Search

The geochemical alteration of host rocks might affect the productivity and the potential for induced seismicity of geothermal systems. In addition to natural alteration, following production and heat extraction, re‐injected fluids at lower temperatures and different pressures may be in chemical disequilibrium with the rock, impacting mineral solubility and dissolution/precipitation processes. In this study, we investigate the effect of geochemical alteration on the frictional behavior of granites, and their seismogenic potential, by conducting direct shear experiments using samples with varying degrees of alteration. The samples originate from the Carnmenellis granite in Cornwall, SW England, and represent the formation used in the United Downs Deep Geothermal Power Project for heat extraction. Experiments were conducted on granite powders (referred to as gouges) at room temperature and 180°C, at simulated in situ confining and pore pressures of 130 and 50 MPa, respectively (∼5 km depth). With increasing degree of alteration, the frictional strength of the gouges decreases while frictional stability increases. At high temperature, frictional stability is reduced for all samples while maintaining the trend with alteration stage. Microstructural investigation of the sheared gouges shows alteration delocalizes shear by reducing grain size and increasing clay fraction, which promotes the formation of pervasive shear fabrics. Our work suggests that, within the range of tested pressures, more alteration of granite initially causes more stable shearing in a fault. This behavior with alteration is sustained at high temperatures, but the overall frictional stability is reduced which increases the potential for induced seismicity at higher temperatures. Plain Language Summary: Geothermal systems are of high interest as renewable energy source. However, hot fluids in the deep subsurface can chemically react with the host rock they flow through. These reactions then affect the fluid chemistry and the rock mineral composition. With changes in mineral composition, changes in mechanical and hydraulic properties are observed. We test the effects of a specific group of reactions (argillic alteration) on the frictional properties of granite powders by using an example rock that is targeted in geothermal projects in Cornwall, SW England. The frictional properties give information about how likely it is for granitic rocks to produce an earthquake while sliding. Our tests show that the more the granite has chemically changed, the easier the powder is to slide but the more stably it will slide. This means that chemically changed powders are less likely to create seismic waves on sliding. In addition, tests at high temperature (180°C) showed the same stabilizing effect within the reacted rocks but the general sliding stability was reduced over all samples. This implies that the potential for earthquakes is higher at higher temperatures, although the analyzed chemical reactions reduce this potential in granitic geothermal systems. Key Points: Large fault systems are targeted at depth as geothermal reservoirs in high‐heat producing granites in CornwallDirect shear experiments were conducted on a series of successively more naturally altered granites from a fault in Carnmenellis graniteAlteration makes sliding more likely but also more stable, while higher temperatures destabilize shearing [ABSTRACT FROM AUTHOR]

Reliable determination of rate-and-state friction (RSF) parameters depends on achieving steady-state (SS) friction conditions before and after experimental velocity-stepping friction tests. This operation, through nonlinear least squares fitting, is commonly preceded by the removal of any overall slip weakening/hardening after friction velocity steps (VSs) through a sufficiently large window of slip displacement at SS ( = linear detrend). However, to date, the identification of SS and thus the correct linear detrend is dependent on the user, which potentially results in differing RSF outputs from the same data set. Here, we demonstrate that large errors in the determination of the fitted RSF parameters can result if SS conditions are not reached before and after VSs. Such errors can be particularly relevant for materials characterized by long evolution of frictional resistance with slip, such as clay-rich gouge layers, in which identifying SS after VSs is not always obvious. To this end, we propose a methodology to accurately and consistently identify where SS is achieved after VSs. This methodology is coded into a new MATLAB-based routine, steadystate. We show the key features of the methodology, as well as how to use steadystate and read its output. We also illustrate the broad applicability of the approach to friction data with different noise levels and sampling frequencies referenced to slip velocity, by reviewing observations from synthetic data sets and specific examples of experiments from different laboratories involving various sheared materials. [ABSTRACT FROM AUTHOR]

Although few marine natural products are currently on the market or in clinical trials, marine organisms represent the greatest unexploited source of potential pharmaceuticals. Because of the unusual diversity of chemical structures isolated from marine organisms, there is intense interest in screening marine natural products for their biomedical potential.

The purpose of this study is to quantify the effect of various design and operating parameters on smoking room performance. Twenty-eight experiments were conducted in a simulated smoking room with a smoking machine and an automatic door opener. Measurements were made of air flows, pressures, temperatures, two particle-phase ETS tracers, two gas-phase ETS tracers, and sulfur hexafluoride. Quantification of leakage flows, the effect of these leaks on smoking room performance and non-smoker exposure, and the relative importance of each leakage mechanism are presented. The results indicate that the first priority for an effective smoking room is to depressurize it with respect to adjoining non-smoking areas. Another important ETS leakage mechanism is the pumping action of the smoking room door. Substituting a sliding door for a standard swing-type door reduced this source of ETS leakage significantly. Measured results correlated well with model predictions (R2 = 0.82-0.99).

This final report presents the results of research completed during Phase III of the project, "Localized Thermal Distribution (LTD) for Office Buildings," sponsored by the California Institute for Energy Efficiency. The project team consisted of researchers from the University of California, Lawrence Berkeley Laboratory, and Humboldt State University. Work was performed in three task areas: (1)Whole-Building Energy Simulations, (2)Field Studies, and (3)LTD Engineering and Applications Guide Outline. Following this Executive Summary, the final report is presented in four separate parts, each addressing one of the above task areas with two describing work on the two separate field studies.

Results are presented from a research project to investigate the effects of office partition design on air movement, worker comfort, and ventilation in workstations. The objectives of the study were to evaluate the comfort and ventilation conditions produced by a conventional ceiling supply-and-return air distribution system in workstations separated by (1) solid partitions of different height (75 in. [1.9 m], 65 in. [1.65 m], 42 in. [1.1 m], and 0 in. [partitions removed]) and (2) partitions containing a gap positioned at the bottom of the partition. The project consisted primarily of experiments performed in a full-scale controlled environment chamber (CEC) which a typical modular office environment was set up. The range of partition configurations and environmental parameters investigated included (1) partition height, (2) solid vs. airflow partitions, (3) airflow gap size, (4) supply air volume, (5) supply~room temperature difference, (6) supply diffuser location, (7) heat loud density, (8) workstation size, and (9) cooling vs. heating mode. Under steady-state conditions, multipoint measurements were made of air velocities, air temperatures, and radiant (globe) temperatures to characterize the key environmental variables affecting thermal comfort, and tracer gas methods using multipoint sampling locations were employed to determine the ventilation performance within the test chamber.The results indicated that variations in solid partition height produce only small differences in overall thermal and ventilation performance. Results also showed that while the existence of an airflow opening at the bottom of office partitions can, in some cases, produce slight increases in air velocities near the floor, there are no significant improvements in comfort conditions or ventilation efficiency within the workstations compared to results obtained for solid partitions. Test parameters that were found to have a more substantial impact on air movement and comfort included heat load density and distribution, supply air temperature, and supply diffuser location.