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    The creation of calcite microcrystals and microporosity through deep burial basinal flow processes driven by plate margin obduction – A realistic model?

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    Type
    Article
    Authors
    Wei, Wenwen cc
    Whitaker, Fiona cc
    Hoteit, Hussein cc
    Vahrenkamp, Volker cc
    KAUST Department
    Physical Science and Engineering (PSE) Division
    Energy Resources and Petroleum Engineering Program
    Ali I. Al-Naimi Petroleum Engineering Research Center (ANPERC)
    KAUST Grant Number
    ORS #4174
    Date
    2021-11-15
    Embargo End Date
    2023-11-15
    Submitted Date
    2021-03-04
    Permanent link to this record
    http://hdl.handle.net/10754/673764
    
    Metadata
    Show full item record
    Abstract
    Calcite microcrystals and associated microporosity are ubiquitous and extensively developed in Jurassic and Cretaceous carbonate sequences in the Middle East. Clumped isotope analyses of calcite microcrystals in the Lower Cretaceous Thamama-B strata in UAE reservoirs indicate temperatures of 60–90 °C and burial of 1.5–2.5 km suggesting formation synchronous with and updip of Late Cretaceous ophiolite obduction at the Eastern Arabian continental margin. Assuming that recrystallization of precursor calcite to calcite microcrystals requires initially undersaturation to drive dissolution/re-precipitation a basin-scale 2D reactive transport model (RTM) was constructed. The model is constrained by hydro-mechanical simulations and used to quantitatively evaluate the hypothesis that the formation of calcite microcrystals and associated microporosity is driven by expulsion of compaction fluids during rapid burial. The combined influence of fluid flux and cooling results in trace net calcite dissolution (porosity increase <0.1 vol %) focused at depths of 2.7–5.1 km. The presence of even minor amounts of minerals with common ions (dolomite and anhydrite) induces additional dissolution but does not change its’ spatial distribution. Whilst RTMs only yield a minimum estimate of the degree of recrystallization that likely occurs driven by calcite disequilibrium, simulations suggest these reactions occur at temperatures of 95–170 °C, markedly higher than those estimated from clumped isotopes of the calcite microcrystals. Mixing of fluids leaked from underlying strata up faults into the lateral flow system could play an important role in burial diagenesis, with the slow leakage dissolving up to ten times greater mass of calcite than a shorter pulse of equivalent fluid volume. A previously unrecognized effect of the introduction of H2S(aq)-rich fluids, derived from accelerated thermal maturation or thermochemical sulphate reduction (TSR), into formation water with high CO2(aq) concentration is CO2 degassing that drives net calcite precipitation (<3 vol %). This suite of numerical simulations suggest that calcite disequilibrium will have occurred in fluids expelled during ophiolite obduction, but that any associated recrystallization will have occurred at depths greater than those inferred from temperatures measured in the calcite microcrystals. Recrystallization at shallower depths may have been associated by fluid-mixing around the injection points, but reaction kinetics suggests that laterally pervasive alteration would require very rapid flow rates. These results suggest that alternative mechanism(s) are needed to be considered to explain the extensively developed calcite microcrystals and associated microporosity in Mesozoic carbonates of the Middle East.
    Citation
    Wei, W., Whitaker, F., Hoteit, H., & Vahrenkamp, V. (2021). The creation of calcite microcrystals and microporosity through deep burial basinal flow processes driven by plate margin obduction – A realistic model? Marine and Petroleum Geology, 105432. doi:10.1016/j.marpetgeo.2021.105432
    Sponsors
    We would like to thank Maxim Yutkin, KAUST, for many discussions during this work. This work was supported by a KAUST funded Collaborative Research Project (reference ORS #4174) and KAUST baseline research funding to V. Vahrenkamp and H. Hoteit. The suggestions of two reviewers helped improved the final manuscript and we are particularly grateful for thoughtful input from David Budd. We also thank CMG Ltd. for providing the academic license for CMG-GEM simulator used for the hydro-mechanical model.
    Publisher
    Elsevier BV
    Journal
    Marine and Petroleum Geology
    DOI
    10.1016/j.marpetgeo.2021.105432
    Additional Links
    https://linkinghub.elsevier.com/retrieve/pii/S0264817221005353
    ae974a485f413a2113503eed53cd6c53
    10.1016/j.marpetgeo.2021.105432
    Scopus Count
    Collections
    Articles; Energy Resources and Petroleum Engineering Program; Ali I. Al-Naimi Petroleum Engineering Research Center (ANPERC); Physical Science and Engineering (PSE) Division

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