Geohazard Prediction and Real-time Updates with Uncertainties

Large-scale capital assets and human life are all at risk in exploration for oil and gas. Pre-drill assessment of geohazards has, therefore, become an essential component of well planning. No well is drilled without such an assessment. Quality seismic data hold the key to accurate pre-drill pressure prediction. The behavior of rock velocities with depth is related to the state of shale dewatering and compaction, and consequently, the pore pressure that can be expected at depth. Clearly, seismic velocity is the key to pore-pressure prediction. However, as velocity estimation from seismic data is not unique, incorporation of velocity uncertainty in drilling risk analysis can yield a better understanding of the range of potential costs. Therefore, quantification of velocity and correspondingly geohazard uncertainties is essential in decision-making during drilling operations, and, thus, managing these uncertainties generates business value. In particular, decisions for casing points should take into account the geohazard risk associated with the uncertainty in our knowledge of the velocity model. This paper introduces workflows for pore-pressure and fracture-pressure prediction that account for seismic and related uncertainties associated with the ambiguity of tomographic velocity model building. Also, we demonstrate how the geohazard uncertainty can be updated in real drilling time.