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TitleGas hydrate saturation in the Krishna - Godavari basin from P-wave velocity and electrical resistivity logs
AuthorShankar, U; Riedel, M
SourceEarth and Planetary Science Letters 2010.,
Alt SeriesEarth Sciences Sector, Contribution Series 20100037
PublisherElsevier BV
Mediapaper; on-line; digital
File formatpdf
AreaKrishna - Godavari basin; India
Lat/Long WENS 81.5000 83.7500 16.7500 15.7500
Subjectsfossil fuels; geophysics; hydrocarbons; hydrocarbon potential; hydrocarbon gases; hydrate; p waves; seismic waves; geophysical surveys; electrical resistivity; resistivity; resistivity surveys
Illustrationslogs; tables; plots; location maps
ProgramGas Hydrates
AbstractDuring the Indian National Gas Hydrate Program (NGHP) Expedition 01, a series of well logs were acquired at several sites across the Krishna-Godavari (KG) Basin. Electrical resistivity logs were used for gas hydrate saturation estimates using Archie's method. The measured in situ pore-water salinity, seafloor temperature and geothermal gradients were used to determine the baseline pore-water resistivity. In the absence of core data, Arp's law was used to estimate in situ pore-water resistivity. Uncertainties in the Archie's approach are related to the calibration of Archie coefficient (a), cementation factor (m) and saturation exponent (n) values. We also have estimated gas hydrate saturation from sonic P-wave velocity logs considering the gas hydrate in-frame effective medium rock-physics model. Uncertainties in the effective medium modeling stem from the choice of mineral assemblage used in the model. In both methods we assume that gas hydrate forms in sediment pore space. Combined observations from these analyses show that gas hydrate saturations are relatively low (<5% of the pore space) at the sites of the KG Basin. However, several intervals of increased saturations were observed e.g. at Site NGHP-01-03 (Sh = 15-20%, in two zones between 168 and 198 mbsf), Site NGHP-01-05 (Sh = 35-38% in two discrete zone between 70 and 90 mbsf), and Site NGHP-01-07 shows the gas hydrate saturation more than 25% in two zones between 75 and 155 mbsf. A total of 10 drill sites and associated log data, regional occurrences of bottom-simulating reflectors from 2D and 3D seismic data, and thermal modeling of the gas hydrate stability zone, were used to estimate the total amount of gas hydrate within the KG Basin. Average gas hydrate saturations for the entire gas hydrate stability zone (seafloor to base of gas hydrate stability), sediment porosities, and statistically derived extreme values for these parameters were defined from the logs. The total area considered based on the BSR seismic data covers not, vert, similar720 km2. Using the statistical ranges in all parameters involved in the calculation, the total amount of gas from gas hydrate in the KG Basin study area varies from a minimum of not, vert, similar5.7 trillion-cubic feet (TCF) to not, vert, similar32.1 TCF.

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