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SWLGS Luncheon Topics

Updated Feb. 10, 2006

Febuary 2006

An Example of Integrated AVO Prospecting in the Gulf Of Mexico By: Brian Schulte and Robert Schneider

Abstract Summary

3-D seismic data from offshore Louisiana are examined in an integrated seismic attributes/AVO analysis for prospectivity and geological understanding. We use a fast and accurate approach to identify attributes that highlight known pay zones, then extrapolate to illuminate potential prospects for lower Miocene sands. Data quality is critical to the proper amplitude interpretation of seismic data. The integration of gather conditioning and attribute analysis to known production is critical to establishing intelligent parameters to constrain cross plot information. Preprocessing is required to condition CDP gathers to account for residual velocity, NMO stretch, gain and overburden effects. If gathers are not conditioned properly, the subsequent interpretation of AVO and other attributes may be seriously in error. Conditioning the gathers improves signal/noise and often extends the usable offset/angle range of the gather for AVO analysis. We begin by examining individual and combinations of seismic attributes to interpret those cross plot constraints that correlate well to seismic data near production locations. These are applied to the entire 3D volume to highlight locations having AVO properties similar to known pay. We then create a 'Pay Flag' (PF) volume which highlights areas where all constraints have been satisfied. By comparing the known production at the different zones to our chosen multiattribute constraints, we can then predict other areas of exploration interest in the 3-D volume. By examining time slices with PFs and wells overlaid, we create arbitrary lines across the wells to observe the PFs in the vertical slice. It is interesting to note that attribute character seems to be dependent on the orientation of the arbitrary line and local geological setting. Therefore, we suggest that AVO analysis should be done in a time slice or true 3D sense. Using individual PFs within the 3-D volume, we extract CDP gathers to examine AVO response at their locations. This allows us to simultaneously examine the quality of fit of the intercept and gradient; to observe the CDP gather itself; and to view the angle of incidence range. In this study, we were able to tie seismic attributes to production and subsequently identify new prospects at 3 different zones for the lower Miocene sands in this area. Furthermore, we demonstrate that this procedure can be used to identify deeper lower Miocene sands which can be classified as class3/class 2 AVO anomalies.

Biographical Sketch
Brian Schulte was born and raised in Calgary, Alberta, Canada and graduated in 1989 with a B.Sc. in Geology from the University of Calgary. He has worked for Geco-Prakla, Vastar and BP working around the world from North Slope, Alaska to Ushuaia, Tierra del Fuego, Argentina and throughout Asia and Europe. His ultimate goal in life is to visit all 7 continents and he would like to one day travel around Asia looking at history and the culture maybe writing a book on his travels for Westerners to understand Asia. He has been a pioneer throughout his career. He has been involved in AVO for over 8 years working the Gulf of Mexico shelf within Vastar and BP. He has presented to different forums on AVO and pore pressure. Most of his concentration of late has been developing processing techniques in order to condition the gathers for AVO and to create better AVO attributes. He currently is working for Explora seismic Processing in Houston.