-07NA27344. This report was reviewed and released as LLNL-MI-753464.

aquifer↗
DOE OSTI2014

Model Evaluation Report for Corrective Action Unit 98: Frenchman Flat, Nevada National Security Site, Nye County, Nevada, Revision 1

Model evaluation focused solely on the PIN STRIPE and MILK SHAKE underground nuclear tests’ contaminant boundaries (CBs) because they had the largest extent, uncertainty, and potential consequences. The CAMBRIC radionuclide migration experiment also had a relatively large CB, but because it was constrained by transport data (notably Well UE-5n), there was little uncertainty, and radioactive decay reduced concentrations before much migration could occur. Each evaluation target and the associated data-collection activity were assessed in turn to determine whether the new data support, or demonstrate conservatism of, the CB forecasts. The modeling team—in this case, the same team that developed the Frenchman Flat geologic, source term, and groundwater flow and transport models—analyzed the new data and presented the results to a PER committee. Existing site understanding and its representation in numerical groundwater flow and transport models was evaluated in light of the new data and the ability to proceed to the CR stage of long-term monitoring and institutional control.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS2011

In Situ Trace Element Measurements on Roda and the Origin of Diogenites

The origin of diogenites remains poorly understood. A recent model interprets many diogenites to have been formed from melts that were derived by remelting initial magma ocean cumulates, and these penultimate parent melts were then contaminated by melts derived from remelting of the basaltic (eucritic) crust to form the ultimate diogenite parent melts [1] (hereafter the remelting model). This is a very complicated petrogenesis that has profound implications for the geological evolution of 4 Vesta if correct. This model was developed based on trace element analyses of bulk rock samples that had been leached in acids to remove phosphates; the compositions of the residues were interpreted to be close to those of cumulus orthopyroxenes plagioclase, chromite and olivine [1]. In situ measurements of phases in diogenites can be used to test this model. We have begun a campaign of laser ablation ICP-MS of orthopyroxene grains in diogenites for this purpose. Here we report our first results on one diogenite, Roda. We have determined a suite of trace lithophile elements on nine, mm-sized pyroxene grains separated from Roda that have previously been studied [2, 3]. A key observation supporting the remelting model is the very low Eu/Eu* of leached residues; values too low to represent orthopyroxene that crystallized from melts with chondritic Sm/Eu and Gd/Eu [1]. (Eu* = Eu interpolated from REE diagrams.) Crustal remelts have low Sm/Eu and Gd/Eu, and orthopyroxenes that crystallized from parent melts contaminated by them would have very low Eu/Eu* [1]. Roda grains have Eu/Eu* of 0.243 to 0.026; the latter a value lower than any measured on bulk diogenite leached residues (0.041) [1]. There is a general negative correlation between Eu/Eu* and some incompatible elements (Zr, Nb, Hf), but not others (LREE). This appears inconsistent with the remelting model as it would suggest an evolving parent melt with La de-creasing as Zr increased and Eu/Eu* decreased. Grain R-15 includes trace-element-rich trapped melt phases [2, 3]. This grain has the highest Eu/Eu* and LREE contents, indicating that the trapped melt had a high Eu/Eu*. Thus, our first data on one diogenite do not provide support for the remelting model [1]. Roda is unusual in that its orthopyroxene grains show wide ranges in trace element contents [4]. Previous in situ REE analyses of grain R-15 did not reveal evidence for subsolidus equilibration with trace-element-rich trapped melt phases, and led to the suggestion that Roda may be polymict, with different grains representing different lithologies of diverse compositions [3]. Thus, based on our results on Roda, it is perhaps premature to abandon the remelting model. In situ measurements on a suite of diogenites is planned to further address this issue.

Mittlefehldt, David W.↗
DOE OSTI2016

Spatial Modeling of Geometallurgical Properties: Techniques and a Case Study

High-resolution spatial numerical models of metallurgical properties constrained by geological controls and more extensively by measured grade and geomechanical properties constitute an important part of geometallurgy. Geostatistical and other numerical techniques are adapted and developed to construct these high-resolution models accounting for all available data. Important issues that must be addressed include unequal sampling of the metallurgical properties versus grade assays, measurements at different scale, and complex nonlinear averaging of many metallurgical parameters. This paper establishes techniques to address each of these issues with the required implementation details and also demonstrates geometallurgical mineral deposit characterization for a copper–molybdenum deposit in South America. High-resolution models of grades and comminution indices are constructed, checked, and are rigorously validated. The workflow demonstrated in this case study is applicable to many other deposit types.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Determining the source characteristics of explosions near the Earth's surface

We present a method to determine the source characteristics of explosions near the airearth interface. The technique is an extension of the regional amplitude envelope method and now accounts for the reduction of seismic amplitudes as the depth of the explosion approaches the free surface and less energy is coupled into the ground. We first apply the method to the Humming Roadrunner series of shallow explosions in New Mexico where the yields and depths are known. From these tests, we find an appreciation of knowing the material properties for both source coupling/excitation and the free surface effect. Although there is the expected tradeoff between depth and yield due to coupling effects, the estimated yields are generally close to the known values when the depth is constrained to the free surface. We then apply the method to a regionally recorded explosion in Syria. We estimate an explosive yield less than the 60 tons claimed by sources in the open press. The modifications to the method allow us to apply the technique to new classes of events, but we will need a better understanding of explosion source models and properties of additional geologic materials.

45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEF↗
DOE OSTI2022

Application of machine learning to characterize gas hydrate reservoirs in Mackenzie Delta (Canada) and on the Alaska north slope (USA)

Here, artificial neural network-trained models were used to predict gas hydrate saturation distributions in permafrost-associated deposits in the Eileen Gas Hydrate Trend on the Alaska North Slope (ANS), USA and at the Mallik research site in the Beaufort-Mackenzie Basin, Northwest Territories, Canada. The database of Logging-While-Drilling (LWD) and wireline logs collected at five wells (Mount Elbert, Ignik Sikumi, and Kuparuk 7–11–12 wells at ANS, plus 2L-38 and 5L-38 wells at the Mallik research site) includes more than 10,000 depth points, which were used for training, validation, and testing the machine learning (ML) models. Data used in training the ML models include the well logs of density, porosity, electrical resistivity, gamma radiation, and acoustic wave velocity measurements. Combinations of two or three out of these five well logs were found to reliably predict the gas hydrate saturation with accuracy varying between 80 and 90% when compared to the gas hydrate saturations derived from Nuclear Magnetic Resonance (NMR)-based technique. The ML models trained on data from three ANS wells achieved high fidelity predictions of gas hydrate saturation at the Mallik site. The results obtained in this study indicate that ML models trained on data from one geological basin can successfully predict key reservoir parameters for permafrost-associated gas hydrate accumulations within another basin. A generalized approach for selecting a well log combination that can improve model accuracy is discussed. Overall, the study outcome supports earlier work demonstrating that ML models trained on non-NMR well logs are a viable alternative to physics-driven methods for predicting gas hydrate saturations.

58 GEOSCIENCES↗
DOE OSTI2017

The influence of seawater carbonate chemistry, mineralogy, and diagenesis on calcium isotope variations in Lower-Middle Triassic carbonate rocks

The geological calcium cycle is linked to the geological carbon cycle through the weathering and burial of carbonate rocks. As a result, calcium (Ca) isotope ratios ( 44 Ca/ 40 Ca, expressed as δ 44/40 Ca) can help to constrain ancient carbon cycle dynamics if Ca cycle behavior can be reconstructed. But, the δ 44/40 Ca of carbonate rocks is influenced not only by the δ 44/40 Ca of seawater but also by diagenetic processes and fractionation associated with carbonate precipitation. In this study, we investigate the dominant controls on carbonate δ 44/40 Ca in Upper Permian to Middle Triassic limestones (ca. 253 to 244 Ma) from south China and Turkey. This time interval is ideal for assessing controls on Ca isotope ratios in carbonate rocks because fluctuations in seawater δ 44/40 Ca may be expected based on several large carbon isotope (δ 13 C) excursions ranging from -2 to + 8‰. Parallel negative δ 13 C and δ 44/40 Ca excursions were previously identified across the end-Permian extinction horizon. Here, we find a second negative excursion in δ 44/40 Ca of ~ 0.2‰ within Lower Triassic strata in both south China and Turkey; however, this excursion is not synchronous between regions and thus cannot be interpreted to reflect secular change in the δ 44/40 Ca of global seawater. Additionally, δ 44/40 Ca values from Turkey are consistently 0.3‰ lower than contemporaneous samples from south China, providing further support for local or regional influences. By measuring δ 44/40 Ca and Sr concentrations ([Sr]) in two stratigraphic sections located at opposite margins of the Paleo-Tethys Ocean, we can determine whether the data represent global conditions (e.g., secular variations in the δ 44/40 Ca of seawater) versus local controls (e.g., original mineralogy or diagenetic alteration). The [Sr] and δ 44/40 Ca data from this study are best described statistically by a log-linear correlation that also exists in many previously published datasets of various geological ages. By using a model of early marine diagenetic water-rock interaction, we illustrate that this general correlation can be explained by the chemical evolution of bulk carbonate sediment samples with different initial mineralogical compositions that subsequently underwent recrystallization. Although early diagenetic resetting and carbonate mineralogy strongly influence the carbonate δ 44/40 Ca values, the relationship between [Sr] and δ 44/40 Ca holds potential for reconstructing first-order secular changes in seawater δ 44/40 Ca composition.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

A net-zero emissions strategy for China’s power sector using carbon-capture utilization and storage

Decarbonized power systems are critical to mitigate climate change, yet methods to achieve a reliable and resilient near-zero power system are still under exploration. This study develops an hourly power system simulation model considering high-resolution geological constraints for carbon-capture-utilization-and-storage to explore the optimal solution for a reliable and resilient near-zero power system. This is applied to 31 provinces in China by simulating 10,450 scenarios combining different electricity storage durations and interprovincial transmission capacities, with various shares of abated fossil power with carbon-capture-utilization-and-storage. Here, we show that allowing up to 20% abated fossil fuel power generation in the power system could reduce the national total power shortage rate by up to 9.0 percentages in 2050 compared with a zero fossil fuel system. A lowest-cost scenario with 16% abated fossil fuel power generation in the system even causes 2.5% lower investment costs in the network (or $16.8 billion), and also increases system resilience by reducing power shortage during extreme climatic events.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2019

The Effect of Fault Geometry and Minimum Shear Wavespeed on 3D Ground-Motion Simulations for an M w 6.5 Hayward Fault Scenario Earthquake, San Francisco Bay Area, Northern California

We investigated the effects of fault geometry and assumed minimum shear wavespeed (V Smin ) on 3D ground-motion simulations (0–2.5 Hz) in general, using a moment magnitude (M w ) 6.5 earthquake on the Hayward fault (HF). Simulations of large earthquakes on the northeast-dipping HF using the U.S. Geological Survey (USGS) 3D seismic model have shown intensity asymmetry with stronger shaking for the Great Valley Sequence east of the HF (hanging wall) relative to the Franciscan Complex to the west (footwall). We performed simulations with three fault geometries in both plane-layered (1D) and 3D models. Results show that the nonvertical fault geometries result in larger motions on the hanging wall relative to the vertical fault for the same Earth model with up to 50% amplifications in single-component peak ground velocity (PGV) within 10 km of the rupture. Near-fault motions on the footwall are reduced for the nonvertical faults, but less than they are increased on the hanging wall. Simulations assuming V Smin values of 500 and 250 m/s reveal that PGVs are on average 25% higher west of the HF when using the lower V Smin ,with some locations amplified by a factor of 3. Increasing frequency content from 2.5 to 5 Hz increases PGV values. Spectral ratios of these two V Smin cases show average amplifications of 2–4 (0.5–1.5 Hz) for the lower V Smin west of the fault. Large differences (up to 2×) in PGV across the HF from previous studies persist even for the case with a vertical fault or V Smin of 250 m/s. We conclude that assuming a V Smin of 500 m/s underestimates intensities west of the HF for frequencies above 0.5 Hz, and that low upper crustal (depth <10 km) shear wavespeeds defined in the 3D model contribute most to higher intensities east of the HF.

58 GEOSCIENCES↗