Abstract

The steam assisted gravity drainage (SAGD) has been successfully tested in field pilots and commercial applications are currently underway by a number of oil companies. The process yields higher oil rates and faster reservoir depletion, as compared to other in-situ oil recovery processes. Current developments of the SAGD process are aimed at improving oil rates, improving oil-to- steam ratios "OSR", reducing energy and minimizing water disposal requirements. In addition to SAGD, progress has been made in the development of solvent injection processes. These processes result in lower oil rates and energy requirements as compared to SAGD. At the present time, limited field results are available for the solvent processes to allow for adequate evaluation of field performance.

A novel approach for combining the benefits of steam and solvents in the recovery of heavy oil and bitumen has been undertaken at the Alberta Research Council (ARC). A newly patented Expanding Solvent-SAGD "ES-SAGD" process has been developed. The process has been successfully field-tested and resulted in improved oil rates, improved OSR and lower energy and water requirements as compared to SAGD.

The paper discusses the concept and laboratory testing of the ES-SAGD process.

Introduction

The most promising in-situ thermal recovery technology is the SAGD process. In this process, two horizontal wells separated by a vertical distance are placed near the bottom of the formation. The top horizontal well is used to inject steam and the bottom well is used to collect the produced liquids (formation water, condensate, and oil).

Following the success of the UTF project at Fort McMurray, Alberta, a number of field pilots are in progress in other heavy oil reservoirs in western Canada (Alberta and Saskatchewan), and around the world. These pilots tested the use of surface accessed horizontal wells and extended SAGD applications to problem reservoirs. These reservoirs often have lower permeabilities, are deeper, have bottom water transition zones, with initial gas-saturated "live" oil and top water / gas caps. In Alberta, the success of these pilots has led to a number of commercial SAGD projects that are currently underway.

Current developments of the SAGD process at ARC are aimed at improving oil rates, improving OSR, reducing energy and minimizing water disposal requirements. Progress has been made in the development of combined steam-solvent injection processes, a novel approach for combining the benefits of steam and solvents in the recovery of heavy oil and bitumen. A newly patented(1) Expanding Solvent-SAGD "ES-SAGD" process has been successfully field-tested and has resulted in improved oil rates and OSR, and lower energy and water requirements as compared to conventional SAGD. The ES-SAGD concept and laboratory testing using the high pressure/high temperature experimental facilities at ARC are presented in this paper.

THE ES-SAGD CONCEPT

Figure 1 illustrates the ES-SAGD concept. In this concept, a hydrocarbon additive at low concentration is co-injected with steam in a gravity-dominated process, similar to the SAGD process.

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