Browsing by Subject "Heat flow"
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Item An analysis of geothermal viability in Pecos County, Permian Basin, West Texas(2022-05-06) Pastorek, Nathan; Young, Michael H.; Wisian, Kenneth W.Pecos County, located in the Permian Basin of west Texas, is a deep sedimentary basin within which the Delaware Basin and Central Basin Platform are located. Significant oil and gas activity has occurred here over nearly 100 years. This activity has yielded substantial available well data for temperature and heat flow analyses. While several national-scale heat flow and temperature-at-depth data sets exist, very few county-level studies within Texas are available. Well data from the National Geothermal Data System (NGDS) are used to construct a Pecos County heat flow model and four temperature-at-depth models (3.5, 5.0, 6.5, and 10.0 km depths), using 947 data points available in Pecos County. Wells are distributed throughout the county, with higher well densities occurring in the north, northeast, and south-central portions. A radiogenic heat production model was incorporated to account for radioactive decay within the basement and sedimentary sections. Results show below-average heat flow (< 65 mW/m²) across the Central Basin Platform and average to above-average heat flow in the Delaware Basin in comparison to previous national heat flow models. High heat flows (>90 mW/m²) were calculated in portions of south and south-central Pecos County. Temperature-at-depth models indicate the lowest temperatures occurring across the Central Basin Platform and eastern Delaware Basin. Temperatures are elevated near the center of the county, with the highest temperatures located in south and south-central Pecos County. Temperature-at-depth model values are comparable with recorded well datapoints around the depth intervals of interest. Maximum temperatures for developed models at 3.5, 5.0, 6.5, and 10.0 km depths are 195°C, 213°C, 232°C, and 273°C, respectively. Findings show that calculated heat flow and temperature-at-depth in southern Pecos County is higher than those calculated for the region in existing national-scale models. Higher than average heat flow and temperature-at-depth anomalies can be attributed in part to higher radiogenic heat production (15.26 mW/m²) than previously estimated and increased model resolution compared to earlier national-scale heat flow and temperature models. Other possible explanations include shallow plutonic complexes, advective groundwater flow, and the Sierra Madera impact and crater. Pecos County has suitable temperatures for geothermal electricity production (> 150°C) at as shallow as 3.5 km depth, and most of the county reaches this temperature by 6.5 km depth. Opportunity exists for co-production of oil and gas and geothermal energy from existing wells at depths where this temperature is met or exceededItem Fluid description of relativistic, magnetized plasmas with anisotropy and heat flow : model construction and applications(2009-08) TenBarge, Jason Michael; Hazeltine, R. D. (Richard D.)Many astrophysical plasmas and some laboratory plasmas are relativistic: either the thermal speed or the local bulk flow in some frame approaches the speed of light. Often, such plasmas are magnetized in the sense that the Larmor radius is smaller than any gradient scale length of interest. Conventionally, relativistic MHD is employed to treat relativistic, magnetized plasmas; however, MHD requires the collision time to be shorter than any other time scale in the system. Thus, MHD employs the thermodynamic equilibrium form of the stress tensor, neglecting pressure anisotropy and heat flow parallel to the magnetic field. We re-examine the closure question and find a more complete theory, which yields a more physical and self-consistent closure. Beginning with exact moments of the kinetic equation, we derive a closed set of Lorentz-covariant fluid equations for a magnetized plasma allowing for pressure and heat flow anisotropy. Basic predictions of the model, including its thermodynamics and the dispersion relation's dependence upon relativistic temperature, are examined. Further, the model is applied to two extant astrophysical problems.Item Heat flow variability at the Costa Rica subduction zone as modeled by bottom-simulating reflector depths imaged in the CRISP 3D seismic survey(2012-08) Cavanaugh, Shannon Lynn; Bangs, Nathan Lawrence Bailey; McIntosh, Kirk D.; Barnes, Jaime; Tatham, Robert3D seismic reflection data were acquired by the R/V Langseth and used to extract heat flow information using bottom-simulating reflector (BSR) depths across the southern Costa Rica convergent margin. These data are part of the CRISP Project, which will seismically image the Middle America subduction zone in 3D. The survey was conducted in an area approximately 55x11 km, northwest of the Osa Peninsula, Costa Rica. For the analysis presented here, seismic data were processed using a post-stack time migration. The BSR—a reverse polarity seismic reflection indicating the base of the gas hydrate phase boundary—is imaged clearly within the slope-cover sediments of the margin wedge. If pressure is taken into account, in deep water environments the BSR acts as a temperature gauge revealing subsurface temperatures across the margin. Two heat flow models were used in this analysis. In the Hornbach model BSR depth is predicted using a true 3D diffusive heat flow model combined with Integrated Ocean Drilling Program (IODP) thermal conductivity data and results are compared with actual BSR depth observations to constrain where heat flow anomalies exist. In the second model heat flow values are estimated using the heat flow equation. Uniform heat flow in the region should result in a deeper BSR downslope toward the trench due to higher pressure; however results indicate the BSR is deepest at over 325 meters below the seafloor (mbsf) further landward and shoals near the trench to less than 100 mbsf, suggesting elevated heat flow towards the toe of the accretionary prism. Heat flow values also reflect this relation. In addition to this survey-wide trend, local heat flow anomalies appear in the form of both circular patterns and linear trends extending across the survey, which can be related to mounds, thrust faults, folds, double BSRs, and seafloor erosion imaged in the seismic data. I suggest that these areas of higher local heat flow represent sites where advection of heat from deep, upward-migrating, thermogenically-sourced fluids and/or gases may be taking place. These heat flow trends have implications for not only earthquake nucleation, but also methane hydrate reserve stability.Item The structural and thermal evolution of upper oceanic crust in the western South Atlantic : insights from seismic velocities and hydrothermal models(2021-01-22) Kardell, Dominik A.; Christeson, Gail L.; Gulick, Sean P. S.; Reece, Robert S.; Hesse, Marc A.; Lavier, Luc L.; Hayman, Nicholas W.The evolution of oceanic crust plays an integral role in global heat flow, geochemical cycles, and in shaping the environmental conditions harboring the crustal biosphere. Because oceanic crust is normally buried beneath several kilometers of water and encompasses a vast area of the Earth’s rigid surface, spatially extensive and coherent geophysical data are difficult to acquire in the oceanic domain. Consequently, our current understanding of the evolution of oceanic crust is based on partially conflicting compilations of data that are acquired at different scales and using different methods. Here I present geophysical constraints from an extensive seismic dataset that continuously covers 0-70 Ma crust in the western South Atlantic. Analysis of regional seismic velocity trends in the upper crust shows a continuous increase in basement velocity to crustal ages of at least 58 Ma. This trend indicates an evolution of upper crustal velocities that lasts significantly longer than measured or predicted by previous studies. The results provide evidence for ongoing hydrothermal circulation in relatively old upper crust, which is consistent with heat flow studies. To further test this concept, I used high-resolution seismic velocity models to estimate detailed porosity and permeability distributions that constrain models of hydrothermal fluid flow at five different crustal ages. The resulting advective and conductive surface heat fluxes are consistent with both predictions of heat flux by lithospheric cooling models and measured conductive heat flux at the seafloor. Additionally, computed hydrothermal volume fluxes largely agree with global estimates for the modeled crustal ages. The models are therefore consistent with a “sealing age” of ~65 Ma, which is also inferred from a compilation of global heat flow measurements at the seafloor. Close to the Rio Grande Rise, an oceanic plateau west of the study area, a fine-scale seismic velocity model reveals multiple large fault zones penetrating at least ~1.5 km into the crust. These faults likely accommodate differential subsidence between thickened, warm oceanic plateau crust and cold oceanic crust. Modeled fluid fluxes are elevated along the interpreted fault zones and across the seafloor. Crust adjacent to oceanic plateaus may exhibit elevated levels of tectonic activity and fluid flow globally. The estimated global volume of fluid entering the ocean in this type of setting amounts to 43 km³, which is ~2% of the hydrothermal flux in the axial region. This potentially has implications for global chemical cycles, the hydration of mature oceanic crust, and the oceanic crustal biosphere.