During the Indian National Gas Hydrate Program(NGHP)Expedition 02,Logging-while-drilling(LWD)logs were acquired at three sites(NGHP-02-11,NGHP-02-12,and NGHP-02-13)across the Mahanadi Basin in area A.We applied rock p...During the Indian National Gas Hydrate Program(NGHP)Expedition 02,Logging-while-drilling(LWD)logs were acquired at three sites(NGHP-02-11,NGHP-02-12,and NGHP-02-13)across the Mahanadi Basin in area A.We applied rock physics theory to available sonic velocity logs to know the distribution of gas hydrate at site NGHP-02-11 and NGHP-02-13.Rock physics modeling using sonic velocity at well location shows that gas hydrate is distributed mainly within the depth intervals of 150-265 m and 100 -215 mbsf at site NGHP-02-11 and NGHP-02-13,respectively,with an average saturation of about 4%of the pore space and the maximum concentration of about 40%of the pore space at 250 m depth at site NGHP-02-11,and at site NGHP-02-13 an average saturation of about 2%of the pore space and the maximum concentration of about 20%of the pore space at 246 m depth,as gas hydrate is distributed mainly within 100-246 mbsf at this site.Saturation of gas hydrate estimated from the electrical resistivity method using density derived porosity and electrical resistivity logs from Archie's empirical formula shows high saturation compared to that from the sonic log.However,estimates of hydrate saturation based on sonic P-wave velocity may differ significantly from that based on resistivity,because gas and hydrate have higher resistivity than conductive pore fluid and sonic P-wave velocity shows strong effect on gas hydrate as a small amount of gas reduces the velocity significantly while increasing velocity due to the presence of hydrate.At site NGHP-02-11,gas hydrate saturation is in the range of 15%e30%,in two zones between 150-180 and 245-265 mbsf.Site NGHP-02-012 shows a gas hydrate saturation of 20%e30%in the zone between 100 and 207 mbsf.Site NGHP-02-13 shows a gas hydrate saturation up to 30%in the zone between 215 and 246 mbsf.Combined observations from rock physics modeling and Archie’s approximation show the gas hydrate concentrations are relatively low(<4%of the pore space)at the sites of the Mahanadi Basin in the turbidite channel system.展开更多
The floods in river Mahanadi delta are due to either dam release of Hirakud or due to contribution of intercepted catchment between Hirakud dam and delta. It is seen from post-Hirakud periods (1958) that out of 19 flo...The floods in river Mahanadi delta are due to either dam release of Hirakud or due to contribution of intercepted catchment between Hirakud dam and delta. It is seen from post-Hirakud periods (1958) that out of 19 floods 14 are due to intercepted catchment contribution. The existing flood forecasting systems are mostly for upstream catchment, forecasting the inflow to reservoir, whereas the downstream catchment is devoid of a sound flood forecasting system. Therefore, in this study an attempt has been made to develop a workable forecasting system for downstream catchment. Instead of taking the flow time series concurrent flood peaks of 12 years of base and forecasting stations with its corresponding travel time are considered for analysis. Both statistical method and ANN based approach are considered for finding the peak to reach at delta head with its corresponding travel time. The travel time has been finalized adopting clustering techniques, there by differentiating high, medium and low peaks. The method is simple and it does not take into consideration the rainfall and other factors in the intercepted catchment. A comparison between both methods are tested and it is found that the ANN methods are better beyond the calibration range over statistical method and the efficiency of either methods reduces as the prediction reach is extended. However, it is able to give the peak discharge at delta head before 24 hour to 37 hour for high to low peaks.展开更多
The tephra layers in multiple sediment cores from the offshore region of the Mahanadi basin in the northern Bay of Bengal were investigated for possible volcanic sources. The glass shards from those tephra layers were...The tephra layers in multiple sediment cores from the offshore region of the Mahanadi basin in the northern Bay of Bengal were investigated for possible volcanic sources. The glass shards from those tephra layers were studied for size distribution, texture, and elemental geochemistry to establish chronostratigraphic markers for regional and global Quaternary correlation. The textural features of fine-grained(silty) volcanic glasses suggest the distal source of these tephra deposits. Major element composition with elevated SiO_(2) contents ranging between75%–76% and dominance of K_(2)O(> 4.5%) over CaO(< 0.9%) suggest ashes have originated from siliceous rhyolitic melts, similar to the petrographic composition of tephra from the Toba volcano. The bulk trace element compositions of the same glass shards were comparable with those reported in the youngest Toba tephra reported elsewhere. Likewise, the LREE-dominated chondrite normalized REE profiles of tephra from the Mahanadi basin closely resemble the characteristic REE patterns in Toba ash from other parts of the Indian Ocean and thus confirmed the contribution of the youngest Toba super-eruption for this ash layers.展开更多
Given the challenges of re-creating complex bed load(BL)transport processes in rivers,models are preferred over gathering and examining field data.The highlight of the present research is to develop an approach to det...Given the challenges of re-creating complex bed load(BL)transport processes in rivers,models are preferred over gathering and examining field data.The highlight of the present research is to develop an approach to determine the ungauged bed load concentration(BLC_(u))utilizing the measured suspended sediment concentration(SSC)and hydraulic variables of the last four decades for the Mahanadi River Basin.This technique employs shear stress and SSC equations for turbulent open channel flow.Besides,the predicted BLC_(u)is correlated with SSC using a power relation to estimate BLC_(u)on the river and tributaries.Eventually,different BL functions(BLF)efficiency is assessed across stations.The model predicted BLC_(u)is comparable with the published data for sandy rivers and falls within±20%.Outliers in hydraulic and sedimentological statistics significantly influence estimating the BL fraction apart from higher relative ratios and catchment geology.The constants of power functions are physically linked to sediment transport configuration,mechanism,and inflow to the stream.The stream power-based BLF best predicts the BL transport,followed by shear stress and unit discharge approaches.The disparity in the estimation of BLC_(u)results from station-specific physical factors,sampling data dispersion,and associated uncertainties.展开更多
文摘During the Indian National Gas Hydrate Program(NGHP)Expedition 02,Logging-while-drilling(LWD)logs were acquired at three sites(NGHP-02-11,NGHP-02-12,and NGHP-02-13)across the Mahanadi Basin in area A.We applied rock physics theory to available sonic velocity logs to know the distribution of gas hydrate at site NGHP-02-11 and NGHP-02-13.Rock physics modeling using sonic velocity at well location shows that gas hydrate is distributed mainly within the depth intervals of 150-265 m and 100 -215 mbsf at site NGHP-02-11 and NGHP-02-13,respectively,with an average saturation of about 4%of the pore space and the maximum concentration of about 40%of the pore space at 250 m depth at site NGHP-02-11,and at site NGHP-02-13 an average saturation of about 2%of the pore space and the maximum concentration of about 20%of the pore space at 246 m depth,as gas hydrate is distributed mainly within 100-246 mbsf at this site.Saturation of gas hydrate estimated from the electrical resistivity method using density derived porosity and electrical resistivity logs from Archie's empirical formula shows high saturation compared to that from the sonic log.However,estimates of hydrate saturation based on sonic P-wave velocity may differ significantly from that based on resistivity,because gas and hydrate have higher resistivity than conductive pore fluid and sonic P-wave velocity shows strong effect on gas hydrate as a small amount of gas reduces the velocity significantly while increasing velocity due to the presence of hydrate.At site NGHP-02-11,gas hydrate saturation is in the range of 15%e30%,in two zones between 150-180 and 245-265 mbsf.Site NGHP-02-012 shows a gas hydrate saturation of 20%e30%in the zone between 100 and 207 mbsf.Site NGHP-02-13 shows a gas hydrate saturation up to 30%in the zone between 215 and 246 mbsf.Combined observations from rock physics modeling and Archie’s approximation show the gas hydrate concentrations are relatively low(<4%of the pore space)at the sites of the Mahanadi Basin in the turbidite channel system.
文摘The floods in river Mahanadi delta are due to either dam release of Hirakud or due to contribution of intercepted catchment between Hirakud dam and delta. It is seen from post-Hirakud periods (1958) that out of 19 floods 14 are due to intercepted catchment contribution. The existing flood forecasting systems are mostly for upstream catchment, forecasting the inflow to reservoir, whereas the downstream catchment is devoid of a sound flood forecasting system. Therefore, in this study an attempt has been made to develop a workable forecasting system for downstream catchment. Instead of taking the flow time series concurrent flood peaks of 12 years of base and forecasting stations with its corresponding travel time are considered for analysis. Both statistical method and ANN based approach are considered for finding the peak to reach at delta head with its corresponding travel time. The travel time has been finalized adopting clustering techniques, there by differentiating high, medium and low peaks. The method is simple and it does not take into consideration the rainfall and other factors in the intercepted catchment. A comparison between both methods are tested and it is found that the ANN methods are better beyond the calibration range over statistical method and the efficiency of either methods reduces as the prediction reach is extended. However, it is able to give the peak discharge at delta head before 24 hour to 37 hour for high to low peaks.
基金We thank the Directors of CSIR-NIO and CSIR-NGRI,for supporting this studyThis work is a part of a multidisciplinary program under the aegis of the National Gas Hydrate Program(NGHP),India,on gas hydrate exploration in the Eastern continental margin of India.The incharge of IPEV operations is thanked for providing onboard technical support and facilities.This research was funded by MoES,Govt.of India.Mr.Girish Prabhu and Mr.Vijay Khedekar are thanked for XRD and SEM analyses,respectively.This is NIO contribution no.7047.
文摘The tephra layers in multiple sediment cores from the offshore region of the Mahanadi basin in the northern Bay of Bengal were investigated for possible volcanic sources. The glass shards from those tephra layers were studied for size distribution, texture, and elemental geochemistry to establish chronostratigraphic markers for regional and global Quaternary correlation. The textural features of fine-grained(silty) volcanic glasses suggest the distal source of these tephra deposits. Major element composition with elevated SiO_(2) contents ranging between75%–76% and dominance of K_(2)O(> 4.5%) over CaO(< 0.9%) suggest ashes have originated from siliceous rhyolitic melts, similar to the petrographic composition of tephra from the Toba volcano. The bulk trace element compositions of the same glass shards were comparable with those reported in the youngest Toba tephra reported elsewhere. Likewise, the LREE-dominated chondrite normalized REE profiles of tephra from the Mahanadi basin closely resemble the characteristic REE patterns in Toba ash from other parts of the Indian Ocean and thus confirmed the contribution of the youngest Toba super-eruption for this ash layers.
基金Ministry of Water Resources,Government of India,No.28/1/2016-R&D/228–245。
文摘Given the challenges of re-creating complex bed load(BL)transport processes in rivers,models are preferred over gathering and examining field data.The highlight of the present research is to develop an approach to determine the ungauged bed load concentration(BLC_(u))utilizing the measured suspended sediment concentration(SSC)and hydraulic variables of the last four decades for the Mahanadi River Basin.This technique employs shear stress and SSC equations for turbulent open channel flow.Besides,the predicted BLC_(u)is correlated with SSC using a power relation to estimate BLC_(u)on the river and tributaries.Eventually,different BL functions(BLF)efficiency is assessed across stations.The model predicted BLC_(u)is comparable with the published data for sandy rivers and falls within±20%.Outliers in hydraulic and sedimentological statistics significantly influence estimating the BL fraction apart from higher relative ratios and catchment geology.The constants of power functions are physically linked to sediment transport configuration,mechanism,and inflow to the stream.The stream power-based BLF best predicts the BL transport,followed by shear stress and unit discharge approaches.The disparity in the estimation of BLC_(u)results from station-specific physical factors,sampling data dispersion,and associated uncertainties.
