Structural Evolution of the Northern Assam Basin: A Case for a Dynamic Hydrocarbon System Model*
By
W. Norman Kent1
Search and Discovery Article #10111 (2006)
Posted September 25, 2006
*Oral presentation at AAPG Annual Convention, Houston, Texas, April 9-12, 2006
Click to view presentation in PDF format (~2.7mb).
1Kent GeoScience Associates, Richmond, TX ( [email protected] ).
Abstract
The upper Assam basin is an intermountain basin
surrounded on three sides by fold and thrust belts. The area is known as one of
the most seismic
active areas of the world. It has experienced two of the
largest earthquakes in recorded history. Upper Assam basin is also the home to
two of the world's largest oil and gas fields. These two superlative
characteristics of the basin suggest the temporal nature of oil and gas
accumulations and underline the significance of viewing petroleum systems as
dynamic processes as opposed to static entities.
An integrated regional study was conducted part of a
petroleum exploration program of the Jaipur anticline area. In this study,
structural modeling
and sequence stratigraphy techniques were used to define the
stratigraphic and structural evolution of the basin and to relate that geologic
history to timing of maturation and migration of hydrocarbons.
During the study, regional unconformities,
recognizable on geologic maps, seismic
profiles and well logs, were identified.
Mapping truncation of formations at each of the unconformities and construction
of isopach maps provided insight into the development of regional structural
features. Maturity data for the source rocks in the basin indicate that
hydrocarbon generation began as early as mid-Oligocene, with a major pulse
occurring in late Miocene. These data also show that the source rocks are now at
peak maturity for oil generation in parts of the basin. This interval of
hydrocarbon generation includes nearly the entire time in which the region
evolved from an extensional plate margin to an intermountain basin between two
orogenic belts. Sustained hydrocarbon generation throughout a complex structural
history implies a complex history for migration and accumulation of hydrocarbons
in the basin.
Selected Figures