Chemomechanical evolution of pore space in carbonate microstructures upon dissolution: Linking pore geometry to bulk elasticity

Abstract

One of the challenges faced today in a variety of geophysical applications is the need to understand the changes of elastic properties due to time‐variant chemomechanical processes. The objective of this work is to model carbonate rock elastic properties as functions of pore geometry changes that occur when the solid matrix is dissolved by carbon dioxide. We compared two carbonate microstructures: porous micrite (“mudstone”) and grain‐supported carbonate (“packstone”). We formulated a mathematical model that distinguishes the effects of microporosity and macroporosity on stiffness changes. We used measures of mechanical and chemical porosity changes recorded during injection tests to compute elastic moduli and compare them to moduli obtained from wave velocity measurements. In mudstones, both experimental and numerical results indicate that bulk moduli change by less than 5%. The evolution of elastic moduli is controlled by macropore enlargement. In packstones, model predictions underestimate changes of elastic moduli with total porosity by 10% to 80%. The total porosity variation is 60% to 75% smaller than the chemical porosity variation, which indicates that pore expansion due to dissolution is counterbalanced by pore shrinkage due to compaction. Packstone elastic properties are controlled by grain sliding. The methodology presented in this paper can be generalized to other chemomechanical processes studied in rocks, such as dislocations, glide, diffusive mass transfer, recrystallization, and precipitation.

A review of geochemical–mechanical impacts in geological carbon storage reservoirs

“…For most models, a dual porosity, nano-and micropores, is taken into account. [173][174][175] Finally, a few models take into account the heterogeneity of the solid skeleton. 173,175 The major challenge consists in predicting the evolution of the poroelastic properties, yield criterion, and failure behavior as a function of physical (e.g., porosity) and compositional parameters that can be derived from drilling logs for input into large-scale reservoir geomechanical simulation tools.…”

“…In general, a granular microstructure is modeled, which agrees with microstructural observations. For most models, a dual porosity, nano‐ and micropores, is taken into account . Finally, a few models take into account the heterogeneity of the solid skeleton .…”

“…A limitation of the model was the large role attributed to the interface between carbonate grains and the surrounding cement phase, with limited independent experimental validation. Arson and Vanorio proposed a similar two‐scale porosity scheme to model alterations in elastic properties in mudstone and capstone resulting from geochemically induced changes. Geomechanical changes were attributed to pore changes of two kinds: porosity compaction under stress and porosity enhancement caused by dissolution.…”

Pressure Solution Compaction During Creep Deformation of Tournemire Shale: Implications for Temporal Sealing in Shales

“…Active deformation mechanisms underlying this mechanical behavior include grain rearrangement, micro‐cracking, subcritical crack growth, dislocation gliding, and diffusive mass transfer promoted by pressure solution processes. Significant progress has been made in understanding brittle to semi‐brittle failures (Fredrich et al., 1989; Nicolas et al., 2017a; Paterson & Wong, 2005; T. F. Wong et al., 1997), but most studies primarily focus on underlying mechanical processes instead of chemo‐mechanical interactions (Arson & Vanorio, 2015; Vanorio et al., 2011). Evidence suggests that chemical fluid‐rock interaction processes, such as crack sealing and creep compaction, might enhance the sealing capacity and inter‐seismic strength gain/recovery of rocks (Beeler et al., 2001; Hickman & Evans, 1995; Lang et al., 2015).…”

Self‐similar distributions of fluid velocity and stress heterogeneity in a dissolving porous limestone

“…Elastic properties change during rock transformation (dissolution and precipitation) and depend on the initial microstructure [ Wojtacki et al , ]. For example, if either micropores or macropores dissolve preferentially in a limestone rock, the resulting change of elastic parameters and seismic wave velocities would be different [ Arson and Vanorio , ].…”