Emissivity Mapping of Onshore Sedimentary Basins for Hydrocarbon Exploration

Abstract

Satellite remote sensing may be used for mapping onshore hydrocarbon microseeps and is a useful and inexpensive tool for unconventional hydrocarbon exploration. Visible, Near Infrared [VNIR] and Shortwave Infrared [SWIR] satellite systems may be used to map surface alteration associated with buried hydrocarbons while Midwave and Longwave Infrared [MWIR/LWIR] sensors can be used to directly map fugitive gas exhalations by direct detection of the transmission and absorption spectra of methane gas. We present several examples including the Owambo Basin in Northern Namibia where apparent thermal inertia maps the Otavi Group Carbonates which are associated with hydrocarbon deposits. The Kwanza basin in Cabinda yields a thermal signature for marine limestone/shale lithologies which correlate well with the location of known oil and gas seeps mapped by Sonangol. In the onshore portion of the Potiguar Basin of northeastern Brazil hydrocarbons occur in the Acu sandstone formation for which a unique thermal emissivity signal exists which may be extracted from Aster satellite imagery. 90m spatial resolution LWIR images were corrected for temperature/emissivity and decomposed into 16 spectral mixtures. We are in effect assuming the emissive response (which may be sensed through moderate vegetation and transported cover) is a linear combination of up to 16 different geological units. Three of these units are identified as sandstone and show good correlation with well locations. The best correlation is with the mapped Jandaira formation while micaceous red sandstone, ferruginous sandstone and fossiliferous limestone units are also mapped. Thanks to the emissivity property of rocks and minerals, thermal signatures may be unmixed from targets covered by moderate amounts of vegetation and transported materials. While 90m spatial resolution with 5 spectral bands between 8.3 and 11.3 microns is spatially and spectrally relatively crude, hyperspectral airborne thermal scanners are available to increase the number of bands by an order of magnitude while decreasing spatial resolution to around 5m. Satellite and airborne remote sensing thermal imagery offers a rapid, cost effective means of generating targets for onshore hydrocarbon and exploitation of shale hosted hydrocarbon resources via fracking.

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018