wellbore stability analysis and prediction of minimum mud weight for few wells in krishna godavari basin india abstract analysis of wellbore instability contains evaluation of rock mechanical properties and the state of in situ stresses in this analysis the only convenient factor is the mud weight i e the fluid density of the drilling fluid if the mud weight is greater than the predicted the mud will enter into the formation causing tensile failure fracture stress conversely a lower mud weight can result in shear failure collapse stress of rock which is known as borehole breakout here we present three types of failure criteria mohr coulomb mogi coulomb and modified lade rock mechanical rocks such as poisson s ratio uniaxial compressive strength cohesion have been computed from compressional and shear wave velocities internal friction angle is obtained from gamma ray log the failure criteria have been applied to two wells located at krishna godavari k g onshore and three wells at offshore to obtain minimum mud weight required to sustain its stability the caliper log for above mentioned wells have experienced complete to moderate failure considered as a lower bound of onset of failure at selected depth intervals it is observed that mohr coulomb failure criteria overestimates the predicted mud weight for the safe drilling on the contrary mogi coulomb failure criteria is closer to the expected result

origin of overpressure and pore pressure prediction in the baram province brunei accurate pore pressure prediction is critical in hydrocarbon exploration and is especially important in the rapidly deposited tertiary baram delta province where all economic fields exhibit overpressures commonly of high magnitude and with narrow transition zones a pore pressure database was compiled using wireline formation interval tests drillstem tests and mud weights from 157 wells in 61 fields throughout brunei overpressures are observed in 54 fields both in the inner shelf deltaic sequences and in the underlying prodelta shales porosity vs vertical effective stress plots from 31 fields reveal that overpressures are primarily generated by disequilibrium compaction in the prodelta shales but have been generated by fluid expansion in the inner shelf deltaic sequences however the geology of brunei precludes overpressures in the inner shelf deltaics being generated by any conventional fluid expansion mechanism e g kerogen to gas maturation and we propose that these overpressures have been vertically transferred into reservoir units via faults from the prodelta shales sediments overpressured by disequilibrium compaction exhibit different physical properties to those overpressured by vertical transfer and hence different pore pressure prediction strategies need to be applied in the prodelta shales and inner shelf deltaic sequences sonic and density log data detect overpressures generated by disequilibrium compaction and pore pressures are accurately predicted using an eaton exponent of 3 0 sonic log data detect vertically transferred overpressures even in the absence of a porosity anomaly and pore pressures are reasonably predicted using an eaton exponent of 6 5

the evolution of the east coast of india abstract the evolution of the east coast of india from the permian up to the end of the cretaceous is traced peninsular india had an imprint of hercynian epeirogeny manifested in the formation of some regional geofracture and rift systems the east coast basins mahanadi godavari krishna palar and cauvery basins are pericratonic the structural style and regional trends during the jurassic are ne sw the basin architecture during the late jurassic is of horst graben type the close of the mesozoic was marked by regional easterly regression basinal tilt and formation of monoclinal post mesozoic sedimentary cover the oldest sequence in these basins is of permian age and is known in the palar basin the triassic sediments are not known in the land area from the faunistic and floristic evidence the uppermost jurassic lower cretaceous gondwana sediments are paralic the occurrence of marine permian palynofossils in the indian east coast sediments points to the presence of a narrow paleo shelf to the east prior to the break up and drift of gondwanaland different continental fits offered by various authors are analysed to understand the evolution of the indian ocean the structural grain and basin architecture of the pre drift and post drift basins of the east coast of india are similar to that of the western and northwestern coastal basins of australia it is postulated that permian sediments were extensive and have since been eroded such a pattern of erosion of permian beds is also observed in northwestern australia the most favoured fit of western australia against northern india does not conform to the regional geotectonic pattern and the nature of sediments that are present in india and the australian counterparts in addition to geological evidence palaeo biological evidence has been considered which favours the juxtaposition of the east coast of india with western australia the authors are of the opinion that palaeomagnetic interpretations which have of late gained importance fail to explain the pre drift geological similarities of the east coast of india and western coast of australia

an overview of indian sedimentary basins with special focus on emerging east coast deepwater frontiers this article will provide an overview of the current indian petroleum exploration scenario with special focus on the east coast deepwater basins an attempt has been made to distinguish the hydrocarbon system and play types for both rift related and other structural styles using high quality 2d and 3d seismic imaging information integrating the geologic information with state of the art seismic data has generated a large portfolio of play types e g channel levee complex lobes synrift structural closures and wedge outs against basement highs worthy of exploration

mapping crustal heterogeneity using lg propagation efficiency throughout the middle east mediterranean southern europe and northern africa in this paper we describe a technique for mapping the lateral variation of lg characteristics such as lg blockage efficient lg propagation and regions of very high attenuation in the middle east north africa europe and the mediterranean regions lg is used in a variety of seismological applications from magnitude estimation to identification of nuclear explosions for monitoring compliance with the comprehensive nuclear test ban treaty ctbt these applications can give significantly biased results if the lg phase is reduced or blocked by discontinuous structure or thin crust mapping these structures using quantitative techniques for determining lg amplitude attenuation can break down when the phase is below background noise in such cases lg blockage and inefficient propagation zones are often mapped out by hand with our approach we attempt to visually simplify this information by imaging crustal structure anomalies that significantly diminish the amplitude of lg the visualization of such anomalies is achieved by defining a grid of cells that covers the entire region of interest we trace lg rays for each event station pair which is simply the great circle path and attribute to each cell a value equal to the maximum value of the lg p coda amplitude ratio for all paths traversing that particular cell the resulting map from this empirical approach is easily interpreted in terms of crustal structure and can successfully image small blockage features often missed by analysis of raypaths alone this map can then be used to screen out events with blocked lg prior to performing q tomography and to avoid using lg based methods of event identification for the ctbt in regions where they cannot work for this study we applied our technique to one of the most tectonically complex regions on the earth nearly 9000 earthquake station raypaths traversing the vast region comprised of the middle east mediterranean southern europe and northern africa have been analyzed we measured the amplitude of lg relative to the p coda and mapped the lateral variation of lg propagation efficiency with the relatively dense coverage provided by the numerous crossing paths we are able to map out the pattern of crustal heterogeneity that gives rise to the observed character of lg propagation we observe that the propagation characteristics of lg within the region of interest are very complicated but are readily correlated with the different tectonic environments within the region for example clear strong lg arrivals are observed for paths crossing the stable continental interiors of northern africa and the arabian shield in contrast weakened to absent lg is observed for paths crossing much of the middle east and lg is absent for paths traversing the mediterranean regions that block lg transmission within the middle east are very localized and include the caspian sea the iranian plateau and the red sea resolution is variable throughout the region and strongly depends on the distribution of seismicity and recording stations lg propagation is best resolved within the middle east where regions of crustal heterogeneity on the order of 100 km are imaged e g south caspian sea and red sea crustal heterogeneity is resolvable but is poorest in seismically quiescent northern africa

pore pressure prediction in gas hydrate bearing sediments of krishna godavari basin india abstract predrill estimate of pore pressure pp is important for well design especially in areas containing gas hydrate bearing sediments here we report the pressure distribution in the gas hydrate bearing sediments in krishna godavari k g basin predicted from the seismic data along two lines passing through the site 10 of expedition 01 exp 01 conducted by the indian national gas hydrate programme nghp a series of elastic parameters namely p wave velocity vp s wave velocity vs density vp vs p impedance zp and s impedance zs were derived from seismic data using pre stack inversion first the pp estimated from a sonic transit time log was calibrated with pressure core measurements in the depth interval of 1060 1280 m its magnitude is found to be ranging from 10 5 to 12 9 mpa where the vertical stress varies from 10 7 to 13 4 mpa within the same depth interval this estimated pp was next treated as a target log desired output and seismic attributes resulting from pre stack seismic inversion were used as input parameters in the training of a multi layered feedforward network mlfn finally we use the trained network to generate a subsurface pp distribution map along two 2d multichannel seismic profiles line x and line y passing through nghp01 10 within a time interval of 1420 1620 ms corresponding to a depth interval of 1060 1280 m this corresponds to sedimentary column from 22 to 242 mbsf our results demonstrate that the pressure remains hydrostatic within the gas hydrate bearing sediments and is mostly above hydrostatic below the gas hydrate bearing zone

an inversion of lg wave attenuation and site response from seismic spectral ratios in the eastern china region abstract both lg wave attenuation and site responses are determined in the eastern china region the region ranges from 26 n to 33 n and 117 e to 124 e we analyze over 1360 three component seismograms from 92 local and regional earthquakes the seismograms are recorded in the distance range of 100 600 km the earthquakes occurred between 2002 and 2012 in the region and varied in magnitude between 2 0 and 4 7 m l a combined inversion method which can simultaneously estimate attenuation and site response from seismic spectral ratios is implemented in the study modeling errors are determined using a delete j jackknife resampling technique fourier spectral amplitudes are measured from lg phases windowed between the group velocity limits 2 6 and 3 6 km s the inversion are performed in a frequency range of 1 6 hz with an interval of 0 2 hz the frequency dependent quality factor is modeled in the form of q q 0 f the eastern china region displays high q 0 and a weaker frequency dependence characterized by the functions q 335 16 f 0 45 0 02 q 411 21 f 0 26 0 01 and q 432 26 f 0 24 0 01 for vertical north south and east west components respectively the values are similar to the average for other stable regions of the globe site responses from 32 stations are estimated in the region most stations do not show obvious amplification the site responses are mainly smooth flat and less than 5 in the frequency range of 1 6 hz

velocity determination for pore pressure prediction overpressured formations exhibit several of the following properties when compared with a normally pressured section at the same depth dutta 2002 1 higher porosities 2 lower bulk densities 3 lower effective stresses 4 higher temperatures 5 lower interval velocities and 6 higher poisson s ratios

predrill pore pressure prediction using seismic data 1a predrill estimate of pore pressure can be obtained from seismic velocities using a velocity to pore pressure transform but the seismic velocities need to be derived using methods having sufficient resolution for well planning purposes for a deepwater gulf of mexico example significant differences are found between the velocity field obtained using reflection tomography and that obtained using a conventional method based on the dix equation these lead to significant differences in the predicted pore pressure parameters in the velocity to pore pressure transform are estimated using seismic interval velocities and pressure data from nearby calibration wells the uncertainty in the pore pressure prediction is analyzed by examining the spread in the predicted pore pressure obtained using parameter combinations which sample the region of parameter space consistent with the available well data if calibration wells are not available the ideas proposed in this paper can be used with measurements made whi

effective stress coefficient in shales and its applicability to eaton s equation pore pressure within formations determines the mud weight required to build a balancing fluid pressure downhole an improper understanding of the subsurface geology and the formation pressures may result in fracturing the formation if the mud weight is too high in contrast if mud weight is too low then formation fluids can flow into the well potentially leading to well blowouts if not controlled complex geological settings make pore pressure prediction difficult and often inaccurate due to uncertainty in pressure generating mechanisms estimation of proper pore pressures is necessary for designing stable holes and an optimized casing program in exploration knowledge of pore pressures can assist in assessing seal effectiveness and in high grading reservoir sweet spots it also provides useful calibration information for basin modeling hence it becomes very important to accurately predict pore pressures

detection of overpressure zones and a statistical model for pore pressure estimation from well logs in the krishna godavari basin india abnormally high pressures measured by repeat formation tester rft and detected by well log data from 10 wells in the krishna godavari k g basin occur in the vadaparru shale of miocene and raghavapuram shale of early cretaceous age overpressures generated by disequilibrium compaction and pore pressures have been estimated using the conventional eaton sonic equation with an exponent of 3 0 the observed abnormal pore pressure gradient ranges from 11 85 to 13 10 mpa km whereas fracture pressure gradient varies from 17 40 to 19 78 mpa km the magnitude of vertical stress sv has a gradient from 21 00 to 23 10 mpa km the minimum horizontal principal stress sh magnitude is found to vary from 64 to 77 of the sv in normally pressured to overpressured sediments a multiple linear regression model with a squared multiple correlation coefficient r2 of 0 94 is proposed for pore pressure prediction from gamma ray density and sonic logs to focus on efficient drilling operations and to prevent borehole instability the statistical model has been calibrated with the rft data from five wells covering about 3400 sq km area of the onshore k g basin the model predicted pore pressure values are in close agreement with the actual rft data for another four wells including a well in the offshore k g basin hence the proposed regression model may be useful for predicting pore pressure from other well logs in the k g basin

strong lg wave attenuation in the northern and eastern tibetan plateau measured by a two station two event stacking method 1 the regional seismic phase lg which involves shear wave reverberations in the crust is strongly attenuated along propagation paths in northern and eastern tibet robust estimates of the attenuation quality factor qlg in these regions are obtained using a two station two event stacking method for broadband vertical component lg data in the passband 0 2 1 0 hz we find average 1 hz qlg values qo of 79 4 in northern central tibet and 119 17 in eastern tibet for the 0 2 0 5 hz passband localized regions of eastern tibet have qo estimates ranging from 66 to 121 these results confirm and augment the spatial coverage of recent estimates of low qo values in north central and south central tibet and support the notion of widespread partial melting of the crust throughout the plateau

integration of knowledge based seismic inversion and sedimentological investigations for heterogeneous reservoir abstract conventional geological modelling methods are not capable to provide precise and comprehensive model of the subsurface structures when dealing with insufficient data knowledge based methods employing rule bases techniques are found vast applications in geoscience studies these methods are applicable for petroleum reservoir geological modelling and characterizations specifically for geologically complex structures in this study we present a knowledge based seismic acoustic impedance inversion method which employs rule based method for porosity estimation the back propagation algorithm and the fuzzy neural network are also used in the methodology for parameter optimization and definition of nonlinear relationship between seismic attributes and porosity of the reservoir rock the methodology initiates by seismic acoustic impedance inversion followed by conventional porosity estimation subsequently a knowledgebase was designed by investigation on more than 24 published case studies this knowledgebase was used for definition of rules and optimization number of rules and improve efficiency of the inference engine the porosity model obtained by conventional method in previous step would be used for primary evaluation of the rules the extracted rules and optimized number rules then would be used for rule based porosity estimation the methodology was applied on a petroleum field containing two heterogeneous reservoir formations result of application of the proposed approach was evaluated with core analysis thin sections and drilling data consistency of result obtained by the proposed method with geological data has shown its capability to resolve problem of insufficient data in reservoir geological modelling

detecting high overpressure normal pressure is pore fluid pressure that equals the hydrostatic pressure of a column of formation water extending to the surface overpressure is pore fluid pressure greater than normal pressure however no standard definition exists for what constitutes high overpressure what can be said is that high overpressure often means trouble for an explorationist it could mean blown reservoir seals for a driller it could mean excessive time spent fighting formation fluid influxes and or drilling fluid losses

strong lg attenuation in the tibetan plateau the widespread existence of strong lg attenuation in the tibetan plateau is further demonstrated by analysis of lg spectra on many paths within the plateau and quantitative estimates of the lg attenuation from low frequency lg signals for new localized path geometries strong path length dependent shifts of the lg spectra to lower corner frequencies with increasing distance are observed across the plateau consistent with a low regional average 1 hz lg attenuation value q 0 of about 125 there are clearly lateral variations within the plateau found in this and other recent studies with localized areas having q 0 values of 60 90 low enough to eliminate high frequency lg energy over path lengths of just several hundred kilometers while some localized areas may have higher q 0 values of up to 147 or higher a q 0 value of 103 is found in south central tibet compatible with recent work by others for higher frequencies on very localized scales and values from 83 to 147 are found in eastern tibet the lowest q 0 estimates found in tibet tend to be in areas for which there is evidence of volcanism and or partial melting within the crust however the strong regional attenuation may have a contribution from scattering by small scale crustal heterogeneity the strong lg attenuation in tibet gives a new constraint for understanding the tectonic development of the plateau and presents challenges to seismic monitoring of the region for possible clandestine nuclear tests

multi channel 2d seismic constraints on pore pressure and vertical stress related gas hydrate in the deep offshore of the mahanadi basin india abstract estimation of pore pressure and in situ vertical stress magnitude is essential for understanding the geomechanical behavior of the gas hydrate sediments in deep offshore of the mahanadi basin the basin located at northern side of eastern continental margin of india ecmi contains gas hydrate in clay silt sediments the pore pressure and vertical stress are mapped on two 2d multi channel seismic data of lines mh 38a and mh 38b with aid of information of three wells namely nghp 01 19 nghp 01 09 and nghp 01 08 initially the coefficients of best fit curve have been computed from velocity effective stress plot for the individual wells and applied on the seismic velocity to transform into the effective stress the vertical stress has been computed from both the seismic and log data therefore the pore pressure is predicted by subtracting the effective stress from the vertical stress the pore pressure have been mapped in gas hydrate stability zone ghsz and sediments below bottom simulating reflector bsr the pore pressure and vertical stress gradient are 10 11 mpa km and 10 67 mpa km respectively the pore pressure and vertical stress from seismic data are closely matched at well location with excellent goodness of fit r2 varying from 0 82 to 0 95 normal pressure is observed in the gas hydrate bearing sediments but slightly high pressures are noticed below the bsr indicating presence of free gas the pore pressure from seismic data will guide drillers for choosing the mud weight during well drilling and casing optimizing in other part of deep offshore in the mahanadi basin

seismic imaging of a fractured gas hydrate system in the krishna godavari basin offshore india gas hydrate was discovered in the krishna godavari kg basin during the india national gas hydrate program nghp expedition 1 at site nghp 01 10 within a fractured clay dominated sedimentary system logging while drilling lwd coring and wire line logging confirmed gas hydrate dominantly in fractures at four borehole sites spanning a 500 m transect three dimensional 3d seismic data were subsequently used to image the fractured system and explain the occurrence of gas hydrate associated with the fractures a system of two fault sets was identified part of a typical passive margin tectonic setting the lwd derived fracture network at hole nghp 01 10a is to some extent seen in the seismic data and was mapped using seismic coherency attributes the fractured system around site nghp 01 10 extends over a triangular shaped area of 2 5 km2 defined using seismic attributes of the seafloor reflection as well as seismic sweetness at the base of the gas hydrate occurrence zone the triangular shaped area is also showing a polygonal nearly hexagonal fault pattern distinct from other more rectangular fault patterns observed in the study area the occurrence of gas hydrate at site nghp 01 10 is the result of a specific combination of tectonic fault orientations and the abundance of free gas migration from a deeper gas source the triangular shaped area of enriched gas hydrate occurrence is bound by two faults acting as migration conduits additionally the fault associated sediment deformation provides a possible migration pathway for the free gas from the deeper gas source into the gas hydrate stability zone it is proposed that there are additional locations in the kg basin with possible gas hydrate accumulation of similar tectonic conditions and one such location was identified from the 3d seismic data 6 km nw of site nghp 01 10

attenuation of 1 6 s lg waves in eurasia we report our investigation of the lg attenuation characteristics in eurasia using digital recordings from the incorporated research institutions for seismology chinese digital seismic network broadband stations to maximize the utilization of the current station and source distribution in the region we have derived a new technique known as the source pair receiver pair sprp method for lg attenuation measurement the procedure eliminates seismic source and site effects leaving behind decontaminated amplitude data from which regional wave attenuation is estimated for lg attenuation studies the sprp method is more flexible and of greater general applicability than its predecessor the reversed two station method chun et al 1987 the application of the sprp method to our time domain analysis of 33 regional and far regional seismic events has provided stable regional average for lg attenuation in periods of 1 6 s our time domain analysis aided by a damped least squares inversion algorithm has led to robust measurements of lg attenuation q and its frequency dependence in nine subregions of tectonic significance regions of active tectonics and seismicity generally have lower q0 than that in the stable continental interior subregional q and are found compatible with the published results in areas of relatively uniform geology values are comparatively poorly determined suggesting that they are susceptible to the presence of crustal heterogeneities along the wave paths

gas hydrates in india potential and development abstract the shallow sediments along the indian continental margin are good hosts for gas hydrates and the methane within gas hydrates has been prognosticated as more than 1500 times of india s present natural gas reserve production of even 10 from this natural reserve is sufficient to meet country s vast energy requirement for about a century hence it was felt necessary to map the most prospective zones of gas hydrates and evaluate their energy potential along the indian margin first of all we have updated the gas hydrates stability thickness map along the indian shelf to provide the spatial and depth domains within which gas hydrates can be looked for we have identified the bottom simulating reflectors bsrs the main marker for gas hydrates in the krishna godavari kg mahanadi andaman kerala konkan and saurashtra regions respectively the total organic carbon content toc sediment thickness and rate of sedimentation indicate that the cauvery and kerala laccadive basins are also prospective for gas hydrates seismic attenuation q 1 reflection strength instantaneous frequency and blanking have been computed to characterize the sediments containing gas hydrates and free gas the faulting or gas chimneys have also been used for the identification of gas hydrates we have developed several approaches based on seismic traveltime tomography full waveform inversion amplitude versus offset avo modeling and avo attributes each coupled with rock physics modeling and utilized them for the quantification of gas hydrates a large volume of multi channel and ocean bottom seismic data have been acquired in 2010 between 500 to 2500 m water depths in kg and mahanadi basins the new data exhibit wide spread occurrences of bsrs reveal new prospective zones of gas hydrates and are being modeled for the delineation of sediments hosting gas hydrates and evaluation of their resource potential efforts are on to develop suitable technology for exploitation we anticipate that free gas lying below gas hydrate bearing sediments can be produced economically in near future however it may take longer time to retrieve gas from gas hydrates

attenuation of high frequency shear waves in the crust measurements from new york state south africa and southern california we compare the attenuation of high frequency 3 30 hz shear waves for crustal paths in new york state south africa and southern california over source receiver distances of about 10 400 km the data consist of digital recordings of s waves 5 100 km and lg waves 100 400 km produced by earthquakes we use a coda normalization method to remove the effects of site amplification and source excitation from the amplitudes of the s and lg waves over the entire distance range studied 10 400 km the amplitude decay of 3 hz shear wave energy is considerably less for the tectonicaily stable areas of new york and south africa than for the tectonicaily active region of southern california high frequency 30 hz s wave attenuation is significantly less for new york and south africa than for southern california for distances between 15 and 90 km we parameterize the decay with distance r of coda normalized shear wave amplitudes with a frequency independent q and geometrical spreading exponent where geometrical spreading is proportional to r for new york state the s wave amplitude decay 3 30 hz is well described by a frequency independent q of 2100 330 490 and of 1 3 0 1 the decay of lg wave amplitudes from 3 to 15 hz in the new york state region is fit with a frequency independent q of 1600 280 330 of 0 70 0 2 the s wave amplitudes 3 30hz in south africa yield a q of 1500 190 380 and of 1 3 0 1 fixing the geometrical spreading at r 0 5 produces an lg wave q estimate at 3 hz in south africa of 360 50 80 this lg wave q is low considering that south africa is a cratonic tectonicaily stable area the s wave amplitudes from southern california are described with a frequency independent q of 800 150 240 and a large geometrical spreading exponent of of 1 9 0 2 we find an lg wave q at 3 hz of 260 30 for southern california after constraining the geometrical spreading at r 0 5

estimation of gas hydrate and free gas saturation concentration and distribution from seismic data gas hydrates contain a major untapped source of energy and are of potential economic importance the theoretical models to estimate gas hydrate saturation from seismic data predict significantly different acoustic elastic properties of sediments containing gas hydrate we do not know which to use thus we develop a new approach based on empirical relations the water filled porosity is calibrated using well log data to acoustic impedance twice one calibration where gas hydrate is present and the other where free gas is present the water filled porosity is used in a combination of archie equations with corresponding parameters for either gas hydrate or free gas to estimate gas hydrate or free gas saturations the method is applied to single channel seismic data and well logs from ocean drilling program leg 164 from the blake ridge area off the east coast of north america the gas hydrate above the bottom simulating reflector bsr is estimated to occupy 3 8 of the pore space 2 6 by volume free

delineation of the 85 e ridge and its structure in the mahanadi offshore basin eastern continental margin of india ecmi from seismic reflection imaging abstract the passive eastern continental margin of india ecmi evolved during the break up of india and east antarctica in the early cretaceous the 85 e ridge is a prominent linear aseismic feature extending from the afanasy nikitin seamounts northward to the mahanadi basin along the ecmi earlier workers have interpreted the ridge to be a prominent hot spot trail in the absence of conclusive data the extension of the ridge towards its northern extremity below the thick bengal fan sediments was a matter of postulation in the present study interpretation of high resolution 2 d reflection data from the mahanadi offshore basin located in the northern part of the ridge unequivocally indicates continuation of the ridge across the continent ocean boundary into the slope and shelf tracts of the ecmi its morphology and internal architecture suggest a volcanic plume related origin that can be correlated with the activity of the kerguelen hot spot in the nascent indian ocean in the continental region the plume related volcanic activity appears to have obliterated all seismic features typical of continental crust the deeper oceanic crust over which the hot spot plume erupted shows the presence of linear ns aligned basement highs corresponding with the ridge underlain by a depressed moho discontinuity in the deep oceanic basin the ridge influences the sediment dispersal pattern from the early cretaceous early part of late cretaceous times till the end of oligocene which is an important aspect for understanding the hydrocarbon potential of the basin

gas hydrate stability thickness map along the indian continental margin abstract the gas hydrate stability thickness ghst map along the indian continental margin is prepared from available bathymetry sea bottom temperature and geothermal gradient data the bottom simulating reflector bsr often marks the base of gas hydrate stability zone the prior information about the stability thickness in a particular area will help in identifying bsr on seismic data the map is also useful to the exploration scientists to set a depth window within which proxies for gas hydrate can be looked into a ghst map was initially prepared in 1998 based on the then available data a lot of new data has been generated by various organizations under the indian national gas hydrate programs for the advancement of exploration and exploitation activities by incorporating the new data from the published and available documents we have modified the ghst map along the indian margin besides filling the data gap the new map shows the gas hydrate stability zone in the andaman offshore in addition we show maps of sea bottom temperature sediment thickness geothermal gradient and heat flow to provide a bird s eye view of these parameters along the continental margin of india

assessment of gas hydrate saturation in marine sediments from resistivity and compressional wave velocity log measurements in the mahanadi basin india abstract gas hydrate was recovered in the mahanadi basin along the eastern continental margin of india during the india national gas hydrate program nghp expedition 01 in 2006 infrared imaging of recovered core confirmed gas hydrate occurs predominantly in discrete layers pore water chemistry electrical resistivity and acoustic velocity down hole logs were used to estimate gas hydrate saturations at three of the sites in the mahanadi basin sites nghp 01 08 09 and 19 gas hydrate saturation estimated from pore water chloride concentrations shows values up to 10 of the pore space at 200 m below seafloor just above the base of the gas hydrate stability zone bghsz gas hydrate saturations estimated from electrical resistivity and acoustic velocity logs using standard relations and modeling approaches are comparable to each other and saturations are 10 15 of the pore space seismic reflection data were also analyzed for the evidence of gas hydrate and a bottom simulating reflector bsr was imaged along the seismic profiles in the study area the depth of the bsr is varying from 200 m to 300 m below seafloor depending on water depth in the mahanadi basin the occurrence of gas hydrate was observed to be associated with deep water channel and levee complexes especially at site nghp 01 19 based on the regional seismic data but the cored logged section at each site lacked any significant sand fraction which does not allow for higher gas hydrate saturations as identified from seismic time slice data all sites drilled in the mahanadi basin are within the steeper slope region of the channel system and any sand bypassed this region significant sand deposition would occur further down slope where typical fan type deposits can be inferred from the seismic data and thus higher accumulations of gas hydrate would be expected

geophysical log responses and their correlation with bed to bed stress contrasts in paleozoic rocks appalachian plateau new york a 1 km profile of in situ stress and geophysical log data was acquired in the wilkins well to study the relationship between rock properties and in situ stress contrasts the wilkins well penetrates devonian clastic rocks on the appalachian plateau near the town of south canisteo new york open hole hydraulic fracture stress measurements were made in stratigraphic sequences where geophysical logs indicated significant bed to bed variations in elastic and lithologic properties analysis of stress magnitudes and interval averaged geophysical data shows that principal horizontal stress magnitudes correlate directly with elastic stiffness and inversely with clay content a similar relation is found for older paleozoic strata penetrated by a well at auburn new york correlations between stress magnitude and geophysical properties observed in the wilkins and auburn wells provide strong evidence that bed to bed stress variations arise from a uniform ene wsw directed strain acting on beds of different young s modulus rather than from variations in rock shear strength because of their high young s modulus sandstones siltstones and limestones in the northern appalachian basin are likely to be stronger barriers to hydraulic fracture propagation than shales porosity logs in the wilkins well show that the large decrease in horizontal stress found at the base of the rhine street formation occurs where shales are less compacted the correlation with undercompaction is consistent with a paleo overpressure drainage mechanism as the cause for the stress decrease

geologic implications of gas hydrates in the offshore of india krishna godavari basin mahanadi basin andaman sea kerala konkan basin gas hydrate resource assessments that indicate enormous global volumes of gas present within hydrate accumulations have been one of the primary driving forces behind the growing interest in gas hydrates gas hydrate volumetric estimates in recent years have focused on documenting the geologic parameters in the gas hydrate petroleum system that control the occurrence of gas hydrates in nature the primary goals of this report are to review our present understanding of the geologic controls on the occurrence of gas hydrate in the offshore of india and to document the application of the petroleum system approach to the study of gas hydrates national gas hydrate program of india executed the national gas hydrate program expedition 01 nghp 01 in 2006 in four areas located on the eastern and western margins of the indian peninsula and in the andaman sea these areas have experienced very different tectonic and depositional histories the peninsular margins are passive continental margins resulting from a series of rifting episodes during the breakup and dispersion of gondwanaland to form the present indian ocean the andaman sea is bounded on its western side by a convergent margin where the indian plate lithosphere is being subducted beneath southeast asia nghp 01 drilled logged and or cored 15 sites 31 holes in the krishna godavari basin 4 sites 5 holes in the mahanadi basin 1 site 2 holes in the andaman sea and 1 site 1 hole in the kerala konkan basin holes were drilled using standard drilling methods for the purpose of logging while drilling and dedicated wireline logging as well as through the use of a variety of standard coring systems and specialized pressure coring systems nghp 01 yielded evidence of gas hydrate from downhole log and core data obtained from all the sites in the krishna godavari basin the mahanadi basin and in the andaman sea the site drilled in the kerala konkan basin during nghp 01 did not yield any evidence of gas hydrate most of the downhole log inferred gas hydrate and core recovered gas hydrate were characterized as either fracture filling in clay dominated sediments or as pore filling or grain displacement particles disseminated in both fine and coarse grained sediments geochemical analyses of gases obtained from sediment cores recovered during nghp 01 indicated that the gas in most all of the hydrates in the offshore of india is derived from microbial sources only one site in the andaman sea exhibited limited evidence of a thermogenic gas source the gas hydrate petroleum system concept has been used to effectively characterize the geologic controls on the occurrence of gas hydrates in the offshore of india