Understanding Reservoir Quality in Ara Stringers (South Oman Salt Basin): Diagenetic Relationships in Space and Time

Becker, Simon; Reuning, Lars; Kukla, Peter A.; Abe, Steffen; Shi-yuan, LI; Urai, János; Farqani, S.; Rawahi, Zuwena

doi:10.3997/2214-4609-pdb.248.351

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“…Average maximum burial temperatures of 128 + 12°C (1s, n = 30) were calculated from the bitumen reflectance, which fit well with basin modeling results for the study area (Table 1; Figure 10; [34]). Most samples show maximum Figure 10).…”

Section: Resultssupporting

confidence: 68%

“…The maximum burial temperature (T peak burial ) was calculated from the VRr using the equation of Barker & Pawlewicz [33]. For further details on the applied methods, see Becker et al [34].…”

Section: Methodsmentioning

confidence: 99%

“…Salt tectonic deformat. Figure 13: Summary of diagenetic processes and burial graph for the A2C reservoir (modified from [34]). Numbers refer to important steps in the diagenetic history of the Ara carbonate stringer.…”

Section: Diagenetic Zonementioning

confidence: 99%

“…Finite element models (FEM) indicate that only 50-100 m differential load is needed to form fractures within the stringers (Figure 13; [8]). Anhydrite-cemented veins formed predominantly around the minibasin in the center of the study area [34]. These veins often postdate bedding parallel stylolites but are cross-cut by vertical stylolites that are interpreted to have formed during salt tectonic folding of the stringer (Figure 13).…”

Section: Geofluidsmentioning

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: Resultssupporting

confidence: 68%

Section: Methodsmentioning

confidence: 99%

Section: Diagenetic Zonementioning

confidence: 99%

Section: Geofluidsmentioning

confidence: 99%

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