Patent Publication Number: US-2015075769-A1

Title: Set of equipment for extracting highly viscous oil

Description:
The invention is in the field of oil production, specifically extracting highly viscous oil with the use of elastic vibrations energy and increasing efficacy of ultrasonic processing via intensification of additional chemical treatment of oil in the casing string, and can be applied in operations carried out under low climatic temperatures. 
     The use of the invention provides both extraction of highly viscous oil, and its transportation to major pipelines. 
     In practice, rheological characteristics of highly viscous oil are usually lowered by dilution in a lighter solvent, oil, or gas condensate. The main reason of anomalously high viscosity of heavy oils and natural bitumen is a high concentration of resin and asphaltene components (RAC) that, upon reaching a critical level, sharply changes the rheological parameters and reveals, to a significant degree, structural-mechanical properties due to inter-molecular interactions of RAC [M. Y. Dolmatov, A. G. Telin, N. I Khisamutdinov. Phisico-khimicheskiye osnovy napravlennogo podbora rastvoritelei asfaltosmolistyh veschestv//M.: CNIITENeftehim.-1991.-p. 47]. 
     Devices allowing regulation of the degree of dispersion ability of an oil system using ultrasonic influence or electromagnetic field energy are known in prior art. 
     A device [RU 9305476] generating ultrasonic energy to reduce oil viscosity is known in prior art. Electro-acoustic transducer of ultrasonic energy converts signals of a chosen AC voltage into ultrasonic energy, wherein the transducer is positioned in the material being treated and has acoustic connection with said material. 
     The limitation is that using only a high frequency electromagnetic field to improve the rheological properties of oils with high content of resin and asphaltene components is not always reasonable due to polarization of resin components in the electromagnetic field and, as a consequence, formation of large associates that increase oil viscosity. 
     A device [RU 2026969] is known in prior art in which a downhole tool is connected to the above-ground power supply of industrial frequency and contains a single ultrasonic emitting piezoelectric transmitter with rather narrow gain-frequency characteristics that enables generation of elastic high frequency vibrations on its resonance frequency. 
     In general, a significant limitation of using only an electromagnetic field is the reversibility of aftereffect. Specifically, it is known in the field [U.S. 2008257414] that applying an electric field strength of 6-10 kW/cm for 60 sec allows the viscosity of heavy oil-containing fractions to be reduced by 17-20%; however, after 30 minutes the viscosity restores half-way and in 8-10 hours it restores completely, which limits the use of said technology in preparing highly viscous oil for pipeline transportation. 
     Preparation of highly viscous oil for extraction and transportation is being increasingly carried out on the basis of making purposeful changes in the balance of inter-molecular interaction forces in order to regulate the degree of dispersion ability of an oil system, using a combination of chemical reagents and ultrasound. 
     In the known method [RU 2108452] of chemical treatment of a reservoir using downhole ultrasonic generators, tubing strings are firstly lowered along the downhole to the bottom, following which a treating liquid is injected through them, following which the strings are lifted to the surface and an ultrasonic generator is lowered into the well and placed in front of the reservoir&#39;s portion being treated. Treatment of the reservoir and the downhole is carried out in this liquid. 
     A significant limitation of this method, from the financial perspective, is the intermittent nature of the treatment and high consumption of the treating liquid. In addition, this method does not enable removal of products of decay of asphalt-resin-paraffin deposits and clogging impurities without additional lowering and lifting of the device which, of course, reduces the efficiency of the treatment. 
     A set of equipment for realization of the method of combined treatment of a well bottom zone [RU 2261986] is known in prior art, comprising a device with ultrasonic generator that is lowered into a well on a column of tubing strings. The device that is lowered into the well on a column of tubing strings comprises a pump followed by a perforated string section with a downhole tool containing an ultrasonic generator. The space between the strings that is above the perforation zone is separated by a packer. Ultrasonic treatment of the well-bottom zone of the downhole by elastic vibrations of ultrasonic frequency is carried out in an active technological liquid and acid solution. Asphalt-resin-paraffin deposit solvent is used as the active technological liquid. 
     The limitation of the above-described set of equipment is that pre-flushing of acid solution into the reservoir is required with production seasoning for the reaction with the acid. Only then the drainage of the reservoir is carried out by generating oscillating movement of the fluid in the perforation zone, and by weak depressing pulses under the constant influence of ultrasound on the reservoir, with pumping down the reaction products and simultaneous washing out of treatment products. The cyclic nature of the process is evident. 
     The second limitation is that the ultrasound is applied in the perforated section of tubing strings, while treatment of the entire productive zone of the reservoir would be of benefit, in particular of the liquid located between the well&#39;s casing string and tubing string. 
     It has been established empirically that the best viscosity efficacy indicators are achieved under the influence of a chemical reagent pre-activated by ultrasound. 
     An invention is known in prior art [application RU No.2010145489] (prototype) that aims to develop equipment allowing oil viscosity to be significantly reduced in a constant mode using a chemical reagent activated by ultrasound, in various production fields, directly in the space between the well&#39;s casing string and the pipe string, and to maintain viscosity characteristics for the period of time sufficient for the transportation of produced oil along the pipe line. 
     A set of equipment for extracting highly viscous oil comprises a pump-compressor string with an oil-pump drive placed therewithin and a consecutive arrangement consisting of an oil pump, a perforated string section with pump anchor, and a downhole tool, which is in the form of a cylindrical body in which a hermetic cavity and an annular chamber with radial channels are arranged consecutively; a high-frequency elastic-oscillation source in the form of a cylinder-shaped ultrasonic converter is arranged in said hermetic cavity of the body of the downhole tool, and said hermetic cavity, along the axis of the arrangement, is provided with a tie bar having an internal through channel leading into the annular chamber; the downhole tool is connected via the electrical cable to an above-ground electric power source, wherein the set is provided with an above-ground pump and a line for supplying a liquid chemical reagent to an internal channel of the hermetic cavity tie, and the perforated string section between the oil pump and the pump is provided with an opening for connecting the electric power cable and the chemical reagent supply line, wherein the connection of the chemical reagent supply line to the internal through channel of the tie bar and the connection between the tie cavity and the near-bottom annular chamber are hermetically sealed with annular gaskets (collars) and the hermetic cavity of the downhole tool is filled with a liquid electro-insulating medium, most often a heat-resistant organic-silicon liquid. 
     The limitation of this invention is a relatively small zone of active influence of ultrasound and chemical reagents on the rheological properties of oil, especially when the structure of an oil reservoir is non-homogeneous, and that it is impossible to use it in marginal wells. 
     The technical goal of the proposed invention is to increase efficiency of the combined influence of ultrasound and chemical reagents on the rheological properties of oil with various concentrations of resin and asphaltene components, and also to significantly reduce reagent consumption. The technical outcome is achieved due to the fact that ultrasound exerts its influence on the rheological properties of oil in a medium comprising activated liquid chemical reagent in the space between the well&#39;s casing string and the pipe string, and a special distributing device positioned on the downhole tool allows substantial expansion of the area of active influence. 
     Moreover, in order to increase the efficiency, a single source of elastic high frequency vibrations simultaneously exerts influence on the liquid chemical reagent before it dissolves high-viscous oil, and on the actual mixture of oil and pre-activated chemical reagent, and a special distributing device positioned on the downhole tool allows the area of active influence to be significantly increased on highly viscous oil. 
    
    
     
       The proposed schematic of the invention “A set of equipment for extracting highly viscous oil” is shown in  FIG. 1 , wherein:  1 —pump-compressor string;  2 —oil-pump drive;  3 —oil-pump;  4 —perforated string section;  5 —pump anchor;  6 —downhole tool;  7 —electric power cable of downhole tool;  8 —above-ground electric power source;  9 —chemical reagent supply line;  10 —above-ground pump to supply chemical reagent;  11 —hermetic cavity;  12 —ultrasonic cylinder-shaped transducer;  13 —annular chamber with radial channels in the body of the downhole tool;  14 —annular gaskets;  15 —tie of hermetic cavity having an internal through channel;  16 —collars;  17 —opening for electric-power cable and chemical reagent supply line;  18 —distributing device designed as an annular bushing set on the outer surface of downhole tool  6  in the zone of cylindrical chamber with radial channels  13 , with internal cylindrical cavity  19  and multiple-thread screw channels (not shown) with an exit to the bottom end surface of distributing device  18 , wherein it is mounted in a movable manner on the outer surface of downhole tool  6  and its reverse motion is achieved by spring regulating mechanism  20 . The set is provided with above-ground tank with reagent  21  connected via lines  22  to pump  10  and regulating valve  23 . 
     
    
    
     A screw pump as well as a sucker-rod pump can be used as an oil-pump. 
     The use of a perforated string section between the pump and the downhole tool allows extraction of oil from the casing string. 
     Pump anchor is designed for fixing of the oil-pump below the dynamic level of oil in the casing string, and for compensation of torque when the screw pump is used. The leaf-shaped design of the anchor does not impede the motion of oil along the casing string. 
     The downhole tool, connected to the perforated string section of tubing by threaded coupling, is designed for a combined chemical-physical treatment of oil entering the casing string. Thus, an additional pre-activation of the chemical reagent by ultrasound is carried out. 
     The line for supplying the chemical reagent and the electric-power cable of the downhole tool are connected to the downhole tool through the opening in the perforated string section positioned between the oil-pump and the pump anchor, which prevents their destruction by the anchor&#39;s leaves should it start spinning. 
     The hermetic cavity is designed for placement of the ultrasonic transducer therein, whose operating conditions provide for filling of the cavity with a liquid electro-insulating medium. 
     The use of the cylindrical chamber allows accumulation of the chemical reagent, activated by ultrasound, so that it is continuously supplied into the casing string through the radial channels in the body of the downhole tool and the screw channels (not shown in  FIG. 1 ) of a special distributing bushing positioned on the outer surface of the body of the downhole tool. 
     The hermetic cavity tie, being an element of construction, has an additional function because, while passing via inner through channel, the chemical reagent passes through the zone of ultrasonic influence. 
     The set works as follows (see  FIG. 1 ). 
     Downhole tool  6  is installed above ground with pump anchor  5 , perforated string section  4  and oil-pump  3 . The entire resultant assemble is lowered, in a stepwise manner, into the downhole on pump-compressor string  1  to the depth at which downhole tool  6  is situated in the reservoir&#39;s productive zone. Electric power is supplied via electric power cable of downhole tool  7  to downhole tool  6  from above-ground source  8 . Chemical reagent  9 , flowing via supply line with the help of above-ground pump  10 , enters channel of tie  15  of hermetic cavity  11  of downhole tool  6 , where activation of the chemical reagent by ultrasound from ultrasonic cylinder-shaped transducer  12  situated in said hermetic cavity  11  takes place. Further, activated chemical reagent enters annular chamber  13  and, from it, via radial channels in the body of the downhole tool, it enters the annular cavity of distributing device  18 , from which —via screw channels (not shown in FIG.  1 )—the reagent enters the space between the strings that is filled with oil. Hermetic state of cavity  11  is ensured because the connection of tie  15  with near-bottom annular chamber  13  is fitted with annular gaskets  14 , and the connection of the chemical reagent  9 &#39;s supply line to the internal channel of tie  15  is done via collars  16 . For the connection of electric-power cable to the chemical reagent supply line, the perforated string section is provided with opening  17 . To expand the zone of ultrasonic influence, distributing device  18  of downhole tool  6  is provided with spring regulating mechanism  20  enabling reverse motion of distributing device  18 , which can operate in a pulse mode. Fine-tuning of spring regulating mechanism  20  is carried out while taking into consideration the rheological properties and flow rate of oil. When distributing device  18  operates in the pulse mode, in order to reduce overpressure in the chemical reagent supply line, the set is provided with regulating valve  23  connected by lines  22  with above-ground tank with reagent  21  and pump  10 . The mixture of oil with activated chemical reagent is lifted by oil pump  2  to the perforated section of string  4 , flowing around cylindrical body of downhole tool  6 , in whose zone the extracted oil is treated in the medium of activated chemical reagent. 
     Research studies of dependence of viscosity on the nature of a chemical reagent demonstrated that the best results have been obtained with the use of toluene pre-activated by ultrasound with the subsequent ultrasound treatment of oil in the medium of activated toluene. 
     Indicators of using a set of equipment (in the optimal range of reagent consumption) obtained based on experimental testing are shown in Tab. 1 
     
       
         
           
               
               
               
               
            
               
                   
               
               
                 Concentration 
                 Initial 
                 Time after oil extraction, hours 
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 of 
                 value 
                 0 
                 24 
                 48 
                 72 
               
            
           
           
               
               
            
               
                 toluene, % 
                 Dynamic viscosity, MPa · sec. 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 0.2 
                 1014 
                 811 
                 823 
                 876 
                 903 
               
               
                 0.5 
                 1014 
                 732 
                 777 
                 784 
                 801 
               
               
                 1 
                 1014 
                 449 
                 502 
                 671 
                 675 
               
               
                 1.5 
                 1014 
                 401 
                 403 
                 479 
                 483 
               
               
                   
               
            
           
         
       
     
     As evident from Tab. 1, ultrasonic treatment of the mixture oil and toluene pre-activated by ultrasound coupled with the use of a special distributing device, allowed oil viscosity to be significantly reduced directly in the space between the well&#39;s casing string and the pipe string and the viscosity parameters to be maintained for the period of time sufficient to transport the oil to major pipelines.