Publications

Conventional approaches to build velocity models for depth imaging are heavily dependent upon “flattening of gathers” as the criterion. While this is necessary, it is not sufficient, in that it produces velocities that are typically unfit for beyond imaging analyses such as pore pressure. Because of this, the Earth Model for Imaging is usually not the same as that needed for pore pressure analysis. In the “Rock Physics Guided Migration - RPGMIG* (Dutta et al., 2011) approach, rock physics templates are used as a constraint to estimate seismic velocities and build velocity models. RPGMIG is based on the fundamental idea that rock velocity is dependent primarily upon lithology, porosity and effective pressure (defined as the difference between overburden and pore pressure). Initial estimates of effective pressure are generated using a simple time-temperature history model that includes burial, compaction and thermal diagenesis of rocks. Using this simulated effective stress (for a given lithology unit and average porosity), rock velocity can be estimated. In the RPGMIG* approach, the thermal history plays a critical role in estimating the velocity of a rock without seismic or well control. The rock physics constrained velocities are then applied as a guide function to build the final velocity model. Using a tomographic approach and input to a chosen migration algorithm, the process can generate not only a superior image at the correct depth but also a consistent velocity field that yields a correct pore pressure. The process eliminates extra steps that are currently used to convert the migrated gather and velocity back to time domain to do further velocity analysis for pore pressure prediction purpose and then revert them back to depth domain. In the RPGMIG* approach, the resulting velocities from Depth Imaging are used directly into beyond imaging products.