Iron sulfide minerals at Cement oil field, Oklahoma: Implications for magnetic detection of oil fields (original) (raw)
Related papers
Sulfidization and magnetization above hydrocarbon reservoirs
Geochemical and rock magnetic studies of strata over Cement oil field (Anadarko basin, Oklahoma), Simpson oil field (North Slope basin, Alaska), and the Edwards deep gas trend, south Texas coastal plain, document changes in original magnetizations caused by postdepositional iron sulfide minerals that are, or may be, related to hydrocarbon seepage. At Cement, ferrimagnetic pyrrhotite (FeâSâ) formed with pyrite and marcasite in Permian red beds. The Fe-S minerals contain isotopically heavy, abiogenic sulfur derived from thermal degradation of petroleum and (or) isotopically light sulfur derived from sulfate-reducing bacteria fed by leaking hydrocarbons. At Simpson, ferrimagnetic greigite (FeâSâ) dominates magnetizations in Upper Cretaceous nonmarine beds that contain biodegraded oil. Sulfur isotopic data are consistent with, but do not prove, a genetic link between the greigite (δ³â´S < +20 per mil) and seepage. In middle Tertiary sandstones of southeast Texas, pyrite and marcas...
2003
Past research shows that active sulfide mineralization occurs at the base of the sulfate reduction zone (SRZ) in modern, deep-water, continental-margin sediments that overlie methane gas hydrate. These sulfide minerals (elemental sulfur, Sº; iron monosulfides, ~FeS; and pyrite, FeS2) are enriched in 34 S because of sulfate reduction and anaerobic methane oxidation (AMO) processes occurring above and near the sulfate-methane interface (SMI). The data in this study show that 5 discrete zones of sulfide minerals are preserved in a 703.8-meter sediment column associated with methane gas hydrate. These zones of sulfide minerals are also enriched in 34 S. The shallowest zone is the present-day SMI, and we infer that the other 4 zones are past locations of the SMI. Today, enrichments of 34 S in sulfide minerals occur because of anaerobic methane oxidation (AMO) carried out by methanotrophs and sulfate-reducing microbes in areas that have significant methane delivery to the SMI in methane gas hydrate terranes. Thus, these 34 S enrichments are a diagenetic indicator that point out occurrences of high methane delivery to the sulfate-methane interface and the action of the AMO consortium. From the data, we infer that these conditions exist not only today, but also have existed at several discrete times since the mid-Miocene, when sulfur isotopic composition of sulfide minerals is similar to or heavier than that occurring today.
Santa Barbara Basin sediments host a complex network of abiotic and metabolic chemical reactions that knit together the carbon, sulfur, and iron cycles. From a 2.1-m sediment core collected in the center of the basin, we present high-resolution profiles of the concentrations and isotopic compositions of all the major species in this system: sulfate, sulfide ( P H 2 S), elemental sulfur (S 0 ), pyrite, extractable organic sulfur (OS), proto-kerogen S, total organic and dissolved inorganic carbon, and total and reducible iron. Below 10 cm depth, the core is characterized by low apparent sulfate reduction rates (<0.01 mM/yr) except near the sulfate-methane transition zone. Surprisingly, pyrite forming in shallow sediments is $30‰ more 34 S-depleted than coexisting P H 2 S in porewater. S 0 has the same strongly 34 S-depleted composition as pyrite where it forms near the sediment-water interface, though not at depth. This pattern is not easily explained by conventional hypotheses in which sedimentary pyrite derives from abiotic reactions with porewater P H 2 S or from the products of S 0 disproportionation. Instead, we propose that pyrite formation in this environment occurs within sulfate reducing microbial aggregates or biofilms, where it reflects the isotopic composition of the immediate products of bacterial sulfate reduction. Porewater P H 2 S in Santa Barbara Basin may be more 34 S-enriched than pyrite due to equilibration with relatively 34 S-enriched OS. The difference between OS and pyrite d 34 S values would then reflect the balance between microbial sulfide formation and the abundance of exchangeable OS. Both OS and pyrite d 34 S records thus have the potential to provide valuable information about biogeochemical cycles and redox structure in sedimentary paleoenvironments.
Chemistry of iron sulphides in sedimentary environments
1995
Recent advances in understanding the chemistry of iron sulfides in sedimentary environments are beginning to shed more light on the processes involved in the global sulfur cycle. Pyrite may be formed via at least three routes including the reaction of precursor sulfides with polysulfides, the progressive solid-state oxidation of precursor iron sulfides and the oxidation of iron sulfides by hydrogen sulfide. The kinetics and mechanism of the polysulfide pathway are established and those of the H 2 S oxidation pathway are being investigated. Preliminary considerations suggest that the relative rates of the three pathways are H 2 S oxidation > polysulfide pathway> > solid-state oxidation. The kinetics and mechanisms of iron(II) monosulfide formation suggest the involvement of iron bisulfide complexes in the pathway and iron bisulfide complexes have now been identified by voltammetry and their stabililty constants measured. The framboidal texture commonly displayed by sedimentary pyrite appears to be an extreme example of mosaicity in crystal growth. Framboidal pyrite is produced through the H 2 S oxidation reaction. Frontier molecular orbital calculations are beginning to provide theoretical underpinning of the reaction mechanisms. Recent progress in understanding iron sulfide chemistry is leading to questions regarding the degree of involvement of precursor iron sulfides in the formation of pyrite in sediments. Spin-offs from the work are addressing problems relating to the involvement of iron sulfides in the origin of life, the nature of metastability, the mechanism of precipitation reactions and the use of iron sulfides in advanced materials.
Biogeochemical transformation of Fe minerals in a petroleum-contaminated aquifer
Geochimica et Cosmochimica Acta, 2004
The Bemidji aquifer in Minnesota, USA is a well-studied site of subsurface petroleum contamination. The site contains an anoxic groundwater plume where soluble petroleum constituents serve as an energy source for a region of methanogenesis near the source and bacterial Fe(III) reduction further down gradient. Methanogenesis apparently begins when bioavailable Fe(III) is exhausted within the sediment. Past studies indicate that Geobacter species and Geothrix fermentens-like organisms are the primary dissimilatory Fe-reducing bacteria at this site. The Fe mineralogy of the pristine aquifer sediments and samples from the methanogenic (source) and Fe(III) reducing zones were characterized in this study to identify microbiologic changes to Fe valence and mineral distribution, and to identify whether new biogenic mineral phases had formed. Methods applied included X-ray diffraction; X-ray fluorescence (XRF); and chemical extraction; optical, transmission, and scanning electron microscopy; and Mössbauer spectroscopy. All of the sediments were low in total Fe content (Ϸ 1%) and exhibited complex Fe-mineralogy. The bulk pristine sediment and its sand, silt, and clay-sized fractions were studied in detail. The pristine sediments contained Fe(II) and Fe(III) mineral phases. Ferrous iron represented approximately 50% of Fe TOT. The relative Fe(II) concentration increased in the sand fraction, and its primary mineralogic residence was clinochlore with minor concentrations found as a ferroan calcite grain cement in carbonate lithic fragments. Fe(III) existed in silicates (epidote, clinochlore, muscovite) and Fe(III) oxides of detrital and authigenic origin. The detrital Fe(III) oxides included hematite and goethite in the form of mm-sized nodular concretions and smaller-sized dispersed crystallites, and euhedral magnetite grains. Authigenic Fe(III) oxides increased in concentration with decreasing particle size through the silt and clay fraction. Chemical extraction and Mössbauer analysis indicated that this was a ferrihydrite like-phase. Quantitative mineralogic and Fe(II/III) ratio comparisons between the pristine and contaminated sediments were not possible because of textural differences. However, comparisons between the texturally-similar source (where bioavailable Fe(III) had been exhausted) and Fe(III) reducing zone sediments (where bioavailable Fe(III) remained) indicated that dispersed detrital, crystalline Fe(III) oxides and a portion of the authigenic, poorly crystalline Fe(III) oxide fraction had been depleted from the source zone sediment by microbiologic activity. Little or no effect of microbiologic activity was observed on silicate Fe(III). The presence of residual "ferrihydrite" in the most bioreduced, anoxic plume sediment (source) implied that a portion of the authigenic Fe(III) oxides were biologically inaccessible in weathered, lithic fragment interiors. Little evidence was found for the modern biogenesis of authigenic ferrous-containing mineral phases, perhaps with the exception of thin siderite or ferroan calcite surface precipitates on carbonate lithic fragments within source zone sediments.
Geochimica et Cosmochimica Acta, 1987
Ah&act-The rek~tionship hetweett pyritic solfur cotttettt (S& and organic carbon content (0 of shales analyzed from the New Albany Group depends upon C,. For samples of <6 wt.% &, s, and c, ate stron8ly correlated (r = 0.85). For C&"rich" shales (>6 wt.%), no !&-Cm correlation is apparent. The degne of Fe pyritization (DGP) shows similar relationships to C,. These C-S-Fe relationships su88est that pyrite formation was limited hy the avaihthihty of metaholizahle organic carhott in samples when C, < 6 wt.96 and hy the avaii&ihty of reactive Fe for samples where C, > 6 wt.%. Apparent sulfur isotope hattionatiotts relative to ~n~rn~~~~ seawater sulfate (A%) for pyrite fo~ation avera@ -40% for noncaicareous shaies and -25%~ for cakamous shales. A?? valuea hecome smaller with incmasin8 C,, f&, and DOP for all &-'w (~6 wt.%) and some Cm-"rich" (~6 wt.%) shalea. These trends stt8@st that pyrite formation occmred in a cktsed system or that instantaneous bacterial fractionation for sol&e redttction decmamdinma@tudewith inueasin8 organic carbon content. The isotopic trends oheerved in the New Albany Group are not neceskly repremntative of other shales having a contparahle range of oqanic carbon content, e.g. Cmtaceous shales and mudstones from the western interior of North America (GA~JTIW, 1986). A?S values in the remainder of the &-rich New Albany Group shahs are mhttivety Fargo (-38 to -47%) and independent of C,, &, and DOP, which sugaests that pyrite in them shaks formed mostly at or ahove the sediment-water interface hy precipitation from an isotopically uniform reservoir of dissolved i&S.
Crystal-size distributions and possible biogenic origin of Fe sulfides
European Journal of Mineralogy, 2001
Sedimentary greigite (Fe 3 S 4 ) can form either by "biologically controlled " or by "biologically induced min eralization " (BCM and BIM, respectively). In order to identify the origin of magnetic Fe sulfides, we studied and compared the sizes and morphologies of greigite crystals produced by a magnetotactic microorganism (previously described and referred to as the "many-celled magnetotactic prokaryote ", MMP) and Fe sulfides from two specimens of Miocene sedimentary rocks (from £±ka, in the foredeep of the Western Carpathians and from Michalovce, in the Transcarpathian Depression). Greigite grains from the MMP and the £±ka rock show nearly Gaussian crystal-siz e distributions (CSDs), whereas the CSD is lognormal for Fe sulfides from the Michalovce rock. We simulated various crystal-growth mechanisms and matched the calculated and observed CSDs; crystals from the MMP and the £±ka rock have CSDs that are consistent with random growth of crystal nuclei in an open system, whereas the CSD of the Michalovce Fe sulfides is consistent with surface-controlled growth followed by supply-controlled growth in an open system. On the basis of CSDs and characteristic contrast features in the transmission electron microscope, greigite in the £±ka rock is likely of BCM origin, whereas the Fe sulfide crystals in the other rock sample were produced by BIM processes. Our results indicate that the methods we applied in this study may contribute to the identification of the origin of magnetic Fe sulfide minerals in sedimentary rocks.
Journal American Society of Mining and Reclamation
X-ray photoelectron spectroscopy (XPS), evolved gas analysis (EGA), and froth flotation tests were used to compare iron disulfides of hydrothermal, sedimentary/hydrothermal, and sedimentary origin. A specimen composed of equal amounts of pyrite and marcasite was also evaluated, The susceptability of iron disulfide surfaces to oxidation was measured using XPS and EGA techniques. XPS analyses indicated the following order of increasing oxidation rate at 21 pct oxygen and 88 pct relative humidity: sedimentary/hydrothermal pyrite (0.70 mg so4-2/hr per gram of FeS2)< hydrothermal pyrite (0.83 mg S04-2/hr per gram of FeS2)< hydrothermal pyrite/marcasite (1.34 mg S04-2/hr per gram of FeSz)< sedimentary pyrite (3.53 mg So4-2/hr per gram of FeS2). Oxidation rates measured by XPS are based solely on the sulfate/sulfide ratios at the surface, where oxidation is not inhibited by mass transfer limitations. Therefore, the~e rates are much higher than previously published rates based on bulk iron disulfide content. The comparison of EGA results with oxidation rates measured by XPS showed that for sedimentary pyrites, higher temperatures of S02 evolution corresponded to lower oxidation rates. Weathering rates for hydrothermal iron disulfides appear to be independent of S02 evolution temperatures. In flotation tests with an anionic fluorosurfactant collector, hydrothermal pyrite floated and sedimentary pyrite was depressed. Hydrothermal pyrite floated because it developed a positive surface charge in solution that allowed the attachment of the anionic collector. The negative charge developed by sedimentary pyrite in this solution repelled the anionic collector, depressing sedimentary pyrite. This research provides a better understanding of iron disulfide oxidation and illustrates inherent differences in physical and chemical properties that significantly alter the behavior of pyrites of different geologic provenance.
Annales de Paléontologie, 2015
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