A key element in any pore pressure prediction study is the comparison between the predicted pore pressure at the prospect location and the formation pressure measurements in offset wells. In order to understand, and predict, pressure distribution within a basin, pressure data and the sediments within which pressure regimes are confined need to be analyzed within a robust and consistent stratigraphic framework. This comparison is primarily required for: a) calibration for forward modelling and b) to have an idea of the extremes in the various pore pressure scenarios in a particular basin. The formation pressure measurements are acquired in permeable units like sands and are assumed to be in pressure equilibrium with adjacent shales. Thus, the predicted estimates in shales are compared with pore pressure measurements from sands in offset wells. This comparison is imprecise until and unless the offset pressure measurement is normalized to the same frame of reference at the prospect. The normalization process of offset pressure data can be broadly classified into two types: a) the simplistic depth normalization and b) the more detailed stratigraphic normalization. The simplistic depth normalization involves mere normalization of offset pressure measurements with respect to change in the positioning of the datum reference in the prospect location; this method precludes consideration of the structural difference (current plumbing) of each geological unit or in-depth analyses of depositional setup in offset and prospect locations presuming connected sands with constant overpressure. The second method entails the understanding of the regional stratigraphy, the structural differences in positioning of each stratigraphic unit in the prospect location and offset wells, depositional setting including sand connectivity and overpressure-generating mechanisms. This method can be invoked through appropriate approaches; a) constant overpressure (OP) method, b) constant vertical effective stress (VES) method and c) ratio method (ratio of either constant OP or VES to the normal effective stress i.e. NES). Stratigraphic normalization also includes the correct positioning of the offset pressure data in each stratigraphic unit at the prospect. Whilst the above normalization methods are extremely useful concepts, they form only part of the geological definition of the pressure system for predicting pore pressure profiles in an undrilled prospect. On the basis of geological understanding, stratigraphic normalization method may be preferred over the simplistic depth normalization method. An optimized normalization process for offset well data integrated with predicted pore pressure estimates at prospect locations illustrates a realistic scenario in terms of bounds of uncertainty. This paper brings forth a new dimension in predicting pore pressures at new prospects by describing scenarios within the framework of the conceived geological model. Also, the methods discussed provide the scope of capturing a valid uncertainty envelope that is imperative for a robust well design to define possible risks and foresee mitigation measures.
Underwater acoustic communication has several applications for civilians and defence. It is a challenging engineering problem, where large variability of ambient noise and highly variable channel characteristics limits the performance of communication system. In addition horizontal transmissions in shallow water is considered very challenging due to time varying delay spread and significant Doppler spread. An experiment was conducted to study the diurnal variability of underwater acoustic communication channel properties of the south west coast of India. Time spread and bit error rate for different ranges and depths are compared in this paper. Influence of prevailing sound speed profile on acoustic communication link is also discussed.
Acoustic properties of seafloor sediments can be estimated using theoretical models by giving geophysical properties of sediments as inputs to the respective models. Empirical relations connecting the geophysical and geoacoustic properties are available in literature. In this study an experimental assessment of two such theoretical models viz., Biot-Stoll model (BSM), a poro-elastic model and the Buckingham’s grain shearing (GS) model, a visco-elastic model is done by estimating the compressional wave speed. Compressional wave speed is measured using in-house developed sediment velocimeter and is compared with the speed estimated using both the models and a regression analysis was done. It was observed that the Coefficient of determination R2 for BSM and GS model are 0.769 and 0.729, respectively. It shows that once the constants used in GS model are evaluated for the Indian waters, then it can be used to estimate the acoustic properties of sediments.
During November 2017, an active source seismic survey was performed in Andaman sea to study the acoustic propagation characteristics. High power low frequency acoustic signals generated by 20-air gun array onboard ORV Samudra Ratnagar were recorded from INS Sagardhwani at four different depths within 8 km ranges in shallow and deep waters. Low frequency sound levels were estimated using root mean square and power spectral values. Amplitude levels were analysed with respect to arrival time variation with frequency and is presented.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.