Showing papers on "Silt published in 2020"

Study on the surface particle distribution characteristics of silt with different moisture content

Abstract: Soil structure and particle distribution determine the action form of water and the distribution and movement form of water in the soil, which may cause many engineering and environmental problems, so it is of great significance to study the distribution form of soil particles under different moisture content. Taking the silt as the research object, the surface micro features of soil samples with the same dry density and different moisture content were collected, and the binarization analysis and particle statistics were carried out to study the action mode between water and particles. The results show that (1) moisture content has a certain impact on the micro features. With the increase of moisture content, the pores between soil particles gradually decrease, and the fractal dimension of surface particles also decreases. (2) In the case of the difference of specific surface area, the smaller the particle size, the more obvious the response to water. For this silt sample, the particles with a size of 0.03~0.05 mm are relatively stable. With the increase of moisture content, small particles flocculate to form large particles under a series of forces. (3) When the moisture content was 8.92% and 13.78%, the soil features changed significantly, which may be the critical moisture contents affecting the structural quality of the sample. (4) Advantage orientation of silt particles is 90°~105°, which may cause the soil mechanics characteristics of anisotropy. (5) The interaction model between water and soil particles is as follows: dissolution, the change of stress on particles, and the change of electrical double layer on the surface of soil particles.

Soil microbial diversity and composition: Links to soil texture and associated properties

Abstract: Soil texture is an essential component of soil survey for estimating potentials and limitations of land use and management. It has been appreciated as an important predictor for numerous soil processes. However, its connections with the diversity and composition of the soil microbial community remain less understood. This work employed a marker gene high-throughput sequencing approach to determine soil texture-based patterns of bacterial and fungal distribution. Thirty-six intact soil cores were sampled from bermudagrass ecosystems across seven soil texture classes with sand fraction varying from 30.3 to 83.4% and clay fraction from 4.4 to 53.0%. These soil cores were arranged into three sets of equal numbers, and each set of 12 was subjected to three moisture regimes (dry spell, field moisture, and saturation-field capacity), respectively, for 15 days. Soil cores were further stratified into top and bottom sections, leading to a total of 72 samples with varying soil physical and chemical properties. Our data revealed that fungal alpha diversity was more strongly related to soil texture than bacterial alpha diversity, with fungal species richness and Shannon diversity being positively correlated with the sand fraction. Soil texture was the second most important factor after soil pH in shaping the soil microbial community. Relative abundances of some fungi (Basidiomycota and Eurotiomycetes) and filamentous bacteria (Actinobacteria, Chloroflexi) significantly increased with silt and/or clay content. The genetic potential for the degradation of organic compounds also appeared to be higher in finer textured soils than the coarse-textured soils. By identifying sand, silt or clay-preferred microbial taxa and characterizing mineral particle-dependent genetic potential of organic carbon degradation and nitrogen cycling, this work highlighted the significance of soil texture and texture-associated pores, and resource locality, in regulating microbial diversity and community composition.

Formation of Soil Aggregates and Accumulation of Soil Organic Matter

Abstract: Soil structure is the arrangement of particles in soil and the particles of sand, silt, and clay, bound together into aggregates of various sizes by organic and inorganic materials. The structural stability is the ability of the aggregates and pores to remain intact when subjected to stress, e.g. when aggregates are wetted quickly. In soils stabilized by organic matter, these stages of aggregation, or aggregate hierarchy, probably develop over many years, during the growth of roots, especially roots of grasses. Aggregation has been studied in at least two ways: the formation and stabilization of aggregates in suspensions of pure clay, and the separation of aggregates from soil disrupted by different amounts of energy. Microaggregates, which can be further divided into different sizes, are held together by different organic and inorganic materials. Microaggregates less than 2 im diameter have been studied in suspensions of pure clay, or have been isolated from soils subjected to ultrasound.

Variations of the temperatures and volumetric unfrozen water contents of fine-grained soils during a freezing–thawing process

Abstract: In this study, the variations of the temperatures and volumetric unfrozen water contents for two fine-grained soils (i.e., silty clay and silt) with high degrees of saturation during a freezing–thawing process were experimentally studied. Experimental results show that for the two soils, the supercooling phenomenon only happens in the early stage of freezing process, and the supercooling temperature and its duration of the silty clay are both larger than those of the silt under similar temperatures; furthermore, the hysteresis effect of volumetric unfrozen water content exists during the whole freezing–thawing process, and the maximum hysteresis levels both occur at the soil freezing points; however, the maximum value of the hysteresis level of the silt is larger than that of the silty clay.

Soil organic matter and silt contents determine soil particle surface electrochemical properties across a long-term natural restoration grassland

Abstract: Vegetation restoration is an effective way to rebuild degraded ecosystems and restore soil function. Soil surface electrochemical properties, including specific surface area, cation exchange capacity, surface charge density, surface electric field strength, and surface potential, are often used as indicators to evaluate agricultural soil quality and fertility. However, little attention has been payed to the effect of natural revegetation on soil surface electrochemical properties. In this work, we selected a grassland restoration chronosequence (slope cropland, 0 years; natural grasslands restored for 3, 8, 22 and 24 years, i.e. NR3, NR8, NR22 and NR24, respectively) to investigate the changes of soil surface electrochemical properties along with vegetative restoration. Our results showed that surface charge density and surface potential for restored grassland ranged from 0.16 to 0.20 C m−2 and from −94 to −109 mV, with an average of 0.18 C m−2 and −101 mV, respectively. The value of surface electric field strength could reach to the order of magnitude of −107 V m−1 and showed a decreasing trend with increasing period of natural vegetation recovery. Cation exchange capacity and specific surface area significantly increased with the extension of natural restoration period except for NR3 (P

Prediction of soil texture classes through different wavelength regions of reflectance spectroscopy at various soil depths

Abstract: The demand for quality and low-cost soil information is growing due to the demands of land use planning and precision agriculture. Soil texture is one of the key soil properties, as it determines other vital soil characteristics such as soil structure, water and thermal regime, diversity of living organisms, plant growth, as well as the soil quality in general. It is usually not constant over an area, varying in space and with soil depth. Routine soil texture analysis is, however, time consuming and expensive. Because of this, the success of proximal soil sensing techniques in estimate soil properties using the VIS-NIR-SWIR and MIR regions is increasing. Advantages of soil spectroscopy include time efficiency, economic convenience, non-destructive application and freeing of chemical agents involved. Therefore, the objectives of this study were: (a) to explore the potential of clay, sand and silt prediction using reflectance spectroscopy; (b) assess the performance of predictive models in different spectral regions, i.e. VIS-NIR-SWIR and MIR; (c) assess the effect of different soil depths on predictive models; and finally (d) explain the differences in prediction accuracy in the means of the input data structure. Soil samples were collected at three depths (0–20, 20–40 and 40–60 cm) at 70 sampling sites over a study area located in the State of Rio Grande do Sul (Brazil). The content of soil texture was determined by Pipette method, and soil spectra were obtained with FieldSpec Pro (VIS-NIR-SWIR) and by Alpha Sample Compartment RT (MIR). Cubist regression algorithm was applied to train predictive models in three separate modeling modes differing in spectral region: (i) VIS-NIR-SWIR, (ii) MIR and (iii) VIS-NIR-SWIR plus MIR. The results showed that the combination of all three soil depths led to a more accurate prediction of soil texture compared to subdivided soil depths. This was explained by variability of the data, which was larger for the total dataset than for the depth-specific data. Consequently, we suggested that no precise comparison between different studies can be made without a proper description of the input data. For all-depths models, the MIR calibration obtained the best accuracy, which was explained due to more information comprised in the MIR region against the VIS-NIR-SWIR. The bands that were more important in predicting soil texture in MIR are related to mineralogy, specifically to kaolinite. This study demonstrated that the MIR spectroscopy technique is capable to complement the standard soil particle size analysis, specially where a large number of soil samples need to be treated in a short period of time.

Mud in rivers transported as flocculated and suspended bed material

Abstract: Riverine transport of silt and clay particles—or mud—builds continental landscapes and dominates the fluxes of sediment and organic carbon across Earth’s surface Compared with fluxes of sand-sized grains, mud fluxes are difficult to predict Yet, understanding the fate of muddy river sediment is fundamental to the global carbon cycle, coastal landscape resilience to sea-level rise, river restoration and river–floodplain morphodynamics on Earth and Mars Mechanistic theories exist for suspended sand transport, but mud in rivers is often thought to constitute washload—sediment with settling velocities so slow that it does not interact with the bed, such that it depends only on upstream supply and is impossible to predict from local hydraulics To test this hypothesis, we compiled sediment concentration profiles from the literature from eight rivers and used an inversion technique to determine settling rates of suspended mud We found that mud in rivers is largely flocculated in aggregates that have near-constant settling velocities, independent of grain size, of approximately 034 mm s−1, which is 100-fold faster than rates for individual particles Our findings indicate that flocculated mud is part of suspended bed-material load, not washload, and thus can be physically described by bed-material entrainment theory Fast settling rates of suspended silt and clay particles suggest that mud in rivers is largely flocculated and part of suspended bed-material load

Undrained anisotropy and cyclic resistance of saturated silt subjected to various patterns of principal stress rotation

Abstract: Although the undrained anisotropic behaviour of sand has been extensively studied, little is known about undrained anisotropy and liquefaction susceptibility of silt soil. This paper presents a sys...

Influence of Floods, Tides, and Vegetation on Sediment Retention in Wax Lake Delta, Louisiana, USA

Abstract: Sediment is the most valuable natural resource for deltaic environments, and to build new land sediment must be retained in the delta instead of being transported offshore. Despite this, we do not know what controls sediment retention within a delta. Here we use a calibrated numerical model of Wax Lake Delta, LA, USA to analyze sediment retention for different flood-wave magnitudes, tidal amplitudes, and vegetation extents. We only model transport of silt since it comprises most of the incoming sediment load. Our results show that as flood size increases, areally-averaged vertical accretion increases from 0.33 cm to 2 cm, but this comes at a cost because delta-scale sediment retention decreases from 72% to 34%. On a fully vegetated delta, we show that the buffering effect of vegetation reduces island-directed sediment flux by 14 to 22% because sediment takes the less resistive path in the channel. When sediment gets onto the islands, the trapping effect of vegetation increases retention by ~10%. But, this is not enough to offset the buffering effect, and vegetation decreases vertical accretion and sediment retention across the delta reduces by up to ~0.5 cm and 6%, respectively. We suggest that vegetation will increase sedimentation only when trapping compensates for buffering. Finally, greater tidal amplitude at higher discharges enhances vertical accretion by ~0.5 cm per flood as compared to a minimum tidal amplitude condition. These results inform how coastal deltaic systems grow and suggest how to operate sediment diversions more efficiently in deltas with reduced sediment supply.

The Impact of No-Till, Conservation, and Conventional Tillage Systems on Erosion and Soil Properties in Lower Austria

Abstract: The effect of long-term (about 25 years) use of different farming practices on a set of soil properties and development of erosion in Lower Austria has been studied. Three tillage systems—zero, or no-till (NT); minimum, or conservation (CS); and conventional (CV)—are compared. The comparison demonstrates that the properties of Typic Argiudols (Luvic Phaeozems), formed on steep (13.2%) slopes, change depending on both the tillage type and the position on the slope. Unlike the CV tillage, the soil-saving technologies provide higher contents of nutrients, silt, and clay, as well as better water permeability and water stability of soil aggregates. Despite an almost doubled amount of lumpy fractions (>10 mm), the soil aggregate states after NT and CS tillage are estimated as “excellent”. Independently of the tillage system, all agrochemical, electrophysical, and hydrophysical parameters (except for pH and bulk density) increase downward the slope, which is associated with erosion, namely, the washout of suspended sediments by water flows. The Corg content in the soil tightly correlates with the water stability of soil aggregates (r = 0.91), the concentration of soluble humic substances and fine solids (SAK; r = 0.76), and electroconductivity (r = 0.75). An anti-erosion efficiency of tillage practice increases in the series CV–CS–NT. The NT or CS systems are recommended for the erosion-prone slopes of Alpine foothills.

Variations in soil chemical and physical properties explain basin-wide Amazon forest soil carbon concentrations

Abstract: . We investigate the edaphic, mineralogical and climatic controls of soil organic carbon (SOC) concentration utilising data from 147 primary forest soils (0–30 cm depth) sampled in eight different countries across the Amazon Basin. Sampled across 14 different World Reference Base soil groups, our data suggest that stabilisation mechanism varies with pedogenetic level. Specifically, although SOC concentrations in Ferralsols and Acrisols were best explained by simple variations in clay content – this presumably being due to their relatively uniform kaolinitic mineralogy – this was not the case for less weathered soils such as Alisols, Cambisols and Plinthosols for which interactions between Al species, soil pH and litter quality are argued to be much more important. Although for more strongly weathered soils the majority of SOC is located within the aggregate fraction, for the less weathered soils most of the SOC is located within the silt and clay fractions. It thus seems that for highly weathered soils SOC storage is mostly influenced by surface area variations arising from clay content, with physical protection inside aggregates rendering an additional level of protection against decomposition. On the other hand, most of the SOC in less weathered soils is associated with the precipitation of aluminium–carbon complexes within the fine soil fraction, with this mechanism enhanced by the presence of high levels of aromatic, carboxyl-rich organic matter compounds. Also examined as part of this study were a relatively small number of arenic soils (viz. Arenosols and Podzols) for which there was a small but significant influence of clay and silt content variations on SOM storage, with fractionation studies showing that particulate organic matter may account for up to 0.60 of arenic soil SOC. In contrast to what were in all cases strong influences of soil and/or litter quality properties, after accounting for these effects neither wood productivity, above-ground biomass nor precipitation/temperature variations were found to exert any significant influence on SOC stocks. These results have important implications for our understanding of how Amazon forest soils are likely to respond to ongoing and future climate changes.

Multiple AI model integration strategy—Application to saturated hydraulic conductivity prediction from easily available soil properties

Abstract: A multiple model integration scheme driven by artificial neural network (ANN) (MM-ANN) was developed and tested to improve the prediction accuracy of soil hydraulic conductivity (Ks) in Tabriz plain, an arid region of Iran. The soil parameters such as silt, clay, organic matter (OM), bulk density (BD), pH and electrical conductivity (EC) were used as model inputs to predict soil Ks. Standalone models including multivariate adaptive regression splines (MARS), M5 model tree (M5Tree), support vector machine (SVM) and extreme learning machine (ELM) were also implemented for comparative evaluation with MM-ANN model predictions. Based on several performance indicators such as Nash Sutcliffe Efficiency (NSE), results showed that the calibrated MM-ANN model involving the predictions of MARS, M5Tree, SVM and ELM models by considering all the soil parameters used in this study as inputs provided superior soil Ks estimates. The proposed hybrid model (MM-ANN) emerged as a reliable intelligence model for the assessment of soil hydraulic conductivity with an NSE = 0.939 & 0.917 during training and testing, respectively. Accurate prediction of field-scale soil hydraulic conductivity is crucial from the view point of agricultural sustainability and management prospects.

Transpiration Reduction in Maize (Zea mays L) in Response to Soil Drying

Abstract: The relationship between leaf water potential, soil water potential, and transpiration depends on soil and plant hydraulics and stomata regulation. Recent concepts of stomatal response to soil drying relate stomatal regulation to plant hydraulics, neglecting the loss of soil hydraulic conductance around the roots. Our objective was to measure the effect of soil drying on the soil-plant hydraulic conductance of maize and to test whether stomatal regulation avoids a loss of soil-plant hydraulic conductance in drying soils. We combined a root pressure chamber, in which the soil-root system is pressurized to maintain the leaf xylem at atmospheric pressure, with sap flow sensors to measure transpiration rate. The method provides accurate and high temporal resolution measurements of the relationship between transpiration rate and xylem leaf water potential. A simple soil-plant hydraulic model describing the flow of water across the soil, root, and xylem was used to simulate the relationship between leaf water potential and transpiration rate. The experiments were carried out with 5-week-old maize grown in cylinders of 9 cm diameter and 30 cm height filled with silty soil. The measurements were performed at four different soil water contents (WC). The results showed that the relationship between transpiration and leaf water potential was linear in wet soils, but as the soil dried, the xylem tension increased, and nonlinearities were observed at high transpiration rates. Nonlinearity in the relationship between transpiration and leaf water potential indicated a decrease in the soil-plant hydraulic conductance, which was explained by the loss of hydraulic conductivity around the roots. The hydraulic model well reproduced the observed leaf water potential. Parallel experiments performed with plants not being pressurized showed that plants closed stomata when the soil-plant hydraulic conductance decreased, maintaining the linearity between leaf water potential and transpiration rate. We conclude that stomata closure during soil drying is caused by the loss of soil hydraulic conductivity in a predictable way.

Gravimetric Separation of Heavy Minerals in Sediments and Rocks

Abstract: The potential of heavy minerals studies in provenance analysis can be enhanced conspicuously by using a state-of-the-art protocol for sample preparation in the laboratory, which represents the first fundamental step of any geological research. The classical method of gravimetric separation is based on the properties of detrital minerals, principally their grain size and density, and its efficiency depends on the procedure followed and on the technical skills of the operator. Heavy-mineral studies in the past have been traditionally focused on the sand fraction, generally choosing a narrow grain-size window for analysis, an approach that is bound to introduce a serious bias by neglecting a large, and sometimes very large, part of the heavy-mineral spectrum present in the sample. In order to minimize bias, not only the largest possible size range in each sample should be considered, but also, the same quantitative analytical methods should be applied to the largest possible grain-size range occurring in the sediment system down to 5 μm or less, thus including suspended load in rivers, loess deposits, and shallow to deep-marine muds. Wherever the bulk sample cannot be used for practical reasons, we need to routinely analyze the medium silt to medium sand range (15–500 μm) for sand and the fine silt to sand range (5–63 or > 63 μm) for silt. This article is conceived as a practical handbook dedicated specifically to Master and PhD students at the beginning of their heavy-mineral apprenticeship, as to more expert operators from the industry and academy to help improving the quality of heavy-mineral separation for any possible field of application.

Effects of Soil and Water Conservation Measures on Soil Quality Indicators: The Case of Geshy Subcatchment, Gojeb River Catchment, Ethiopia

Abstract: Land degradation is a global negative environmental process that causes the decline in the productivity of land resources’ capacity to perform their functions. Though soil and water conservation (SWC) technologies have been adopted in Geshy subcatchment, their effects on soil quality were limitedly studied. The study was conducted to evaluate the effects SWC measures on soil quality indicators in Geshy subcatchment, Gojeb River Catchment, Ethiopia. A total of 54 soil samples (two treatments–farmlands with and without SWC measures three slope classes three terrace positions three replications) were collected at a depth of 20 cm. Statistical differences in soil quality indicators were analyzed using multivariate analysis of variance (ANOVA) following the general linear model procedure of SPSS Version 20.0 for Windows. Means that exhibited significant differences were compared using Tukey’s honest significance difference at 5% probability level. The studied soils are characterized by low bulk density, slightly acidic with clay and clay loam texture. The results revealed that farmlands with SWC measures had significantly improved soil physical (silt and clay fractions, and volumetric soil water content (VSWC)) and chemical (pH, SOC, TN, C : N ratio, and Av. phosphorus) quality indicators as compared with farmlands without SWC measures. The significantly higher VSWC, clay, SOC, TN, C : N ratio, and Av. P at the bottom slope classes and terrace positions could be attributed to the erosion reduction and deposition effects of SWC measures. Generally, the status of the studied soils is low in SOC contents, TN, C : N ratio, and Av. P (deficient). Thus, integral use of both physical and biological SWC options and agronomic interventions would have paramount importance in improving soil quality for better agricultural production and productivity.

Protocol for sand control screen design of production wells for clayey silt hydrate reservoirs: A case study

Abstract: The process of extracting natural gas from gas hydrate-bearing sediments (GHBS) may yield significant sand influx due to the metastable nature of GHBS Selecting appropriate sand control media is vital to addressing the challenges caused by excessive sand production This study proposes a protocol called holding coarse expelling fine particles (HCEFP) for sand control design The protocol aims to provide a new optimization method for screen mesh size selection for clayey silt hydrate reservoirs Detailed optimizing procedures of proper candidate screen mesh sizes in hydrate exploitation well in clayey silt hydrate reservoirs are depicted based on the HCEFP Then, the site W18, which is located in the Shenhu area of the northern South China Sea, is taken as an example to illustrate the optimization procedure for screen mesh size selection The results reveal that complete solid retention via a standalone screen is rarely beneficial as high clay contents can adversely affect wellbore productivity due to excessive plugging Screen aperture size selection for clayey silt hydrate wells should strike a balance between retaining coarser particles and avoiding screen blockage by the relatively fine particles Furthermore, longitudinal heterogeneity of the PSDs also increases the difficulties associated with sand control design Multistage sand control optimization is necessary in hydrate production wells For Site W18, we recommend that the entire production interval can be divided into two subintervals for multistage sand control operations

Determining the Distribution and Interaction of Soil Organic Carbon, Nitrogen, pH and Texture in Soil Profiles: A Case Study in the Lancangjiang River Basin, Southwest China

Abstract: The profile distributions of soil organic carbon (SOC), soil organic nitrogen (SON), soil pH and soil texture were rarely investigated in the Lancangjiang River Basin. This study aims to present the vertical distributions of these soil properties and provide some insights about how they interact with each other in the two typical soil profiles. A total of 56 soil samples were collected from two soil profiles (LCJ S-1, LCJ S-2) in the Lancangjiang River Basin to analyze the profile distributions of SOC and SON and to determine the effects of soil pH and soil texture. Generally, the contents of SOC and SON decreased with increasing soil depth and SOC contents were higher than SON contents (average SOC vs. SON content: 3.87 g kg−1 vs. 1.92 g kg−1 in LCJ S-1 and 5.19 g kg−1 vs. 0.96 g kg−1 in LCJ S-2). Soil pH ranged from 4.50 to 5.74 in the two soil profiles and generally increased with increasing soil depth. According to the percentages of clay, silt, and sand, most soil samples can be categorized as silty loam. Soil pH values were negatively correlated with C/N ratios (r = −0.66, p < 0.01) and SOC contents (r = −0.52, p < 0.01). Clay contents were positively correlated with C/N ratios (r = 0.43, p < 0.05) and SOC contents (r = 0.42, p < 0.01). The results indicate that soil pH and clay are essential factors influencing the SOC spatial distributions in the two soil profiles.

Life Cycle of Oil and Gas Fields in the Mississippi River Delta: A Review

Abstract: Oil and gas (O&G) activity has been pervasive in the Mississippi River Delta (MRD). Here we review the life cycle of O&G fields in the MRD focusing on the production history and resulting environmental impacts and show how cumulative impacts affect coastal ecosystems. Individual fields can last 40–60 years and most wells are in the final stages of production. Production increased rapidly reaching a peak around 1970 and then declined. Produced water lagged O&G and was generally higher during declining O&G production, making up about 70% of total liquids. Much of the wetland loss in the delta is associated with O&G activities. These have contributed in three major ways to wetland loss including alteration of surface hydrology, induced subsidence due to fluids removal and fault activation, and toxic stress due to spilled oil and produced water. Changes in surface hydrology are related to canal dredging and spoil placement. As canal density increases, the density of natural channels decreases. Interconnected canal networks often lead to saltwater intrusion. Spoil banks block natural overland flow affecting exchange of water, sediments, chemicals, and organisms. Lower wetland productivity and reduced sediment input leads to enhanced surficial subsidence. Spoil banks are not permanent but subside and compact over time and many spoil banks no longer have subaerial expression. Fluid withdrawal from O&G formations leads to induced subsidence and fault activation. Formation pore pressure decreases, which lowers the lateral confining stress acting in the formation due to poroelastic coupling between pore pressure and stress. This promotes normal faulting in an extensional geological environment like the MRD, which causes surface subsidence in the vicinity of the faults. Induced reservoir compaction results in a reduction of reservoir thickness. Induced subsidence occurs in two phases especially when production rate is high. The first phase is compaction of the reservoir itself while the second phase is caused by a slow drainage of pore pressure in bounding shales that induces time-delayed subsidence associated with shale compaction. This second phase can continue for decades, even after most O&G has been produced, resulting in subsidence over much of an oil field that can be greater than surface subsidence due to altered hydrology. Produced water is water brought to the surface during O&G extraction and an estimated 2 million barrels per day were discharged into Louisiana coastal wetlands and waters from nearly 700 sites. This water is a mixture of either liquid or gaseous hydrocarbons, high salinity (up to 300 ppt) water, dissolved and suspended solids such as sand or silt, and injected fluids and additives associated with exploration and production activities and it is toxic to many estuarine organisms including vegetation and fauna. Spilled oil has lethal and sub-lethal effects on a wide range of estuarine organisms. The cumulative effect of alterations in surface hydrology, induced subsidence, and toxins interact such that overall impacts are enhanced. Restoration of coastal wetlands degraded by O&G activities should be informed by these impacts.

Pressure coring a Gulf of Mexico deep-water turbidite gas hydrate reservoir: Initial results from The University of Texas–Gulf of Mexico 2-1 (UT-GOM2-1) Hydrate Pressure Coring Expedition

Abstract: The University of Texas Hydrate Pressure Coring Expedition (UT-GOM2-1) recovered cores at near in situ formation pressures from a gas hydrate reservoir composed of sandy silt and clayey silt beds in Green Canyon Block 955 in the deep-water Gulf of Mexico. The expedition results are synthesized and linked to other detailed analyses presented in this volume. Millimeter- to meter-scale beds of sandy silt and clayey silt are interbedded on the levee of a turbidite channel. The hydrate saturation (the volume fraction of the pore space occupied by hydrate) in the sandy silts ranges from 79% to 93%, and there is little to no hydrate in the clayey silt. Gas from the hydrates is composed of nearly pure methane (99.99%) with less than 400 ppm of ethane or heavier hydrocarbons. The δ13C values from the methane are depleted (−60‰ to −65‰ Vienna Peedee belemnite), and it is interpreted that the gases were largely generated by primary microbial methanogenesis but that low concentrations of propane or heavier hydrocarbons record at least trace thermogenic components. The in situ pore-water salinity is very close to that of seawater. This suggests that the excess salinity generated during hydrate formation diffused away because the hydrate formed slowly or because it formed long ago. Because the sandy silt deposits have high hydrate concentration and high intrinsic permeability, they may represent a class of reservoir that can be economically developed. Results from this expedition will inform a new generation of reservoir simulation models that will illuminate how these reservoirs might be best produced.