Geomorphic analysis of upper Assam Plains and adjoining areas for hydrocarbon exploration

Abstract

‘Terrain Analysis’ of the the Assam Plains and adjoining areas of the Naga foothills and Mikir hills plateau has been carried out using LANDSAT images and cartographic maps, essentially as an aid for planning seismic surveys for hydrocarbon exploration. The terrain is divisible into five geomorphic zones of distinct characters and processes of evolution. They are: i) Brahmaputra flood plains, ii) Assam Alluvial Plains, iii) Naga Piedmont plains, iv) Mikir Denudational hills, and v) Naga Structural Hills. A number of geomorphic anomalies have been identified in these zones. Maximum number of the anomalies occur in the piedmont zone which is considered to be most prospective since suitable hydrocarbon generation and entrapment conditions exist in that part of the basin. There dominant trends of lineaments striking ENE-WSW NW-SE and E-W are observed in the area in that order of extent and frequency. The last mentioned appears to be youngest which has off-setted even the Naga Thrust. Five distinct planation surfaces/summit levels have been identified in the Mikir as well as Naga hills. They are correlatable with the known unconformities at the top of basement, top of Barails, top of Girujan, top of Namsang and top of Dihing Formations. The subsurface lithology expected during shot hole drilling for seismic surveys has been predicted considering the process of evolution of each zone.