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

COMPUTATION OF GRADIENTS OF TWO-DIMENSIONAL POTENTIAL FIELDS FROM BOUNDARY DATA: THEORY AND PRACTICE
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


Abstract

 

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.

 

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