January, 2019

January, 2019   ||  Volume 23 No.1

Viscoelastic seismic modeling and Q estimation for an attenuating media+

Nimisha Vedanti1,2* and Ajay Malkoti2
1CSIR-National Geophysical Research Institute, Uppal Road, Hyderabad-500007, India
2Academy of Scientific and Innovative Research-NGRI, Uppal Road, Hyderabad-500007, India
*Corresponding Author: nimisha@ngri.res.in

In seismic modelling experiments, the propagating seismic wave experiences attenuation when real media is simulated. However, for computational ease, we often ignore this effect and model the Earth as either an acoustic or an elastic medium. In this paper, we briefly discuss the importance of considering attenuation in seismic modelling, by using a viscoelastic wave equation. Further we also briefly discuss the effects of attenuation on seismic data and its incorporation in seismic modelling. We find that the attenuation has a large effect on synthetic seismogram, which should be properly addressed in advanced seismic processing and imaging methods.

Characterising the source rocks in petroleum systems using organic and stable isotope geochemistry: An overview+

Devleena Mani
Centre for Earth, Ocean and Atmospheric Sciences (CEOAS),
University of Hyderabad (UoH), Hyderabad- 500046, India
Email: dtiwarisp@uohyd.ac.in

Geochemical investigations for correlating the petroleum (oil and gas) with source rocks and that with petroleum itself, which can be produced from a similar or dissimilar source rock, is important for the assessment of generation potential of a prolific or potential petroleum system. Analytical advancements have synergized the hydrocarbon exploration methods, with exploration geochemistry becoming increasingly an integral part of source rock characterization. Geochemical studies investigate the presence and properties of hydrocarbons trapped in geological formations, or the potential to generate such hydrocarbons and provide source rocks properties, by measuring the compositional changes associated with hydrocarbon generation, migration, accumulation and production. These are critical for proper and efficient management of the hydrocarbon assets at all stages. The source rocks and the petroleum are primarily characterized utilizing the organic geochemical and stable isotope techniques. Organic geochemistry deciphers the source, depositional environment and thermal maturity of sedimentary organic matter from which the hydrocarbons are generated and the stable isotopes of carbon, nitrogen and hydrogen describe the paleo productivity, origin, evolution and correlation of organic matter with generated or in situ hydrocarbon components. The paper presents an overview of the stable isotopic and organic geochemical properties of shales from Damodar Valley basin of India in the light of its gas generation potential.
Key words: Source rocks; organic matter; kerogen; isotopes; biomarkers; thermal maturity; Damodar Valley; Permian; Shale Gas.

Delineation of the Trap and sub-trappean sediments in Kutch, Deccan syneclise and Bengal basins-An analysis

A.S.N. Murty1*, A.S.S.S.R.S. Prasad2, and Kalachand Sain2
1*19-104/4, Kalyanpuri, Uppal, Hyderabad-500 039, India
2CSIR-National Geophysical Research Institute, Uppal Road, Hyderabad, India
*Corresponding Author: asnngri@gmail.com

Conventional seismic reflection data are not well suited for imaging sub-trappean sediments. In this paper, we report on seismic imaging investigations that used large-offset refraction and wide-angle reflection data from three regions of India, namely, the Kutch basin, the Deccan syneclise, and the Bengal basin. We use travel time modeling of refracted and reflected phases to derive the basement configuration, including the Trap and subtrappean sediment thickness. Some of the record sections show sharp amplitude decays (attenuation) of the refracted phase from the high velocity Traps and travel time delays between the Trap and basement refracted phases, which can be diagnostic of the presence of a low-velocity zone (LVZ) consisting of sediments beneath basalt. We identify reflected phases from the top and bottom of the LVZ. Analysis of the refracted and reflected phases suggests that the relative thickness of the overlying high-velocity and underlying low- velocity sediments, play a major role in the seismic data quality. The sediment thickness also affects the magnitudes of the attenuation, the travel time delay, and the strength of the reflection. In the Kutch area, we find that the Deccan Traps are thin (about 100-800 m), and sub-trappean Mesozoic sediments are about 2 km thick. In the Deccan syneclise, the Traps are relatively thin in the north and Tertiary and sub-trappean Mesozoic sediments are thick in the southwest. Towards the east, the Trap and subtrappean Mesozoic sediments are about 1 km thick. Further east, near the Satpura basin, the Deccan Traps are about 1 km thick, and sub-trappean Gondwana sediments are quite thin (100-400 m). Similarly, in the west Bengal basin, the Rajmahal Traps are about 1 km thick, while the subtrappean Gondwana sediments are 1.8 km thick near Palashi. These results provide crucial information needed for more detailed hydrocarbon exploration in sub-trappean sediments.
Key Words: Seismic refraction, 2-D Travel time inversion, Mesozoic sediments, Deccan Traps, Saurashtra.

Dimensionality and directionality analysis of the magnetotelluric data along the coastal part of western Saurashtra, Gujarat

K. Dilip Singh*, Kapil Mohan, and Mehul Nagar
Institute of Seismological Research, Raysan, Gandhinagar-382009 (Gujarat)
Also at Gujarat University, Navrangpura, Ahmedabad, Gujarat, 380009.
* Corresponding Author: ds200705@gmail.com  

The Magnetotelluric (MT) data from 14 MT stations along a NW-SE profile, having a length of 40 km, is processed for a period range of 0.01-100s along the coastal part of north-western Saurashtra, India to estimate the dimensionality of the MT data, using three different approaches, that is, Phase Tensor (PT) technique, WALDIM code, Swift’s and Bahr’s Skew technique. The Swift’s and Bahr’s skew result suggests 1D structure for low periods (0.01-1 s) and 2D structure for high periods (1-100 s), except for some sites which show a 3D subsurface structure for high periods (1-100 s). The results generated through PT and WALDIM code are consistent with those from Swift’s and Bahr’s skew technique. The strike estimated through Phase Tensor (PT), Groom-Bailey (GB) and Becken and Burkhardt (BB) technique for broad period 0.01-100s suggest NNE-SSW regional strike direction, which is well correlated with the Delhi-Aravalli tectonic trend. From the 1D inverse model, the Quaternary and Tertiary sediments are found up to the depth of 300-400m followed by Deccan Trap. A conductive zone (having resistivity <20 Ohm-m) in the central part of the profile near Okha Rann is also observed which suggests the presence of a fault.
Keywords: Magnetotellurics, Dimensionality, Strike, Galvanic distortion, Western Saurashtra coast, Gujarat

Performance evaluation of different interpretation techniques of vertical electrical sounding data

P. Venkateswara Rao1, M. Subrahmanyam1* and D. Ratnakar2
*1Department of Geophysics, Andhra University, Visakhapatnam-530003, India
2CSIR-National Geophysical Research Institute, Uppal Road- Hyderabad.
*Corresponding Author: smangalampalli@rediffmail.com.

Numerous interpretation techniques are available in the literature to interpret Vertical Electrical Sounding (VES) data and thus it becomes very difficult to choose one of them. A performance analysis of each method and its comparison with other techniques would aid the geophysicists to choose a better technique. An attempt has been made here to evaluate the performance and comparison of a few widely used interpretation techniques. The computer oriented interpretation techniques RESIST, IRESAN and IPI2Win have been subjected to rigorous analysis using input model parameters. These techniques are applied to interpret the theoretical three and five layered earth models generated for various combinations of resistivities and thicknesses and the output results are analyzed for their accuracy for all the three techniques. The analysis of their performance reveals that IPI2Win technique yields comparatively better results with minimum errors in the output of the interpreted parameters.
Key words: Vertical electrical sounding, Inversion algorithm, Percentage error, RMS error.

Runoff estimation using SCS-CN method for degrading lakes/tanks: a case study of Bilikere and Halebidu tanks, Karnataka (India)

Pradeep Raja K.P.1*, Suresh Ramaswwamyreddy2
1Research Scholar, Department of Civil Engineering, BMS College of Engineering, Basavanagudi, Bengaluru,
Karnataka, India -560019.
2Department of Civil Engineering, BMS College of Engineering, Basavanagudi, Bengaluru, Karnataka, India -560019.
* Corresponding author: kppradeepraja@yahoo.co.in

Rainfall and runoff are essential components of water resources in a watershed. Similarly, the rainfall is a principal source of surface water storage in lakes or tanks. Assessment of water availability for storage, in artificial/manmade structures depends upon the rainfall and runoff characteristics in a catchment. Surface water storage in tanks/lakes is also an important factor in tank irrigation and enhancement of ground water level. It is fairly well known that the runoff in a catchment is governed by several factors like land use/land cover, amount of rainfall, intensity of rain, type of soil, soil moisture and other hydro-geomorphological features. In view of this, the present study considers two minor irrigation (MI) tanks, Bilikere and Halebidu, which have dried up completely since 2004. The collective catchment (BKHB) of both the tanks is a mini watershed that covers 46.33 km2 area, in Lakshman Theertha River basin, which is a sub-basin of the river Cauvery flowing through semi-arid region of Mysore district of Karnataka. Soil Conservation Service Curve Number (SCS-CN) method is integrated with RS and GIS technology to estimate the runoff. Study reveals that the volume of runoff is decreasing in recent times due to the change of land use pattern and significant decrease in intensity of rainfall in the studied region.
Key words: Bilikere and Halebidu tanks, Mean daily intensity (MDI), Antecedent moisture condition (AMC), Surface runoff, Soil conservation service curve number (SCS-CN)..

Sub-watersheds wise slope instability analysis and prioritization
of the Balason River Basin of Darjeeling Himalaya, India
using compound ranking method

Subrata Mondal1* and Sujit Mandal2
1*Department of Geography, University of Gour Banga, West Bengal-732103, India
2Department of Geography, Diamond Harbour Women’s University, Sarisha, West Bengal-743368, India
*Corresponding Author: subratapanchagram@gmail.com

To balance between the demand and supply and ever increasing demand, it is necessary to conserve natural resources like watersheds, with proper prioritization. In that sense, morphometric analysis of any drainage basin is considered of high importance in hydrological investigation. Morphometric parameters describe the topology, the structure, the platform and the relief of basin, applied for the prioritization of watersheds. Some pre-information such as runoff, stages of its development and soil loss etc. are also provided by the analysis of morphometric parameters. In the present study, an attempt has been made to prioritize sub-watersheds based on morphometric analysis in relation to slope instability. The base map of stream network were digitized from toposheets no. 78A/4, 78A/8, 78B/1, 78B/5 and 78B/6 (Scale 1:50000) and then updated on Google earth. Arc GIS 9.3 software and MS excel-2007 was used to assess 13 morphometric parameters i.e. bifurcation ratio (Rb), length of overland flow (Lof), drainage density (Dd), stream frequency (Fs), texture ratio (Rt), drainage texture (Td), compactness coefficient (Cc), constant of channel maintenance (Ccm), shape factor/ basin shape (Sf), form factor (Ff), circularity ratio (Rc), elongation ratio (Re) and relief ratio (Rr). The results showed that SW 4, SW 5 and SW 8 fall under very high priority class in respect of soil erosion and soil loss or simply instability, having Rb of 3.532 – 4.002, Dd of 5.986 – 6.538, Fs of 14.934 – 29.447, Td of 9.765 – 23.158, Rt of 7.055 – 16.958, Lof of 0.069 – 0.084, Rr of 0.209 – 0.302, Cc of 1.265 – 1.554, Ccm of 0.139 – 0.167, Sb of 2.969 – 5.556, Ff of 0.180 – 0.337, Rc of 0.420 – 0.634 and Re of 0.479 – 0.655. Sub-watershed wise highest priority was obtained by SW 5 followed by SW 8, SW 4, SW3, SW 9, SW 1, SW 6, SW 16, SW 2, SW 17, SW 15, SW 13, SW 7, SW 10, SW 11, SW 12, SW 14, and SW 18.
Keywords: Sub-watersheds, Morphometric parameters, GIS, Compound Ranking Method, Prioritization.

OMNI (Ocean Moored buoy Network for northern Indian Ocean) Buoy System—a critical component of ocean observational programme of ESSO (Earth System Science Organization), Ministry of Earth Sciences, Government of India

Raja Acharya* and Suman Chattopadhyay 
India Meteorological Department, Regional Meteorological Centre, Ministry of Earth Sciences, 4, Duel Avenue, Alipore, Kolkata-700027
*Corresponding Author: raja.acharya2011@gmail.com

The NIOT (National Institute of Ocean Technology) Chennai deployed moored bouys attached with sensors to collect subsurface oceanographic parameters on real time basis at selected locations in Eastern Arabian Sea and Bay of Bengal and named it as the OMNI (Ocean Moored Bouy Network for Northern Indian Ocean) bouy system. This paper presents the usefulness of OMNI Bouy programme, in terms of technical advancements and met-ocean data quality and future strategies related to the programme.
Keywords: OMNI Bouy, Ocean Observational programme, ESSO .