Seismic Facies Analysis of Lower Productive Series of Gurgan-Deniz Field in South Caspian Basin with the Aid of Seismic Attributes

Abstract

Abstract Drilled for the first time in 1946 and one of the oldest fields in the South Caspian Basin located in the western part of Apsheron sill, Gurgan-Deniz has been subject to redevelopment. A 3D seismic survey, conducted over the area for the first time, has been interpreted, analysing the lower Productive Series with regard to seismic facies and prospectivity. The facies analysis allows for better understanding of eustatic levels in the region and depositional environments of lower Productive Series in the area. A composite seismic attribute Sweetness and an RGB blend of Spectral Decomposition have been applied to the 3D volume, as well as to the interpreted stratigraphic surfaces. With the aid of the attributes and petrophysical well description, direct and indirect facies interpretation have been carried out. First, considering reflection parameters such as parallelism, continuity and hummockiness, as well as sedimentary features. Subsequently, reaching conclusions on depositional processes, environments, and geological evolution. Finally, analysing field prospectivity and migration pathways. Eight seismic facies have been identified by analysing stratigraphic horizons representing the tops of Kalin Suite (KaS), Pre-Kirmaky Sand Suite (PK) and Kirmaky Suite (KS). Facies have been interpreted as mass-flow deposits, amalgamated channel systems, channel and bar systems, sheetflow and floodplain deposits in a varying lacustrine-fluvial environment. KaS has been deposited following a sea- level drop and increased sediment inflow from Palaeo-Volga. The origin of the mass-flow facies is thought to be related to the increase of sedimentation speed, as well as tectonics decreasing the terrace stability. PK shows evidence of further sea-level drop and shows mainly fluvial depositional environment. Starting from KS, sea level has started to rise, once again showing mixed depositional environment. Attribute anomalies have been explored in the lower wing of the anticline structure in PK and KaS. A 3-way trap and possible migration pathways generate considerable risks.