Micro- and nano-pores in intrasalt, microbialite-dominated carbonate reservoirs, Ara Group, South-Oman salt basin

Smodej, Jörg; Reuning, Lars; Becker, Simon; Kukla, Peter A.

doi:10.1016/j.marpetgeo.2019.03.036

Cited by 9 publications

(7 citation statements)

References 38 publications

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“…13 Geofluids presence of a geothermal gradient during burial [57]. Recrystallization and chemical compaction affected the calcite matrix to a larger extent compared to the dolomite matrix leading to a near complete porosity reduction in limestone due to the formation of an anhedral crystal mosaic [26]. This is supported by clumped isotope measurements for the studied stringer indicating a mean recrystallization temperature of~90°C, with somewhat higher temperatures for calcite than for dolomite for the complete Ara Group [57].…”

Section: Diagenetic Processes and Fluid Composition Duringmentioning

confidence: 85%

“…Mettraux et al [36,37] describe microbial fossils from calcitic and dolomitic Ara Group carbonates exposed in a salt dome in central Oman and argue that the fine crystalline matrix dolomite is of primary, microbial origin. The dolomitic matrix in the studied reservoirs is also very fine crystalline and preserves high microporosity [26].…”

Section: Diagenetic Processes and Fluidmentioning

confidence: 94%

“…Generally, shallow-water grainstones, thrombolites, and peritidal facies are characterized by relatively high primary porosity whereas deeper ramp and downslope mudstones show poor reservoir quality [15]. The preservation of depositional or very early diagenetic microcrystalline dolomites in microbialite facies leads to generally high intercrystalline microporosities [26]. Due to a combination of depositional and diagenetic factors, the crinkly laminites from the deeper ramp form a major reservoir facies in the A4C interval [25] but are characterized by strongly reduced porosities in other intervals [15].…”

Section: Geological Settingmentioning

confidence: 99%

“…Composition in the Near-Surface Diagenetic Realm. Carbonate facies of the Ara Group are thought to be microbially influenced, except for some packstones to grainstones [15,26]. Mettraux et al [36,37] describe microbial fossils from calcitic and dolomitic Ara Group carbonates exposed in a salt dome in central Oman and argue that the fine crystalline matrix dolomite is of primary, microbial origin.…”

Section: Diagenetic Processes and Fluidmentioning

confidence: 99%

“…The fact that clastic-textured grainstone-packstones are almost invariably dolomitized [15] indicates that dolomitization is not restricted to microbial facies. However, microbially mediated dolomite precipitation might have occurred in the microbial-influenced facies [26] and could have acted as seeds for later reflux-related dolomitization [38].…”

Section: Diagenetic Processes and Fluidmentioning

confidence: 99%

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Diagenetic Processes and Reservoir Heterogeneity in Salt-Encased Microbial Carbonate Reservoirs (Late Neoproterozoic, Oman)

et al. 2019

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A common problem in dolomite reservoirs is the heterogeneous distribution of porosity-reducing diagenetic phases. The intrasalt carbonates of the Ediacaran-Early Cambrian Ara Group in the South Oman Salt Basin represent a self-sourcing petroleum system. Depositional facies and carbonate/evaporite platform architecture are well understood, but original reservoir properties have been modified by diagenesis. Some of the carbonate reservoirs failed to produce hydrocarbons at acceptable rates, which triggered this study. The extent of primary porosity reduction by diagenetic phases was quantified using point counting. To visualize the distribution of diagenetic phases on a field scale, we constructed 2D interpolation diagenesis maps to identify patterns in cementation. The relative timing of diagenetic events was constrained based on thin-section observations and stable isotope analyses. Near-surface diagenesis is dominated by reflux-related processes, leading to porosity inversion in initial highly porous facies and a patchy distribution of early cements. This strong diagenetic overprint of primary and early diagenetic porosity by reflux-related cements leads to a reduction of stratigraphic and facies control on porosity. Calcite was identified as a burial-related cement phase that leads to an almost complete loss of intercrystalline porosity and permeability. Bitumen is an important pore-occluding phase and time marker of the deep-burial realm. The stratigraphic position of the dolomite reservoirs embedded at the base of a salt diapir had a strong impact on its diagenetic development. The salt isolated the dolomites from external fluids, leading to a closed system diagenesis and the buildup of near lithostatic fluid pressures. In combination, these processes decreased the impact of further burial diagenetic processes. The study highlights that cement distribution in salt-encased carbonate reservoirs is mainly related to early diagenetic processes but can be very heterogeneous on a field scale. Further work is needed to implement these heterogeneities in an integrated numerical reservoir model.

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Section: Diagenetic Processes and Fluid Composition Duringmentioning

confidence: 85%

Section: Diagenetic Processes and Fluidmentioning

confidence: 94%

Section: Geological Settingmentioning

confidence: 99%

Section: Diagenetic Processes and Fluidmentioning

confidence: 99%

Section: Diagenetic Processes and Fluidmentioning

confidence: 99%

See 3 more Smart Citations

Diagenetic Processes and Reservoir Heterogeneity in Salt-Encased Microbial Carbonate Reservoirs (Late Neoproterozoic, Oman)

et al. 2019

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Reservoir quality of Upper Cretaceous limestones (Ahlen-Fm., Beckum Member, Münsterland Cretaceous Basin): effects of cementation and compaction on the compactable depositional volume

Ölmez,

Busch,

Hilgers

2024

Int J Earth Sci (Geol Rundsch)

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The Upper Cretaceous limestones unconformably overlie Upper Carboniferous coal-bearing lithologies and are studied to assess their effect on rising mine-water levels in the Ruhr mining district. Upper Cretaceous sedimentary rocks from the Münsterland Cretaceous Basin have previously been studied regarding their sedimentary structures and fossil content. However, understanding the petrophysical and petrographic heterogeneity in regard to sedimentary properties and their effect on fluid migration pathways is yet missing. Utilizing He-pycnometry, Klinkenberg-corrected air permeabilities, p-wave velocities, transmitted and reflected light analyses, point-counting and cathodoluminescence, we assess the petrophysical, geomechanical and mineralogical properties. Porosity ranges from 1.0 to 18.7% and permeability ranges from < 0.0001 to 0.2 mD, while p-wave velocity ranges between 2089 and 5843 m/s. Mechanical compaction leads to grain rearrangement, deformation of calcispheres, foraminifera and ductile clay mineral laminae. Above and below clay laminae, compaction bands of deformed calcispheres develop. Early diagenetic mineral precipitation of ferroan calcite in inter- and intragranular pores reduces porosity and permeability and influences geomechanical properties. An underestimated aspect of limestone petrography is the relationship of the original primary compactable depositional volume and the influence of compaction, deformation and cementation during early and late diagenesis on reservoir properties. The detrital dominated limestones show an originally high compactable depositional volume (CDV). Overall, reservoir qualities are poor and indicate the sealing potential of the studied lithologies. The Upper Cretaceous (Campanian) limestones thus may act as a barrier for increasing mine-water levels from dismantled, post-mining subsurface hard coal mines in the region. Graphical abstract

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The multistage dissolution characteristics and their influence on mound–shoal complex reservoirs from the Sinian Dengying Formation, southeastern Sichuan Basin, China

Yan

et al. 2022

Marine and Petroleum Geology

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Micro- and nano-pores in intrasalt, microbialite-dominated carbonate reservoirs, Ara Group, South-Oman salt basin

Cited by 9 publications

References 38 publications

Diagenetic Processes and Reservoir Heterogeneity in Salt-Encased Microbial Carbonate Reservoirs (Late Neoproterozoic, Oman)

Diagenetic Processes and Reservoir Heterogeneity in Salt-Encased Microbial Carbonate Reservoirs (Late Neoproterozoic, Oman)

Reservoir quality of Upper Cretaceous limestones (Ahlen-Fm., Beckum Member, Münsterland Cretaceous Basin): effects of cementation and compaction on the compactable depositional volume

The multistage dissolution characteristics and their influence on mound–shoal complex reservoirs from the Sinian Dengying Formation, southeastern Sichuan Basin, China

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