Specific Features of Realizing the Generation Potential of Carbonate and Carbonate–Siliceous Domanik Rocks by Treatment with Sub- and Supercritical Water

Abstract

Comparative studies on transformation of the organic matter (OM) of high-carbon carbonate–siliceous–clay rock with С_оrg 7.07% and low-carbon carbonate rock with С_оrg 0.33% from Domanik deposits in Tatarstan in sub- (SBW) and supercritical (SCW) water were performed. The potential of the carbonate rock is utilized virtually completely in SBW at 320°С. From the high-carbon Domanik rock, SBW allows only more complete extraction of free hydrocarbons, asphaltene compounds, and solid n-alkanes without significantly altering the kerogen structures. The kerogen degradation occurs most intensely in SCW and is accompanied by a decrease in the generation potential and by an increase productive capacity of the rock. In the oil extracted from the high-carbon rock with SCW at 374°С, the content of saturated and aromatic fractions increases by a factor of more than 2, the content of asphaltenes and resins decreases, and carbenes/carboids are formed. At 420°С, the oil yield and the content of carbenes/carboids decrease. In the extraction from the carbonate rock, on the contrary, at 374°С the content of light oil fractions decreases, and the fraction of resins increases by a factor of more than 1.5; at 420°С, the content of asphaltenes increases by a factor of more than 2. Irrespective of the lithological composition of the rocks, with an increase in the SCW temperature, the yield of the gas phase and the content of alkanes, phenanthrenes, and dibenzothiophenes in the oil fractions increase, whereas the content of alkyltrimethylbenzenes, naphthalenes, and dibenzothiophenes decreases. The extent of utilizing the generation potential of OM of Domanik rocks depends on the content and composition of kerogen and high-molecular mass components and on their thermal stability in sub- and supercritical water.