IntroductionOil 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 AbstractElectrical heating of the Alberta oil sands for the recovery of bitumen has been studied since the early 1970's (1)(2)(3)(4)(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 (ET-DSP™), for the production of bitumen from the oil sands.Given that heat is created in the oil sand as a current flows 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.sweeping much of the bitumen from the formation when driving agents are externally injected or when autogenous 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, electromagne...

FIGURE 7: Temperature contours in the contaminated soil of a decommissioned gas station after 115 days of electrical heating.

The purpose of this paper is to present the modifications to a multi-component, thermal reservoir simulator to incorporate electrical heating equations. The results of the simulator are compared with actual field data and a semi-analytical model. The visco-skin is described and the use of electrical heating to remove the visco-skin and increase the productivity of the well is demonstrated. The visco-skin concept is a physical phenomenon which explains the rapid productivity increase of some wells undergoing electrical heating. It is important to include the visco-skin concept in the discussion of electrical heating since it develops in the near wellbore, as does the temperature distribution from electrical heating. The electric field equations have been solved using a 3D finite differencing technique coupled to a multi-purpose reservoir simulation program. The resulting program can be used forpredicting the fluid rates from a well undergoing electrical resistance heating,calculating the temperature distribution in the reservoir and on the electrode,obtaining the voltage-current relationship for designing power supplies,establishing operational criteria such as input power requirements as a function of flow rate and reservoir heterogeneity, andwell completion design. Introduction Electrical Resistance Heating Electrical heating is a thermal process which can be applied to a well to increase its productivity. The productivity increase is substantial and comes about because of the removal of thermal adaptable skin effects (visco-skin for example) and the reduction of the oil viscosity in the vicinity of the wellbore. Salient features of the process are:It is a continuous, not a cyclic process. Electrical heating occurs simultaneously with production of fluids.Low frequency power (not microwave frequency) is used.All the downhole equipment can be contained within a single wellbore. FIGURE 1: Electrical healing single wellbore configuration (oil production equipment not shown). (Available in full paper) Figure 1 describes how the process works. The specific system described here is similar to Gill, 1969; Spencer, 1988; and Rice, 1992. The essential components of an electrical heating system are:power supply,power delivery system,electrode assembly, andground return. The variable frequency (2 to 60 Hz), power supply (Isted, 1992), is capable of delivering up to 300 kW of power. The power delivery system may consist of tubing, cables or a combination of both. The electrode assembly consists of bare casing pipe with FIGURE 2: Visco-skin concept. (Available in full paper) fiberglass electrical isolation joints attached to the ends. The length of the electrode and location in the reservoir is a matter of engineering design. The current return or ground can be the casing string above the fiberglass insulation. Current leaves the power supply and is conducted down the power delivery system to the electrode assembly. The electrode is in electrical contact with the reservoir formation. From the electrode, the current is forced to flow through the reservoir and return to the power supply up the casing.

The implementation and performance results of the Electro-Thermal Dynamic Stripping Process (ET-DSP™)

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