PNNL

Abstract

Thin sections and hand samples from 50 sidewall cores from the Wallula Basalt Pilot Demonstration, a carbon sequestration project, provide the opportunity for in-depth analysis of the formation of carbonate minerals formed in situ from the injection of supercritical CO2. Previously, extensive carbonate mineralization was found, mostly in the form of nodules, but also as cement and aragonite. It has also been found that the nodules are chemically zoned and are Mn and Ca rich in their cores and the outer regions are Fe and Ca rich. The aim of this study is to characterize the physical and chemical characteristics of the carbonate material within the three target injection zones and between them, in the context of the mineralogy of the host rock. The mineralogy is different among the three zones, as are the morphology and sizes of the carbonate nodules. Techniques for analysis included petrographic and scanning electron microscopy-energy dispersive X-ray spectroscopy. There are many similarities among zones, but each zone also has its unique features regarding the size and morphology of nodules. Here we report a possible dependence on nodule morphology on mineralogy of the host rock, and structural heterogeneities in the carbonate nodules.