Sedimentological Characterization of the Surakhany Suite (Lower Pliocene Productive Series): Integration of Outcrop - Subsurface Data

Bagir Ibrahimov
bp Azerbaijan, Baku, Azerbaijan

The Surakhany suite represents the uppermost lithostratigraphic subdivision of the Lower Pliocene Productive Series (the main reservoir unit of South Caspian Basin). Reason why Surakhany is important in the oil development is not it's large hydrocarbon reservoirs (limited reservoir potential primarily onshore), but as an overburden interval which must be penetrated and as an interval where casing points are required to control the pressures seen in this section.
At outcrop (Lokbatan, 12km South of Baku) it is estimated to be approximately 500m thick - about the half of real thickness observed in Azeri-Chirag-Gyuneshli (ACG, 90km offshore East of Baku) field. Section comes thinner at outcrop because of erosion/weathering as well as poor consolidation and disruption by a number of small-scale faults.
Both at outcrop and in ACG examined formation is described as an argillaceous succession dominated by thick beds of varicolored claystones packages (at outcrop the desiccation cracks are frequently observed) with minor quantities of siltstones, fine-grained sandstones and very rare channelized sandstones / isolated channels (developed generally towards the base). Thin anhydrite layers occurred in the top of the section (rare centimeter thick at outcrop and laterally extensive, perfectly correlated by well logs & seismic within ACG) are very characteristic for this interval.
Deposition of Surakhany suite is considered to take place in both terrestrial and subaqueous environments during the period of coarse sediment starvation. Significant quantities of fine-grained material were delivered by fluvial distributaries (delta progradation into long-lived evaporate lakes) interrupted by cycles of exposure and desiccation.

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