Multiscale Characterization of a Microbialite-Rich Lacustrine Reservoir of the Green River Formation (Eocene, U.S.A.)

Abstract

Subsalt reservoirs are difficult to image, both in terms of physical properties, geophysical signature and facies distributions. Reservoir outcrop analogues are commonly used to characterize reservoir architectures. Outcrop analogues play a key role in improving our understanding of subsurface subsalt reservoir architectures, and provide valuable information to better understand and constrain reservoir architectures and facies heterogeneity distribution at field scale.Sedimentology and geophysical approaches make possible to assess the physical reservoir properties and to evaluate the parameters required to build accurate reservoir models. However, the occurrence of heterogeneity at many nested scales makes the definition of upscaling rules very challenging to obtain a relevant reservoir model.

The La Clede Beds of the Laney Member correspond to marginal lacustrine carbonates, and are considered as one of the most valuable analogue of the South Atlantic carbonates outcropping system. It includes a large variety of facies such as insect-microbial build-ups, tufas, coquinas, skeletal and oolithic grainstones, and silty marls. In terms of architecture, this interval is organized in patches of reef-like morphologies made up of insect microbial build-ups, with intercalated breccia and shales.

The internal architecture of the microbialite build-ups is really complex, with various nested scales of heterogeneities. To better characterize this complexity, we designed an integrated workflow based on the integration of sedimentological, geophysical and petrophysical data at different scales (decametric field scale, metric log scale and centimetric plug scale). A field survey permitted to describe sedimentological logs along which Gamma-ray and sonic (P-wave and S-wave) logs were measured, as well as refraction-seismic to provide P-wave and S-wave velocities along 1D and 2D profiles. The multiscale dataset was completed with petrophysical measurements (porosity and permeability) and ultrasonic velocities on samples collected along the sedimentological sections.

Finally, this complete dataset acquired on the field permitted rely subsurface and outcrop scale to the reservoir scale taking into account the different scales of heterogeneities. This workflow based on exhaustive geophysical and sedimentological data and on an integrated interpretation is a powerful tool to understand seismic and log issues at the reservoir scale in subsurface, in such geological complex.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018