Detection Of Hydrocarbon Seeps Using Remote Sensing Technique In The Rufiji Onshore Basin

ABSTRACT

Hydrocarbon seeps cause chemical and mineralogical alterations at the surface, which can be identified geologically but also detected by remote sensing techniques. This work aimed at detecting mineral alteration induced by hydrocarbon seeps in a sandstone formation in Rufiji basin (Wingayongo), South Coast Tanzania. For this study, rock samples collected during fieldwork were petrographically analysed and the multispectral ASTER data was downloaded and utilized to characterize the identified alteration minerals in the Wingayongo sandstone. The area is covered by medium grained gray to brown chocolate bituminous sandstone, which acts as reservoir rock but with no cap rock overlaying it. The contact between sandstone layers were identified and defined as the main source of hydrocarbon migration pathways. Large area of this sandstone is bleached indicating discoloration of ferric iron into ferrous iron. Elemental sulfur greenish yellow in color together with sulphur smell were identified around the seep. Petrographic analysis (XRD and Thin Section) have shown high value of ferrous iron but there was no evidence of clay (kaolinite) or carbonate minerals. Remote sensing spectral signature through band ratio enhancement indicated the presence of siderite material, altered vegetation together with un-vegetation signals. The observed signals are potential vectors for oil seeps. Other prospective areas were identified using similar spectral signals in the surrounding areas. The use of more than one dataset together with the use of more powerful remote sensing technique are recommended to overcome challenges in interpretation and issues of scale of alteration and other controversor.