ABSTRACT

The Lower Cretaceous Bluesky sand of the Bassett Area in northwestern Alberta produces gas from a series of structural-stratigraphic traps formed as the Bluesky sand follows the structural configuration of the pre-Cretaceous unconformity. A hydrodynamic analysis of the Bluesky sand drill-stem tests indicates a number of pressure systems, each with a separate gas-water contact. Miami Amoco Bassett 10-16-105-1 W6 and Amoco Miami A-1 Bassett 6-12-105-1 W6 are situated in the same pressure system and are structurally above a gas-water contact. These wells have recovered significant volumes of gas upon evaluation. Can Hunter et al. Haig 10-34-104-3 W6 is located in a separate pressure system to the west and is also structurally above a gas-water contact, but failed to recover gas upon evaluation.

Core plugs were cut from the Bluesky sand in Miami Amoco Bassett 10-16-105-1 W6. From these plugs were derived porosity, permeability, mercury-injection capillary pressure curves, X-ray analysis, petrographic analysis, and scanning electron microscope photographs. The Bluesky sand is a fine- to very fine-grained, poorly to well sorted clay-bearing sand which exhibits intergranular and dissolution porosity. Three rock types were established from the porosity, permeability and mercury-injection data. The 25 percentile level of mercury saturation was found to be equivalent to the most effective pore-throat radius. The pore-throat-radius size range in microns was determined for each rock type and the mercury-injection pressure was converted to height above free-water level. The amount of structural relief required to allow gas to enter the pore throats of each rock type was established. Miami Amoco Bassett 10-16-105-1 W6 and Amoco Miami A-1 Bassett 6-12-105-1 W6 are gas-productive because of the rock types available and the structural relief of the Bluesky sand in these locations. Can Hunter et al. Haig 10-34-104-3 W6 is not structurally high enough above the gas-water contact to allow gas to enter the available pore systems.