Contents
of April, 1999 - Vol. XX No.2
INTEGRATED FACIES ANALYSIS TO IDENTIFY
DEPOSITIONAL ENVIRONMENTS IN EOCENE SEQUENCE IN KRISHNA-GODAVARI BASIN
K. Satyanarayana, G. N. Rao, M. S. K. Bhagwan and P. V. S. Prasad
INTERRELATIONSHIP OF BOUGUER REGIONAL
AND RESIDUAL GRAVITY ANOMALIES - A CASE STUDY FROM EARTHQUAKE - PRONE LATUR
REGION, MAHARASHTRA, INDIA
K. Mallick and K. K. Sharma
GEOPHYSICAL RESPONSES OF CHATTISGARH
REGION, MADHYA PRADESH, INDIA
S. Srinivas, A. S. K. Murthy, G. S. Yadav and K.M. Srivastava
TECTONIC HISTORY DEDUCED FROM A
COMBINED STUDY OF BOUGUER GRAVITY AND LINEAMENTS OF GONDWANA BASINS IN MAHARASHTRA
R. N. Padhi and T. S. Ramakrishna
S. K. Laskar
INFLUENCE OF RANDOM THERMAL CONDUCTIVITY
ON THE SUBSURFACE TEMPERATURE FLUCTUATIONS
Kirti Srivastava and R. N. Singh
INTEGRATED FACIES ANALYSIS TO IDENTIFY DEPOSITIONAL ENVIRONMENTS
IN EOCENE SEQUENCE IN KRISHNA-GODAVARI BASIN
K. Satyanarayana*, G. N. Rao**, M. S. K. Bhagwan*** and P. V. S.
Prasad****
*ONGC, Kanjurmarg, Mumbai
** Excom, SRBC, ONGC, Chennai
***Geology
Section, ONGC, Rajahmundry
****EBG,
ONGC, Nazira
Abstract
The hydrocarbon exploration in
Krishna-Godavari Basin was started with deep drilling in 1978 and so far more
than 250 wells were drilled over 125 structures. Though initial success was
registered in Upper Cretaceous sequence, now the basin has proved hydrocarbon
potential in all geological sequences from Pliocene to Permian. However, the
Eocene section towards south-eastern coastal tracts is found to be more
prolific. The lower Tertiary section in this part of the basin is identified as
separate petroleum system Paleocene argillaceous source, Lower Eocene sandy
reservoirs and middle Eocene carbonate cap facies.
In this paper, an attempt has been made
to integrate the available information including cores, electrologs and seismic
data to bring out a depositional model for most promising Lower Eocene sand
bodies which are identified as near-shore and/or channel fill deposits.
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INTERRELATIONSHIP OF
BOUGUER REGIONAL AND RESIDUAL GRAVITY ANOMALIES - A CASE STUDY FROM EARTHQUAKE
- PRONE LATUR REGION, MAHARASHTRA, INDIA
K. Mallick* and K. K. Sharma**
*National Geophysical Research Institute,
Hyderabad - 500 007
**Department of Applied Geology, University of Madras, Chennai - 600 025
Abstract
Bouguer gravity anomaly is often
partitioned into regional and residual components in order to model geological
structures. However, since the regional - residual by most of the existing
methods is seldom exact, there is a certain amount of uncertainty in the
interpretation. A new regional - residual separation scheme, based on finite
element approximation and briefly outlined in this paper, does not reduce such
uncertainties.
A case study of Bouguer gravity anomaly
in earthquake-prone Latur area, Maharashtra was chosen to compute the regional
and residual components by this scheme and establish their inter-relationships.
Ideally the regional and residual anomalies should be uncorrelated.
Computations show that the correlation coefficients between Bouguer and
regional, and Bouguer and residual are 0.789 and 0.529 respectively. The
regional and the residual anomalies, on the other hand, show a small inverse
correlation (correlation coefficient = - 0.105), thereby proving that the
regional and residual anomalies are nearly uncorrelated. A change in gradient
in regional gravity starting eastward from the epicentral region near Killari
appears tectonically significant. The NW-SE striking residual low in the
central part seems to correspond to a fracture zone.
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GEOPHYSICAL RESPONSES OF CHATTISGARH REGION, MADHYA PRADESH, INDIA
S. Srinivas*, A. S. K. Murthy**, G. S. Yadav** and K.M.
Srivastava**
*presently with National Geophysical Research
Institute, Uppal Road, Hyderabad - 500 007.
** Department of Geophysics, Banaras Hindu University, Varanasi - 221 005.
Abstract
Under the deep continental studies
project, gravity surveys were undertaken along a transect of 382 Km. length in
near east-west direction across the Chattisgarh region, Madhya Pradesh, India.
An attempt is made to address the gravity and magnetic signatures in terms of
lithological and structural features for the first time, which were so far
remained uninvestigated in good deal. The gravity and magnetic responses of the
region are quite revealing. The gravity profile defined the Chattisgarh basin
configuration and demarcated the Sakoli metasedimentary belt and Sonakhan
greenstone belt on either side of the Chattisgarh basin. The Chattisgarh basin
recorded a broad magnetic high compared to Sakoli belt and Sonakhan anomalies brought
out the presence of possible basic intrusives into the sediments/basement.
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TECTONIC HISTORY DEDUCED
FROM A COMBINED STUDY OF BOUGUER GRAVITY AND LINEAMENTS OF GONDWANA BASINS
IN MAHARASHTRA
R. N. Padhi and T. S. Ramakrishna*
Retired, Geological Survey of India
*'The Anomaly', 1250 B, Road No. 62, Jubilee Hills, Hyderabad - 500 003
In the present study, lineaments as
identified from the Landsat (MSS) imagery of the Gondwana basins and adjoining
terrain in Maharashtra are analyzed together with the Bouguer gravity map of
the area so as to obtain a more conclusive information in respect of
deep-seated features and related tectonic history of the area. It is observed
that basin boundaries of the Gondwana coincide with gravity lineaments while
the imagery lineaments show lateral shift away from these boundaries.
The deposition of Gondwana rocks, as
studied from geology, geomorphology, geophysics and tectonics of the area,
appears to be controlled by i) two major NW-SE trending crustal faults passing
through Hinganghat and Kharsingi in the south and central parts, ii) a two
stage crustal subsidence in the northern part in the Katol basin, iii) fan
shaped palaeo depressions around Nagpur and iv) a few subbasinal faults.
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COMPUTATION OF GRADIENTS
OF TWO-DIMENSIONAL POTENTIAL FIELDS FROM BOUNDARY DATA: THEORY AND PRACTICE
S. K. Laskar
Department of Mathematical Sciences, Tezpur
University, Tezpur - 7840001, Assam
Abstract
Gradients of a potential field are
computed on reproduction of the field from boundary data by simple and double
layer boundary sciences. It is shown theoretically that the gradients computed
at the boundary are highly sensitive to error in input data, the normal
derivative appearing with more error than the tangential derivative. The error
in them considerably reduces when computed at a level above boundary. It is
shown that the horizontal gradient computed at a higher level is stable and
more reliable than the vertical gradient computed at the same level.
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INFLUENCE OF RANDOM THERMAL CONDUCTIVITY ON THE SUBSURFACE TEMPERATURE
FLUCTUATIONS
Kirti Srivastava and R. N. Singh*
National Geophysical Research Institute, Uppal
Road, Hyderabad 500 007, India
*CSIR Center for Mathematical Modelling and Computer Simulation (C-MMACS) NAL,
Belur Campus, Bangalore, 560 037, India.
Abstract
The subsurface rocks show complex
variability in the thermal parameters and sources. As the knowledge of the
subsurface thermal fields is being increasingly used in understanding global
processes, it is necessary to study the heat, conduction problem in a
stochastic framework. In this paper the stochastic heat conduction equation has
been solved by a new pertubation method incorporating randomness in the thermal
conductivity to estimate analytically the first two statistical moments i.e,
mean and variance of the temperature field. The randomness in the thermal conductivity
is expressed by a mean part plus a fluctuation part where the fluctuation part
is represented by a known correlation function. The information on the
correlation on the correlation structure for most geological situations is
easily available. The analytical expression obtained for the variance in
temperature reveals that it is a function of the coefficient of variability of
the thermal conductivity and the correlation length scale. The methodology
developed in this paper has been applied to a sedimentary basin example.
Results obtained bring out the thermal state with its associated error bounds.
The error bounds is seen to broaden with depth and increases with an increase
in the coefficient of variability in the thermal conductivity.