A Comprehensive Approach in Velocity Modelling Minimizes Structural Uncertainties for Offshore Brown Field Development

Time depth conversion, commonplace in the geophysical workflow, is the key link between interpretive work in time and geological representation in depth. Often, the uncertainty between trying to place time values in depth has been a challenge to capture as it requires thorough study and also careful consideration of all input data and parameters. Whether the outcome of depth outputs is to produce realistic maps or to aid in well placement, there is essential need in being able to quantify this through comprehensive velocity modelling methods. This paper describes the use of scenario based modelling that is combined with geostatistical applications for a brown field development in offshore Malaysia. This is an attempt to capture uncertainty in time to depth conversion and possible cases extensively. Having been in production for more than 30 years, optimizing the value provided by newly acquired 3D broadband seismic and vertical seismic profile (VSP) would allow for improved de-risking when coupled with this comprehensive velocity modelling approach. Three velocity models were built based through varying input data available to cover a spectrum of possible scenarios. Gross rock volume (GRV) calculations from each model were then subjected to a Monte Carlo Simulation based on the respective parameters. Comparison of the GRV from each of the model’s multiple realization illustrates how this hybrid approach proved to be successful in capturing the uncertainty range sufficiently for depth conversion. Due to successful integration of new data and these approaches, it improved understanding of structural uncertainty for reservoir modelling.