Clay Deposits Research Articles

Assessment of Mineralogical Characteristics of Clays and the Effect of Waste Materials on Their Index Properties for the Production of Bricks.

Significant research investigations on the characteristics of unexplored clay deposits are being conducted in light of the growing need for clay in the ceramic industry and the variable chemistry of clays. Parallel to this, the generation of waste materials like fly ash, ferrochrome slag, and silica fume is also increasing, responsible for environmental degradation. This paper aims to study the mineralogical properties of pure clays (one specimen from Siberia and five specimens from different locations in Turkey), and the effect of mentioned waste materials on the index properties of clays obtained. This study is divided into two phases, wherein in the first phase, the pure clay specimens are analyzed against mineralogical properties (i.e., chemical composition, thermal analysis, and particle size distribution). While in the second phase, index properties of pure clay specimens and clay specimens modified with 0-50% fly ash, ferrochrome slag, and silica fume are analyzed. The results reveal that the clay specimens from Turkey (USCS classification: CL) are fit for the ceramic industry and bricks production, and incorporation of waste materials can further improve their index properties. It is also observed that incorporation of 10-30% fly ash and ferrochrome slag have higher efficiency in reducing the plasticity index of clays studied as compared to the addition of silica fume.

Preliminary Investigations on Murunkan Clay Deposit in Sri Lanka

Journal of the Geological Society of Sri Lanka is a peer-reviewed and open access journal published by the Geological Society of Sri Lanka. It aims to publish the most topical and highest quality papers, summarizing the results of recent research across all sub-disciplines of the Earth Science. Papers are frequently interdisciplinary covering both pure and applied fields of Geology. Contributions often refer to local, regional and/or international studies and emphasize the development of the understanding of fundamental geological processes.

Application of the unified CPT method for driven piles to layered deposits

The ongoing and increasing demand for offshore piles has motivated the development of more reliable design methods and led to the recent development of ‘unified’ cone penetration test design methods to predict the axial capacity of driven piles installed in sand deposits and in clay deposits. However, many sites encountered in practice contain both sand and clay layers as well as silt layers and it is therefore important to assess the reliability of these new methods at such sites. This paper presents this assessment using a newly compiled database of pile load tests in interlayered deposits. It is shown that satisfactory predictions of capacities are attained using the sand and clay formulations of the ‘unified’ method with a correction applied to the sand method to enable prediction of shaft friction in silt deposits.

Numerical investigation of the settlement behavior of hybrid system of floating stone columns and granular mattress in soft clay soil

The composite system of stone columns reinforced soil overlaid by granular mattress (GM) has been given more attention as a hybrid improvement technique. This work presents 3D finite element analyses using PLAXIS 3D software for a composite system of floating stone columns group constructed in a deep soft clay deposit in Port-Said in Egypt. The limited area of loading was investigated in conjunction with the system key parameters, i.e., length, diameter, and the GM main properties. Results validated the effectiveness of the GM in settlement reduction and system behavior enhancement. The GM thickness results in considerable settlement reduction up to value of 1.5d where d is the stone column diameter. The thickness increase can be an economical substitution instead of increasing stone column length where a new factor named “Mattress improvement factor: Ƞgm” is defined to represent the occurring improvement due to GM existence. Results also show notable reduction of settlement with increasing the length to a limiting value of L = 1.8B where B is the footing width.

Application of geostatistical methods to estimate the mineral contents in the alluvial clay deposit, Monoum plain, West Cameroon

Application of geostatistical methods to estimate the mineral contents in the alluvial clay deposit, Monoum plain, West Cameroon

Experience in studying natural fractals

We investigate the fractal characteristics of diverse natural objects and discuss their possible applications. Fractal dimensions of the suture lines of ammonite shells, granite textures, the portions of the river network in the Onega and the Ladoga lakes basin and the multi-fractal spectra of varved clay sedimentation in these lakes were calculated. It is shown that the fractal dimensions of the suture lines of shells can be used to identify ammonites. Fractal textures of granites can be applied to improve their aesthetic perception. The fractal parameters of the river network and the sedimentation regimes in the lakes may be related to tectonics.

Assessment limestone of Ghar Formation in Al-Busaiyah Area in southern Iraq as Raw Materials for the Manufacture of ordinary Portland cement (OPC)

Six samples of limestone rocks were selected for the Early Miocene Ghar Formation in the Busayyah area south of Nasiriyah city in the southern desert of Iraq, and one sample of clay deposits of the Quaternary age was selected for the purpose of geochemical and mineral evaluation for the manufacture of ordinary Portland cement. The results of the analyzes of limestone for the formation of Ghar showed that it contains Ratios (less than 2%) of magnesium oxide, and the percentage of calcium oxide to more than (52%),Which was in conformity with the Iraqi and international specifications [1] and [2] for the cement industry. playa clays in the region study were analyzed for the purpose of testing and demonstrating their suitability for the cement industry, as recent clays have a high percentage of magnesium oxide, as well as its scarcity in the study sections, as the results showed their suitability for the cement industry. The ratios of lime saturation (LSF), alumina ratio (AR) and silica ratio (SR) were calculated for the mixture consisting of limestone to Ghar Formation, clay, Bauxite and iron oxides. (3) Mixtures of different exposed of Ghar formation were burned at a temperature of 1200 and 1450 °C, and the results showed the validity of the produced clinker and its conformity with international specifications when burning at 1450 °C, while the burnt clinker failed at 1200 °C due to incomplete form of cement phases. The proportions of the mineral phases of clinker were calculated after burning and it was found that the phases and minerals of belite, lalite, ferrite aluminate and portlandite.
 Physical and mechanical tests were carried out on limestone from the Ghar Formation, where the compressive strength, specific weight, total density, moisture content and apparent porosity were analyzed

English

Climate change, environmental degradation, loss of biodiversity, changes in the ecosystem and disasters play an important role in the development and economic advancement. In Zororo Village, Zimbabwe, environmental degradation, changes in the ecosystem and biodiversity have occurred rapidly during the last few decades. A literature review, key informant interviews, and focus group discussions were the methodologies used for this research. All the participants agreed that environmental changes had occurred during the last few decades, however, they could not connect these to activities such as brick moulding. Brick moulding is a lucrative and economic backbone of many communities in rural Zimbabwe and other Southern African countries. It is a way of value adding to the clay deposits for economic development but the practice is associated with various environmental challenges linked to the various stages in the brick production process. The process impacts on the environment, ecosystem, biodiversity and human health. Vegetation, indigenous trees, edible insects, small animals and wild fruit trees have disappeared from the environment. Children and domestic animals drown in uncovered holes which also become breeding sites for mosquitoes and other vectors. This article discusses community contributions to the negative impacts of environmental degradation, changes in the ecosystems, biodiversity and human health, through the destruction of anthills in the process of brick moulding in rural Zimbabwe.   Key words: Brick moulding, kiln, climate change, communities, disasters, anthills (mounds), health impact, sustainable livelihoods, vertical shaft brick kiln.

The effect of clay type and solid wettability on bitumen extraction from Canadian oil sands

Clays (<2 μm) in oil sands ores have a significant impact on the processability of the ores. The present study aims at understanding the effects of the type and wettability of clays on the performance of bitumen extraction from mined oil sands. The results from batch extraction tests showed a detrimental effect of doping with hydrophilic clays (kaolinite, illite and montmorillonite), with montmorillonite being the worst. The crucial role of clays in bitumen slime-coating was studied through atomic force microscopy and clay deposition tests. For the hydrophilic clays, clay concentration was an essential parameter in determining the bitumen-clay hetero-coagulation process. Strong slime-coating of clay particles on bitumen droplets occurred only above a critical clay concentration. This critical concentration varied with clay type and water chemistry. Compared with earlier studies, kaolinite was found to deposit strongly on bitumen surfaces for the first time in this study. Hydrophilic clays were contaminated by soaking in toluene-diluted-bitumen solutions to investigate the effect of solid hydrophobicity on bitumen extraction. Hydrophobic clays had a less significant depression on bitumen recovery but a more significant deterioration on froth quality than hydrophilic clays. Similar slime-coating was observed for the different clays once contaminated by diluted bitumen. Furthermore, the presence of a large content of clays in bitumen extraction could result in excessive emulsification of bitumen into small droplets, leading to low bitumen recovery. This work provides useful insights into the fundamental interactions of clays and bitumen, with implications for developing a viable solution in dealing with clays in oil sands operations.

Environmental shifts in and around Lake Pannon during the Tortonian Thermal Maximum based on a multi-proxy record from the Vienna Basin (Austria, Late Miocene, Tortonian)

The Neogene Lake Pannon was the largest lake that ever existed in Europe. It attained its greatest extent during the Tortonian Thermal Maximum. For the first time, results from a detailed lake record documenting about 85 kyr of Late Miocene time in a continuously recovered, 60-m-long, clay-rich core of Lake Pannon are reported. This record includes the transition from the lake's maximum transgression into its highstand at around 10.4 Ma. The environmental development of Lake Pannon during its maximum extent is interpreted based on integrated paleontological, sedimentological, mineralogical and geochemical data. The maximum extent coincided with stable sedimentation of clay, little influx from the hinterland, low surface productivity and severe bottom-water anoxia. The clay mineralogy of the lower part of the core points to prevailing chemical weathering based on the illite/smectite ratios. Distinct Fe, Mn and Ba enrichments are interpreted to have formed close to sulfate-methane transition zones during the maximum flooding. The highstand phase was marked by rapid environmental shifts with frequent phases of well‑oxygenated bottom waters. These phases are reflected by rich benthic communities including stenohaline tunicates. The increased input of detritic kaolinite suggests a shift towards physical weathering and higher precipitation coinciding with a shift in the provenance of clay minerals.Increasing amounts of nutrients stimulated surface water productivity and nannoplankton blooms. Despite the offshore position of the core at ∼8 km from the mountainous ranges of the Alps, strong fluvial input is reflected from 32.5 to 30.3 m by coarser sediment and the occurrence of terrestrial and freshwater molluscs. The Rhenodanubian Flysch Unit was the main source of the siliciclastics of the core and was drained by the Paleo-Wien river. Drainage from the Calcareous Alps was limited to an exceptionally strong fluvial event and related deposits, which documents the presence of a second river in the southwest, which might represent the Paleo-Liesing.The dominance of smectite throughout the core suggests a temperate climate with distinct seasonality during the Tortonian Thermal Maximum. In view of the autochthonous ascidian sclerites in three samples, and assuming generally similar ecological requirements for both Pannonian and modern tunicates, we conclude a polyhaline salinity for Lake Pannon around 10.4 Ma.

Mineral composition of terrigenous components in loess and clay deposits of Western Mongolia

Introduction. The paper considers the results of a study associated with the mineral composition of terrigenous components in loess and clay deposits of Western Mongolia. The study was performed by the method of quantitative immersion analysis using samples obtained in the framework of geological studies during the seismic microzoning of certain cities.Aim. Determination and analysis of variations in the mineral composition of terrigenous components of loess quaternary alluvial, eolian, diluvial-eolian and diluvial-proluvial complexes, as well as Neogene-lower Quaternary lake-alluvial and Cretaceous-Paleogene lake “brick” clays.Materials and methods. The database is represented by quantitative data on the content of light and heavy minerals (0.01—0.25 mm fraction) in various geological and genetic deposit complexes, sampled from outcrops with the thickness of 6–8 m and test wells with the depth of 20–30 m (72 samples in total). During the compositional characterisation of light and heavy fractions, mineral associations were established, as well as maturity (Кz) and stability coefficients (KU) were calculated. Four territorial zones, including northern (territory of Sükhbaatar and Mörön), central (Zuunmod), western (Uliastai) and southern (Dalanzadgad), were isolated. A Q-type cluster analysis program was applied to process mineralogical data.Results. Variations in mineral associations of the studied objects were established related both to their belonging to the selected geological and genetic complexes and the possibility of eolian process effects. The factors of influence include climatic conditions during the formation of complexes, the composition of rocks in geological formations abundant in these territories and contemporary climatic zoning.Conclusion. Representative data were obtained for the central and southern zones, where the mineral composition of terrigenous components was determined using samples from test wells having clearly observed variations in the mineral composition of deposits during the change of a geological and genetic complex. Since the immersion method is still essential for studies of sedimentary rocks, the information on a new object, represented by the territory of West Mongolia, obtained for the first time, appears to be of a particular interest both from scientific and practical points of view.

Assessment of existing Vs-Lab correlations regarding Eastern Canadian clays

The small strain shear modulus, Gmax, is an important parameter for characterizing the seismic response of deposits to dynamic loading. The parameter is related to shear wave velocity (Gmax=ρVs2) only via the soil density. Existing Vs correlations established in the laboratory were compiled in this paper and grouped into different general forms. Laboratory Vs measurements using the piezoelectric ring-actuator technique, P-RAT, incorporated in conventional oedometer cells, were performed for six Eastern Canadian clay deposits. Specific correlations were established between normalized shear wave velocities, Vs1, with the overconsolidation (OCR) and void ratios (e). The paper examines the applicability of existing correlations by comparing Vs1 values obtained from P-RAT correlations to those predicted by published laboratory correlations. While several correlations can be used to predict Vs for Eastern Canadian clay, the applicability of other correlations has however been questioned. The analysis reveals the importance of considering the effect of the percentage of fine particles (<2 μm). This effect changes the void ratio variation range, which in turn has a significant impact on Vs values. Furthermore, two general correlations are suggested based on P-RAT results and considering the clay content of analyzed sites. These general correlations can be readily used to estimate Vs1 values for low and high plasticity clays.

The Influence of the Reduction in Clay Sediments in the Level of Metals Bioavailability-An Investigation in Liujiang River Basin after Wet Season.

The seasonal elevation of metals' bioavailability can aggravate the threat of metal contamination in the aquatic environment. Nevertheless, their regulations have rarely been studied, particularly the connections between metals' transformation and environmental variations. Therefore, the catchment area of Liujiang River was taken as an example in this study, their seasonal variations in metals' bioavailability in sediments, especially during the wet season, was investigated to recover the processes associated with metals' speciations and multiple environmental factors. The results revealed that the concentration of metals in sediments were high overall in the wet season, but low in the dry season. The significantly reduced ratio of metals in non-residual forms was largely related to the overall reduction in metals in oxidizable and reducible forms after the wet season. However, the elevated BI indexes of most metals suggested their increased bioavailability in the dry season, which should be closely related to their corresponding elevations in carbonate-bound and exchangeable forms after the wet season. The variations in metals' bioavailability were primarily related to their predominance of exchangeable and carbonate-bound form. The higher correlation coefficients suggested the destabilization of the oxidizable form should be treated as a critical approach to the impact of metals' bioavailability after the wet season. In view of that, sediments' coarsening would pose the impacts on the destabilization of exogenous metals in sediments, the reduction in clay sediments should be responsible for the elevation of metals bioavailability after the wet season. Therefore, the monitoring of metals' bioavailability in sediments should be indispensable to prevent metal contamination from enlarging the scope of their threat to the aquatic environment of the river, especially after the wet season.

Comparative settlement response of soft clays reinforced with granular columns under widespread loads

This paper examines the consolidation and settlement behaviour of soft clay deposits treated with granular columns (single and in groups). Two Rowe cell loading chambers were used to conduct the investigations on samples of kaolin and a local Belfast natural estuarine alluvium called ‘sleech’. Tests were carried out on unreinforced samples and then reinforced samples with single and multiple column configurations. The test duration for each test was between 3 and 4 months, depending on the test material and the granular column configuration. The settlement reduction factors based on primary and secondary consolidation were examined. The study suggests that the effectiveness of granular columns at mitigating primary and/or secondary settlement is directly related to the loading intensity, the stress history and the creep characteristics of the subsoil. It was also found that the stress concentration ratio reduced with the stress level. Secondary consolidation also has some effects on the stress concentration ratio.

A 7000‐year record of environmental change: Evolution of Holocene environment and human activities in the Hangjiahu Plain, the lower Yangtze, China

AbstractThe Hangjiahu Plain in the lower Yangtze is one of the core areas that sustained the flourishment of the Liangzhu Civilization. This study reconstructed Holocene environmental change on the Hangjiahu Plain based on a sediment core collected from the Tangqi ZK‐3 location situated on the low‐lying Hangzhou‐Taihu region of the Yangtze Delta. We applied OSL dating, grain size analysis, pollen analysis, and magnetic susceptibility to reconstruct Holocene environmental change and compared our data with other published results. Our results showed that (i) before ~7.0 ka B.P., the ZK‐3 core recorded a strong hydrodynamic force, resulting in the widespread deposition of light grayish silt clay or clayey silt in the region. The climate was warm and humid, and the vegetation was mixed evergreen deciduous coniferous forest. (ii) Between 7.0 and 6.0 ka B.P., the hydrodynamic condition in ZK‐3 core became weaker, and the climate remained warm and humid. Although most of the Hangjiahu Plain were still covered by the light grayish silt clay or clayey silt, some higher grounds began to emerge as sea‐level rise slowed, which coincided with the development of the Majiabang culture. (iii) Between 6.0 and 4.5 ka B.P., the deposition of yellowish silty clay indicates a shallow‐water hydrological environment at ZK‐3, as the regional water level was dropping while more land was emerging, which provided a favorable physical environment for the prosperity of the Songze and Liangzhu cultures. The period experienced a drier and cooler climate, with evidence of deforestation. (iv) Between 4.5 and 3.0 ka B.P., the sediments in the ZK‐3 core were dominated by light grayish clay, indicative of a return to a deep‐water environment with a prolonged waterlogging condition. The climate remained dry and cool with further deforestation. However, the widely distributed yellowish silt clay suggests frequent floods in the region, resulting in a sharp reduction of settlement sites and the eventual decline of the Liangzhu Civilization.

Influence of firing temperature on the ceramic properties of illite-chlorite-calcitic clays

The influence of firing temperature on the ceramic properties of illite-chlorite-calcitic clays has been investigated. Three samples of the same clay deposit have been selected. Weight loss, dimensional changes, water absorption, bulk density, open porosity, flexural and compressive strengths, initial capillary water absorption rate and thermal conductivity have been determined as a function of firing temperature in the range 900-1200 °C with 1 h of soaking time. The microstructures of the fired samples have been examined by SEM and the phase evolution studied by XRD. The water absorption capacity decreased from ∼ 22% at 900 °C/1 h to a maximum of 12% at 1200 °C/1 h with a maximum linear shrinkage of ∼ 2.7%. The open porosities decreased from ∼ 36% at 900 °C/1 h up to ∼ 20% at 1200 °C/1 h as an effect of progressive sintering with higher densification degree of the ceramic bodies. The flexural strength reached a maximum value of ∼ 34 MPa at 1200 °C/1 h. In contrast, the compressive strengths increased by firing up to a maximum of ∼ 114 MPa at 1200 °C/1 h. The thermal conductivity increased slightly as increasing firing temperature with a maximum value of 0.582 W/m·K in samples fired at 1200 °C/1 h. The Ryshkevitch-Duckworth equation was applied and the results indicated that compressive strength is related linearly with open porosity. A linear correlation was found between thermal conductivity and open porosity. The microstructural evolution by SEM indicated that there is a change of the fired samples at 1100 °C as compared to SEM observations at 900 and 1000 °C. There is an increase of contacts between particles and layered structures associated to dehydroxylated clay minerals (illite and chlorite), quartz particles and pores developed by firing. At 1200 °C/1 h, the microstructures have changed associated to the higher degree of vitrification in the fired sample, with consolidation of the material, interparticle and neck contacts with formation of vitrified bridges. The formation of closed and large open pores of several sizes has been achieved by firing. Small particles were observed as a fine precipitation of crystals in the vitrified structures associated to anorthite, hematite and quartz relicts. This change in microstructure allowed deduce that the compressive strength increased upon firing, with maximum values of this ceramic property at 1200 °C. The ceramic bodies were more sintered by firing and the open porosity decreased progressively. Brickmaking is the main application of these fired illite-chlorite calcitic clays. These clays fired at 900–1100 °C, with 1 h of soaking time, could be applied in the fabrication of clay roofing tiles, tiles and even porous ceramic supports with small variations on shrinkage and porosity, good flexural strengths and high compressive strengths. Samples fired at higher temperatures, 1100 °C/1 h, could be applied as ceramic bricks showing a medium porosity (∼ 20%). They show almost the same bulk density when they are fired at lower temperatures (900 °C). Samples fired at higher temperatures (1150–1200 °C/1 h) could be applied as dark ceramic products. This investigation was interesting because a better knowledge of illite-chlorite-calcitic clays applied as ceramic raw materials has been achieved.

DEVELOPMENT OF HIGH ENERGY AND FUEL ECONOMY CERAMIC INSULATED BIOMASS MULTI COOKING SYSTEM

The analysis of Inyi clay and its utilization in the production of an improved cook-stove is significant to the existence of mankind and his community. This study was carried out to analyse the mixture of clay, cassava peel and grog and its utilization in the production of an improved cook-stove. The clay deposits were collected from Inyi Local Government, Enugu State. Different ratios of the mixture was used in the following percentage proportions by weight of clay to cassava peel to grog: A (40:40:20), B (40:30:30), C (40:20:40), D (40:10:50) at firing temperatures 900oC and 1000oC. The physical analysis (apparent porosity, linear shrinkage, dry-fired shrinkage, total shrinkage, bulk density, water absorption and percentage making moisture) was carried out using rectangular shape test piece to ascertain the feasibility in the lightweight stove production, the strength and the durability of products. The chemical analysis (xrd and xrf) was carried out using x-ray diffractometer and x-ray fluorescence in order to determine their crystallographic parameters and elemental composition respectively. The morphological analysis (SEM) was carried out using the scanning electrode microscope to obtain the resolutions and magnifications. The addition of cassava peel and grog was found to have great effect on the insulating properties (shrinkage, bulk density, apparent porosity and water absorption) of the clay. Chemical analysis revealed SiO2 (45.26%) and Al2O3 (35.19%) as major constituent. The result of this study showed that cassava peel was suitable in enhancing the insulating properties of Inyi clay and can be utilized to induce insulation in clay minerals when desired.

Expansion/shrinkage history of the Paratethys Sea during the Eocene: New insights from eolian Red Clay records in the Altyn Mountains, northern China

Uplift of the Tibetan Plateau, expansion/shrinkage of the Paratethys Sea, and global climate are three major forcings for central-east Asian climatic and environmental variations during the Cenozoic. However, knowledge of expansion/shrinkage history of the Paratethys Sea is much less well known in comparison with the other two forcings. Here, we present a first multiple-parameter environmental magnetic and diffuse reflectance spectroscopy study of the Eocene eolian Red Clay deposits (∼51–40 Ma) in the Xorkol Basin of the northeastern Tibetan Plateau, which is near the easternmost maximum boundary of the Eocene Paratethys Sea. The first detailed Eocene expansion/shrinkage history of the Paratethys Sea was reconstructed based on the hematite content of the Eocene Red Clay, which shows remarkable consistency with the previous low-resolution Paratethys Sea paleowater depth record in the southwestern Tarim Basin. These results demonstrate that the Paratethys Sea experienced a three-stage (shrinkage-expansion-shrinkage) evolution between ∼51 and 40 Ma, with boundaries at ∼46.2 and 42 Ma. Superimposed on this framework, the Paratethys Sea experienced four times of rapid shrinkages at the expansion phase (shows 400-kyr cycles) during ∼44–42 Ma modulated by eccentricity forcings. These new results are of great significance to evaluate respective role of Tibetan uplift, global climate, and Paratethys Sea area variations in Asian climate and environmental change over the Eocene.

Experimental Investigation of Consolidated Undrained Shear Behavior on Peaty Soil in Dian-Chi, China

Peat deposits are extensively distributed worldwide, and the various common engineering-failure problems involving peat have attracted greater attention from researchers in regard to understanding the mechanical behavior of peat. This study investigated extensive index and consolidated undrained triaxial compression tests applied to the peaty soils of Dian-Chi Lake, located in Yunnan, China. A series of consolidated undrained triaxial compression tests on peat specimens were carried out in this study, and the influences of confining pressure, organic matter content and strength parameters were investigated. The test results indicate that, to obtain a B-value greater than 0.98, the average back pressure of the Dian-Chi Lake peaty soil should be at least 150 kPa, with organic matter contents N ranging from 30% to 85%. Compared with the existing oedometer consolidation results of the research team, the values of compressibility and permeability behavior under the oedometer and isotropic consolidation conditions are not significantly different. In addition, the average failure strain, εf, ranged from 9% to 15% for the investigated normally consolidated specimens, and the average effective angle of internal friction was 43.8°, which is greater than the maximum internal friction angle of 35° for typical soft clay and silt soils. A correlation was proposed by curve fitting the experimental data to better capture the nonlinear relationship between φ′ and N. Furthermore, the values of the normalized undrained strength, Su/σc′, varied from 0.56 to 0.84, which is larger than that of the inorganic soft clay and silt deposits.

Analysis of the effect of hydrate on water retention curves in gas hydrate-bearing sediments using gas drainage combined with NMR

Water retention curves play a critical role in numerical simulations for predicting fluid production and sediment deformation behaviors in gas hydrate-bearing sediments (GHBSs). This study uses a new testing assembly that combines gas drainage and low-field nuclear magnetic resonance (NMR) tests to determine the water retention curves of artificially synthesized clay silty specimens. The effect of hydrate on the pore size distributions and water retention curves is analyzed via NMR transverse relaxation time curve distributions, and the mechanism of changes in the water retention curve parameters is further discussed. The results show that hydrate formation decreases the proportion of pores with sizes greater than 15 μm and increases the proportion of pores with sizes less than 3.5 μm in clay silty sediments. Hydrate formation increases capillary pressure and prevents available water migration. The presence of hydrate exponentially increases the normalized capillary pressure but exponentially decreases the normalized curve shape factor, yielding narrower curve distributions. The gas entry pressure and curve shape factor exhibit linear correlations with the pore size distribution parameters. The results imply that the changes in the water retention curves are strongly related to the initial pore size distributions. This study offers a deep understanding of capillary effects-related water retention characteristics and their underlying links with the pore size distributions, and demonstrates that low-field NMR has great potential for characterizing water retention curves of GHBSs.