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

Oolite sand shoals are common in the ancient rock record, not only forming very productive hydrocarbon and water reservoirs, but also playing important roles in preserving modern shorelines with rising and falling sea levels. The stability of oolite sand shoal is affected by early cementation process. Such cementation process associated with calcite precipitation is dynamic and controlled by pore fluid flow in particular. Therefore, it is imperative to study the impact of fluid type on calcite precipitation and the petrophysical evolution which would help understand the hydrogeological variability. Previous studies have shown that non-invasive geophysical tool such as spectral induced polarization (SIP) has the ability to non-invasively monitor in-situ calcite precipitation and to provide spatiotemporal information on petrophysical properties of porous media. In this study, a novel approach 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 by 1) directly introducing supersaturated solution with respect to calcite (cement) and aragonitic ooids (substrate) and 2) 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. This study advances 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.