--> Abstract: Carbonate Pore Type Classification in Tengiz Field, Republic of Kazakhstan, by J. Kenter and M. Skalinski; #90090 (2009).

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Carbonate Pore Type Classification in Tengiz Field, Republic of Kazakhstan

Kenter, Jeroen 1; Skalinski, Mark 2
1 Chevron ETC, San Ramon, CA.
2 TengizChevroil, Atyrau, Kazakhstan.

Carbonate reservoirs are characterized by a highly heterogeneous and variable pore network which exerts a significant impact on reservoir performance. Recent work to define Petrophysical Rock Types (PRT) and pore types has led to improved characterization of pore geometry and distribution of key properties in Tengiz Field, one of the world’s deepest supergiant fields.

Carbonate rock typing and pore type identification are a critical control on the distribution of reservoir properties. Tengiz is an isolated Paleozoic carbonate build-up in the Pricaspian Basin, Republic of Kazakhstan, and is considered a super giant carbonate reservoir. The distribution of PRTs and associated pore types in the platform is determined by the diagenetic modification of an earlier reservoir system that included late burial diagenesis increasing porosity by dissolution in the center of the platform and reduced porosity through compaction, calcite cementation and pyrobitumen cementation towards the margins. Upper slope microbial boundstone represents the dominant source for the middle and lower slope breccias. The diagenetic overprint is often associated with the presence of bitumen emplacement.

Pore type classification schemes proposed in the literature were initially based on textural properties only and later expanded using a simpler pore type system and pore-perm relationships . This paper proposes a pore type classification based on pore throat distributions and pore scale. This classification includes nano-porosity, micro-porosity, meso-porosity, macro-porosity, isolated and connected vugs. Modified Winland equations were developed for carbonate Tengiz field to allow prediction of pore types from logs. Classification of pore types and their prediction algorithms are based on an extensive data set of 550 mercury injection pressures at Tengiz. These MICP data were integrated with petrographic observations, SEM and CT-microscanner analyses to understand the link between pore types, rock fabric and diagenetic processes.

The Tengiz classification is scale-driven and has a direct impact on permeability and flow performance.

The resulting pore type classification scheme was combined with PRTs in the latest reservoir simulation to better distribute porosity, oil and define the permeability field. This has resulted in a significantly improved History Match, improved delineation of reservoir heterogeneity and OOIP.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009