Abstract:
A well bore fluid is being heated to prevent paraffin build-up in the production line by an electrical heating element lowered into a pre-determined subterranean location. The heating element is controlled by a control unit that is connected to a temperature sensor, which detects temperature in the vicinity of the heating element and energizes an above-the-surface electric power source to deliver sufficient electric power to the electric heating element to keep the paraffin substance in a liquefied state.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation-in-part of my co-ending application, Ser. No. 10/886,526 filed on Jul. 7, 2004 and entitled “Inline Oilfield or Pipeline Fitting Element,” which is based on my provisional application Ser. No. 60/397,723 filed on Jul. 22, 2002, the full disclosures and priority of which are hereby claimed. This application also claims the priority of application Ser. No. 10/614,580 filed on Jul. 7, 2003 (now abandoned). 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     This invention relates to an apparatus and method for heating fluid in a subterranean formation, which has poor flowabilty due to the buildup of paraffin, or asphaltene on the walls of the production tubing or in the well bore. More particularly, the present invention relates to an apparatus and method of improving flowabilty of subterranean formation fluid by using an inline heating method.  
         [0003]     One of the problems associated with oil production is the deposition of paraffin or asphaltene on the walls of production tubing or the well bore. The oil is pumped to the surface or forced to the surface from a relatively hot area through a cool zone where the temperature of formation is less that the solidification temperature of paraffin. Once paraffin or asphaltene separate from the crude oil fluid flow, they tend to adhere to the production line walls causing a restriction in the tubing. Over time the paraffin builds up on the walls of the production tubing and significantly affects the production flow. As the crude oil is pumped to the surface, the gas from the reservoir also rises to the surface. Reservoir gas tends to decrease the reservoir pressure and increase the time the crude oil is flowing through the production tubing. As a consequence, the reduced flow of oil loses speed and pressure as it travels from downhole to the surface. The decreased temperature increases the viscosity of the oil and further reduces the flow rate.  
         [0004]     Such phenomenon is well known in the field and various methods have been employed to solve the problem. One such method is the so-called “Hot Oil Treatment.” According to the hot oil treatment method steam is pumped under significant pressure in the area between the casing and the tubing. The pressure applied during this process forces paraffin residue into the production formation. This method is ineffective as interaction of steam pressure in the producing zone frequently results in clogged perforations and ultimately the decline or loss of production. The pressure steam method is also time consuming, and requires down time to complete, is expensive and presents significant risks to the operator.  
         [0005]     Another method that is conventionally used in the oil industry to treat paraffin deposits requires stopping on the production, retrieval of the tubing, cleaning by scraping or steam, the inner wall of the well string to remove the paraffin and asphaltene deposits and then replacing the tubing back into the well. This method is also time consuming and costly and does not prevent future paraffin deposits in the pipes. The method is merely a maintenance procedure that works for a short period of time. Additionally, the risk of loss of production while the well is shut-in, coupled with the maintenance expense, makes many wells unprofitable to produce if such method is used.  
         [0006]     Still another commonly employed method is a chemical treatment using solvents that are introduced in the well bore in an effort to dissolve the paraffin deposits and improve the flow of crude oil.  
         [0007]     All these methods and systems have minimal success in addressing the problem as it occurs. Additionally, the conventional solutions do not take into consideration the flash ignition prevention in the design. The conventional tools are single units with limited heating capabilities that cannot be extended or added to, to cover a greater zone of treatment. Furthermore, the electrical heating devices used in conventional downhole heaters tend to allow leakage at electrical connections or at wire feed-through areas, which caused serious problems in the volatile environment downhole.  
         [0008]     One of the more serious problems is the failure of the conventional tools to detect and monitor downhole temperatures at the vicinity of the heater and thereby regulate the temperature in the critical areas. Another serious problem associated with conventional tools is failure to allow dumping of the fluid while at the bottom of the downhole fluid and crude oil while the heater is introduced in the flow path as part of the well string. Additionally, solid wall liners used in the heating devices do not prevent gas lock whereby gasses are prevented from escaping from the well bore tubing, which significantly impairs the production pressure.  
         [0009]     The present invention contemplates elimination of drawbacks associated with conventional systems and provision of an inline downhole heater that can be controlled and regulated from the surface as it heats the oil passing through the production tubing.  
       SUMMARY OF THE INVENTION  
       [0010]     It is, therefore, an object of the present invention to provide an inline heating apparatus that can be positioned as part of tubing in the well bore for heating the fluid as it passes from the hot temperature zone to the cold temperature zone.  
         [0011]     It is another object of the present invention to provide a method of heating production fluid by positioning the heating apparatus as part of the well string in the locations where the paraffin is likely to solidify.  
         [0012]     It is a further object of the present invention to provide an apparatus and method for heating fluid that can incorporate a number of heating assemblies for improving heating capabilities.  
         [0013]     These and other objects of the present invention are achieved through a provision of an apparatus for heating a fluid flow to treat a well bore and retain paraffin and asphaltene in a liquefied state while traveling through a production tubing, or line. The well bore treating apparatus comprises an elongated hollow body sized and configured for extending a production line therethrough, said hollow body being adapted for positioning in a pre-determined location within the well bore. The hollow body has an inner housing surrounding the production line and an outer housing mounted in a spaced-apart surrounding relationship to said inner housing. The inner housing and the outer housing are maintained in a spaced-apart relationship by a plurality of transverse plates extending in the body, and wherein an annular space is defined between the inner housing and the outer housing.  
         [0014]     The body is divided into a plurality of dry zones and wet zones defined in an annular space between the inner housing and the outer housing, although it may be sufficient that at least one dry zone and at least one wet zones be formed by the hollow body. The inner housing comprising a perforated wall portion located in the wet zone to facilitate fluid communication and heat transfer with the interior of the well bore.  
         [0015]     A heating means comprising at least one heating element extends in the wet zone in a heat-transferring relationship to the production line, said heating means being operationally connected to an above-the-surface electric power source. A control means for controlling operation of the power source depending on current temperature conditions in the pre-determined location in the well bore is operationally connected to the heating element(s), said control means comprising a temperature sensor mounted on said housing and operationally connected to a control unit positioned on the surface.  
         [0016]     The sensor generates a signal indicative of the ambient temperature near the heating element positioned in the well bore and sends the signal to a control unit positioned above the surface. The control unit is operationally connected to a pulse generator capable of being energized by the power source and transmitting electrical power to the subterranean location where the well bore treating apparatus is located. The heat from the heating element is transferred to the well bore fluid and then to the fluid in the production line, melting paraffin and asphaltene and preventing their solidification. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     Reference will now be made to the drawings, wherein like parts are designated by like numerals, wherein  
         [0018]      FIG. 1  is schematic view illustrating position of the apparatus in accordance with the present invention in a well bore.  
         [0019]      FIG. 2A  and  FIG. 2B  illustrate portions of the apparatus of the present invention, with the interrupt lines introduced to fit the page size.  
         [0020]      FIG. 3  is a cross-sectional view taken along lines  3 - 3  in  FIG. 2A .  
         [0021]      FIG. 4  is a cross-sectional view of the apparatus of the present invention taken along lines  4 - 4  in  FIG. 2A .  
         [0022]      FIG. 5  is a detail, partially cross-sectional view of the temperature sensor device used in the apparatus of the present invention.  
         [0023]      FIG. 6  is a cross-sectional view of the apparatus of the present invention taken along lines  6 - 6  in  FIG. 2B .  
         [0024]      FIG. 7  is a schematic view illustrating the circulation flow in a wet zone of the apparatus of the present invention.  
         [0025]      FIG. 8  is detail view illustrating purging of oxygen from the interior of the apparatus of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0026]     Turning now to the drawings in more detail, numeral  10  designates the inline heating apparatus in accordance with the present invention. As can be seen in  FIG. 1 , the apparatus  10  is operationally connected to a transformer  12  and a pulse generator  14  positioned above the surface. The transformer  12  is adapted for connecting to a source of electrical power, for instance a 480-watt power source. The pulse generator  14  transmits electrical power to the heating elements positioned in the well  16  formed in the ground formation. The power generator  14  receives a signal from a temperature controller  18  that is operationally connected to a temperature sensor  20 .  
         [0027]     The apparatus  10  is positioned in a selected pre-determined location in the “cool zone”  22  of the well  16  wherein paraffin solidification is likely to occur. A hot zone  24  is usually located below the cool zone  22  and thus, it will not be necessary to position the apparatus zone in the zone  24 . As can be seen in  FIG. 1 , the apparatus  10  can be connected end-to-end with a well bore string  26  which extends in the well bore  16  toward a production zone  28 .  
         [0028]     Extending through the central opening in the apparatus  10  and through the well bore string  26  is a production line, or production tubing  30 , through which crude oil is pumped from the production zone  28  to the surface. The transformer  12 , the power generator  14 , and the temperature controller  18  are positioned on the surface above a wellhead  32 .  
         [0029]     The apparatus  10  has distinct portions that for the ease of explanation are designated as “dry zone” and “wet zone.” As can be seen in  FIGS. 2A and 2B , three wires  36 ,  37 , and  38  positioned in a cable  34  extend into the well  16  from the pulse generator  14 . A cable  35  is a ground wire, and a cable  33  extends from the temperature controller  18  to the temperature sensor  20 .  
         [0030]     Each of the wires  36 ,  37 , and  38  is connected to a respective heating element  40 ,  41  and  42 . Each of the heating elements comprises an elongated heating member extending longitudinally in the elongated hollow body  50  of the apparatus  10 . The body  50  comprises a top plate  52 , that is sealed against the interior of the well bore  16  and carries the connecting wires  36 ,  37  and  38  that extend through the plate  52  into the interior of the housing  50 . The wires  36 ,  37  and  38  may be Kapton-coated wires that are sealed with graphite seals  43 ,  44  and  45  that are crimped around the wires to prevent liquid from entering a the body  50 . The plate  52  defines one end of a dry zone  60 , while another transverse plate  54  defines another end of the dry zone  60 . An opposite surface of the plate  54  defines one end of a wet zone  62 , while still another transverse plate  84  separates the wet zone  62  from the next dry zone  86 .  
         [0031]     The body  50  comprises an outer housing  51  and an inner housing  64 ; the housings  51  and  64  are spaced apart, defining an annular space  66  therebetween. A first insulation layer  56  is located inwardly from the outer housing  51 , and a second insulation layer  58  is located on the outside of the inner housing  64 . The operating wiring and the connectors extending through the dry zone  60  are thereby protected from the heat generated in the well bore and from the heat generated by the heating elements of the apparatus  10 .  
         [0032]     The inner housing  64  extends formed longitudinally substantially through the entire length of the tool  10  and in a parallel relationship to the outer casing  51 . The inner housing is sized and configured to allow extension of the production tubing  30  through a central opening  63  formed in the inner housing  64 . A bushing  70  is mounted on the plate  52  in fluid communication with the annular space  66 . A valve  72  is connected to the bushing  70  to allow evacuation of oxygen from the space  66  and introduction of a neutral gas into the annular space  66  as shown by arrows in  FIG. 8 . The neutral gas, for instance nitrogen prevents flash ignition in the electrical connection environment in the dry zone  60 .  
         [0033]     The inner housing  64  extends both through the dry zone  60  and the wet zone  62 . The portion of the inner housing  64  located in the wet zone  62  is provided with perforations  74  made through the wall of the inner housing  64 . The perforations  74  allow heat exchange between the well bore liquid, such as salt water and the like, entering annulus  66  from the central opening  63  in the wet zone  62 . The flow of fluids in the wet zones of the body  50  is schematically illustrated in  FIG. 7 .  
         [0034]     The heating elements  40 ,  41  and  42  that extend in the wet zone  62  heat the liquid circulating through the perforations  74  and transfer the heat to the flow of crude oil passing through the production tubing  30 . As a result, paraffin suspended in the crude oil flow does not cool to a temperature low enough to cause paraffin to be separated and attaching to the wall of the production line  30 .  
         [0035]     The wires  36 ,  37  and  38  extend from the dry zone  60  to the wet zone  62  by passing through a sleeve  80  positioned in the annulus  66  and subsequently through the entire apparatus  10  between the dry zones and the wet zones. Of course, the apparatus  10  can have more than one dry zone and more than one wet zone; the number of the zones and the number of heating elements will depend on the conditions of the well so that the heating elements are positioned in strategic locations for introducing a heating power to the crude oil.  
         [0036]     If desired, a guide plate  82  can be positioned in the dry zone  62  for retaining the heating elements  41 ,  42  and  43  in alignment in relation to the central axis of the well casing  17  and the body  50 . Another wet zone  88  can be formed next to the dry zone  86  and the tool  10  can be thus extended for providing several heating or wet zones in the well bore  16 . The wet zone  88  has separate heating elements  89  that extend through the wet zone  88 . Each wet zone has independent heating elements.  
         [0037]     The top of the body  50  can be connected by a suitable coupling  93  to a well string sub  95 , while a free end  90  of the body  50  can be provided with a threaded connector  92  that allows the apparatus  10  to be connected to another Sub (not shown) that forms a part of a well string.  
         [0038]     The temperature sensor  20  detects the temperature in the area near the heating elements and sends a signal to the controller  18  at the surface. The sensor  20  is positioned within a temperature sensor housing  21 , which is secured to the outer housing  51 . The temperature sensor  20  is fittingly engaged in a receiver  23  that is secured at one end of the sensor housing  21 . An opening  94  in the outer housing  51  admits temperature from the body  50  to the end  98  of the sensor  20  thereby allowing the sensor  20  to generate a signal of the current temperature and send the signal to the controller  18 . The controller  18  determines whether the temperature has been raised sufficiently to maintain paraffins in a viscous state as a three-phase electric pulse generator  14  generates an electrical current and transmits it to the heating elements  40 ,  41 , and  42 . If the temperature is too high, the transformer generates less electricity. If the temperature is too low, the transformer is activated to supply more electric power to the downhole heating elements.  
         [0039]     A bleed valve  96  ( FIGS. 2B and 8 ) is set in the casing  51 . A set screw opens the valve  96  to allow bleeding of oxygen from the dry zone and introduction of neutral gas, for instance nitrogen into the dry zones. The bleed valve  96  is removable to allow removal of oxygen.  
         [0040]     The apparatus of the present invention can be also used for generating steam in a downhole location, which will require connection of the body  50  to a source of water. The heating elements, then activated all across the surrounding areas can be heated, thereby generating steam that would melt paraffin. The length of the tool  10  can be extended by adding multiple stages, dry zones followed by wet zones, followed by dry zones, etc. The number of heating assemblies will be determined by the rate of flow and diameter of the well. The multiple stage system dramatically increases the heat output variable thereby increasing the volume of fluid that can be heated.  
         [0041]     The use of Kapton-coated wires and graphite seals crimped around the wires form a leak-proof seal around the electrical wires where they enter the dry zones  60 . Of course, the use of an insulation coating in a hot temperature environment is not limited to the use of polymer Kapton, and other suitable insulation coating can be used.  
         [0042]     The use of 480-watt 3-phase heating elements with three heating wires increases the heat output and makes the apparatus  10  more efficient and cost effective. The transformer  12  positioned on the surface eliminates fire hazard problems that can result from the use of a heat source downhole. The fiber optic source or probe  98  monitors downhole temperature and regulates operations at the surface.  
         [0043]     The system of the present invention, when electrically connected elements are activated, controls electrical currents to the elements within SCR or pulse method. The pulse power supply is delivered by processors and through the downhole sensors. The control system  18  prevents the operating wires and heating elements from extending and contracting which extends the lifetime of the elements. Additionally, the pulsing system significantly reduces electrical consumption making the apparatus  10  more economical.  
         [0044]     The present invention is designed to accommodate the insertion and placement of the downhole pump through the hollow inner core of the inner casing. As a consequence, the downhole pump can pass through the body  50  during normal installation. The perforated inner housing  64  prevents “gas locking” of the downhole production pump.  
         [0045]     A particular advantage of the present invention is that it can be used in both horizontal and vertical piping systems and is not limited only to vertical placement. The apparatus  10  is a circulation heater as opposed to a probe heater, which is conventionally used in the field. It is envisioned that once the operator identified the cold zones, the apparatus  10  can be installed with the well bore string at a point approximately 100 to 200 feet below the deepest cold zone. In the flow or fluid lines, the problem areas can be identified by conventional tests and the apparatus  10  be installed within the line 50 to 100 feet before the paraffin build-up can occur.  
         [0046]     In addition to preventing paraffin problems, the apparatus  10  can be utilized in low gravity heavy hydrocarbon recovery. If the producing zone requires heating to raise the temperature to convert the heavy hydrocarbons to light hydrocarbons, the apparatus  10  can be used as well. Rather than using a boiler system on the surface as a steam source, the apparatus  10  provides a tool to produce and deliver steam downhole directly to the producing line. In the injection well, the apparatus  10  can be installed as a production zone.  
         [0047]     The heating elements  41 ,  42  and  43  are single end heat-generating elements; the apparatus  10  can therefore be safely used in a situation where the power source is electric power. Conventional tools utilize heating elements that must be terminated at each end (double-ended termination), which does not allow for extension of the heating element when heated. When necessary, the elongated heating elements can be extended to 20-feet length.  
         [0048]     The pulse power supply delivered by the transformer  12  and the pulse generator  14  is regulated by processors receiving data from the downhole sensor  20 . This control system prevents the heating elements from expanding and contracting in excess of the optimum operating environment, which extends the life of the elements to a significant degree. Many changes and modifications can be made to the apparatus and method of the present invention without departing from the spirit thereof. I therefore pray that my rights to the present invention be limited only by the scope of the appended claims.