thinkpool

We conducted a quantitative analysis on physical properties of Grosmont formation, Alberta, Canada, using well-log data. Grosmont formation is divided into four units by the shale breaks: LG; UG-1; UG-2; and UG-3 from the bottom. Two lower units is mainly composed of limestone, while upper units are mostly dolomite with vuggy porosity by dissolution and fractures resulting from karstification, which makes the upper units be a good reservoir. Rock physics modeling was then performed to quantify velocity-porosity relations for the four units, which enables us to predict porosity from seismic data. In order to incorporate the pore-scale details in the modeling, we used DEM (differential effective medium) models. Two lower units are very similar in velocity-porosity domain, thus the relations can be represented by one velocity-porosity model, which is used as our reference model. For the UG-2 unit, we found that one model cannot represent the unit since the degree of fracturing is heterogeneous from location to location. We thus suggested three different DEM models for the UG-2 unit: vuggy-dominant; mildly-fractured; and heavily-fractured. The UG-3 units can be modeled with vuggy porosity, and fractures were not very noticeable. We also investigated the spatial variation of the UG-2 unit, and found that the degree of fracturing is generally proportional to the proximity to the unconformity boundary, where the fresh water invasion can be dominant. As a result, we proposed velocity-porosity relations for the four units in Grosmont formation, and believe that these models can help to characterize the reservoir quality. In addition, since the proximity of reservoir to the unconformity boundary highly affects the degree of fracturing, a careful analysis of spatial variation would be essential for the successful characterization of Grosmont formation.