Hydrocarbon composition of bitumen from deeply buried terrestrial organic matter (zone of apocatagenesis)

Abstract

We present new results on catagenetic alteration of dispersed organic matter (DOM) and individual hydrocarbon composition of bitumen extracts from the lower mesocatagenesis and apocatagenesis zone, based on the study of core samples from superdeep well SV-27 (Vilui syneclise), which penetrated Permian and Upper Carboniferous coal-bearing strata. The vitrinite reflectance data show a progressive increase in the thermal maturity of DOM at a depth of ~4 km. The major biomarker indicators of the thermal history of DOM in the central part of the Vilyui syneclise appear to play only a minor role below this depth, thus reflecting the early stages of mesocatagenesis. The pristane/phytane ratios begin to invert at the same depth. Bitumen extracts from core samples collected from this depth contain new hydrocarbons in trace amounts, which increase with depth. The identified compounds include homologous series of alkenes, 2,4- and 2,7-dimethylalkanes, and alkylcyclohexanes with a prevalence of compounds with an odd carbon number predominance. Unusual differentiation of aliphatic and cyclic hydrocarbons with even and odd carbon-numbered chains occurs at the maximum depth (6458 m). Among aromatic hydrocarbons, four new diastereomers are identified: 17-desmethyl–23-methylmonoaromatic steroids C27. Considerable variations in the composition of bitumen extracts from the apocatagenetically altered core samples appear to reflect the termination of hydrocarbon generation from kerogen and further thermolysis of residual bitumens, including their asphaltene components. This explains the low values of maturity biomarker indicators corresponding to the apocatagenesis grade, since in this case they reflect the composition of hydrocarbons generated during the early stages and later occluded and adsorbed by asphaltenes. “Deep-seated” microoil from Permian, Carboniferous, and Cambrian deposits did not participate in the formation of oil rims and major gas condensate pools in the Vilyui petroleum area.

Resins and Asphaltenes of Light and Heavy Oils: Their Composition and Structure

“…It should be noted that olefins were also identified in bituminoids of terragenic OM, the Devonian oils of Canada, Paleozoic oils, and the Mezo-Cenozoic oils of Russia …”

“…It should be noted that olefins were also identified in bituminoids of terragenic OM, 76 the Devonian oils of Canada, 77 Paleozoic oils, 78 and the Mezo-Cenozoic oils of Russia. 79 The results of the comparative analysis show that some compounds identified in the low-polar fractions of maltenes are also included in the structure of HMA molecules.…”

Molecular Indicators of Sources and Biodegradation of Organic Matter in Sediments of Fluid Discharge Zones of Lake Baikal

“…Besides the traditional set of molecular markers, a series of methylated alkanes (3,5-, 3,6-, 3,7-dimethylalkanes -DMA, m/z 99, 113, 127; Figure 8) were also identified in bottom sediments of Lake Baikal. These structures have been previously detected in OM of recent and partially lithified deposits of Siberia and the Russian Platform [63,117,118] and in sediments of the Academician Ridge of Lake Baikal [111]. Precursors of these compounds with a high probability are di-and tetraether lipids of archaea and bacteria [63,119].…”

Deposits of Hydrocarbons with Renewable Reserves and Experience of New Estimation Methods

“…Gavrilov V.P. considers that general characteristics of oil and gas recovery of such fields are pulsating reservoir condition against the background of continuous development [2,7,8,9].…”