Fracture and fluid flow paths analysis of an offshore carbonate reservoir using oil-based mud images and petrophysical logs
- Authors: Momeni, Aliakbar , Rostami, S. , Hashemi, Sam , Mosalman-Nejad, H. , Ahmadi, Ali
- Date: 2019
- Type: Text , Journal article
- Relation: Marine and Petroleum Geology Vol. 109, no. (2019), p. 349-360
- Full Text: false
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- Description: Hydrocarbon production and development of carbonate reservoirs mainly depend on fractures that cross wells. Therefore, quantification of their characteristics has a crucial role in reservoir management. In this research, bedding planes, faults and different types of fractures of a Cenomanian-Turonian carbonate reservoir in the Persian Gulf were studied. Image logs including the oil-based mud image (OBMI) and the ultrasonic borehole image (UBI) were used. The results from conventional petrophysical log suites were compared to the image logs results. Based on the image logs, structural characteristics of bedding planes were reconstructed by estimating their strike, dip, dip direction and layer thickness. Fracture types and their distribution and the geometry in the well were determined. Also, fault zone geometry and type of faults were evaluated. The results indicate that majority of the bedding planes have a N58W strike with an average dip of 18° towards NE. Furthermore, both tensile and shear fractures were distinguished, although shear fractures dominated and the 328/36SW and 29/45NW were found to be the prevalent orientation of fractures. Based on petrophysical logs analyses, four facies groups are distinguished and two statistical relationships are proposed for estimation of discontinuities. The proposed index for evaluation of fractures using petrophysical logs shows good performance and it could be used for wells when no image log is available. Especially in offshore reservoirs, lack of outcrop and unavailability of image logs of old wells lead to unknown fractures characteristics which will be addressed by the suggested equations.
Mechano-chemical oxidation of arsenopyrite
- Authors: Koroznikova, Larissa , McKnight, Stafford , Veder, Jean-Peirre , Giri, Jason , Palaniandy, Samayamutthirian , Williams, Gordon
- Date: 2019
- Type: Text , Journal article
- Relation: Minerals Engineering Vol. 141, no. (2019), p. 1-7
- Full Text: false
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- Description: This paper presents the results from the investigation of arsenopyrite oxidation via mechano-chemical activation, using a stirred mill. Water and hydrogen peroxide were chosen as the lixiviant and oxidant, respectively, and maintained at a relatively low temperature (50 °C). The milling media size, mill speed, slurry percent solids and amount of H2O2 added were all kept constant throughoust these experiments. The only operational variable for this investigation was the milling time, which results in increasing levels of specific energy provided by the mill. The products of activated arsenopyrite are characterised in terms of phase composition, particulate and structural characteristics, along with reactivity. Mechano-chemical activation of arsenopyrite under oxidizing conditions shows a maximum dissolution of around 9 wt% for iron and 7 wt% for arsenic after 2 h of milling. After 3 h of milling, the main phase present is found to be amorphous in nature.
First Holocene cryptotephras in mainland Australia reported from sediments at Lake Keilambete, Victoria, Australia
- Authors: Smith, Rebecca , Tyler, Jonathan , Reeves, Jessica , Blockley, Simon , Jacobsen, Geraldine
- Date: 2017
- Type: Text , Journal article
- Relation: Quaternary Geochronology Vol. 40, no. (2017), p. 82-91
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- Description: We report the first observations of Holocene cryptotephra deposits in lacustrine sediments from mainland Australia. All counts of cryptotephra shards are presented, but we focus on two prominent peaks of dark coloured glass shards representing, distinct cryptotephras within the sediments of Lake Keilambete, Victoria, southeast Australia. These two basaltic cryptotephras, aged 4589-3826 cal BP and 7149-5897 cal BP, may have derived from eruptions of Mts Gambier or Schank, South Australia. In addition, colourless shards, most likely of silicic composition and therefore unlikely to emanate from an Australian volcano were observed, suggesting a distant volcanic source beyond Australia. The presence of both the 'local' basaltic shards and the distal silicic shards highlights the potential to identify isochronous marker horizons in southern Australian sediments, thus potentially enabling a long-term goal of establishing a novel chronostratigraphic tool based on a cryptotephra network. (C) 2016 Elsevier B.V. All rights reserved.
Stable sulfur isotope dynamics in an acid sulfate soil landscape following seawater inundation
- Authors: Maher, Crystal , Sullivan, Leigh
- Date: 2016
- Type: Text , Journal article
- Relation: Chemical Geology Vol. 439, no. (2016), p. 205-212
- Full Text: false
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- Description: In 2002 a tidally driven seawater exchange remediation strategy was successfully implemented on a severely acidified tropical coastal landscape dominated by acid sulfate soils (ASS) in northern Australia. This study examined changes in the stable sulfur isotope signatures in a range of sulfide and sulfate (SO4) fractions at three sites with different levels of exposure to the tidally driven seawater exchange remediation. delta S-34 in the acid soluble SO4 fraction (e.g. jarosite) was less depleted in S-34 than the corresponding sulfide, indicating a degree of fractionation during sulfide oxidation and jarosite precipitation. The delta S-34 ofjarositic-SO4 was similar at all three sites indicating the appreciable stability of jarositic-SO4 even after extended exposure to seawater. delta S-34 of the water soluble, exchangeable and schwertmannitic-SO4 reflect conditions post remediation and indicate the relative contributions from two potential SO4 sources - a lighter SO4 derived from the oxidation of pyrite, and a heavier SO4 derived from the seawater. The delta S-34 of the contemporary surficial sulfide accumulations also reflect a SO4 contribution from seawater used for remediation and were isotopically different from the relict sulfides found at depth at all sites. delta S-34 of water soluble sulfate allowed the progress of the remediation to be traced down the soil profile. This study demonstrates the utility of stable sulfur isotope signatures in various sulfide and SO4 fractions to trace the sulfur geochemical pathways occurring in soils, in this case as a result of the introduction of tidally driven sea water. (C) 2016 Elsevier B.V. All rights reserved.
Was the Oligocene-Miocene a time of fire and rain? Insights from brown coals of the southeastern Australia Gippsland Basin
- Authors: Holdgate, Guy , Wallace, Malcolm , Sluiter, Ian , Marcuccio, Daniel , Fromhold, Thomas , Wagstaff, Barbara
- Date: 2014
- Type: Text , Journal article
- Relation: Palaeogeography Palaeoclimatology Palaeoecology Vol. 411, no. (2014), p. 65-78
- Full Text: false
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- Description: Lithotype cycles (ranging from 10 to 30 m thick) in the brown coals of the Latrobe Valley, Gippsland Basin, Australia, display well-developed lightening-upward trends. Cycle tops are characterized by abrupt and unconformable boundaries with the overlying cycle. Geological, geochemical, palynological and macrofossil evidence is consistent with a relative drying (terrestrialization) upward depositional model for the cycles. The abundance of charcoal in dark lithotypes near the cycle bases is explained by the fire-prone and highly flammable nature of the herbaceous/reed wetlands, in common with similar modem wetlands in modem Australasia, in which the dark lithotypes are suggested to have formed. This, together with the greater preservation potential of charcoal in subaqueous environments, results in the wettest facies of the Latrobe Valley coals having the highest charcoal contents. Despite prevailing warm, wet climate conditions and the predominance of rainforests that are suggested to have characterized the Cenozoic of southern Australia, some swamp taxa were clearly already pre-adapted to tolerate fire and are likely to have been the ancestors of the fire-adapted floral communities of modem arid Australia. (c) 2014 Elsevier B.V. All rights reserved.
Quantifying alkalinity generating processes in a tidally remediating acidic wetland
- Authors: Johnston, Scott , Keene, Annabelle , Burton, Edward , Bush, Richard , Sullivan, Leigh
- Date: 2012
- Type: Text , Journal article
- Relation: Chemical Geology Vol. 304-305, no. (2012), p. 106-116
- Full Text: false
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- Description: Lime-assisted tidal exchange (LATE) is a new remediation technique that is demonstrably effective at decreasing acidity in coastal acid sulfate soils (CASS). However, the relative magnitude of the major in situ alkalinity generating processes and external alkalinity inputs that dominate neutralization of acidity during LATE have not been quantified. Here, we combine investigations of porewater and solid-phase geochemistry from a remediating CASS wetland to derive first-order estimates of alkalinity generating processes and inputs after 6years of LATE. Quantified inputs include: marine derived HCO 3 - from tidal exchange; hydrated lime additions; and in situ alkalinity from anaerobic metabolism of organic carbon coupled with reduction of iron and sulfate. A progressive increase in tidal inundation led to the development of significant relationships (α=0.01) between topography and both non-sulfidic, solid-phase Fe(II) and solid-phase reduced inorganic sulfur species. These topographic relationships were conjoined with a digital elevation model, enabling up-scaling of alkalinity estimates to a sub-catchment level. Estimates indicate the relative order of importance of alkalinity generating processes and inputs is Fe reduction (50-64%)>tidal exchange (25-42%)>sulfate reduction (7-13%)>>hydrated lime addition (<1%). Accurately attributing the relative contributions due to Fe and SO 4 2- reduction was limited by an inability to distinguish between non-sulfidic, solid-phase Fe(II) generated by microbial dissimilatory reduction of Fe(III) or chemical reduction of Fe(III) by H 2S. Nevertheless, the combined alkalinity contribution of these two electron accepting processes accounts for between 58 and 74% of the total. The majority (>99%) of net alkalinity generation was due to either tides or microbial metabolism. This indicates that the LATE remediation technique is both a cost effective means of decreasing soil acidity and is readily transferable to similar CASS landscapes - provided there is adequate supply of suitable electron donors and sufficient regenerative capacity in the adjacent estuarine/marine tidal HCO 3 - pool. © 2012 Elsevier B.V.
Iron geochemical zonation in a tidally inundated acid sulfate soil wetland
- Authors: Johnston, Scott , Keene, Annabelle , Bush, Richard , Burton, Edward , Sullivan, Leigh , Isaacson, Lloyd , McElnea, Angus , Ahern, Col , Smith, C. Douglas , Powell, Bernard
- Date: 2011
- Type: Text , Journal article
- Relation: Chemical Geology Vol. 280, no. 3-4 (2011), p. 257-270
- Full Text: false
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- Description: Tidal inundation is a new technique for remediating coastal acid sulfate soils (CASS). Here, we examine the effects of this technique on the geochemical zonation and cycling of Fe across a tidally inundated CASS toposequence, by investigating toposequence hydrology, in situ porewater geochemistry, solid-phase Fe fractions and Fe mineralogy. Interactions between topography and tides exerted a fundamental hydrological control on the geochemical zonation, redistribution and subsequent mineralogical transformations of Fe within the landscape. Reductive dissolution of Fe(III) minerals, including jarosite (KFe3(SO4)2(OH)6), resulted in elevated concentrations of porewater Fe2+ (>30mmol L-1) in former sulfuric horizons in the upper-intertidal zone. Tidal forcing generated oscillating hydraulic gradients, driving upward advection of this Fe2+-enriched porewater along the intertidal slope. Subsequent oxidation of Fe2+ led to substantial accumulation of reactive Fe(III) fractions (up to 8000μmol g-1) in redox-interfacial, tidal zone sediments. These Fe(III)-precipitates were poorly crystalline and displayed a distinct mineralisation sequence related to tidal zonation. Schwertmannite (Fe8O8(OH)6SO4) was the dominant Fe mineral phase in the upper-intertidal zone at mainly low pH (3-4). This was followed by increasing lepidocrocite (γ-FeOOH) and goethite (α-FeOOH) at circumneutral pH within lower-intertidal and subtidal zones. Relationships were evident between Fe fractions and topography. There was increasing precipitation of Fe-sulfide minerals and non-sulfidic solid-phase Fe(II) in the lower intertidal and subtidal zones. Precipitation of Fe-sulfide minerals was spatially co-incident with decreases in porewater Fe2+. A conceptual model is presented to explain the observed landscape-scale patterns of Fe mineralisation and hydro-geochemical zonation. This study provides valuable insights into the hydro-geochemical processes caused by saline tidal inundation of low lying CASS landscapes, regardless of whether inundation is an intentional strategy or due to sea-level rise. © 2010 Elsevier B.V.
Metal partitioning dynamics during the oxidation and acidification of sulfidic soil
- Authors: Claff, Salirian , Burton, Edward , Sullivan, Leigh , Bush, Richard
- Date: 2011
- Type: Text , Journal article
- Relation: Chemical Geology Vol. 286, no. 3-4 (2011), p. 146-157
- Full Text: false
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- Description: The oxidation and acidification of sulfidic soil can lead to changes to metal mobility that can have far-reaching environmental consequences. In this study, we examined changes in the partitioning and mobility of Fe, Cr, Cu, Mn, Ni and Zn in four sulfidic soils, due to sulphide oxidation driven acidification, over a 90. day period. These changes were examined using a novel six-step sequential extraction procedure specifically developed for acid sulphate soil materials. The results demonstrate two distinct steps for the mobilisation of metals in disturbed acid sulphate soil materials, associated with (i) oxidation and (ii) acidification. Initially, oxidation causes metals to be redistributed from the "pyritic" and "organic" fractions to the "acid-soluble" fraction. Subsequent acidification, due to exceedance of the acid neutralising capacity of the soil, drives the release of metals to the "labile" fraction. This study demonstrates the importance of these metal pools in understanding the short-term processes which mobilise metals in sulfidic soils. © 2011 Elsevier B.V.
Sulfur biogeochemical cycling and novel Fe-S mineralization pathways in a tidally re-flooded wetland
- Authors: Burton, Edward , Bush, Richard , Johnston, Scott , Sullivan, Leigh , Keene, Annabelle
- Date: 2011
- Type: Text , Journal article
- Relation: Geochimica et Cosmochimica Acta Vol. 75, no. 12 (2011), p. 3434-3451
- Full Text: false
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- Description: Sulfur biogeochemical cycling and associated Fe-S mineralization processes exert a major influence over acidity dynamics, electron flow and contaminant mobility in wetlands, benthic sediments and groundwater systems. While S biogeochemical cycling has been studied intensively in many environmental settings, relatively little direct information exists on S cycling in formerly drained wetlands that have been remediated via tidal re-flooding. This study focuses on a tidal wetland that was drained in the 1970s (causing severe soil and water acidification), and subsequently remediated by controlled re-flooding in 2002. We examine SO42- reduction rates and Fe-S mineralization at the tidal fringe, 7years after the commencement of re-flooding. The initial drainage of the wetland examined here caused in-situ pyrite (FeS2) oxidation, resulting in the drained soil layers being highly acidic and rich in SO42--bearing Fe(III) minerals, including jarosite (KFe3(SO4)2(OH)6). Tidal re-flooding has neutralized much of the previous acidity, with the pore-water pH now mostly spanning pH 5-7. The fastest rates of in-situ SO42- reduction (up to ~300nmolcm-3day-1) occur within the inter-tidal zone in the near-surface soil layers (to ~60cm below ground surface). The SO42- reduction rates correlate with pore-water dissolved organic C concentrations, thereby suggesting that electron donor supply was the predominant rate determining factor. Elemental S was a major short-term product of SO42- reduction, comprising up to 69% of reduced inorganic S in the near-surface soil layers. This enrichment in elemental S can be partly attributed to interactions between biogenic H2S and jarosite - a process that also contributed to enrichment in pore-water Fe2+ (up to 55mM) and SO42- (up to 50mM). The iron sulfide thiospinel, greigite (Fe3S4), was abundant in near-surface soil layers within the inter- to sub-tidal zone where tidal water level fluctuations created oscillatory redox conditions. There was evidence for relatively rapid pyrite re-formation within the re-flooded soil layers. However, the results indicate that pyrite re-formation has occurred mainly in the lower formerly drained soil layers, whereas the accumulation of elemental S and greigite has been confined towards the soil surface. The discovery that pyrite formation was spatially decoupled from that of elemental S and greigite challenges the concept that greigite is an essential precursor required for sedimentary pyrite formation. In fact, the results suggest that greigite and pyrite may represent distinct end-points of divergent Fe-S mineralization pathways. Overall, this study highlights novel aspects of Fe-S mineralization within tidal wetlands that have been drained and re-flooded, in contrast to normal, undisturbed tidal wetlands. As such, the long-term biogeochemical trajectory of drained and acidified wetlands that are remediated by tidal re-flooding cannot be predicted from the well-studied behaviour of normal tidal wetlands. © 2011 Elsevier Ltd.
Schwertmannite transformation to goethite via the Fe(II) pathway : Reaction rates and implications for iron-sulfide formation
- Authors: Burton, Edward , Bush, Richard , Sullivan, Leigh , Mitchell, David
- Date: 2008
- Type: Text , Journal article
- Relation: Geochimica et Cosmochimica Acta Vol. 72, no. 18 (2008), p. 4551-4564
- Full Text: false
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- Description: Schwertmannite (Fe8O8(OH)6SO4) is a common Fe(III)-oxyhydroxysulfate mineral in acid-sulfate systems, where its formation and fate strongly influence water quality. The present study examines transformation of schwertmannite to goethite (FeOOH), as catalyzed by interactions with Fe(II) in anoxic aquatic environments. This study also evaluates the role of the Fe(II) pathway in influencing the formation of iron-sulfide minerals in such environments. At pH > 5, the rates of Fe(II)-catalyzed schwertmannite transformation were several orders of magnitude faster than transformation in the absence of Fe(II). Complete transformation of schwertmannite occurred within only 3-5 h at pH > 6 and Fe(II)(aq) ≥ 5 mmol L-1. Model calculations indicate that the Fe(II)-catalyzed transformation of schwertmannite to goethite greatly decreases the reactivity of the Fe(III) pool, thereby favoring SO4-reduction and facilitating the formation of iron-sulfide minerals (particularly mackinawite, tetragonal FeS). Examination of in situ sediment geochemistry in an acid-sulfate system revealed that the rapid Fe(II)-catalyzed transformation was consistent with an abrupt shift from an acidic Fe(III)-reducing regime with abundant schwertmannite near the sediment surface, to a near-neutral mackinawite-forming regime where goethite was dominant. This study demonstrates that the Fe(II) pathway exerts a major influence on schwertmannite transformation and iron-sulfide formation in anoxic acid-sulfate systems. These findings have important implications for understanding acidity dynamics and trace element mobility in such systems. © 2008 Elsevier Ltd. All rights reserved.