Heavy Oil: Optimize Cyclic Steam Stimulation Though Experimental Design

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 109826, "Peace River Carmon Creek Project Optimization of Cyclic Steam Stimulation Through Experimental Design," by P.F. Koci, SPE, and J.G. Mohiddin, SPE, Shell International E&P, prepared for the 2007 SPE Annual Technical Conference and Exhibition, Anaheim, California, 11–14 November. The paper has not been peer reviewed. Peace River Carmon Creek is an ultra-heavy-oil lease in northwestern Alberta, Canada, holding nearly 1.27×109 m3 of 7°API oil. The Carmon Creek Project targets approximately half of that oil for development by cyclic steam stimulation (CSS). There are plans for a significant increase in oil production over the next 5 years. The purpose of this study was to optimize CSS well configuration and steaming strategy. Introduction Various thermal-recovery schemes have been piloted at Peace River. At present, CSS is used to extract the oil, most recently with closely spaced multilateral horizontal wells drilled from a central surface pad. The CSS target is the Bluesky formation, an approximately 30-m-thick semiconsolidated-sand layer buried at a depth of approximately 600 m and characterized by a wide range of reservoir properties. These varying reservoir features are expected to result in different optimum CSS-well configurations and steaming strategies for each geologically unique portion of the field. Geological Models Full-Field Model. The Bluesky reservoir in the Carmon Creek Project area generally is classified into two intervals, a poorer-quality estuarine zone with an order of magnitude lower vertical-/horizontal-permeability ratio compared to the underlying better-quality deltaic zone. This generalization does not apply to the entire Peace River field. In some parts of the field, the estuarine zone is of better quality than the deltaic zone. Lower portions of the deltaic zone typically have higher water saturation, termed "basal water zone" (BWZ). The total gross reservoir thickness and the BWZ thickness vary greatly across the field. Bitumen viscosity also is highly variable, both areally and vertically, throughout the Bluesky reservoir. A full-field static reservoir model was built covering an area of approximately 2000 km2 and including more than 400 wells. The main objective was to capture and characterize the regional reservoir differences by use of a 250×250-m coarse areal grid with 0.5-m vertical resolution. Area Models. The full-field static model was divided into six distinct geological areas, and a relatively fine-grid (25×25 m) sector model was constructed for each of these areas. Areas 1 and 2, characterized by high permeability, good seals, thick pay, high oil concentration, high hot-oil mobility, and either an insignificant or no BWZ, have the most favorable reservoir properties for CSS. Area 3 is poorer than Areas 1 and 2 because of the thicker BWZ and somewhat higher oil viscosity (lower hot-oil mobility). Area 4 can be characterized by thin pay, top-gas presence, and very high oil viscosity. This area is likely to be very marginal for CSS application.