Influence of soluble organic matter on characterization of shale reservoir

Shale with a maturity within “oil window” contains a certain amount of residual soluble organic matter. This soluble organic matter will have an important influence on the characterization of shale reservoir. In this study, two shale samples were collected from the Upper Permian Dalong Formation in the northwestern margin of Sichuan Basin. Their geochemistry, mineral composition, pore structure (surface area and pore volume) were investigated before and after removing soluble organic matter (SOM) by the extraction with dichloromethane or trichloromethane. The results show that the TOC, S1, S2, and IHof the extracted samples decrease obviously, but the mineral composition has no significant change as compared with their raw samples, thus the original pore structure is thought to be unaltered from the extraction. SOM occupies pore volume and hinders pore connectivity, and the extraction greatly increases the surface area and pore volume of the samples. The residual SOM in the shale samples occur mainly in the micropore and small mesopore, and their occupied pore size range seems being constrained by the maturity. For the shale samples with lower maturity, SOM is mainly hosted in organic pores with diameter less than 5 nm. For the shale samples with moderate maturity, micropores and some mesopores ranging between 2 nm and 20 nm are the main storage space for the SOM. ©, 2015, Science Press. All right reserved.