Landsat Thematic Mapper and G.S.I. special applications to the mapping of fractures in the Austin Chalk of south central Texas

Abstract

Specially processed Landsat Thematic Mapper (TM) data are calibrated to the spectral characteristics of the greater Pearsall Oilfield deduced from geochemical and laboratory spectral analyses of soil samples to develop a model for hydrocarbon exploration in the Austin Chalk of the south central Texas. Initial Landsat reconnaissance of the study area reveal enigmatic lineaments, the nature of which is unknown since the generic relationships between remotely sensed data and oilfield parameters are poorly understood. The possibility that stressed vegetation observed in TM images and on the ground are manifestations of migrating petroleum hydrocarbons is examined. Geochemical analyses (headspace, total scanning fluorescence, and gas chromatography) demonstrate that migrating petroleum exists along the mapped distribution of TM derived lineaments. Laboratory spectral analysis suggests that carbonate enriched zones, hypothesized to overlie oil seeps, may be discerned on TM images if a modified principal component analysis (PCA) technique is applied to TM data. Image analysis reveals that lineaments share nearly identical azimuths with fracture orientations published in independent sources. Interpretation of laboratory analytic results, the PCA images, and seismic data demonstrate that the TM derived lineaments are the surface traces of oil-bearing fractures and faults that extend down to the buried (+5000 feet) Austin Chalk. Further, migration pathways are interpreted as being collimated, that is, restricted to these faults and fractures. Application of this new method of exploration successfully addresses the need for quick, accurate, and low cost identification of high probability horizontal drilling azimuths in fractured reservoirs.