Petrophysical Rock Types - a Building Block For the Tengiz Field

Mark Skalinski¹, Steve Jenkins², Bruce Caplan³, Travis Billiter¹, and Jeroen Kente^4
1TengizChevroil, Atyrau, Kazakhstan
²CABGOC, Luanda, Angola
³Chevron ETC, San Ramon, CA
⁴Chevron Energy Technology Company, Voorburg, Netherlands

Carbonate facies definitions are a critical control on the distribution of reservoir properties. Recent work to define reservoir rock types at Tengiz Field in Kazakhstan, have lead to improved characterization of key properties (porosity, permeability and water saturation). The new rock types defined from petrophysical data are the basis for the in-place oil volume and more reliable oil recovery estimates.
Tengiz is an isolated carbonate buildup. The distribution of rock types in the platform is determined by diagenetic modification of an earlier reservoir system that included meteoric alteration and porosity enhancement . Upper slope microbial boundstone represents the dominant source for the middle and lower slope breccias. Periodic failure of the rim resulted in a high degree of lateral facies discontinuity and during late diagenesis formed a high-permeability, well-connected reservoir. This diagenetic overprint is often associated with the presence of bitumen.
New petrophysical rock types (PRT) represents a step improvement over depositional facies used in previous model generations. Petrophysical rock types were defined for Volcanic, Bitumen Rich, Tight/Cemented, and reservoir facies of varying quality. Key logs for the definition of these facies include Spectral Gamma, Multimin-derived bitumen volume and porosity, and T2 distribution from CMR log.
Petrophysical Rock Types were distributed using the Multi Point Statistics (MPS) and SGS. They have lead to improved distribution of porosity and oil volume in reservoir model and resulted in significant redistribution of oil between platform and flank. The history matching process shows that they allow better control of the permeability distribution.

AAPG Search and Discovery Article #90072 © 2007 AAPG and AAPG European Region Conference, Athens, Greece