Atlas of Gas Chimney Occurrences Associated With Oil and Gas Fields

Abstract

Most hydrocarbon producing basins of the world are dominated by vertical hydrocarbon migration. This vertical hydrocarbon migration is often directly detected in the seismic record as zones of vertically chaotic, low energy data, or “gas chimneys”. Geophysicists have noted that successful oil and gas wells are frequently less well imaged than wells over barren structures. Chimneys have often been observed in relationship to producing fields. However, this relationship has not been systematically documented, thus the need for a comprehensive atlas of these features. Chimneys can provide evidence of vertical hydrocarbon charge into a reservoir. Chimneys can also provide indications of the vertical seal integrity of the reservoir. The position of gas chimneys in relationship to the trap can also provide clues to the most likely fluid contacts. In mixed phase petroleum systems the morphology of chimneys can provide a clue to hydrocarbon phase. The diffuse nature of chimneys makes them difficult to map with 3D or 2D seismic data. Thus a method was developed to highlight and visualize these gas chimneys in normally processed seismic data. Gas chimneys are detected using a supervised neural network trained on reliable examples of gas chimneys. The resultant chimneys are validated based on a set of criteria. By detecting and mapping these chimneys, we can determine their origin (in a known or suspected source rock interval), their morphology, and how they are linked to known or suspected reservoirs. Using this chimney detection methodology, an atlas of chimney occurrences over known oil and gas fields (or discoveries) and dry holes in 3D seismic data is being compiled. Dry holes or sub-economic discoveries are chosen over valid anticlinal structures with effective reservoir (failure due to charge or seal). This atlas includes key interpreted and uninterpreted seismic lines through the wells to show the seismic character of identified chimneys. It also includes horizon slices, both above and below the reservoir intervals, to demonstrate charge and seal morphology. 3D images showing the relationship of chimney and reservoir geo-bodies are also displayed. Highlights of this atlas will be shown with examples from the Gulf of Mexico, North Sea, West Africa, Oriente Basin of Ecuador, Neuquén Basin of Argentina, and Gippsland Basin of Australia. The atlas is intended to provide useful analogs for hydrocarbon charge and seal assessment in various geologic settings.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015