Localized reactive flow in carbonate rocks: Core‐flood experiments and network simulations

Abstract

We conducted four core‐flood experiments on samples of a micritic, reef limestone from Abu Dhabi under conditions of constant flow rate. The pore fluid was water in equilibrium with CO2, which, because of its lowered pH, is chemically reactive with the limestone. Flow rates were between 0.03 and 0.1 mL/min. The difference between up and downstream pore pressures dropped to final values ≪1 MPa over periods of 3–18 h. Scanning electron microscope and microtomography imaging of the starting material showed that the limestone is mostly calcite and lacks connected macroporosity and that the prevailing pores are few microns large. During each experiment, a wormhole formed by localized dissolution, an observation consistent with the decreases in pressure head between the up and downstream reservoirs. Moreover, we numerically modeled the changes in permeability during the experiments. We devised a network approach that separated the pore space into competing subnetworks of pipes. Thus, the problem was framed as a competition of flow of the reactive fluid among the adversary subnetworks. The precondition for localization within certain time is that the leading subnetwork rapidly becomes more transmissible than its competitors. This novel model successfully simulated features of the shape of the wormhole as it grew from few to about 100 µm, matched the pressure history patterns, and yielded the correct order of magnitude of the breakthrough time. Finally, we systematically studied the impact of changing the statistical parameters of the subnetworks. Larger mean radius and spatial correlation of the leading subnetwork led to faster localization.

Evolving Viscous Anisotropy in the Upper Mantle and Its Geodynamic Implications

“…However, Hansen, Warren, et al's (2016) laboratory experiments were only able to test a small number of deformation paths (i.e., first extension, then torsion, and vice versa), making it difficult to directly apply their results to deformation in the mantle. To apply their results more generally to mantle deformation, Hansen, Conrad, et al (2016) used the existing experiments to define and calibrate a mechanical model of slip system activities and texture development within olivine aggregates. This model can predict both the evolution of olivine textures and the associated anisotropic viscous behavior for olivine aggregates undergoing arbitrary deformation paths.…”

“…Here we have modified the director method to accommodate three-dimensional deformations of olivine aggregates using the micromechanical approach of Hansen, Conrad, et al (2016). This model is calibrated by laboratory constraints on slip system activities and parameters of texture development (i.e., the relative rotation rates of the different olivine slip systems, see Table 1 in Hansen, Conrad, et al, 2016.…”

The Role of Chemistry in Fracture Pattern Development and Opportunities to Advance Interpretations of Geological Materials

“…A campaign of experimental rock mechanics testing under reactive conditions is needed. Some work in this direction is already being undertaken (e.g., Brantut et al, 2012Brantut et al, , 2013Bernabé & Evans et al, 2014;Evans, 2005;Kubicki & White, 2008;Rinehart et al, 2016;Wang et al, 2016). Possibly, the use of artificial or engineered rock/fracture systems with artificial cement could circumvent challenges of replicating high-temperature/pressure conditions.…”

An Analytical Algorithm of Porosity–Permeability for Porous and Fractured Media: Extension to Reactive Transport Conditions and Fitting via Flow-Through Experiments Within Limestone and Dolomite

“…Reactive transport models are increasingly popular for predicting the long-term evolution, performance, and lifetimes of geothermal reservoirs (Steefel and Van Cappellen 1990;Appelo and Postma 2005;Steefel et al 2005;Xu et al 2014;Menke et al 2016;Wang et al 2016). However, they rely on published thermodynamic and kinetic databases that span limited ranges of temperature, pressure, and composition compared to natural systems.…”

“…Also, several authors have observed that n can also be a function of fluid composition. For example, CO 2 can influence fluid-rock interaction within limestone, dolomite, and sandstone systems, either where added alone (Noiriel et al 2004;Luhmann et al 2012Luhmann et al , 2014Hao et al 2013;Tutolo et al 2014Tutolo et al , 2015Huq et al 2015;Soong et al 2016;Smith et al 2017) or as CO 2 -saturated brine (Kong et al 2016;Wang et al 2016;Orywall et al 2017).…”