Seismic Reservoir Characterization (Sable Basin)

The Sable Offshore Energy Project is a multi-company endeavor that formed in order to develop approximately five TCF of gas, contained in six fields in the Sable Basin of offshore eastern Canada. The reservoir sandstones in the Sable fields are late Jurassic and early Cretaceous in age and are interpreted to be of deltaic and shallow marine origin. The depths to the various pay horizons ranges from 3500 to 5500 meters. The main gas reservoirs vary from normally pressured to highly overpressured.

Field development and field management decisions are based on an accurate characterization of the producing reservoirs. Reservoir characterization is an integrated effort, making use of data from numerous sources including seismic attributes, log and core measurements, production information, and geologic models. This talk begins with a brief account of the overall project and then examines the area of reservoir characterization with an emphasis on the use of seismic data. Seismic attribute analysis begins with an understanding of the acoustic properties of the reservoir. Using core and log measurements, models are developed to describe the expected porosity, net to gross ratio, and permeability trends within different facies. These trends are then related to acoustic properties of velocity and density. Gassman calculations are used to model the effect of gas saturation. Well logs are used to create synthetic seismic traces (AVO synthetic if needed) using extracted or modeled wavelets. The synthetics are used to calculate and apply phase corrections to the seismic and to calculate the scale factor between the seismic and the reflectivity sequence.

After calibrating the seismic to the well data, the next step is to predict the lateral variations in reservoir properties from seismic data. Preliminary analysis is done using mapped horizons as guides and extracting seismic attributes at stratigraphic levels at and near mapped horizons. These attribute maps are examined for patterns indicating depositional variations and for anomalies representing fluid levels. The initial analysis is used as a guide for the construction of a field wide multi-layer geologic model, built to the same level of detail (vertically) as desired for the reservoir simulation. The model and the acoustic trend curves are then used in a seismic inversion process to derive the desired properties for the reservoir units. These properties form the new model which is then used as the input to the reservoir simulator.