Sanjeev Rajput

Signal preserving seismic interference noise attenuation on 3D marine seismic data

In a study of the contamination of reflection seismic data by interfering noise from other seismic crews, the seismic interference noise attenuation technique, which uses frequency-shot-receiver (f-x-y) prediction filters for detection of noise, is applied in f-x domain to the noisy frequencies of the shots. The method has been tested on real datasets and impressive results have been obtained. The seismic interference noise from other seismic vessel, as well as random noise on 3D marine seismic survey data can be significantly detected and suppressed hence we conclude that the f-x-y interference attenuation mechanism preserves the primary signal and eliminate the seismic interference in a very efficient way.

World’s Oil and Natural Gas Scenario

Recent studies suggest that the earths crust may hypothetically hold 6,000 Billion Barrels of oil as its reserves, which also include 3,000 Billion Barrel un-recovered oil resource. However, owing to the complexities in geology associated with the reservoirs one can only indirectly get some inference about the quantum of reserves based on some probabilistic distribution. With 95% probability the world may touch ultimate recovery of 2,248 Billion Barrels. Owing to the non-encouraging scenario of oil production and likely higher cost of oil in future, may lead to search for alternative replacement to oil. The world gas reserves are estimated to the order of 10,000 Trillion Cubic Feet (TCF) out of which only 6,186 TCF are the proven reserves. The projected world natural gas consumption may reach to 158 TCF by 2030. This chapter provides an overview of present oil production, its consumption and future prospects.

Seismic indicators of gas hydrates and associated free gas

Summary Ga s hydrates are found worldwide and many studies have been carried out to develop an efficient method to identify and quantify them using various geophysical as well as other anomalies. In this paper, we model P- and S-wave velocities of gas hydrates and associated gas, and generate synthetic seismic response for different models by 2D wave equation technique. Various patterns in synthetic seismograms related to gas hydrates and associated free gas are analyzed. Datasets from different regions of the world along with synthetic modeling results are used to evaluate our observations. The results reveal that bottom simulating reflector (BSR), enhanced seismic reflections below BSR, seismic chimneys, mounds, and amplitude blanking are the key seismic indicators for gas hydrates.

Identification to Quantification of Gas Hydrates

In order to meet the world’s energy requirements, identification to quantification of potential energy resources such as gas hydrates is of prime importance. Here we present details of different interpretation techniques and seismic characteristics for drawing inference about the presence of gas hydrates in a region of investigations. The regional identification of gas hydrates could be achieved by travel time inversion schemes. Full waveform modeling is useful in studying the different characteristics, including finer velocity and density estimates of gas hydrates and associated free gas. Seismic attributes are necessary in the direction of predicting gas hydrate saturation. The calculation of seismic attributes can be achieved by the integrated workflows of seismic, geology, pertophysics and rock physics techniques. Modeling for estimating BSR strength in terms of thickness of hydrate/free gas layers with information contained in the velocity estimation is a useful tool for estimating the reflection coefficients, Poisson’s ratios and quantification of gas hydrate resources. This chapter summarizes the prevalent techniques for regional to local mapping of gas hydrates. To this end few synthetic and real data examples of gas hydrate characterizations from different regions of the world are discussed.

Geophysical Surveys and Data Analysis

Gas hydrates occur worldwide in marine sediments and can play a major role in contributing world’s energy requirements. The identification and assessment of gas hydrate volume can be done by different geophysical techniques including various types of seismic surveys, like (2D/3D conventional, ocean bottom seismic, vertical seismic profiling, cross-well seismic and multi-component), well logging, and control source electromagnetic surveys. This chapter provides a brief of various survey designs and optimal survey parameters for gas hydrate exploration. Reflection seismic profiles are useful to construct the compressional velocity (VP) model for hydrate bearing formations and to explore its possible lateral variation and thereby provide possible relevant interpretations in terms of the geology/tectonics of the subsurface earth. Ocean bottom seismic surveys are the key to explore deeper structures and to build the shear velocity model for hydrates. The results of various gas hydrate models together with the field data reveals that seismic methods are able to detect the lower stratigraphic bound of the hydrates as there is no seismic reflection from upper bound and there is no seismic signature within the hydrate stability zone. Another technique for hydrate detection includes well logging (electrical resistivity, gamma ray etc.) which, provide point measurements and provide no information into the lateral distribution of hydrates. Electromagnetic methods for hydrate detection are also feasible but require more field attempts and laboratory studies.

Pre-stack Seismic Inversion Based Case Study On Tight Laminated Sands From East Coast of India

The east coast of India comprises a number of northeastsouthwest trending horsts and grabens defined by faultblocks movements. The Krishna and western part of the Godavari troughs are filled with mainly Paleozoic and Mesozoic sediments while the eastern part of the Godavari trough contains a predominantly Upper Mesozoic and Tertiary section. The block investigated by this study consisted of reservoirs characterized by tight thinly laminated sand packages. A pre-stack AVO simultaneous inversion followed by lithology classification based on a Bayesian formulation scheme using the rock physics analysis of the available wells was used to better define the reservoir packages. The case study looks at the prediction challenges and an interpretation workflow to reduce risks of identifying prospective drilling locations.

2D traveltime inversion for gas hydrates in Kerala‐Konkan basin, western offshore India

A huge reservoir of carbon resides as methane in clathrate deposits in sediments under the world’s oceans as well as in on-shore sediments in the Arctic. As the search for oil and gas extends to deeper waters, gas hydrates are becoming more of a concern in terms of both safety and as a potential energy source. In this paper, we present the results of 2D travel time inversion on multichannel seismic data of Kerala-Konkan (KK) basin, western offshore India for gas hydrates investigations. The lateral and vertical extent of gas hydrate and free gas zone within the sedimentary cover of the passive KK basin has been mapped.