Quartz Stressing and Fracturing by Pore Pressure Dropping Down to Negative Pressure

Abstract

In water-bearing porous rocks, pore pressure variations play a major role in deformation, through dissolution−precipitation and fracturing processes. An often-overlooked variation where pressure falls to negative pressure or tension can operate whenever aquifer formations dry out, for instance, in deep storage (nuclear or industrial wastes, long-term CO 2 mitigation, short-term energetic resources, etc.). This can generate capillary tension within the aquifers. This study investigates the mechanical effect of such in-pore tension in the surrounding crystal field, through laboratory experiments at the one-pore scale. Microthermometric procedures were carried out on synthetic fluid inclusions to generate large tensile stress and were combined with Raman microspectrometry to visualize the resulting stress fields in the host quartz. For comparison, we numerically modeled the stress field by linear elasticity theory. The experiments demonstrate that significant damage is produced in crystalline materials by the pore tension. Despite the induced stress measured by micro-Raman spectrometry to remain moderate, it is able to fracture the quartz. The volume of the cavity is a prominent controlling parameter for the stress amplitude. The crystalline heterogeneities of the solid are another major parameter for localizing the mean weak stress and accumulating overstress. Our results call for bringing pore-scale micromechanics into the safety assessment of the geological storage of various wastes inside depleted aquifers. They also show the magnifying effect of heterogeneities on propagating stress and localizing it along certain directions, promoting the final failure of water-bearing minerals, rocks, or pore networks. KEYWORDS: tensile strength, pore rock damage, storage safety, Raman scattering, quartz weakening, fluid inclusions 45 of chemical origin, which contributes to water weakening. 5,6 In 46 particular, imaging and quantification of the microstress in the 47 solid network, before and after fluid tension sets up in the 48 pores, have been missing until now. 49 The challenges associated with this area of research are first 50 in materials science in which several examples of tension-51 driven fracture processes still require mechanistic explanations 52 or quantification. While sol−gel processing explains how 53 drying-driven stress causes bodies to crack, how nanoparticle 54 suspensions dry is much less understood, depending 55 appreciably on molecular-scale physics combining capillary 56 and viscous forces (e.g. , refs. 7,8 ). How cementitious materials 57 dry is also of interest. There is little doubt there, ever since the 58 pioneering work 9,10 showing that the main driving force is

Fluid Pressure Changes Recorded by Trace Elements in Quartz

“…One reason is intrinsic to the fluid inclusion record, and results from the fact that, even within a single growth domain of quartz, fluid inclusions are trapped diachronously during fluid pressure variations. Then, there are extrinsic reasons for the fluid inclusion population to record varying pressures: (a) Post‐entrapment modifications of fluid inclusions, even methane‐rich, cannot be ruled out (Bodnar, 2003; Vityk & Bodnar, 1995a, 1995b; Vityk et al., 1994), these modifications being in some cases impossible to detect by optical microscopy (Mercury et al., 2021); (b) in the quartz veins considered, fluid inclusions are so abundant that some of them might be secondary, despite our effort to avoid them. For these extrinsic reasons, we believe that considering statistical variables such as average or median values, rather than all individual data points in the distribution, is a more robust analysis.…”

Mineralogical and Geochemical Characteristics of Banded Agates from Placer Deposits: Implications for Agate Genesis

“…They are related to the rotational or translational vibrations of [SiO4] and the symmetric stretching–bending vibration of Si–O–Si, respectively. 11 , 31 In addition, spectrum b exhibits a peak at 808 cm –1 caused by the symmetric stretching vibration of Si–O–Si in quartz. 32 In both spectra, the presence of goethite is confirmed by peaks at 205, 240, 300, and 403 cm –1 , while the peak at 501 cm –1 is attributed to moganite.…”

“…Both spectra show characteristic peaks of quartz at 126 and 465 cm –1 . They are related to the rotational or translational vibrations of [SiO4] and the symmetric stretching–bending vibration of Si–O–Si, respectively. , In addition, spectrum b exhibits a peak at 808 cm –1 caused by the symmetric stretching vibration of Si–O–Si in quartz . In both spectra, the presence of goethite is confirmed by peaks at 205, 240, 300, and 403 cm –1 , while the peak at 501 cm –1 is attributed to moganite. − In spectrum a, the presence of hematite is confirmed by peaks at 223, 288, and 606 cm –1 , and weak carbonate features are observed at 688 and 1067 cm –1 . , In spectrum b, the vibrational peaks of Si–O–Si and [SiO4] are observed at 268, 353, 916, and 1024 cm –1 , while the vibrational peak of Al–O appears at 737 cm –1 , and these peaks are characteristic of illite .…”