Distribution and significance of maleimides in organic matter-enriched shales and derived crude oils

Abstract

The maleimides, or 1H-pyrrole-2, 5-diones, are one of the novel types of biological markers existed in both sedimentary organic matter and petroleum, which could be products derived from the degradation of chlorophylls and bacteriochlorophylls. In this study, the maleimides composition was investigated in detail for several crude oils and petroleum source rocks with varying depositional settings, and abundant 2-methyl-3-n-propyl (Me, n-Pr) and 2-methyl-3-isobutyl (Me, i-Bu) maleimide, together with aryl isoprenoids were detected. These pigments-derived products were prominently generated by Chlorobiaceae and are especially abundant in the saline and marine black shales and related oils, indicating that PZE (photic zone euxinia) occurred in the brackish water environment of the Nenjiang Formation in the Songliao Basin, the saline to semi-saline water environment of the Shahejie Formation in the Bohai Bay Basin, and the marine environment of the Napo Formation in the Oriente Basin, showing strong reduction preservation conditions. It can be concluded that PZE is a favorable factor for the enrichment of organic matter and the development of high-quality source layers. In addition, the ratios of Me, i-Bu/Me, Et and Me, n-Pr/Me, when coupled together, could be used to diagnose the depositional conditions such as marine, saline, semi-saline or brackish water column.

Keywords

• aryl isoprenoid
• maleimide
• chlorobiaceae
• pze (photic zone euxinia)
• om-rich shales
• source rock
• deposition environment