Thermal Decomposition of Kerogen in High-Carbon Domanic Rock of the Romashkino Oilfield in Sub- and Supercritical Water

Abstract

The thermal decomposition of kerogen of the high-carbon Domanic rock from the Romashkino oilfield (Russia) in sub- and supercritical water (SCW) at 320, 374, and 420 °C was studied. The Rock-Eval analysis shows that the isolated kerogen from the native rock with an organic carbon (C org) content of 55.69% is a high-molecular structure (S 2 is 159.38 mg HC/g of rock) with an extremely low content of free hydrocarbons (HC) (S 1 is 0.33 mg HC/g rock). The kerogen samples contain predominantly iron-bearing minerals (pyrite, ferrihydrite, marcasite, and iron oxide), which form organomineral complexes with kerogen and are poorly soluble in acids. The subcritical water treatment of Domanic rock at 320 °C (17.0 MPa) does not lead to noticeable changes in the kerogen structure. Intensive kerogen decomposition in SCW at 374 °C (24.6 MPa) and 420 °C (24.4 MPa) is accompanied by the formation of gases, saturated and aromatic HC, as well as solid carbonaceous substances such as carbenes/carboids. According to Fourier-transform infrared (FTIR) spectroscopy, the kerogen decomposition is accompanied by a decrease in the length of its aliphatic fragments and an increase in the degree of their branching, as well as an increase in the content of aromatic carbon in comparison with aliphatic one. The number of hydrogen atoms directly associated with ring aromatic structures also decreases, which leads to an increase in the degree of condensation of the kerogen structure. Almost complete destruction of sulfur-containing bonds in the kerogen structure is observed at 420 °C (24.4 MPa), in contrast to other experiments. Electron paramagnetic resonance (EPR) analysis data indicate the destruction of vanadylporphyrin complexes with the increase in the concentration of free radicals in the kerogen structure under the SCW influence. Distinctive features of the composition and distribution of biogenic, rare-earth, and radioactive trace elements (TE) in the rock and isolated kerogen samples were revealed by inductively coupled plasma–mass spectrometry (ICP–MS). Based on the ratios of H/Cat to O/Cat on the van Krevelen diagram, hydrogen index to T max, FTIR spectral parameters (A factor to C factor) of kerogen samples, and the biomarker parameters of saturated and aromatic HC, it was determined that with an increase in the temperature and pressure of SCW, the degree of kerogen maturity increases. Changes in the pore space of the kerogen structure have been established by scanning electron microscopy: the pore size increases at 374 °C (24.6 MPa) and decreases at 420 °C (24.4 MPa) due to the contamination by carbonaceous substances, which affects the oil recovery from Domanic rocks.

Experimental Study on Hydrocarbon Generation Characteristics of Type II Kerogen from Low-Maturity Shale in Supercritical Water

“…The decreasing trend in X brn and the A factor with temperature indicated the cleavage of branched side chains of kerogen macromolecules, which could also be demonstrated by the increase in saturates and aromatic contents of generated oil and in gas yield. The results were consistent with Nasyrova’s study that the A factor and C factor of the spent kerogen decreased with reaction temperature from 320 to 420 °C. The value of the C factor varied differently from Hou’s pyrolysis results, in which the C factor of spent kerogen decreased from 300 to 400 °C but increased at 420 °C.…”

Catalytic Conversion of Oil in Model and Natural Reservoir Rocks

“…All of the studied asphaltenes have the same SFR/VP ratio. This indicates that the catalytic action of carbonate rock does not affect the condensed naphthenoaromatic structures in which SFR and VP are localized, unlike high-temperature processes in which demetalization begins at temperatures above 300 • C [28]. Thus, the activity of natural carbonate rocks in the processes of low-temperature (25 • C) conversion of petroleum components was proven.…”

Theoretical Analysis of the Effect of Electrical Heat In Situ Injection on the Kerogen Decomposition for the Development of Shale Oil Deposits

“…Kerogen is a complex mixture of organic compounds, consisting of a high-molecular structure with a large organic carbon content [26,27]. Under thermal stimulation, kerogen decomposes into various bituminous products, which further crack into different low-carbon products [28].…”