Design Of A Field-Wide Hydrocarbon Miscible Flood For The Kaybob Beaverhill Lake" A" Pool
Authors: MacLean D.A. 
Published: March 2010

There are currently 56 hydrocarbon miscible flood projects operating In Alberta of which 12 are horizontal water alternating gas (WAG) processed. Seven of the 12 horizontal schemes are in the Upper Swan Hills formation of the Beaverhill Lake group. In most cases the miscible floods were introduced after years of waterflooding.

In general, a solvent is injected into the previously water flooded zone to displace residual oil. The methods used to estimate this tertiary oil recovery are unique to each project and operator. This paper presents a cost-effective method off forecasting ultimate oil recovery from a planned hydrocarbon miscible flood in a Beaverhill Lake reservoir.

Introduction

The Kaybob Beaverhill Lake (BHL) "A" Pool is located 240 km (150 miles) north and west of Edmonton, Alberta (Fig. 1). Plans are to convert from a horizontal patterned waterflood to a horizontal water alternating gas patterned hydrocarbon miscible flood in 1988.

This paper describes the proposed Kaybob miscible flood project with emphasis on miscible flood pattern selection, miscible solvent design and forecasting remaining secondary and tertiary oil recovery.

Previous attempts to model and history match the waterflood performance in the Kaybob field have been unsuccessful. The miscible flood forecast is therefore, a combination of expected secondary recovery under the current waterflood and tertiary recovery under miscible flood.

In this paper, miscible flood patterns and infill locations are defined first, followed by the waterflood and tertiary forecasts for each pattern and infill well. The design of the miscible solvent is also given.

Background

The Kaybob BHL "A" Pool is a multi-layered carbonate reef discovered in 1957 with the drilling of the well Phillips Kaybob "A-1" at 7–22–64–19 W5M. The field covers an area of 7067 ha (17 462 acres) and has been drilled up to an average spacing of 64 ha (160 acres) with a total of 93 wells. The original oil-in-place (OOIP) is estimated at 44.3 ×106 m3.

Oil is produced from the Upper Swan Hills Formation of the Beaverhill Lake Group which is middle to early Devonian. Typical facies distribution in the pool are shown in Figure 2, with the cross section of each reefal stage (platform, Stage II to VI) given in Figure 3. Schultheis(2) found the best reservoir characteristics exist in the reef margin. The less permeable and less porous reservoiroccurs in the back reef.

A line drive water flood in the south end of the pool was initiated in 1964 to maintain reservoir pressure. In 1978 the line drive was replaced by inverted nine spot patterns on 64 ha spacing (Fig. 4). Recovery to July 1987 was 15.68 ×106 m3 or 35.3% of the OOIP.

Pattern Selection

Patterns for the miscible flood were selected on the basis of preferentially using existing water injection wells as solvent injectors. In order to optimize miscible displacement, patterns were designed to follow permeability trends observed from the progress of the waterflood (Fig. 5). The number of patterns chosen represents the maximum number of inverted nine spots on 64 ha well spacing (Fig. 6).