Abstract:
The present invention utilizes the ability of electromagnetic energy at the appropriate frequency to selectively deposit thermal energy in the heavy oil for precise control of cracking temperature throughout a given volume of material. Selective electromagnetic energy absorption in the heavy crude oil provides energy efficient transfer of heat at the molecular level and thereby insures precise temperature control throughout the treatment volume. This allows for optimization of the visbreaking process using electromagnetic energy.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S)  
       [0001]     This application claims priority from U.S. provisional patent application No. 60/645,154, which was filed on Jan. 19, 2005, and which is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to the use of electromagnetic energy to subject heavy crude oil to mild thermal cracking conditions, thereby lowering the viscosity, pour point, and specific gravity of the oil and rendering it easier to recover and handle. More particularly, this invention relates to methods for applying electromagnetic energy to heavy oils in the reservoir to promote in situ upgrading and facilitate recovery. This invention also relates to systems to apply electromagnetic energy to heavy oils in situ.  
       BACKGROUND OF THE INVENTION  
       [0003]     Heavy crude oil presents problems in oil recovery and production. Crude oils of low API gravity and crude oils having a high pour point present production problems both in and out of the reservoir. Extracting and refining such oils is difficult and expensive. In particular, it is difficult to pump heavy crude oil or move it via pipelines.  
         [0004]     Various methods to ameliorate the disadvantages of heavy crude oil are used today. For example, the oil industry reduces surface handling problems by blending heavy crude oil with light oils and liquid proprane gas to make them easily handled in pipelines and storage facilities. This method has drawbacks, however, as it does not assist in the initial recovery of the oil, and it is expensive.  
         [0005]     A process called “visbreaking,” or mild thermal cracking, may also be used to reduce the viscosity of heavy crude oil. “Visbreaking” is an oil refinery process for increasing the pumpability of heavy crudes. It typically is accomplished by heating heavy crude oil in a furnace. The process is characterized by mild decomposition, minimum coke formation and the retention of the cracked product in the original feed stock. The resultant mixture has viscosity, pour point, and specific gravity values that are lower than the original oil. However, ask applied today, visbreaking cannot be used on oil in situ.  
         [0006]     The present invention applies visbreaking new contexts and for new purposes, and proposes improved methods for the application of visbreaking. In the present invention, visbreaking is accomplished using electromagnetic energy to heat the heavy crude oil, rather than heating it in a furnace. Furthermore, the present invention is suitable for use in the treatment of oil in situ. Such treatment permits the upgrade of the oil in reservoir and assists in the recovery of the oil.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007]     The present invention utilizes the ability of electromagnetic energy at the appropriate frequency to selectively deposit thermal energy in the heavy oil for precise control of cracking temperature throughout a given volume of material. Selective electromagnetic energy absorption in the heavy crude oil provides energy efficient transfer of heat at the molecular level and thereby insures precise temperature control throughout the treatment volume. This allows for optimization of the visbreaking process using electromagnetic energy.  
         [0008]     Proper selection of frequency and power duration results in the rapid cracking of heavy hydrocarbons to any degree desired by electromagnetic energy absorption. When the desired degree of cracking is reached, the hot oil matrix provides a significantly different set of electrical properties which can be measured on the surface during the “electromagnetic visbreaking process.” (EVP) to insure precise down hole temperature and power control.  
         [0009]     This proposed EVP provides efficient energy absorption and control of thermal cracking of heavy oils for in-situ upgrading. The application of low power (a few ten&#39;s of kilowatts) electromagnetic energy to the formation for visbreaking will provide mild decomposition of the heavy oil, minimum coke formation and the retention of the cracked product in the original feedstock. The resultant mixture has viscosity, pour point, and specific gravity values which are lower than those of the original oil.  
         [0010]     The present invention several promising applications. It can be used to upgrade heavy crude oil in situ. It can also assist in the recovery of heavy crude oil from reservoirs. Further, the present invention can be used to more efficiently recovery hydrocarbons from oil shale, such as that present in the Western United States.  
         [0011]     In one embodiment of the invention, a system may be provided for use in treating heavy crude oil underground. The system may comprise a borehole in an area in which crude oil exists in the ground, an electromagnetic energy applicator positioned within the borehole in the vicinity of the heavy crude oil to be treated, a cable attached to the electromagnetic energy applicator to supply electromagnetic energy to the applicator, an electromagnetic energy generator attached to the cable to generate electromagnetic energy to be supplied to the applicator, and a product return pipe running through the borehole, the product return pipe comprised of a distal end positioned in the vicinity of the electromagnetic energy applicator through which oil or other products may be recovered and a proximal end on or near the surface of the ground.  
         [0012]     In another embodiment of the invention, a method for treating heavy crude oil underground is provided. The method comprises the steps of positioning an electromagnetic energy applicator in a borehole in the vicinity of heavy crude oil, generating electromagnetic energy, applying the electromagnetic energy to the heavy crude oil with the applicator to achieve thermal cracking, and recovering heavy crude oil through a product return pipe.  
         [0013]     While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. As will be realized, the invention is capable of modifications in various obvious aspects, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a perspective view of a single borehole radiation type applicator.  
         [0015]      FIG. 2  is a close up view of a portion of the applicator system.  
         [0016]      FIG. 3  is a perspective view of a portion of another configuration of a single borehole applicator.  
         [0017]      FIG. 4  is a perspective view of a wellhead for use with the applicator system.  
         [0018]      FIG. 5  shows a sample of the absorption data from experiments on the application of electromagnetic energy to large oil molecules in oil shale. 
     
    
     DETAILED DESCRIPTION  
       [0019]     A variety of different types of down hole electromagnetic structures may be employed to apply electromagnetic energy to heavy crude oil in situ. The proper structure for any particular application depends on a variety of factors, including depth, heat uniformity, and minimizing the degree of coking and production of unsaturated hydrocarbons.  
         [0020]      FIG. 1  is a perspective view of a single borehole radiation type applicator. Applicator system  10  is positioned within borehole  12 . Borehole  12  is supported by casing  14 . Applicator system  10  is then used to apply electromagnetic energy to heavy crude oil in the vicinity of borehole  12 .  
         [0021]     Applicator structure  20  is a transmission line retort. For a point of reference, a typical applicator  20  may be approximately 70 feet long. In a typical configuration, the applicator  20  may be positioned from between 100 to 600 feet underground in borehole  12 . Radiofrequency (“RF”) energy is supplied to applicator  20  by an RF generator (not shown). The RF generator is connected to applicator  20  via a portion of flexible coaxial cable  30 . In turn, the flexible coaxial cable  30  is connected to a portion of rigid coaxial cable  32 . The coaxial cable may or may not be supported by ceramic beads, which are desirable at higher temperatures. By this means, the RF generator supplies RF energy to applicator  20 , which in turn applies RF energy to the target volume to achieve visbreaking. This allows in situ upgrading of the heavy crude oil and assists in recovery.  
         [0022]     Recovery of the oil and related products is achieved by means of production pipe  40 . This non-metallic pipe runs from the production area of borehole  12  through the borehole to surface  16 . At the surface, production pipe  40  is connected via a product return line to a storage or processing facility (no shown).  
         [0023]     Production pipe  40  provides a firm mounting base for the RF hardware of applicator system  10 . Coaxial cables  30  and  32  can be attached directly to production pipe  40  using connectors  42 . Applicator  20  also attaches to production pipe  40 .  
         [0024]      FIG. 2  is a close up view of a portion of the applicator system. Applicator structure  20 , rigid coaxial cable  32 , and production pipe  40  are all positioned within borehole  12 . Typical dimensions for such a system are shown in  FIG. 2 . Ceramic support beads  34  support rigid coaxial cable  32 . Further, ceramic pressure window  36  is placed at the tope of applicator  20 .  
         [0025]      FIG. 3  is a perspective view of a portion of another configuration of a single borehole applicator. In this configuration, a dipole feed is used. Coaxial feed  38  surrounds production pipe  40 . Ceramic window  36  is placed at the bottom of coaxial feed  38 .  
         [0026]     Although specific examples of applicator structures are given, it is understood that other arrangements known in the art could be used as well. Uniform heating may be achieved using antenna array techniques, such as those disclosed in U.S. Pat. No. 5,065,819. Such techniques can be used to minimize coking conditions at the applicator borehole and avoid excessive electrode voltage gradients at high power. Arrays reduce excessive voltage gradients at the borehole by means of mutual coupling. The ability to separately measure reflected power from each applicator borehole containing radiator and mutual impedance coupling between any pair of applicator boreholes insures precise temperature control of the heated volume.  
         [0027]     Other variations are possible, including non-radiation structures such as those proposed in J. Bridges, et al., “RF Heating of Utah Tar Sands,” Final Report, IIT Research Institute. However, such structures are sensitive to high voltage breakdown and require extensive drilling which is not economical.  
         [0028]     A special wellhead may be used in conjunction with applicator system  10 . Properly designed, the wellhead can be used to provide safe and efficient delivery of RF energy to the applicator.  
         [0029]      FIG. 4  is a perspective view of a wellhead for use with the applicator system. The weight of the down hole applicator (not shown) rests on a special bellows  46  within the wellhead. This insures that any heat induced mechanical movements of the down hole apparatus during energy transfer do not interrupt power flow. An input opening  44  permits nitrogen to be introduced into the interior of the wellhead and borehole, further ensuring the safe application of RF energy. Insulators  45  are positioned above the bellows  46 , and a center conductor expansion joint is positioned on top of that. At the top of the wellhead, where coaxial cable  30  exits and runs to RF generator  28 , a coaxial line seal and vertical alignment clamp  26  secure the cable to the wellhead. Product return line  41  carries the product recovered through the system to a storage or processing facility (not shown), and water extraction line  43  permits the removal of water from borehole  12 .  
         [0030]     The present invention also has application in oil shale fields, such as those present in the Western United States. Large oil molecules that exist in such oil shale have been heated in a series of experiments to evaluate the dielectric frequency response with temperature. The response at low temperatures is always dictated by the connate water until this water is removed as a vapor. Following the water vapor state, the minerals control the degree of energy absorption until temperatures of about 300-350 degrees centigrade are reached. In this temperature range, the electromagnetic energy begins to be preferentially absorbed by the heavy oil. The onset of this selective absorption is rapid and requires power control to insure that excessive temperatures with attendant coking do not occur.  FIG. 5  shows a sample of the absorption data from such experiments.  
         [0031]     Because of the high temperature selective energy absorption capability of heavy oil, it is therefore possible to very carefully control the bulk temperature of down hole crude oil heated by electromagnetic energy. The energy requirement is minimized once the connate water is removed by steaming. It takes much less energy to reach mild cracking temperatures with electromagnetic energy than any other thermal means to provide visbreaking.  
         [0032]     Kasevich has published a molecular theory that relates to the specific heating of heavy of oil molecules. He found that by comparing cable insulating oils with kerogen (oil) from oil shale, a statistical distribution of relaxation times in the kerogen dielectric gave the best theoretical description of how electromagnetic energy is absorbed in oil through dielectric properties. With higher temperatures and lowering of potential energy barriers within the molecular complex a rapid rise in selective energy absorption occurs.  
         [0033]     In use, a user of an embodiment of the present invention would position an applicator system in a borehole in an area in which heavy crude oil exists. The user would position the applicator structure itself in the borehole in the target area for application of RF energy. The user would connect the applicator structure to an RF generator via coaxial cable. A production pipe would run from the area of production to the surface, and from there to a storage or processing facility. The user would then apply RF energy using the RF generator to the applicator, thereby applying the RF energy to the heavy crude oil in situ. The RF energy would be controlled to minimize coking and achieve the desired cracking and upgrading of the heavy crude oil. The resulting products would then be recovered via the production pipe and transferred to a storage or processing facility.  
         [0034]     Although the present invention has been described with reference to preferred embodiments, persons skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.