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Detecting Vertical Hydrocarbon Expulsion from Source Rock in Seismic Data*

David L. Connolly¹

Search and Discovery Article #40331 (2008)

Posted October 15, 2008

*Adapted from oral presentation at AAPG Annual Convention, San Antonio, TX, April 20-23, 2008

¹dGB USA, Sugar Land, TX. ([email protected])

Abstract

Modeling petroleum systems accurately in a basin requires a good understanding of the areal distribution of source rocks, the stratigraphic intervals in which source rocks occur, and their thermal maturity. These models have depended on assumptions about source rock presence based on regional outcrop information or limited well information because wells are rarely drilled in the hydrocarbon kitchen lows. These models also must be based on assumptions about regional heat flow which have a high degree of uncertainty. Direct detection of vertical hydrocarbon expulsion from source rock in seismic data is a promising approach to constrain geologic models. The methodology involves detecting vertically aligned low-energy chaotic zones in the seismic data (gas chimneys) through a supervised, multi-attribute, neural network approach. By determining the origin of these chimneys, we can infer both the stratigraphic interval from which the hydrocarbons originate, the distribution of source prone facies, and the distribution of thermally mature source rock. The chimney information can also be used to show migration pathways into potential reservoir intervals and possible leakage via faults or top seal failure from these reservoirs. This information can then be input into the basin model to constrain model inputs. Similarly basin models can constrain the results of chimney processing. Case studies are shown from the North Sea, South Atlantic, and Gulf of Mexico.

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