AAPG Annual Convention and Exhibition

Datapages, Inc.Print this page

Seismic Attribute Workflow for Mapping Middle Triassic Doig Sandstone Reservoirs in Northeast British Columbia, Canada


The Middle Triassic Doig Formation of Western Canada is seen to occur in north-western Alberta, north-eastern British Columbia and southern Yukon provinces of Canada and is composed of argillaceous siltstone and calcareous shale. It is uncomformably overlain by the Halfway Formation and itself overlays the Montney Formation. While the maximum thickness of the Doig Formation reaches over 180 m in the foothills of the Rocky Mountains, it thins out to the north and the east. Within the Doig Formation, thick sandstone bodies occur, and many of them are found to be economic hydrocarbon reservoirs, hence the attraction for their exploration and development. These reservoirs occur in the study area as N-S trending linear sandstone geobodies 10-30 m in thickness at many places, and some tens of kilometers long. Examination of the available core from the Doig sandstone reservoirs suggests an association between sedimentary facies such as shoreface, offshore transition and offshore/shelf. Phosphates and other accessory minerals in the Doig sandstone bodies can drive the gamma ray tool response and mask the sands, so correct identification of the bodies on logs requires multiple curves. The challenge is the determination of the reservoir sands 20m in thickness from seismic data that has an average bandwidth of 10-60 Hz. In the area under study in northeast British Columbia, the reactivation of the deeper fault structures also have some tectonic control on the Doig sandstones of interest. Therefore, the challenge is to identify not only the spatial variability of these Doig sands but also the crosscutting faults and fractures. We address these challenges by first enhancing the bandwidth of the available seismic data using spectral inversion to estimate thin-bed reflectivity, which helped with the detailed mapping of seismic facies and improved definition of the reservoir sands. Relative acoustic impedance inversion on thin-bed reflectivity as well as absolute model-based acoustic impedance inversion indicated variations in the quality of the Doig sandstones that matched other well control. This variation resembled the facies variation determined based on seismic waveform classification. Coherence and curvature attributes indicated the local structural deformation in terms of folds, small faults and fractures. Such a seismic attribute workflow enabled accurate characterization of the Doig sandstones.