Characterization and Controls on Slope Geometry, Framework and Internal Heterogeneity in the Unit 1 Tengiz Field (Kazakhstan), and Comparison with Outcrop Analogs
Tengiz Field is an isolated carbonate platform in the Precaspian Basin, Kazakhstan, of late Famennian to Bashkirian age. Tengiz Unit 1 (late Visean to Bashkirian) is the main producing reservoir unit. The margin/slope region (dominated by non-matrix fractures and cavernous porosity) is a primary target for future development, however considerable uncertainty in geological heterogeneity still exists.
The margin/slope forms a discontinuous late Visean to Serpukhovian-aged progradational wedge that filled approximately 800 m of bathymetric relief above the Famennian platform edge created by Tournaisian through late Visean platform aggradation and backstepping. Margin/slope facies were identified in core and from FMI logs, and include (from distal to proximal slope environments) mudstone, volcanic ash, platform-derived grainstone, coarse skeletal rudstone with boundstone clasts, massive boundstone breccia, and in-situ microbial boundstone ranging from upper slope to outer platform settings. These facies partly control non-matrix porosity distribution in the margin/slope as well as connectivity with the adjacent platform reservoirs. Their spatial distribution and proportions are inferred from well data and outcrop analog concepts. Key elements for geological characterization are syn-depositional “retrogradational” escarpments, multiple scales of mechanical failure, allochtonous breccia wedges, high strike variability, syn-depositional fracturing, early (meteoric) and burial karst systems, and discontinuous platform to slope transitions.
The integration of concepts from outcrop analogs,
well data and observations from the new seismic dataset form the basis for the
characterization of heterogeneity in the margin/slope region. Resulting
end-member models better represent the uncertainty in the distribution of
reservoir quality in geostatistical models that are critical for future
development and production.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California