Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Freezing and thawing characteristics of pore fluid in rocks: Saturation, pore fluid distribution, andpermeability
Jiuhui Cheng a,b, Xuanzhe Xia a,b, Linlin Wang a,b,*a State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum-Beijing, Beijing, Chinab College of Safety and Ocean Engineering, China University of Petroleum-Beijing, Beijing, China

poses significant challenges to the construction and maintenance of rockand soil infrastructure and the stability of surrounding rocks (Humlum etal. 2003). Thus, understanding freezing and thawing characteristics are
critical for rock projects' safe construction and operation in cold regions.

ABSTRACT
Pore fluid (e.g., water and methane) phase transition in rocks determines
many geology properties of the polar strata, including heat transfer,deformation, and percolation. In this article, low-field nuclear magnetic
resonance tests are conducted to investigate the freezing and thawing
characteristics of pore fluid in rocks, including saturation, pore fluid
distribution, and permeability. During the phase transition, nuclear
magnetic resonance tests provide the unfrozen pore fluid saturation
variation and unfrozen pore fluid distribution evolution (including
unfrozen bound pore fluid and unfrozen movable pore fluid). The
experimental results indicate that most movable pore fluid is frozen at
the lowest temperature, whereas many bound pore fluids graduallyattenuate. Also, the freeze and thaw-induced strains of sandstones aretheoretically calculated based on a frost heave model. The calculated
results indicate that the phase transition of the pore fluid induces a sharpchange in strain, and the difference appears in the two processes. The
permeability measured demonstrates that ice growth tends to be between
pore cementation and pore-filling. This study quantifies the unfrozen
pore fluid saturation, pore fluid distribution, and phase transitioninduced strain in sandstones.

It is well known that porewater in geomaterials such as soil and rock haveno single freezing point and freezes gradually as the ambient temperaturedrops (Watanabe and Mizoguchi, 2002). When the ambient temperaturedrops, the pore fluid transforms into a solid phase, reducing saturation
and redistribution of the pore fluid. The extra pressure causes the rock to
deform in the presence of the solid phase (Winkler 1968). Water exerts
erosion and destructive impacts on geotechnical engineering in coldregions, which relates to strain and permeability. Thus, investigating thestrain and permeability changes produced by phase transition is essentialfor the early design and stability maintenance of geotechnicalengineering in cold regions. The total strain of rocks is associated withtemperature and pore fluid saturation, and the permeability is determinedby the flow channels of rocks (Backeberg et al. 2017). Thus, thecharacterization of unfrozen water saturation and distribution needs to besolved urgently. Nuclear magnetic resonance has been proven beneficial
to probe pore fluid content and distribution (Dillinger and Esteban, 2014).
Compared with other technologies, including mercury intrusion, sonicmethod, and differential scanning calorimetry, this technology has theadvantages of being fast, non-destructive, and have high-precision.

KEY WORDS: Low-field nuclear magnetic resonance; phasetransition; saturation; pore fluid distribution; permeability; strain.

This paper presents a preliminary study on the freezing and thawing
characteristics of pore fluid in sandstone, including saturation, pore fluiddistribution, and permeability. Two probes monitor the temperaturechanges for the tight sandstone during the freezing and thawing process,and nuclear magnetic resonance detects saturation and pore fluiddistribution. Then, phase transition-induced strain is calculated based ona frost heave model. Movable water is the main factor inducing strain,
which is confirmed by pore fluid distribution. In addition, pore fluid
distribution provides the phase transition process in detail. Finally, theINTRODUCTION
In cold regions, the temperature alternates with the seasons (Giorgi et al.
1999). A growing number of geotechnical projects are underconstruction or planned in cold regions of the world, including Siberia,
the polar region, and northwestern China. In addition, polar engineering
is carried out under extremely complex geological formations, intrusive
water, low temperature, and other environmental conditions, which

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