Heavy-Oil Recovery From Thin Pay Zones by Electromagnetic Heating

Abstract

SPE Members Abstract There are many heavy oil reservoirs with thin pay zones (less than 10 m). Conventional thermal recovery methods such as steam injection, are not cost effective for these thin reservoirs due to the excessive heat loss through the overburden. In order to minimize heat losses, it is necessary to have the ability to carry out controlled heating of the pay zone. One such way to introduce heat to the reservoir in a controlled manner is electromagnetic heating. This paper describes laboratory studies on electromagnetic heating of scaled thin heavy oil reservoir pay zone models. Combination of electromagnetic heating and gas injection with horizontal wells was studied. Higher electromagnetic frequencies provide faster heating rate and can overcome problems associated with discontinuity of the media through which electromagnetic waves must propagate in the reservoir. Heat loss can also be minimized with the use of higher frequencies. For moderately heavy oil reservoirs (less than 1000 mPs.s), it is not necessary to heat the entire pay zone. Heating of the wellbore vicinity is sufficient. Oil recoveries as high as 45% of OIIP (Original Oil in Place) were achieved using electromagnetic heating and gas injection compared to estimated primary recovery rates of less than 5%. The results obtained in this work clearly show that electromagnetic heating provides an effective mean of recovering heavy oil from reservoirs with thin pay zones. Introduction There are a number of heavy oil reservoirs in regions bordering Alberta and Saskatchewan, where the reservoir thickness is relatively low and in most of the cases less than 10 m. The main geometric characteristics of these reservoirs are that they are relatively thin but cover a wider reservoir area. In such cases, conventional heavy oil recovery methods, such as steam injection, is usually economically less attractive due to excessive heat losses through the overburden. One alternative way of heating the reservoir fluids without much loss of heat to the surroundings, is to employ electromagnetic heating. Electromagnetic heating is capable of heating a confined zone, without heating the entire oil bearing zone of the reservoir. Selective electromagnetic heating near the wellbore lowers the viscosity of the oil significantly, so that the fluid mobility becomes several hundred times higher than the rest of the reservoir. Use of horizontal wells as electrodes can be effective for the heating of heavy oil and tar sands formations. Oil recovery by electromagnetic heating is superior to that by conduction heating. Heat propagates by conduction mode only, in the case of conduction heating. Whereas, in the case of electromagnetic heating, heat is propagated due to the flow of electromagnetic waves through the reservoir. This allows larger reservoir area to be covered by the heating process with greater efficiency. Oil displacement by electromagnetic heating is, however, inferior to that by steam injection heating, due to the absence of any significant convective transport of the heated oil. P. 525^