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Geohazard detection and other applications of chimney cubes

dGB-USA, Houston, Texas, U.S.

Roar Heggland and Paul Meldahl

Statoil, Stavanger, Norway

Paul de Groot

dGB BV, Enschede, Netherlands

Corresponding author: faz@dgbusa.com

For biographies of other authors see TLE, April 2002 and February 2001.

The first 20% of the full text of this article appears below.

The "chimney cube" is a new processing and interpretation tool that highlights vertical anomalies on seismic data associated with gas clouds and gas chimneys. They are used to address drilling hazards caused by shallow gas pockets and platform stability problems due to subsea mud volcanoes. Chimney cube data also assist exploration of hydrocarbon targets by high grading prospects and improving understanding of the petroleum system.

Practically, chimney cubes can reveal where hydrocarbons originated, how they migrated into a prospect, and how they spilled or leaked from this prospect and created shallow gas, mud volcanoes, or pockmarks at the sea bottom. Current applications include detecting shallow gas and geohazards, distinguishing between charged and noncharged prospects, determining vertical migration of gas, and unraveling a basin's migration history. New applications include identifying potential for overpressure, predicting hydrocarbon phase and charge efficiency (especially in multiphase petroleum systems), distinguishing active versus nonactive fault migration pathways, predicting seal capacity, and supporting and refining basin models. This paper presents initial models for applications of these very new concepts. The payback from the concepts is expected to increase significantly by gathering experience and updating the initial models.

The Chimney Cube is a new concept that uses a 3D volume of stacked seismic data with prior information (e.g., the interpreter's insight and/or other geologic data) to highlight vertical chaotic seismic character often associated with gas chimneys. Figure 1 shows a slice of a chimney cube overlaid on a conventional seismic cross-section. The methodology was discussed in detail in Meldahl's "Interpreter's Corner" article in the May 2001 TLE. The appendix overviews the methodology and processing sequence. The main body of this article will highlight specific applications of chimney cubes for different geohazard problems.

View larger version (125K): [in this window] [in a new window]   Figure 1. A slice of a chimney cube overlaid on a conventional seismic cross-section. (Figure courtesy of ChevronTexaco.)

	Detecting shallow gas pockets