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Bed-Scale Modeling of Deep-Water Architectural-Elements: What Heterogeneities Matter to Flow?


Bed-Scale Modeling of Deep-Water Architectural-Elements: What Heterogeneities Matter to Flow?

Daniel Bell1, Anna S. M. Pontén2, Ian A. Kane1, Krishnakumar Nair2, Arnau Obradors Latre2, Camilla Thrana2, and David M. Hodgson3

1SedResQ, School of Earth and Environmental Sciences, University of Manchester, Manchester, M13 9PL, U.K.

2Equinor Research Center, 7053 Ranheim, Trondheim, Norway

3Stratigraphy Group, School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, U.K.

The organization of architectural elements that govern the volume and connectivity at the grid-cell scale, and textural properties of deep-water systems that control porosity and permeability at the core-plug scale, is well-recognized. However, modeling studies which address the intermediate bed-scale heterogeneities, and their influence on fluid flow at larger scales, are limited. Lobe 6 of Fan 3, Tanqua Basin, South Africa, is well-constrained spatially allowing confident interpretation of lobe sub-environments. This permits study of the spatial variability of bed-scale heterogeneity within sub-environments of an individual architectural element. Fifty-nine logged sections were modelled using SBEDTM, individually realized three times, and populated with reservoir rock-property data from the subsurface X Formation, North Sea. SBEDTM was used to upscale horizontal permeability (Kh) derived from core-plug measurements to vertical permeability (Kv) at bed- and architectural element-scale to determine which heterogeneities influence fluid flow. Results reveal that: 1) increasing siltstone thickness causes an exponential decrease in Kv, and a 2cm thick siltstone can reduce Kv by 50%; 2) mudstone clast density exerts a logarithmic decrease in Kv, and a 1% density of clasts can reduce Kv by 10%; 3) lobe axis and distal lobe finger positions exhibit the best upscaled Kv, whereas the lateral fringe has the poorest upscaled Kv; and 4) off-axis and distal fringe positions exhibit similar upscaled Kv, implying that low density turbidites and hybrid beds exert similar controls on Kv. The implications are: i) bed-and lamina-scale heterogeneities can exert a strong control at architectural element scale; ii) vertical permeability varies strongly spatially within lobes; iii) good reservoir quality sands can extend into the distal lobe fringe, enabling migration pathways kilometers away from the lobe axis. This challenges the characterization of distal lobe fringes as dominated by poor reservoir quality sands due to hybrid bed development.