ICE 2022


Time-to-depth conversion of seismic volume is a required workflow when interpreting seismic data and defining the spatial location of a reservoir. This essential step is often approximated with vertical scaling method, which may only be valid for simple “layer-cake” geology. Consequently, in complex areas, it is very common to see disruptions and pull-ups in the depth converted volumes, which could result in missed targets, added costs, drilling hazards and delays in the subsequent exploration and production operations. In this presentation we will introduce a more accurate approach for re-depthing (time-depth or depth-to-depth conversion) of seismic volume in any kind of structural environment. The workflow is based on applying sequentially poststack RTM Demigration and poststack RTM Remigration. Demigration of stacked images is the reverse process of migration and generates zero-offset unmigrated seismic volume (time stack volume). The Demigration phase uses a depth migrated image and its corresponding anisotropic velocity model. After Demigration, the zero-offset time stack volume is remigrated with alternative sets of updated anisotropic velocity models. This approach allows interpreters to economically evaluate different interpretation scenarios in the velocity model, by incorporating their experience and knowledge of the field, maintaining consistency with available dataset such as outcrops and validating the viability of each scenario. This is particularly important to decrease imaging uncertainty in complex foothills areas where signal-to-noise ratio is poor, and reflectors lack continuity. The output of the workflow are multiple depth images and velocity models. Because the method runs both in anisotropic and isotropic modes, one can change any of the anisotropic parameters such as delta or epsilon, then use those as the updated model parameter. Advantages: Because the method is based on RTM, it can accurately handle seismic data acquired over complex geologic media. No prestack gather is needed since it is a poststack process. The Demigration process need to be carried out only once but Remigration can be done as many times as needed, each time using alternative velocity models. There are no limitations on the dips of the formations, no requirement about smoothness of the velocity models, therefore, medium parameters within the layers can vary abruptly.