Suman Paul

Overpressure Zones in Relation to In Situ Stress for the Krishna-Godavari Basin, Eastern Continental Margin of India: Implications for Hydrocarbon Prospectivity

An analysis for over pressure zone (OPZ) prevailing in parts of the Krishna-Godavari Basin (KG-B) at the Eastern Continental Margin of India (ECMI) is found promising from the viewpoint of its hydrocarbon potentials. Pressure coefficients estimated from pore pressure studies reveal that there is a rather extensive (lateral) OPZ in the study area than hitherto expected with maximum pressure coefficient of 1.31 or more. The stress magnitudes like vertical stress (Sv), minimum horizontal stress (Sh) and pore pressure gradient (PPG) and fracture pressure gradient (FPG) are predicted from well log data for 15 available wells distributed over an area of 6022 km2 in KG-B. The wells are drilled to depths of 3660 m on-land (#Wells 1–9) and up to 4000 m in offshore (#Wells 10–15). The PPG ranges from 11.85 to 13.10 MPa/km, whereas, the FPG varies from 17.40 to 19.78 MPa/km in sediments penetrated by the wells displaying normal pressured sediment to a significantly higher value of 19.78 MPa/km for the over-pressured sediments. The values of vertical stress gradient (VSG) varies from 14.67 to 23.10 MPa/km, whereas, the values of Sh magnitude varies from 64 to 77 % of the Sv in normally-pressured to over-pressured sediments. VSG, PPG and FPG tend to decrease with corresponding increase in water column for the studied offshore wells. These results are utilized for constructing contour maps for observing the variations in the VSG and in the OPZ-top, also for constructing PPG contour map in 3D along the vertical section connecting all 15 wells extending from onshore to offshore regions. Any significant increase in pore pressure means the decrease of effective horizontal stress in respect of depth. As a result, the safety windows or safe mud-weight windows (the difference between PPG and FPG corresponding to particular depth interval in a well) will also decrease with the increase of PPG and FPG. Analytical approach adopted above is then critically examined to recommend how a priori steps based on petrophysical characters of a formation are closely monitored in time and optimum mud weight maintained during drilling.

Estimation of In-situ Stress and Coal Bed Methane Potential of Coal Seams from Analysis of Well Logs, Ground Mapping and Laboratory Data in Central Part of Jharia Coalfield—An Overview

Well log data of thirty (30) boreholes from central part of Jharia coalfield have been analysed for estimation of petrophysical and rock mechanical properties of coal seams to facilitate assessment of Coal Bed Methane (CBM) reservoir potentiality of those coal seam. Wells from Jharia area showed 18 major correlatable seams, intersected between 214 and 1324 m depth. The resistivity, density and natural gamma ray log data from the wells of the study area have been utilized for: (a) Estimation of permeability of coal seams from resistivity log data; (b) Computation of in-situ stress magnitudes—vertical stress, effective vertical stress and effective horizontal stress at seam horizons; (c) Establish relationship between in-situ stress and permeability; (d) Estimation of gas content of coal seams and identification of most potential zones for CBM exploration. It is observed that the permeability values ranging from 0.82 to 1.12 md with average gas content of 11.50 to 11.75 cc/gm. By comparing gas content, coal seam thickness as well as coal bed permeability of these major coal seams, the most viable CBM potential zone is mapped for this area.

Thermal Anomalies Around the Time of Nepal Earthquakes M 7.8 April 25, 2015 And M 7.3 May 12, 2015

TwoconsecutivelargeearthquakeshavingMvalues7.8and7.3occurredonApril25andMay12, 2015,respectivelyatNepal.Duringtheiroccurrences,abruptincreaseingreenhousegases(likeCO2, CH4,H2etc.)andenhancementofradonemanationsarefound.Theseattainhighmomentumthat introduceanomalyinthefluidexpulsionfromseismicallyactivefaultswhichproduceairionization beforetheselargeearthquakes.Theprocessmaybeverymuchrelatedtothelatentheatreleasedue tocondensationofionizedaerosols,producedbyenergeticalphaparticlesfromradonjustbeforethe earthquake.Thisprobablyintroduceschangesintheobservedmeteorologicalparametersintheregion. Suchvariationsmaybeduetosiesmotectonicallyinducedradonanomalybeforetheearthquake.

Time series modelling of maximum tsunami wave heights recorded in Sibolga (Sumatra)

This study reports univariate modeling methodologies applied to the maximum tsunami wave height over Sibolga, Sumatra. The univariate time series models fitted are autoregressive model (AR), autoregressive integrated moving average (ARIMA) and autoregressive neural network (AR-NN). Goodness of fit of the models to the time series of maximum tsunami wave height has been assessed using percentage of prediction error, Pearson correlation coefficient, and Willmotts indices. After rigorous skill assessment using the above three models, the AR-NN model with seven previous values as predictor has been identified as the best predictive model for the time series under study.

Dynamical evolution of Schumann resonance frequency spectra during some strong Q-bursts

Schumann resonances (SR) observations from a tropical region near Kolkata at the estuary of the river Ganges merging into the Bay-of-Bengal (21.48° N, 88.61° E) are being made frequently. Several Q-bursts spectra are observed. Strong ELF transients are detected in the recorded data of SR. The dynamic evolution of electric and magnetic field components of the Q-bursts will be presented in this paper. Time series evolutions of signals of several Q-bursts are analyzed in the present study. It is observed that, the Q-burst amplitudes from 1 to 300 Hz of Q-bursts spectra for 1 sec FFT reaches about −47 dB near the first mode of SR frequency. This shows that Q-burst has the tendency to dominate within 1 to 300 Hz.

Studies on the effects of AILA-2009 on VLF Integrated Field Intensity of Atmospherics

Remarkable effects on the records on Integrated Field Intensity of Atmospherics (IFIA) over Kolkata (latitude: 22.56° N, longitude: 88.5° E) at 3 kHz and 9 kHz are observed due to severe electrical activity in a thunderstorm, AILA, followed by severe thundershowers and lightning. The analyses and evaluation of the recorded data have been presented here.

Studies on the short-range pressure pulse generation within the auroral ionosphere

Auroral electric field is a probable source of Atmospheric Gravity Waves (AGW) in the thermospheric region of Auroral zone of the ionosphere and associated Traveling Ionospheric Disturbances (TID). This field is considered to be active through Lorentz force and Joule dissipation that influence the neutral gas of the medium through collision. The process introduces the short-range gravity waves. The expressions for the low frequency part of the fractional pressure variations have been derived within the auroral region of the ionosphere. The results of numerical analyses are presented graphically.