Charged Waters Research Articles

Our Lady of the Workboats: Solidarity and Spirituality on the Bay of All Saints

At the end of Jorge Amado’s Mar Morto (1936), a sailor’s grieving widow defies a fate that seems inevitable. Instead of resigning herself to a life of precarity, she takes command of her husband’s boat. In doing so, she aligns herself with Iemanjá, a sea deity from the Afro-Brazilian religion of Candomblé. This essay takes this episode, and Amado’s novel, as its intellectual point of departure. Joining literary studies with maritime social history and nautical science, it charts the physical characteristics and cultural histories of the Baia de Todos os Santos in the Brazilian state of Bahia, which influenced Mar Morto on the level of form and theme. In the spiritually charged home waters of Amado and his characters, ocean literacy is both locally specific and diasporic: intertwined with African-descended cosmologies and ongoing struggles for sovereignty and freedom. By attending to these forms of what Justin Dunnavant (riffing on Katherine McKittrick) calls “livingness on the sea,” this essay models a maritime literary studies that recovers gendered and racialized ocean literacies and demonstrates the importance of local ways of knowing the ocean to the global literature of the sea. It is drawn from a book project tentatively titled “Atlantic Shapeshifters: Sea Literature’s Fluid Forms.”

Developing a Phototactic Electrostatic Insect Trap Targeting Whiteflies, Leafminers, and Thrips in Greenhouses.

Simple SummarySilverleaf whiteflies (Bemisia tabaci), vegetable leafminers (Liriomyza sativae), and western flower thrips (Frankliniella occidentalis) are very serious pests of greenhouse tomatoes. In Japan, growers of organic tomatoes currently use large numbers of yellow sticky traps to control insects, but these traps need replacing very regularly, as the sticky surface becomes clogged with insects. An electric field-generating apparatus, described herein, is a potential physical tool to control these pests that have entered greenhouses. The electric field was formed in the space between oppositely electrified insulated conductors arrayed in parallel with fixed separation. Although these conductors created a sufficiently strong force to capture insects entering the field, the force was insufficient to capture insects outside the field. The positive phototaxis of these insects was an inspiration to develop an improved electrostatic insect trap, which was constructed by introducing oppositely charged yellow-colored water into paired transparent insulator tubes to produce opposite poles. The finished apparatus exhibited coloration and insect attraction characteristics similar to commercial yellow sticky traps, but had the advantage that they could be cleaned easily and remain effective for long periods. The surfaces of the insulator tubes containing the charged yellow water were electrostatically active, but not excessively sticky, thus, the apparatus could be placed close to the plants. The close location of the devices enabled preferential attraction of flying or plant-settling insects to the trap. The present study provided an experimental basis for developing an electrostatic device to attract and capture insects that enter greenhouses.Our aim was to develop an electrostatic apparatus to lure and capture silverleaf whiteflies (Bemisia tabaci), vegetable leafminers (Liriomyza sativae), and western flower thrips (Frankliniella occidentalis) that invade tomato greenhouses. A double-charged dipolar electric field producer (DD-EFP) was constructed by filling water in two identical transparent soft polyvinyl chloride tubes arrayed in parallel with fixed separation, and then, inserting the probes of grounded negative and positive voltage generators into the water of the two tubes to generate negatively and positively charged waters, respectively. These charged waters electrified the outer surfaces of the opposite tubes via dielectric polarization. An electric field formed between the oppositely charged tubes. To lure these phototactic insects, the water was colored yellow using watercolor paste, then introduced into the transparent insulator tubes to construct the yellow-colored DD-EFP. This apparatus lured insects in a manner similar to commercially available yellow sticky traps. The yellow-colored DD-EFP was easily placed as a movable upright screen along the plants, such that invading pests were preferentially attracted to the trap before reaching the plants. Furthermore, pests settling on the plants were attracted to the apparatus, which used a plant-tapping method to drive them off the plants. Our study provided an experimental basis for developing an electrostatic device to attract and capture insects that enter greenhouses.

Portable Raman can be the new hammer for architects restoring 20th‐century built heritage elements made of reinforced concrete

AbstractThe use of portable Raman is proposed as the modern hammer of architects to inspect protected buildings of the 20th century, where reinforced concrete was used for structures and Portland type cement for mortars/binders in the walls. Two different buildings in the province of Biscay (North of Spain) were selected, the Punta Begoña Galleries, Getxo (1918), qualified as monument, affected by a direct marine and hard industrial environment from the Bilbao Commercial Harbor, the Library of the University of the Basque Country UPV/EHU, Campus of Leioa (1968), affected by the diffuse urban‐industrial atmosphere of metropolitan Bilbao. For both cases, original and decayed compounds were searched by portable Raman spectroscopy (785‐ and 532‐nm lasers) in raw materials and efflorescence salts over them. In the Galleries, the expected raw materials of Portland‐type mortars and reinforced concrete were detected, such as alite (3CaO·SiO2), belite (2CaO·SiO2), calcite (mortar and gravel) and gypsum together with quartz and aragonite, which indicates the use of beach sand as aggregate. Other compounds like nitratine (NaNO3), nitrocalcite/niter (Ca (NO3)2.6H2O/KNO3), γ‐anhidrite (CaSO4), bassanite (CaSO4·1/2H2O), mackinawite ((Fe,Ni)S), lepidocrocite (γ‐FeO (OH)), haematite (Fe2O3) and whewellite (CaC2O4·H2O) indicated also a heavy decay, because of chemical reactions between compounds in the aerosols around the building and original materials. In the Library of the UPV/EHU, apart from the same kind of original compounds, high amounts of niter (KNO3) were detected in efflorescence just underneath the upper gardens of the building, suggesting a decay due to the infiltration of ammonium nitrate charged waters. Moreover, thenardite (Na2SO4), syngenite (K2Ca(SO4)2·H2O), gypsum (in efflorescence salts), aphthitalite (K3Na(SO4)2), haematite and anatase (TiO2) were also detected in other efflorescences.

Just-in-time faculty development: a mobile application helps clinical teachers verify and describe clinical reasoning difficulties

BackgroundAlthough clinical teachers can often identify struggling learners readily and reliably, they can be reluctant to act upon their impressions, resulting in failure to fail. In the absence of a clear process for identifying and remediating struggling learners, clinical teachers can be put off by the prospect of navigating the politically and personally charged waters of remediation and potential failing of students.MethodsTo address this gap, we developed a problem-solving algorithm to support clinical teachers from the identification through the remediation of learners with clinical reasoning difficulties, which have significant implications for patient care. Based on this algorithm, a mobile application (Pdx) was developed and assessed in two emergency departments at a Canadian university, from 2015 to 2016, using interpretive description as our research design. Semi-structured interviews were conducted before and after a three-month trial with the application. Interviews were analysed both deductively, using pre-determined categories, and inductively, using emerging categories.ResultsTwelve clinical teachers were interviewed. Their experience with the application revealed their need to first validate their impressions of difficulties in learners and to find the right words to describe them before difficulties could be addressed. The application was unanimously considered helpful regarding both these aspects, while the mobile format appeared instrumental in allowing clinical teachers to quickly access targeted information during clinical supervision.ConclusionsThe value placed on verifying impressions and finding the right words to pinpoint difficulties should be further explored in endeavours that aim to address the failure to fail phenomenon. Moreover, just-in-time mobile solutions, which mirror habitual clinical practices, may be used profitably for knowledge transfer in medical education, as an alternative form of faculty development.

Hydrated proton and hydroxide charge transfer at the liquid/vapor interface of water.

The role of the solvated excess proton and hydroxide ions in interfacial properties is an interesting scientific question with applications in a variety of aqueous behaviors. The role that charge transfer (CT) plays in interfacial behavior is also an unsettled question. Quantum calculations are carried out on clusters of water with an excess proton or a missing proton (hydroxide) to determine their CT. The quantum results are applied to analysis of multi-state empirical valence bond trajectories. The polyatomic nature of the solvated excess proton and hydroxide ion results in directionally dependent CT, depending on whether a water molecule is a hydrogen bond donor or acceptor in relation to the ion. With polyatomic molecules, CT also depends on the intramolecular bond distances in addition to intermolecular distances. The hydrated proton and hydroxide affect water's liquid/vapor interface in a manner similar to monatomic ions, in that they induce a hydrogen-bonding imbalance at the surface, which results in charged surface waters. This hydrogen bond imbalance, and thus the charged waters at the surface, persists until the ion is at least 10 Å away from the interface.

Effects of Magnesium on Cation Selectivity and Structural Stability in prominent Vertisols of Karnataka

A study was conducted to evaluate the effects of Mg on ternary (Na-Ca-Mg) exchange and intern structural stability in prominent Vertisols of TBP (Tungabhadra Project) and UKP (Upper Krishna Project) irrigation commands of Karnataka State, India. Surface soil samples representing typical Vertisols derived from granite-gneiss (Gangavati and Kavadimatti), limestone (Devapur and Islampur) and basalt (Kadliwad and Mannapur) were included in the study. These soils were subjected to equilibration with waters of varying sodium adsorption ratio (SAR-5,20,40,60,80 and 100 millimoles per liter1/2) with different Ca/Mg ratio (4:1,2:1,1:1,1:2and 1:4).Exchangeable Na increased as the Mg/Ca ratio increased from 1:4 to 4:1 indicating that Mg charged waters are more detrimental for structural integrity of the soils. Averaged from all SAR treatments, the Mg-Na systems had between 10.5 to 12.1% more exchangeable Na than did the Ca-Na systems. The Mg-induced increase in exchangeable Na was directly related to a preference by the soils for Ca over Mg, which makes Na more competitive against Mg than against Ca. The influence of Mg on soil structural stability was examined by measuring degree of dispersion, capillary raise and moisture diffusivity using Na-Ca-Mg solutions varying with Ca/Mg ratios and SAR values. In order to segregate the specific effect of Mg, separate binary systems (exclusive Ca-Mg solutions with varying concentrations without Na) were used to examine the degree of dispersion. The Mg-Na system developed considerably lower soil moisture diffusivity and higher degree of dispersion as well as capillarity than did the Ca-Na system when equilibrated with solutions having total electrolyte concentration 20 m mol liter-1. Dispersion and water transmission tests confirmed that the effect of Mg was greater than could be explained by the higher exchangeable Na alone in the Mg system or else Mg had a specific effect on clay dispersion. It was obviously proved that Mg does have the effect on clay dispersion in the binary system involving diminishing Ca concentration where Na was completelyexcluded. Our results suggest that exchangeable Mg is about 1/10th, 1/20th, and 1/30th as dispersive as Na in granite-gneiss, limestone and basalt derived soils, respectively.

Utilizing Rare Earth Elements as Tracers in High TDS Reservoir Brines in CCS Applications

Abstract In this paper we report the result of research associated with the testing of a procedures necessary for utilizing natural occurring trace elements, specifically the Rare Earth Elements (REE) as geochemical tracers in Carbon Capture and Storage (CCS) applications. Trace elements, particularly REE may be well suited to serve as in situ tracers for monitoring geochemical conditions and the migration of CO 2 -charged waters within CCS storage systems. We have been conducting studies to determine the efficacy of using REE as a tracer and characterization tool in the laboratory, at a CCS analogue site in Soda Springs, Idaho, and at a proposed CCS reservoir at the Rock Springs Uplift, Wyoming. Results from field and laboratory studies have been encouraging and show that REE may be an effective tracer in CCS systems and overlying aquifers. In recent years, a series of studies using REE as a natural groundwater tracer have been conducted successfully at various locations around the globe. Additionally, REE and other trace elements have been successfully used as in situ tracers to describe the evolution of deep sedimentary Basins. Our goal has been to establish naturally occurring REE as a useful monitoring measuring and verification (MMV) tool in CCS research because formation brine chemistry will be particularly sensitive to changes in local equilibrium caused by the addition of large volumes of CO 2 . Because brine within CCS target formations will have been in chemical equilibrium with the host rocks for millions of years, the addition of large volumes of CO 2 will cause reactions in the formation that will drive changes to the brine chemistry due to the pH change caused by the formation of carbonic acid. This CO 2 driven change in formation fluid chemistry will have a major impact on water rock reaction equilibrium in the formation, which will impart a change in the REE fingerprint of the brine that can measured and be used to monitor in situ reservoir conditions. Our research has shown that the REE signature imparted to the formation fluid by the introduction of CO 2 to the formation, can be measured and tracked as part of an MMV program. Additionally, this REE fingerprint may serve as an ideal tracer for fluid migration, both within the CCS target formation, and should formation fluids migrate into overlying aquifers. However application of REE and other trace elements to CCS system is complicated by the high salt content of the brines contained within the target formations. In the United States by regulation, in order for a geologic reservoir to be considered suitable for carbon storage, it must contain formation brine with total dissolved solids (TDS) > 10,000 ppm, and in most cases formation brines have TDS well in excess of that threshold. The high salinity of these brines creates analytical problems for elemental analysis, including element interference with trace metals in Inductively Coupled Plasma Mass Spectroscopy (ICP-MS) (i.e. element mass overlap due to oxide or plasma phenomenon). Additionally, instruments like the ICP-MS that are sensitive enough to measure trace elements down to the parts per trillion level are quickly oversaturated when water TDS exceeds much more than 1,000 ppm. Normally this problem is dealt with through dilution of the sample, bringing the water chemistry into the instruments working range. However, dilution is not an option when analyzing these formation brines for trace metals, because trace elements, specifically the REE, which occur in aqueous solutions at the parts per trillion levels. Any dilution of the sample would make REE detection impossible. Therefore, the ability to use trace metals as in situ natural tracers in high TDS brines environments requires the development of methods for pre-concentrating trace elements, while reducing the salinity and associated elemental interference such that the brines can be routinely analyzed by standard ICP-MS methods. As part of the Big Sky Carbon Sequestration Project the INL-CAES has developed a rapid, easy to use process that pre-concentrates trace metals, including REE, up to 100x while eliminating interfering ions (e.g. Ba, Cl). The process is straightforward, inexpensive, and requires little infrastructure, using only a single chromatography column with inexpensive, reusable, commercially available resins and wash chemicals. The procedure has been tested with synthetic brines (215,000 ppm or less TDS) and field water samples (up to 5,000 ppm TDS). Testing has produced data of high quality with REE capture efficiency exceeding 95%, while reducing interfering elements by > 99%.

The geology and water chemistry of the Hellisheidi, SW-Iceland carbon storage site

The subsurface rocks at the Hellisheidi carbon injection site are primarily olivine tholeiite basalts consisting of lava flows and hyaloclastite formations. The hyaloclastites are low permeability glassy rocks formed under ice and melt water during glaciations that serve as the cap rock at the injection site; the boundaries between hyaloclastites and lava flows and those between individual lava flows boundaries are preferential fluid flow pathways. Some alteration is observed in the hyaloclastite cap rock situated at 100–300m depth consisting primarily of smectite, calcite, Ca-rich zeolites, and poorly crystalline iron-hydroxides. Alteration increases with depth. These alteration phases lower the porosity and permeability of these rocks. Carbon dioxide injection will be targeted at a lava flow sequence at 400–800m depth with the main aquifer located at 530m depth. Loss on ignition suggests that over 80% of the primary rocks in the target zone are currently unaltered. The target zone rocks are rich in the divalent cations capable of forming carbonates; on average 6 moles of divalent cations are present per 1kg of rock.The water in the target zone ranges in temperature from 15 to 35°C; the in situ pH ranges from 8.4 to 9.8. The partial pressure of CO2 and O2 suggest that the water in this system is isolated from the atmosphere. The concentration of Ca and Mg in these waters are limited by secondary mineral precipitation. All the waters are supersaturated with Ca-zeolite, analcime, Ca–Mg–Fe smectite, calcite, and aragonite, and some are supersaturated with respect to dolomite and Fe–Mg carbonates.Pure commercial CO2 and a 75%–24.2%–0.8% mixture of CO2–H2S–H2 gases will be dissolved into water prior to its injection into this system. The injected water will have a temperature of ∼25°C and be equilibrated with ∼25bar pressure of the CO2 gas, and ∼14bar pressure of the CO2–H2S–H2 mixture. The injected gas will have total CO2 concentrations of ∼0.8–0.42mole/kg H2O and a pH of 3.7–4.0, depending on the H2S concentration of the injected gas. All host rock minerals and glass will be strongly undersaturated with respect to the gas charged injection waters. The water will therefore create porosity in the near vicinity of the injection by dissolving primary and secondary minerals. Further from the injection, secondary minerals will precipitate, potentially clogging the system. Reaction path modeling shows that 1–2 moles of basaltic glass are needed to lower the injected CO2 concentration down to natural pre-injection concentrations, but less than 1 mole is needed for the sequestered H2S. Major carbonates formed were Ca–Mg–Fe–carbonate and dolomite at pH <5, whereas ankerite and calcite formed later at higher pH. Associated minerals at lower pH were chalcedony, kaolinite and iron hydroxide, followed by smectite and zeolites at higher pH. Modeling result suggest that the first sulfur bearing phase to precipitate is elemental sulfur, followed by greigite and mackinowite upon further basalt dissolution.

Mineral sequestration of carbon dioxide in basalt: A pre-injection overview of the CarbFix project

In this paper we describe the thermodynamic and kinetic basis for mineral storage of carbon dioxide in basaltic rock, and how this storage can be optimized. Mineral storage is facilitated by the dissolution of CO 2 into the aqueous phase. The amount of water required for this dissolution decreases with decreased temperature, decreased salinity, and increased pressure. Experimental and field evidence suggest that the factor limiting the rate of mineral fixation of carbon in silicate rocks is the release rate of divalent cations from silicate minerals and glasses. Ultramafic rocks and basalts, in glassy state, are the most promising rock types for the mineral sequestration of CO 2 because of their relatively fast dissolution rate, high concentration of divalent cations, and abundance at the Earth's surface. Admixture of flue gases, such as SO 2 and HF, will enhance the dissolution rates of silicate minerals and glasses. Elevated temperature increases dissolution rates but porosity of reactive rock formations decreases rapidly with increasing temperature. Reduced conditions enhance mineral carbonation as reduced iron can precipitate in carbonate minerals. Elevated CO 2 partial pressure increases the relative amount of carbonate minerals over other secondary minerals formed. The feasibility to fix CO 2 by carbonation in basaltic rocks will be tested in the CarbFix project by: (1) injection of CO 2 charged waters into basaltic rocks in SW Iceland, (2) laboratory experiments, (3) studies of natural analogues, and (4) geochemical modelling.

IFC(Executive Eds,Associate Eds,Founding Eds...)

The eastern part of the Adelaide Geosyncline contains well preserved glaciomarine sequences of the Sturtian glaciation (≈750–700 Ma) including calcareous or dolomitic siltstone, manganiferous siltstone, dolostone and diamictite units and the associated Braemar ironstone facies. The ironstone facies occurs as matrix to diamictites and as massive to laminated ironstones and comprises abundant Fe oxides (hematite, magnetite) and quartz, minor silicates (muscovite, chlorite, biotite, plagioclase, tourmaline), carbonate and apatite, and detrital mineral grains and lithic clasts. Micro-textures indicate that magnetite and hematite are of metamorphic origin. They are intergrown with silicates and carbonates, with the mineral assemblage indicative of greenschist facies (biotite grade) metamorphism. Chemical compositions of ironstones vary greatly and reflect changes from silica-, alumina-poor ironstones formed by predominantly chemical precipitation processes to silica-, alumina-rich examples with a significant detrital component. Silica-, alumina-poor ironstones are characterised by low concentrations of transition metals and large ion lithophile and high field strength elements and display REE signatures of modern coastal seawater. The Braemar facies accumulated in a marine basin along the border of a continental glaciated highland and a low-lying weathered landmass. Wet-based glaciers originated from the Palaeoproterozoic to Mesoproterozoic metamorphic basement and debouched into a fault-controlled depocentre, the Baratta Trough. The intimate association of dolostones, manganiferous siltstones, ironstones and diamictites can be explained by a transgressive event during a postglacial period. Hydrothermal exhalations added significant amounts of Fe and other metals to Neoproterozoic seawater. Melting of floating ice led to an influx of clastic detritus and deposition of glaciomarine sediments from wet-based glaciers and to oxygenation of ferriferous (±manganiferous), carbonate and CO2 charged coastal waters. Release of CO2 to the atmosphere from the oxygenated waters resulted in the precipitation of carbonate as dolostones and oxygenation of ferriferous (±manganiferous) waters led to the precipitation of Fe3+ oxides as laminated ironstones and as matrix of diamictic ironstones. Further increases in Eh conditions led to the precipitation of Mn oxides or carbonates and their incorporation in clastic sediments. Thus the Braemar ironstone facies is the result of chemical precipitation of dissolved Fe (and Mn) during a postglacial, transgressive period and formed in a near-coastal environment under significant terrestrial influences.

The aqueous solvation of sodium chloride: A Monte Carlo transition path sampling study

We study the dissociation of sodium chloride in an environment of simple point charged model waters using a stochastic transition path sampling method. The method is able to analyze the structure and dynamics (including transition states) of rare events without any a priori assumption. After an ensemble of reactive paths between stable states has been constructed, a set of transition state configurations can be derived. Technical details of the simulation are discussed. We observe that the structure found from the ensemble of transition state configurations is qualitatively equal to the structure obtained when the interionic distance is assumed as the reaction coordinate. We also discuss energetic aspects of the ion pair dissociation: A free energy profile of the dynamical process reveals the contribution of solvent degrees of freedom to the reaction barrier.

Geochemistry, petrology and origin of Neoproterozoic ironstones in the eastern part of the Adelaide Geosyncline, South Australia

The eastern part of the Adelaide Geosyncline contains well preserved glaciomarine sequences of the Sturtian glaciation (≈750–700 Ma) including calcareous or dolomitic siltstone, manganiferous siltstone, dolostone and diamictite units and the associated Braemar ironstone facies. The ironstone facies occurs as matrix to diamictites and as massive to laminated ironstones and comprises abundant Fe oxides (hematite, magnetite) and quartz, minor silicates (muscovite, chlorite, biotite, plagioclase, tourmaline), carbonate and apatite, and detrital mineral grains and lithic clasts. Micro-textures indicate that magnetite and hematite are of metamorphic origin. They are intergrown with silicates and carbonates, with the mineral assemblage indicative of greenschist facies (biotite grade) metamorphism. Chemical compositions of ironstones vary greatly and reflect changes from silica-, alumina-poor ironstones formed by predominantly chemical precipitation processes to silica-, alumina-rich examples with a significant detrital component. Silica-, alumina-poor ironstones are characterised by low concentrations of transition metals and large ion lithophile and high field strength elements and display REE signatures of modern coastal seawater. The Braemar facies accumulated in a marine basin along the border of a continental glaciated highland and a low-lying weathered landmass. Wet-based glaciers originated from the Palaeoproterozoic to Mesoproterozoic metamorphic basement and debouched into a fault-controlled depocentre, the Baratta Trough. The intimate association of dolostones, manganiferous siltstones, ironstones and diamictites can be explained by a transgressive event during a postglacial period. Hydrothermal exhalations added significant amounts of Fe and other metals to Neoproterozoic seawater. Melting of floating ice led to an influx of clastic detritus and deposition of glaciomarine sediments from wet-based glaciers and to oxygenation of ferriferous (±manganiferous), carbonate and CO 2 charged coastal waters. Release of CO 2 to the atmosphere from the oxygenated waters resulted in the precipitation of carbonate as dolostones and oxygenation of ferriferous (±manganiferous) waters led to the precipitation of Fe 3+ oxides as laminated ironstones and as matrix of diamictic ironstones. Further increases in Eh conditions led to the precipitation of Mn oxides or carbonates and their incorporation in clastic sediments. Thus the Braemar ironstone facies is the result of chemical precipitation of dissolved Fe (and Mn) during a postglacial, transgressive period and formed in a near-coastal environment under significant terrestrial influences.

Meteroic Diagenesis and Porosity Enhancement in Fluvio-Deltaic Reservoir Facies: B-6 Sands, Maracaibo Basin, Venezuela: ABSTRACT

The Eocene northwest-southeast-trending fault-bounded reservoirs reveal a systematic diagenetic evolution due to changing physical and chemical conditions related to an Oligocene uplift, separating an Eocene and a subordinate Miocene phase of subsidence. Compaction, cementation, and dissolution during Eocene subsidence reduced original porosity to about 20%. The Oligocene uplift created abundant secondary porosity, raising the total porosity to around 30%, especially near the truncated erosion surface on the northwest. Here, abundant lamellar porosity is characteristic. Intense leaching action by undersaturated meteoric CO{sub 2}-charged waters may be responsible for the regenerated porosity. The sandstones immediately below the unconformity surface show the best reservoir quality. Leaching of monocrystalline and polycrystalline quartz, feldspar, rock fragments, and clays has produced a highly porous and permeable diagenetic quartzarenite. Porosity and permeability decrease systematically southeastward as the vertical distance from the unconformity surface increases. Labile grains largely persist, and compaction and cementation (calcite, silica, and clays) reduce the reservoir quality. A patchily welded texture observed in the southeast may be due to silica cement originated from grain dissolution near the unconformity surface on the northwest. Presence of highly degraded crudes lends additional support to the influence of meteoric waters on these reservoirs. Similar processes of silica dissolutionmore » through the action of acidic meteoric water presently occur in extensive outcrops of Precambrian karstic quartzarenites in Venezuela. These tropical analogs support the efficacy of freshwater flushing mechanism and consequent enhancement of reservoir quality in the Eocene sequence.« less

Impact of Freshwater Diagenesis on Reservoir Quality: B-6 Sands, Mosoa Formation, Venezuela: ABSTRACT

Various northwest-southeast-trending fault-bounded Eocene reservoirs in the Maracaibo basin exhibit a systematic trend of diagenetic evolution as a response to changing chemical and physical conditions related to two phases of subsidence (Eocene and Miocene) separated by a period of major Oligocene uplift. The initial subsidence, more important than that of the Miocene, caused compaction, cementation, and dissolution, reducing original porosity from 40% to about 20%. The Oligocene regional uplift created abundant secondary porosity, specifically in the vicinity of the truncated erosion surface at the northwest limit of the reservoirs, through intensive meteoric leaching of framework grains and cements by undersaturated CO/sub 2/-charged waters. Both the porosity and permeability systematically decrease southeastward as the vertical distance from the unconformity surface increases. The sands immediately below the erosional unconformity have the best reservoir quality. They show profuse leaching of monocrystalline and polycrystalline quartz and are virtually free of unstable rock fragments, feldspar, and authigenic clays. In contrast, labile grains largely persist in the areas away from the unconformity where cements of calcite and clays have moderately reduced the reservoir quality. Some of the dissolved silica, resulting from quartz and feldspar dissolution near the unconformity surface, would have precipitated in the areas to more » the southeast where a patchily welded texture commonly was observed. Similar processes of silica dissolution through meteoric water leaching occur in outcrops of Precambrian karstic quartzarenites in Venezuela. These modern analogs in areas of heavy rainfall and copious production of inorganic and organic acids corroborate the efficacy of a freshwater flushing mechanism and consequent enhancement of reservoir quality in the Eocene sequence. « less

Controls on Early Retention and Late Enhancement of Microporosity in Reefal Gas Reservoirs, Offshore North Sumatra Basin: ABSTRACT

Chalky lime-matrix texture is pervasive in 300 m of coralgal and skeletal carbonates in the NSB-A (North Sumatra basin-A) gas field (lower-middle Miocene), offshore northern Sumatra. Much of the reservoir quality can be attributed to matrix with abundant intercrystalline, vuggy, and channel-form micropores. Matrix is composed of calcite microrhombs which are interpreted to have developed during stabilization of the precursor mud. On the same shelf, the smaller NSB-H oil field is composed of more than 45-m thick buildup of similar lithofacies which lack abundant microporosity. In both fields, early diagenesis included dissolution of aragonitic skeletal material, matrix neomorphism, and precipitation of nonluminescent calcite followed by zoned, luminescent calcite cements. Stable isotopes from matrix reflect a more open or water-dominated matrix diagenesis at NSB-H field. More active flushing of oversaturated, organically charged meteoric waters was responsible for thorough matrix cementation and microporosity occlusion at NSB-H field. Calcite cements show progressive enrichment of iron and manganese and depletion of magnesium and strontium during growth. The matrix at NSB-H field contains iron-rich dolomite. At A field, remnant matrix microporosity and intraparticle microporosity in calcitic skeletal material were greatly enhanced after all phases of cementation. Some pore-rimming cements are partially dissolved. At NSB-H field,more » late-phase dissolution is limited to the vicinity of open fractures where matrix-calcite and dolomite crystals are leached. Reservoir brines have a limey marine origin but are depleted in Ca and Mg relative to seawater, and carbon dioxide accounts for 31% of reservoir gas. If present brines are carbonate undersaturated, they may be substantially enhanced microporosity at NSB-A field. Late-stage dissolution is insignificant at NSB-H field due to the lack of early formed matrix microporosity.« less

In a Persian Oil Field: a Study in Scientific and Industrial Development

THE Tigris and Euphrates join north-west of Basrah and thence flow to the Persian Gulf as the broad, silt-filled stream known as the Shattel-Arab. For some hundred miles the combined rivers wind their way between low banks of alluvium, on which, except for the small areas cultivated around the Arab villages, nothing of value grows save the date palm. The scene and the surrounding country have probably been much the same for the past two thousand years, although evidences of Roman irrigation works indicate that, at one time, vast areas of the country must have been under effective cultivation and,iave remained so until the system, lapsing into disrepair, enabled the highly charged waters of the two rivers again to impreg nate the soil with mineral salts so as to render it productive of little but the camel thorn. In a Persian Oil Field: a Study in Scientific and Industrial Development. By J. W. Williamson. Pp. 189 + 24 plates. (London: Ernest Benn, Ltd., 1927.) 7s. 6d. net.