DEEP KARST AREAS EVIDENCED BY SEISMIC RESEARCH IN MOESIAN PLATFORM

Abstract

Around half of the total carbonate rocks of Romanian territory are Upper Jurassic-Lower Cretaceous age. Most of them are able to develop karst phenomena. In the southern-central part of the Moesian Platform Jurassic-Cretaceous deposits are at 2000-3000 m depth. The existence of the hydrocarbon accumulations in the area was just proved (Talpa, Harlesti, Videle fields). In the calcareous deposits, the seismic profiles and the attributes of seismic traces highlighted some specific geological features: The collapse karst areas, formed in Jurassic-Neocomian deposits. The seismic expression of these areas is one of chaotic reflections zone flanked by converging, strong tilted faults. The paleo-valley systems formed by erosion of the Cretaceous relief, filled with different terms of the Lower Sarmatian (a succession of marls and sands). The reflections configuration is specific to the passing from the valley fill lithology to the Cretaceous calcareous formations of the adjacent areas. The reef build-ups in Upper Jurassic-Lower Cretaceous formations, expressed by chaotic reflection mound zones draped for quasi horizontal superimposed strata. The seismic trace attributes and velocity analyses are important tools in reservoir quality definition, giving information regarding porosity and fluid contents.

Keywords

• deep karst
• carbonate deposits
• seismic analysis
• reservoir properties