Experimental study of the interaction of mineral-forming hydrothermal solutions with oil and their joint migration

Abstract

Interaction between oil and hydrothermal solutions of different compositions was experimentally studied in a wide range of temperature (260-490 ° C) and pressures (8-150 MPa). This study was based on a new technique involving simultaneous occurrence of water-hydrocarbon interaction and growth of quartz, cal- cite, and fluorite crystals with fluid inclusions from the same solution. Fluid inclusions were studied to charac- terize the behavior of oil and aqueous solutions at elevated and high temperatures and pressures. It was shown that, owing to interaction with hydrothermal solutions, oil is intensely removed from the source rock and accu- mulated in the frontal part of hydrothermal convective flow. During this process, the oil is partially transformed into hydrocarbons, light oil, semiliquid and solid bitumens. At temperatures of 300-350 ° C and pressures of 50 − 100 MPa, oil and its fractionation products migrate in hydrothermal solution mainly in a drop-liquid state. At higher temperatures (360-395 ° C), when the oil/water ratio in the initial mixture is no higher than 1/70-1/35, liquid and gaseous hydrocarbons are completely dissolved in hydrothermal solutions forming a complex homogenous water-hydrocarbon fluid. The fluid can exist and migrate in this state, but it becomes heteroge- neous with decreasing P-T parameters. Under favourable structural and lithological conditions, this can lead to the formation of displaced oil-and-gas deposits, with oil enriched in light components. The experiments unam- biguously confirmed the concept that bitumen inclusions in minerals can serve as indicators of hydrocarbon migration paths in the Earth's crust.