Waterflooding Jin A Small Pinnacle Reef Reservoir With A Single Wellbore
Authors: Boutette Michael J. , Ko Stephen C.M. , Withers R. Louis 
Published: March 2010

The feasibility of implementing a pressure maintenance scheme in a small pinnacle reef reservoir in the Shekilie area of northwestern Alberta was assessed. Detailed geological and reservoir simulation studies were conducted on the single well Shekilie Keg River III Pool to Investigate lire alternatives for enhanced oil recovery in a pinnacle reef oil reservoir, with Jess than one million barrels Of original oil-in-place (OOIP).

An excellent history match of the primary production performance by the simulation model provided a sound basis for studying different pressure maintenance schemes at various stages of primary depletion. A single-well waterflood recovery scheme, with an estimated recovery factor of 49.7% of OOIP. was recommended for the pool and subsequently implemented in October 1987. Actual field production and injection performance of this scheme is also included for early evaluation of the project.

Introduction

An oil productive Keg River biohern was found with the drilling of the Ultramar et al. Shekilie 6-13-119-7 W6M well in December 1985. This well encountered 86.4 m of net oil pay, of which 7.2 m occurs in the overlying Zama member of the Muskeg Formation, and 79.2 m in the Keg River Formation. The oil-water contact in this well is at 1825 m KB, and the bottom 39 m of porosity is water-bearing. The reservoir discovery pressure was 19481 kPa abs. No initial gas cap was present. The oil was undersaturated, with an initial gas-oil ratio of 147.5 m3/m3. The solution gas is sour and contains 6.80/0 hydrogen sulphide.

The Shekilie 6–13 well began production on January 22. 1986, and has recovered 26 × 103m3 (164 mstb) of oil to December 31,1987. The producing gas-oil ratio has steadily increased, with no significant amount of water being produced. Due to declining reservoir pressure and increasing gas-oil ratios, a waterflood scheme utilizing a single wellbore was implemented in October 1987. The implementation of this single wellbore waterflood was based on the recommendations of a detailed geological review and reservoir simulation.

Early waterflood performance provided useful data for recalibration of the model for ongoing waterflood performance monitoring and optimization. This paper demonstrates the successful application of reservoir simulation in formulating operational strategies and implementing reservoir management plans.

Geology

Oil pools of the Givetian (Middle Devonian) Keg River Formation are abundant in the Shekilie Basin of northwestern Alberta in the form of isolated patch reefs (bioherms). The seal for the oil pools occurs in overlying anhydritic and dolomitic evaporites of the Muskeg Formation. One member of the Muskeg Formation, the Zama dolomite, comprises minor segments of some Keg River oil pools at Shekilie. Source rocks of the oil are the bituminous laminates which about the base of the Keg River bioherms.

Most of the Shekilie 6–13 oil reservoir occurs within the Keg River bioherm, as shown in Figure 1. The bioherm attains 132 m in height and is much broader at the base than at the crest. The crestal position occurs on the north side, which was the upwind direction during Givetian bioherm growth.