Effects of organic components on the relationships between specific surface areas and organic matter in mudrocks

Abstract

Mudrocks formed in different sedimentary environments of the Dongying Sag (eastern China) were used for the analyses and measurements of specific surface area, X-ray diffraction, palynofacies and pyrolysis, to examine the correlations and influencing factors of different organic components with specific surface areas (SSAs) in mudrocks. The results indicate that total organic matter in the mudrocks is composed of amorphous organic matter (AOM) and morphological organic matter (MOM, palynomorphs plus structured organic matter). Specific surface areas in mudrock consist of inner and external surface areas. The ratio of AOM/MOM and characteristics of inner and external surface areas are varied in different mudrocks. The relationships between SSAs and organic matter of which the occurrence of different organic components are not consistent: organic matter in MOM-dominated mudrocks is negatively correlated with external, inner and total surface areas, which are related to the MOM occurring independently as organic particles without being adsorbed onto mineral surfaces; organic matter in mudrocks dominated by the AOM is negatively correlated with external surface area and positively correlated with inner and total surface areas, which are ascribed to the more feasible adsorption of the AOM on mineral surfaces (particularly the inner surface) and the adsorption of the MOM on mineral surfaces in the form of fine particulate organic matter. In addition, the combination of organic components (including the AOM and MOM) with carbonates has an effect on the relationships between SSAs and organic matter. Therefore, the organic component morphology and mode of occurrence in mudrock have an influence on the relevance of total organic carbon (TOC) with specific surface areas. Further study on the relationships between TOC and specific surface areas of mudrocks is of great significance to reveal the occurrence mechanisms of organic matter and unconventional petroleum and to assess the effectiveness and persistence of carbon sequestration.