Investigation of Multiscale Heterogeneities of Microbialite Reservoirs Using Forward Modeling: A Modern Analog From Shark Bay, Western Australia

Abstract

Paleozoic or older microbialite has recently been identified as an important carbonate play worldwide. The microbialite reservoirs are extremely heterogeneous over a range of scales, presenting a greater challenge to petroleum exploration and development. The renowned Hamelin Pool stromatolites (microbialite), located in Shark Bay, Western Australia, provide a unique modern analog to understand the evolution of stromatolites and their reservoir properties at different scales.

Stratigraphic forward modelling was utilized to mimic the growth of stromatolites over the past 1500 years at individual colony scales (cm), multiple colonies and then upscaling to the reservoir scale (10s of m). We constructed three models with horizontal resolutions of 2 cm over an area of 1 m by 1 m, 4 cm over an area of 2 m by 2 m and 50 m over an area of 2.5 Km by 2.5 Km, respectively. The environmental conditions used in the simulation have been taken from the literature.

The multiscale models suggest that (i) at the scale of single stromatolite with cm resolution, the growth of stromatolites are mainly controlled by temperature and salinity variations, sea-level fluctuations, siliciclastic supply and directional wave action, with the water level oscillation appearing to have a significant control on the growth rate of stromatolites; (ii) at the scale of multiple colonies with a resolution of meters, the growth rate of stromatolites with different initial topography seems to be varying greatly within the same period, and the porosity of the individual stromatolites is higher than that in-between stromatolites; (iii) at reservoir scale, the microbialite growth spacing often depends on the changes of sea level, and is characterized by lateral migration, with stromatolites growth rates being similar at the same water depth; (iv) the original porosity and permeability appear to be well correlated to the growth rate of the microbialite in the vertical direction. In the horizontal direction, the permeability of the principal axis is primarily influenced by the wave direction.

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