Affiliation:
1. Alberta Research Council
Abstract
Abstract
Canada has declining reserves of conventional oil, but vast reserves of heavy oil and bitumen. Over 90% of the world's heavy oil and bitumen trapped in sandstones and carbonates are deposited in Canada and Venezuela. Up to 80% of estimated reserves could be recovered by in-situ thermal operation. The current in-situ thermal technologies such as cyclic steam stimulation (CSS), steam flooding and steam-assisted gravity drainage (SAGD) are energy intensive and use large quantities of fresh water. Increasing pressure of environmental concerns and the threat of a carbon tax will make it imperative to find new oil extraction technologies that are less energy intensive and that use less water. Combining technologies in the form of hybrid steam-solvent processes offer the potential of higher oil rates and recoveries, but at less energy and water consumption than processes such as SAGD.
At the Alberta Research Council, new hybrid steam-solvent processes have been undergoing development in recent years. The Expanding Solvent-SAGD (ES-SAGD)(1–2), is aimed at improving and extending SAGD performance by solvent addition to steam. The improvements include higher and faster drainage rates, lower energy and water requirements and reduced green house gas (GHG) emissions. The Thermal Solvent Hydrid process focuses on combining solvent with a small amount of steam in a VAPEX (vapour extraction) process (3–4). This process offers the potential of higher rates than cold solvent VAPEX at less energy consumption than SAGD.
Hybrid steam-solvent processes, when fully developed, will extract oil at lower cost than SAGD and will also open currently marginal resources for exploitation, increasing oil reserves. This paper presents and discusses the principal concepts and key parameters for the new hybrid steam-solvent processes and compares expected performance to SAGD.
Introduction
The goal of this paper is to provide a summary of the hybrid steam-solvent processes developed at the Alberta Research Council (ARC), which include ES-SAGD and thermal solvent hybrid and provide some laboratory and field examples of these and other steam-solvent hydrid processes developed in recent years. The hybrid steam-solvent processes results at ARC illustrated the potential to develop an improved process that will significantly reduce energy, water and GHG intensity as compared to SAGD, therefore reducing operating cost while maintaining economic oil recovery rates.
ES-SAGD laboratory experimental results in Athabasca illustrate 17–30% increase in oil production over that from SAGD, for the same amount of steam injected. This indicates an improvement in oil-steam ratio (OSR) by the same magnitude. More importantly, the experimental results indicate that the time required to produce the same amount of oil in ES-SAGD could be half that of SAGD. Such accelerated oil production results in significant increase in oil rates and reduction (∼50%) in steam requirements. As a consequence, natural gas burning, water requirement and GHG emissions would be reduced. This is quite significant given the large production volumes from commercial SAGD projects.
The thermal solvent hybrid experimental results at ARC provided data for comparison of the process with other low energy intensity processes, like thermal solvent reflux and VAPEX(3–4).
Expanding Solvent SAGD (ES-SAGD)
Concept and Principles of ES-SAGD
In ES-SAGD recovery process(1,2), a solvent or a solvent mixture is co-injected with steam in a hybrid process, as opposed to the injection of only steam in the SAGD process or only solvent in the VAPEX process. In the ES-SAGD process, the solvent or solvent mixture additive, whose vapourization thermodynamic behaviour is similar, or close, to that of water thermodynamic behaviour for a given reservoir condition is considered the most appropriate.