Remote detection and geochemical studies for finding hydrocarbon-induced alterations in Lisbon Valley, Utah

Abstract

Long-term hydrocarbon microseepages develop diverse arrays of chemical and mineralogical changes in rocks and soils. Alterations that are reported to have affected the Wingate Sandstone, Lisbon Valley, Utah, include bleaching of red beds, precipitation of high limonite and carbonate concentrations, anomalous weathering patterns, and high clay content. To investigate sandstone color alteration patterns, spectroscopy, ASTER multispectral remote sensing and Synthetic Aperture Radar (SAR) data were used as well as geochemical analyses of selected samples. Using ASTER satellite images and SAR data, the altered areas of the Wingate Sandstone were identified and mapped at the northwest and southwest part of the Lisbon Valley anticline. Based on sandstone color alteration patterns three different zones were identified in the Wingate Sandstone; the southwest zone is the most altered, the middle part is unaltered, and the northwest part shows minor alteration. Spectroscopy and thin section studies revealed higher content of clay minerals in altered than in unaltered zones. Major elemental concentrations suggest removal of iron cement and addition of calcite during diagenesis. Trace elemental concentrations in selected altered sandstone samples are characteristic of geochemical halos forming over oil fields. The methodology being developed in this work can provide a completely new technique for petroleum exploration in remote regions of the world where field work is difficult.