Tertiary Recovery Modeling By Hybrid Simulation For Kaybob Beaverhill Lake 'A' Pool Hydrocarbon Miscible Flood
Authors: Behrens R.A. 
Published: March 2010

Abstract
A Hybrid finite-difference/stream tube simulation was run for Kaybob BHL ‘A’ HCMF to identify optimization opportunities and provide an accurate forecast. Five different cross-sections were chosen to represent the different geologic regions of the Kaybob reef. Detailed 2-D simulation models were built and run with many operating variations. The 2-D cross-section results were mapped onto a field-wide stream tube model giving 3-D results for each pattern under a variety of operating conditions. The model was restricted to tertiary oil only and an excellent match was found with field data. The accuracy of the simulation without history matching shows the modeling benefits of incorporating: (1) detailed rock property distributions in a cross-section to model channeling and override mechanisms, (2) geologic diversity, and (3) off-pattern migration and variations in areal sweep efficiency unique to each pattern.

Introduction

Background of Pool
Kaybob Beaverhill Lake ‘A’ Pool is a carbonate reef with multiple growth stages. Original oil in place is estimated at 40.3 106m3 covering approximately 7,700 ha. The pool produced 5% OOIP under primary depletion between discovery in 1957 and start of line drive water injection in January 1964. From 1964 to 1973 the number of injectors expanded slowly from four to eight: recovery increased to 26%. The waterflood was converted to pattern injection in 1978, which expanded to 15 injectors by the start of miscible flood in July 1988. Well rates changed greatly during the waterflood with different wells being on injection and producers often shut in upon initial water production in the early days. Recovery was 15.8 106m3 or 39% prior to solvent injection.
Waterflood production in Kaybob has been extremely good with ultimate recovery expected at 18.7 106m3 or 46.5%. The waterflood benefits from the unusually high viscosity ratio of µw/ µo= 2.5.
A hydrocarbon miscible flood (HCMF) was chosen for tertiary recovery. Phase 1, containing eight patterns of the horizontal drive miscible flood, started in July 1988. Phase 2, with eight more patterns, started in March 1989. Phase 3 has not yet been implemented as originally planned. The initial design has been described previously(1,2).

Objectives of Hybrid Simulation Study
Previous studies were not able to address several outstanding concerns for miscible flood operation because they did not include the necessary level of detail. Two years after solvent injection started, this simulation project was started. This study had three primary objectives:optimization of individual patternssolvent slug size and WAG ratio chase fluid designforecasts for economic justificationswell workovers and stimulationssurface facilitiesflood expansionbusiness plan and marketing forecastsoil productionsolvent injection and production
FIGURE 1: Hybrid model uses results from a 2-D finite-difference cross-section model mapped unto a 2-D streamtube areal model. (Available in full paper)

Background of Hybrid Simulation Method
The concept of combining a finite-difference simulation of a vertical cross-section with an areal streamtube simulation was first reported in 1981(3). This method was used to reduce the finite-difference simulation to a manageable size for a surfactant/polymer flood.