Imaging Super-Deep Gas Plays Across the Gulf of Mexico Shelf with Multicomponent Seismic Technology

This continuation report is the final reporting requirement for Year 2 of the project, "Imaging Super-Deep Gas Plays across the Gulf of Mexico Shelf with Multicomponent Seismic Technology." The objective of our research is to investigate the value of long-offset multicomponent seismic data for studying deep gas geology across the northern shelf of the Gulf of Mexico (GOM). WesternGeco has allowed our research team to analyze their long-offset, multi-client, 4-component ocean-bottom-cable (4-C OBC) seismic data across a large area spanning approximately 24,500 km2 (about 9,600 mi2) of the northern shelf so that this research could be done. This study area is the largest ever interpreted with multicomponent seismic data. These OBC data were processed by WesternGeco using source-to-receiver offsets extending to 10 km, which is the offset range required for optimal imaging of geology at depths of 10 km. Our research demonstrates that the popular P-P seismic mode used by most of the gas exploration industry images geology beneath the northern GOM shelf to depths of 12 to 13 km, which is a depth range that exceeds the industry's current objective of drilling targets to depths of 9 to 10 km (30,000 to 33,000 ft). A more important research finding, in our opinion, is that the converted S-P (P-SV) mode images geology beneath our study area to depths of 9 to 10 km, which allows super-deep gas plays to be analyzed with multicomponent seismic data and with elastic wavefield stratigraphy (combined P-P and P-SV images), rather than limiting prospect evaluation to single-component seismic data and to conventional P-P seismic stratigraphy.

An important aspect of our research has been the application of elastic wavefield stratigraphy through the comparison of P-P and P-SV seismic sequences and seismic facies across deep target intervals. Our investigation shows that although P-P seismic sequences and seismic facies often differ from P-SV sequences and facies across these intervals, both the P-P and the P-SV sequence interpretations and facies models are correct when proper rock physics theory is used to describe the seismic propagation medium. We use several rock physics concepts to calculate P-P and P-SV reflectivity behaviors that explain why P-P seismic sequences and facies differ from P-SV sequences and facies and then demonstrate these reflectivity behaviors with real P-P and P-SV images.