ROCK PHYSICS GUIDED VELOCITY MODELING AND REVERSE-TIME MIGRATION FOR PORE PRESSURE PREDICTION AND DEPTH IMAGING IN COMPLEX AREAS

摘要

An Earth model solely based on tomography is nonuniquern- especially, in the presence of anisotropy orrncomplex geology, such as highly folded overthrustrnzone, where tomography velocity inversion becomesrnhighly non-linear. This is often the case with sub-saltrnor sub-basalt, where incidence angles are small. Tornmanage the inherent non-uniqueness, we constrainrnthe tomography using geologic information inrnconjunction with thermal history modelling and rockrnphysics principles. The resulting constrained modelrnis then input to Reverse Time Migration (RTM) forrnimaging. This workflow is termed Rock PhysicsrnGuided Velocity Modelling for Migration and PorernPressure (Dutta et al. 2011). A novel feature of thisrntechnology is to use predicted pore pressure as arnguide to improve the quality of the Earth Model.rnThus, we produce a velocity model that not onlyrnflattens the CIP gathers but also limits the velocityrnfield to its physically and geologically plausiblernranges. To facilitate the implementation of thisrnworkflow, we also introduce a new technique basedrnon this concept to quality control the velocity model.rnThis is called “pore pressure scan” technology. It isrnsimilar to conventional velocity scan approach, but itrnworks directly in the pore pressure domain using arnrock physics template. The results of this newrnmethod have been evaluated on several blind wellsrnand it shows a significantly improved pore pressurernestimation over that obtained by the conventionalrntomography based approach. In addition, we find thatrnthe new approach also improves the image quality.rnWe present case studies from both Indonesia and thernUSA to illustrate how the technology works.