Improved seismic stratigraphic interpretation of carbonates using outcrop data
Carbonate systems hold vast amounts of the world's oil reserves, and seismic data is the largest subsurface data set in the oil industry. Thus it is vital that new advances be made in using seismic data to construct predictive subsurface models. This thesis uses three key case studies to demonstrate how carbonate outcrops can enhance seismic stratigraphic interpretation and create subsurface predictive models in carbonates. The methodology involves detailed outcrop characterization, a seismic simulation of the outcrop data, and an iterative interpretation of the subsurface data and outcrop data to produce a predictive subsurface model. Seismic-scale outcrops are used to construct seismic simulations of two carbonate settings: an isolated platform margin, and a low angle ramp. Forward seismic modelling of the high-resolution sequence stratigraphic outcrop models is used to create the seismic simulations, and is a very powerful way to calibrate geological information and seismic data. The outcrop platform architecture of a shelfal algal mound field was applied to interpreting subsurface seismic data using forward seismic modelling of well logs. Interpretation of multi-frequency synthetic seismic outcrop simulations identified specific seismic characteristics for various carbonate depositional environments, which enhanced the confidence in interpretations of the subtle seismic characteristics on lower frequency subsurface seismic as being caused by actual geologic characteristics. This is particularly critical in the platform and ramp margin areas where interpretation pitfalls could occur, for example, missing the platform or ramp margin or interpreting the data as seismic artefacts. The platform, or ramp, margin is a key seismic geometry to identify on subsurface data. Its identification aids in the prediction of the platform architecture, and the spatial relationships between the basin (potential source rocks) and the platform (potential reservoir). The comparison between outcrop and subsurface data can be used at either the exploration or production scale. At the exploration scale the main aim is to identify the platform margin, while the main aim at the production scale is to identify the reservoir architecture, predict stratigraphic traps, and to use the subsurface data to obtain reservoir parameters as input for reservoir models.