Combining A Volumetric Model With A Pseudo-Miscible Field Simulation To Achieve Uniform Fluid Levelling In The Rainbow Keg River "B" Pool
Authors: Fong D.K. , Wong F.Y. , Nagel R.G. , Peggs J.K. 
Published: March 2010

A vertical first-contact hydrocarbon miscible flood is being applied to the Rainbow Keg River "B" Pool since June 22, 1984 as a tertiary process to recover additional oil from the previously water-swept oil zone. The "B" Pool is a reef of Middle Devonian age containing the largest oil accumulation in the Rainbow Field. The pool consists of a North Lobe and a South Lobe separated by a saddle. The major EOR target in this pool is represented by the 19 × 106 m3 (120 × 106 STB) of residual oil left unswept in the water flooded region. One of the key operating objectives is to achieve horizontal fluid levels having a uniform solvent bank across the pool at the time when the solvent bank merges at the saddle.

A three-dimensional pseudo-miscible reservoir simulation model updated with the latest results from 3-D seismic, geology and petrophysics was constructed to successfully match the pool's 19 years of waterflood and 3 years of tertiary hydrocarbon miscible flood history. An analytical volumetric model was developed to define parameters such as fluid levels and rates in conjunction with the field scale 3-D simulation model. A solvent-in-place cutoff volume was used to determine when the miscible flood ceased and became an immiscible gas flood.

Ultimate recovery in the order of 70% to 80% is anticipated depending on the solvent slug size and solvent production.

This paper describes how an analytical volumetric model can be run in synergy with a complex full field simulator to achieve the objective of obtaining and maintaining horizontal fluid levels throughout the pool.

Introduction

The Rainbow Keg River "B" Pool is located in northwestern Alberta (Fig. 1) and contains the largest oil accumulation of the Rainbow Field, having 43 × 106 m3 (270 × 106 STB) of original oil-in-place (OOIP). Total oil production as of March 1990 amounted to 19.7 × 106 m3 (124 × 106 STB) or 46%, of the OOIP. The pool isopach, reef top to original oil-water contact (OOWC), shown in Figure 2, illustrates the reef's geometry as inferred from excellent quality 3-D seismic data and well information.

The geological model contains three horizontal zones within the original oil column arranged in a more-or-less "Layer-cake" fashion as shown in Figure 3. The uppermost, the thin "A" zone is largely limestone. Underlying the capping "A" zone is the "B" zone, which is all dolomite. Generally, increased vugginess in the pool coincides with the top of the "B" zone. The "B" zone is also recognized by an absence of the ubiquitous pyrobitumen which characterizes the basal "C" zone. The "C" or pyrobitumen (properly carbon) zone shows an oil-wet tendency. Both the dolomite and the pyrobitumen extend to and below the pool's OOWC. Highly fractured and vuggy intervals were not co relatable from well to well and do not in themselves form a definable zone or zones. Instead, high incidence of fracture and vuggy intervals were reported on an individual well bases for incorporation into the numerical model.