A major challenge facing exploration in the Gulf of Mexico is drilling below salt. Abnormal high pressures below salt creates a difficult drilling environment which can result in loss of well control and subsequently needing to sidetrack the well at a substantial cost. Seismic velocity is typically used for subsalt pore pressure estimation, however seismic velocity measurements have large uncertainties below salt and, in many cases, no velocity subsalt can be estimated due to limited seismic illumination. Targeted walkaway VSP measurements acquired in the salt before exiting salt have been used to reduce this uncertainty and improve subsalt pore pressure estimates. The elastic parameters have previously been estimated using 1D AVO and travel time approaches. In this paper we apply 2D waveform inversion to estimate the P-wave and S-wave velocity models from a walkaway VSP survey acquired in a well in the deep water Gulf of Mexico.
展开▼
