Comprehensive analysis of the correlation between structural and material heterogeneities of different layers of the lithosphere of the Dnieper-Donetsk Basin

Abstract

The calculations of thermal field parameters at oil and gas fields for the Chernihivskyi and Lokhvitskyi blocks of DDB allowed us to define geothermal gradient changes with depth. At all fields, there are wells with stable gradients of 19—21 °C/km, and ones with sharp changes. On the Chernihivskyi block territory, these changes are negative (the gradient decreases to 15—17 °C/km); between the Kherson—Smolensk tectonic suture to the Pereiaslav-Khmelnytskyi—Pryluky Fault, changes are both negative and positive, and to the southeast from it (at the Lokhvitskyi block) they are exclusively positive (increases of up to 35—55 °C/km). Here, the depth of the gradient jump corresponds with the depth of the hydrogeological inversion — the change of the highly mineralized chloride-calcium waters of the upper hydrodynamic layer to thermal, weakly mineralized hydrocarbonate-sodium waters of the lower layer. Also, within the Lokhvitskyi block, a connection has been established between the gradient jump depths and layering of strata with AHSP (Abnormally high stratum pressure). Its occurrence is a consequence of the gas accumulating in tectonically or lithologically shielded traps. The area of layers with AHSP distribution, where only an increase in the geothermal gradient was recorded, is limited by decompression zones, revealed by the gravity modeling data. Within its boundaries, the gradient change is either negative or changes in both directions. The reasons for this pattern need further analysis.