The effects of composition, laminar structure and burial depth on connected pore characteristics in a shale oil reservoir, the Raoyang Sag of the Bohai Bay Basin, China

To evaluate the effects of the composition, laminar structure and burial depth on pore volumes connected by pore-throats of different sizes in a shale oil reservoir, the Es1x formation in the Raoyang Sag of the Bohai Bay Basin was selected as an example. The effects of component contents, laminar structure and burial depth on pore volumes connected by pore-throats with widths of < 100 nm, 100-1000 nm and 1000-10000 nm were discussed based on total organic carbon (TOC), X-ray diffraction, low-temperature N-2 adsorption and mercury intrusion porosimetry methods. The results show that pore volumes connected by pore-throats with widths of < 100 rim decrease with increasing contents of TOC and carbonate and increase with increasing clay content. The pore volumes connected by pore-throats with widths of 100-1000 nm initially decrease with increasing quartz + feldspar content and then increase when the content exceeds 20%. The pore volumes connected by pore-throats with widths of 1000-10000 nm increase with increasing TOC content, and then decrease when TOC content exceeds 2.5%. They also exhibit a negative relationship with clay content. The pore volumes connected by pore-throats with widths of < 100 rim are initially similar in nonlaminated and laminated samples with equivalent burial depths and decrease with increasing burial depth. However, at depths in excess of 3100 m, the connected pore volumes in the nonlaminated samples increase with increasing burial depth and become larger than those of the laminated samples. The pore volumes connected by pore-throats with widths of 100-1000 nm in the nonlaminated and laminated samples are similar, and there are no obvious changes with increasing burial depth. The pore volumes connected by pore-throats with widths of 1000-10000 nm in the nonlaminated and laminated samples are also similar and decrease with increasing burial depth at burial depths less than 3100 m, and then connected pore volumes in the laminated samples increase with increasing burial depth at burial depths exceeding 3100 m. The connected pore volumes in the laminated samples are larger than those in the nonlaminated samples at burial depths exceeding 3400 m.