Barite Cement Research Articles

Effect of weighting materials on carbonation of oil well cement-based composites under high temperature and CO2-rich environment

As an indispensable part of cement slurry for high temperature and high pressure oil and gas wells, weighting materials have a significant impact on the carbon dioxide corrosion of oil well cement-based composites.This paper studied the carbonation process of cement with three weighting agents, and evaluated the compressive strength and carbonation depth of cement at 150 ℃. XRD, SEM and MIP were used to study the carbonation mechanism of cement. When 21 days of carbonation, the carbonation depth growth rate of hausmannite cement was 0.21 mm/d, hematite cement was 0.24 mm/d, and barite cement was 0.31 mm/d. The compressive strength of cement decreased after carbonation,and the carbonation had a minor influence on the compressive strength of hausmannite cement and the most significant impact on barite cement. The carbonation product of oil well cement was mainly calcite. Unstable vaterite mainly existed in the barite cement sample, indicating that the barite cement sample was the most serious corrosion. In the carbonation zone, the number of pores smaller than 10 nm increased the most in the hausmannite cement sample. Pores with a diameter greater than 100 nm accounted for 1.9 % in the hausmannite cement, 3.0 % in hematite cement, and 4.8 % in barite cement. The result shows that hausmannite is the most conducive to the corrosion resistance of oil well cement.

Development of a Model Material for Dynamic Geotechnical Model Tests

To develop a model material suitable for analysing the stability of sandstone slopes during strong earthquakes, an orthogonal test was designed by selecting seven physico-mechemical parameters, a combination of dynamic and static parameters, as research indexes. Then, the influence of the proportion of each component in the model material on each test index was determined by sensitivity analysis, and the quantitative relationship between physico-mechanical parameters and component proportions was established by multiple linear regression analysis to develop a model material similar to sandstone. Finally, a sandstone slope along the Duxiang Expressway was taken as an example, and the proportions of the components suitable for a model of the rock mass in this area were determined. The test results showed that (1) the physico-mechanical parameters selected for the dynamic and static tests were used to effectively develop model materials for dynamic geotechnical model tests; (2) samples of model materials composed of barite powder, quartz sand, ferric powder, gypsum and cement met the requirements for dynamic testing of geotechnical models of sandstone slopes; and (3) through sensitivity analysis of various factors and multiple linear regression analysis, the required model materials were efficiently configured, and the failure mode, failure process and physico-mechanical parameters of the model materials accurately simulated the original rock materials.

Barite concrete-based cement composites for 252Cf spontaneous neutron and 60Co/192Ir shielding based on Monte Carlo computation

Barite concrete composite materials have been investigated for 252Cf spontaneous neutron and 60Co/192Ir gamma sources’ shielding using Monte Carlo computational method. The Particle and Heavy Ion Transport code System (PHITS) was used to compute the shielding properties of three different materials (barite concrete, barite cement, and barite aggregate) used as structural walls in fixed neutron & gamma industrial radiography for Non-Destructive Testing applications. The obtained results displayed good properties of barite concrete in shielding spontaneous neutrons emitted from the 252Cf source, as the effective dose drops about 108 times in only 140 cm wall thickness, and it was found to be about 10 times more effective than other materials investigated. In addition, the investigated gamma shielding properties of the barite concrete showed a relatively smaller wall thickness compared to the ordinary concrete. The decision-making process based on the ALARA principle of dose limitation showed that the use of barite concrete in such facilities is more effective than the use of barite cement and barite aggregate, for both gamma and neutron radiography shielding design. To achieve an average value of 1 μSv/h, the obtained result shows that 80 cm of Barite concrete is needed, while 125 and 130 cm of barite cement and barite aggregate are needed, respectively to shield the Co-60 source. Meanwhile, 50 cm of wall made of barite concrete is sufficient to cut down the effective dose rate to 1 μSv/h (for 50 Ci and 55 cm for 150 Ci 192Ir), which is an appropriate design for the public area adjacent to the industrial radiographic facility. It was therefore concluded from the obtained data that barite concrete is the most effective shielding material for radioactive sources (60Co, 192Ir, and 252Cf) used in radiographic applications.

A Mississippi Valley–type Zn-Pb mineralizing system in South China constrained by in situ U-Pb dating of carbonates and barite and in situ S-Sr-Pb isotopes

AbstractThe ages of Zn-Pb deposits are exceptionally challenging to determine owing to the lack of suitable mineral chronometers and techniques. Here we present the first result for in situ LA-ICP-MS U-Pb dating of carbonates and barite from a Mississippi Valley– type (MVT) Zn-Pb deposit in South China. Hydrothermal dolomite in close textural and paragenetic association with Zn-Pb sulfides, and calcite and barite cement from the breccia ores, yield ages of 473.4 ± 2.7 Ma and 368.7 ± 3.1 Ma, respectively. Together with new in situ S-Pb-Sr isotope values, these data reveal an epigenetic Zn-Pb mineralization history, agreeing well with a model involving basinal brine accumulation and MVT Zn-Pb sulfide precipitation. Because carbonate is a common mineral in Zn-Pb deposits worldwide, and other minerals in such deposits suitable for isotope dating are generally absent, in situ U-Pb dating of gangue carbonates opens a new window for better defining the ore genesis of this globally important Zn-Pb deposit type and for tracking hydrothermal fluid flow in sedimentary basins.

Bioclast-controlled patchy barite cementation – Origin and impact on reservoir properties in deeply buried Upper Jurassic sandstones, North Sea

Reservoir non-destructive patchy barite cement occurs in volumes up to 16 vol% in deeply (>5150 m) buried shoreface sandstones in the Hejre field, Danish Central Graben, North Sea. Barite typically occurs as an accessory cement in the sandstones of the Upper Jurassic Heno Formation; however in the Hejre field, barite appears more abundant in the crestal-most well than in other wells. The purpose of this study is to describe the characteristics and the origin of patchy barite cement besides implications for reservoir properties. Petrographic investigations by optical and scanning electron microscopy supplemented by isotopic analysis by SIMS (secondary ion mass spectroscopy) were applied to reveal the barite cementation process. Porosity and permeability of the sandstones were measured by conventional core analysis. Barite cement occurs in the Hejre field with three morphologies: crystals arranged in rosettes, crystal fillings of bioclasts, and multiple-oriented intergrown small crystals in veins. SIMS showed similar sulphur and oxygen isotopic compositions for these barite morphologies, and this composition resembles evaporite-derived barite cement. A hydrothermal origin of the fluid is supported by the associated precipitation of pyrite, chalcopyrite, sphalerite and galena, and a high Sr/Ba ratio in barite. Conventional core analysis revealed major reductions in porosity and permeability when barite cement occurs as fracture filling or in combination with calcite cement in shell lags. However, these occurrences are rare and have a minor influence on the overall reservoir properties. Minor reduction of porosity and permeability characterizes sandstones with barite cement in rosettes of radiating crystals. This growth pattern was probably promoted by slow seep of sulphate-rich fluids which, by mixing with barium-bearing formation water became super-saturated with respect to barite as they moved towards lower temperature and pressure zones. Faults acted as pathways for transport of sulphate-rich fluids possibly from evaporite deposits, whereas barium may have originated from compactional fluids leached out of underlying volcaniclastic rocks. Thermochemical sulphate reduction led to precipitation of sulphide minerals, minor sulphur fractionation and fluid acidification, whereby calcareous bioclasts dissolved. Barite precipitated when the fluids entered these large- or over-sized pores with small obstacles causing prolonged fluid-rock interaction. The bioclast-replacing and patchy barite cement caused only limited reduction of reservoir porosity and permeability compared with barite-free sandstones from the Heno Formation found at a similar burial depth.

Effect of Perlite Particles on Barite Cement Properties

Conventional heavy-weight oil and gas well cement systems formulated with barite exhibit high viscosities. Additionally, the heavy-weight powder tends to settle, causing density variation and disruption in the porosity of the hardened cement cores. Studies have shown that such problems can be mitigated by controlling the particle size distribution of the cement system. The main objective of this study is to evaluate the effect of perlite powder particles on the fluid and hardened properties of barite-based cement systems. Barite heavy-weight cement slurries containing 0, 1, 2, and 3% by weight of dry cement (BWOC) of perlite powder were prepared. The rheological study was performed at a bottomhole circulating temperature (BHCT) of 150 °F and ambient pressure. An ultrasonic cement analyzer (UCA) and a high-temperature–high-pressure (HTHP) curing chamber were used to cure samples for 24 h at a bottomhole static temperature (BHST) of 292 °F and pressure of 3000 psi. Porosity measurements were performed using the nuclear magnetic resonance (NMR) technique. The results indicate that the incorporation of perlite powder into conventional barite-based heavy-weight cement slurry causes modifications in the properties of the systems. In general, the plastic viscosity decreases, while the yield point and gel strength increase with increasing perlite concentration. The reduction in plastic viscosity also reduces the pump pressure, while the increase in yield point and gel strength reduces particle sedimentation. Additionally, the compressive strength and tensile strength of hardened cement increase, while the wait-on-cement time decreases. NMR studies indicate that perlite reduces the porosity variation that exists in conventional barite-based cement systems due to the formation of stable cement systems.

Influence of Weighting Materials on the Properties of Oil-Well Cement

The integrity of oil and gas wells is largely dependent on the cement job. Maintaining the properties of the cement layer throughout the life of a well is a difficult task, particularly in high-temperature and -pressure conditions such as those in deep wells. Cementing deep wells require slurries with high densities. Heavyweight cement systems are those designed with weighting materials. These materials have a higher specific gravity in comparison to cement. The purpose of this work is to investigate the influence of weighting materials on the properties of Class G oil-well cement and to make necessary recommendations for their use. The rheology, fluid loss, gas migration, and dynamic elastic properties of three cement slurries containing different weighting materials, namely, hematite, barite, and ilmenite, were studied. The results indicate that cement slurry designed with barite exhibits the best rheological behavior that would provide a perfect solution for deep wells where cement placement is a concern. The barite slurry had the lowest plastic viscosity. The plastic viscosity of the hematite and ilmenite-weighted systems was higher by 11.5 and 12.4%, respectively. The barite-based slurry also had the highest yield point of 84.3 lbf/100 ft2, whereas the yield points of hematite and barite cement were 37.9 and 29.5 lbf/100 ft2, respectively. Furthermore, the gel strengths of barite cement were the highest, with 10 s and 10 min gel strengths of 11.5 and 39.5 lbf/100 ft2, respectively. Ilmenite had the most positive impact on fluid loss control, which would be appropriate in high permeable formations. It had a fluid loss of 66 mL/30 min, lower than those of the hematite (80 mL/30 min) and barite (82 mL/30 min) systems. Furthermore, the best dynamic elastic properties were exhibited by the ilmenite system, with the smallest Young’s modulus (27.3 GPa) and the highest Poisson ratio (0.252). This would make the ilmenite to be very useful in developing heavyweight cement composites that could withstand severe external loads imposed on the casing and cement. The hematite cement was the most impermeable to gas migration, with a gas volume of 127.8 cm3, whereas the volume measured in the barite and ilmenite systems were 20.9 and 78% higher, respectively. This makes the hematite to be very useful in deep gas wells where gas migration control is important.

Origin of sulfate-rich fluids in the Early Triassic Montney Formation, Western Canadian Sedimentary Basin

Abstract This study investigates diagenetic and geochemical processes that control regional distribution and formation of sulfate minerals (i.e., anhydrite and barite) in the Early Triassic Montney Formation in the Western Canadian Sedimentary Basin. The generation of H2S in hydrocarbon reservoirs is often associated with the dissolution of sulfate minerals, as a major source of sulfate required for sulfate-reducing reactions. The formation of pervasive late diagenetic anhydrite and barite in the high H2S zone of the Montney Formation is therefore contrary to the normal paragenetic sequence of sour gas reservoirs. Petrographic observations revealed early and late anhydrite and barite cement. The early fine-crystalline anhydrite cement is dominant in northeastern British Columbia (low H2S zone), while the late-stage coarse-crystalline cement and fracture/vug-filling anhydrite are dominant in Alberta (high H2S zone). The bulk isotopic values (δ34S: +2.9 to +24.7‰ V-CDT, δ18O: −11.2 to +15.7‰ V-SMOW) suggest that sulfate-rich fluids originated mainly from modified Triassic connate water was the origin of early anhydrite. In contrast, the SIMS isotopic values of late anhydrite (δ34S: +18.5 to +37‰ V-CDT, δ18O: +12 to +22‰ V-SMOW) and barite cement (δ34S: +23.3 to +39‰ V-CDT, δ18O: +13.2 to +18.7‰ V-SMOW) as well as fracture/vug-filling anhydrite (δ34S: +23.5 to +24.7‰ V-CDT, δ18O: +13.3 to +14.7‰ V-SMOW) from Alberta represents a mixed isotopic signature of Triassic connate water and contribution of dissolved sulfate-rich fluids derived from dissolution of Devonian evaporites. The 87Sr/86Sr isotope ratios of the fracture/vug-filling anhydrite (0.7092–0.7102) are highly radiogenic suggesting extensive water/rock interactions between sulfate-rich fluids and siliciclastic and basement rocks. The similar isotopic composition of the late anhydrite/barite and fracture/vug-filling anhydrite in western Alberta with Devonian evaporites isotopic signature, and the highly radiogenic 87Sr/86Sr ratio further supports sulfate-bearing fluids were mainly originated from underlying Devonian evaporites and migrated upwards through deep-seated faults/fractures to the Montney Formation.

Factors Controlling Reservoir Quality of a Paleozoic Tight Sandstone, Rub’ al Khali Basin, Saudi Arabia

The heterogeneity of depositional and diagenetic controls on the reservoir quality of tight sandstones is a major challenge. Understanding which factors are the most influential is significant for improving reservoir evaluation and prediction. This study utilized sedimentological core descriptions, thin-section petrography, quantitative evaluation of mineralogy by scanning electron microscope, X-ray diffractometry, scanning electron microscopy and porosity–permeability measurements to define and characterize the factors that control reservoir quality in the Upper Ordovician Sarah Formation of the Rub’ al Khali Basin. Four facies associations (FA), including fluvial (FA1), glaciolacustrine delta (FA2), subglacial (FA3) and glaciofluvial (FA4), have been recognized. The results show that the highest reservoir quality was enhanced by feldspar dissolution in FA1. The development of its reservoir quality was, however, partially limited by compaction, and authigenic pore filling and grain coating with the clay mineral, illite. The lowest reservoir quality, related to FA3, appears to have been influenced by the detrital matrix content, compressibility and siderite cement precipitation. The presence of a detrital matrix, anhydrite and barite cement, and grain compaction reduced the reservoir quality in FA2. On the other hand, intergranular porosity, and fractures that facilitated the development of dual porosity and permeability systems in this FA, might have slightly enhanced its reservoir quality. Factors such as grain-size distribution and sorting influenced the reservoir quality of all the FAs, but these were the main controls on the reservoir quality of FA4, in addition to compaction. The reservoir quality of this FA might have also been improved by fractures and the dissolution of unstable grains.

Chapter 36 Neoproterozoic glacial record in the Mackenzie Mountains, northern Canadian Cordillera

Abstract In the Mackenzie Mountains, an arcuate foreland thrust-fold belt of Late Cretaceous–Paleocene age in the northern Canadian Cordillera, two discrete glacial–periglacial sequences of Cryogenian age (the Rapitan Group and the Stelfox Member of the Ice Brook Fm.) are separated by c. 1.0 km of non-glacial strata. The older Rapitan diamictite occurs in an amagmatic rift basin; the younger Stelfox diamictite occurs on a passive-margin continental slope. The Rapitan Group consists of three formations. The lower Mount Berg Fm. is a complex of diamictites and conglomerates of limited extent. The middle Sayunei Fm. is a thick sequence of maroon-coloured mudrocks hosting innumerable graded layers of silt- and fine-grained sandstone. It lacks wave- or traction current-generated bedforms, and is lightly sprinkled with granule aggregates (‘till pellets’) and lonestones of dolostone and rare extrabasinal granitoids. It is capped by a hematitic Fe-formation that was reworked into the disconformably overlying Shezal diamictite. The Shezal Fm. is a complex of olive-green coloured boulder diamictites with subordinate, dark-grey shales, siltstones and parallel-sided sandstones. Some of the boulders are faceted and striated, and include dolostone, quartzite, siltstone and gabbro in declining order of abundance. Diamictite terminates abruptly at the top of the Shezal Fm., which is sharply overlain by dark shales or by <52 m of fetid, dark-grey, 13 C-depleted limestone with graded bedding. The Stelfox Member is dominated by non-stratified, carbonate-clast diamictite with faceted and striated clasts, locally associated with subordinate, well-laminated shales containing till pellets and ice-rafted dropstones. It is thin or absent on the palaeocontinental shelf, but thickens seaward (southwestward) on the palaeocontinental slope. A thin clay drape separates it from a laterally continuous post-glacial ‘cap’ dolostone, which is a very pale coloured, micro- to macropeloidal dolostone with low-angle cross-laminae, giant wave ripples and local bioherms of corrugated stomatolites. In the NW, the dolostone is followed by reddish and greenish marls, followed by black shale of the Sheepbed Fm. In the SE, the dolostone is overlain by pink or grey limestones with well-developed sea-floor cements pseudomorphic after aragonite. In this area, the top of the dolostone is ferruginous and contains digitate rosettes of sea-floor barite cement, variably calcitized. The dolostone–limestone contact is perfectly conformable, and synclinal structures previously intepreted as karst features are tectonic in origin. The grand mean palaeomagnetic pole for the well-studied Franklin Large Igneous Province ( c. 718 Ma) of Arctic Laurentia, coeval with the basal Rapitan Group in the Mount Harper area, Yukon Territory, places the Mackenzie Mountains firmly in the tropics, at 18±3°N palaeolatitude, at the onset of the Rapitan glaciation. Carbon (δ 13 C), oxygen (δ 18 O) and strontium ( 87 Sr/ 86 Sr) isotopes have been measured in carbonates bracketing the Rapitan and Stelfox diamictites. Sulphur isotope data (δ 34 S) have been obtained from carbonate-associated sulphate and barite above the younger diamictite, and calcium isotope data (δ 44 Ca) from the younger carbonate itself. The results are broadly consistent with data from other areas. Iron isotope (δ 57 Fe) and cerium anomaly (Ce/Ce*) values increase systematically upwards through the Sayunei Fe-formation, supporting an interpretation that deposition occurred within a redox chemocline through which the basin floor descended as a consequence of isostatic loading by the advancing Shezal ice sheet. Supplementary material: Data are available at http://www.geolsoc.org.uk/SUP18470 .

Chaotic breccia along the Dent Fault, NW England: implosion or collapse of a fault void?

A body of chaotic breccia along the reverse-oblique Dent Fault zone is ascribed to hanging-wall collapse into persistent voids created by geometric mismatch of fault walls, although some implosion into transient voids is a possibility. The breccia comprises a 20 m wide body of hanging-wall lithologies, with a chaotic clast-supported fabric that contrasts with the fitted-fabric breccias typical of the Dent Fault damage zone. The breccia body has crude bedding defined by clast shape and size contrasts. The void fill is cut by Variscan fault strands, which, together with its ferroan calcite and barite cement, prove its late Carboniferous rather than recent age. It is shown that any fault void, transient or persistent, had a smaller aperture than the final width of the breccia body, and no more than 5 m; a span that can be supported to depths of 2 or 3 km. However, cement zonation in the breccia fill suggests that the void opened in multiple increments, each of an aperture compatible with the maximum displacement in any one event along the Dent Fault. The Dent Fault example highlights the possible general importance of fault-void collapse but also the problems in distinguishing it from implosion processes.

Sedimentary environment and diagenesis of the Lower Cretaceous Chaswood Formation, southeastern Canada: The origin of kaolin-rich mudstones

The Lower Cretaceous fluvial sandstone–mudstone succession of the Chaswood Formation is the proximal equivalent of offshore deltaic rocks of the Scotian Basin that are reservoirs for producing gas fields. This study interprets the mineralogical consequences of Cretaceous weathering and early diagenesis in a 130-m core from the Chaswood Formation in order to better understand detrital and diagenetic minerals in equivalent rocks offshore. Mineralogy was determined by X-ray diffraction, electron microprobe analysis and scanning electron microscopy. The rocks can be divided into five facies associations: light gray mudstone, dark gray mudstone, silty mudstone and muddy sandstone, sorted sandstone and conglomerate, and paleosols. Facies transitions in coarser facies are related to deposition in and near fluvial channels. In the mudstones, they indicate an evolutionary progression from the dark gray mudstone facies association (swamps and floodplain soils) to mottled paleosols (well-drained oxisols and ultisols following syntectonic uplift). Facies transitions and regional distribution indicate that the light gray mudstone facies association formed from early diagenetic oxidation and alteration of the dark gray mudstone facies association, probably by meteoric water. Principal minerals in mudstones are illite/muscovite, kaolinite, vermiculite and quartz. Illite/muscovite is of detrital origin, but variations in abundance show that it has altered to kaolinite in the light gray mudstone facies association and in oxisols. Vermiculite developed from the weathering of biotite and is present in ultisols. The earliest phase of sandstone cementation in reducing conditions in swamps and ponds produced siderite nodules and framboidal pyrite, which were corroded and oxidized during subsequent development of paleosols. Kaolinite is an early cement, coating quartz grains and as well-crystallized, pore-filling booklets that was probably synchronous with the formation of the light gray mudstone facies association. Later illite and barite cement indicate a source of abundant K and Ba from formation water. This late diagenesis of sandstone took place when the Chaswood Formation was in continuity with the main Scotian Basin, prior to Oligocene uplift of the eastern Scotian Shelf. Findings of this study are applicable to other mid-latitude Cretaceous weathering and early diagenetic environments.

Vein and Karst Barite Deposits in the Western Jebilet ofMorocco: Fluid Inclusion and Isotope (S, O, Sr) Evidence for Regional FluidMixing Related to Central Atlantic Rifting

Numerous vein and karst barite deposits are hosted by Hercynian basement and Triassic rocks of the western Jebilet in Morocco. Sulfur, oxygen, and strontium isotope analyses of barite, combined with fluid inclusion microthermometry on barite, quartz, and calcite were used to reveal the nature and source of the ore-forming fluids and constrain the age of mineralization. The δ 34S values of barite between 8.9 and 14.7 per mil are intermediate between the sulfur isotope signatures of Triassic evaporites and Triassic-Jurassic seawater and lighter \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(SO_{4}^{2{\mbox{--}}}\) \end{document}, probably derived from the oxidation of dissolved H2S and leaching of sulfides in the Hercynian basement. The 87Sr/86Sr ratios of barite between 0.7093 and 0.7130 range between the radiogenic strontium isotope compositions of micaceous shale and sandstone and the nonradiogenic isotopic signature of Triassic to Jurassic seawater and Cambrian limestone. The δ 18O values of barite between 11 and 15 per mil (SMOW) support mixing between two or more fluids, including Late Triassic to Jurassic seawater or a water dissolving Triassic evaporites along its flow path, hot basinal, or metamorphic fluids with δ 18O values higher than 0 per mil and/or meteoric fluids with δ 18O values lower than 0 per mil. The general trend of decreasing homogenization temperatures and initial ice melting temperatures with increasing salinities of H2O-NaCl ± CaCl2 fluid inclusions trapped in barite, quartz, and calcite indicates that a deep and hot basinal fluid with salinities lower than 6 wt percent NaCl equiv might have mixed with a cooler surficial solution with a mean salinity of 20 wt percent NaCl equiv. Calcium was leached from the Cambrian limestone and the clastic and mafic volcanic rocks of the Hercynian basement. Alkali feldspars and micas contained in the Cambrain sandstones provided most of the Ba to the hydrothermal system. Vein and karst deposits are modeled as a two-component mixing process in which the temperature and the S and Sr isotope composition of the end members changed during the 220 to 155 Ma interval. The hot basinal fluid remained volumetrically dominant during the entire mineralization process. Differences in mean S, O, and Sr isotope compositions among the barite families are interpreted as reflecting differences in mineralization age. Most barite deposits formed before the Kimmeridgian, except for north-south-oriented vein barite, karst barite, and barite cement in the conglomeratic Upper Jurassic, which were deposited later, possibly around 155 Ma. Similar genetic processes have been described for late Paleozoic to Mesozoic F-Ba vein deposits in western Europe. The vein and karst barite in the western Jebilet of Morocco reveals a wide-scale regional mineralization event related to Central Atlantic rifting.

Origin of Authigenic Mn-Fe Carbonates and Pore-Water Evolution in Marine Sediments: Evidence from Cenozoic Strata of the Arctic Ocean and Norwegian-Greenland Sea (ODP Leg 151)

Early diagenetic Mn-Fe carbonates, occurring in thin layers, nodules, and burrows, were recovered from Cenozoic silts and clays from the Arctic Ocean and the Norwegian-Greenland Sea during Ocean Drilling Program Leg 151. At Sites 909 (Fram Strait; Miocene-Quaternary) and 911 (Yermak Plateau; Pliocene-Quaternary), fine-crystalline siderite, enriched in Ca and/or Mg, is the predominant carbonate. Variable δ13C values (-21.8 to +7.9‰ PDB) suggest that dissolved carbon was derived from the Fe-reduction suboxic zone, the oxidation of marine organic matter in the bacterial sulfate-reduction zone, and the early stages of methanogenesis. The range of δ18O values for siderite (-6.3 to +5.1‰ PDB) indicates precipitation over a temperature range of 4-56°C during successive burial. At Site 913 (East Greenland Margin; Eocene-Quaternary), concentrically zoned microspherules and rhombohedra of ferroan rhodochrosite and manganoan siderite, 20-600 μm in diameter, are the main authigenic carbonates. Although they have low δ13C values (-22.3 to -13.8‰ PDB), elevated pore-water sulfate concentrations indicate low sulfate-reducing activity and suggest that dissolved carbon may have been partially derived from thermogenic methane. The variable δ18O values for rhodochrosite (-11.9 to +1.5‰ PDB) and siderite (-11.4 to -10.3‰ PDB) suggest precipitation at elevated temperatures (60-100°C) during progressive burial. The close association with barite cement suggests that carbonate precipitation at Site 913 may have been influenced by hydrothermal fluids. However, active circulation of hydrothermal fluids is precluded by the occurrence of geochemical gradients in Site 913 pore waters. Pore waters at the three sites reflect various evolutionary pathways that are partly due to variations in the extent of interaction with volcanic ash layers and the underlying basaltic crust, which led to an overall decrease in Mg2+, K+, and δ18O and an increase in Ca2+ with depth. However, pore waters at Site 913 have evolved more extensively to Na-Ca-Cl brines. The sources of freshwater that cause the downhole decrease in Cl- and Na+ concentrations at Sites 909 and 913 are poorly constrained. The possible influence of meteoric-water incursion is suggested by the δD-δ18O relationship of pore waters and the low δ18O values of Site 913 authigenic carbonates.

Thermal History Constraints from Studies of Organic Matter, Clay Minerals, Fluid inclusions, and Apatite Fission Tracks at the Ardeche Paleo-margin (BA1 Drill Hole, GPF Program), France

ABSTRACT The thermal history of the Ardeche paleo-margin (southeastern France) has been reconstructed using various analytical data from minerals and organic matter and conventional interpretation. These methods comprise Tmax and vitrinite reflectance measurements on organic matter, determination of the smectite content in mixed-layer illite/smectite, fluid-inclusion microthermometry in quartz, barite, dolomite, and anhydrite, and fission-track analyses in apatite. The Balazuc (BA1) drill hole, 1730 m deep, intersects mainly Jurassic carbonate rocks, Triassic sandstones, and sulfate-rich claystones and ends in Carboniferous rocks. The present bottom-hole temperature is 70°C. Other drill holes, less than 6 km away, were studied when necessary. One of the main objectives of this paper is to ssess the agreement between the different geothermometric methods, and to check their limitations and convergence when used on carbonate- and sandstone-dominated reservoirs. In the Triassic sandstones, primary aqueous inclusions in anhydrite cement and at the boundary between the detrital quartz grain and the quartz overgrowth are one-phase brine inclusions entrapped below 70°C. The homogenization temperature determined on the later barite cement is about 100°C. Aqueous two-phase inclusions in healed microfractures in anhydrite are present at the base of the drill core near major faults. Temperatures as high as 210°C recorded for these fluid inclusions could be associated with episodic fluid injections from below through the fault zones during the Early Jurassic. The fluid inclusions in dolomite, most of them reequilibrated during burial, indicate a trapping temperature of 130-145°C at 1600 m and a temperature decrease towards the surface. This value is in good agreement with the MPTB (maximum paleotemperature of burial) method on organic matter, which converges to a maximum burial temperature of 130°C at the same depth. The apatite fission-track data agree with these temperatures and indicate that the temperature decreased below 120 ± 10°C during the Eocene. These paleotemperatures, much higher than the present ones, can be explained by the erosion of 1900 m of mainly Cretaceous sediments. This interpretation implies a high average sedimentation rate during the Cretaceous, in agreement with data determined on a regional scale. A time-temperature evolution is proposed for the formations present in the Balazuc drill hole and the eroded sedimentary rocks. The application of the dual reaction model of the transformation of smectite to illite (Velde and Vasseur 1992) shows that the data are in good agreement with the kinetic model. However, the vitrinite reflectance variation trend with depth, predicted from the Burnham and Sweeney model (1989), is different from the data variation. No definitive explanation can be proposed for the failure of aturity assessment through vitrinite reflectance in the BA1 drill hole.

Multiple-stage diagenetic alteration and fluid history of Ordovician carbonate-hosted barite mineralization, Southern Quebec Appalachians

Lower Ordovician bioclastic limestone of the Upton Group, southern Quebec Appalachians, hosts stratabound Ba-Zn-Pb mineralization. The Upton Group, a mixed platform carbonate-siliciclastic-volcanic succession, is exposed as windows within the tectonically overlying Cambrian siliciclastics of the Granby Nappe. Mineralization consists mostly of barite and minor amounts of sulfides (sphalerite, pyrite, galena, and chalcopyrite), in addition to calcite, quartz and bitumen cements. It is hosted by a bioclastic limestone which is interbedded with and capped by a black calcareous shale, and underlain by a mudstone-siltstone-volcanic succession and a lower poorly fossiliferous limestone. The lower limestone recorded early extensive dolomitization followed by meteoric alteration (dedolomitization, sulphate dissolution, vadose cements, soil pisoids, etc.), and burial diagenesis (recrystallization, fracturation, and cementation). The vadose gravitational calcite cements yield δ 18O PDB values of −8.4 to −11.0‰ andδ 13C PDB values of +2.4 to +2.8‰. The thin soil profiles with pisoids have a δ 18O PDB value of −8.2‰ and a δ 13C PDB value of +2.0‰. These data suggest an evaporative 18O-enrichment of near-surface trapped soil moisture (vadose water) in a rock-dominated diagenetic system. The recrystallized limestone hasδ 18O PDB values of −11.4 to −15.5‰ and near Early Ordovician marine δ 13C PDB values of −0.2 to +2.5‰. These data suggest a final stabilization of the limestone from high temperature fluids in a rock-dominated diagenetic system. The mineralized bioclastic limestone shows rare evidence of early submarine cementation which is overprinted by significant post-depositional recrystallization and hydrothermal alteration. The latter resulted in the generation of secondary porosity and precipitation of a subhedral barite cement, a bladed barite cement, and fracture-filling barite. Fracture- and void-filling calcite, sulfides, quartz and bitumen cementation followed barite mineralization. Pre-barite syntaxial calcite overgrowths on crinoids yieldδ 13C PDB values of −3.9 to −15.0‰ andδ 18O PDB values of −13.7 to −14.8‰. Post-barite sparry calcite cement and fracture-filling calcite haveδ 13C PDB values of −2.6 to −13.0‰ and −2.4 to −17.9‰, respectively, andδ 18O PDB values of −13.6 to −14.2‰ and −14.0 to −15.8‰, respectively. The δ 18O values suggest relatively high-temperature re-equilibration in a deep-burial environment. The variable and depleted 13C values appear to reflect fluid-rock interaction and addition of significantδ 13C-depleted CO 2 from thermochemical sulphate reduction of organic matter. Mixing of reduced, hot basinal brines with oxidizing sulphate-rich fluids resulted in barite precipitation.

Cements and In-Situ Widths of Natural Fractures, Almond Formation, Green River Basin, Wyoming: ABSTRACT

Abstract In-situ fracture width and extent of cementation are evaluation characteristics useful in the exploration and development of naturally fractured reservoirs. A joint field test of the Amoco Champlin No. 254B-2H, a horizontal well in the Almond Formation at the northern extent of the Echo Springs Field, Green River Basin, Wyoming, provided an opportunity to examine natural fracture cementation histories and widths at in-situ pressures using slant and horizontal cores. In this field, natural fractures in the Mesaverde Group provide increased production rates and ultimate recoveries of natural gas. Conventional core plug samples were taken from this well so as to orient the trace of natural fractures parallel to the plug axis. These samples were epoxy impregnated at an effective horizontal pressure of 2500 psi, representative of reservoir conditions. Polished thin sections were used to image the in-situ fracture widths using back-scattered scanning electron microscopy. The fracture cementation includes quartz overgrowths locally followed by sparse kaolinite cement. Patchy barite cement followed kaolinite. Sparry calcite was the latest mineralization. Both barite and calcite prop open the fractures; quartz and kaolinite do not. In-situ fracture width (both open and mineralized) measurements were collected perpendicular to the length of the fracture traces. Average widths range from 59 to 118 μm (micrometers). Apparent one-inch plug permeabilities can be calculated from open fracture widths, and range from 297 md to 3108 md. In-situ fracture permeabilities of this magnitude should provide high rates of production if the fractures are numerous, have extensive areal dimension, and are not plugged with either natural cements or drilling and completion fluids. Borehole imaging of the sampled well indicates numerous fractures at a spacing of one to two meters, yet production rates are less than the production anticipated from the calculated permeability. Since both this study and borehole imaging indicate the presence of open fractures at in-situ conditions, then either the areal extent of the fractures is limited or the fracture apertures have been reduced during drilling and completion or by the presence of natural cements.

Hydrogeochemical exploration for barite, Ouachita Mountains, U.S.A.

Approximately 100 springs were sampled as part of a general geochemical survey in a 130 by 140 km multi-mineralized area of the Ouachita Mountains. The study area was subdivided into Area I and Area II based on differences in lithology and mineralization. Area I is composed primarily of the Paleozoic Stanley Shale and the Arkansas Novaculite Formation, and has considerable manganese (often present as psilomelane) and barite mineralization. The barite occurs primarily as replacement deposits in shale in Area I. Area II is composed of Paleozoic and Cretaceous sedimentary rocks, and Quaternary alluvium. Mercury, antimony, strontium and barite mineralization is present. The barite mineralization occurs as cement in the Cretaceous sandstone and gravel in this area. The widely prevalent barite cement in Area II is reflected by higher median and upper range values of barium concentration and also higher median and threshold % BaSO 4 saturation values. The presence of barite as cement in the sediments of Area II tends to mask the detection of the barite deposits in this area. Approximately 83% of the sites within 1.7 km of known barite mineralization in Area I were characterized by anomalous barium concentration, and 67% within 3.4 km. Anomalous % BaSO 4 saturation values and Ba/Sr ratios produced success rates generally similar to those of anomalous barium concentrations. Anomalous strontium concentrations did not prove effective in detecting barite mineralization.

Intriguing examples of geology applied to industrial minerals

It is noted that the dollar value of the industrial minerals produced in the United States stands, in relation to the dollar value of the metals produced, in the ratio of $3.2 billion for the nonmetals to $2.2 billion for the metals (1957). The tonnage of crushed stone, and of sand and gravel, each exceeds the tonnage of all the metallic ores produced, and even exceeds the tonnage of solid fuels. Comparatively few geologists have been attracted to the study of industrial minerals. A selection of some of the outstanding problems, mostly geological, but also mineralogical and chemical, offered by the occurrences of the industrial minerals, is the subject of this paper. Asbestos, barite, B, Br, fluorspar, lime and pozzolan cement, pegmatites, sand and gravel, and Ti deposits are discussed.