What Could Be Improved
Published:January 01, 1999
Potential improvements will play an important role in shear wave technology, not only because the technology is “emerging,” but also because it is necessary to fully justify the use of several wave modes instead of only one. Every step of the shear wave observation has potential improvements.
Today multicomponent processing is mainly mono-mode. A significant step will follow by moving from scalar processing towards vectorial processing. This fact implies some essential improvements regarding acquisition and/or computer algorithms. At this very moment 3, 4 or 9 components are at our disposal, but that does not mean 3, 4 or 9 vectors, for many reasons(Fig 8.1).
The growth rate of multicomponent activity(Fig 8.2) over the past four years is directly related to the high data quality obtained at the sea bottom. Nevertheless, the first interest of OBC acquisition remains the cost saving in areas with surface obstruction. The second interest is the possible application of the 3D properties of cross-spread acquisition.
At the bottom of the sea, the state-of-the-art for removing water layer reverberation calls for using two components (hydrophone plus geophone). If the additional cost of recording four components (2 orthogonal, horizontal receivers) is negligible then the application of mode-converted waves becomes a real opportunity for the multicomponent processors. Most of the 3D × 4C data recently acquired were pilot surveys used to define larger surveys for 4D purpose.
Figures & Tables
Shear Waves from Acquisition to Interpretation
“This book, produced for use with the third SEG/EAGE Distinguished Instructor Short Course, addresses the practical aspects of multicomponent data acquisition, processing, and interpretation. The first part of the book is devoted to overcoming the difficulties associated with shear-wave acquisition. Converted-mode operation is covered in detail using real-life examples. The particularities of sea-bottom receivers also are examined. The second part reviews the processing and the main challenges of the shear-converted modes: static corrections, gathering, velocity analysis, and compensation for shear-wave splitting in axial anisotropy. The book gives a detailed description of processing sequences, and 2D and 3D results, yielding natural axis orientation of layers, are compared in shear and PS converted modes. The third part is devoted to case histories in which new attributes, such as VP/VS ratio, crack density, or fracture orientation, are illustrated in a reservoircharacterization context. These case histories can guide the geophysicist to decide if a particular geologic situation can be handled best using shear waves.”