Using Integrated Gas Chimney Processing, Frequency Attenuation Attributes, and Seismic Facies Classification to Delineate Oil Filled Reservoirs: Case Studies from the Oriente Basin, Ecuador
The Oriente Basin of Ecuador is one of the most prolific oil producing basins in South America. Oil has been discovered in both structural and stratigraphic traps in the Cretaceous Napo Fm and Paleocene Basal Tena Fm. However, it is often difficult to distinguish oil filled from wet sands on 3d seismic data. The reservoirs are generally low amplitude. It is therefore critical to be able to delineate the extent of oil filled reservoir to predict recoverable reserves. Subtle diffuse gas chimneys (gas clouds) have been observed over many of the producing fields in the Oriente Basin. Also reconnaissance of the 3d seismic data in the vicinity of the discovery wells showed subtle frequency attenuation.
Therefore an integrated three part strategy was designed to highlight areas for development drilling and further exploration. 1) A horizon based seismic waveform classification was done in a narrow window around the major producing reservoir. 2) Gas chimneys were highlighted in the seismic data using a supervised neural network approach. 3) A hydrocarbon probability volume was created, again using a supervised neural network approach based on frequency and energy attributes.
The results of the neural network processing showed prominent gas chimneys which charged the Napo reservoirs. Recognized source rocks are in the inter-bedded shales of the Napo Fm. Which are immature in this area. Thus lateral migration is the dominant process. Chimneys may be important in moving these laterally migrated hydrocarbons from the underlying continuous Hollin Fm into the more discontinuous Napo reservoirs. Waveform segmentation showed the major reservoirs occur in the same facies. However they may be compartmentalized. Significantly, the HC Probability showed a fair correlation to structure and upside potential in a reservoir found tight in the discovery wells.
AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas