Pyrolytic Gaseous Hydrocarbon Generation and the Kinetics of Carbon Isotope Fractionation in Representative Model Compounds With Different Chemical Structures

Abstract

Five model compounds with representative chemical structures were selected for use in simulation experiments of pyrolytic gas production. The gas production and isotopic fractionation characteristics were observed and analyzed. Then, the factors affecting carbon isotope fractionation during natural gas generation were discussed, and a fractionation model was established and calibrated. We concluded that the final hydrocarbon gas (C1–5) yield of octadecane, octadecylamine, octadecanoic acid, decahydronaphthalene, and 9‐phenylanthracene decreased in turn with the effective hydrogen content. Compared with linear alkanes or alkyl compounds, cycloalkanes have higher thermal stability and generate gas later. The variation in the carbon isotopic composition of natural gas is primarily controlled by the following three factors: (a) the thermal evolution of organic matter results in a gradually heavier isotopic composition for the main gas production stage. (b) Gas inherits the isotopic composition of its parent material, and this effect is evident when the chemical structure and gas generation mechanism between parent materials are similar. (c) The structure of organic matter determines the reaction mechanism of gas generation, which has a significant influence on the range and trend of carbon isotope fractionation in the process of methane generation. An improved chemical kinetic model can accurately characterize carbon isotope fractionation during gas generation.

Constrain on Oil Recovery Stage during Oil Shale Subcritical Water Extraction Process Based on Carbon Isotope Fractionation Character

“…However, the effect on the δ 13 C CO 2 − CH 4 characteristics may be less, as it is a relative change. The organic matter type with a heterogenous structure in the rock may also have an influence on the carbon isotope fractionation, but the evolution characteristic of δ 13 C CO 2 − CH 4 may be slight, as the gas product at different decomposition stages is similar to that of different organic matter [30]. Thus, the result of this research can be used to indicate the oil shale pyrolysis process, and it can help determine when to stop heating during oil shale exploitation and lower the production costs.…”

“…The carbon isotope characteristics in those C-H-O systems are largely considered to be determined by kinetics or/and a thermodynamic equilibrium mechanism [29]. For the organic matter decomposition process, the carbon isotope of gases is mainly related to the former [30], and researchers have established many models to describe the carbon isotope evolution characteristics during natural gas generation process, e.g., the Rayleigh model [31], Cramer model [32], Tang model [33], etc. The effect caused by the thermodynamic equilibrium process has been rarely considered to date; there has been much debate in the literature about the relative importance of kinetics and thermodynamic equilibrium in controlling the isotopic distribution among C-H-O gases, especially in aqueous conditions [28,29].…”

Carbon Isotope Kinetics Effect on the Natural Gas Accumulation: A Case Study of the Baimiao Area, Dongpu Depression, North China

“…Carbon isotope kinetics based on hydrocarbon generation kinetics can solve the scientific problems of carbon isotope evolution and fractionation regularity under certain geological conditions. − Moreover, the kinetic process of natural gas generation and migration is objectively evaluated; the natural accumulation process is clarified; and the favorable blocks for gas accumulation are pointed out. Therefore, the study of the carbon isotope kinetics is of great significance for solving the problem of natural gas accumulation. − In recent years, the carbon isotope kinetics of natural gas has become an important research focus in the field of petroleum geochemistry − and has important application potential for explaining the process of natural gas accumulation. − …”

“…With the establishment and improvement of the above kinetic models, carbon isotope kinetics research has accomplished many achievements and have been applied in many petroliferous basins. − ,, Most scholars simulate the natural gas accumulation process mainly using carbon isotope kinetics software with the Tang model as the principal model or use the GOR-Isotope Kinetics software with the Crammer model as the principal model. Its application mainly focuses on the analysis of the evolution law of δ 13 C 1 of natural gas, gas source conditions, maturity determination, and natural gas migration, and it also focuses on establishing accumulation research and mode of accumulation. , In addition, many scholars have performed exploratory work and achieved corresponding results, − ,, such as the coal-to-methane carbon isotope kinetic fractionation model and the chemical kinetic model of carbon isotope fractionation during gas production of organic matter …”

“…Its application mainly focuses on the analysis of the evolution law of δ 13 C 1 of natural gas, gas source conditions, maturity determination, and natural gas migration, and it also focuses on establishing accumulation research and mode of accumulation. 27,28 In addition, many scholars have performed exploratory work and achieved corresponding results, [12][13][14][15][16][17][18][19][20][21][22][23][24]26,27 such as the coal-to-methane carbon isotope kinetic fractionation model 26 and the chemical kinetic model of carbon isotope fractionation during gas production of organic matter. 14 In the past 20 years, the petroleum exploration difficulty in the Dongpu depression has gradually increased and petroleum reserves and production are decreasing.…”