Abstract:

This study focuses on productivity of low-permeability shallow biogenic gas reservoirs of the Upper Cretaceous Milk River Formation. This formation is one of the major producing intervals of biogenic gas in southeastern Alberta and southwestern Saskatchewan, Canada. We show in situ stress measurements for shallow depths in this region that indicate a cross-over between the vertical stress and minimum horizontal stress at about 370 m depth; shallower than 370 m, the vertical stress is the minimum principal stress. In situ stresses have a profound effect on the orientation of induced hydraulic fractures and stress information can be used to predict whether induced hydraulic fractures are vertical or horizontal. This information is helpful in designing an optimum completion strategy for multi-layered compartmentalized shallow reservoirs and on choosing the best assets to develop. A vertical in situ stress map is constructed for the top of the Milk River Formation to examine possible relationships between the overburden stress and the productivity of the Milk River Formation reservoirs. We demonstrate that a strong relationship exists between the in situ stress and productivity: better well performance is observed in the regions where the vertical stress is lowest. Hence, vertical in situ stress mapping is helpful to delineate areas of best productivity "sweet spots".

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