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At least 199 records · Page 11Linked to original sources
USGS2016

Hydrogeochemistry and coal-associated bacterial populations from a methanogenic coal bed

Biogenic coalbed methane (CBM), a microbially-generated source of natural gas trapped within coal beds, is an important energy resource in many countries. Specific bacterial populations and enzymes involved in coal degradation, the potential rate-limiting step of CBM formation, are relatively unknown. The U.S. Geological Survey (USGS) has established a field site, (Birney test site), in an undeveloped area of the Powder River Basin (PRB), with four wells completed in the Flowers-Goodale coal bed, one in the overlying sandstone formation, and four in overlying and underlying coal beds (Knoblach, Nance, and Terret). The nine wells were positioned to characterize the hydraulic conductivity of the Flowers-Goodale coal bed and were selectively cored to investigate the hydrogeochemistry and microbiology associated with CBM production at the Birney test site. Aquifer-test results indicated the Flowers-Goodale coal bed, in a zone from about 112 to 120 m below land surface at the test site, had very low hydraulic conductivity (0.005 m/d) compared to other PRB coal beds examined. Consistent with microbial methanogenesis, groundwater in the coal bed and overlying sandstone contain dissolved methane (46 mg/L average) with low δ 13 C values (−67‰ average), high alkalinity values (22 meq/kg average), relatively positive δ 13 C-DIC values (4‰ average), and no detectable higher chain hydrocarbons, NO 3 − , or SO 4 2− . Bioassay methane production was greatest at the upper interface of the Flowers-Goodale coal bed near the overlying sandstone. Pyrotag analysis identified Aeribacillus as a dominant in situ bacterial community member in the coal near the sandstone and statistical analysis indicated Actinobacteria predominated coal core samples compared to claystone or sandstone cores. These bacteria, which previously have been correlated with hydrocarbon-containing environments such as oil reservoirs, have demonstrated the ability to produce biosurfactants to break down hydrocarbons. Identifying microorganisms involved in coal degradation and the hydrogeochemical conditions that promote their activity is crucial to understanding and improving in situ CBM production.

Montana, Wyoming↗
USGS2021

A review of spatially resolved techniques and applications of organic petrography in shale petroleum systems

This review examines new techniques and applications of organic petrography in source-rock reservoir petroleum systems that have occurred along with development of the global ‘shale revolution’ in energy resources. The review is limited to techniques and instrumentation that provide spatially resolved information, typically at or below microscales, for dispersed organic matter occurring in situ in samples of shale and mudrock. A brief summary of ion beam sample preparation is followed by discussion of the most common analytical techniques and applications. Advantages and limitations of each technique, including requisite sample preparation, types of information generated [e.g., molecular or elemental (isotopic) abundance], sensitivity, and resolution are discussed. In a few cases, techniques not yet applied to organic petrology of shale or mudrock are described (e.g., X-ray photoelectron spectroscopy imaging), in anticipation of near-term future application. The most common in situ techniques applied for characterization of organic matter in shale and mudrock include optical (including fluorescence) and electron microscopies, Raman, fluorescence, and infrared spectroscopies, and surficial measurements via force microscopy. Techniques that show growing application to organic petrography of shale include tip-enhanced photothermal infrared spectroscopy, mass spectrometry imaging, and synchrotron-based spectroscopies, among others. It is anticipated that the future of dispersed organic matter petrography will hold continued development of integrated instrument techniques (e.g., simultaneous or sequential correlative microscopies and/or spectroscopies of the same location), increased instrumental resolution, increased use of multiscale and multimodal organic petrography investigations, and three-dimensional imaging and chemical speciation mapping applications via multiple analytical approaches.

International Journal of Coal Geology↗
USGS2022

Relating systematic compositional variability to the textural occurrence of solid bitumen in shales

This study presents Raman spectroscopic data paired with scanning electron microscopy (SEM) images to assess solid bitumen composition as a function of solid bitumen texture and association with minerals. A series of hydrous pyrolysis experiments (1–103 days, 300–370 °C) using a low maturity (0.25% solid bitumen reflectance, BR o ), high total organic carbon [(TOC), 14.0 wt%] New Albany Shale sample as the starting material yielded pyrolysis residues designed to evaluate the evolution of solid bitumen aromaticity with increasing temperature and heating duration. Solid bitumen was analyzed by Raman spectroscopy wherein point data were collected from accumulations that ranged in size and degree of association with the mineral matrix. Raman spectroscopy results show that with increasing temperature and experimental duration, solid bitumen aromaticity increases and compositional variability decreases. With regards to texture and composition, coarser-grained solid bitumen (>1.3 μm from nearest mineral grain) has consistently higher, but less variable aromaticity than thinner, wispy solid bitumen which is more intimately associated with the mineral matrix. Collocated scanning electron microscope images were used to provide qualitative assessments of porosity hosted by the organic matter. These paired data sets suggest that solid bitumen porosity development and molecular composition are linked, and these parameters are related to the textural relationships of the organic matter within the whole rock. These results are discussed with perspective towards understanding how rock fabric and texture can influence organic matter evolution during thermal maturation of organic-rich marine shales and inform our broader understanding of these important energy resources.

International Journal of Coal Geology↗
USGS2011

A feasibility study of geological CO2 sequestration in the Ordos Basin, China

The Shaanxi Province/Wyoming CCS Partnership (supported by DOE NETL) aims to store commercial quantities of CO2 safely and permanently in the Ordovician Majiagou Formation in the northern Ordos Basin, Shaanxi Province, China. This objective is imperative because at present, six coal-to-liquid facilities in Shaanxi Province are capturing and venting significant quantities of CO2. The Wyoming State Geological Survey and the Shaanxi Provincial Institute of Energy Resource and Chemical Engineering conducted a feasibility study to determine the potential for geological CO2 sequestration in the northern Ordos Basin near Yulin. The Shaanbei Slope of the Ordos Basin is a huge monoclinal structure with a high-priority sequestration reservoir (Majiagou Formation) that lies beneath a 2,000+ meter-thick sequence of Mesozoic rocks containing a multitude of lowpermeability lithologies. The targeted Ordovician Majiagou Formation in the location of interest is more than 700 meters thick. The carbonate reservoir is located at depths where pressures and temperatures are well above the supercritical point of CO2. The targeted reservoir contains high-salinity brines (20,000-50,000 ppm) that have little or no economic value. The targeted reservoir is continuous as inferred from well logs, and cores show that porosity ranges from 1 to 15% with average measured porosity of 8%, and that permeability ranges from 1-35 md. This paper focuses on calculations that will help evaluate the capacity estimates through the use of high-resolution multiphase numerical simulation models, as well as a more simple volumetric approach. The preliminary simulation results show that the Ordovician Majiagou Formation in the Ordos Basin has excellent potential for geological CO2 sequestration and could store the CO2 currently emitted by coal-to-liquid facilities in Shaanxi Province for hundreds of years (i.e., 9 Mt/year CO2; 450 Mt over a 50-year period at one injection site). ?? 2011 Published by Elsevier Ltd.

Conference Paper↗
USGS2016

Multireaction equilibrium geothermometry: A sensitivity analysis using data from the Lower Geyser Basin, Yellowstone National Park, USA

A multireaction chemical equilibria geothermometry (MEG) model applicable to high-temperature geothermal systems has been developed over the past three decades. Given sufficient data, this model provides more constraint on calculated reservoir temperatures than classical chemical geothermometers that are based on either the concentration of silica (SiO 2 ), or the ratios of cation concentrations. A set of 23 chemical analyses from Ojo Caliente Spring and 22 analyses from other thermal features in the Lower Geyser Basin of Yellowstone National Park are used to examine the sensitivity of calculated reservoir temperatures using the GeoT MEG code (Spycher et al. 2013, 2014) to quantify the effects of solute concentrations, degassing, and mineral assemblages on calculated reservoir temperatures. Results of our analysis demonstrate that the MEG model can resolve reservoir temperatures within approximately ±15°C, and that natural variation in fluid compositions represents a greater source of variance in calculated reservoir temperatures than variations caused by analytical uncertainty (assuming ~5% for major elements). The analysis also suggests that MEG calculations are particularly sensitive to variations in silica concentration, the concentrations of the redox species Fe(II) and H 2 S, and that the parameters defining steam separation and CO 2 degassing from the liquid may be adequately determined by numerical optimization. Results from this study can provide guidance for future applications of MEG models, and thus provide more reliable information on geothermal energy resources during exploration.

Idaho, Montana, Wyoming↗
USGS2014

Geologic implications of gas hydrates in the offshore of India: results of the National Gas Hydrate Program Expedition 01

The Indian National Gas Hydrate Program Expedition 01 (NGHP-01) is designed to study the occurrence of gas hydrate along the passive continental margin of the Indian Peninsula and in the Andaman convergent margin, with special emphasis on understanding the geologic and geochemical controls on the occurrence of gas hydrate in these two diverse settings. The NGHP-01 expedition established the presence of gas hydrates in the Krishna-Godavari and Mahanadi Basins, and the Andaman Sea. The expedition discovered in the Krishna-Godavari Basin one of the thickest gas hydrate accumulations ever documented, in the Andaman Sea one of the thickest and deepest gas hydrate stability zones in the world, and established the existence of a fully developed gas hydrate petroleum system in all three basins. The primary goal of NGHP-01 was to conduct scientific ocean drilling/coring, logging, and analytical activities to assess the geologic occurrence, regional context, and characteristics of gas hydrate deposits along the continental margins of India. This was done in order to meet the long-term goal of exploiting gas hydrate as a potential energy resource in a cost effective and safe manner. During its 113.5-day voyage, the D/V JOIDES Resolution cored and/or drilled 39 holes at 21 sites (1 site in Kerala-Konkan, 15 sites in Krishna-Godavari, 4 sites in Mahanadi, and 1 site in the Andaman deep offshore area), penetrated more than 9250 m of sedimentary section, and recovered nearly 2850 m of core. Twelve holes were logged with logging-while-drilling (LWD) tools and an additional 13 holes were wireline logged. The science team utilized extensive on-board laboratory facilities to examine and prepare preliminary reports on the physical properties, geochemistry, and sedimentology of all the data collected prior to the end of the expedition. Samples were also analyzed in additional post-expedition shore-based studies conducted in leading laboratories around the world. One of the specific objectives of this expedition was to test gas hydrate formation models and constrain model parameters, especially those that account for the formation of concentrated gas hydrate accumulations. The necessary data for characterizing the occurrence of in situ gas hydrate, such as interstitial water chlorinities, core-derived gas chemistry, physical and sedimentological properties, thermal images of the recovered cores, and downhole measured logging data (LWD and/or conventional wireline log data), were obtained from most of the drill sites established during NGHP-01. Almost all of the drill sites yielded evidence for the occurrence of gas hydrate; however, the inferred in situ concentration of gas hydrate varied substantially from site to site. For the most part, the interpretation of downhole logging data, core thermal images, interstitial water analyses, and pressure core images from the sites drilled during NGHP-01 indicate that the occurrence of concentrated gas hydrate is mostly associated with the presence of fractures in the sediments, and in some limited cases, by coarser grained (mostly sand-rich) sediments.

Marine and Petroleum Geology↗
USGS2019

Compressibility and particle crushing of Krishna-Godavari Basin sediments from offshore India: Implications for gas production from deep-water gas hydrate deposits

Depressurizing a gas hydrate reservoir to extract methane induces high effective stresses that act to compress the reservoir. Predicting whether a gas hydrate reservoir is viable as an energy resource requires enhanced understanding of the reservoir’s compressibility and susceptibility to particle crushing in response to elevated effective stress because of their impact on the long-term permeability and geomechanical stability of the reservoir. This study investigates physical and geomechanical properties of natural sediments with and without tetrahydrofuran (THF) hydrate subjected to high effective stresses of up to 25 MPa. Experimental results show the stiffness of hydrate-free sediments is mainly governed by the stress state and history, while the stiffness of hydrate-bearing sediments reflects both the grain supporting nature of the interconnected hydrate phase and stress effects. The Poisson’s ratio of hydrate-bearing sediments at low stresses is dominated by the Poisson’s ratio of the interconnected pore-filling phases, and dominated at high stresses by elastic properties of both the skeleton and pore-filling phases. The stress-void ratio responses of hydrate-bearing sediments above the pre-consolidation stress yields a slightly convex-downward trend, suggesting compressibility is influenced by the stiffness of THF hydrate and sediment grains rather than only by void space reduction. The shape of the compression index (Cc) trend may be attributed to an increasing effective gas hydrate saturation as the total pore volume decreases under loading. The results also show that the presence of THF hydrate in sediments can mitigate particle crushing by suppressing particle rearrangement and supporting a portion of the load that would otherwise have to be carried by the sediment. Therefore, the loss of hydrate crystals during gas production may exacerbate sand crushing.

Marine and Petroleum Geology↗
USGS2019

Multi-measurement approach for establishing the base of gas hydrate occurrence in the Krishna-Godavari Basin for sites cored during Expedition NGHP-02 in the offshore of India

The 2015 National Gas Hydrate Program of India's second expedition, NGHP-02, acquired logging and coring datasets for constraining the base of the gas hydrate occurrence zone (deepest GH) and the theoretical base of gas hydrate stability zone (BGHS). These data are used here for two primary goals: to constrain the deepest occurrence of gas hydrate relative to predicted stability limits and the observed BSR, and to characterize the nature of the contact between gas hydrate-bearing sediment and the underlying gas hydrate-free sediment. A consensus depth for the deepest GH is derived for each NGHP-02 coring site from downhole indicators of gas hydrate occurrence obtained from well-log electrical resistivity and acoustic data, pressure core compressional wave velocity measurements, and conventional core measurements of anomalously low temperatures. To establish the theoretical BGHS, models of gas hydrate phase stability with depth are compared with downhole temperature profiles derived from: 1) assuming a constant geothermal gradient consistent with downhole temperature measurements, and 2) assuming constant heat flow using a geotherm through the downhole temperature measurements and incorporating thermal conductivity calculated from borehole logging data. Although the deepest NGHP-02 GH occurrences are controlled at several sites by a lithologic boundary, most sites have deepest GH occurrences within a single coarse-grained lithology. Cutoffs within a single coarse-grained lithology, which occur for the primary NGHP-02 Area B gas hydrate reservoir, will inhibit pore-pressure drawdowns used to extract methane from gas hydrate as an energy resource.

Bay of Bengal↗
USGS2019

Pressure core analysis of geomechanical and fluid flow properties of seals associated with gas hydrate-bearing reservoirs in the Krishna-Godavari Basin, offshore India

Physical properties of the sediment directly overlying a gas hydrate reservoir provide important controls on the effectiveness of depressurizing that reservoir to extract methane from gas hydrate as an energy resource. The permeability of overlying sediment determines if a gas hydrate reservoir’s upper contact will provide an effective seal that enables efficient reservoir depressurization. Compressibility, stiffness and strength indicate how overlying sediment will deform as the in situ stress changes during production, providing engineering data for well designs. Assessing these properties requires minimally-disturbed sediment. India’s National Gas Hydrates Program Expedition 2 (NGHP-02) provided an opportunity to study these seal sediment properties, reducing disturbance from gas exsolution and bubble growth by collecting a pressure core from the seal sediment just above the primary gas hydrate reservoir at Site NGHP-02-08 in Area C of the Krishna-Godavari Basin. The effective stress chamber (ESC) and the direct shear chamber (DSC) devices in the suite of Pressure Core Characterization Tools (PCCTs) were used to measure permeability, compressibility, stiffness and shear strength at the in situ vertical stress. Geotechnical properties of the predominantly fine-grained seal layer at in situ vertical stress are in typical clay sediment ranges, with low measured permeability (0.02 mD), high compressibility (Cc = 0.26 – 0.33) and low shear strength (404 kPa). Though pressure and temperature were maintained throughout the collection and measurement process to stabilize gas hydrate, the lack of effective stress in the pressure core storage chamber and the chamber pressurization with methane-free water caused core expansion and gas hydrate in a thin coarser-grained layer to dissolve. The PCCTs can reapply in situ stress with incremental loading steps during a consolidation test to account for sediment compaction. Gas hydrate dissolution can be limited by storing cores just above freezing temperatures, and by using solid spacers to reduce the storage chamber’s free volume.

Marine and Petroleum Geology↗
USGS2019

Pressure core based onshore laboratory analysis on mechanical properties of hydrate-bearing sediments recovered during India's National Gas Hydrate Program Expedition (NGHP) 02

A solid understanding of the mechanical properties of hydrate-bearing sediments is essential for the safe and economic development of methane hydrate as an energy resource. In 2015, 104 pressure cores were collected, recovering sediments from above and within concentrated hydrate reservoirs in the Krishna-Godavari Basin, as part of India’s National Gas Hydrate Program Expedition 02 (NGHP-02). These cores provided minimally-disturbed sediment, retained at pressures and temperatures within the hydrate stability field, for the first-ever systematic triaxial test of dozens of subsections of hydrate-bearing pressure core sediments. Post-cruise testing in Japan, evaluated multiple physical and hydro-mechanical properties. Consolidated drained and undrained triaxial compression tests, uniaxial (unconfined in effective stress) compression tests, multistage consolidation and compression tests, and alternating strain-rate compression tests were also performed. Triaxial compression test results showed an increase in the strength and stiffness, as well as the positive dilatancy, with increasing hydrate saturation, supporting previous research on laboratory-formed and natural hydrate-bearing sediments. However, some strength results in this study were low compared to prior analyses of hydrate-bearing sediments. This low strength was likely caused by the host sediment’s small particle size and loose packing, and the relatively slow applied compression strain rate. Results from uniaxial compression and multi-step compression tests confirmed that pore-space hydrates produce an apparent cohesion in hydrate-bearing sediment. More severe strength loss in sediments during the initial loading for multistage compression was also attributable to the presence of hydrates. The applicability of this multistage compression test for determining in situ properties was not confirmed, but results do provide bounds on the in situ values. Finally, from the variable strain-rate tests, it was revealed that strength in hydrate-bearing sediment has a large strain-rate dependence.

Marine and Petroleum Geology↗
USGS2019

Preface: Marine gas hydrate reservoir systems along the eastern continental margin of India: Results of the National Gas Hydrate Program Expedition 02

The 2015 India National Gas Hydrate Program (NGHP) Expedition 02 was conducted to obtain new information on the occurrence of gas hydrate systems and to advance the understanding of geologic controls on the formation of gas hydrate accumulations in the offshore of India. The ultimate goal of the NGHP effort is to assess the energy resource potential of marine gas hydrates in India. The Guest Editors for this special thematic issue of the Journal of Marine and Petroleum Geology (JMPG) have worked with more than 100 scientists and engineers to prepare the 45 individual reports included in this special issue to address the operational and technical contributions of the NGHP-02 Expedition. This thematic issue on natural gas hydrates in the offshore of India is built on the foundation of five previous JMPG thematic issues that focused on the scientific results of other marine gas hydrate expeditions. These foundational contributions include: (1) the “Scientific Results of the 2005 USDOE-Chevron JIP Drilling for Methane Hydrates Objectives in the Gulf of Mexico” (Volume 25, Issue 9, November 2008), (2) the “Resource and Hazard Implications of Gas Hydrates in the Northern Gulf of Mexico: Results of the 2009 Joint Industry Project Leg II Drilling Expedition” (Volume 34, Issue 1, June 2012), (3) the “Scientific Results of the Second Gas Hydrate Drilling Expedition in the Ulleung Basin (UBGH2), East Sea of Korea” (Volume 47, November 2013), (4) “Geologic Implications of Gas Hydrates in the Offshore of India: Results of the National Gas Hydrate Program Expedition 01” (Volume 58, Part A, December 2014), and (5) “Gas Hydrate Drilling in Eastern Nankai” (Volume 66, Part 2, September 2015). The NGHP-02 Expedition was conducted from 03-March- 2015 to 28-July- 2015 off the eastern coast of India. The first two months of the expedition were dedicated to establishing 25 new research sites that featured the drilling of a dedicated downhole logging hole at each site. The next three months of the NGHP-02 Expedition were dedicated to sediment coring and other downhole measurement operations at 10 of the sites established during the expedition’s first phase. The results of downhole logging, coring and formation pressure testing operations during NGHP-02 have confirmed the presence of large, highly concentrated gas hydrate accumulations in coarse-grained, sand-rich depositional systems throughout large portions of the Krishna-Godavari Basin. Post expedition research and reporting efforts included collaborative analysis of the unprecedented number of shipboard acquired data sets and core samples obtained during NGHP-02. The presentation of the scientific results of the NGHP-02 Expedition has culminated in the publication of the NGHP Expedition 02 Scientific Results Volume, which is represented by this Special Issue of the Journal of Marine and Petroleum Geology. This Special Issue features a series of four reports that summarize the operational and scientific results of NGHP-02 Expedition that are presented in the 41 technical reports included this Special Issue. The first summary report, “India National Gas Hydrate Program Expedition 02: Operational and Technical Summary,” focuses on reviewing the tools and operational procedures for the NGHP-02 Expedition that led to the acquisition of an unprecedented amount of high-quality downhole logging and core data from numerous pore-filling, fracture-filling, and sediment-displacement type gas hydrate occurrences. The summary report titled “India National Gas Hydrate Program Expedition 02 Summary of Scientific Results: Gas Hydrate Systems Along the Eastern Continental Margin of India” documents gas hydrate occurrences discovered during the NGHP-02 Expedition and examines geologic controls on the gas hydrate systems along the Eastern Continental Margin of India.

Journal of Marine and Petroleum Geology↗
USGS2024

Consumer isoscapes reveal heterogeneous food webs in deep-sea submarine canyons and adjacent slopes

The deep sea is the largest biome on earth, but one of the least studied despite its critical role in global carbon cycling and climate buffering. Deep-sea organisms largely rely on particulate organic matter from the surface ocean for energy – these organisms in turn play critical roles in energy transport, transformation, storage, and sequestration of carbon. Within the deep sea, submarine canyons are amongst the most complex and dynamic environments in our oceans, where varied morphology, powerful currents, and variable nutrient conditions influence the distribution of species and transport of organic material throughout the water column and the seafloor. Significant habitat heterogeneity provides ideal substrates for cold-water corals, making submarine canyons of interest to conservation and management. However, how these and other topographic features in the deep ocean influence energy flow and trophic pathways is poorly known. Thus, submarine canyons serve as model systems to track variability in organic material flux and consequential utilization and assimilation by the benthos. In this study, we used an extensive stable isotope dataset to examine food-web structure in Baltimore and Norfolk submarine canyons and compared them to their adjacent slopes located along the U.S. Atlantic margin. Linear models were used to construct geospatially-explicit consumer isoscapes that predicted variation in carbon and nitrogen isotopes across the canyon-slope seascape, providing a predictive map from which to test hypotheses on the distribution and flow of energy resources, relevant to understanding whole community function. Communities were composed of isotopically diverse feeding groups with photosynthetically-derived organic carbon providing the basal food resource. Canyon communities were distinct from the slope, with canyon consumers significantly 13 C-depleted, indicating a greater supply and/or utilization of fresh organic matter compared to the slope. Isoscapes for benthic and suspension feeders were distinct, possibly due to the consumption of different quality organic matter sources (fresh = suspension feeders, old = benthic feeders), each with distinct isotope composition. To our knowledge, our modeled isoscapes represent the first spatially extensive isotopic maps of deep-sea consumers, providing insights into regional-scale variation in stable carbon and nitrogen isotopes for different consumer groups. They provide a baseline for tracking climate-change induced fluctuations in the quality and availability of surface primary production and the consequential impact to benthic communities, which play critical roles in carbon cycling in our world’s oceans.

Progress in Oceanography↗
USGS1997

Coal quality trends and distribution of potentially hazardous trace elements in eastern Kentucky coals

Coal in the Eastern Kentucky coalfield has been, and continues to be, a valuable energy resource, especially for the electric utility industry. However, Federal mandates in Titles III and IV of the Clean Air Act Amendments of 1990 have placed increasingly stringent demands on the type and grade of coal that can be burnt in an environmentally acceptable manner. Therefore, a greater understanding of the spatial and temporal distribution of thickness and quality parameters, and the geologic factors that control their distribution, is critical if the Eastern Kentucky coalfield is to continue to be a major producer of high-quality coal. Information from the Kentucky Geological Survey's Coal Resource Information System database is used in this paper to document the geographic and stratigraphic distribution of important factors such as bed thickness, calorific value, ash yield and total sulfur content. The distribution of 15 elements that naturally occur in trace amounts in Kentucky coal is also discussed, as these elements may require monitoring with passage of Title III of the Clean Air Act Amendments of 1990.

Kentucky↗
USGS1996

Petrography, geochemistry and palynology of the Stockton coal bed (Middle Pennsylvanian), Martin County, Kentucky

The Middle Pennsylvanian (Westphalian D) Stockton (also known as the Broas) coal bed of the Breathitt Formation is an important energy resource in Kentucky. Petrographic, geochemical and palynologic studies were undertaken from mine, core and highway exposures in Martin and northern Pike counies, Kentucky, in order to determine the influence of the Stockton depositional ecosystem on those parameters. Vitrinite-rich Stockton lithotypes are dominated by Lycospora . Dull lithotypes, including both high- and low-ash yield durains, generally have abundant Densosporites , suggesting that the parent plant inhabited a fairly wide range of environments. Lithologies having tree ferns as an important component also have high fusinite + semifusinite and a low telinite/gelocollinite ratio. The aerial root bundles of the tree ferns were susceptible to oxidation and, for tissue not oxidized to inertinite, to preservation as gelocollinite. In the initial stages of formation, the Stockton mire was discontinuous and had a rather restricted floral assemblage. The presence of durains higher in the Stockton section, particularly the low-ash yield durains having petrographic indicators of degradation, suggests that portions of the mire developed as a domed peat. The termination of the mire as a high-sulfur, arboreous lycopod-domimated mire is consistent with the return to more planar mire development.

International Journal of Coal Geology↗
USGS2014

Methane hydrates in nature - Current knowledge and challenges

Recognizing the importance of methane hydrate research and the need for a coordinated effort, the United States Congress enacted the Methane Hydrate Research and Development Act of 2000. At the same time, the Ministry of International Trade and Industry in Japan launched a research program to develop plans for a methane hydrate exploratory drilling project in the Nankai Trough. India, China, the Republic of Korea, and other nations also have established large methane hydrate research and development programs. Government-funded scientific research drilling expeditions and production test studies have provided a wealth of information on the occurrence of methane hydrates in nature. Numerous studies have shown that the amount of gas stored as methane hydrates in the world may exceed the volume of known organic carbon sources. However, methane hydrates represent both a scientific and technical challenge, and much remains to be learned about their characteristics and occurrence in nature. Methane hydrate research in recent years has mostly focused on: (1) documenting the geologic parameters that control the occurrence and stability of methane hydrates in nature, (2) assessing the volume of natural gas stored within various methane hydrate accumulations, (3) analyzing the production response and characteristics of methane hydrates, (4) identifying and predicting natural and induced environmental and climate impacts of natural methane hydrates, (5) analyzing the methane hydrate role as a geohazard, (6) establishing the means to detect and characterize methane hydrate accumulations using geologic and geophysical data, and (7) establishing the thermodynamic phase equilibrium properties of methane hydrates as a function of temperature, pressure, and gas composition. The U.S. Department of Energy (DOE) and the Consortium for Ocean Leadership (COL) combined their efforts in 2012 to assess the contributions that scientific drilling has made and could continue to make to advance our understanding of methane hydrates in nature. COL assembled a Methane Hydrate Project Science Team with members from academia, industry, and government. This Science Team worked with COL and DOE to develop and host the Methane Hydrate Community Workshop, which surveyed a substantial cross section of the methane hydrate research community for input on the most important research developments in our understanding of methane hydrates in nature and their potential role as an energy resource, a geohazard, and/or as an agent of global climate change. Our understanding of how methane hydrates occur in nature is still growing and evolving, and it is known with certainty that field, laboratory, and modeling studies have contributed greatly to our understanding of hydrates in nature and will continue to be a critical source of the information needed to advance our understanding of methane hydrates.

Journal of Chemical and Engineering Data↗
USGS2012

Hydrate morphology: Physical properties of sands with patchy hydrate saturation

The physical properties of gas hydrate-bearing sediments depend on the volume fraction and spatial distribution of the hydrate phase. The host sediment grain size and the state of effective stress determine the hydrate morphology in sediments; this information can be used to significantly constrain estimates of the physical properties of hydrate-bearing sediments, including the coarse-grained sands subjected to high effective stress that are of interest as potential energy resources. Reported data and physical analyses suggest hydrate-bearing sands contain a heterogeneous, patchy hydrate distribution, whereby zones with 100% pore-space hydrate saturation are embedded in hydrate-free sand. Accounting for patchy rather than homogeneous hydrate distribution yields more tightly constrained estimates of physical properties in hydrate-bearing sands and captures observed physical-property dependencies on hydrate saturation. For example, numerical modeling results of sands with patchy saturation agree with experimental observation, showing a transition in stiffness starting near the series bound at low hydrate saturations but moving toward the parallel bound at high hydrate saturations. The hydrate-patch size itself impacts the physical properties of hydrate-bearing sediments; for example, at constant hydrate saturation, we find that conductivity (electrical, hydraulic and thermal) increases as the number of hydrate-saturated patches increases. This increase reflects the larger number of conductive flow paths that exist in specimens with many small hydrate-saturated patches in comparison to specimens in which a few large hydrate saturated patches can block flow over a significant cross-section of the specimen.

Journal of Geophysical Research B: Solid Earth↗
USGS2018

Impact of pore fluid chemistry on fine-grained sediment fabric and compressibility

Fines, defined here as grains or particles, less than 75 μm in diameter, exist nearly ubiquitously in natural sediment, even those classified as coarse. Macroscopic sediment properties, such as compressibility, which relates applied effective stress to the resulting sediment deformation, depend on the fabric of fines. Unlike coarse grains, fines have sizes and masses small enough to be more strongly influenced by electrical interparticle forces than by gravity. These electrical forces acting through pore fluids are influenced by pore fluid chemistry changes. Macroscopic property dependence on pore fluid chemistry must be accounted for in sediment studies involving subsurface flow and sediment stability analyses, as well as in engineered flow situations such as groundwater pollutant remediation, hydrocarbon migration, or other energy resource extraction applications. This study demonstrates how the liquid limit‐based electrical sensitivity index can be used to predict sediment compressibility changes due to pore fluid chemistry changes. Laboratory tests of electrical sensitivity, sedimentation, and compressibility illustrate mechanisms linking microscale and macroscale processes for selected pure, end‐member fines. A specific application considered here is methane extraction via depressurization of gas hydrate‐bearing sediment, which causes a dramatic pore water salinity drop concurrent with sediment being compressed by the imposed effective stress increase.

Journal of Geophysical Research↗
USGS2019

Introduction to special issue on gas hydrate in porous media: Linking laboratory and field‐scale phenomena

The proliferation of drilling expeditions focused on characterizing natural gas hydrate as a potential energy resource has spawned widespread interest in gas hydrate reservoir properties and associated porous media phenomena. Between 2017 and 2019, a Special Section of this journal compiled contributed papers elucidating interactions between gas hydrate and sediment based on laboratory, numerical modeling, and field studies. Motivated mostly by field observations in the northern Gulf of Mexico and offshore Japan, several papers focus on the mechanisms for gas hydrate formation and accumulation, particularly with vapor phase gas, not dissolved gas, as the precursor to hydrate. These studies rely on numerical modeling or laboratory experiments using sediment packs or benchtop micromodels. A second focus of the Special Section is the role of fines in inhibiting production of gas from methane hydrate, controlling the distribution of hydrate at a pore scale, and influencing the bulk behavior of seafloor sediments. Other papers fill knowledge gaps related to the physical properties of hydrate-bearing sediments and advance new approaches in coupled thermal-mechanical modeling of these sediments during hydrate dissociation. Finally, one study addresses the long-standing question about the fate of methane hydrate at the molecular level when CO2 is injected into natural reservoirs under hydrate-forming conditions.

Journal of Geophysical Research B: Solid Earth↗