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ÇAĞRILI KONUŞMALAR / KEYNOTES Invited Speeches ... - TPJD

ÇAĞRILI KONUŞMALAR / KEYNOTES Invited Speeches ... - TPJD

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The Use of Gas Chimneys for Risk Mitigation in All Elements of a Petroleum<br />

System<br />

Philip Nantais 1 , Michael McRae 2 , Bradley Ritts 3 , Stanley Roe 4<br />

1 Chevron Blacksea B.V., Ankara<br />

2 Chevron Energy Technology Company, Houston, USA<br />

3 Chevron Asia Pacific Exploration and Production, Singapore<br />

4 Chevron Europe, Eurasia And Middle East Exploratıon & Production Company, San Ramon, USA<br />

Gas chimneys and hydrocarbon seepage are well known from many offshore basins around the<br />

world with prolific petroleum systems. Also, there are many hydrocarbon accumulations with no<br />

observed gas chimneys. The presence of gas chimneys is often used to make inferences about<br />

source rocks and seal. The objective of this paper is to demonstrate that the application of a simple<br />

gas chimney classification scheme and critical thinking can also reveal significant information<br />

about reservoir, trap geometry, seal capacity, hydrocarbon phase and migration. Several examples<br />

from a number of basins will be used to demonstrate the concepts. Gas chimney is a poorly<br />

defined generic term that is typically used to describe areas of seismic data exhibiting a vertical<br />

diffuse, chaotic or degraded quality reflection character on 2D or 3D data. Gas chimneys can<br />

also be accompanied by velocity and amplitude anomalies or even complete wipeout zones. The<br />

perturbations on the seismic are thought to be caused by the presence of free gas in the section;<br />

although fracturing and overpressure might contribute to the deteriorated seismic response.<br />

Gas chimneys can generally be distinguished from other vertical seismic noise bands caused<br />

by near surface/seafloor effects, permafrost, hydrates or very shallow gas by the direction of<br />

propagation of the noise – top down or bottom-up. In-basin calibration organized by play-type is<br />

also an important element of this analysis and can be used to high-grade an exploration portfolio<br />

or play trend. The integration with basin modeling can further constrain interpretations and<br />

contribute to the understanding of geological risk. Characterization, classification and calibration<br />

of gas chimneys are a best practice for mitigating geological risk in an exploration basin. A gas<br />

chimney can be a positive sign for many exploration opportunities but the lack of a gas chimney<br />

cannot automatically be taken as negative evidence.<br />

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