The evolution of acids and neutral nitrogen-containing compounds during pyrolysis experiments on immature mudstone

Abstract

Abstract Pyrolysis experiments were conducted on immature(Ro = 0.47%) organic-rich (TOC = 6.0%)mudstone, and the liquid products at 10 different temperature stages were detected by negative ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI− FT-ICR MS). Seven classes of acids and neutral nitrogen-containing compounds, namely, N1, N2, O1, O2, O3, O4 and N1O1, were detected in all the products. The O2 class accounted for the largest proportion (50.56 %–91.65%) among all the products, followed by the O1 class (1.70 %–28.80%). The % O1 and % N1 classes showed a clear upward trend with the increase in experimental temperature due to their organic resources, and the % O2 class showed the exact opposite trend, which could be explained by the chemical reactions that occurred during the maturation process, such as decarboxylation and dehydration. In addition, the relative abundances of the classes with high double bond equivalents (DBE) (≥9) and low DBE (≤7) showed a significant upward trend and a clear downward trend, respectively. The main reasons were aromatization and condensation during thermal evolution. This series of thermal evolution characteristics indicated that a set of new thermal parameters, such as ∑%DBE ≥9/∑%DBE≤8 (O2 compounds) = 0.0007T2 - 0.372T + 48.594(R2 = 0.9088) may be used as a new maturity parameter after further verified with crude oils.