Architecture Variability in the Pereriva and Balakhany Suites of the Neogene Productive Series, Azerbaijan: Implications for Reservoir Quality
D. J. Hinds, M. D. Simmons, M. B. Allen, E. Aliyeva, 2007. "Architecture Variability in the Pereriva and Balakhany Suites of the Neogene Productive Series, Azerbaijan: Implications for Reservoir Quality", Oil and Gas of the Greater Caspian Area, Pinar O. Yilmaz, Gary H. Isaksen
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The Pereriva and Balakhany suites of the mainly Pliocene Productive Series are the major reservoir units in the Azerbaijan sector of the South Caspian basin. Facies distribution throughout this succession is interpreted as representing an evolving fluvial system, from one of low sinuosity with highly amalgamated, relatively coarse-grained facies (Pereriva Suite) to one of increased sinuosity, with a lower degree of amalgamation, and relatively fine-grained facies (Balakhany Suite). Four models characterize the architecture and heterogeneity of these strata, with variations related to changing accommodation space/sediment supply (A/S) ratio. The lower 55 m (180 ft) of the Pereriva Suite represents the least heterogeneous part of the succession. Well-sorted, sheet sandstones are divided by the laterally continuous erosive horizons of alluvial degradational phases (low A/S ratio). Few permeability barriers to fluid flow exist. Qualitatively, this is the best part of the studied succession for reservoir properties. The upper 50 m (164 ft) of the Pereriva Suite is similar, but erosive lags form laterally discontinuous mud intraclast horizons. These horizons, and localized mudstone and siltstone facies, represent potential baffles and barriers to fluid flow. Most of the lower 70 m (229 ft) of the Balakhany Suite displays low heterogeneity, especially above and below a central interval of amalgamated erosion surfaces. The overlying 80 m (262 ft) of the Balakhany Suite represents the highest A/S ratio conditions of the studied succession. Reservoir heterogeneity is potentially created by contorted sandstones and by the preservation of the finer grained parts of channel fills. Laterally extensive mudstone and silt-stone horizons form potential barriers to fluid flow. Speculatively, the changes in architecture are controlled by climatic fluctuations on several scales, acting on a basin subject to increasing influence of the rising Greater Caucasus.
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Throughout time, the greater Caspian area has maintained its position as one of the major petroleum provinces in the world. Its early history as a prolific producer of oil is well known. Caspian region exploration dates to the seventh century B.C., during the time of the Median Kingdom in today's southern Azerbaijan. Oil played an important role in the everyday lives of these ancient tribes of the region, and it is still a very important commodity today. The past two decades have seen many important advances in our knowledge of the geological evolution of hydrocarbon-bearing sedimentary basins. The success of modern exploration is, to a large extent, based on new advances in both deep and 3-D seismic imaging, as well as improved pressure-prediction and pre-drill oil and gas quality predictive methodologies, to mention just a few. Nevertheless, large areas of the greater Caspian region have remained unexplored due to a variety of factors such as deep-water conditions and zones with high pore-pressures in the South Caspian Sea and The Black Sea, and vast shallow-water regions with harsh winter ice conditions in the North Caspian Sea. This publication contains 12 extended abstracts and 6 full-length papers that discuss technology development, challenges in estimating proven and potential reserves, outcrop-based studies of potential reservoirs, regional tectonics and geodynamic evolution, and source rock and stratigraphic analyses of the greater Caspian area.