Clay Flocs Research Articles

The shale characteristics and shale gas exploration prospects of the Lower Silurian Longmaxi shale, Sichuan Basin, South China

The Lower Silurian Longmaxi Formation is a key target for shale-gas exploration in South China and comprises organic-rich black shale unit deposited in an anoxic deep-water setting. Mineral components are dominated by quartz and clay minerals with minor amounts of plagioclase, potassium feldspar, calcite and pyrite. The brittle mineral content ranges from 45% to 80% by weight (average: 62.5 wt. %). Organic geochemical analyses (TOC, organic matter type, Ro and gas content) show that the shale has good source rock potential. Matrix pores include organic pores; inter-particle pores between clay floccules, faecal pellets, organic matter particles and quartz and framboidal pyrite; and inter-crystalline pores within clay minerals and pyrite framboids. Fractures are also present. The development of storage space is controlled by the TOC content, the thermal maturity and type of organic matter present, by mineral composition and structural deformation. Factors which support the occurrence of shale gas accumulations in the study area include a high TOC content together with thermal maturity and organic matter type; the presence of thick and widespread shales; high rock fragility; and a stable, anoxic deep-water environment during shale deposition.

Thixotropism of micron-sized saltwater clay flocs

Results from microcompression testing of micron-sized saltwater individual kaolinite flocs with different ageing times of up to 152 days show that the rearrangement of flaws or weak links towards a more uniform distribution contributes to the thixotropic increase in floc mechanical properties. Evidence of this newly identified thixotropism of clay flocs is provided by the Weibull moduli of floc stiffness and yield shear strength, which are well fitted using the stretched exponential thixotropy model. The Weibull modulus is a good quantitative descriptor of the thixotropic evolution of clay floc microstructure.

Characterization of particle size and settling velocity of cohesive sediments affected by a neutral exopolymer

In natural waters, exopolymers or extracellular polymeric substances (EPS) exuded by microorganisms interact with clay particles, resulting in the flocculation of clays and hence alteration to the properties of suspended cohesive sediments. To investigate and further understand how neutral EPS affect cohesive sediment transport and the final sediment yield, an experimental study was conducted on laboratory-prepared clay and guar gum (used as an analog for neutral EPS) suspensions to characterize EPS-induced flocculation and the settling velocity of resultant flocs. Four different clays consisting of kaolinite, illite, Ca-montmorillonite, and Na-montmorillonite were studied to examine the influence of different layer charges on clay flocculation induced by neutral EPS. Floc size was determined by a laser particle size analyzer, and settling velocity estimated by analyzing the time-series floc settling images captured by an optical microscope. Results indicate that neutral EPS promote clay-EPS flocculation for all four clays with the particle/floc size significantly increased from ∼0.1-60 μm to as large as ∼600 μm. Clays' layer charge has a profound influence on the clay-EPS flocculation. With the same floc size, the settling velocity of clay-EPS flocs is typically smaller than that of pure clay flocs, which is attributed to the reduced density of flocs caused by the EPS. However, for flocs of the same composition (e.g. pure clay or hybrid clay-EPS mixture), the settling velocity increases with size. The fractal dimension of these clay-EPS flocs estimated from settling velocity ranges from 1.39 to 1.47, which are smaller than that of pure clay flocs, indicating that these flocs are less compacted than the pure clay flocs.

Important geological properties of unconventional resource shales

AbstractThe revelation of vast global quantities of potentially productive gas and oil-prone shales has led to advancements in understanding important geological properties which impact reservoir performance. Based upon research on a variety of shales, several geological properties have been recognized as being common and important to hydrocarbon production. (1) transport/depositional processes include hemipelagic ‘rain’, hyperpycnal flows, turbidity current flows, tempestites, wave-reworking, and contour currents in both shallow and deep water settings. (2) Common shale minerals include clays, quartz, calcite, dolomite, apatite, and pyrite; organic constituents include spores (Tasmanites), plant remains, biogenic quartz and calcite, and arenaceous foraminifera. (3) Porosity and permeability are characteristically low with pore sizes ranging down to the nanoscale. Main pore types include intergranular (including pores within clay floccules), porous organic matter, porous fecal pellets, and microfractures. (4) Important geochemical characteristics include organic richness (>3%), maturity (>1.1%Ro for shale gas and 0.6–0.9% for shale oil) and type (I–IV), in addition to certain biomarkers which are indicators of bottom water oxicity during deposition. Remaining hydrocarbon potential [RHP = (S1 + S2)/TOC] also reflects temporal environmental changes. ‘Isotopic reversals’ can be used to detect best producing areas in shale-gas plays. (5) Lithofacies stacking patterns and sequence stratigraphy are the result of eustatic depositional history. A general sequence stratigraphic model is presented here that highlights this commonality. (6) Geomechanical properties are key to drilling, fracturing and production of hydrocarbons. Brittle-ductile couplets at several scales occur in shale sequences. (7) Geophysical properties, when calibrated to rock properties, provide a means of regionally to locally mapping the aforementioned properties. (8) Economic and societal considerations in the exploration and development of resource shales are garnering attention. Many potentially economic shale-gas and shale-oil plays are being identified globally. Risks and uncertainties associated with gas- and oil-rich shales include the lack of long-term production histories, environmental concerns related to hydraulic fracturing, uncertainty in calculating hydrocarbons-in-place, and fluctuations in supply, demand, and price.

Accretion of Mudstone Beds from Migrating Floccule Ripples

Mudstones make up the majority of the geological record. However, it is difficult to reconstruct the complex processes of mud deposition in the laboratory, such as the clumping of particles into floccules. Using flume experiments, we have investigated the bedload transport and deposition of clay floccules and find that this occurs at flow velocities that transport and deposit sand. Deposition-prone floccules form over a wide range of experimental conditions, which suggests an underlying universal process. Floccule ripples develop into low-angle foresets and mud beds that appear laminated after postdepositional compaction, but the layers retain signs of floccule ripple bedding that would be detectable in the rock record. Because mudstones were long thought to record low-energy conditions of offshore and deeper water environments, our results call for reevaluation of published interpretations of ancient mudstone successions and derived paleoceanographic conditions.

Separation Characteristics of Inorganic Particles from Rainfalls in Dissolved Air Flotation: A Korean Perspective

Many reservoirs have been constructed in Korea to store water resources utilizing the terrain of the land. In general, dam source waters contain algae species that have densities close to that of water. Consequently algae are difficult to remove by conventional gravity sedimentation (CGS), while dissolved air flotation (DAF) is known to be an effective process for the purpose. The same source waters usually also have high turbidities due to mineral soil particles in the wet summer season. Systematic studies on the effect of high turbidity on the DAF process are very limited. In this work, DAF and CGS experiments were carried out to investigate water treatment characteristics and removal efficiencies under various COD/SS and chlorophyll‐a/SS ratios. A kinetic DAF process model was employed to describe bubble‐floc collision and agglomeration, as well as the rising velocity of bubble‐floc agglomerate. Our results showed that the initial collision‐attachment efficiency for the clay floc size range of 100−400 µm was a relatively low value of 0.3. The removal efficiency by DAF was greater than by CGS when chlorophyll‐a/SS ratio was high. It was also found that sedimentation prior to flotation is required for the effective separation of large clay flocs caused by runoff. Our experimental and theoretical results also suggest that the DAF process requires carefully operation in Korea, especially, in the rainy summer season.

Influence of structural properties of alum and ferric flocs on sludge dewaterability

Sludges are made of flocs produced during the coagulation stage. Their dewatering not only depends on the equipment used but also on the chemical, structural and physical characteristics of flocs. In this study, the relation between floc structure and sludge dewaterability is investigated beside the influence of the operating conditions during coagulation. Eight synthetic clay flocs families are produced using clay suspensions with four initial solids concentrations ranging from 0.5 to 5 g L −1 and two coagulants (Al 2(SO 4) 3 and FeCl 3). Flocs structure is characterised by their fractal dimension and by the size of the basic units (clusters, aggregates) they are made from. Fractal dimension values about 2.5 are indicative of rather compact structures with slightly looser flocs obtained when using FeCl 3. Except for clusters, larger in ferric flocs, the basic units sizes are similar whatever the coagulant used and they decrease when the solids concentration during coagulation is increased. Sludge dewaterability is estimated from the bound water content and the capillary suction time (CST) giving respectively information on the extent and on the rate of water removal. Ferric flocs contain about 20% less bound water but exhibit higher CST values and therefore higher resistance to water removal than alum ones. Flocs structure and sludge dewaterability are found linked. The sludge bound water content is found to decrease with the floc fractal dimension: less compact flocs contain more water but less bound water. And the capillary suction time is lower when sludges are made of smaller flocs.

Hydrophobic attraction may contribute to aqueous flocculation of clays

SEM observations of low solid content vitrified clay suspensions reveal that clay platelets build porous three-dimensional networks with platelets contacting each other mostly by their edges. To explain this behaviour, which must require long range edge-to-edge (EE) attractive forces, a hydrophobic-like interaction has been proposed. This interaction may be induced by the presence of nano-bubbles existing on the edges of clay crystals which may cause clay particles to flocculate. The following indirect evidence for such hydrophobic behaviour is presented. First, a clay platelet is shown attached to an oil drop by its edge; second, clay flocs were attracted by a vertically placed Teflon strip but not to the hydrophilic mica basal surface; third, a much thicker porous sediment occurred in CO2-saturated water solution compared with vacuum degassed water.

Formation and extraction of persistent fumigant residues in soils.

Fumigants are commonly thought to be short-lived in soil, but residues have been found in soils years following application. In this study, formation and extraction of persistent soil fumigant residues were investigated. Fumigants 1,3-dichloropropene (1,3-D), chloropicrin (CP), and methyl isothiocyanate (MITC) were spiked into Arlington, Glenelg, and Hagerstown soils and incubated for 30 d under controlled conditions. The incubated soils were evaporated for 20 h prior to extraction with a variety of organic solvents at different temperatures. Extraction with acetonitrile in sealed vials at 80 degrees C for 24 h was the most efficient method to recover persistent soil fumigant residues. At application rates of 1000-1700 mg (kg of soil)(-1), persistent residues of 1,3-D, CP, and MITC in the three soils ranged from 5 to 67 mg kg(-1). The residue content increased with application rate, correlated positively with soil silt content, decreased dramatically as indigenous organic matter (OM) was removed, and changed little with external OM addition. Adsorption to clay surfaces was not important in fumigant retention, while pulverization of soil aggregates significantly decreased persistent fumigant residues. The results suggest that persistent fumigant residues are retained in soil intra-aggregate micropores resulting from binding clay flocs and silt particles by humic substances.

Anionic Polyacrylamide Polymers Effect on Rheological Behavior of Sodium-Montmorillonite Suspensions

Polyacrylamide (PAM) is a long-chain synthetic polymer that acts as a strengthening agent, binding clay particles together. The interaction between anionic PAM and clay particles is not well understood yet. This interaction was evaluated by rheological measurements for Na-montmorillonite suspensions. Three anionic PAMs of three molecular weights (MWs) (3.5 × 103, 2 × 105, and 8 × 106 g mol −1) at similar hydrolysis levels (>85%) and three anionic PAMs at various degrees of hydorlysis (DH) (15, 33, and 92%) of similar MW were studied. In an electrolyte-free clay suspension at DH >85%, only the polymers with high MWs (2 × 105, and 8 × 106) could form a three-dimensional structure of clay platelets. The smallest polymer molecule size (3.5 × 103) was too short for bonding two adjacent platelets. At similar MW, the effect of the polymers increased with DH. At NaCl concentration of 10 mmolc L−1, at which the attractive forces between clay platelets were weak, the polymers had a significant impact on flow behavior. The effectiveness of the polymers increased with increasing MW and DH. At NaCl concentration of 100 mmolc L−1, the three polymers of DH > 85% stabilized flocs that already existed in the clay suspension. The effectiveness of the polymers in bridging adjacent clay flocs increased as their DH decreased. The polymer conformation factor has a greater impact on clay structure stabilization in suspension than the electrostatic repulsion effect. The clay structure stability was increased with increasing polymer electrostatic negative charge for similar molecular weights.

Anionic Polyacrylamide Polymers Effect on Rheological Behavior of Sodium‐Montmorillonite Suspensions

Polyacrylamide (PAM) is a long‐chain synthetic polymer that acts as a strengthening agent, binding clay particles together. The interaction between anionic PAM and clay particles is not well understood yet. This interaction was evaluated by rheological measurements for Na‐montmorillonite suspensions. Three anionic PAMs of three molecular weights (MWs) (3.5 × 103, 2 × 105, and 8 × 106 g mol −1) at similar hydrolysis levels (>85%) and three anionic PAMs at various degrees of hydorlysis (DH) (15, 33, and 92%) of similar MW were studied. In an electrolyte‐free clay suspension at DH >85%, only the polymers with high MWs (2 × 105, and 8 × 106) could form a three‐dimensional structure of clay platelets. The smallest polymer molecule size (3.5 × 103) was too short for bonding two adjacent platelets. At similar MW, the effect of the polymers increased with DH. At NaCl concentration of 10 mmolc L−1, at which the attractive forces between clay platelets were weak, the polymers had a significant impact on flow behavior. The effectiveness of the polymers increased with increasing MW and DH. At NaCl concentration of 100 mmolc L−1, the three polymers of DH > 85% stabilized flocs that already existed in the clay suspension. The effectiveness of the polymers in bridging adjacent clay flocs increased as their DH decreased. The polymer conformation factor has a greater impact on clay structure stabilization in suspension than the electrostatic repulsion effect. The clay structure stability was increased with increasing polymer electrostatic negative charge for similar molecular weights.

Flocculation behaviour and mechanisms of cationic inorganic microparticle/polymer systems

Flocculation systems involving anionic microparticles/cationic polymers have become increasingly important in the past decade. However, very little work using inorganic cationic microparticles (CM) has been reported. In this work, fine clay flocculation was induced by a range of cationic colloidal alumina in conjunction with various linear polymers. Dynamic flocculation experiments, conducted with a photometric dispersion analyser (PDA 2000), showed that the effectiveness of CM as a single component flocculant was limited. However, in conjunction with an anionic polyacrylamide based copolymer, the flocculation efficiency improved significantly. Strong synergy between CM and anionic polymers also allow the system to be effective in a wide pH range and resistant to high shear. The sizes of clay flocs, formed by CM and various polymers under different levels of shear rates, have been characterised, and flocculation mechanisms have been revealed. The mechanisms suggest that bridging flocculation, contributed from the interaction between CM and anionic polymer, is the main function.

Comparison of pelagic and nepheloid layer marine snow: implications for carbon cycling

Marine snow from upper and mid-water (i.e., pelagic) depths on the California margin is texturally and compositionally different from that traveling in the nepheloid layer. Transmission electron microscopy shows that pelagic marine snow consists primarily of bioclasts (e.g., diatom frustules, foram tests), organic matter, and microbes. These components are entrained as discrete particles or small aggregates (≤10 μm in diameter) in a loose network of exocellular, muco-polysaccharide material. Clays are infrequent but, when present, are constituents of comparatively compact organic-rich microaggregates. Microbes are abundant and appear to decrease in number with increasing water depth. In contrast, marine snow aggregates collected from just above the sea floor in the nepheloid layer are assemblages of clay particles, clay flocs, and relatively dense clay–organic-rich microaggregates in an exocellular organic matrix. Bioclasts and microorganisms occur only rarely. The prevalence of clay–organic-rich aggregates in the nepheloid layer suggests that, prior to final deposition and burial, marine snow from the pelagic zone is subject to disaggregation and recombination with terrigenous detrital material near or at the sea floor. Results have significant implications for the accumulation and burial rates of organic carbon on continental margins and the aging and bioavailability of sedimentary organic matter. Samples examined were collected offshore of northern and central California.

Syneresis cracks: subaqueous shrinkage in argillaceous sediments caused by earthquake-induced dewatering

Syneresis cracks, often confused with subaerial desiccation phenomena, are traditionally ascribed to subaqueous shrinkage whereby salinity changes caused deflocculation of clay. This and other previously proposed mechanisms fail to account for their occurrence in low-energy, typically non-evaporitic facies, stratigraphically sporadic distribution, intrastratal formation under shallow burial depths, variation in morphology, degree of contraction, generation of sedimentary dikelets as crack fills, and deformation of dikelets and enclosing layers. Instead, it is suggested that ground motion from strong synsedimentary earthquakes caused argillaceous sediments to dewater, interbedded sands and silts to be almost simultaneously liquefied and injected into the resulting fissures, and then these dikelets to be distorted. Comparative rarity of syneresis cracks in Phanerozoic versus Precambrian marine strata is considered to be primarily an evolutionary consequence of theological changes caused by increased organic binding of clay flocs in the water column, greater input of organic matter into the sediment, and the diversification of sediment-dwelling bacteria and meiofauna in Phanerozoic deposits.

Transport of Coarse Particles in a Fine Suspension Medium.

The rheology of suspensions of coarse particles in non-Newtonian fluidshas not been the subject of much investigation. There are distinct advantagesin using non-Newtonian carrier fluids in the transportation of solids, forexample in coal slurry transport. The objective of this work is to investigatethe flow behaviour exhibited by a concentrated mixture of coarse particles ina medium consisting of suspensions of fine particles. Steady state viscositymeasurements of suspensions of mono-sized coal, ballotini and styreneacrilonitrileparticles suspended in a non-Newtonian bentonite clay carrier fluid havebeen made using a Contraves Rheomat 115 rheometer. Measurements werecarried out with various particle concentrations and shear rates ranging from 2.22s-1 to 345s-1. It was found that variation of viscosity due to coarse particlesize did not follow any trend. It is thougth that this behaviour in due tothe interaction between the clay flocs and the coarse particles. Modellingwork assuming interacting coarse particles and flocs coexisting as in a bimodalmixture was shown to simulate this behaviour.

Aggregation of break-up of clay flocs in turbulent flow

Flocculated clay particles make up the suspended matter found in the waters of river estuaries, and their properties are strongly influenced by the flow field in which they find themselves. The size distribution of the clay flocs is determined by an equilibrium between the general tendency of the flow to enhance aggregation and break-up are investigated and expressions for the size distribution of the flocs are obtained.

Design of Filters for Clay Cores of Dams

The clay core of the Balderhead Dam Suffered cracking and internal erosion in 1967. Segregation of the eroded debris was observed and the filter failed to retain the finer particles that reached it. This observation has lead to the development of a method of filter design for clays in flocculating conditions, based on the retention of clay flocs, which are the smallest particles which can arise during erosion. Such a filter will operate irrespective of cracking and the amount of segregation of the eroded debris. Factors controlling floc size are described, and an experimental relationship between permeability of a filter and the size of particle which will pass through it is presented. It is suggested that the retention characterists of a filter can be described more generally by its permeability than by its grading.

A physical model for the transport and sorting of fine‐grained sediment by turbidity currents

ABSTRACTTurbidite muds in cores from the outer Scotian continental margin, off eastern Canada, contain abundant thin silt laminae. Graded laminated units are recognized in parts of this sequence. These represent single depositional events, and show a regular decrease in modal grain size and thickness of the silt laminae through the unit. A similar fining trend is shown by both silt and mud layers over hundreds of kilometres downslope. Textural analysis of individual laminae allows the construction of a dynamically consistent physical model for transport and sorting in muddy turbidity currents. Hydraulic sorting aggregates finer material to the top and tail regions of a large turbidity flow which then overspills its channel banks. Downslope lateral sorting occurs with preferential deposition of coarser silt grains and larger mud flocs. Depositional sorting by increased shear in the boundary layer separates clay flocs from silt grains and results in a regular mud/silt lamination. Estimates can be made of the physical parameters of the turbidity flows involved. They are a minimum of several hundreds of metres thick, have low concentrations (of the order of 10−3 or 2500 mg 1−1), and move downslope at velocities of 10‐20 cm s−1. A 5 mm thick, coarse silt lamina takes about 10 h to deposit, and the subsequent mud layer ‘blankets’ very rapidly over this. A complete unit is deposited in 2‐6 days which is the time it takes for the turbidity flow to pass a particular point. These thick, dilute, low‐velocity flows are significantly different from the ‘classical’ turbidity current. However, there is mounting evidence in support of the new concept from laboratory observations and direct field measurements.

Percolation rates with surface layers of gravel or clay flocs on soil fed clear and turbid waters

Suspended solids in water can plug the surfaces of aquifer recharge basins, and they are often chemically flocculated and removed in costly separate floc‐settling basins. This work evaluated floc and gravel filters on recharge surfaces as substitutes for settling basins. Disturbed soil in permeameters was treated with layers of small gravel and constant feedwater heads of either clear tapwater, untreated turbid runoff water, or turbid runoff water treated to form and retain flocs. Untreated turbid water reduced percolation rates more than the other feedwaters, and gravel layers markedly reduced percolation of all feedwaters. The percolation rate of water with flocs was only slightly less than that of tapwater. These results suggested that untreated turbid water or gravel layers are unacceptable for recharge surfaces. However, combinations of soil, gravel, and clay may have considerable potential for reducing percolation in water retention basins. Flocculation and settling seldom remove all fine particles from turbid water; thus a filter layer of flocs may extend the effective life of a recharge surface and eliminate costly separate floc‐settling basins.

Flocculation Behavior of Suspended Sediments and Oil Emulsions

ABSTRACT Laboratory studies performed upon the flocculation tendencies of dispersed clay particles and oil emulsions in both fresh and brackish waters demonstrate that oils and clays form spontaneous association colloids or colloidal electrolytes in the presence of dissolved salts. Oil sedimentation seems to be caused mainly by adsorption of oil films onto clay particles which are subsequently flocculated by electrolytic action, rather than by the adsorption of discrete oil globules onto the clay floccules. Observed sinks of surface oil slicks in marine areas may therefore be due to the colloidal flocculating abilities of the dissolved salt, rather than to inherent coagulation properties of oils and suspended clays.