Molecular dynamics study of confined water in the periclase-brucite system under conditions of reaction-induced fracturing

Reaction‐Induced Fracturing: When Chemistry Breaks Rocks

“…This effect would then reduce the access of water to mineral surfaces and decrease the overall kinetics of reaction. Molecular dynamics simulations demonstrate that increasing normal stress can squeeze out the water between periclase surfaces (Guren et al, 2021). These simulations, motivated by the experimental results of Zheng et al (2019), indicate that above 30 MPa effective pressure only one water layer is confined between periclase surfaces, over a range of temperatures from ambient to 250°C.…”

“…This effect would then reduce the access of water to mineral surfaces and decrease the overall kinetics of reaction. Molecular dynamics simulations demonstrate that increasing normal stress can squeeze out the water between periclase surfaces (Guren et al., 2021). These simulations, motivated by the experimental results of Zheng et al.…”

“…Other effects may therefore cancel swelling at pressures much lower than the theoretical limit. For example, the squeezing of the water film at grain contacts, could reduce the actual swelling pressure by stopping the chemical reaction along grain boundaries (Guren et al., 2021). One consequence of this effect would be that complete serpentinization of oceanic crust may be reached only in the first kilometers near the surface, where the confining pressure is low enough to allow a positive feedback between volume increase and fracturing, unless external perturbations such as earthquakes or thermal cooling continue to fragment the rock and produce new reactive surfaces.…”

“…The authors reproduce and quantify the fracture patterns observed in serpentinized oceanic lithosphere rocks collected during the Oman Drilling Project. Their study is complementary to recent studies where laboratory experiments (Zheng et al, 2019;Zhu et al, 2016) and numerical modeling (Guren et al, 2021;Zhang et al, 2019) have identified key parameters that control the rate of reaction-induced fracturing and identified under which conditions this rate may increase or decrease. These parameters include the temperature, the amount of available water, the effective pressure, and the strength and initial porosity of the rock.…”

“…These microfractures lengthen and widen with increasing reaction and accommodate the dilation of the rock (O'Hanley, 1992). However, negative feedbacks may cause reaction‐induced fracturing to be self‐limiting because fluid‐rock reactions that increase the solid volume may (i) fill the pore space and thus reduce permeability (Aharonov et al., 1998), (ii) passivate the solid‐fluid interface with reaction rims, (iii) close existing fracture and prevent fracture propagation due to the local increase of confining pressure, and (iv) reduce the access of water to grain‐grain boundaries by squeezing out the confined water film (Guren et al., 2021).…”