Brine Migration Research Articles

The fluid regime during fracturing of the Embla field, Central Trough, North Sea

The deep Embla field, located in the Central Trough, North Sea, represents the first oil reservoir in Paleozoic rocks to be developed on the Norwegian shelf. The reservoir consists of braided fluvial and alluvial fan sandstones interlayered with floodplain/lacustrine mudstones and volcanics and intrusives. Extensive fracturing of the reservoir has led to the formation of numerous mineralised veins. Three main types of mineralised fractures can be identified: (1) early diagenetic veins and veins which occur in and around mafic igneous rocks; (2) carbonate-dominated veins; (3) barite, clay minerals and bitumen veins. This article presents fluid inclusion evidence from fracture-filling minerals, suggesting that the fractures were important fluid conduits of both petroleum and brine migration. The petroleum inclusion data are consistent with an undersaturated oil composition. A range in salinity between 23 and 12 wt % NaCl eq is found for the aqueous inclusions. The variation in salinity indicates mixing between a high saline fluid, related to evaporites, and a fluid with lower salinity. Microthermometry data suggest that the fracturing events occurred at deep basinal levels, at temperatures in excess of 100°C.

Origin, Migration, and Mixing of Brines in the Permian Basin: Geochemical Evidence from the Eastern Central Basin Platform, Texas

Formation waters from producing reservoirs in Paleozoic carbonates have been studied to determine the origin of brines on the eastern Central Basin platform in west Texas. Chemical and isotopic analyses of these waters indicate mixing of brines of quite different origins in the deep subsurface of the Permian basin. Formation waters from the middle Permian San Andres Formation at 1430 m (4700 ft) and from Devonian limestones at 3200 m (10,500 ft) have salinities of 26-59 g/L and dD-d18O values in the same range as modern precipitation and groundwater in the near-surface Ogallala aquifer. Na-Cl-Br concentrations and molar ratios show that the salinity of these waters was largely acquired through halite dissolution. Formation waters from Pennsylvanian and Lower Permian shelf limestones at 2600-3000 m (8500-9800 ft) are more saline (70-215 g/L) and apparently represent a mixture of two different fluids. One end member was highly saline, derived from seawater evaporated well beyond halite saturation, and the other end member was a moderately saline meteoric water similar to the San Andres and Devonian formation waters. Halite beds occur only in Upper Permian (upper Guadalupian and Ochoan) strata in this area; hence, extremely saline evaporated seawater apparently descended into the Paleozoic carbonates during halite deposition in the Late Permian, mixing with and displacing marine formation waters by buoyancy-driven convective flow. These modified evaporitic brines were the dominant fluids in the Paleozoic carbonates until the late Tertiary, when meteoric water began to flow into deeper Paleozoic strata from outcrops and near-surface aquifers in southeastern New Mexico in association with tectonic uplift that began at 5-10 Ma. The meteoric water dissolved halite and anhydrite from Permian evaporites near the basin margin and moved eastward along the regional hydraulic gradient, mixing with and displacing the modified evaporitic brine in deeper hydrogeologic systems. These late Cenozoic meteoric fluids probably are responsible for widespread biodegradation of oil in the San Andres/Grayburg interval. The results of this study indicate that meteoric waters can migrate large distances and displace saline waters deep in a basin that has numerous oil reservoirs that have solution-gas drive. Understanding the history of formation waters can assist in exploration and production through improved (1) interpretation of reservoir-rock diagenesis, (2) prediction of oil biodegradation and displacement, (3) understanding of subsurface water pressures, and (4) interpretation of hydrocarbon saturations from resistivity logs.

Non-linear thermal transport and brine convection in first-year sea ice

We report the first results from a programme recently set up to directly measure the thermal conductivity of young sea ice. An array of thermistors frozen into first-year Antarctic sea ice provides temperature vs depth data, which is fitted directly with a partial differential equation for heat conduction. Temperatures are recorded every hour at 20 vertical intervals of 100 mm over a period of 5 months, allowing accurate and direct estimation of the thermal conductivity. Preliminary results indicate that the thermal conductivity is in the expected range, with some evidence of non-linear effects deeper in the ice. A larger variance in data is evident at higher temperature gradients and at greater depths in the ice. Preliminary modelling of the impact of brine migration on heat transport through first-year sea ice is presented. Diffusion-driven brine pocket migration is too slow to contribute significantly to heat flow, but the convective instability of inclined brine slots or tubes is a promising mechanism.

Fluid migration and coal-rank development in foreland basins

Research Article| August 01, 1998 Fluid migration and coal-rank development in foreland basins Rod Gayer; Rod Gayer 1Department of Earth Sciences, Cardiff University, P.O. Box 914, Cardiff CF1 3YE, United Kingdom Search for other works by this author on: GSW Google Scholar Grant Garven; Grant Garven 2Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, Maryland 21218 Search for other works by this author on: GSW Google Scholar David Rickard David Rickard 1Department of Earth Sciences, Cardiff University, P.O. Box 914, Cardiff CF1 3YE, United Kingdom Search for other works by this author on: GSW Google Scholar Author and Article Information Rod Gayer 1Department of Earth Sciences, Cardiff University, P.O. Box 914, Cardiff CF1 3YE, United Kingdom Grant Garven 2Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, Maryland 21218 David Rickard 1Department of Earth Sciences, Cardiff University, P.O. Box 914, Cardiff CF1 3YE, United Kingdom Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1998) 26 (8): 679–682. https://doi.org/10.1130/0091-7613(1998)026<0679:FMACRD>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Rod Gayer, Grant Garven, David Rickard; Fluid migration and coal-rank development in foreland basins. Geology 1998;; 26 (8): 679–682. doi: https://doi.org/10.1130/0091-7613(1998)026<0679:FMACRD>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Mathematical modeling of regional fluid flow in the South Wales foreland basin shows that heat was transferred from internal to peripheral parts of the basin, where very high geothermal gradients and surface heat flow would have developed. In the fluid-discharge areas, temperatures are modeled to have reached 300 °C within the coal measures section and would have generated anthracite, while more internal parts of the basin were cooled by descending fluid flow, and temperatures of only 220 °C resulted, sufficient to form bituminous coal. The modeled thermal regime appears to match the pattern of coal rank observed in the basin. The regional flow probably continued for 1 to 2 m.y. before erosion diminished the topographic gradient driving brine migration in the late Paleozoic. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Burial diagenesis of middle Ordovician carbonate buildups (Alabama, USA): documentation of the dominance of shallow burial conditions

Middle Ordovician carbonate buildups at two localities (Red Mountain Expressway = RME; Tidwell Hollow = TWH) record evidence of burial diagenesis. Burial diagenetic phases include (from oldest to youngest): (1) blocky calcite, (2) planar dolomite associated with stylolites, (3) saddle dolomite in primary voids and late veins, and (4) blocky calcite in late veins. All blocky calcite cements post-date Ordovician meteoric cement based on cross-cutting and superposition relationships and blocky calcite is the most common burial diagenetic phase present in the Chickamauga buildups. Blocky calcite (not in late veins) formed from post-Ordovician meteoric water based on the multiple lines of evidence, which include: (1) variable δ 18O values (−5.2 to −11.4‰ some of which are significantly more negative than values from Ordovician meteoric cement; (2) non-radiogenic 87 Sr 86 Sr values (0.70847 to 0.70869); and (3) low Fe and Mn values near or below detection limit (400 ppm). Planar dolomite associated with stylolites has variable δ 18O values (−1.4 to −6.1%e), is Ca-rich (non-stoichiometric), and has relatively low Mn and Fe values. This phase is interpreted as forming during the Mississippian or earliest Pennsylvanian at a relatively shallow burial depth. Rare saddle dolomite has 880 = −5.9 to −7.2%0. This phase post-dates planar dolomite and appears to record migration of basinal brines into the platform succession during the Alleghenian orogeny. Late veins filled with saddle dolomite and blocky calcite have variable δ 18O compositions like blocky calcite (−4.8 to −12.8%0) and likely formed under elevated temperature conditions if precipitation from δ 18O-enriched burial brines is assumed.

Uncertainty and sensitivity analysis for gas and brine migration at the Waste Isolation Pilot Plant: permeable shaft without panel seals

Latin hypercube sampling, partial correlation analysis, stepwise regression analysis and examination of scatterplots are used in conjunction with the BRAGFLO model in an uncertainty and sensitivity analysis of gas and brine movement at the Waste Isolation Pilot Plant. Topics investigated include (1) gas production due to corrosion of steel and microbial degradation of cellulosics, (2) gas saturation and pressure in the repository, (3) gas movement in anhydrite marker beds, and (4) gas and brine movement through a short, low permeability shaft seal to the Culebra Dolomite. Important variables identified in the analysis include initial brine saturation of the waste, stoichiometric terms for corrosion of steel and microbial degradation of cellulosics, corrosion and microbial degradation rates, porosity of the Salado Formation, transition (disturbed) zone porosity, marker bed (anhydrite) permeability, and seal permeability. Published by Elsevier Science Limited.

Petroleum Hydrogeology of the Cooper and Eromanga Basins, Australia: Some Insights from Mathematical Modeling and Fluid Inclusion Data

Mathematical modeling and fluid inclusion data analysis are used to reconstruct the petroleum hydrogeology of the Australian Cooper and Eromanga basins. Our analysis focuses on the development of topography- and compaction-driven groundwater flow systems and their role in heat redistribution, petroleum generation, and oil and brine migration during basin evolution. Finite-element models of basin transport processes are constructed along northeast-southwest (AA´) and northwest-southeast (BB´) cross sections that generally follow the present-day groundwater flow patterns through these basins. Numerical results are presented in the ©Copyright 1997. The American Association of Petroleum Geologists. All rights reserved.1Manuscript received September 19, 1995; revised manuscript received July 3, 1996; final acceptance November 11, 1996. 2Independent Consultant, 12 Rinzee Road, Dracut, Massachusetts 01826. 3CSIRO Division of Petroleum Exploration, 51 Delhi Road, North Ryde, NSW 2113, Australia. 4Department of Geology and Geophysics, University of Minnesota, 310 Pillsbury Drive SE, Minneapolis, Minnesota 55455 (E-mail: mperson@ darcy.geo.umn.edu) 5GZA GeoEnvironmental Inc., 380 Harvey Road, Manchester, New Hampshire 03103. 6Santos Ltd., 101 Grenfell Street, Adelaide, SA 7000, Australia. This research is supported by a grant from the Petroleum Research Fund, administered by the American Chemical Society, PRF 24184-AC8. We would also like to acknowledge the Orpha and George Gibson Hydrogeology Endowment and the McKnight Land-Grant Professorship Program at the University of Minnesota. We thank the CSIRO Division of Exploration Geosciences for providing support for travel costs within Australia. Data provided by Santos Ltd. and the Department of Mines and Energy, South Australia, are also gratefully acknowledged. Computational work performed on this project was done at the Gibson Computational Hydrogeology Laboratory at the University of Minnesota, which is supported by the National Science Foundation under EAR 94-05807. Special thanks go to M. A. Habermehl of the Australian Geological Survey Organization, David Gravestock of the South Australia Bureau of Mines and Mineral Resources, and Mike Congreves of Santos Ltd. for their assistance on interpreting the petroleum geology and hydrogeology of the Cooper and Eromanga basins. The review comments of Joseph Toth, Stefan Bachu, and Michelle Walvoord, as well as discussions with Ward Sanford, greatly improved the quality of this manuscript. Three-dimensional model results presented in this paper are available in animated form on VHS videocassette and can be obtained by contacting Mark Person at the address listed for him as the corresponding author.

The age and timing of folding in the central Appalachians from paleomagnetic results

Comparison of the paleomagnetic pole positions of late Paleozoic secondary magnetizations with a time-averaged reference apparent polar wander path for North America shows that sedimentary rocks within the central Appalachians were remagnetized in the later half of the Permian, between ca. 255 and 275 Ma. Ages of remagnetization do not vary for sites distributed along or across strike of the central Appalachian fold and thrust belt or across the Appalachian Plateau in New York, nor do they vary with stratigraphic position of the host rocks. However, the pattern of folding relative to remagnetization across the Valley and Ridge and Great Valley in Pennsylvania, Maryland, and West Virginia shows a distinct temporal variation. Individual fold tests yield postfolding magnetizations near the hinterland margin of the fold and thrust belt, synfolding magnetizations in the central part of the belt, and prefolding magnetizations near the foreland. Because of the similar age of the late Paleozoic magnetization, we conclude that rocks across the central Appalachians were remagnetized in a relatively short period of time as folding and thrusting propagated more slowly toward the foreland. We interpret this pattern to indicate that older folds near the hinterland grew prior to remagnetization, folds in the central region grew during remagnetization, and folds near the foreland grew after remagnetization. Rapid remagnetization relative to folding is also evident from the physical characteristics and magnetic properties of secondary hematite in remagnetized (synfolding) folds. In such folds, rocks were apparently remagnetized during an increment of fold growth, in which there was partial and possibly negligible fold-limb rotation. Collectively, these results may constrain the mechanism for basinal fluid mobilization during deformation. Current models for remagnetization involve the migration of chemically active brines into the foreland during tectonism. If realistic, our results bear on this model by suggesting that brine migration was not directly related to the successive emplacement of individual thrust sheets, as has been suggested for other fold and thrust belts.

Structural control of deep fluid circulation at the Soultz HDR site, France: a review: Y. Benderitter & P. Elsass, Geothermal Science & Technology, 4(4), 1995, pp 227–237

HDR research in Europe now places emphasis on the stimulation of a preexisting unsealed fracture network in hot deep rocks. The Soultz-sous-Forets site, located on the thermal anomaly of the Upper Rhine Valley, is strongly structured by Rhine Graben tectonics, and hydrothermal brines occur at depth in sediments and granite. According to the literature, the thermal anomaly is best explained by a general horizontal migration of brines in the sedimentary cover and local vertical convective loops within the granite basement. Observations made in deep reconnaissance boreholes at Soultz, down to 3600m, show that the granite is affected by hydrothermally altered fracture zones, some of which are still permeable and carry hydrothermal brines. These fracture zones, which could constitute an interconnected network, appear to belong to two main north-trending sets, dipping respectively east and west and corresponding to Tertiary Rhine Graben tectonics, and to a NW-SE-trending set, interpreted as reactivated pre-Rhine Graben basement faulting. The deep thermal exchanger to be created at Soultz could take advantage of the flow paths of natural convective loops in granite by connecting drill holes with major permeable fracture zones

Uncertainty and sensitivity analysis for gas and brine migration at the Waste Isolation Pilot Plant: Permeable shaft with panel seals

Uncertainty and sensitivity analysis techniques based on Latin hypercube sampling, partial correlation analysis, stepwise regression analysis and examination of scatter plots are used in conjunction with the BRAGFLO model to examine two-phase (i.e., gas and brine) flow at the Waste Isolation Pilot Plant (WIPP), which is being developed by the US Department of Energy as a disposal facility for transuranic waste. The following topics are investigated to develop insights on factors that are potentially important in establishing compliance with applicable regulations of the US Environmental Protection Agency (i.e., 40 CFR 191, Subpart B; 40 CFR 268): (1) gas production due to corrosion of steel; (2) gas production due to microbial degradation of cellulosics; and (3) gas migration through a sealed shaft to the Culebra Dolomite. Important variables identified in the analysis include initial brine saturation of the waste, stoichiometric terms for corrosion of steel and microbial degradation of cellulosics, and seal permeabilities.

K/Ar Dating of Authigenic Illite Constrains the Time of Diagenesis and Brine Migration in the Weber Sandstone of the Uinta-Piceance Basin, Colorado and Utah: ABSTRACT

K/Ar Dating of Authigenic Illite Constrains the Time of Diagenesis and Brine Migration in the Weber Sandstone of the Uinta-Piceance Basin, Colorado and Utah: ABSTRACT

Uncertainty and Sensitivity Analysis for Gas and Brine Migration at the Waste Isolation Pilot Plant: Fully Consolidated Shaft

Uncertainty and sensitivity analysis techniques based on Latin hypercube sampling, partial correlation analysis, stepwise regression analysis, and examination of scatterplots are used in conjunction with the BRAGFLO model to examine two-phase flow (i.e., gas and brine) at the Waste Isolation Pilot Plant, which is being developed by the US Department of Energy as a disposal facility for transuranic waste, to provide insights on factors that are potentially important in showing compliance with applicable regulations of the US Environmental Protection Agency. Specific regulations include Petitions to Allow Land Disposal of a Waste Prohibited Under Subpart C of Part 268 (40 CFR 268.6), which implements the Resource Conservation and Recovery Act and establishes maximum environmental concentrations for regulated chemicals such as volatile organic compounds (VOCs) and heavy metals, and Environmental Standards for the Management and Disposal of Spent Nuclear Fuel, High-Level and Transuranic Radioactive Wastes (40 CFR 191, Subpart B), which places a probabilistic limit on allowable radioactive releases from a disposal facility over a 10,000-yr time period. The primary topics investigated are (a) gas production due to corrosion of steel, (b) gas production due to microbial degradation of cellulosics, and (c) gas migration into anhydrite marker beds in the Salado Formation,more » which is the host unit into which the waste will be emplaced. Gas production and movement is of particular importance in establishing compliance with 40 CFR 268.6 because of its influence on the movement of VOCs. Important variables identified in the analysis include (a) initial brine saturation of the waste, (b) stoichiometric terms for corrosion of steel and microbial degradation of cellulosics, and (c) gas barrier pressure in the anhydrite marker beds.« less

Basement Unconformity Control on Alteration, St. Francois Mountains, SE Missouri

The basement-Lamotte Formation unconformity in southeastern Missouri shows evidence of several distinctive alteration events, some of which may be related to migration of ore-forming fluids or K-rich basinal brines. The alterations are spatially related to the unconformity, suggesting that the unconformity was a preferred pathway for fluid migration. Unconformity-related rocks in five cores penetrating both the Lamotte Formation and the basement have been characterized by bulk chemistry, mineralogy, textures, and paleotopographic position. The alteration history along the unconformity includes: (1) Pre-Lamotte hydrothermal alteration affecting basement, (2) Pre-Lamotte weathering, and (3) Post-Lamotte hydrothermal and diagenetic events. The third group is particularly complex, including early diagenetic hematite and calcite cementation, later quartz cementation, secondary biotite growth, K-metasomatism that generated adulaira, and K-leaching that left a narrow dickite-rich zone along the unconformity. Sev...

Origin of Iodine in the Anadarko Basin, Oklahoma: An 129I Study

Iodine comes almost exclusively from organic matter in sedimentary basins and, therefore, can be used as a source indicator for hydrocarbons. The long-lived (half-life 15.7 m.y.) cosmogenic and fissiogenic isotope 129I has been applied to tracing brine migration in the Anadarko basin, Oklahoma. Because all of the likely source formations for I are Paleozoic, the cosmogenic 129I component has decayed to undetectable levels and all of the measured 129I is of fissiogenic origin. Comparison of 129I/127I ratios measured in 12 brines from the platform area of the Anadarko basin with ratios determined for potential source rocks reveals that the Woodford Shale is the probable source formation for the extremely high I concentr tions observed in these brines. If the Woodford Shale is the exclusive source for I, the time of expulsion can be constrained to between 2 and 90 Ma. Although this date is much later than most estimates of expulsion time derived from conventional methods, a case is presented for more recent expulsion in the northern part of the basin, which was the sample area.

Determination of source ages and migration patterns of brines from the U.S. Gulf Coast basin using 129I

The long-lived cosmogenic and fissiogenic isotope 129I has been applied to the study of source ages and migration patterns of oil field brines from the U.S. Gulf Coast basin. 129 I I ratios were measured in sixty samples of saline formation water from depths of 660–4503 m in several oil fields in southeast Texas, south-central Louisiana, and offshore Louisiana. Comparisons between measured ratios and the decay curve for surface hydrospheric 129I result in minimum source ages much older than present host formation ages, indicating vertical migration of brine from older, deeper sources. Conservative corrections for a fissiogenic component due to spontaneous fission of 238U in the subsurface result in the following median source ages: Iberia field: 55 Ma, Port Barre field: 53 Ma, and Eugene Island Blocks 316 and 330: 55 Ma, pointing to Wilcox Group shales as source formations. Mesozoic sources cannot be ruled out, due to the uncertainties in estimating the fissiogenic component. Some of the ratios measured in Texas Gulf Coast brines show evidence of a greater fissiogenic component which indicates that the brines have resided in formations with locally high U concentrations.

Mechanisms of sulfate removal from subsurface calcium chloride brines: Heletz-Kokhav oilfields, Israel

The evolution of the Ca-chloride brines in the Heletz Formation, Lower Cretaceous, in the southern coastal plain of Israel was reconstructed through the study of its sulfate concentration and isotopic composition. Particular emphasis was given to the brine-oil interaction in the oilfields and to the sulfate depletion and lower SO4/Cl ratio in brines in contact with hydrocarbons (oil brines) relative to “oil-free” from dry wells in the same oilfields.A method is presented for a calculation of the amount of sulfate removed from the original seawater in the various stages of its evolution to Ca-chloride brine. These stages include evaporation, dolomitization, and sulfate reduction in different stages of its evolution, from early diagenetic processes to the contact with crude oil. In the present study, based on the δ34SSO4 and SO4/Cl ratio, it was found that in the Heletz brines most of the sulfate (80–94%) was removed from the original seawater prior to their interaction with the hydrocarbons and only a negligible fraction of few percent of the sulfate was removed during the crude oil-water contact.The Ca-chloride brines evolved from Messinian (Upper Miocene) seawater that underwent evaporation during the desiccation of the Mediterranean. Sulfate was removed from Messinian lagoon (s) during gypsum precipitation due to evaporation and dolomitization. Bacterial sulfate reduction further depleted the brine in sulfate and changed its isotopic composition, from its original Miocene seawater composition of δ34SSO4 ∼ 20%o, 26%o. Overall, some 50% of the original sulfate, as normalized to chloride, was removed from the original lagoon through the above processes, mostly by gypsum precipitation. Eastward migration of the Messinian Ca-Chloride brine into the Heletz Formation was accompanied by dolomitization of the country rock.Final depletion of sulfate from the brines took place, and possibly still occurs, in the presence of crude oil in the oilfields. The two oil-producing fields, Heletz and Kokhav, occupy different areas on a Rayleigh distillation diagram. Sulfate depletion in both fields is accompanied by an increase in δ34SSO4, which reaches a maximum value of 59%o. The above correlation is explained by bacterial sulfate reduction facilitated by the contact with the crude. Samples collected from the same boreholes at time intervals of several months show two opposing trends: sulfate concentration decrease accompanied by increase in δ34SSO4, and vice versa. While the first can be explained as in situ bacterial sulfate reduction, the latter attest to subsurface brine migration, as would be expected in oil-producing fields.

Secondary K-feldspar at the Precambrian–Paleozoic unconformity, southwestern Ontario

The Precambrian–Paleozoic boundary in the subsurface of southwestern Ontario commonly is characterized by secondary K-feldspar. In the weathered and altered Precambrian granitoid gneisses at the unconformity, secondary K-feldspar has replaced preexisting minerals, and also occurs as discrete crystals of adularia, overgrowths on altered minerals, and microcrystalline veinlets. The K-feldspar is chemically pure (Or99–100) and has high δ18O values (+18.9 to +21.4‰ Vienna Standard Mean Ocean Water), features that indicate crystallization at low temperatures. Secondary K-feldspar also occurs in Cambro-Ordovician clastic and carbonate rocks that immediately overlie the Precambrian basement. K/Ar (453 ± 9 to 412 ± 8 Ma) and Rb/Sr (440 ± 50 Ma) dates obtained for secondary K-feldspar from the Precambrian host rocks suggest that its crystallization is unrelated to Precambrian weathering or early diagenesis of the immediately overlying Cambro-Ordovician strata. Estimated crystallization temperatures for the secondary K-feldspar (≥100 °C) exceed presumed burial temperatures for the Precambrian–Paleozoic boundary in southwestern Ontario during Late Ordovician–Silurian time. We infer that secondary K-feldspar formed from a hot brine that moved preferentially along the Precambrian–Paleozoic unconformity. The wide distribution of secondary K-feldspar of Late Ordovician–Silurian age throughout mid-continental North America at the Precambrian–Paleozoic boundary records the regional extent of this process. Some Cambro-Ordovician rocks elsewhere in the mid-continent also contain secondary K-feldspar and illitic clay of Late Pennsylvanian–Early Permian age, suggesting more than one episode of fluid movement. Major pulses of orogenic activity may have initiated brine migration. We speculate that the brine originated as connate (sea) water trapped in lower Paleozoic strata, and was modified by rock–water interaction at elevated temperatures, and by mixing with meteoric water.

Thermal comparison of mississippi valley-type lead-zinc deposits and their host rocks using fluid inclusion and conodont color alteration index data

Fifteen North American Mississippi Valley-type districts, distributed from the Arctic archipelago to Arkansas and in host rocks ranging in age from Late Cambrian to early Carboniferous, were selected for abroad test survey of Mississippi Valley-type district thermal histories. For each district in which data were collected, histograms of homogenization temperatures for the ore minerals were compared with the temperature range of the corresponding host rocks, as indicated by color alteration index (CAI) determinations on conodonts in the host-rock carbonates. Although a special effort was made to collect conodonts from the Upper Cambrian Bonneterre Formation, host rock to the Southeast Missouri district, all samples were devoid of conodonts. Thus only 14 districts were used in the final analysis.Comparison of fluid inclusion homogenization temperatures in main-stage ore minerals with color alteration index-determined host-rock temperatures reveals that a majority of Mississippi Valley-type districts (Pine Point, Newfoundland Zinc, Mascot-Jefferson City, Copper Ridge, Sweetwater, Central Missouri, Northern Arkansas, and Tri-State) are representative of group 1 (i.e., they are in thermal equilibrium with their host rocks insofar as could be determined by the color alteration index method). Ore minerals in group 2 districts (Upper Mississippi Valley, Polaris, and central Tennessee) are significantly hotter than surrounding host rocks and, as such, define a positive thermal anomaly. Host rocks to the Austinville-Ivanhoe, northern Newfoundland, and Robb Lake deposits (group 3) revealed the highest color alteration index values of North American Mississippi Valley-type districts, with host-rock temperatures greatly exceeding ore mineral fluid inclusion temperatures (negative thermal anomaly).With respect to major tectonic elements of North America, group 3 deposits (cool ore in hot rocks) are positioned within orogenic belts but on the continental side. Some group 1 deposits (ore temperature = host-rock temperature) are well within the continental interior but others are adjacent to orogenic belts on the continental side. Group 2 deposits (hot ore in cool rocks) are all within the continental interior.Current hypotheses regarding the formation of Mississippi Valley-type deposits and simultaneous heating of their host rocks invoke the migration of hot brines set into motion craton-ward by the hydraulic gradient produced by orogenic uplift at the craton edge. Once the ore-bearing fluids entered the foreland carbonate platforms, they traveled through sedimentary aquifers of the continental interior raising the temperature of the thinly covered carbonate rocks. The fluids left, as evidence of their passage, elevated color alteration index values and group 1 Mississippi Valley-type deposits distributed with decreasing homogenization temperatures away from the orogenic front. The correspondence between host-rock and ore temperatures suggests that group 1 deposits were deposited essentially within their own aquifers.Group 2 deposits were formed when the same, or genetically similar, fluids rose from the regional aquifer(s) into structurally controlled conduits in the continental interior, possibly developed as a result of synorogenic doming and arching. This upward channeling of the fluids resulted in rapid and localized fluid flow which precluded or at least inhibited wide-spread heating of the host rocks by ore fluids; consequently, color alteration index values in group 2 districts record only maximum burial depths of the host rocks and bear little relation to temperatures of the ore fluids. Although the cause of the unusually high color alteration index values (4-5) of group 3 districts is not fully understood, it is noted that these districts occur near the extreme outward edge of foreland platforms, near or within the leading margins of orogenic belts. Whether these group 3 host rocks were heated by simple tectonic burial or by passage of heated fluids under shallower conditions is not known.

Saline groundwater in Israel: its bearing on the water crisis in the country

One of the major causes for the deterioration of water quality bearing heavily on the water crisis in Israel is the ongoing contamination of its water resources by saline water bodies. The present paper reviews the geochemical processes forming saline water, lists and explains certain chemical and isotopic parameters which enable understanding these processes and describes the saline groundwater bodies and various salinization phenomena occurring in the country's various aquifers. Deterioration of groundwater in Israel is caused by numerous natural processes such as encroachment of sea water, migration of connate, highly pressurized brines penetrating into fresh groundwater, by subsurface dissolution of soluble salts originating in surrounding country rocks and by water-rock interaction. In addition to sea water, two saline water bodies were identified as the main factors causing salinization of fresh groundwater: (a) Ca-chloride brines encountered in the Jordan-Dead Sea Rift Valley, in various parts of the Negev and of the Coastal Plain, and (b) Na-chloride saline water identified in the subsurface of the Negev and in the southern part of the Coastal Plain. Intensive exploitation of groundwater in Israel has disturbed the natural equilibrium which prevailed between fresh and saline water. The newly established groundwater flow regimes have facilitated the migration of saline water bodies, their participation in the active hydrological cycle and the progressive contamination of fresh groundwater. These processes which were not anticipated by planners and water resources managers emphasize that large-scale groundwater exploitation was undertaken without giving sufficient consideration to the occurrence and subsurface migration of saline water and brines.

A Methodology to Evaluate Regional Hydraulic Controls on Flow from Hydrocarbon Reservoirs into Overlying Aquifers: ABSTRACT

Because drilling, completion, and abandonment practices for oil and gas wells have improved over the past century, some older abandoned wells may be mechanically deficient or inadequately plugged, thus posing a risk of contamination to underground sources of drinking water. The risk of saltwater contamination of freshwater aquifers through inadequately plugged, abandoned wells increases if the hydraulic potential of the oil- and-gas-bearing brine formations is higher than that in the overlying freshwater aquifers. First, average regional potentiometric surfaces of aquifers and reservoirs are generated from aquifer water-level measurements and the conversion of bottom-hole pressure measurements from oil and gas reservoirs to hydraulic heads. Next, differences in hydraulic heads between aquifers and reservoirs are calculated to delineate regional residual areas of upward (positive) or downward (negative) hydraulic gradients. Third, locations of abandoned wells and class II injection wells are plotted relative to residuals to examine where water flooding, pressure maintenance, and saltwater disposal may cause or exacerbate the potential for upward flow. Three areas were used as case studies for testing the method. Positive residuals in the South Texas basin (informally defined to include the Val Verde basin, Maverick basin, part of the Rio Grande Salt basin, and the Austin Chalkmore » trend) result from natural geopressuring in formations deeper than 6000 ft, which are negligibly affected by class II injection wells. Positive residuals in the greater Permian basin (including the northwestern shelf, Delaware basin, part of the Palo Duro basin, Central Basin platform, Midland basin, southern shelf, and Fort Worth basin) may reflect injection for enhanced recovery in the west and natural hydrologic processes in the eastern shelf region. Residual surfaces for the San Juan basin indicate several areas with a natural potential for upward migration of brine.« less