The Milk River Formation (Eagle Equivalent) in Alberta and Saskatchewan 2: Stratigraphy and Trapping

O’Connell, Shaun¹ (1) Belfield Resources Inc, Calgary, AB

In outcrop the Milk River Formation comprises three members: the Telegraph Creek, Virgelle, and Deadhorse Coulee (lower Eagle Formation equivalent). These members form a regressive succession from offshore marine to non marine coastal plain deposits. A major regional unconformity separates the shoreline sediments of the Milk River Formation from the offshore marine deposits of the Alderson Member (upper Eagle Formation equivalent) which in Canada is present only in the subsurface.

The Alderson Member in Alberta and Saskatchewan can be divided into five major stratigraphic units. These units resulted from multiple episodes of variable tectonic subsidence and uplift, giving rise to a series of highstand, lowstand, and transgressive systems tracts, which are often truncated by large regional erosion surfaces. Milk River gas production in the mature field areas is from various sands within the lower and middle part of the Alderson Member. Gas production from recently discovered Milk River fields in Saskatchewan is from lowstand units in the lower Alderson Member.

There are two main constraints upon Milk River (Alderson Member) production: 1. Lithological Quality; this is highly influenced by proximity to sand sources. The greatest volumes of sand are present in the proximal highstand systems tracts. Sandy lowstand units are prime exploration targets in more distal areas. Lithological texture is also highly important since much of the Alderson is texturally homogenous, severely reducing overall permeability. Well preserved primary lamination is an important reservoir characteristic. 2. Water Production; this is closely tied to structure. In both Alberta and Saskatchewan there are critical structural levels below which Milk River gas production is highly unlikely.

AAPG Search and Discovery Article #90055©2006 AAPG Rocky Mountain Section Meeting, Billings, Montana