Abstract
Mineral precipitation significantly alters the transport properties of fractured rock. Chemical solubility gradients that favor precipitation induce mineral growth, which decreases the local aperture and alters macro-scale flow and transport properties. We present experimental results that quantify the influence of aperture variability on the evolution of mineral growth patterns in a transparent, analog fracture. A continuous flow ISCO pump injected a supersaturated calcite solution, O = 31.6, into our analog fractures at 0.5 ml/min. Light transmission techniques quantified the evolution of local transmissivity and transport. Preliminary results from these experiments demonstrate that minerals preferentially precipitate in small aperture regions. This enhanced reduction of low transmissivity regions in turn catalyzes the organization of preferential flow paths, which persist despite continued mineral precipitation.
1. INTRODUCTION
Mineralization of dissolved ions in the subsurface leads to local changes in permeability and perturbs transport characteristics. Understanding the feedback between permeability reduction and transport is critical to engineered systems such as geologic storage of supercritical CO2 [1, 2], enhanced soil stabilization [3, 4], and co-precipitation of heavy metals in contaminated aquifers [5, 6]. Induced mineralization is commonly engineered using two approaches: (1) barrier production along a mixing interface [7,8], and (2) distributed mineralization via the injection of a solution that becomes supersaturated throughout the formation [9,10]. The gradual transition to mineralization using approach (2) results in growth structures that alter transmissivity in dramatically different ways [11, 12]. Our ability to predict the outcome of induced mineralization strategies relies on our mechanistic understanding of the feedback between mineral precipitation, transmissivity reduction, and solute transport.
A number of sources suggest that the distribution and extent of transmissivity reduction can be controlled using microbially induced calcite precipitation (MICP) strategies [9, 13, 14]. This approach relies on coupled physical, chemical, and biological mechanisms that change local properties. In fractured rocks, MICP is expected to reduce fracture aperture, but the parameters that control the temporal and spatial distribution of mineral precipitation are not well understood.
