Oceanic methane layers: the hydrocarbon seep bubble deposition hypothesis

ABSTRACT Bubble plumes from hydrocarbon seeps drive upwelling flows in the water column that can disappear if the bubbles dissolve. This may lead to formation of a layer enriched in gases and substances transported by the bubbles, a process we term bubble deposition. A review of observed dissolved methane layers in the North Sea showed their existence in an area of active seeping pockmarks at a height of ∼ 20–30 m above the sea bed, well below the thermocline. To test the bubble deposition hypothesis, rising seep bubbles were simulated numerically. The model predicted a dissolution depth consistent with the observed methane layer for ∼ 2700-µm-radius bubbles. The model also predicted that bubbles smaller than 3400 µm dissolved subsurface, decreasing to 2000 µm for a 10-cm s⁻¹ upwelling flow. We speculate that this layer may be attractive to marine organisms. Although North Sea seeps are not oily, this mechanism also applies to oily bubbles from hydrocarbon seeps or a leaking undersea gas/oil pipeline. Thus bubble deposition can create a subsurface oil layer which rises far slower than either the bubble stream or droplets entrained in the stream.     

Effects of surfactant adsorption and surface forces on thinning and rupture of foam liquid films

The properties of thin liquid films (TLF) are of paramount significance for colloidal disperse systems, and a number of industrial processes, including froth flotation. In flotation, the bubble–particle attachment is controlled by the thinning and rupture of the intervening liquid film between an air bubble and a mineral particle. The froth evolution and its transient stability are also a function of the drainage and rupture of liquid films between air bubbles. Surface-active substances (surfactants) are used as flotation reagents to control the behavior of the liquid films. This paper presents a review of our research in the area of surfactant adsorption, surface forces and liquid films. It mainly focuses on the validation, application and extension of the Stefan–Reynolds theory on the liquid drainage. The extension of the Stefan–Reynolds theory comprises surface forces (disjoining pressure), surface tension variation, caused by the adsorption and diffusion of surfactants. Both the experimental and theoretical results are mostly related to the free (foam) films formed between two bubbles but can be principally extended to emulsion films between two oil drops and wetting films between an air bubble and a solid surface.     

喀斯特地区瀑布效应产生的自然水软化过程

在喀斯特地区,水流过瀑布后硬度会发生降低,这种现象一般称为瀑布效应,其中包括汽化,射流和低压作用。瀑布效应会引起两种河水物理性质的变化,即气水界面面积和涡流的增加。为了弄清瀑布效应和这些物理性质变化是否会减少水的硬度,本研究设计并进行了一系列的试验。通过改变气水界面面积试验,发现界面面积越大,导电率降低的速率越快,由此造成Ca2+的沉淀。利用自行设计的气泡生成器进行试验,发现有气泡发生的地方,水的硬度降低很快。试验还发现,从射流器喷出的超饱和溶液的硬度快速减小,而pH值增大。鸭河和滴水岩瀑布的实际观测证实,有汽化现象发生的地方,水的硬度降低很快,钙沉淀的平均速率也最高。     

煤层气排采非饱和流阶段煤粉–气泡耦合作用机理

揭示煤层气排采储层非饱和流阶段煤粉与气体相互作用机理,对制定排采制度和提高产气量具有重要意义。通过气泡–煤粉微观作用实验装置,系统开展了不同直径大小的气泡对不同粒度和密度煤粉的作用实验,分析了气泡对煤粉运移轨迹和速度的影响及捕获煤粉特征。结果表明,气泡产出能够影响煤粉的运移轨迹,甚至能够捕获煤粉;煤粉通过气泡时会产生3种运动类型：沿着气泡表面运移到气泡底部最后被捕获、沿着气泡表面运移到气泡底部最后脱落及接近气泡时被排斥而轨迹发生偏转。煤粉若被气泡捕捉,则运动速度呈现出减小–增大–减小的变化特征;若未被气泡捕获,速度呈现出减小–增大–减小–增大的变化特征。不同条件下气泡对煤粉的捕获效率高达64.38%～86.64%;在气泡表面最高点附近发生碰撞煤粉被捕获的概率最大,并且随着偏离角度的增大,气泡捕获效率均呈现出逐渐减小的趋势;在相同的碰撞位置下,气泡对煤粉的捕获效率随着煤粉密度、煤粉粒径的增大而减小,随着气泡直径的增大而增大。煤层气产气初期应根据储层的实际导流能力合理控制降压速率,若储层导流能力较强,应加大排采速率,增大气体解吸对煤粉的扰动和捕获作用,促使大量煤粉随地下水或气泡产出;若储层...     

边坡虹吸排水管内空气积累原因及应对措施

坡体地下水位上升是诱发滑坡的重要因素,实时排出地下水是防治边坡地质灾害的有效手段。虹吸排水具有免动力和流动过程由液位变化自动控制的物理特性,可满足实时排出坡体地下水的需要,但虹吸管中空气积累会导致虹吸过程中断,制约了边坡虹吸排水技术的推广应用。溶解于水的空气因虹吸管内压力降低而释出是形成气泡的物理基础。实验结果表明,虹吸进水口水面以上垂直高度3.5 m以上就会出现大量气泡,经过虹吸顶点后,气泡发生强烈的兼并形成大气泡。当虹吸管的进出水口的水头差较大时,气泡间的水弹容易推动气泡从出水口排出。当虹吸管直径大于5 mm时,缓慢的虹吸流动,会发生管内气泡的积累,最终破坏虹吸过程;虹吸管的直径小于4 mm时,可以形成基本稳定的弹状流。因此,为保持边坡虹吸过程长期有效,经常性降雨并且坡体地下水丰富的地区可选用直径为5 mm的虹吸管,非经常性降雨的地区应选择小于等于4 mm的虹吸管。     

Growth of disk-shaped bubbles in sediments

Disc-shaped methane bubbles, often observed in marine sediments, result from growth in a medium that elastically resists expansion of the bubbles and yields by fracture. We have modeled this process to obtain estimates of growth times by using a reaction-diffusion model coupled to a linear elastic fracture mechanics (LEFM). For comparison, we also modeled the growth of a constant eccentricity bubble in a nonresistant medium. Discoidal bubbles that grow in sediments that obey LEFM grow much faster than spherical bubbles (two- to fourfold faster for the times and conditions tested here) and become more eccentric with time (aspect ratios falling from 0.3 to 0.03 over 8 d of growth). In addition, their growth is not continuous but punctuated by fracture events. Furthermore, under some conditions, LEFM predicts that bubble growth can become arrested, which is not possible for a bubble in a nonresistant medium, even for nonspherical bubbles. Cessation of growth occurs when the dissolved gas concentration gradient near the bubble surface disappears as a result of the increase in bubble gas pressure needed to overcome sediment elasticity.     

Segregating gas from melt: an experimental study of the Ostwald ripening of vapor bubbles in magmas

Diffusive coarsening (Ostwald ripening) of H₂O and H₂O-CO₂ bubbles in rhyolite and basaltic andesite melts was studied with elevated temperature–pressure experiments to investigate the rates and time spans over which vapor bubbles may enlarge and attain sufficient buoyancy to segregate in magmatic systems. Bubble growth and segregation are also considered in terms of classical steady-state and transient (non-steady-state) ripening theory. Experimental results are consistent with diffusive coarsening as the dominant mechanism of bubble growth. Ripening is faster in experiments saturated with pure H₂O than in those with a CO₂-rich mixed vapor probably due to faster diffusion of H₂O than CO₂ through the melt. None of the experimental series followed the time^1/3 increase in mean bubble radius and time⁻¹ decrease in bubble number density predicted by classical steady-state ripening theory. Instead, products are interpreted as resulting from transient regime ripening. Application of transient regime theory suggests that bubbly magmas may require from days to 100 years to reach steady-state ripening conditions. Experimental results, as well as theory for steady-state ripening of bubbles that are immobile or undergoing buoyant ascent, indicate that diffusive coarsening efficiently eliminates micron-sized bubbles and would produce mm-sized bubbles in 10²–10⁴ years in crustal magma bodies. Once bubbles attain mm-sizes, their calculated ascent rates are sufficient that they could transit multiple kilometers over hundreds to thousands of years through mafic and silicic melt, respectively. These results show that diffusive coarsening can facilitate transfer of volatiles through, and from, magmatic systems by creating bubbles sufficiently large for rapid ascent.     

Sub-sea-floor metamorphism,heat and mass transfer; an additional comment

Attention is drawn to the fact that the warm geothermal brines of Matupi Harbour (New Britain) are of sea water origin, contain amounts of total dissolved solids comparable to those in sea water, but are remarkably enriched in heavy metals (Ferguson and Lambert, 1972). This evidence supports the proposal that metal enriched brines, of sea water origin, may be generated in sub-sea-floor geothermal systems by a high temperature leaching process, and may form a metal enriched sedimentary component on discharge back into sea water (Spooner and Fyfe, 1973).The chloride contents of the Matupi Harbour brines are low, relative to other known hydrothermal solutions which carry comparable amounts of heavy metals in solution. This evidence indicates that high dissolved chloride contents of the order of 160000 ppm, compared with sea water which contains 19800 ppm, are not a prerequisite for a high metal carrying capacity in natural brines.     

Bubble growth in slightly supersaturated albite melt at constant pressure

Bubble growth experiments were performed in a piston-cylinder by hydrating albite melt with ∼11 wt.% H₂O at 550 MPa followed by rapid decompression at 1 MPa s⁻¹ to pressures of 450 or 400 MPa. At these conditions the melt was supersaturated with ∼0.5 or ∼1.5 wt.% H₂O, respectively, which caused rapid exsolution and bubble growth. Results at 1200 °C demonstrate that portions of the initial cumulative bubble-area distributions may be characterized by a power law with an exponent near 1, but they rapidly evolve to exponential distributions and approach a unimodal distribution after 32 h of growth. This evolution occurs by the growth of larger bubbles at the expense of smaller ones. The growth rate of the average bubble radius in these experiments is described by a power law whose exponent is 0.35, close to the theoretical exponent of 1/3 for phase growth in which coalescence is dominated by Ostwald ripening of the bubbles. Over the range of pressures and water contents investigated at 1200 °C, the bubble-size distributions and growth rate are not significantly affected by changes in the amount of exsolved water or by splitting the decompression path into two steps. Similar decompression experiments at 800 °C are dominated by smaller bubbles than in the 1200 °C experiments and also demonstrate exponential cumulative size distributions, but consistently contain a small fraction of larger bubbles. The growth rate of these bubble radii cannot be fit with a power law, but a logarithmic dependence of the bubble radii on time is possible, suggesting a difference in the growth mechanisms at low and high temperatures. This difference is attributed to the orders of magnitude changes in melt viscosity and water diffusion in the melt as the temperature varies from 800 to 1200 °C. At 1200 °C the transport properties of albite melt resemble those of natural basaltic melts whereas at 800 °C the properties are similar to those of andesitic to dacitic melts. The decompression rate used in this study exceeds natural rates by one to two orders of magnitude. Thus, these results indicate that natural mafic-to-intermediate magmas supersaturated with only a small excess of water should easily nucleate bubbles during ascent and that bubble growth in mafic magmas will proceed much more rapidly than in andesitic to dacitic magmas. Intermediate composition magmas also may be capable of forming bimodal bubble-size distributions even in the case when only one nucleation event occurred. The rapid evolution of the bubble-size distribution from a power law to an exponential may be useful in constraining the time duration between bubble nucleation and the quenching of natural samples.     

Correlation of shape and size of methane bubbles in fine-grained muddy aquatic sediments with sediment fracture toughness

Gassy sediments contribute to destabilization of aquatic infrastructure, air pollution, and global warming. In the current study a precise shape and size of the buoyant mature methane bubble in fine-grained muddy aquatic sediment is defined by numerical and analytical modeling, their results are in a good agreement. A closed-form analytical solution defining the bubble parameters is developed. It is found that the buoyant mature bubble is elliptical in its front view and resembles an inverted tear drop in its cross-section. The size and shape of the mature bubble strongly correlate with sediment fracture toughness. Bubbles formed in the weaker sediments are smaller and characterized by a larger surface-to-volume ratio that induces their faster growth and may lead to their faster dissolution below the sediment–water interface. This may prevent their release to the water column and to the atmosphere. Shapes of the bubbles in the weaker sediments deviate further from the spherical configuration, than those in the stronger sediments. Modeled bubble characteristics, important for the acoustic applications, are in a good agreement with field observations and lab experiments.     

Investigation on foaming properties of some organics for oily bubble bitumen flotation

Studies have shown that using organic coated bubbles (“oily” bubbles) could increase bitumen recovery rate in flotation. One way to coat bubbles is that used in the air-assisted solvent extraction process where solvent foam is formed and injected through a capillary to release solvent coated bubbles in a controlled manner into the aqueous system. To investigate adapting this approach, the foaming properties of some organics (Hexane, Heptane, Hexadecane, Petroleum Ether, Toluene, Benzene and Kerosene and their binary mixtures) of potential interest in oily bubble bitumen flotation were investigated. Silicone oil was found to be a good foaming agent in some cases. Bubble stability and film thickness experiments were carried out to help select candidate organics. Surface tension and dynamic viscosity measurements were conducted to examine the mechanism of foaming. Attachment studies showed that droplets of the selected organics readily attached to a bitumen surface compared to air bubbles. From a combination of criteria, 25:75 Hexadecane/Heptane appears to be a promising candidate.     

海洋飞沫及其对海—气相互作用影响的研究进展

按照海水滴生成机制和粒径大小,由海浪破碎生成的海洋飞沫分为膜滴、射滴和裂滴三大类,较小的海水滴在大气中滞留时间长,成为云的凝结核,对长期气候变化有重要影响,较大的海水滴参与海—气界面动量和热量交换过程,有利于热带气旋的形成和发展。海洋飞沫的生成与海上风速、海浪、海流和大气稳定度等因素有关,但由于缺乏观测数据,刻画海洋飞沫效应的关键物理量——海洋飞沫生成函数通常用海上风速进行参数化,忽略其他因素的影响,彼此间的差异非常大,给研究海洋飞沫对气候和海—气相互作用的影响造成困难,需要进一步开展海洋飞沫的观测,考虑风速之外的其他因素对海洋飞沫生成函数的作用,改进海洋飞沫热量和动量效应的参数化方案,进而阐明海洋飞沫对气候和海—气相互作用的影响。     

Magnetite scavenging and the buoyancy of bubbles in magmas. Part 1: Discovery of a pre-eruptive bubble in Bishop rhyolite

Little is known about the presence, distribution and size of bubbles in rhyolitic magmas prior to eruption. Using X-ray tomography to study pumice from early-erupted Bishop rhyolite, we discovered a large vesicle with abundant magnetite crystals attached to its walls. Attachment of magnetite crystals to bubble walls under pre-eruptive conditions can explain the cluster of magnetite crystals as a result of bubbles rising and collecting magnetite crystals. Alternatively, bubbles may have nucleated on magnetite crystals and then coalesced to form one large bubble with multiple magnetite crystals attached to it. We argue that the clusters of magnetite crystals could not have formed during or after eruptive decompression, and conclude that this vesicle corresponds to a bubble present prior to eruptive decompression. The inferred presence of pre-eruptive bubbles in the Bishop magma confirms the interpretation that the magma was volatile-saturated prior to eruption. The pre-eruptive size of this bubble is estimated based on three independent approaches: (1) the current size of the vesicle, (2) the total cross-sectional area of the magnetite crystals, and (3) the bubble size required for the aggregate to be neutrally buoyant. These approaches suggest a pre-eruptive bubble 300–850 μm in diameter, with a preferred value of 600–750 μm. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Atmochemical mercury dispersion aureoles over active geologic structures of the northern Sea of Japan

In the autumn of 2010, contrasting dispersion aureoles of atomic mercury were revealed in the northern Sea of Japan, in the vicinity of the Vityaz’ and Alpatov Rises. Based on the elimination method, the assumption is made that the aureoles resulted from the supply of mercury from hydrothermal or water-gas bottom sources through the sea water column, either in gas bubbles or as a result of diffusion and turbulent mixing. It is inferred that gas-mercury measurements can be used in geological research in sea water areas.     

Flotation and dispersal of eelgrass seeds by gas bubbles

The formation of gas bubbles byZostera marina immediately prior to seed release is described together with evidence for its role as a seed dispersal mechanism. The gas bubbles, ranging in volume from 1.1 to 3.4 mm³, escape from the funiculus and adhere to the seed coat. As a bubble expands, the seed is pushed clear of the ovary and rises to the water surface with the bubble attached. Field data suggest that approximately 5–13% of the seeds produced are released with gas bubbles, and in some cases are transported more than 200 m (float time≥40 min).     

淮南丁集煤矿A组煤中稀土元素地球化学特征

采用电感耦合等离子质谱（ICP—MS）对淮南丁集煤矿A组煤18个煤样、9个顶底板样品中稀土元素进行测试分析,研究了稀土元素的含量变化及其地球化学特征。结果表明：丁集煤矿A组煤稀土元素相对富集。其中元素Tm是邻区淮北煤和中国煤中近10倍。且LREE明显富集,HREE相对亏损,既较明显的负异常,说明成煤沼泽环境受海水影响较大,且1煤到3煤受海水影响逐渐减弱。     

A contribution to physicochemical conditions for the formation of syngenetic sulfide ores

The results of thermodynamic calculations demonstrate that the pH and Eh values for bottom sea water enriched in organic matter tend to decrease drastically as a result of bacterial reduction of sulfates in sea water. Syngenetic sulfide ore beds associated with the Jiashengpan strata-bound Pb-Zn-S ore deposit are believed to have been precipitated under the conditions of pH varying from 7.08 to 7.17 and Eh from −0.232 to −0.418V. It is established that in the reducing system in sea water where reduction of sulfates by anaerobic bacteria took place, paleosalinity is an important factor affecting pH and Eh changes and controlling the formation of sulfide ore beds. The present study shows that the quantitative evaluation of physicochemical conditions can be effected from thermodynamic calculations on the basis of geochemical data.     

黄铁矿叠层石丘堆式沉积与块状硫化物的富集作用

通过对黄铁矿叠层石组构、成分、微量元素、硫同位素、分子生物标志物与产出的构造环境背景的研究可知 ,黄铁矿叠层石的形成是通过沿同生断裂上升喷溢入海的热流体长期脉动作用 ,构成栖息在热水喷口与热液丘堤周围的嗜热微生物群落生存的食物链基础 ,使嗜热微生物围绕热水喷口繁殖的结果。沿同生断裂上升喷溢入海的热流体长期脉动过程中不断吸附、富集成矿元素 ,并将海水中的硫酸盐还原为H2 S。微生物吸附的Fe2 + 与S2 -作用 ,形成黄铁矿叠层石。微生物群落在热水喷口与丘堤附近不均衡发展 ,产生了成矿带内块状硫化物矿床中的黄铁矿叠层石丘堆。这种黄铁矿叠层石丘堆体是寻找富矿的显著标志 ,具有重要的成因与找矿意义