Effect of Fluid Chemistry on the Interfacial Composition, Adhesion, and Frictional Response of Calcite Single Crystals—Implications for Injection‐Induced Seismicity

Abstract

While it has been shown that the mechanical properties and the reactivity of carbonate‐bearing rocks may be influenced by the chemical composition of the fluids, little is known about how the fluid composition affects their frictional response. Here, we have used atomic force microscopy to investigate the frictional characteristics of single calcite crystals in calcium carbonate saturated solutions and in two brines, NaCl and CaCl2, at a wide range of geologically relevant concentrations. Surface forces were measured to determine the ion‐specific composition of the confined fluid films and the adhesion between the confining surfaces. The effect of fluid chemistry on calcite's (dynamic) frictional response significantly depends on the normal stress. At low stresses, the confined fluid film lubricates the single‐asperity contact efficiently, resulting in low friction coefficients, especially in the case of NaCl solutions. When the pressure solution of calcite is triggered at sufficiently high stress, a significant reduction of the friction coefficient was observed, and in this case, CaCl2 solutions were shown to promote this frictional weakening more significantly than NaCl. This is the first experimental investigation of the ion‐specific frictional characteristics of calcite at the level of a single‐asperity contact. The presence of infiltrated fluids in carbonate faults may also play a critical role in fault dynamics. Hence, the results of this nanoscale study are extrapolated to carbonate fault friction in the presence of infiltrated fluids, and they contribute to advance our understanding of induced seismicity at geological scale.

Velocity-weakening and -strengthening friction at single and multiasperity contacts with calcite single crystals

“…6 A ). Although in our previous studies on smooth calcite crystals ( 11 , 12 ), we did not notice this linear relation, we have confirmed that it describes those reported results as well.…”

“…A few atomic force microscopy (AFM) studies ( 14 – 17 ) have reported the stress-induced dissolution of minerals also while sliding. Our nanoscale studies with an AFM tip sliding on atomically smooth calcite crystals ( 11 , 12 ) showed a remarkable decrease of the kinetic friction coefficient and a prominent deviation from at high normal stresses. Experiments with a surface forces apparatus (SFA) revealed that the decrease in friction happens concurrently with the pressure-induced dissolution of calcite ( 13 ), a lubrication mechanism that we called “pressure solution–facilitated slip” ( 11 ).…”

“…Nanoscale friction measurements can help us understand the mechanisms underlying the frictional response of geological materials ( 8 – 17 ). The kinetic friction at nanoscale single-asperity dry contacts exhibits often increasing and/or decreasing trends with , like the direct and evolution effects in the RSF law.…”

The dynamic nature of natural and fatty acid modified calcite surfaces

“…In recent years, the complex processes occurring at calcite surfaces in contact with water have also been investigated by direct force measurements using techniques such as AFM 85,[103][104][105][106][107] and the surface forces apparatus (SFA). 85,108,109 The difference between these measurements and those reported previously is that the focus has shifted to events taking place between two calcite surfaces under compression and in close contact.…”