Hyperspectral analysis (VNIR-SWIR) applied to the characterization of a dolomitization context: a case study in Rio Bonito Quarry, Brazil

Hyperspectral analysis is of great potential use in the characterization of carbonate rocks, in special to the petroleum industry as they occur as reservoirs of oil and natural gas. In this context, the Rio Bonito Quarry was selected for the hyperspectral study because it is an analog of hydrocarbons reservoir, and previous studies indicate a complex context of multistage dolomitization with the generation of dolomitic breccia. The breccia shows three different generations of carbonates, a dolomitic phase in the clasts, and saddle dolomite with a late calcite phase in vugs. Hyperspectral signatures were determined using a non-imaging spectro-radiometer to understand which physical and chemical factors presented on the spectrum may be correlated to the dolomitization events. Position, depth, full-width half-maximum, and asymmetry were the hyperspectral parameters described for characteristic absorption bands of carbonate ions between 2320 and 2340 nm in the visible, near-infrared, and shortwave infrared region (350-2500 nm). The X-ray diffractometry analysis and the electron probe microanalysis were also applied to the samples to understand the chemical influence, while the physical parameters were investigated from the chromatic, porous, and granulometric aspects. The results show that the hyperspectral technique is capable to detect variations in color, granulometry, molecular water content, and the chemical composition of the carbonates, with Fe, Ca, Mg, and Mn content variations and even Ca2+ and Mg2+ substitution by Fe2+ in saddle dolomite. Therefore, the hyperspectral analysis is presented as an important characterization tool of complex dolomitization contexts such as the Rio Bonito Quarry.