Delineation of a sand reservoir at Manitou Lake, Saskatchewan: Interpretation of 3C-3D seismic data

Roxana Maria Varga, Robert R. Stewart

Exploration targets of this survey undertaken in the Manitou Lake heavy oilfield include the Colony and Sparky sand channels, both members of the Cretaceous Mannville Group. These intervals are currently producing oil and gas in the area. Our goal is to investigate the usefulness of 3C-3D seismic in discriminating sand versus shale and find gas-charged porosity. Detailed registration of multicomponent seismic data aims to reduce the uncertainty of interpretation and improve well targeting. Seismic attributes, AVO, LMR and elastic impedance methods can complement the information for drilled wells and possibly identify new drilling locations.

We know from previous work that increasing sand yields greater porosity. Greater porosity can lower the P-wave velocity. So, a good reservoir should have a lower Vp value. The presence of hydrocarbons also lowers the Vp. The S-wave velocity is often seen to increase from shale to sand. Hence, Vp/Vs is lowered in hydrocarbon bearing sandstones. The interpretation of P-wave seismic reflection data can lead to ambiguous conclusions in certain exploration situations. Differentiation of prospective channel sands and non-productive shales could be problematic due to the similarity in P wave impedance of these two lithologies. We expect the PS data to be a direct measurement of the channel system, knowing the fact that should respond largely to the lithology and less to the fluid content.