Swan Hills Unit Build-Up and Platform: A Tale of Two Reservoirs

Alexis Anastas and Judi Dobbin
Devon Canada Corporation, Calgary, AB

The Swan Hills Unit #1 Field is located in west-central Alberta, about 120 miles from Edmonton. Discovered in 1957 by the Home Regent HB Swan Hills 8-11-68-10W5 well, it represents one of a number of important Devonian carbonate reservoirs that opened up oil and gas development in Central Alberta in the late 1940's and 1950's. It is the largest conventional carbonate oilfield in Canada with an OOIP of 1.8 MMBOE. The reservoir is located within Givetian to Frasnian-aged limestones of the Swan Hills Formation (Build-up) and Slave Point Formation (Platform). The trap is stratigraphic with the seals being the shales, tight lime mudstones and wackestones of the Beaverhill Lake Group. The drive started as simply solution gas with no bottom water. Sw in the field is now rather complex and related to reservoir quality and the numerous depletion schemes.

The reservoir can be divided into two units : 1) Build-up formed by a massive isolated carbonate bank with associated foreslope, margin, and lagoonal facies and 2) Platform composed of finer grained lagoonal, patch reef and associated facies. Over the years, the Build-up received most of the attention with its thick pay zones (up to 60m) and excellent porosity and permeability (Core averages of 7.8 % and 20 md). Development in the Platform has been minor with some reefal and lagoonal zones being perforated but yielding poor results. The carbonates are generally transgressive with 8 stages in the Buildup and 5 stages in the Platform, each characterized by a generally shallowing-upwards motif and backstepping geometry (T-R Cycles). Dolomite represents a minor component of the reservoir rock occurring as a cement.

Devon, through Anderson and Home Oil, has been the operator since the field's discovery and has taken it from primary to secondary to tertiary recovery.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005