The Mechanisms of Electrical Heating For the Recovery of Bitumen From Oil Sands

Abstract

Abstract Electrical heating of the Alberta oil sands for the recovery of bitumen has been studied since the early 1970's(1–5). The technology has evolved as an additional technology to SAGD and surface mining. This paper describes the heat and mass transfer mechanisms associated with a specific application of electrical heating, the Electro-Thermal Dynamic Stripping Process (ETDSP ™), for the production of bitumen from the oil sands. Given that heat is created in the oil sand as a current flow through the connate water and that initially all the fluids are immobile, the end result is a pressure and temperature distribution that is characteristic of an electrical heating process. To effectively recover the heated bitumen from the oil sand requires an understanding of the heat and mass transfer mechanisms associated with the pressure and temperature distribution, as well as gravity forces. The electrical heating process changes as the oil sand increases in temperature and the bitumen is produced. This results in a dynamic process whereby the heat, mass and electromagnetic fields are strongly coupled and in a transient state throughout the entire recovery process. The dominant mechanisms of the electrical heating recovery process are presented in terms of fundamental equations and solved numerically. A 3D quasi-harmonic finite element electromagnetic model is coupled to the mass and energy equations and solved in time. A recovery strategy based on an understanding of the recovery mechanisms is presented in terms of electrode spacing, duration of heating, energy supply and favourable operating requirements. Introduction Oil sands are a mixture of sand, bitumen and water. The bitumen is defined as oil that is less than 10 API and will not flow to a well in its naturally occurring state. The Alberta Energy & Utilities Board (AEUB) estimates that given current technology, over 300 billion barrels are expected to be recovered from the Alberta oil sands. There are presently two techniques used to produce bitumen; open pit mining and in situ thermal recovery, which involves drilling wells and injecting steam to heat the bitumen allowing it to flow and be produced from a well. Of the in situ methods now used, steam assisted gravity drainage (SAGD) is the most promising, having the advantages of lower energy requirements and higher recovery factors over other steam injection methods. In-situ thermal recovery methods as applied in oil sand deposits have the common objective of accelerating the hydrocarbon recovery process. Raising the temperature of the host formation reduces the bitumen viscosity allowing the near solid material at original temperature to flow as a liquid. These effects assist in sweeping much of the bitumen from the formation when driving agents are externally injected or when autogenously processes, such as gravity drainage, come into play. Transferring electromagnetic energy to the deposit is proving to be an effective means of supplying the necessary heat. In the electro-thermal process, electromagnetic energy is converted to heat in situ using a system of electrodes from which a current flows through the formation.