Alkaline Fluids Research Articles

An experimental study of basaltic glass–H2O–CO2 interaction at 22 and 50 °C: Implications for subsurface storage of CO2

A novel high pressure column flow reactor was used to investigate the evolution of solute chemistry along a 2.3m flow path during pure water- and CO2-charged water–basaltic glass interaction experiments at 22 and 50°C and 10−5.7 to 22bars partial pressure of CO2. Experimental results and geochemical modelling showed the pH of injected pure water evolved rapidly from 6.7 to 9–9.5 and most of the iron released to the fluid phase was subsequently consumed by secondary minerals, similar to natural meteoric water–basalt systems. In contrast to natural systems, however, the aqueous aluminium concentration remained relatively high along the entire flow path. The aqueous fluid was undersaturated with respect to basaltic glass and carbonate minerals, but supersaturated with respect to zeolites, clays, and Fe hydroxides. As CO2-charged water replaced the alkaline fluid within the column, the fluid briefly became supersaturated with respect to siderite. Basaltic glass dissolution in the column reactor, however, was insufficient to overcome the pH buffer capacity of CO2-charged water. The pH of this CO2-charged water rose from an initial 3.4 to only 4.5 in the column reactor. This acidic reactive fluid was undersaturated with respect to carbonate minerals but supersaturated with respect to clays and Fe hydroxides at 22°C, and with respect to clays and Al hydroxides at 50°C. Basaltic glass dissolution in the CO2-charged water was closer to stoichiometry than in pure water. The mobility and aqueous concentration of several metals increased significantly with the addition of CO2 to the inlet fluid, and some metals, including Mn, Cr, Al, and As exceeded the allowable drinking water limits. Iron became mobile and the aqueous Fe2+/Fe3+ ratio increased along the flow path. Although carbonate minerals did not precipitate in the column reactor in response to CO2-charged water–basaltic glass interaction, once this fluid exited the reactor, carbonates precipitated as the fluid degassed at the outlet. Substantial differences were found between the results of geochemical modelling calculations and the observed chemical evolution of the fluids during the experiments. These differences underscore the need to improve the models before they can be used to predict with confidence the fate and consequences of carbon dioxide injected into the subsurface.

Turbulent acidic jets and plumes injected into an alkaline environment

AbstractThe characteristics of an acidic turbulent jet and plume injected into an alkaline environment are examined theoretically and experimentally. Fluid-flow and chemistry models are combined to understand how the concentration of acid in a parcel of fluid changes as it reacts with alkaline fluid entrained from the ambient. The resulting model is tested in an experimental study in which nitric acid jets or plumes are injected into a large tank containing a variety of alkaline substances. A video camera records a pH-sensitive dye in the jet or plume, which changes colour with variations in the pH. The results were time averaged and processed to measure distance from the source to the point of neutralization. The agreement between predictions and observations of neutralization distances is good, confirming that the model captures the salient physics of the problem. Using empirically determined titration curves, a combined fluid flow and chemistry model is applied to discuss the environmental implications of a warm acidic turbulent plume injected into an alkaline river or sea.

Assessment of environmental controls on acid‐sulfate alteration at active volcanoes in Nicaragua: Applications to relic hydrothermal systems on Mars

A variety of secondary mineralogies has been detected on Mars from both orbiters and landers, indicating widespread aqueous alteration of the crust. Many of these locales exhibit sulfates, which in some cases imply acidic fluids. At present, there are few constraints on the paleoenvironmental conditions that existed during formation of the widespread and diverse classes of secondary minerals on Mars. We investigated hydrothermal systems at three active acidic volcanic systems in Nicaragua, including Cerro Negro, Momotombo, and Telica. The recently erupted materials are similar in composition to the Martian crust and are undergoing extensive acid‐sulfate alteration predominately in gas‐dominated settings (fumaroles). We characterized the secondary mineralogy and local variables, including temperature, pH, rock and gas composition, and fluid‐rock ratio. We find that these environmental parameters exhibit strong controls on the alteration mineralogy. The environments studied include pH that ranged from −1 to 6, temperatures from ambient to hundreds of degrees Celsius, and fumaroles to hot springs. The hottest and most acidic systems contained sulfur, silica, and minor gypsum, while moderately acidic and cooler fumaroles included abundant silica, gypsum and other hydrated sulfates, and phyllosilicates. A setting with a higher fluid‐rock ratio but similar temperature and acidity was dominated by phyllosilicates and, to a lesser degree, sulfates. The characterization of aqueous alteration of basalts under a variety of environmental conditions provides a conceptual framework for interpretation of similar relic environments on Mars. Finally, while identification of phyllosilicates on Mars is generally thought to require neutral to alkaline fluids, we documented significant formation of these minerals in the acidic volcanic systems.

Magnets in the GI tract

Magnets in the GI tract

Amethyst occurrences in Tertiary volcanic rocks of Greece: mineralogical and genetic implications

Epithermal-altered volcanic rocks in Greece host gem-quality amethyst veins in association with various silicates, carbonates, oxides, sulfides and halides. Host rocks are Oligocene to recent calc-alkaline to shoshonitic lavas and pyroclastics of intermediate- to acid composition. The amethyst-bearing veins occur in the periphery of porphyry-type and/or high-sulfidation epithermal mineralized centers in northern Greece (e.g. Sapes, Kirki, Kornofolia/Soufli, Lesvos island) and on Milos island in the active Aegean Volcanic Arc. Hydrothermal alteration around the quartz veins includes sericitic, K-feldspar (adularia), argillic, propylitic and zeolitic types. Precipitation of amethyst in the northern Greece occurrences, took place during the final stages of the magmatic-hydrothermal activity from near-neutral to alkaline fluids, as indicated by the presence of gangue adularia, calcite, smectite, chlorite, sericite, pyrite, zeolites (laumontite, heulandite, clinoptilolite), analcime and minor amounts of barite, halite, epidote and fluorite in the quartz veins. Amethyst at Milos Island (Chondro Vouno and Kalogries-Vani areas), is accompanied by barite, smectite and lepidocrocite. Colloform-crustiform banding with alternations of amethyst, chalcedony and/or carbonates is a common characteristic of the studied amethyst-bearing veins. Fluid inclusion- and mineralogical data suggest that the studied amethyst were formed at: 174-246 °C (Sapes area), 100-175 °C (Kirki and Kornofolia areas) and 223-234°C (Lesvos island). The amethyst formation requires oxidizing conditions and is probably the result of mixing between meteoric or seawater with upwelling hydrothermal fluids. The involvement of seawater in the studied mineralization is supported by the presence of halite and abundant barite in the veins. Finally, the studied amethyst deposits should be evaluated as potential gemstone sources in Greece.

Precipitation of chlorite-like structures during OPC porewater diffusion through compacted bentonite at 90 °C

The reactivity between concrete and bentonite is a key issue in the performance of a deep geological repository for radioactive waste. The long-term reaction of alkaline solutions representative of early and late stages of concrete degradation (K–Na–OH, pH 13.5, and Ca–OH, pH 12.5, synthetic solutions) was studied by diffusion experiments with compacted bentonite columns at 90°C. Relevant mineralogical alterations were produced with the K–Na–OH solution and consisted mainly of the precipitation of a non-expandable 14.4–7.4Å chlorite-like phase at the alkaline interface and through the first 2–3mm. The chlorite-like phase, a non-swelling layer silicate, was characterized as a brucite–montmorillonite complex produced by a brucite monolayer intercalation in the montmorillonite interlayer and its predicted formation would thus impact upon the safety functions of the bentonite buffer. The precipitation of discrete brucite was not significant, being this, the main difference found in comparison with previous studies at temperatures lower than 90°C. The high intensity of the 7.4Å X-ray diffraction peak, in the absence of iron components, and the rise of new hk0 trioctahedral bands, determined by X-ray diffraction and electron diffraction on plate-like mineral aggregates, indicate the possible formation of new Mg-layer silicates, although they were not clearly defined. In contrast to K–Na–OH experiments, mineralogical alterations with the Ca–OH solution were almost non-existent, including insignificant changes in the Ca/Mg cation exchange distribution. The buffer capacity of the bentonite against the migration of alkaline fluids is driven by mineralogical reactions affecting a few millimeters thickness from the alkaline solution–bentonite interface. The nature of these reactions is critically affected by the temperature change within the expected designed conditions for radioactive waste repositories.

Sources and cycling of carbon in continental, serpentinite-hosted alkaline springs in the Voltri Massif, Italy

Active serpentinization systems are abundant on present-day Earth and are of increasing interest because water–rock reactions lead to alkaline, Ca–OH fluids that have the potential to sequester CO2 and form reduced chemical species (e.g. CH4 and H2) that can support chemolithoautotrophy. We present a study of alkaline (pH 10–12) springs in the Voltri Massif (Italy) that focuses on the sources and cycling of inorganic carbon in the basement rocks, the interacting fluids, and the resulting surface carbonate deposits. Most springs are located in mantle rocks that underwent varying degrees of ocean-floor serpentinization and incorporation of carbon (as carbonate and organic carbon) in the Jurassic, which is preserved during subsequent subduction and uplift onto the continent.The springs are fed by meteoric water that evolves into alkaline, Ca-rich spring waters that have 2–3 times higher Ca concentrations than the adjacent rivers. Our study is consistent with previous reaction path modeling and identifies the formation of clay minerals in serpentinites that have been altered by alkaline fluids. These strongly altered basement rocks contain up to 2wt.% C in the shallow subsurface, also documented by the presence of late calcite veins. Concentrations of dissolved inorganic carbon (DIC) of the alkaline fluids are generally low (<16μmol/L) and δ13CDIC is between −24.2‰ and +1.3‰. We argue that the concentrations and isotopic composition of the DIC in the alkaline waters provide evidence for 1) the precipitation of calcium carbonate under closed-system conditions with respect to atmospheric CO2 and 2) removal of DIC by microbial activity in the subsurface. Late-stage uptake of atmospheric CO2 in the shallow subsurface or at the exit sites subsequent to water–rock–microbe interactions in the basement result in fluids with lower pH and Ca, and enrichment in DIC and 13C. At the surface, interaction of the high pH, Ca–OH fluids with atmospheric CO2 causes precipitation of carbonates as travertines or crusts on the basement rocks, storing CO2 as calcium carbonate. Carbonate precipitation at the exit sites is strongly dominated by kinetic processes leading to carbon and oxygen isotope compositions as low as −27.2‰ and −18.7‰, respectively. With increasing distance from the springs, the 13C and 18O content of the carbonate increases and the fluid pH changes towards neutral. Our study shows that surficial carbonate precipitation plays a subordinate role in carbon sequestration, but that the evolution from Mg–HCO3 spring waters to Ca–OH waters removes significant amounts of carbon, presumably in the subsurface. We calculate that the serpentinites have the capacity to sequester up to 0.50 to 2.05×109mol carbon per year and conclude that they can take up significantly more CO2 than they currently contain.

Serpentinization and carbon sequestration: A study of two ancient peridotite-hosted hydrothermal systems

Fluid circulation in peridotite-hosted hydrothermal systems influences the incorporation of carbon into the oceanic crust and its long-term storage. At low to moderate temperatures, serpentinization of peridotite produces alkaline fluids that are rich in CH4 and H2. Upon mixing with seawater, these fluids precipitate carbonate, forming an extensive network of calcite veins in the basement rocks, while H2 and CH4 serve as an energy source for microorganisms. Here, we analyzed the carbon geochemistry of two ancient peridotite-hosted hydrothermal systems: 1) ophiolites cropping out in the Northern Apennines, and 2) calcite-veined serpentinites from the Iberian Margin (Ocean Drilling Program (ODP) Legs 149 and 173), and compare them to active peridotite-hosted hydrothermal systems such as the Lost City hydrothermal field (LCHF) on the Atlantis Massif near the Mid-Atlantic Ridge (MAR).Our results show that large amounts of carbonate are formed during serpentinization of mantle rocks exposed on the seafloor (up to 9.6wt.% C in ophicalcites) and that carbon incorporation decreases with depth. In the Northern Apennine serpentinites, serpentinization temperatures decrease from 240°C to <150°C, while carbonates are formed at temperatures decreasing from ~150°C to <50°C. At the Iberian Margin both carbonate formation and serpentinization temperatures are lower than in the Northern Apennines with serpentinization starting at ~150°C, followed by clay alteration at <100°C and carbonate formation at <19–44°C. Comparison with various active peridotite-hosted hydrothermal systems on the MAR shows that the serpentinites from the Northern Apennines record a thermal evolution similar to that of the basement of the LCHF and that tectonic activity on the Jurassic seafloor, comparable to the present-day processes leading to oceanic core complexes, probably led to formation of fractures and faults, which promoted fluid circulation to greater depth and cooling of the mantle rocks. Thus, our study provides further evidence that the Northern Apennine serpentinites host a paleo-stockwork of a hydrothermal system similar to the basement of the LCHF. Furthermore, we argue that the extent of carbonate uptake is mainly controlled by the presence of fluid pathways. Low serpentinization temperatures promote microbial activity, which leads to enhanced biomass formation and the storage of organic carbon. Organic carbon becomes dominant with increasing depth and is the principal carbon phase at more than 50–100m depth of the serpentinite basement at the Iberian Margin. We estimate that annually 1.1 to 2.7×1012g C is stored within peridotites exposed to seawater, of which 30–40% is fixed within the uppermost 20–50m mainly as carbonate. Additionally, we conclude that alteration of oceanic lithosphere is an important factor in the long-term global carbon cycle, having the potential to store carbon for millions of years.

Long-lived LREE mobility in the cratonic, rift and foredeep to foreland sedimentary cover at the western margin of the Karelia Province

The western margin of the Karelia Province of the Fennoscandian Shield consists of Archean crust covered by remnants of Paleoproterozoic (c. 2.5–1.9Ga) metasedimentary rocks. The study area in the eastern part of the margin shows 2.3–2.1Ga cratonic sedimentation followed by 2.1–2.05Ga rift sedimentation and c. 1.91–1.92Ga foredeep to foreland sedimentation related to continent–arc/continent collision. Extreme LREE mobility (loss up >95% of La) is recorded by many samples from these units. Monazite, bastnäsite and, in some cases, allanite have been the prealteration LREE host phases in the LREE depleted samples. Monazite was altered to Th-silicates with variable loss of the LREE, the remaining part of which was incorporated in Th-poor monazite.The depositional age of the sedimentary units was studied by dating (LA-MC-ICPMS) detrital zircon grains, and the age of LREE mobility by dating monazite and xenotime and by whole-rock Sm–Nd modeling. The maximum deposition age of the foredeep to foreland basin is 1.91–1.92Ga based on detrital zircon data and the minimum age of the main foliation in the study area is 1.87–1.86Ga based on the younger age limit of late-to post-tectonic xenotime and the ages of few probable metamorphic zircons. Coeval bastnäsite, with xenotime in a LREE enriched sample, suggests that this was also one important stage of LREE mobility. Monazite crystallizations have occurred 1.76–1.78Ga ago while the Rb–Sr whole rock data suggest that the closure of this isotope system took place 1732±21Ma ago. The Sm–Nd modeling gives ages at 0.4–1.0Ga for LREE depletion. The Sm–Nd age of 412±27Ma can be considered as the age of the latest major LREE depletion event.We propose that alkali-bearing oxidizing fluids started to form in the cratonic sequences due to diagenetic reactions maybe as early as 2.3–2.1Ga. Alkalinity of fluids was later increased by interaction with alkaline 2.05Ga source materials before and during the c. 1.91–1.92Ga foredeep to foreland basin stage. Basin inversion and metamorphic crystallization occurred at 1.91–1.87Ga. Episodes of fluid migration at 1.78–1.73Ga and afterwards were focused along fracture zones and in microfracture networks. The 0.4Ga stage is the most prominent of the <1.7Ga events and is best explained by assuming shield-scale foreland basin related to the Caledonian orogenic front, causing heat redistribution and also fluid circulation in the underlying crystalline basement. The 2.1Ga formed marginal fault has been a very important shield-scale tectonic element and a pathway for fluid circulation for almost 2billion years.

The Cystic Fibrosis of Exocrine Pancreas

The cystic fibrosis transmembrane conductance regulator (CFTR) protein is highly expressed in the pancreatic duct epithelia and permits anions and water to enter the ductal lumen. This results in an increased volume of alkaline fluid allowing the highly concentrated proteins secreted by the acinar cells to remain in a soluble state. This work will expound on the pathophysiology and pathology caused by the malfunctioning CFTR protein with special reference to ion transport and acid-base abnormalities both in humans and animal models. We will also discuss the relationship between cystic fibrosis (CF) and pancreatitis, and outline present and potential therapeutic approaches in CF treatment relevant to the pancreas.

Protein phosphatase 1 coordinates CFTR‐dependent airway epithelial HCO3− secretion by reciprocal regulation of apical and basolateral membrane Cl−‐HCO3− exchangers

Our recent studies on human airway serous-like Calu-3 cells showed that cAMP agonists stimulated a HCO3(-) rich secretion containing up to 80 mM HCO3(-). This alkaline secretion relied on a coordinated switch in the activity of distinct Cl(-)-HCO3(-) anion exchangers (AE) located at different regions of the cell. At the apical membrane, cAMP agonists activated the electroneutral AE pendrin (SLC26A4), together with cystic fibrosis transmembrane conductance regulator (CFTR), while at the basolateral membrane the agonists inhibited AE2 (SLC4A2). However, the underlying mechanism(s) that orchestrates this cAMP-dependent switch in AE activity has not been elucidated. Apical and basolateral Cl(-)-HCO3(-) exchange was assessed by measuring Cl(-)-dependent changes in intracellular pH (pH(i)). We show that protein phosphatase 1 (PP1), together with CFTR, play central roles in this reciprocal regulation of AE activity. Activation of pendrin by cAMP agonists, but not inhibition of the basolateral exchanger, was protein kinase A-dependent. Knocking down CFTR expression, or blocking its activity with GlyH-101, led to incomplete inhibition of the basolateral AE by cAMP, supporting a role for CFTR in this process. Addition of the PP1/2A inhibitor, okadaic acid, but not the PP2A specific inhibitor fostreicin, mimicked the effect of cAMP stimulation. Furthermore, okadaic acid-treated Calu-3 monolayers produced a more alkaline fluid than untreated cells, which was comparable with that produced by cAMP stimulation. These results identify PP1 as a novel regulator of AE activity which, in concert with CFTR, coordinates events at both apical and basolateral membranes, crucial for efficient HCO3(-) secretion from Calu-3 cells.

An Al/Zr-Based Clay Stabilizer for High pH Applications

Sandstone formations are exposed to a variety of high pH fluids, including: hydraulic fracturing using high pH borate gels, alkaline-based chemical enhanced oil recovery (EOR) methods, water-based drilling fluids, and cementing filtrate. High pH values can trigger fines migration, and subsequent loss of permeability and well productivity. An aluminum/zirconium-based (Al/Zr) clay stabilizer was developed to control fines migration at high pH applications. The objective of this study is to assess the effectiveness of this new stabilizer and compare its performance with commercially available stabilizers. Laboratory studies were performed using Berea sandstone (8 wt. % clays; mainly kaolinite) cores, 6 in. length and 1.5 in. diameter. Tetramethyl ammonium chloride (TMAC) and choline chloride were used for comparison as two commercial clay stabilizers. Various coreflood experiments were conducted to determine the effect of the three stabilizers on core permeability (from 64 to 100 mD) at various temperatures up to 300 °F. In these experiments, a preflush that included 2 wt. % stabilizer was injected, followed by injection of 2 wt. % NaOH solution. The latter represented high pH filtrate that can invade the formation during any treatment that includes alkaline fluids. The pressure drop across the core was measured and samples of the core effluent were collected. Inductively coupled plasma optical emission spectrometry (winlab32 software) was used to measure the concentrations of Al, Zr, Fe, Ca, and Mg. ZetaPALS (BIC software) was used to measure the surface charge on the kaolinite particles. Lab results indicated that the new clay stabilizer worked effectively up to 300 °F following 2 wt. % NaOH. No reduction in permeability was noted in any of coreflood tests using sandstone cores of various initial permeabilities. The concentrations of various cations were found to be a function of core mineralogy. TMAC and choline chloride were not effective when followed by fresh water and incompatible with the high pH fluids. The new stabilizer is environmentally friendly, and can be used in hydraulic fracturing, and alkaline-based chemical EOR methods to mitigate clay related problems.

Rare earth elements in metarhyolite dyke constraints on processes in a dynamic hydrothermal system, Um Ghannam, South Eastern Desert, Egypt

The Um Ghannam area lies within the core of Hafafit Complex, South Eastern Desert. This area is occupied mainly by granitic gneiss (orthogneiss). However, the granitic gneiss is extruded by swarm metarhyolite dykes and quartz veins. The studied metarhyolite dyke is classified into two distinctive zones. However, the intense degree of hydrothermal alteration can partition this dyke into weakly and extremely altered zones. According to the extraordinary diversity in color, this dyke is distinguished into gray to dark gray (weakly altered) and greenish (extremely altered) metarhyolite. Petrographical, mineralogical, and geochemical characteristics of the two distinctive zones are detected in a representative sample. Petrographically, the weakly altered zone is mainly represented by chloritization of primary biotite, garnet, and epidote, and argillitization of primary plagioclase. Although the extremely altered zone contains intensely altered remnants of the original rock, the extremely altered zone is distinguished by intense oxidation products (carbonate minerals and quartz, with significant amounts of secondary Cr-muscovite and hematite). The mineralogical studies are imposed on the millimeter and the micrometer scale in this important hydrogeothermal system. Except for Ca and Mg, most of the major elements are depleted at the extremely altered zone. However, the extremely altered zone is enriched in trace elements (Cr, Mn, Co, and Ni). The major elements of the extremely altered zone reflect the significant alterations (desilication, muscovitization, and carbonatization). These alteration processes have taken place in the hydrogeothermal system in the extremely altered zone. The geothermal fluid is responsible for these hydrothermal alterations. High fO2 and high temperature are characteristic features of this fluid. Then, the high-field-strength elements such as Zr, Ti, and P are depleted as a significant hydrothermal alteration. Also, nuclear elements with the anion of (CO3)2− can travel as molecular complexes (carbonates), as long as the chemical and structural conditions are suitable for the movement of these elements from the metarhyolite dyke to redeposit and accumulate in another geologic formation. The rare earth elements La and Ce, as well as Yb and Lu, are partially mobilized during intensity alterations. The rare earth elements (REEs) are depleted in abundance with enrichment of CO2 from the weakly altered zone to the extremely altered zone. The REE budget is decreased from the weakly altered zone to the extremely altered zone as 121.17 to (27.38 − 16.52), respectively. The significant depletion of ∑REEs is controlled by dissolution of monazite. Monazite breakdown and even apatite formation can be caused by alkaline fluid. This fluid is related to event and thermal stage. However, the negative anomaly of Eu can be noticed in all studied samples. Then, Eu anomaly may be formed from plagioclase fractionation. The weakly altered metarhyolite zone and orthogneiss have lower HREE/LREE (0.07–0.11), respectively, relative to the extremely altered metarhyolite zone (0.17 − 0.2). Even all studied samples at two significant zones are characterized by the enrichment of ∑LREEs relative to ∑HREEs.

Sources of organic nitrogen at the serpentinite‐hosted Lost City hydrothermal field

The reaction of ultramafic rocks with water during serpentinization at moderate temperatures results in alkaline fluids with high concentrations of reduced chemical compounds such as hydrogen and methane. Such environments provide unique habitats for microbial communities capable of utilizing these reduced compounds in present-day and, possibly, early Earth environments. However, these systems present challenges to microbial communities as well, particularly due to high fluid pH and possibly the availability of essential nutrients such as nitrogen. Here we investigate the source and cycling of organic nitrogen at an oceanic serpentinizing environment, the Lost City hydrothermal field (30°N, Mid-Atlantic Ridge). Total hydrolizable amino acid (THAA) concentrations in the fluids range from 736 to 2300nm and constitute a large fraction of the dissolved organic carbon (2.5-15.1%). The amino acid distributions, and the relative concentrations of these compounds across the hydrothermal field, indicate they most likely derived from chemolithoautotrophic production. Previous studies have identified the presence of numerous nitrogen fixation genes in the fluids and the chimneys. Organic nitrogen in actively venting chimneys has δ(15) N values as low as 0.1‰ which is compatible with biological nitrogen fixation. Total hydrolizable amino acids in the chimneys are enriched in (13) C by 2-7‰ compared to bulk organic matter. The distribution and absolute δ(13) C(THAA) values are compatible with a chemolithoautotrophic source, an attribution also supported by molar organic C/N ratios in most active chimneys (4.1-5.5) which are similar to those expected for microbial communities. In total, these data indicate nitrogen is readily available to microbial communities at Lost City.

Influence of Oil Viscosity on Alkaline Flooding for Enhanced Heavy Oil Recovery

Oil viscosity was studied as an important factor for alkaline flooding based on the mechanism of “water drops” flow. Alkaline flooding for two oil samples with different viscosities but similar acid numbers was compared. Besides, series flooding tests for the same oil sample were conducted at different temperatures and permeabilities. The results of flooding tests indicated that a high tertiary oil recovery could be achieved only in the low‐permeability (approximately 500 mD) sandpacks for the low‐viscosity heavy oil (Zhuangxi, 390 mPa·s); however, the high‐viscosity heavy oil (Chenzhuang, 3450 mPa·s) performed well in both the low‐ and medium‐permeability (approximately 1000 mD) sandpacks. In addition, the results of flooding tests for the same oil at different temperatures also indicated that the oil viscosity put a similar effect on alkaline flooding. Therefore, oil with a high‐viscosity is favorable for alkaline flooding. The microscopic flooding test indicated that the water drops produced during alkaline flooding for oils with different viscosities differed significantly in their sizes, which might influence the flow behaviors and therefore the sweep efficiencies of alkaline fluids. This study provides an evidence for the feasibility of the development of high‐viscosity heavy oil using alkaline flooding.

Putative interaction of brush cells with bicarbonate secreting cells in the proximal corpus mucosa

The gastric epithelium is protected from the highly acidic luminal content by alkaline mucus which is secreted from specialized epithelial cells. In the stomach of mice strong secretion of alkaline fluid was observed at the “gastric groove,” the border between corpus and fundus mucosa. Since this region is characterized by numerous brush cells it was proposed that these cells might secrete alkaline solution as suggested for brush cells in the bile duct. In fact, it was found that in this region multiple cells express elements which are relevant for the secretion of bicarbonate, including carbonic anhydrase (CAII), the cystic fibrosis transmembrane conductance regulator (CFTR) and the Na+/H+ exchanger (NHE1). However, this cell population was distinct from brush cells which express the TRP-channel TRPM5 and are considered as putative sensory cells. The location of both cell populations in close proximity implies the possibility for a paracrine interaction. This view was substantiated by the finding that brush cells express prostaglandin synthase-1 (COX-1) and the neighboring cells a specific receptor type for prostaglandins. The notion that brush cells may be able to sense a local acidification was supported by the observation that they express the channel PKD1L3 which contributes to the acid responsiveness of gustatory sensory cells. The results support the concept that brush cells may sense the luminal content and influence via prostaglandins the secretion of alkaline solution.

Identification of coupling parameters between shear strength behaviour of compacted soils and chemical’s effects with an evolutionary-based data mining technique

When subjected to a very high-pH, most of the soil minerals undergo physico-chemical transformation. This could induce strong modifications of the shear strength behaviour of the soil. This issue is of high interest in the framework of the design of deep nuclear wastes repositories, since the degradation of the concrete lining of deep galleries after thousands of years will generate an alkaline solute (pH>12) that would circulate through the backfill, and alter its hydromechanical characteristics. A study was undertaken to assess the impact of high-pH fluid circulation on the shear strength behaviour of a backfill material. Because of the complexity of the existing constitutive theories, a new approach was used, based on evolutionary polynomial regression (EPR), for modelling of these processes. EPR is an evolutionary data mining technique that generates a transparent and structured representation of the behaviour of a system directly from data. An EPR model was developed and validated using results from a comprehensive set of triaxial tests. Through a sensitivity analysis, the EPR model permitted to identify the specific surface, and to a lesser extent the micropore void ratio, as coupling parameters between hydromechanical behaviour alteration during alkaline fluid circulation and a physical process.

Fluid Flow of Daxing Conglomerate in Langgu Depression and its Controlling Effects on Reservoir

The Daxing conglomerate in Langgu depression is typical glutenite fan sediment in steep slope belt of faulted basin. By analyzing the data of core, petrographic thin section, scanning electron microscope and “X” ray diffraction, we’ve found that fluid flow controls the reservoir development to a certain degree. The results show that there are four types of fluid affecting the reservoir of Daxing conglomerate-meteoric fresh water, organic acid, alkaline fluid and abnormal high pressure fluid. We’ve studied fluid flows in different diagenetic stages combining the observation of clay mineral and carbonate cement and we find that two acid fluid events and abnormal high pressure fluid have determined the development of three pore belts in the longitudinal section.

THE CORUNDUM + TOURMALINE NODULES RELATED TO HYDROTHERMAL ALTERATION OF SPODUMENE IN THE NANPING No. 31 PEGMATITE DYKE, FUJIAN PROVINCE, SOUTHEASTERN CHINA

The Nanping No. 31 pegmatite is a spodumene-subtype LCT granitic pegmatite in southeastern China. Spodumene mainly occurs as rock-forming mineral in the quartz – coarse albite – spodumene zone (zone III) and the quartz – spodumene – amblygonite zone (zone IV). Various alteration-induced phenomena were observed in spodumene. Spodumene in zone III is usually altered along its {110} cleavages to networks of albite + muscovite, resulting from a replacement of spodumene by an alkaline fluid, which likely begins by Na metasomatism. Extensive alteration of spodumene in zone IV to quartz and muscovite veinlets is related to replacement by K+- and H+-rich fluid. However, alteration by strongly acid fluids also affected spodumene, leading to formation of fine-grained white mica in zones III and IV. In this paper, we focus on the occurrence of nodules of corundum + tourmaline, which are typically restricted to the aggregates of white mica in zone IV. Fibrous corundum and radial tourmaline signify a hydrothermal origin. Their textural relationship with secondary muscovite suggest a close genetic relation with the latter. The corundum + tourmaline nodules arise by alteration of the secondary muscovite by late B-, Mg- and Fe-rich fluids.

Chlorine-rich fluid or melt activity during granulite facies metamorphism in the Late Proterozoic to Cambrian continental collision zone—An example from the Sør Rondane Mountains, East Antarctica

In the granulite facies rocks, the role of low H2O activity fluids is still unclear. The importance of understanding its role is gradually being recognized, and it enables us to help understand the process of granulite formation. Attention has been specifically focused on Cl-rich fluids and high-salinity alkaline fluids in the geochemical modification of continental crust. We have investigated the field distribution of Cl-rich biotite in the pelitic gneisses of the Sør Rondane Mountains, East Antarctica where Late Proterozoic to Cambrian granulites are widely exposed. Among 27 samples studied, a garnet-biotite-sillimanite gneiss from Balchenfjella was selected as best suited sample to constrain the P-T-t conditions of Cl-rich fluid or melt activity. This gneiss contains garnet porphyroblasts that have a P-rich core with oscillatory zoning in P. The garnet core includes Cl-poor biotite and fluorapatite. This core has been partially resorbed and discontinuously overgrown by a P-poor rim, in which Cl-rich biotite and chlorapatite are included. Coarse-grained, rounded zircon grains are exclusively included in the rim of the garnet porphyroblast and are also present in the matrix. This mode of occurrence suggests that the Cl-rich biotite and chlorapatite, together with coarse-grained zircon were formed almost simultaneously. The P-T conditions of Cl-rich biotite entrapment in the garnet rim are estimated to be ca. 800°C and 0.8GPa. In comparison, peak metamorphic condition is ca. 850°C and 1.1GPa. These pieces of observation suggest that Cl-rich fluid or melt infiltrated at the core-rim boundary of garnet. In the case of fluid infiltration, the fHCl/fH2O ratio of the fluid in equilibrium with Cl-rich biotite and chlorapatite in the garnet rim are estimated to be ten times larger than that in equilibrium with Cl-poor biotite and fluorapatite in the matrix and the garnet core. The LA-ICP-MS U-Pb dating of the coarse-grained zircon included in the garnet rim gave concordia age of 603±14Ma. Therefore, Cl-rich fluid or melt infiltration took place close to the metamorphic peak condition of ca. 800°C and 0.8GPa at 603±14Ma. The field distribution of Cl-rich fluid or melt activity is somewhat linear in the Sør Rondane Mountains. High Cl-activity is located near the large scale ductile shear zones, suggesting its relation to high-strain zones. Regional distribution of high-grade Cl-rich fluid or melt activity in the Sør Rondane Mountains implies that it is one of the major phenomena in the continental collision processes.