The cracks in a porous matrix which is subjected to a change in the applied stress or fluid pressure will undergo a distortion related to their orientation relative to the principal directions of the applied stress. Both the crack distribution and the fluid-flow properties of the aggregate will be altered as a consequence of a change in either the applied stress or fluid pressure, resulting in a change in the effective elastic parameters of the material. An effective medium theory, based on the method of smoothing and incorporating a transfer of fluid between connected cracks via non-compliant pores, is used to derive an expression for the effective elastic parameters of the material, to first order in crack density ε. This expression involves a dependence on both the applied stress and the fluid pressure, and is used to determine the effects on the anisotropy of the effective medium of the applied stress and fluid pressure.
Grechka, Vladimir (Center for Wave Phenomena, Department of Geophysics, Colorado School of Mines) | Bakulin, Andrey (Schlumberger Cambridge Research, High Cross, Madingley Road, Cambridge, CB3 0EL, England) | Tsvankin, Ilya (Center for Wave Phenomena, Department of Geophysics, Colorado School of Mines)
van Spaendonck, Rutger L.C. (Department of Electrical and Computer Engineering, Rice University, Houston, TX, USA;) | Fernandes, F.C.A. (Department of Electrical and Computer Engineering, Rice University, Houston, TX, USA;) | Fokkema, J.T. (Applied Earth Sciences, Delft University of Technology, Delft, Netherlands)
A development well was proposed over a natural-gas field in the Central Alberta Foothills. The target was a thrust sheet culmination less than 300 meters wide. The initial well location came from the interpretation of seismic data using poststack time migration, prestack time migration, and prestack depth migration. Each method offered imaging improvements over the previous, but there was little change in the imaging or location of the culmination of the structure. Once it was discovered that the well missed the target, a dip meter was acquired and the seismic data were reprocessed using anisotropic depth migration. The dip meter indicated that the well had missed the leading edge of the structure and the anisotropic depth migration shifted the structure 250 m toward the hinterland. The subsequent sidetrack to the correct position of the structure, indicated by the anisotropic depth migration, resulted in a successful gas well.
O'Brien, John (Anadarko Petroleum Corporation) | Addis, Danny (Anadarko Petroleum Corporation) | Drummond, Jock (Anadarko Petroleum Corporation) | Walraven, David (Anadarko Petroleum Corporation) | Weigant, John (NuTec Sciences, Inc.) | Stein, Jaime (NuTec Sciences, Inc.) | Key, Scott (NuTec Sciences, Inc.)
Subsalt exploration in the Gulf of Mexico has been made feasible in large part by advances in depth imaging technology, leading to several commercial discoveries. These successes, and a new generation of high-powered massively parallel computers, are now leading to the next wave of depth imaging technologies based on full wavefield prestack depth migration. This paper presents the first published case study of 3-D wave-equation imaging in a subsalt setting, based on the Hickory Field in the Gulf of Mexico. The results demonstrate that the technique is now practical and illustrates the potential advantages that can be gained with a shot domain acoustic wave-equation imaging solution.