Conversion of High-Carbon Domanic Shale in Sub- and Supercritical Waters

This paper presents the results of the conversion of high-carbon Domanic rock from sediments of the Semiluki-Mendym horizon of the Volga-Ural petroleum Basin in sub- and supercritical waters at temperatures of 320, 374, and 420 degrees C in a neutral nitrogen environment for 1 h. The initial sample is a siliceous-clay carbonate rock with an organic matter content of 10.6 wt %, the largest part of which is insoluble kerogen. The end products of all experiments are characterized by an increase in the content of saturated hydrocarbons with a noticeable decrease in the content of resins and asphaltenes. The highest yield of the extract (3.98 against 3.12 wt %) compared with the initial rock is observed in the experiment in subcritical water at 320 degrees C as a result of the preferred degradation of resins and more complete extraction of asphaltenes from the rock. With an increase in temperature to supercritical water conditions at 374 degrees C and pressure up to 24.6 MPa, kerogen transformation processes are observed due to the C-C, C-N, and C-O bonds destruction with the formation of low-boiling saturated hydrocarbons and high-carbon components such as carbene-carboids in the products of the experiments. The highest yield of saturated hydrocarbons occurs at the experiment of Domanic rock in supercritical water at 420 degrees C and 24.4 MPa. Under these conditions, in comparison with lower temperatures, the yield of the extract from the rock decreases due to intense gas formation. In the composition of the gases formed in the experiments, there are hydrocarbons: CH4, C2H6, C3H8, and i-C4H10, indicating the destruction of C-C bonds. Dehydrogenation processes in supercritical water at 420 degrees C are noted by the presence of H-2 in the reaction system. Structural and phase changes in the mineral composition of Domanic rock were discovered as a result of supercritical water exposure at 374 and 420 degrees C. In particular, the structure of mica was changed due to the isolation of a separate phase of montmorillonite from it.