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Heating strongly affects the viscosity of the oil in the reservoir porous media and in the wells. The heating effect in the porous media of the reservoirs is simply represented by Darcy's law with a temperature-dependent viscosity, μ(T). The effect of the heating in a well (along the z direction), is represented by a temperature dependent viscosity used in the Hagen-Poiseville law. As in many other applications of electrical heating and in the case of well and reservoir heating, there is a wide range of available frequencies in the electrical spectrum, which can be used in diverse heating schemes. At the low-frequency (LF) end, energy is supplied directly from the 60 Hz distribution grid. Induction heating requires higher frequencies in the radio frequency (RF) range of 103 to 105 Hz, while heating is also possible at frequencies in the microwave (MW) range (MW 109 to 3 1010 Hz). Microwave heating has been widely used industrially in the past, but its application to reservoir heating is not widespread, although it has been receiving more attention lately. In this range of frequencies, the process is commonly defined as electrical heating and the parameters used are voltage, current, resistance, capacitance, and inductance.
The electromagnetic heating of oil wells and reservoirs refers to thermal processes for the improved production of oil from underground reservoirs. The source of the heat, generated either in the wells or in the volume of the reservoir, is the electrical energy supplied from the surface. This energy is then transmitted to the reservoir either by cables or through metal structures that reach the reservoir. The main effect, because of the electrical heating systems used in practice in enhanced oil recovery, has been the reduction of the viscosity of heavy and extra heavy crudes and bitumens, with the corresponding increase in production. Focus is centered on systems (and the models that describe their effects) that have been used for the electromagnetic heating in the production of extra heavy petroleum and bitumen.
Abstract … And expecting different results. Electrical heating of oil reservoirs has fascinated petroleum engineers for more than 70 years - longer, if you include the use of heaters in Siberian oilfields. The earliest laboratory study was done in Pennsylvania in 1940's. Since then, many more studies and field tests have been carried out, none of which was a commercial success. This paper takes a look at different forms of electrical heating, the supporting theoretical work, and field tests. Additionally, several examples are given illustrating the limitations of electrical heating processes. Also discussed is the logic behind the resurgence of electrical heating in recent years. Not discussed are over 200 patents on electrical heating. The major electrical heating processes are resistance heating, using direct current or low frequency alternating current, induction heating, microwave heating, and heating by means of electrical heaters. These are described briefly, and compared. In applications to oil sands, the intent is to utilize the connate water as the heating element (resistance heating) or oil sands as the dielectric (microwave heating). Induction heating is much less effective but has been tested in many field projects. Shale that has a permeability of zero to fluid flow, is electrically conductive, and thus channels much of the electric current flow in resistance heating, which also has other limitations. Microwaves suffer from low depth of penetration (of the order of 20 cm in oil sands) and low power delivery (of the order of 1 MW as a maximum). The power requirements for a typical SAGD pair, in contrast, are 15-30 MW. Electric heaters have been used in oilfields for many years for near-wellbore heating. Two large field pilots used powerful electric heaters, and were recently shut down. Although electrical heating has not had commercial success, recently there has been a resurgence in various electrical processes, as a means of reducing GHG emissions, under the flawed logic that oilfield use of electricity would displace emissions caused by steam generation.
Electrical resistance heating (ERH) is a thermal stimulation technique in which electrical current passes through the formation. Field testing of this process is continuing. The current work uses results generated with reservoir simulation. Two models were used to describe ERH power dissipation (heating patterns): (1) a radial power model, and (2) an r-z power model.
Wattenbarger and McDougal developed a hand method for estimating the heated oil production rate under ERH stimulation. The production rate under ERH stimulation. The first objective of the current paper is to present improvements to that hand method. present improvements to that hand method. The new hand method has the following advantages: (1) downhole electrical power is estimated, (2) well damage is accounted for, and (3) accuracy of heated production rates is improved. This new hand method can be quickly and easily used for screening potential ERH projects. potential ERH projects. The second objective of this paper is to present results from the r-z power model. The r-z power model provides a more detailed description of in situ heating patterns, including areas of intense heating (hot spots) which occur near the ends of the electrode. These hot spots may limit the amount of power that can be used in field installations.
The use of electromagnetic energy to stimulate heavy oil production his been reported as early as 1969. The mechanism by which heat is created is dependent on the electromagnetic frequency. At high frequencies (those between radio frequency and microwave frequency) dielectric heating dominates. Several papers on the topic of high frequency applications occur in the literature.
At low frequencies (less than 300 Hz), resistance heating dominates. Application of low frequency power is discussed in literature and can be called electrical resistance heating (ERH). Fig. 1 shows a diagram of the ERH process. Field testing of ERH is an ongoing activity and has been reported in the literature on several occasions.
Electrical resistance heating occurs when an electric current flows through the reservoir. The electrical energy is converted to heat. Because the electrical path is provided by in situ water, formation path is provided by in situ water, formation temperatures should be kept below the boiling point to maintain electrical continuity. The scope of the current work is limited to low frequency, single phase applications. The objectives are to provide an improved hand method for screening ERH projects, and to present the results of projects, and to present the results of detailed finite difference simulation study.
Radial Power Model
The hand method of screening ERH projects that is presented in this paper was projects that is presented in this paper was developed using a thermal reservoir simulator incorporating the radial power model to describe the in situ ERH heating pattern. The radial power model is a fully pattern. The radial power model is a fully implicit, single phase, thermal reservoir simulator. Fluid flow and current flow are 1-D radial. Heat losses to the overburden and underburden are 1-D vertical.
Ovalles, Cesar (Chevron Energy Technology Co) | Vaca, Pedro (Acceleware) | Okoniewski, Michal (Acceleware) | Dieckmann, Gunther (Chevron Energy Technology Co) | Pasalic, Damir (Acceleware) | Dunlavey, James (Chevron Energy Technology Co.)
Abstract The numerical evaluation of dielectric heating in a heavy oil containing sand is presented using a shaped dipole antenna under static (no oil production) and dynamic (with oil production) conditions. The electromagnetic simulator AxREMS™ was coupled to the commercial reservoir simulator STARS™ to model RF heating using three different shaped antenna designs (Straight dipole, Concave, and Convex design). The static simulations showed that the Concave design offers more uniform radiation pattern and temperature profile than the Straight and Convex counterparts. A conceptual model with seven sands (over- and under-burden and five oil-containing sands) was utilized for the dynamic simulation of downhole RF dielectric heating. The results indicated that all the RF heating cases had accelerated oil production than that found for the Base Case (cold production). Modeling shows that peak production is increased if RF heating is initiated before the start of production. However, all cases studied converged to approximately equal cumulative incremental oil above the Base Case, after about 700 days after the initiation of RF heating.