Variational gridding approach to the lithological modeling of clinoform-type deposits

About the author:

Andrei A. Sidorov, Cand. Sci. (Phys.-Math.), Head of Department of the Mathematical Modeling of Geological Objects, V. I. Shpilman Research and Analytical Centre for the Rational Use of the Subsoil, Tyumen, Russia; darth@crru.ru, https://orcid.org/0000-0002-8639-2644

Abstract:

With the depletion of large oilfields, prospects are associated with non-structural deposits, bounded by impermeable mudstone layers. Reservoir of this type is typical for the Achimov deposits of the West Siberian Neocomian complex, formed in a deep-sea marine conditions. The clinoform type horizons are characterized by nonconformal bedding, as well as a complex lithological structure caused by sea level fluctuations. These features limit the applying of interpolation and stochastic mapping methods for lithological modeling and make it relevant to develop approaches that take into account the physical principles of the sedimentation process.

The article proposes an approach that is often used in basin modeling, in which the sedimentation is presented as the result of a diffusion process. The problem of two-component turbulent diffusion with advection in a quasi-stationary formulation is considered. The diffusion coefficients, as well as the equation term responsible for sediment deposition, are functions of the sea depth. An explicit difference scheme is written for the thickness of accumulated deposits. A stationary diffusion equation is solved on each time layer using the variational gridding method for the concentration of each component.

As a test example, a map of the seabed surface was generated and one transgressive-regressive cycle was simulated. As a result, a typical clinocyclite was obtained. It contains sandstone layers on the shelf, a sandy-siltstone body on the seabed slope and a shale topset bed formed during the maximum flooding period.

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