Detection of Vertical Hydrocarbon Migration Pathways in Seismic Data: Toward the Quantification of Top Seal and Charge Risk

Abstract

Abstract

Most hydrocarbon producing basins of the world are dominated by vertical hydrocarbon migration. This hydrocarbon migration is often directly detected in the seismic record as zones of vertically aligned, chaotic, low energy data, called “gas chimneys” or “gas clouds”, although they are often associated with oil migration. A survey of major exploration companies suggests that seal and charge provide the majority of risk in today's exploration portfolio. The morphology of chimneys directly above the reservoir provides clues to the top seal integrity. THe morphology of vertical chimneys directly beneath the reservoir may provide clues to the effectiveness of hydrocarbon charge. Traps can be classified for charge effectiveness based on the abundance of chimneys in direct communication with the reservoir body. These classifications can then be a guideline for risking untested structures.

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. Not all chimneys, detected by neural network training, are related to hydrocarbon migration. Thus the resultant chimneys must be 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.

Chimneys have often been observed in relationship to producing oil and gas fields. However, this relationship has not been systematically documented. To address this issue we are compiling an atlas of chimney occurrences associated with known oil and gas fields and dry holes using 3D seismic data. Dry holes or sub-economic discoveries are chosen over valid anticlinal structures with effective reservoir (failure due to charge or seal). Highlights of this atlas will be shown with examples from the Northern and Southern Gulf of Mexico offshore. The atlas is intended to provide useful analogs for hydrocarbon charge and seal assessment in various geologic settings worldwide.

AAPG Datapages/Search and Discovery Article #90260 © 2016 AAPG/SEG International Conference & Exhibition, Cancun, Mexico, September 6-9, 2016