Modelling the evolution of seal integrity in deepwater toe thrust anticlines

Abstract

AbstractThis paper describes the results of an empirical one-dimensional model for toe thrust structures that enables both fluid pressure expectations and seal integrity to be evaluated. The growth of a deepwater thrust anticline is forward modelled with calibration made to a present-day structure. Two locations are used to describe the structural evolution: the crest of the anticline and the floor of the adjacent syncline. These locations are followed through structural growth and burial. Pore pressures in the evolving toe thrust are modelled by employing a centroid model for a pre-tectonic target reservoir interval, with shale pressures modelled using the concept of a variable fluid retention depth. A shale compaction model based on critical state soil mechanics is used to model top seal porosity and to aid the evaluation of the capillary top seal. Together with mechanical seal analysis this enables the controls on trapped hydrocarbon column heights to be assessed. Application of the model to two recently drilled toe thrusts is discussed, and results compared to model predictions. The model can be used to offer a generic seal integrity scheme for a toe thrust that may help focus attention on the key exploration risks.