Seismic-driven geocellular modeling of fluvial meander-belt reservoirs using a rule-based method

Abstract

A novel workflow is presented for building static models of fluvial reservoirs composed of large point-bar architectural elements, based on the application of a specialized forward stratigraphic model, named ‘Point-Bar Sedimentary Architecture Numerical Deduction’ (PB-SAND). The approach uses interpreted horizontal slices from 3D seismic datasets to reconstruct the planform evolution of meander loops, on which basis the geometry of point-bar deposits and associated accretion units can be simulated deterministically. The resulting meander-belt geometry is then populated with different types of facies, through a rule-based algorithm that generates facies architectures that reflect geologic understanding, enabling users to establish linkages between styles of meander evolution (e.g., meander growth via expansion, translation, rotation) and facies distributions. Input parameters define the proportions, geometries and distributions of types of point-bar deposits, as captured from subsurface data and/or from geologic analogs. Multiple stochastic realizations of facies architecture can be generated. To demonstrate the application of this modeling approach, the workflow has been applied to a meander-belt reservoir where large point-bar and channel-fill elements are imaged in seismic. A detailed example is used to illustrate workflows that can be used to build high-resolution sector models in pre-drill contexts, suitable for guiding development plans. An additional example is used to show how to achieve well match for densely drilled sectors, by means of a hybrid approach that combines the new algorithm with traditional geostatistical techniques. It is shown how the workflow allows consideration of point-bar growth styles, as inferred from seismic data, on distribution and geometry of heterogeneities, and how this facilitates the reproduction of geologic features that are important controls on the static connectivity of point-bar reservoirs (e.g., distribution and characteristics of bar-front mud drapes, and of mud-prone packages arising from progressive meander-bend tightening or from downstream fining of deposits beyond the apex of a meander bend). A comparison with traditional variogram-based methods is undertaken to compare metrics that describe intra-point-bar static connectivity and that represent proxies for the degree of compartmentalization of upper-bar sands by mud drapes.