Sanjeev Raghav

The Barren Volcano located in the volcanic chain of Burma–Java subduction complex became active during 2005–2006 initially as Strombolian and later on as sub-Plinian type ejecting out ash laden grey smoke and coarse pyroclasts. The pyroclasts are represented by vesiculated (20–30vol.% vesicle) porphyritic basaltic rock where the phenocrysts constituting 20–25vol.% of the total bulk are represented by plagioclase (18–25vol.%), olivine (1–4%), clinopyroxene (0.5–2.5 vol.%) and few iron oxides.

Government of India has set an ambitious target of reducing hydrocarbon import. Increasing oil & gas production is one of the measures by which oil & gas import dependency can be reduced. Despite relatively low crude prices globally, substantial E&P activities have been carried out in the country in the last decade, which has witnessed an exponential increase in exploration of oil and gas reserves. Many new fields were discovered during this exploration campaign out of which, few are potential traps containing hydrocarbons. Kutch and Saurashtra Basin off Gujarat coast is one of the exploration fields that involves trap drilling to explore reservoir sands below. Recently for the very first time, in a decade, oil reserves have been discovered in prospective sedimentary basin of Saurashtra. (DGH India Outlook, 2017-18) Drilling in this basin is characterized by slow rate of penetration (ROP), frequent bit trips, drill string failure, and high well cost. The 12 1/4-in section in this of...

Dissolved molybdenum (Mo) and uranium (U) concentrations were measured in five Indian estuaries; the Narmada, Tapi, Mandovi and the Mahi fall into the Arabian Sea and the Hooghly falling into the Bay of Bengal. Riverine Mo and U vary significantly, in the range of 1 to 90 ...

The 6"hole section in Raageshwari Field NW India (onshore) is typically between 600–800m long and highly challenging in terms of formation strength and abrasiveness. Lithology in the upper part is composed of sandstone, claystone and weathered basalt with unconfined compressive strength (UCS) between 3–5kpsi. The lower section contains basalt, felsic and sub-felsic igneous formations with UCS range of 15–30kpsi. Historically, a two bit strategy was employed. First, a PDC bit on a positive displacement motor (PDM) bottom hole assembly was used to drill the soft 6" section until ROP dropped to an unacceptable level. The BHA was then pulled and followed by a diamond impregnated bit on a turbine BHA to drill the very hard volcanics. Typical average on-bottom ROP for the entire section was 4.5m/hr and took approximately 170 hours to reach total depth (TD). To reduce costs, new technology was proposed to improve bit durability in the hard/abrasive volcanics and drill the entire 6" section in one run at a higher ROP. Recent bit and drilling data from offset wells was analyzed to assist in developing a new, cost effective PDC design to replace the expensive diamond-impregnated bits and drill the 6" hole section in one run. The study resulted in a new six-bladed PDC bit with 13 mm cutters that incorporates superior cutter technology to improve durability and resist physical and thermal degradation. The design includes a row of backup cutters in the shoulder area to increase radial diamond volume for maximum durability. The new PDC bits have been run on a motor and rotary steerable bottom hole assemblies and drilled the 6" section on three consecutive wells in Raageshwari field totaling 2328meters with an average ROP of 10.7m/hr. This represents approx. 47% decrease in drilling time compared to that previously achieved by Impreg/TCI bit runs. Typically, the new bits are pulled in re-runable condition. This improved performance has saved the operator approximately six-days of rig time and approximately USD 480,000/well.

The Indian monsoon activity, coinciding with the Inter-Tropical Convective Zone (ITCZ), progresses from the southern Indian Ocean during the boreal summer and withdraws towards the south in winter. Islands situated to the south of India receive, therefore, the first and last showers of the monsoon; speleothems in such islands have not yet been explored for their potential to reconstruct past monsoon rainfall. Here, we present the first measurements of stable carbon and oxygen isotopic compositions (δ13C andδ18O) of a stalagmite collected from the Baratang Island of Andamans, along with new data onδ18O of modern monsoon precipitation (May to July 2010). The aim was to detect (i) whether these samples are amenable to dating using14C, (ii) whether their oxygen isotopes indicate precipitation under isotopic equilibrium, and (iii) if (i) and (ii) above are true, can we reconstruct monsoon activity during the past few millennia? Our results indicate that whileδ18O of speleothem does show ...

ABSTRACT Quantifying the water loss of Himalayan glaciers due to global warming from direct measurement is difficult, as some glaciers are advancing or stable in spite of an overall retreat. We use a novel approach to provide an alternative estimate of the amount of Himalayan ice melt. Because a major part of this melted ice debouches into the Bay of Bengal through the Ganga–Brahmaputra basin, it causes significant variations in the oxygen isotopic composition (δ18O) and salinity (S) of the sea surface water and their mutual linear relationship. We document the temporal change in the δ18O–S relation for the bay at three different times during the period from 1994 to 2006, and using a model, we infer that 2.4 × 1011 m3 water was lost by melting from the Ganga–Brahmaputra basin during this period.

δ18O measurements in surface dwelling planktonic foraminifera (PF) Globigerinoides (Gs.) ruber from a sediment core from the central Bay of Bengal (BOB) has recorded a gradual depletion from ~ -1‰ during Last Glacial Maximum (LGM) to ~ -3‰ during mid-Holocene suggesting a strengthening of Indian Summer Monsoon (ISM) over the bay during last glacial - interglacial transition. However, this trend is punctuated by abrupt multi-centennial enrichment in the δ18O values of the order of ~ 0.5 ‰. Age model of the core obtained from AMS 14C dates in mixed planktonic foraminifera and in bulk sediment suggests that timing of these abrupt enrichments of the δ18O values corresponds to the Heinrich (H1), Younger Dryas (YD) and 8.2 ka North Atlantic cold events centered at ~ 15.5 cal ka BP, 11.7 cal ka BP and 8 cal ka BP respectively. It is also observed that although there are episodes of significant changes in the sea surface temperature and salinity (as reflected in the periodical enrichment in the δ18O values) between 19ka to 5ka, the abundance of the mixed layer PF - Gs. ruber and Gs. sacculifer - and upper thermocline dweller Neogloboquadrina dutertrei do not show much variation during this period indicating that the upper ocean stratification remained almost same in the bay after the major turnover at the end of LGM. This suggests that this periodical enrichment of δ18O in the surface dwelling PF Gs. ruber is controlled primarily by the episodes of abrupt monsoon decline. The synchrony of cold events of NGIRP ice core and North Atlantic marine records with the central BOB core suggests the existence of a strong tele-connection between the North Atlantic and the monsoon variability as recorded in BOB sediments. We propose that northern hemispheric abrupt cold events like H1, YD and 8.2 ka recorded in the Greenland and the North Atlantic had played a vital role in modulating the ISM over the bay and thus giving rise to a stepwise strengthening of ISM during the last glacial-interglacial transition in the BOB