5 research outputs found
Fracture-fill calcite as a record of microbial methanogenesis and fluid migration: a case study from the Devonian Antrim Shale, Michigan Basin
The Devonian Antrim Shale is an organic-rich, naturally fractured black shale in the Michigan Basin that serves as both a source and reservoir for natural gas. A well-developed network of major, through-going vertical fractures controls reservoir-scale permeability in the Antrim Shale. Many fractures are open, but some are partially sealed by calcite cements that retain isotopic evidence of widespread microbial methanogenesis. Fracture filling calcite displays an unusually broad spectrum of δ 13 C values (+34 to −41‰ PDB), suggesting that both aerobic and anaerobic bacterial processes were active in the reservoir. Calcites with high δ 13 C values (>+15‰) record cementation of fractures from dissolved inorganic carbon (DIC) generated during bacterial methanogenesis. Calcites with low δ 13 C values (<−32‰) are solely associated with outcrop samples and record methane oxidation during cement precipitation. Fracture-fill calcite with δ 13 C values between −10 and −30‰ can be attributed to variable organic matter oxidation pathways, methane oxidation, and carbonate rock buffering. Identification of 13 C-rich calcite provides unambiguous evidence of biogenic methane generation and may be used to identify gas deposits in other sedimentary basins. It is likely that repeated glacial advances and retreats exposed the Antrim Shale at the basin margin, enhanced meteoric recharge into the shallow part of the fractured reservoir, and initiated multiple episodes of bacterial methanogenesis and methanotrophic activity that were recorded in fracture-fill cements. The δ 18 O values in both formation waters and calcite cements increase with depth in the basin (−12 to −4‰ SMOW, and +21 to +27‰ PDB, respectively). Most fracture-fill cements from outcrop samples have δ 13 C values between −41 and −15‰ PDB. In contrast, most cement in cores have δ 13 C values between +15 and +34‰ PDB. Radiocarbon and 230 Th dating of fracture-fill calcite indicates that the calcite formed between 33 and 390 ka, well within the Pleistocene Epoch.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75720/1/j.1468-8123.2002.00036.x.pd
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Preventing Indoor Environment-Related Symptom Complaints in Office Buildings
The goal of this project was to develop, based on the experience of those who investigate health complaints in buildings, practical strategies for preventing building-related symptoms in office buildings, suitable for use by those who own, lease, or manage office space
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Causes and prevention of symptom complaints in office buildings: Distilling the experience of indoor environmental quality investigators
The goal of this project was to develop empirically based recommendations for practical strategies, suitable for use by those who own, lease, or manage office space, to prevent building-related symptoms in office buildings. Ideas from six experienced building investigators were gathered and prioritized in a multi-day workshop. The top ranked problems identified were, in priority order: excessive building moisture, inadequate outdoor air, dust on indoor surfaces, indoor gases and odors, inadequate thermal control, and inadequate attention by management to indoor environments. The highest priority strategies recommended for preventing building-related symptoms were: managing water at building exteriors, operating ventilation systems per design intent, providing at least minimum ventilation rates, and maintaining indoor temperatures at 72 F {+-} 2{sup o}. Findings in the scientific literature were generally consistent with these recommendations. IEQ investigators showed considerable agreement on the most important causes of symptom complaints in office buildings and the key methods for preventing these problems. Despite the range of climates in which they worked, the investigators agreed that the highest priority prevention strategy was managing water at building exteriors. These recommendations, generally consistent with available research findings, provide useful practical guidelines for those who own, manage or maintain office buildings. The empirical knowledge of practitioners offers more guidance here for choosing health-protective strategies than current science, although efficacy of these empirically based strategies generally has not been confirmed