Contents of April, 1998 - Vol. XIX No.2
SEISMIC VELOCITY FOR MATURITY ASSESSMENT: UPPER ASSAM
BASIN, INDIA
R. K. Mallick, S. V. Raju and K. D. Gogoi
SEISMIC VELOCITIES FOR EFFECTIVE PLANNING OF
EXPLORATORY WELL IN VIRGIN AREA - A CASE FROM NORTH BANK AREAS OF UPPER VOLTA
C.
S. Singh, A. K. Khanna and S. N. Singh
PROCESSING AND INTERPRETATION OF GROUND MAGNETIC DATA
ACQUIRED ALONG SILCHAR-IMPHAL-MOREH CORRIDOR (EASTERN CACHAR AND MANIPUR AREA)
D.
Rai and V. Ramaswamy
APPLICATIONS OF MISFIT
FUNCTION TOPOGRAPHY IN GEOPHYSICAL MODEL OPTIMIZATION
Saurabh K. Verma, Makku Pirttijarvi and Sven-Erik Hjelt
AN INTEGRATED CRUSTAL MODEL
ALONG NAGAUR - JHALAWAR GEOTRANSECT
D. C. Mishra, Bijendra Singh, V. M. Tiwari, S. B. Gupta, N.
Kameswara Rao and M. B. S. Vyaghreswar Rao
STUDY OF THE UTTARKASHI
EARTHQUAKE IN TERMS OF RUPTURE MODEL AND ISOSEISMALS
A. Joshi
SEISMIC VELOCITY
ANALYSIS FOR MATURITY ASSESSMENT:
R.K Mallick*, S.V. Raju* and K.D. Gogoi**
*Oil India Limited, Assam
786 602 India
**Department of petroleum technology, Dibrugarh University ,
Assam , India
Abstract
The Upper Assam foreland basin is an
important onshore petroliferous region of
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SEISMIC VELOCITITIES
FOR EFFECTIVE PLANNING OF EXPLORATORY WELL IN VIRGIN AREA - A CASE STUDY FROM
NORTH BANK AREAS OF UPPER ASSAM
C. S. Singh, A. K. Khanna, S. N. Singh
GDAP Department, Oil India Limited, Duliajan , Assam
Abstract
The continuing exploration venture of
Oil India Limited (OIL) in the south bank of river
Based on the interpretation of these
seismic data and other available geological information, OIL planned to drill a
few exploratory wells in the area. Simultaneous to the above geoscientific work
and planning for drilling, OIL deployed one of its 2D seismic crew to acquire
data in the area during the year 1995-96. It was felt prudent to process these
data on a high priority basis and review the exploration target prior to
spudding the first well in the area.
The acquired data processed using Oil's
in-house Landmark Seismic Data Processing system with Promax 6.1 processing
software and the results were made available as expected. This paper discusses
the result of this processing with specific emphasis on the advantage of
interactive velocity analysis which provided reliable lead in guiding the well
planning. It has been observed that the seismic velocity macro model estimated
from the available drilling information in adjacent south bank wells and the
geological correlation from the south bank area, needed considerable validation
to meet the objectives. The generated seismic sections were converted to depth
section using the products of interactive velocity analysis/manipulation and
was a major input to the depth model.
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PROCESSING AND
INTERPRETATION OF GROUND MAGNETIC DATA ACQUIRED ALONG SILCHAR-IMPHAL-MOREH
CORRIDOR (
D. Rai and V. Ramaswamy
Geophysics Division, KDMIPE, ONGC, Dehra Dun
Abstract
Magnetic data of Silchar-Imphal-Ukhrul
and Palel-Moreh corridors (eastern Cachar and Manipur) have been processed and
interpreted to bring out the basement configuration. The study reveals:
·
thickness
of sedimentary cover near Lakhipur (18 km east of Silchar) is about 6.5 km and
it gradually becomes thinner towards Imphal,
·
in the
Manipur valley the maximum sedimentary thickness is about 4.0 km and
·
in the
eastern Manipur Hills the sedimentary thickness again increases and attains a
value of about 6 km near Moreh at Indo-Burmese border where the ophiolite is
exposed at the surface.
The basement configuration along Silchar-Imphal-Moreh corridor
is arc type with convexity upwards. In brief, the study presents some new
results on the subsurface geology which may be used in hydrocarbon exploration
in the area.
Paper
presented at the 23rd Annual Convention and
Seminar on Exploration Geophysics during 18-21 November, 1997 and was
Adjudged as one of the best papers and selected for citation
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APPLICATIONS OF MISFIT
FUNCTION TOPOGRAPHY IN GEOPHYSICAL MODEL OPTIMIZATION
Saurabh K. Verma*, Markku Pirttijarvi** and Sven-Erik Hjelt**
*National Geophysical Research Institute, Hyderabad , India
** Department of Geosciences and Astronomy, University
of Oulu , Oulu , Finland
Abstract
To proceed with any optimization
technique, a measure of the distance between the observation and the response
calculated from the model is required to be defined. This measure is called
'Observation function' or 'Misfit function' (MF, used in this paper). Several
norms (l1, l2, …., lp, etc.) can be used to define this function. The behaviour
of MF over a space described by a combination of model parameters can be
displayed in the form of a MF topography (MFT). Construction of the MFT
requires a thorough scanning of a vast model space.
The MFT maps can provide valuable clues
on the correlation between the parameters defining the model space. For a
dynamic (time-variant) system, such as a transient electromagnetic (TEM)
method, the MFT is found to vary as a function of time. Thus it is possible to
select suitable time-windows of observation which provide optimal resolution of
the model parameters. Since various TEM systems employ different types of
exciting pulses (sinusoidal, ramp, triangular, etc.) and recording time
channels, the MFT's can also be exploited in comparing the performance of
various TEM systems. Also, since MFT's are based on the scanning of a vast
model space, in essence they represent a process similar to the grid search
technique of optimization commonly used in finding non-linear parameters from
geophysical data.
The above applications of the MFT are
shown considering synthetic responses of i) a perfectly conducting half-plane
(minimal) model in frequently domain and ii) a conducting finite plate model to
commonly employed generic TEM systems. Both these models are assumed to be
immersed in a non-conducting medium for the sake of simplicity. A field example
from the nickel sulphide deposit,
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AN INTEGRATED CRUSTAL
MODEL ALONG NAGAUR-JHALAWAR GEOTRANSECT
D. C. Mishra, Bijendra Singh, V. M. Tiwari, S. B. Gupta, N. Kameswara Rao and M. B. S. Vyagreswar Rao
*National Geophysical Research Institute, Hyderabad , India
Abstract
An integrated crustal density model
along Nagaur - Jhalawar geotransect across the Aravalli fold belt is
constructed based on the modelling of gravity data using the constraints from
deep seismic reflection profiling results and near-surface geology. The
observed gravity field along the transect shows "high" Bouger and
Free-air anomalies over the fold belt and "lows" on its flanks over
the Marwar and Vindhyan basins. Results of 2½ dimensional gravity modelling
indicate that the gravity high in the central part of the profile is partly due
to a prismatic shaped high density body (3.09 g/cm3) in the lower crust
extending from 18 Km upto 45 Km and partly due to the exposed high density
metasediments of
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STUDY OF UTTARKASHI
EARTHQUAKE IN TERMS OF RUPTURE MODEL AND ISOSEISMALS
A. Joshi
Lecturer, Department of Geophysics, Kurukshetra University , India
Abstract
Peak ground acceleration for Uttarkashi
earthquake has been compiled by modelling rupture process. Field and simulated
peak acceleration data and the isoseismal map prepared from synthetic and field
data have been compared.
Modelling of the rupture plane is based
on semi empirical method of Irikura (1986) which has been modified by
Midorikawa (1993). Modelling of the rupture plane by this technique gives peak
ground acceleration at the observation point.
After assuming the modelling parameters
of rupture plane, peak acceleration using this approach was calculated at thirteen
different stations that had recorded strong motion data of Uttarkashi
earthquake of 20th Oct, 1991. A comparison of simulated and field peak
acceleration less than 25% at six stations and less than 55% at seven other
stations, thereby confirming the parameters of selected model and efficacy of
the approach.
Hundred and sixty four different
locations surrounding the rupture model for Uttarkashi earthquake were taken
for simulation of peak ground acceleration. Peak acceleration at each location
was converted into intensity on MMI scale by empirical relation between peak
acceleration and maximum intensity on MMI. The comparison between the
isoseismal maps based on synthetic and field data shows that the elongated axis
of isoseismal map is dependent on the position of rupture plane and direction
of rupture propagation from nuclear point.
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