Extraction of Seismic Attributes for Reservoir Characterization in Subsalt Environments, Keathley Canyon and Walker Ridge Areas, Gulf of Mexico
As Lower Tertiary discoveries in the deepwater areas of the Gulf of Mexico continue, along with plans for field development in these challenging environments, it would be nice to have another method for reservoir delineation to help reduce the economic risks. Using high resolution 2D seismic data with 15 km offsets located on or in close proximity to 9 wells drilled to the Lower Tertiary, seismic attributes are compared to known reservoir characteristics determined from well data. The quest is for any attribute or group of attributes that can show consistent correlation to porosity, density, Vp/Vs ratios, or fluid content. Six of these wells are Wilcox discoveries, 2 are dry holes, and the last is a 2013 discovery with as yet unavailable well log data. Geostatistics are used to predict the reservoir characteristics of this well, based on the seismic attribute correlations in the other 8 wells.
The seismic data were processed using a one-way wave equation (WEM) depth migration in order to preserve the true amplitudes found in the raw stacks. The 3D velocity model was built using 200 well logs and 7 velocity surveys from the Keathley Canyon and Walker Ridge areas, including 4 wells in the southwestern corner of Green Canyon. Checkshot data from the seismic was also included. The tedious part in building the 3D velocity model was creating synthetic logs for the above salt portion of the wells. Very few operators will log sonic data above salt or in salt. Due to coverage of such a large geographic area with spotty well control, the velocity model was built in two different software packages (Petrel and Vel Pro) to compare extrapolation algorithms. The seismic data were processed separately with each velocity model to compare differences; and processed again using reverse time migration (RTM) just for image comparison.
AAPG Datapages/Search and Discovery Article #90219 © 2015 GCAGS, Houston, Texas, September 20-22, 2015