NOVEL GEOPHYSICAL APPROACH TO INVESTIGATE CALCITE PRECIPITATION’S DEPENDENCY ON FLUID PROPERTIES

Abstract:

Oolite sand shoals are a common type of carbonate system and play important roles in preserving modern coastlines with rising and falling sea levels. Calcite precipitation alters the microstructure of oolitic sediments and can lead to significant reduction of permeability in a carbonate system. Such pore alteration process is highly heterogeneous and dynamic, and is strongly affected by pore fluid flow through the system. Therefore, studying calcite precipitation’s dependency on different types of pore fluid flow is essential to understand the processes of calcite precipitation associated with carbonate early lithification. Previous studies have shown the non-invasive geophysical tools, like spectral induced polarization (SIP), have the ability to monitor in-situ calcite precipitation and to provide spatiotemporal information on petrophysical properties of porous media. In this study, a novel monitoring method involving SIP technique in conjunctions with reactive transport simulations is applied to investigate the dynamic evolution of petrophysical properties in oolitic sediments column experiencing calcite precipitation. Calcite precipitation was induced both by introducing supersaturated solution with respect to calcite(cement) and aragonitic ooids(substrate) and by injecting CaCl₂ and Na₂CO₃ solutions into the system at two different locations. Our results recognized that calcite precipitation’s dependency on the composition of fluid flow through the porous media and method of inducing calcite precipitation is strong. The reactive transport models indicate the velocity profile and rate of precipitation are significantly different from one another. The ion concentration analysis (ICP-OES) and scanning electron microscopy (SEM) imaging results confirmed the different calcite precipitation rates and distributions. The proposed monitoring method can advance our ability to quantify the geochemical changes from non-invasive geophysical measurements, as well as in understanding the evolution of fluid flow in complex natural subsurface system and engineered treatments.