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Effects of water–rock interaction on elastic behaviours of fully water-saturated lacustrine clay-rich shales: experimental investigation and theoretical modelling

Year: 2026
Type: article
Abstract: SUMMARY Unlike marine shales, lacustrine Gulong shales deposited in semideep-to-deep lakes typically exhibit complex fluid-phase behaviour and high clay mineral content. To study the saturation effects (e.g. frame stiffness, clay-water weakening) of in-situ shale, ultrasonic investigations into lacustrine shales from the Qingshankou (QSK) Formation were conducted under 100 per cent water-saturated and confining (e.g. 5–25 MPa) conditions. The data indicate that water saturation increases the P-wave velocity propagating perpendicular to the bedding plane (P0) by $\sim$14 per cent, while exerting a negligible effect on the P-wave velocity parallel to the bedding plane (P90); S-wave velocities consistently decrease ($\sim$10 per cent for SH wave and $\sim$6 per cent for SV wave) from dry to fully saturated states. Furthermore, the experimental observations indicate a saturation-induced frame-weakening response in clay-rich shales, leading to a $\sim$18 per cent decrease in shear modulus at 100 per cent water saturation. In addition, to qualitatively capturing the frame-weakening effect in 100 per cent water-saturated shales in the velocity estimation, we proposed a Porosity-Clay modified Gurevich Squirt Flow (PCGS) model, which was introduced as a data-constrained phenomenological extension that accounts for effective saturation-induced frame weakening through empirical fitting of modulus variations. Compared with traditional fluid-substitution models, the PCGS model exhibits substantially improved accuracy ($\sim$10 per cent for bulk modulus and $\sim$15 per cent for shear modulus).
DOI: 10.1093/gji/ggag300
Language: English
Subfield: Geophysics
Open Access status: gold
Estimated APC paid: $3,416
OpenAlex ID: W7171504473
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