Chemical structure evolution of the thermally simulated kerogen

Kerogen was isolated from the source rock of Maoming and characterized by element analysis, ¹³C DP/MAS NMR, Rock-Eval and an arti fi cial pyrolysis experiment was carried out in a closed gold tube system with a heating rate of 2 °C/h. Products were collected at ten temperature points from 300 °C to 440 °C. The soluble organic matter and residual kerogens from the experiment were quanti fi ed by weighing. Pyrolysis analysis of the kerogen indicated that it comprised a long, saturated and unbranched hydrocarbon chain (up to C₃₃) structural unit. The maximum oil generation potentials reached 27.0% and was very close to those derived from ¹³C DP/MAS NMR, suggesting that ¹³C NMR is an effective approach for evaluation of oil potentials. In addition, the results suggest that as the temperature increases, aliphatic chains and small clusters of aromatic groups break down from kerogens, generating soluble hydrocarbons at temperatures of less than 390 °C. At higher thermal maturity, a few short aliphatic carbons remain in the structure of residues. The number of aromatic groups increases and their size grows with increasing maturity, with condensation occurring at aromatic groups at high temperature, while these residues have little potential for oil generation.