Performance of South Swan Hills Miscible Flood
Authors: Griffith James D. , Cyca Len G. 
Published: December 2007

A large-scale miscible flood has been in operation in the South Swan Hills Unit (Beaver Hill Lake carbonate) since July 1973. Initial recovery estimates for the project were 45% by waterflood or 65% by miscible flood. Several approaches to evaluating the performance of the project have been applied, including pressure coring, zonal testing, specialized logging, and performance analysis. The pressure core analyses showed oil saturations significantly lower than residual waterflood saturations. These data, supported by other observations and analyses, indicate a generally favorable performance of the project.

Introduction

Since the start-up of the secondary miscible flood in the South Swan Hills Unit in mid-1973, a total of 113 million res bbl (18 x 106 res m3) of hydrocarbon solvent has been injected alternately with water. Oil production has averaged about 50,000 B/D (8000 m3/d). The project now has passed the 6-year mark of operation, and the evaluation of performance is important in view of the continuing investments in increasingly expensive natural gas liquid (NGL) and natural gas for injection and in view of a number of analyses and decisions concerning operation and expansion of tile project.At the time of project start-Lip, only a limited amount of oil production and water injection had taken place in the project area. The evaluation of the performance of an enhanced oil recovery project in this type of operation is not as straightforward as in, for example, a tertiary operation where the reservoir is in an advanced stage of depletion by waterflood and some marked changes in performance can be expected. In contrast, the South Swan Hills project started up at high oil production rates and the depletion has proceeded as expected with increasing amounts of breakthrough with no dramatic responses to miscible injection.Several approaches to the evaluation of the project have been examined and analyzed: performance projection, tracer programs, cores from behind the front, specialized logging, zonal testing, modeling methods, and analysis of selected individual wells or patterns. The most significant to date have been performance projection and coring results.

Project Description

The South Swan Hills Unit is in west-central Alberta (Fig. 1). The waterflood areas and miscible project area are marked in Fig, 2. The unit is developed on 160-acre (647 500-m 2) spacing with some limited 80 acre (323 750-m 2) drilling. The pay section builds up to a maximum of 236 ft (72 m) and a h to 1,600 %-ft (490 % . m). Four geologic zones are mapped across the unit as shown in Fig. 3. The more significant geological natures are the uppermost calcarenite zone and the reef front rim, which are generally of good porosity and high capacity, and the lower-quality lagoon and table reef zones.The production operations from the unit initially were confined to the west waterflood area which was put on injection in 1963. The east side of the waterflood is a low-capacity area which was put on injection in 1976.The project area for the miscible flood was selected to conform to the area between the original waterflood and the eastern edge of the good-quality reef buildup.

JPT

P. 1319^