ABSTRACT

Statistical analyses of size, orientation, and pressure measurements on Cretaceous and Jurassic oil and gas pools in Albeta reveal general predictable trends and some significant anomalies. The total oil and gas in place, and the plan areas of pools, appear to be lognormally distributed although this cannot be proved statistically. For major reservoirs showing a well-defined lognormal size-frequency distribution, the probability of future economic exploration success in that unit can be evaluated from the general trend. Notable deviations from the lognormal distribution pattern occur for Viking oil pools and Wabiskaw (Glauconitic) gas pools. The presence of two populations of pools (one of large pools and one of small pools) can explain the anomalous size-frequency distribution. The large, and therefore more profitable, oil pools in the Viking Formation occur in the "Main" Viking sand in areas of favourable hydrodynamics. For the gas pools in the Wabiskaw, a factor analysis indicates a relationship between the size of the pool and a combination of porosity and elevation of the reservoir. A map of factor loadings defines an area on the southwestern edge of the basin in which the large Wabiskaw pools are more likely to be found.

For oil occurrences in Viking, Cardium, and Belly River reservoirs, the size of the pool can be predicted reliably from its plan area. Consequently, for these reservoirs the reserves potential of an exploration target can be estimated from the untested area. Gas reserves are generally less predictable from plan area.

Diagrams showing the orientation of oil and gas accumulations in major reservoirs have both analytical and predictive applications. The orientations are caused by the original depositional conditions, and by later structural and hydrodynamic effects, and are used to identify the controlling features. A quantitative knowledge of the orientation directions of oil or gas pools in a particular reservoir will influence the extension of a new oil or gas discovery in that reservoir.

Plots of pressure against depth for oil and gas pools reveal that the interconnected reservoir systems such as Gething Formation and Ellerslie (Basal Quartz) Member have well-defined pressure gradients close to hydrostatic. Groupings of pools on the Ellerslie Member plots, when mapped, define a western limit for the occurrence of oil in the Ellerslie.

Maps showing the areal occurrence of oil and gas in Cretaceous and Jurassic reservoirs in Alberta delineate hydrocarbon-rich belts trending NW-SE. Some well-explored areas of the province have very small quantities of oil and gas discovered, apparently for lack of suitable reservoir units.