Impacts of Pore Structure on the Occurrence of Free Oil in Lacustrine Shale Pore Networks

Abstract

The ultimate recovery of shale oil is mostly dependent upon the occurrence and content of free oil within the nano-scaled pore network of shale reservoirs. Due to the nanoporous nature of shale, quantitatively characterizing the occurrence and content of free oil in shale is a formidable undertaking. To tackle this challenge, 12 lacustrine shale samples with diverse organic matter content from the Chang7 Member in the southern Ordos Basin were selected, and the characteristics of free oil occurrence were indirectly characterized by comparing changes in pore structure before and after organic solvent extraction. The free oil enrichment in shale was assessed using the oil saturation index (OSI), corrected oil saturation index (OSIcorr), and percentage of saturated hydrocarbons. The results revealed that slit-like interparticle pores with diameters less than 30 nm are dominant in the Chang7 shale. Conceptual models for the pore structures containing free oil were established for shale with total organic carbon (TOC) content less than 9% and greater than 9%, respectively. Shale samples with TOC content less than 9% exhibit a well-developed pore network characterized by relatively larger pore volume, surface area, and heterogeneity. Conversely, shale samples with TOC content exceeding 9% display a less developed pore network characterized by relatively smaller pore volume, surface area, and heterogeneity. Larger pore volume and lower organic matter abundance favor the enrichment of free oil within the lacustrine shale pore network. This study may have significant implications for understanding oil transport in shales.

Impact of petroleum expulsion and evaporation losses on shale oil assessment using pyrolysis techniques

“…The differences in S 1 loss among these lacustrine shales are not significant and are all lower than that observed in the marine Bakken shale, indicating that these lacustrine shales are denser than Bakken shale. However, the Chang7 shale, which has higher TOC, exhibits lower porosity (Li, Zhou, et al, 2016;You et al, 2023) and higher S 1 loss (Zhao et al, 2023), possibly due to the evaporative loss of light oil adsorbed to the kerogen after sample comminution. The samples used in this experimental study were old samples with an average S 1 value of 3.06 mg/g.…”

Understanding the relationship between pore size, surface charge density, and Cu2+ adsorption in mesoporous silica

“…This influence affects the entire weathering process. Mesoporous structures in shale and tight sandstone are integral features of oil and gas reservoirs 6 . Furthermore, mineral mesopores are instrumental in addressing critical Earth science challenges such as carbon cycling 7 , mineral dissolution and precipitation 8 , and trace element enrichment 9 .…”