REMOTE DETECTION AND GEOCHEMICAL STUDIES FOR FINDING HYDROCARBON-INDUCED ALTERATIONS IN LISBON VALLEY, UTAH, AND GARZA FIELD, TEXAS

Long-term leakages of hydrocarbons develop diverse array of chemical and mineralogical changes in the form of alterations of rocks and soils. Alterations caused by microseepages are reported to have affected sandstones of Wingate Formation in Lisbon Valley, Utah, and of Dockum Group in Garza field, Texas. Alterations in Lisbon Valley include bleaching of redbeds, anomalous limonite and carbonate concentrations, anomalous weathering patterns and anomalous clay content. This study has developed new methodologies using spectroscopy, HYPERION hyperspectral and ASTER multispectral remote sensing data, Synthetic Aperture Radar data, and geochemical analyses (thin sections, ICP-AES analyses, carbon isotopes) to identify and map these changes and confirm the hydrocarbon microseepages source in Lisbon Valley. Using ASTER and HYPERION satellite images and SAR data, the altered areas of the Wingate Formation were identified and mapped at the northwest and southwest part of the Lisbon Valley anticline. Based on alterations three different zones were identified in the Wingate Formation; the southwest zone is the most altered, the middle part is unaltered, and the northwest part shows minor alterations. 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. Currently we are applying similar techniques in Garza field, Texas. Garza field is located along the northeast edge of the Permian basin. Producing rocks have an average depth of around 800m, and are overlain by red shales and sandstones of Dockum Group. Sandstones are in some areas discolored and those bleached mounds are then distributed in narrow areas. Bleaching of redbeds has previously been reported in Garza oil field, Texas, but no detailed work regarding analyses of hydrocarbon-induced alterations has been done. This methodology provides a new technique for petroleum exploration for use in remote regions of the world where the field work is difficult.