2D and 3D models of the geothermal field of the Caspian Sea

Abstract

Relevance. The geological and economic significance of the Caspian Sea offshore area is determined by its existing large oil and gas resources and will increase with the development of already discovered and the identification of new fields. In conditions of limited investment resources for expensive geological and geophysical surveys in the sedimentary basins, relatively inexpensive methods for indirect assessment of hydrocarbon potential based on existing geological and geophysical data are becoming practically important. One such method is thermotomographic imaging of the Earth’s crust based on two- and three-dimensional geothermal modeling. The construction of linear (two-dimensional) and volumetric (three-dimensional) models of temperature and heat flow (HF) distribution allows for the creation of cross-section maps of the geothermal field at any depth, and thus to determine the level at which conditions exist for the organic matter catagenetic transformation, i.e., as a first approximation, it is possible to predict the depth of hydrocarbon deposit placement. Research methods. 1) Review of existing studies and compilation of a new map of the regional heat flow of the Caspian Sea offshore area and surrounding land based on the analysis of the latest global database; 2) Justification of boundary condition assignment and execution of two-dimensional temperature field modeling along geotraverses; 3) Construction of thermotomographic models of subsurface temperatures. Results. The regional distribution of HF has been analyzed within the classification of measurement conditions by sea depth. Two-dimensional modeling of the geothermal field has been performed along long seismic geotraverses, and subsurface temperatures in the Upper Cretaceous and Cenozoic deposits of the sedimentary cover down to a depth of 4-5 km have been determined. For the South Caspian Basin, a 3D model of subsurface temperatures has been constructed, and cross-section maps of temperatures at depths of 5 and 10 km are presented. Thermotomographic modeling provides additional information for hydrocarbon exploration and prospecting.