Geological and geophysical characteristics of the southeastern border of the Pre-Caspian Basin (Onshore Kazakhstan): Analysis and petroleum exploration implications

Abstract

The Pre-Caspian Basin is located in western Kazakhstan north of the Caspian Sea, and extends into Russia. It was filled by a thick sedimentary column up to 20 km in the centre and 5 km in the basin margins. The sedimentary section in the Pre-Caspian Basin is effectively composed of two independent sequences, the Post-Salt (Upper Permian-Tertiary) and the Pre-Salt (Lower Permian-Devonian) separated by the Kungurian evaporites (Lower Permian). New seismic acquisiton and the reprocessing of older seimic, renewed interest in the hydro-carbon potential of the thick Upper Permian (Kazanian)-Triassic deposits during the mid 1990's. The main purpose of this article is to show how integrated and multidisciplinary methodology has led to improved play analysis and prospect evaluation. We show results from the integrated study of the carbonate platform (Lower Carboniferous-Lower Permian) and the stratigraphy and petroleum implications of the Kazanian (Upper Pemian)-Triassic deposits.Salt tectonic and syndeposition during the Upper Permian (Kazanian) to the Triassic pro-vided a wide range of potential petroleum traps; related to either salt features or minibasins. 2D Seismic data permits definition of structural closure while special studies, such as PDSM and gravity modelling, have helped constrain the exploration risk by defining pre-isalt highs that could focus hydrocarbon migration. Regarding the petroleum system, the reservoir presents appropriate porosity and permeability values and the source rock has proven generation in the surrounding areas. In. addition the number and shallowness (1500-2500 m) of the Upper Permian-Triassic prospects favours the project economics. The principal risks are related with uncertainties that will need special studies. The 2D seismic data do not allow defining reservoir (type of fluvial-deltaic? system), seal extension, effectiveness of salt welds, and the filling of structures.