Abstract Low-pressure nitrogen physisorption was performed on Triassic Yanchang mudstones before and after solvent extraction to characterize the extractable organic matter (EOM) occurrence and ascertain the impact of extracts on the nanoporosity of lacustrine mudstone within the oil window. Organic-rich Yanchang mudstones are currently thermally mature (vitrinite reflectance of 0.48%–0.92%). SEM-observed pore types chiefly comprise interparticle and intraparticle pores related to inorganic minerals, with organic matter pores less developed. Pore volume (PV) of the original mudstones is 0.35–2.15 cm3/100 g and the specific surface area (SSA) is 1.22–7.77 m2/g. Brittle minerals (quartz + feldspar + carbonates) and I/S mixed layer jointly show the positive effect on the pore space development in the Yanchang mudstone. Four groups of mudstones with obvious differences in pore structure properties were identified, which probably result from the various development degrees of interparticle pores at the edge of brittle minerals, and intraparticle pores associated with I/S aggregates. Generally, solvent extraction will result in a noticeable increase in the volume of N2 adsorbed due to the reopening of pore space blocked by EOM, which is related to increases in PV an SSA. A declining case, probably caused by the progressive shift of the enlarged open pore space to the larger macropore range (d > 200 nm) which is not detected by N2 adsorption and counteracts the increased porosity by extraction, however, was also observed in the current study. Overall, the infilling degree of EOM increased with increasing thermal evolution degree of shales within the oil window, which mainly blocks minor pores in lower mature samples but larger pores in higher mature samples.
Pore structure of Triassic Yanchang mudstone, Ordos Basin: Insights into the impact of solvent extraction on porosity in lacustrine mudstone within the oil window
Yang Wang,Luofu Liu,Hongfei Cheng
Published 2020 in Journal of Petroleum Science and Engineering
ABSTRACT
PUBLICATION RECORD
- Publication year
2020
- Venue
Journal of Petroleum Science and Engineering
- Publication date
2020-12-01
- Fields of study
Chemistry, Environmental Science, Geology
- Identifiers
- External record
- Source metadata
Semantic Scholar
CITATION MAP
EXTRACTION MAP
CLAIMS
CONCEPTS
- brittle minerals
Hard mineral components including quartz, feldspar, and carbonates that influence pore development in mudstones.
- extractable organic matter
Organic compounds that can be dissolved and removed from rock samples using solvents.
Aliases: EOM
- interparticle pores
Pore spaces located between mineral particles, particularly at the edges of brittle minerals.
- intraparticle pores
Pore spaces within individual mineral particles or clay aggregates.
- i/s mixed layer
Clay mineral aggregates composed of illite and smectite layers associated with intraparticle pore development.
Aliases: illite/smectite mixed layer
- macropore
Pores with diameters greater than 200 nm that fall outside the detection range of N2 adsorption.
- nitrogen physisorption
A low-pressure gas adsorption technique used to characterize nanopore structure in porous materials.
Aliases: N2 physisorption
- oil window
The thermal maturity range in which petroleum generation occurs in source rocks.
- pore space development
The creation and expansion of pore networks within mudstone, influenced by mineral composition and organic matter content.
- solvent extraction
A laboratory procedure using solvents to remove organic matter from rock samples for porosity characterization.
- specific surface area
The total surface area per unit mass of a porous material, measured in m2/g.
Aliases: SSA
- thermal maturity
The degree of thermal alteration of organic matter in shales, indicated by vitrinite reflectance values.
Aliases: thermal evolution
REFERENCES
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