Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Estimation of the Basalt and the Underlying Sediments from Seismic, Gravity, and Geological Data - A Case Study in the Chambal Valley in the Western Part of the Proterozoic Vindhyan Basin, India
(1) Geophysics, ONGC, Dehradun, India.
(2) WOB, Mumbai, ONGC, Mumbai, India.
The Vindhyan basin , is located on the Bundelkhand craton in central India, is one of the largest Proterozoic sedimentary basins of India .The basin is considered to be a high-risk, high-gain frontier area for exploration because of presence of gas and oil show in various levels of pre-Cambrian sediments in some of the exploratory oils. Search for hydrocarbon prospects in sediments underlying basalt have given a new dimension to exploration activities now a days. The presence of thermogenic Methane to Pentane underneath Basalt in Chambal valley of Vindhyan basin clearly indicates existence of favorable petroleum system. Limitation of conventional P-wave seismic method in imaging sub-basalt prospect is well known .
In such areas potential field inputs like Gravity and Magnetic data can address the problem of distribution of sediments. Chambal valley sector is bounded by the latitude 25°30'N to 21°30'N and Longitude 75°E to 77°E. Major part of the Chambal Valley is covered with Basalt. Only a limited part in the where Basalt is more or less absent is covered with seismic that too with a sparse grid. There is no well drilled at present in the Chambal valley.
The objective of the study is to derive the regional thickness of Basalt and then to determine depth to the Basement .In the present study, first a model is conceptualized with seismic, gravity magnetic and surface geological data in the north of the valley where Basalt is exposed and then the model has been extrapolated in the south integrating with surface and gravity and topographical data.
A notable feature in the seismic data of the area is its correlation with gravity data in a quantitative sense. There is a fall of only about 5 mGal across a major thrust having a throw of about 5 km (2T ~ 2.5 sec). This is followed by sharp gravity rise (~10 m gal ) towards the gravity high whereas the seismic marker rises to a few hundred meter. This has been explained with a high density crystal block in the northeast.
Results of modeling suggest that the Basement depth along the two regional north-south profiles taken for the study varies from 4-8 Km and the depth of Basalt is of the ranges 100 mar to1km approximately except in some areas near the thrust plain where the Basalt thickness may rise to near about 1.5 km and thickness of the Mesozoic is coming out to be 3 to 7 km. The thickness of the Basalt and the Mesozoic increases from north to south of the Chambal Valley.