Prospectivity of the Biostromna Zone (Northwestern Shelf of the Black Sea) for hydrocarbon exploration according to density modeling

Abstract

In order to determine the hydrocarbon prospectivity (HC-potential) of the Biostromna zone, located on the northwestern shelf of the Black Sea, a systematic two-dimensional density (gravity) modeling was carried out along 8 submeridional profiles. Particular attention was paid to determining the location of deep faults that could be the source of methane and other hydrocarbon jets that penetrated to the earth's surface. To calculate the fluctuations in the magnitude of the gravity effect associated with changes in the density of sediments, models with minimum and maximum values of this parameter were calculated for each layer separately and for the entire sedimentary cover of the Biostromna zone. It is determined that variations in the density of the sedimentary cover lead to fluctuations in the values of model anomalies up to ±2 mGal. The conducted density modeling has shown a wide variety of basement structure within the Biostromna zone with alternating uplifted and submerged areas of the crystalline crust with a significant change in the structure of the study area in the longitudinal direction. The HC-potential of local structures of the Biostromna zone was assessed by four criteria: 1) by the distance between the base of the sedimentary cover and the roof of the granodiorite layer, since the smaller the value of this parameter, the less the dispersion of mantle material and the greater its flow to potential hydrocarbon traps; 2) by the provision of local structures with deep faults as channels of mantle fluids; 3) by the age of basement formation, which determines the time interval from tectonic activity to the formation of the sedimentary cover; 4) by the level of adjusted gravity difference, which fixes the deconsolidation of certain areas of the sedimentary cover as a factor in improving reservoir properties. Based on the results of the research, the scheme of the Biostromna zone's HC-potential was drawn up. A multi-component analysis of the results of gravimetric studies is proposed, which significantly increases the reliability of selecting priority structures for the search for hydrocarbons from the multitude of objects tracked by seismic exploration.