Dehydration Of Clay Minerals Research Articles

A Smectite Dehydration Model in a Shallow Sedimentary Basin: Model Development

AbstractTraditionally, land subsidence resulting from groundwater over-pumping has often been described by the theory of consolidation. The mechanism of land subsidence due to the dehydration of clay minerals has not been well addressed. Therefore, this study develops a smectite dehydration model to describe the effect of the release of water from the smectite interlayer upon land subsidence. Using a thermodynamic solid-solution model and laboratory studies of clay-water systems, a complete description of the dehydration relationships among the swelling pressure, basal spacing and mw/mc in a Na-smectite water system at 25°C under variable pressure conditions was derived. Accordingly, the evaluation model of the ‘hydration state of smectite’, and the ‘solid-solution model of smectite dehydration’ were formulated rigorously. These two models were applied to quantify the effects of smectite dehydration on the accumulated land subsidence in the Yun Lin offshore industrial infrastructure complex and in the Tai-Shi area. The result reveals that smectite dehydration is of importance in assessing and predicting land subsidence in a shallow sedimentary basin.

Fluid expulsion related to mud extrusion off Costa Rica—A window to the subducting slab

Research Article| March 01, 2004 Fluid expulsion related to mud extrusion off Costa Rica—A window to the subducting slab C. Hensen; C. Hensen 1Sonderforschungsbereich 574, Kiel University, Wischhofstrasse 1-3, 24148 Kiel, Germany, and GEOMAR, Wischhofstrasse 1-3, 24148 Kiel, Germany Search for other works by this author on: GSW Google Scholar K. Wallmann; K. Wallmann 2GEOMAR, Wischhofstrasse 1-3, 24148 Kiel, Germany, and Sonderforschungsbereich 574, Kiel University, Wischhofstrasse 1-3, 24148 Kiel, Germany Search for other works by this author on: GSW Google Scholar M. Schmidt; M. Schmidt 3Institute of Geosciences, Kiel University, Ludewig-Meyn-Strasse 10, 24118 Kiel, Germany, and Sonderforschungsbereich 574, Kiel University, Wischhofstrasse 1-3, 24148 Kiel, Germany Search for other works by this author on: GSW Google Scholar C.R. Ranero; C.R. Ranero 4 GEOMAR, Wischhofstrasse 1-3, 24148 Kiel, Germany, and Sonderforschungsbereich 574, Kiel University, Wischhofstrasse 1-3, 24148 Kiel, Germany Search for other works by this author on: GSW Google Scholar E. Suess E. Suess 4 GEOMAR, Wischhofstrasse 1-3, 24148 Kiel, Germany, and Sonderforschungsbereich 574, Kiel University, Wischhofstrasse 1-3, 24148 Kiel, Germany Search for other works by this author on: GSW Google Scholar Author and Article Information C. Hensen 1Sonderforschungsbereich 574, Kiel University, Wischhofstrasse 1-3, 24148 Kiel, Germany, and GEOMAR, Wischhofstrasse 1-3, 24148 Kiel, Germany K. Wallmann 2GEOMAR, Wischhofstrasse 1-3, 24148 Kiel, Germany, and Sonderforschungsbereich 574, Kiel University, Wischhofstrasse 1-3, 24148 Kiel, Germany M. Schmidt 3Institute of Geosciences, Kiel University, Ludewig-Meyn-Strasse 10, 24118 Kiel, Germany, and Sonderforschungsbereich 574, Kiel University, Wischhofstrasse 1-3, 24148 Kiel, Germany C.R. Ranero 4 GEOMAR, Wischhofstrasse 1-3, 24148 Kiel, Germany, and Sonderforschungsbereich 574, Kiel University, Wischhofstrasse 1-3, 24148 Kiel, Germany E. Suess 4 GEOMAR, Wischhofstrasse 1-3, 24148 Kiel, Germany, and Sonderforschungsbereich 574, Kiel University, Wischhofstrasse 1-3, 24148 Kiel, Germany Publisher: Geological Society of America Received: 13 Aug 2003 Revision Received: 30 Oct 2003 Accepted: 30 Oct 2003 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2004) 32 (3): 201–204. https://doi.org/10.1130/G20119.1 Article history Received: 13 Aug 2003 Revision Received: 30 Oct 2003 Accepted: 30 Oct 2003 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation C. Hensen, K. Wallmann, M. Schmidt, C.R. Ranero, E. Suess; Fluid expulsion related to mud extrusion off Costa Rica—A window to the subducting slab. Geology 2004;; 32 (3): 201–204. doi: https://doi.org/10.1130/G20119.1 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 A large number of mound-shaped structures that originated from mud extrusions is present along the convergent continental margin off Costa Rica and Nicaragua. Active fluid venting is indicated by the existence of CH4- and H2S-rich pore fluids as well as associated benthic fauna and authigenic carbonates. End-member fluid samples from all mounds are significantly depleted in dissolved Cl and other major elements, suggesting a general process of freshwater addition and thus a common source of the fluids. Our data clearly rule out dilution by gas hydrate dissociation as a dominant source of the freshwater. Enrichments of the fluids in B (up to 2 mmol/L) and inversely correlated δ18O vs. δD values point to clay-mineral dehydration as the cause for these anomalies. Calculations assuming a δ18O vs. δD equilibrium between the pore fluid and clay minerals at depth of formation indicate temperatures of dehydration between 85 and 130 °C. This temperature range is in agreement with the B enrichments and the presence of thermogenically formed CH4. Because temperatures above 50 °C are not reached within the sediment cover of the upper plate, the fluids most likely form within the subducted sediments and flow upward along deep-seated faults from ≥12 km depth. Mound-related fluid expulsion may contribute significantly to the recycling of mineral-bound water. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Fluid–sediment interactions at Eastern Mediterranean mud volcanoes: a stable isotope study from ODP Leg 160

Pore fluids from two ODP sites at Eastern Mediterranean mud volcanoes have been analyzed for their Cl concentration and their δ 18O and δD isotopic composition. The Cl data span a wide range of concentrations, from extremely depleted with respect to seawater (as low as 60 mM) at the crest of Milano dome (site 970) to strongly enriched (up to 5.4 M) at Napoli dome (site 971). Chloride enrichment is known to be due to dissolving Messinian evaporites, whereas the source of the low-Cl fluid is deduced from stable isotope data presented here. The isotopic composition of the endmember fluid is found to be +10‰ for δ 18O and −32‰ for δD for low- as well as for high-Cl waters. From this signature it can be concluded that neither gas hydrates nor meteoric water play a significant role in the freshening of the pore water. Several other processes altering the δ 18O/δD composition of pore waters are discussed and considered to be of only negligible influence. The process characterizing the isotopic composition of the fluid is found to be clay mineral dehydration (mainly smectite–illite transformation), corresponding to a depth range of 3.5–7 km and an elevated temperature of about 120–165°C. A quantitative estimate shows that this reaction is capable of producing the observed extreme Cl depletion.

Evolution of gas and aqueous fluid in low-permeability argillaceous rocks during uplift and exhumation of the central Swiss Alps

Fluid chemistry and the hydraulic regime in a marl formation of the Swiss Alps were studied by a number of techniques. Fluid inclusions record the conditions of maximum burial and regional low-temperature metamorphism, whereas fluid samples and hydraulic tests derived from deep boreholes reflect present-day, near-surface conditions. The characterization of the different types of fluids places constraints on the geochemical and hydraulic evolution of low-permeability argillaceous rocks during uplift and exhumation. Fluid inclusions were studied by microthermometry and sampled directly by decrepitation techniques. They contain a two-phase system consisting of an aqueous fluid and a coexisting CH 4-rich gas ( T=190–250°C, P lith≈2500 bar). Bulk and isotopic compositions of aqueous fluid inclusions are consistent with a mixture of connate seawater and water derived from the dehydration of clay minerals. Methane was generated in situ by thermal cracking of kerogen. Textural evidence and stable isotopic signatures of carbonates in veins and in the rock matrix indicate local buffering of fluid compositions and very low water/rock ratios. Free fluids residing in the present-day fracture and matrix porosity consist of CH 4-saturated Na–Cl groundwater with minute amounts of free CH 4 gas which occurs in druses. Their chemical and isotopic compositions are very similar to those of the fluid inclusions, suggesting a common origin. Post-metamorphic admixtures of externally derived waters cannot be identified, and it is suggested that present-day Na–Cl groundwaters that occur in the central parts of the marl have resided in the formation since the time of metamorphism some 20 Ma b.p. The only major change in the fluid composition has been the outgassing of CH 4 from the formation, most probably by diffusion. The hydraulic regime during metamorphism was characterized by localized fluid underpressures in open veins because widely scattered, sub-hydrostatic pressures were often identified in fluid inclusions. The central part of the argillaceous rock body, approximately coinciding with the region where Na–Cl groundwaters occur, has sub-hydrostatic pressures today, as indicated by hydraulic tests in deep boreholes. Both the closed-system behavior derived from the chemical and isotopic characteristics of the fluids and the (recurrent or continuous) existence of hydraulic underpressures suggest very low permeabilities of argillaceous rocks during metamorphism and throughout subsequent uplift and exhumation. All fluids present in the central parts of the formation are either connate or produced in situ. Even though major events of brittle faulting and unloading due to uplift occurred since the peak of metamorphism, fluid flow through the formation has been negligible.

Distribution and origin of underground water chemical fields in Songliao continental oil-bearing sedimentary basin

There are many factors affecting underground water chemistry of an oil-bearing sedimentary basin. The properties of underground water show variations in the vertical direction, giving rise to a vertical zonation with respect to underground water chemistry. Five zones could be divided downwards, including 1) the freshening zone due to meteoric water leaching (A); 2) the evaporation-concentration zone near the surface (B); 3) the freshening zone due to stratum compaction-released water(C1)—infiltration-concentration zone during the mudstone compaction and water releasing (C2); 4) the freshening zone for clay mineral dehydration (D); and 5) the seepage-concentration zone (E).

Principal aspects of compaction and fluid flow in mudstones

Abstract Compaction and fluid flow in sedimentary basins are usually modelled as mechanical compaction assuming that the main driving force is the effective stress. However, in the deeper part of sedimentary basins (> 2–3 km, 70–100°C), compaction also involves dissolution and precipitation of minerals, and these processes are strongly controlled by temperature and to a lesser extent by variations in effective stress. The total pore-water flux is relatively independent of the permeability and pressure gradients because it is controlled by the rate of compaction. The main effect of permeability variations is the focusing of the compaction-driven flow. Fluids are also released by petroleum generation and dehydration of clay minerals; both these processes are also essentially temperature dependent. If the minimum permeability in one sedimentary layer (seal) falls below a critical value and there is little lateral drainage, the pressure will build up to fracture pressure. Pore pressures and fluid flow cannot be calculated from the matrix permeability of the rock when fracture pressures are reached, because much of the flow occurs along the generated fractures. The permeability produced by fracturing is a dynamic variable adjusting itself to the flux; it is not a rock property like the intergranular permeability. The intergranular permeability of shale samples before fracturing is also difficult to measure reliably in the laboratory as a result of unloading. This makes pressure prediction using one-dimensional pressure modelling uncertain. The prediction of permeability distributions in three dimensions is much more difficult.

Chlorine/Fluid Cycling in Subduction Zones: Evidence from Chloride Concentrations and Chlorine Stable Isotopes

Pore waters with chloride concentrations less than seawater are a characteristic feature of accretionary complexes in convergent margins. One well-documented case where such freshened fluids have been documented is in the Nankai Trough, Japan, Ocean Drilling Project (ODP) Site 808. The enigmatic profile of pore water chloride concentration versus depth in these sediments is characterized by an extensive section of lower than seawater chloride concentrations between 560 and -1200 mbsf, with a broad minimum of about 450 mM (~20 % seawater dilution) at ~1,100 mbsf (Fig. 1). Newly obtained chlorine stable isotopic ratios (37C1/35C1) in the pore fluids at the Nankai drill site are highly fractionated (-7.4%0) compared to seawater (0%0), with the most extreme fractionation (Fig. 2) coinciding with the lowest pore water chloride concentration (Fig. 1). Chlorine stable isotopes in subduction zone settings can be fractionated by water-rock exchange when 37C1 is preferentially incorporated over 35C1 into the structural (OH) site of diagenetic or metamorphic hydrous minerals (e.g. smectite, illite, chlorite, serpentine, talc, and amphibole) and by diffusion. In the case of mineral uptake, lower temperature minerals fractionate C1 isotopes more highly than those formed at higher temperatures; but their maximum C1 contents are generally an order of magnitude lower (e.g. < 100 ppm in smectite versus several parts per thousand in amphibole. The source of the freshened fluids at Nankai is presently being debated. On the basis of pore water chloride data alone, previous studies have suggested that clay mineral reactions, in particular those involving smectite, are primarily responsible for the freshening observed. These studies attribute the increase in pore water chloride to ~560 mbsf (Fig. 1) to the in situ hydration of volcanic glass and formation of clays and zeolites. The decrease in chloride between 560 and 1100 mbsf is proposed to result from clay mineral (and zeolite) dehydration reactions. Below 1100 mbsf, the formation of hydrous minerals in the underlying volcaniclastic section is invoked. Data from C1 stable isotopes now permit us to evaluate these hypotheses. In the case of simple loss of H20 from smectite interlayers or zeolites, the CI stable isotope ratios of associated pore waters are unaffected. However, reactions that involve smectite or other Cl-bearing hydrous silicate minerals will affect the C1 stable isotopic signature of the pore fluids. Below -560 mbsf, the two profiles are decoupled. The decrease in pore water chloride to ~1100 mbsf is accompanied by a strong decrease in pore water (~37C1; the opposite of what would be expected if this isotopic signature was the result of clay mineral dehydration that involved the destruction of smectite and/or other low temperature hydrous layer silicates. Such a reaction would tend to release 37C1 into the pore waters, not remove it. Likewise, decoupling is evident between the two profiles below 1100 mbsf where hydration reactions are thought to be occurring. The decoupling of pore water chloride and the chlorine stable isotope data between 560 and 1100 mbsf provides important evidence that H20 in freshened fluids at Nankai are coming from mineral reactions occurring in the seismogenic zone. Calculations demonstrate that contributions to the observed freshening in Nankai, due to the release of H20 from smectite interlayers and zeolites in the section drilled can account for only 4 % freshening of seawater, at best, instead of the 20% observed. Neither is there any physical evidence for recent fluid flow along the drcollement (-960 mbsf). Porosity in sediments below the d+collement is higher (40% vs 30% in the overlying sediments) than in sediments above; and St, He, and O isotope data, as well as pore water chloride and sulphate, suggest that freshened pore waters at Nankai originate from repeated transient episodes of fluid incursion from the high

Thermodynamics of the chemical reactions between clay minerals and iron oxides

The thermodynamics of chemical reactions between clay minerals and iron oxides is considered within the framework of phase diagrams for multicomponent systems. Dominant reactions are identified featuring a thermodynamic probability higher than that of clay mineral dehydration.

Chemical and isotopic evidence for sources of fluids in a mud volcano field seaward of the Barbados accretionary wedge

Chemical, isotopic, and heat budgets are controlled by fluid flow and venting at convergent margins. Fluids vent from accretionary complex sediments via numerous pathways including mud volcanoes, which are common at the Barbados convergent margin. Chemical and isotopic compositions of fluids collected from four mud volcanoes, located east of the Barbados deformation front at 13°50′N, indicate venting is sufficiently rapid to prevent diffusion from seawater. In sediments surrounding the mud volcanoes, the rate of nonfocused fluid flow is ∼0.26 cm/yr. Although this rate is ∼3 orders of magnitude slower than the flow from the mud volcanoes, significantly more fluid vents from the sediments surrounding the mud volcanoes than from the restricted areas of rapid flow from the volcanoes. Chloride concentrations are depleted to a minimum of 211 mM (∼45% of seawater value) primarily by mixing diagenetically altered pore fluids with an 18O‐enriched fresh water released from the dissociation of methane hydrate. This reaction is accompanied by the release of sufficient methane to form a free gas phase and initiate eruption of the mud volcanoes. The geochemical compositions of the diagenetically altered pore fluids reflect the interplay between five major reactions: (1) clay mineral dehydration, which releases H2O and influences a range of chemical and isotopic compositions; (2) organic matter regeneration, which increases alkalinity, NH4+, and Br− and decreases SO42− concentrations; (3) cation exchange with clay minerals, which increases Na+ and decreases NH4+ concentrations; (4) carbonate recrystallization and precipitation, which decrease Ca2+ but increase Sr2+ concentrations; and (5) conversion of volcanic ash to clay minerals, which utilizes H2O and decreases Mg2+ concentrations. The geochemistry of the pore fluids suggests that these reactions occurred at temperatures ranging from ∼75° to 115°C. Thus at the regional geothermal gradients of ∼27 to 40°C/km, these temperatures indicate that the source regions are at ∼2 to 4.5 km depth.

Major and trace element and Sr isotope constraints on fluid circulations in the Barbados accretionary complex. Part 1: Fluid origin

We measured the chemical and Sr isotope compositions of vent and pore fluids and associated sediments from a diapiric field located near 13.5°N, east of the deformation front of the Barbados accretionary complex. The two diapiric structures with the largest thermal anomalies and characterized by active fluid conduits exhibit the strongest chemical and 87Sr/ 86Sr variations. These two diatremes (Atalante and Cyclope) also have low chloride contents and non-radiogenic 87Sr/ 86Sr, which may be explained by interaction between seawater and volcanic ash or with underlying oceanic crust. In the central zone of the two structures, 87Sr/ 86Sr varies little with depth, which implies that fluid expulsion is at such a high rate that it is not affected by seawater 87Sr/ 86Sr. The expelled fluids probably circulate along the decollement zone and ascend along faults which act as channels. A deep component is probably located in the decollement zone whereas another component may be recirculated seawater. The ascending fluid interacted with numerous materials, causing dehydration of clay minerals and alteration of volcanic ash and/or underlying oceanic crust. To explain the low chloride contents of the Atalante fluids, gas hydrate decomposition, yielding dilution of the fluid without modifying its Sr isotope ratio, needs to be superimposed on the mixing between seawater and the deep component. The occurrence of gypsum in these two diatremes implies higher fluid temperatures and more intense activity, at least temporarily, to allow the deposition of such a mineral.

Diagenetic mass transport in the southern San Joaquin basin, California, U.S.A.: Implications from the strontium isotopic composition of modern pore fluids

Three types of chemically and isotopically distinct pore fluids from the southern San Joaquin basin previously recognized by J.B. Fisher and J.R. Boles also have distinctive 87 Sr 86 Sr ratios and Sr concentrations. Meteoric fluids have stable isotopic compositions which lie on or near the meteoric water line and low chlorinities. Sr concentrations are between 0.01 and 2.6 mg l −1, and 87 Sr 86 Sr ratios range from 0.7061 to 0.7078. Diagenetically modified connate marine fluids have δD-and δ 18O-values more positive than −35‰ and 0‰, respectively, and have chlorinities generally comparable to seawater. Sr concentration are much higher than the meteoric group (16–198 mg l −1), although the 87 Sr 86 Sr ratios (0.7070–0.7081) are not distinctive. Mixed meteoric-modified connate fluids have δD, δ 18 O and chlorinity intermediate between the meteoric and modified connate groups. Sr concentrations are also intermediate, between 16 and 22 mg l −1, but 87 Sr 86 Sr ratios (0.7080–0.7087) are generally more radiogenic than either the meteoric or modified connate groups. All of the fluids have 87 Sr 86 Sr ratios comparable to or lower than Tertiary seawater. Alteration of detrital plagioclase is the probable origin of the low isotopic ratios. Mass-balance calculations based on the Sr data suggest that essentially no transport of Sr occurred during diagenesis of sandstones containing modified connate pore fluids, while large amounts of Sr have been transported out of meteoric reservoirs by fluid flow. The chemically anomalous mixed meteoric-modified connate fluids contain the most radiogenic strontium in the basin. These fluids are spatially associated with major faults, and may represent clay mineral dehydration waters which have been transported upward from greater depth. These results suggest that the three types of fluids identified by Fisher and Boles represent three distinct mass transport regimes: a largely stagnant deep-basin system containing modified connate pore fluids; an actively recharging meteoric system along the basin flanks; and a third system restricted to the southern basin which may be characterized by largescale cross-formational fluid flow, rather than dilution by meteoric waters.

Fluids in accretionary prisms

Accretionary prisms are composed of initially saturated sediments caught in subduction zone tectonism. As sediments deform, fluid pressures rise and fluid is expelled, resembling a saturated sponge being tectonically squeezed. Fluid flow from the accretionary prism feeds surface biological cases, precipitates and dissolves minerals, and causes temperature and geochemical anomalies. Structural and metamorphic features are affected at all scales by fluid pressures or fluid flow in accretionary prisms. Accordingly, this dynamic tectonic environment provides an accessible model for fluid/rock interactions occurring at greater crustal depths. Porosity reduction and to a lesser degree mineral dehydration and the breakdown of sedimentary organic matter provide the fluids expelled from accretionary prisms. Mature hydrocarbons expulsed along prism faults indicate deep sources and many tens of kilometers of lateral transport of fluids. Many faults cutting accretionary prisms expel fluids fresher than seawater, presumably generated by dehydration of clay minerals at depth. Models of fluid flow from accretionary prisms use Darcy's law with matrix and fractures/faults being assigned different permeabilities. Fluid pressures in accretionary prisms are commonly high but range from hydrostatic to lithostatic. Matrix or intergranular permeability ranges from less than 10−20 m² to 10−13 m². Fracture permeability probably exceeds 10−12 m². A global estimate of fluid flux into accretionary prisms suggests they recycle the oceans every 500 m.y. Fluid flow out of accretionary prisms occurs by distributed flow through intergranular permeability and along zones of focused flow, typically faults. Focused fluid flow is 3 to 4 orders of magnitude faster than distributed flow, probably representing the mean differences in permeability along these respective expulsion paths. During the geological evolution of accretionary prisms, distributed flow through pore spaces decreases as a result of consolidation and cementation, whereas flow along fracture systems becomes dominant. Although thrust faults are most common in the compressional environment of accretionary prisms, normal and strike‐slip faults are efficient fluid drains, because they are easier to dilate. Observations from both modern and ancient prisms suggest episodic fluid flow which is probably coupled to episodic fault displacement and ultimately to the earthquake cycle.

内外液化用原料炭の基礎性状 （ＩＩ） 鉱物質組成

Reaction characteristics for liquefaction of Japanese and foreign coals are being studied as part of the program of coal liquefaction at the Government Industrial Development Laboratory, Hokkaido. In this study, samples of mineral matter from various coals prepared by a low-temperature ashing technique (LTA) and by a high-temperature ashing technique (HTA) were examined by inductively-coupled plasma emission spectroscopy (ICP), X-ray fluorescence (XRF) and X-ray diffraction in order to obtain fundamental information to clarify the effects of inherent mineral matter on coal liquefaction.The contents of ashes prepared by a low-temperature ashing technique (LTA) and by a high-temperature ashing technique (HTA) range from ca.2wt% to ca.27wt%. The LTA content is higher than the HTA content in most cases due to dehydration and dehydroxylation of clay minerals, decomposition of carbonate minerals, and dehydration of sulfate minerals by high-temperature treatment.According to the results of ICP analysis, the main components of mineral matter in coal are Si, Ti, Al, Ca, Na, K, Fe and Mg, and the minor components (0.01-0.20wt%) are Mn, Zn, V, Cr, Ni, Cu, and Be. Australian Yallourn lignite is rich in Fe and Mg, and poor in Si and Al. Canadian sub-bituminous coals (Egg Lake and Wabamum) and Chinese Shori lignite and sub-bituminous coals (Koken and Karinga) are rich in Ca. American Kaiser #3 bituminous coal is rich in Fe, Mn, Cu and Be, and Colombian Titiribi bituminous coal is rich in Ca, Fe and Cu. Australian sub-bituminous coals (Wandoan and Liddell) and Japanese sub-bituminous coal (Taiheiyo) and bituminous coal (Shin-Yubari) have a comparatively similar elemental composition.According to the results of X-ray diffraction, the LTA contains quartz, kaolinite, illite, calcite, dolomite, pyrite etc. The HTA contains less identifiable components, namely, quartz, metakaolin, anhydrite, bassanite, hexahydrite etc.

X-ray studies on dehydration and rehydration of expansible clay minerals

Homoionic samples of 3 montmorillonites, 1 beidellite, and 1 vermiculite were heated at 300°C, 500°C, and 700°C. After cooling they were kept at 100% R.H., and the changes in basal spacing were measured and discussed in terms of their mineralogical properties including the DTA curves.

Regional studies of fluid inclusions in Paleozoic sediments from southern Scandinavia

Fluid inclusions in diagenetic quartz and calcite have been investigated in order to determine minimum temperatures attained during diagenesis and obtain information on composition of porewaters in the Paleozoic sediments. Surface samples from Bornholm, Skane and Gotland and drill core samples from Frederikshavn 1, R0nde 1, N0vling 1, Abenra 1, Slagelse 1 and 0rslev 1 have been studied. Two major types of fluids are described: aqueous and hydrocarbon mixtures. The aqueous inclusions can roughly be divided into 3 different groups based on homogenisation temperatures with arithmetic means of 82°C (with a salinity around 25 eq. wt. % salts) and 136° and 175°C (with salinities around 5 eq. wt. % salts). The correlation of temperatures and salinities of porewater is tentatively explained by dehydration of clay minerals diluting the porewaters. The hydrocarbon inclusions, some of which fluoresce green-yellow, homogenize into the liquid phase at temperatures between -44° to + 138°C, and are only found in calcite veins from the Silurian of N0vling 1 and the Lower Ordovician Komstad limestone, Bornholm. With regard to the thermal history the data indicate that 1: major thermal maturation occurred in pre­Carboniferious times 2: all Cambro-Ordovician samples are post-mature with respect to hydrocarbon generation and 3: only small, dry gas potentials are present in the upper Silurian to Carbonifereous rocks.

Diagenesis of the shallow marine Fulmar Formation in the Central North Sea

AbstractThe diagenetic history of the Upper Jurassic Fulmar Formation of the Central North Sea is described with emphasis on the Fulmar Field. The Fulmar Formation was deposited on a variably subsiding shallow-marine shelf under the influence of halokinetic and fault movements. The sediments are extensively bio-destratified although large-scale cross-bedding is locally preserved. The dominant mechanism of deposition is thought to have been storm-generated currents. Soft-sediment deformation structures are common and are attributed to syn- and post-depositional dewatering of the sandstones. The dewatering was associated with fractures and shear zones which reflect tectonic instability resulting from periodic salt withdrawal and/or graben fault movements. The dewatering may have been initiated by repacking of the sediments during earth movements or by the gradual build-up and sudden release of overpressures due to compaction and/or clay mineral dehydration during rapid burial at the end of the Cretaceous. The formation is composed of arkosic sandstone of similar composition to Triassic sandstones from which it was probably derived. The sandstones also contain limited amounts of marine biogenic debris including sponge solenasters, bivalve shells, rare ammonites and belemnites. Initial diagenesis began with an environment-related phase during which quartz and feldspar overgrowths and chalcedony and calcite cements were precipitated. These cements appear to form concretions adjacent to local concentrations of sponge debris and shell debris, respectively, and were disturbed after their formation by fracturing and dewatering. This was followed by an early burial stage of diagenesis which resulted in extensive dolomite cementation and minor clay mineral authigenesis (illite and chlorite). The last phase of mineral growth was probably pyrite. During early burial diagenesis, secondary porosity after feldspar and/or carbonate was produced, although the exact timing is not clear. The lack of both stylolitic developments and extensive illitization indicates that the late burial diagenesis stage was never reached, although sufficient clay diagenesis occurred to destroy all traces of mixed-layer illite-smectite (present in some shallower wells). The main control on reservoir behaviour is primary depositional fabric. Diagenesis only overprints these controls. Locally-cemented fracture sets act as baffles to fluid flow, but they are not extensive and the reservoir acts as one unit.

The Relationship Between Permeability and the Morphology of Diagenetic Illite in Reservoir Rocks

The Relationship Between Permeability and the Morphology of Permeability and the Morphology of Diagenetic Illite in Reservoir Rocks Summary The permeability characteristics of two reservoir sandstones from the Magnus and West Sole fields in the U. K. North Sea are essentially similar and are strongly influenced by the occurrence of filamentous illitic clay. However, the amount of illite in the West Sole sandstone is 20 times that in the Magnus sandstone, suggesting that the distribution and form of the clay is more important than its actual amount. Scanning electron microscope (SEM) observations show that the clay mineral occurs as an open, tangled web of long, thin ribbons virtually filling the pore spaces, a morphology that is properly revealed only after critical point drying. Introduction Early work at the BP Research Center on the permeability characteristics of reservoir sandstones from the Magnus permeability characteristics of reservoir sandstones from the Magnus field in the U.K. North Sea revealed puzzling differences between results from well testing and those measured by routine core analysis. Core data always indicated a higher permeability, which, in the case of the water zone, permeability, which, in the case of the water zone, amounted to 20 to 30 times that found by well testing. Similarly, there was a very wide discrepancy between gas and brine permeabilities of sandstone plugs measured in the oven-dried state and in the wet, preserved state. A possible explanation for this anomaly was that there could possible explanation for this anomaly was that there could be dehydration and shrinkage of clay minerals within the sandstone pores. Indeed, conventional SEM observations did reveal the presence of diagenetic filamentous illite coating the pore walls, although at that stage it was thought to be unlikely that this mineral could be responsible for the large differences in permeability. Work at the Macaulay Inst., however, showed that the morphology of the illite in the Magnus sandstones, as inferred through SEM, depended crucially on the manner of drying the specimen. The in-situ morphology of the clay mineral was revealed only after critical-point drying, when it was observed as an open, tangled web of very thin, long ribbons virtually filling the pore spaces. In contrast, after air- or freeze-drying, the illitic mineral occurred in dense mats packed against the pore walls. Following these observations, it was demonstrated conclusively 1 that the "interface-sensitive" nature of the filamentous illite provided a complete explanation for the discrepancies between the well-test data and routine core permeabilities. it was further suggested that the permeabilities. it was further suggested that the indiscriminate adoption of routine core analysis procedures could lead to serious errors in the assessment of reservoir quality. Our investigation compares the permeability and clay mineralogy of Magnus sandstones with those of West Sole sandstones, also in the U.K. North Sea, to show that fluid flow characteristics cannot be predicted from the quantitative clay content of reservoir sandstones. The West Sole sandstones contain abundant filamentous illite, which amounts to about 10% of the rock, compared with about 0.5% in the Magnus sandstones. The SEM and X-ray diffraction characteristics of the separated illite from both sandstones are dissimilar, but despite these differences the fluid flow properties of the two sandstones are comparable. Permeability Measurements Permeability Measurements Core plugs were cut from preserved Magnus and West Sole cores using degassed, simulated formation water as the cutting fluid. The core plugs, 1 in. [2.54 cm] diameter and 1 in. [2.54 cm] long, were cut from the center of the drilled pieces to reduce possible mud contamination. They were stored under formation brine. Complete brine saturation was ensured before permeability measurements were made. The cores were evacuated under brine to remove any gas and a pressure of 1,000 psi [6895 kPa] was then applied for &amp;gt;72 hours to dissolve any remaining gas. After saturation, the initial brine permeability was measured, during which time the sample was confined in a Hassler core holder with a sealing pressure of 400 psi [2758 kPa] on the rubber sleeve. Then the samples were dried in a humidity oven. After drying, the gas permeability was measured. All the samples were then resaturated permeability was measured. All the samples were then resaturated with brine and the brine permeability redetermined. Table 1 shows that the permeability characteristics of the two sandstones are similar and that, in particular, the gas permeability measured after oven drying was 20 times higher than the initial brine permeability measured on preserved samples. The resaturated brine permeabilities are higher than the initial brine values, permeabilities are higher than the initial brine values, indicating a permanent effect caused by drying. JPT P. 2225

Heat flow and energetics of the San Andreas Fault Zone

Approximately 100 heat flow measurements in the San Andreas fault zone indicate (1) there is no evidence for local factional heating of the main fault trace at any latitude over a 1000‐km length from Cape Mendocino to San Bernardino, (2) average heat flow is high (∼2 HFU, ∼80 mW m−2) throughout the 550‐km segment of the Coast Ranges that encloses the San Andreas fault zone in central California; this broad anomaly falls off rapidly toward the Great Valley to the east, and over a 200‐km distance toward the Mendocino Triple Junction to the northwest. As others have pointed out, a local conductive heat flow anomaly would be detectable unless the frictional resistance allocated to heat production on the main trace were ≲100 bars. Frictional work allocated to surface energy of new fractures is probably unimportant, and hydrologic convection is not likely to invalidate the conduction assumption, since the heat discharge by thermal springs near the fault is negligible. Explanations for the low dynamic friction fall into two intergradational classes: those in which the fault is weak all of the time and those in which it is weak only during earthquakes (possibly just large ones). The first class includes faults containing anomalously weak gouge materials and faults containing materials with normal frictional properties under near‐lithostatic steady state fluid pressures. In the second class, weakening is caused by the event (for example, a thermally induced increase in fluid pressure, dehydration of clay minerals, or acoustic fluidization). In this class, unlike the first, the average strength and ambient tectonic shear stress may be large, ∼1 kbar, but the stress allocated to elastic radiation (the apparent stress) must be of similar magnitude, an apparent contradiction with seismic estimates. Unless seismic radiation is underestimated for large earthquakes, it is difficult to justify average tectonic stresses on the main trace of the San Andreas fault in excess of ∼200 bars. The development of the broad Coast Range heat flow anomaly southward from Cape Mendocino suggests that heat flow increases by a factor of 2 within 4 m.y. after the passage of the Mendocino Triple Junction. This passage leaves the San Andreas transform fault zone in its wake; the depth of the anomalous sources cannot be much greater than the depth of the seismogenic layer. Some of the anomalous heat may be supplied by conduction from the warmer mantle that must occur south of the Mendocino transform (where there is no subducting slab), and some might be supplied by shear heating in the fault zone. With no contribution from shear heating, extreme mantle upwelling would be required, and asthenosphere conditions should exist today at depths of only ∼20 km in the northernmost Coast Ranges. If there is an appreciable contribution from shear heating, the heat flow constraint implies that the seismogenic layer is partially decoupled at its base and that the basal traction is in the sense that resists right lateral motion on the fault(s). As a result of these basal tractions, the average shearing stress in the seismogenic layer would increase with distance from the main fault, and the seismogenic layer would offer substantial resistance to plate motion even though resistance on the main fault might be negligible. These speculative models have testable consequences.

Effect of structure on the mechanism of dehydration of clay minerals

The kinetics of the isothermal dehydration of two clay minerals, attapulgite and powdered vermiculite were studied both in vacuo and in the presence of constant water vapour pressure. The mechanism of dehydration was found to be interfacial where diffusion plays a dominant role and it is called “activated diffusion”. A comparison is made with some layered structure clay minerals.

Hydrology of Deep Sedimentary Basins: ABSTRACT

Continental blocks of the earth's crust are mainly deep basin sediments, generally lithified and commonly metamorphosed. Observed rock transformations required input of heat in an environment of pressure ranging from hydrostatic to geostatic, and most occurred in the presence of water. The role of hydrology in diagenesis and lithification of deep basin sediments, and in the leaching, transport, and reprecipitation of mineral constituents is now in a period of intensive reevaluation. New techniques of study, vastly improved methods of data collection and processing, and an enormous store of information on widespread conditions through a great depth range provide effective means for such reevaluation. The hydrologic evolution of deep basin sediments prior to metamorphism occurs in two distinct phases. Discharge of connate water upward and toward the basin margin is the first phase; intake and throughflow of meteoric water comprise the second. The first phase may be considered near completion only when clay-mineral dehydration has entered its final stage. Each phase may span scores to hundreds of millions of years, and different parts of a basin may be in different phases at a specified time. The hydrologic evolution of a sedimentary basin is related to its configuration and dimensions, its depositional and structural history, the relative thickness and areal distribution of sediments (by type) within it, and changes in its regional geomorphic setting. Evolutionary progress is evidenced by changes in formation-water composition and salinity as functions of depth and areal distribution, changes in the geothermal and interstitial fluid pressure regimes, and reduction of the water content of the rocks. Conditions in basin deposits ranging in age from early Paleozoic to Neogene illustrate these evolutionary processes. End_of_Article - Last_Page 725------------