Real-time drilling mud gas monitoring for qualitative evaluation of hydrocarbon gas composition during deep sea drilling in the Nankai Trough Kumano Basin

Background

Riverine particles undergo a rapid transformation when they reach estuaries. The rapid succession of hydrodynamic and biogeochemical regimes forces the particles to flocculate, settle and enter the sediment pool. The rates and magnitudes of flocculation depend on the nature of the particles which are primarily affected by the types and quantities of organic matter (OM). Meanwhile, the OM characteristics vary widely between environments, as well as within a single environment due to seasonal climate and land use variability. We investigated the effect of the OM types and quantities through laboratory experiments using natural estuarine particles from the Mississippi Sound and Atchafalaya Bay as well as model mixtures of montmorillonite and organic molecules (i.e., biopolymers (guar/xanthan gums) and humic acid).

Results

Biopolymers promote flocculation but the magnitude depends on the types and quantities. Nonionic guar gum yields much larger flocs than anionic xanthan gum, while both of them exhibit a nonlinear behavior in which the flocculation is the most pronounced at the intermediate OM loading. Moreover, the effect of guar gum is independent of salinity whereas the effect of xanthan gum is pronounced at higher salinity. Meanwhile, humic acid does not affect flocculation at all salinity values tested in this study. These results are echoed in the laboratory manipulation of the natural estuarine particles. Flocculation of the humic acid-rich Mississippi Sound particles is unaffected by the OM, whereas that of biopolymer-rich Atchafalaya Bay particles is enhanced by the OM.

Conclusions

Flocculation is positively influenced by the presence of biopolymers that are produced as the result of marine primary production. Meanwhile, humic acid, which is abundant in the rivers that drain the agricultural soils of Southeastern United States, has little influence on flocculation. Thus, it is expected that humic acid-poor riverine particles (e.g., Mississippi River, and Atchafalaya River, to a lesser degree) may be prone to rapid flocculation and settling in the immediate vicinity of the river mouths when mixed with biopolymer-rich coastal waters. It is also expected that humic acid-rich riverine particles (e.g., Pearl River) may resist immediate flocculation and be transported further away from the river mouth.     

紊流对粘性细颗粒泥沙絮凝影响

以分形聚集生长模型为基础,通过三维模拟泥沙颗粒在布朗运动、重力沉降和紊流作用下的碰撞、粘结和破碎过程,探讨了紊流对粘性细颗粒泥沙絮凝速度、絮团平均粒径及分形维数的时空影响。试验结果表明:紊流作用下,泥沙絮凝及絮团平均粒径的变化可分为加速段、等速段和减速段,絮凝等速段的作用时间及粒径等速增长段的速度均随紊动强度呈先增后减的规律,且中部区域的絮凝速度和絮团平均粒径较小;泥沙絮团分形维数随水流紊动强度的增加逐渐增大,最终趋于稳定,随时间呈先减后增的规律。模拟空间下部区域分形维数最大,上部次之,中部最小。     

Flocculation Potential of Estuarine Particles: The Importance of Environmental Factors and of the Spatial and Seasonal Variability of Suspended Particulate Matter

Estuarine systems are complex environments where seasonal and spatial variations occur in concentrations of suspended particulate matter, in primary constituents, and in organic matter content. This study investigated in the laboratory the flocculation potential of estuarine-suspended particulate matter throughout the year in order to better identify the controlling factors and their hierarchy. Kinetic experiments were performed in the lab with a “video in lab” device, based on a jar test technique, using suspended sediments sampled every 2 months over a 14-month period at three stations in the Seine estuary (France). These sampling stations are representative of (1) the upper estuary, dominated by freshwater, and (2) the middle estuary, characterized by a strong salinity gradient and the presence of an estuarine turbidity maximum. Experiments were performed at a constant low turbulent shear stress characteristic of slack water periods (i.e., a Kolmogorov microscale >1,000 μm). Flocculation processes were estimated using three parameters: flocculation efficiency, flocculation speed, and flocculation time. Results showed that the flocculation that occurred at the three stations was mainly influenced by the concentration of the suspended particulate matter: maximum floc size was observed for concentrations above 0.1 g l⁻¹ while no flocculation was observed for concentrations below 0.004 g l⁻¹. Diatom blooms strongly enhanced flocculation speed and, to a lesser extent, flocculation efficiency. During this period, the maximum flocculation speed of 6 μm min⁻¹ corresponded to a flocculation time of less than 20 min. Salinity did not appear to automatically enhance flocculation, which depended on the constituents of suspended sediments and on the content and concentration of organic matter. Examination of the variability of 2D fractal dimension during flocculation experiments revealed restructuring of flocs during aggregation. This was observed as a rapid decrease in the floc fractal dimension from 2 to 1.4 during the first minutes of the flocculation stage, followed by a slight increase up to 1.8. Deflocculation experiments enabled determination of the influence of turbulent structures on flocculation processes and confirmed that turbulent intensity is one of the main determining factors of maximum floc size.     

Modeling the influence of settling velocity on cohesive sediment transport in Tanshui River estuary

Settling velocities of suspended cohesive sediment in estuaries vary over a range of several orders in magnitude. Variations in the suspended sediment concentration are often considered as the principal cause. Turbulence and the suspended sediment concentration, as well as other factors such as salinity, dissolved organic substances, flocculation ability, and the rate of floc growth affect setting velocities. A laterally–averaged finite difference model for hydrodynamics and cohesive sediment transport is developed and applied in the Tanshui River estuary, Taiwan. The model has been calibrated and verified with water surface elevation, longitudinal velocity, salinity, and cohesive sediment measured. The overall performance of the model is in qualitative agreement with the available data. The model is used to investigate the influence of settling velocity on cohesive sediment transport dynamics. The simulation indicates that the turbidity maximum zone is near Kuan–Du. When settling velocities increase the surface cohesive sediment concentration at Kuan–Du station trends to decrease and bottom cohesive sediment concentration increases. Both surface and bottom cohesive sediment concentrations decrease at Taipei Bridge and Pa–Ling Bridge. This implies that suspended sediment advected seaward and deposited. There is consequently a net seaward flux of suspended sediment near surface, and a net landward flux near the bed.     

Coagulation and transport of sediments in the Gironde Estuary

The distribution of suspended particle size and concentration were measured along the Gironde Estuary, France, from the river seaward to the ocean. The suspended particle size and volume concentration were measured using in situ holography and onboard optical techniques utilizing special procedures in order to avoid floc breakage. Sediments discharged by the rivers coagulate upon encountering the very low salinities (0.2‰ of the upper estuary (confirmed with laboratory experiments), and are then transported and deposited by currents in the remainder of the estuary. This coagulation, coupled with estuarine circulation, produces a turbidity maximum which is offset between the surface and bottom waters. The floc size maximum is oceanward of the turbidity maximum and is, likewise, offset along the estuary by about 30 km. The estuary can be subdivided into the following zones: (1) coagulation; (2) hydrodynamic, landward of the null point; and (3) hydrodynamic, seaward of the null point. Initial coagulation appears to be completed in coagulation zone (1), and particles are transported and settled (with very little floc breakage and recoagulation) in zones (2) and (3) only. The floc settling velocities, coupled with estuarine circulation, control the concentration and size distributions of flocs in the water column, and eventually control the deposition of sediments.     

Particulate matter grain-size characteristics and flocculation in a partially mixed estuary

The concentration and grain size of the natural and deflocculated inorganic suspended particulate matter were measured along the length of the Miramichi Estuary and interpreted with respect to flocculation and transport properties. Changes in particulate matter concentration are associated with regular changes in grain-size characteristics. In the turbidity maximum region of the estuary the suspended matter occurs mostly as large flocculated particles whereas, in the waters with lower particle concentrations, a larger proportion of the material occurs as fine material. At higher concentrations natural floc modes and inorganic grain modes vary simultaneously but at low concentrations the two modes vary inversely. This modal relationship and the variation in organic matter within the estuary is proposed to result from variation in inorganic—organic composition of flocs. Increase in settling rates due to flocculation is believed to increase the trapping effect of the estuarine circulation that produces the turbidity maximum.     

流态化多级速度梯度混凝反应对絮体的保护作用

多级速度梯度的建立理论上可为絮体的成长创造更理想的环境。目前对流化床混凝工艺的研究多是基于单级速度梯度开展的。以粒径为800 μm 和1 200 μm的树脂颗粒为固相,建立多级速度梯度流化床混凝装置,探讨絮体的成长与形态特征。研究结果表明：在单级速度梯度流化床混凝装置中,当以1 200 μm树脂颗粒为固相颗粒、混凝时间为50.3 s时,絮体发生破碎,混凝效率较混凝时间为41.8 s时降低3%;相同初始填充高度的多级速度梯度条件下,絮体尺寸随着混凝时间的延长而逐渐增加,由5.7 μm成长至70.0~75.0 μm,同时混凝效率也较单级速度梯度下提高了5%~10%。絮体之间的碰撞为絮体成长的主要模式。     

流化床混凝装置中多级速度梯度的建立及其对混凝反应的影响

利用不同性质颗粒在流化状态下可实现自然水力分级的特征,在流化床反应器中沿水流方向实现了多级速度梯度的建立。在研究流化床混凝反应器的混凝动力学特征基础上,探讨了以800 μm和1 200 μm树脂颗粒为固相的多级速度梯度流化床（MGF）的速度梯度分布特征、混凝效率和絮体形态特征,并与以1 200 μm树脂颗粒为固相的单级速度梯度流化床（SGF）进行了对比研究。结果表明：与单级速度梯度相比,多级速度梯度可为胶体或微颗粒的高效碰撞和絮体再增长创造更适宜的环境,有助于形成尺寸更大、密度更大的絮体,提高了絮体的可沉降性;MGF在处理人工配置的高岭土悬浊液和分散红染料废水时,混凝效率比SGF分别提高了2%～4%和7%～20%。     

Iron isotope systematics in estuaries: The case of North River, Massachusetts (USA)

Recent studies have suggested that rivers may present an isotopically light Fe source to the oceans. Since the input of dissolved iron from river water is generally controlled by flocculation processes that occur during estuarine mixing, it is important to investigate potential fractionation of Fe-isotopes during this process. In this study, we investigate the influence of the flocculation of Fe-rich colloids on the iron isotope composition of pristine estuarine waters and suspended particles. The samples were collected along a salinity gradient from the fresh water to the ocean in the North River estuary (MA, USA). Estuarine samples were filtered at 0.22 μm and the iron isotope composition of the two fractions (dissolved and particles) were analyzed using high-resolution MC-ICP-MS after chemical purification. Dissolved iron results show positive δ⁵⁶Fe values (with an average of 0.43 ± 0.04‰) relative to the IRMM-14 standard and do not display any relationships with salinity or with percentage of colloid flocculation. The iron isotopic composition of the particles suspended in fresh water is characterized by more negative δ⁵⁶Fe values than for dissolved Fe and correlate with the percentage of Fe flocculation. Particulate δ⁵⁶Fe values vary from −0.09‰ at no flocculation to ∼0.1‰ at the flocculation maximum, which reflect mixing effects between river-borne particles, lithogenic particles derived from coastal seawaters and newly precipitated colloids. Since the process of flocculation produces minimal Fe-isotope fractionation in the dissolved Fe pool, we suggest that the pristine iron isotope composition of fresh water is preserved during estuarine mixing and that the value of the global riverine source into the ocean can be identified from the fresh water values. However, this study also suggests that δ⁵⁶Fe composition of rivers can also be characterized by more positive δ⁵⁶Fe values (up to 0.3‰) relative to the crust than previously reported. In order to improve our current understanding of the oceanic iron isotope cycling, further work is now required to determine the processes controlling the fractionation of Fe-isotopes during continental run-off.     

Sediment deposition from flocculated suspensions

Suspended sediment in coastal environments with high inorganic content have characteristic broad size distributions and are composed of both single grains and flocculated aggregates. These flocculated suspensions have stable size distributions the modal size of which is dependent on the modal size of the deflocculated single grain distributions. Comparison between theoretical settling speeds of quartz grains and the settling speed of particles in natural suspensions indicates that most grains smaller than the deflocculated single grain mode settle as part of flocs, whereas the particles larger than the mode settle as single grains. As a result the size distribution curves of sediment populations which settle out during consecutive intervals are composed of a modal peak of larger grains and a low flat portion of smaller grains and resemble the asymmetrical non-normal curves common for muddy sediments.     

Flocculation and sedimentation in the ACE Basin, South Carolina

Extremely rapid deposition of fine-grained sediment has been observed near an artificially created channel between the Edisto and Ashepoo Rivers in South Carolina. Accumulation rates on the order of 0.05 m mo⁻¹ formed a region of fluid mud known as the Mud Reach that was present during a study carried out in May 1998. Subsequent surveys in March and May 1999 found no evidence of fluid mud in this area. Image analysis of photographs of the suspended sediment from 1998 showed that the water column was populated by flocs with a median diameter on the order of 0.3 mm which tended to remain in suspension over the tidal cycle, and flocs on the order of 0.8 mm which remained in the near bottom region except at maximum current speeds. In 1999, both the size and concentration of flocs at the surface remained the same, but the size and abundance of flocs near the bottom was reduced. Disaggregated inorganic grain size analysis of the suspension and samples from a core collected in the Mud Reach indicated that in 1998 the accumulation of material on the bottom was the result of floc settling and that in spite of highu _s values, little sorting of this material was occurring. Grain size analysis of samples deeper in the core showed that the rapidly floc-deposited mud was underlain by coarser, well-sorted sediment, confirming that the Mud Reach was a transient feature. The observed flocculation processes may play a significant role in the trapping of fine-grained sediment throughout this region.     

Mercury transformations and exchanges in a high turbidity estuary:: The role of organic matter and amorphous oxyhydroxides

The speciation and partition of mercury in a macrotidal estuary (Seine estuary, France) was studied in order to explore the role of the high turbidity zone (HTZ) in mercury transfer to the adjacent coastal waters. Water and particles were analyzed to determine the concentrations of various mercury species, including monomethylmercury and the inorganic fraction. The exchangeable particulate mercury, which varies with salinity, and the mercury fraction associated with the amorphous oxyhydroxides were evaluated. The distribution of dissolved mercury species during early mixing suggests non-conservative behavior of organically bound mercury at the head of the estuary. Mercury in the particles covaried positively with suspended particulate matter concentrations up to a threshold, which constitutes the typical mercury load of particles and deposited sediments of the HTZ. This distribution pattern is well explained by a dilution model: a slowly settling, low metal population of particle, characterized by relatively invariant turbidity, becomes admixed with a variable amount of higher metal content particles derived from the resuspension in the HTZ. In addition, in the HTZ, which acts as a degradation reactor for particulate organic matter, particulate mercury concentrations increase with increasing C:N ratios and amorphous oxyhydroxides particles. Mercury reaches the estuarine HTZ mainly associated with the riverine and marine particles, including organic matter and oxyhydroxides, which are temporarily trapped in the HTZ and mixed with autochthonous HTZ particles. The largest particles periodically settle and undergo diagenetic reactions and resuspensions, which lead to their mercury enrichment. Depending upon hydrodynamic conditions, mercury escapes seaward as fine particulate within the plume, partially associated with the oxyhydroxides. A surface complexation model reproduces most of the partitioning observed. In the dissolved phase the model simulation suggests that a very strong ligand must be present to explain the field observations.     

Treatment of Acid Mine Drainage (AMD) in South Brazil: Comparative active processes and water reuse

This work describes AMD techniques of neutralization, with lime, flocculation of the precipitates and comparative flocs/liquid separation by flotation with microbubbles or by lamellar settling (LS). The AMD treated water was characterized by its quality for recycling in terms of inorganic or organic elements, suspended or dissolved solids, among others. Two types of flocs were formed, “aerated” or not, in a special flocculation reactor, patented by this research group (RGF^®). Aerated flocs formed (within seconds) entered into contact with microbubbles under high shearing and raised-up at rates > 120 mh^− 1 allowing a rapid solid–liquid separation by flotation (HR-high rate), at about 13–15 m³m^− 2 h^− 1 loading capacity. Conversely, the non-aerated flocs settled at about 5–6 m h^− 1 in a lamella settler. Both AMD treatment techniques showed similar efficiencies (removal of ions > 90%) but the separation by lamella settling presented advantages, namely less reagents (no flotation collector required), lower power requirements and easier to operate. The operating costs (approximate values) of the AMD treatment by LS at pH 9 reaches about 0.3 US$ m^− 3 against 0.6 US$ m^− 3 for the HR-flotation process. Results found were proved to be similar to those found in recent ADM treatment installations in South Brazil. The quality of the treated water is fairly good, nearly free of heavy metals ion, low BOD (biological oxygen demand) and TOC (total organic content), low solids content and may be readily reused for irrigation, industrial processes and as wash water (among others, streets, vehicles, dust control). However, there is a need to extend the use of this treated water resource, but this, at least in Brazil, has not been legislated properly. It is concluded that this research will contribute in the discussion of this old and complex problem in acid mining effluents worldwide.     

Simple approach to estimate flocculent settling velocity in a dilute suspension

A new and simple approach for estimating the flocculent settling velocity of fine suspended particles is presented. The simplified formula has been derived based on a one-dimensional vertical continuity equation and an empirical flocculation equation. The resulting flocculent settling velocity (V_s) is expressed as a function of time, depth, and constants. Depth averaged settling velocity ( _s) is also derived by using the formula proposed. To estimate the order of magnitude of flocculent effects on settling, iso-settling velocity lines are constructed. The effects of initial concentration and ionic strength on flocculent settling velocity are investigated. The results show that as the ionic strength and suspension concentrations increase, flocculent settling velocity also increases due to inter-particle collisions and increased cohesion in suspension.     

盐腔内回填碱渣沉降固结特性室内试验研究

碱渣回填到充满卤水的废弃盐腔后,颗粒会自由沉降到盐腔底部形成沉积层,进而在自重作用下固结。为了解盐腔内回填碱渣的沉降固结特性,以江苏淮安地区碱渣为对象,进行了沉降柱试验和固结试验。试验结果表明:(1)碱渣在卤水中的沉降过程可以分为3个阶段:絮凝阶段、沉降阶段和固结阶段。初始浓度对碱渣的沉降曲线和沉降速率有很大的影响。(2)碱渣颗粒分布、密度、含水率和孔隙比均呈现出分层特性,颗粒粒径、密度随深度的增加而增大,含水率、孔隙比随深度的增大而减小。(3)碱渣具有很高的压缩性,压缩系数a1-2为3.36 MPa-1。在压力范围小于100 kPa下,固结系数随固结压力的增加而显著减小。试验结果对了解盐腔内回填碱渣的沉降固结特性提供了参考,有利于指导回填施工工艺和碱渣的后期处理。     

Distribution of nitrifying activity in the Seine River (France) from Paris to the estuary

The distribution of nitrification has been measured with the H¹⁴CO₃ ⁻ incorporation method in the Seine River and its estuary during summer conditions. The Seine River below Paris receives large amounts of ammonium through wastewater discharge. In the river itself, this ammonium is only slowly nitrified, while in the estuary nitrification is rapid and complete. We show that this contrasting behavior is related to the different hydrosedimentary conditions of the two systems, as nitrifying bacteria are associated with suspended particles. In the river, particles and their attached bacteria either rapidly settle or have a sestonic behavior. Because of the short residence times of the water masses, the slow growing nitrifying population has no time to develop sufficiently to nitrify the available ammonium. The estuary is characterized by strong tidal dynamics. Particles settle and are resuspended continuously with the strong current inversions of ebb and flood. As a result of these dynamics, particles and their attached nitrifying bacteria experience longer residence times in a temporary suspended state than the water masses themselves, providing to slow growing nitrifying bacteria the opportunity to develop a large population capable of nitrifying all the available ammonium.     

末次冰消期以来长江口沉积环境演化及沿岸流变化

长江口附近的沿岸流和水团变化对研究长江三角洲沉积物的“源-汇”机制具有重要意义.对HZK2孔沉积物的粒度、年龄和有孔虫分布特征进行了研究分析.结果表明:HZK2孔52.5 m以上有孔虫均有分布,底栖有孔虫丰度在12 m以上和26.0~52.5 m含量超过40枚/g,代表不同沿岸流和水团的有孔虫属种含量在垂向上呈现明显的分带性.HZK2孔全新世以来经历了河口湾和水下三角洲两大沉积体系,并在全新世早期发育潮流沙脊.末次冰消期,钻孔所在位置受长江冲淡水和苏北沿岸流共同影响.全新世早期,则受苏北沿岸流影响为主;在此之后,长江口冲淡水的作用减弱,苏北、黄海沿岸流影响较强.全新世中晚期,苏北沿岸流、长江冲淡水、江浙沿岸流和东海外海水团多种水体共同作用钻孔所在海域,全新世晚期长江冲淡水作用占绝对优势.      

Characteristics of alkenone distributions in suspended and sinking particles in the northwestern North Pacific

We investigated alkenones recorded in suspended particles and a settling particle time series collected at three stations, 40N (40°N, 165°E), KNOT (44°N, 155°E), and 50N (50°N, 165°E), in the northwestern North Pacific from December 1997 to May 1999. Emiliania huxleyi, the most abundant alkenone producer in this area, is present in surface to subsurface (to ∼50 m depth) waters. The alkenone concentrations recorded in the suspended particles indicated that the seasonal alkenone particle distribution differed significantly interannually. Alkenone export fluxes at the three sediment-trap stations ranged from 0.16 to 49.3 μg m⁻² day⁻¹, and the maximum export flux, which occurred in summer to fall (July-November), was associated with a high organic carbon export flux. The amount of alkenone produced during the maximum export season accounted for 60-80% of the total annual amount of alkenone, and the alkenones accumulated in the sediment below the traps had characteristics corresponding to subsurface waters during the summer-autumn season. Alkenone-derived temperatures recorded in suspended particles corresponded to the in situ temperature within ∼2 °C. Although alkenone-derived temperatures corresponded approximately to the temperatures observed in the stratified subsurface waters at the three trap stations during the high-export season, large differences were observed during the low-export (winter-spring) period. For example, the alkenone-derived temperatures observed at stations KNOT and 50N were much higher than the in situ subsurface temperatures reported in the World Ocean Atlas 2001. Relatively large differences between alkenone-derived temperatures and in situ temperatures in the subarctic might be due to (1) a low-light limitation or (2) contributions of allochthonous alkenones in particulate material transported from subtropical areas within a warm-core ring.     

三峡库区泥沙絮凝临界条件现场测量

三峡库区絮凝现象是细颗粒泥沙淤积的重要原因,泥沙絮凝临界条件对三峡库区泥沙淤积规律和模拟具有重要意义。在三峡库区忠县和奉节河段开展泥沙絮凝的现场测量,基于声学多普勒流速仪（Acoustic Doppler Velocimeter,ADV）和泥沙采样测得同步的瞬时流速和含沙量,通过泥沙扩散理论反算现场泥沙沉速及絮团粒径,得到了三峡库区泥沙絮凝度及其与粒径、流速和含沙量的关系。结果表明:库区细颗粒泥沙发生絮凝,且多为中轻度絮凝,重度絮凝较少;库区泥沙絮凝的临界粒径约为0.018 mm,临界流速约为0.7 m/s,临界含沙量约为0.8 kg/m3。研究结果可为三峡库区泥沙的运动规律以及泥沙淤积模拟等提供一定的理论支撑。