Overpressure in a Compressional Tectonic Setting: The Eastern Bengal Basin

M. S. Hossain¹, A. Uddin¹, M-K. Lee¹, C. E. Savrda¹, W. E. Hames¹, and B. Imam^2
1Department of Geology and Geography, Auburn University, Auburn, AL 36849
²Department of Geology, University of Dhaka, Bangladesh

The majority of the wells drilled so far in eastern fold belts and foreland basin areas of the Bengal basin have encountered overpressured zones in lower Miocene Bhuban Formation (Surma Group) at depths ranging from less than 1 km (well Patharia-5) to 4.5 km (Muladi-1). The basin is surrounded on three sides by the Indian craton, the Himalayas, and the Indo–Burman ranges; and has served as a southward-migrating depocenter of rapid orogenic sedimentation since the early Miocene. The incomplete dewatering of fine–grained sediments, clay diagenesis, and tectonic compression associated with the Indo–Burman ranges are possible causes for overpressure development in the Bengal basin. Based on similar studies of Tertiary deltaic sequences elsewhere, it seems probable that the overpressure zones were caused by compactional disequilibria of thick, rapidly deposited mudrock sequences in the Bhuban Formation. In addition, clay dehydration may have contributed in increasing overpressure; illitization and clay dehydration in Neogene Surma Group argillaceous sequences have been reported in a number of wells in the area.

An integrated approach has been adopted to study the distribution of overpressured zones in the eastern Bengal basin and their relation to compressional tectonics by analyzing geophysical and lithologic logs and subsurface sediment core samples from various exploratory wells.

AAPG Search and Discover Article #90087 © 2008 AAPG/SEG Student Expo, Houston, Texas