--> ABSTRACT: New Challenges for Marine and Lacustrine Microbial Carbonate Reservoir Rocks, by Poli, Emmanuelle; Virgone, Aurélien; Pabian-Goyheneche, Cecile; #90135 (2011)

Datapages, Inc.Print this page

New Challenges for Marine and Lacustrine Microbial Carbonate Reservoir Rocks

Poli, Emmanuelle 1; Virgone, Aurélien 1; Pabian-Goyheneche, Cecile 1
(1)TOTAL SA, Pau, France.

Microbialites are microbial carbonate rocks deposited in marine or lacustrine environments, and resulting from activities of heterotrophic bacteria, cyanobacteria or eucaryotes. Their classification depends of their internal structures: stromatolites present a laminated fabric, thrombolites a clotted fabric, oncolites a concentric fabric and dendrolites a dendritic fabric.

They are known all over the world from the Proterozoic period (Mauritania) until present day (Shark bay) and can be found at water depth ranging from sub-aerial (tufas & travertines) down to thousands of meters. They commonly appear under harsh environmental conditions:

- Anoxic conditions : Mass extinction events are often associated with massive microbial increase (e.g. Permo-triassic boundary in the Khuff Formation or during early Aptian)

- Hypersalinity: Microbialites can develop in strong hypersaline waters (Mediterranean preceding salt deposits during the Messinian salinity crisis

- Association with volcanism: close competition between microbialite and volcanic facies (Limagne-France).

- Association with geothermalism: development on faults of « travertine / tufa » carbonates (Italy, Turkey)

The reservoir potentials of these microbial carbonates is proved either by reservoirs made up of a thick series of microbial carbonates or by alternating series presenting interbedding of microbial series such as in Arab or Khuff Fm in the Middle East.

In all the cases, the reservoirs are characterized by strong heterogeneities depending on growth morphologies (mainly function of accommodation space, hydrodynamics and sediment dynamics), primary or late diagenesis, geodynamic and structural context. In order to better characterized these heterogeneities some outcrop analogs are studied (as Green river Formation - Colorado & Utah)

Diagenesis plays a key role in enhancing or destroying reservoir properties and must be closely considered: the early cementation prevents extensive burial compaction in microbial bindstone facies whereas meteoric diagenesis creates dissolution of ooids in the grainstones increasing permeabilities up to 1.5 D.

The specific challenges of these microbial reservoirs are mainly focused on the vertical & lateral heterogeneities understanding from macroscale (depositional model) to microscale (Phi & K upscaling), on the recovery factor enhancement, on the possible concentration of associated acid gaz and constraints of deep burial reservoirs

 

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.