Belly River Waterfloods Conception to Success
Authors: Howard J.A. , Hedges G.N. 
Published: March 2010

The oil-bearing Belly River pools of the Pembina area of Alberta were discovered in the search for Cardium oil and developed under skepticism by many operator. The indicated high connate water saturation, the presence of swelling clays within the formation and the lack of readily available source water provided poor waterflood potential. After producing the pools for 10 years under a primary solution gas drive mechanism, the operators initiated three water-flood projects. As a result of the outstanding performance of these projects, two reservoir simulation studies were prepared to determine the optimum waterflood scheme. These studies recommended the extension of the waterflood to the majority of the Belly River reservoirs in the area and justified an extensive infill drilling program. An analysis of the Belly River flood performance is presented and the simulation studies are reviewed. The proposed infill drilling and surface facility expansion programs are also illustrated.

Introduction

THE BASAL BELLY RIVER SANDSTONE is found in the central plains and south-central mountains and foothills of Alberta. Although the sand occurs commonly in these areas and is often hydrocarbon-bearing, it is generally considered as a secondary objective. The Alberta Energy Resources Conservation Board currently estimates a total of 526 million barrels of oil in place in recognized Belly River pools. Ninety per cent of this recognized Belly River oil is located in the Keystone and Buck Creek areas of the Pembina Field, which were developed in the early sixties (Fig. 1 and 2).

The Belly River sand has a high connate water saturation and is infilled with kaolinitic clays. For these reasons, a cautious approach to waterflooding the Belly River reservoirs was taken and it was not until 1970 that waterflood projects were initiated in the Pembina Keystone Belly River "B", "M" and "U" pools. Within two years of the start of injection, excellent GOR and production response was observed.

In some cases, the production rate had a three to four-fold increase. Consequently, the Pembina Belly River "B" North Unit ' waterflood project was restudied with a numerical simulation model to investigate infill drilling, as was the Pembina Belly River "C" Pool, which was still on primary depletion.

Both studies indicated that infill drilling was extremely attractive. Accordingly, an estimated 100 infill wells will be drilled in the Keystone Belly River pools and waterflood projects will be extended to the remaining major Belly River pools in the area.

Reservoir Description

GEOLOGY

The Upper Cretaceous Basal Belly River Sandstone is contained in a progradational sequence between the Marine Lea Park Shale and the overlying continental strata. The reservoir rock is a light grey, fairly well sorted fine to medium-grained sandstone with high clay content and interbedded calcareous sands and dark grey silty shales(1,2). The sand was deposited as offshore bars and infilled channels. Bar and channel sands of different depositional ages are discernible in the Pembina Keystone area, with communication apparent between bars and channels of common age.