Evaluation of Attic Oil Recovery Schemes For the Fenn West Leduc D-3E Reef Reservoir
Authors: Romualdez L.A. , Ko S.C.M. , Lam H.C. 
Published: March 2010

Abstract
Reservoir simulation was employed to evaluate various attics oil recovery schemes for the Fenn West Leduc D-3E reef reservoir. Based on geological and seismic data, a three-dimensional reservoir model was constructed to represent the pinnacle-reef reservoir and the adjoining bottom aquifer. The reservoir model was calibrated by history matching the production performance of the two vertical wells in the pool. Model calibration results indicated that water production from the pool is mainly attributable to a rising oil-water contact in the reservoir. Furthermore, the current oil production from the pool results from a reverse oil coning mechanism in the attic portion of the reef.
Various attic oil production schemes were investigated, including increased liquid withdrawals, reactivation of a shut-in vertical well and horizontal well production from the structurally highest location in the pool. Prediction results indicated that these attic oil production schemes will not recover any significant incremental oil reserves from the pool, but will shorten the remaining producing life of the pool by five to 21 years.

Introduction
The Fenn West Leduc D-3E pool, located in Township 36, Range 21, West of the Fourth Meridian (Figure 1), is a pinnacle reef reservoir containing light gravity oil (34 °API). Discovery well 08-11-36-21 W4M commenced production from the pool in January 1983, at an initial oil rate of over 300 m3/d (Figure 2). After producing clean oil for over four years, a series of well recompletions was conducted to arrest the increasing water production from the well (Figure 2). In September 1991, the well was suspended due to a high watercut of about 98%.
Another well, located at 07-11-36-21 W4M, commenced production in December 1985. The well produced clean oil for over three years and is currently producing at an oil rate of about 12 m3/d and a watercut of about 86% (Figure 3). A third well, located at 09-11-36-21 W4M, previously produced from the Nisku Formation and was converted to a water disposal well in 1987 (Figure 1). Based on pool pressure and production data, the main recovery mechanism in the pool is an active bottom water drive.
To April 1992, about 483,500 m3 of oil, 262,900 m3 of water and 38,600,000 m3 of gas have been produced from the pool. Based on data from the Energy Resources Conservation Board (ERCB)(1), the volumetric estimate of original oil-in-place (OOIP) for the pool is about 1,480,000 m3. Correspondingly, the current oil recovery is about 33% of the OOIP.
The objective of this study was to evaluate various attic oil recovery schemes for the pool including increased pumping rate for well 07–11, reactivation of well 08–11 and horizontal well production from the structurally highest location in the reservoir.
FIGURE 1: Pool location map: Fenn West Leduc. D-3E pool. (Available in full paper)

Geology
The Fenn West Leduc D-3E pool is extensively dolomitized, resulting in a very high quality reservoir. The average porosity is about 6% and the average horizontal permeability is in the order of several Darcies.