Patent Publication Number: US-2012034120-A1

Title: Arrangement for hydrocarbon extraction in wells using progressive cavity pumps

Description:
FIELD OF THE INVENTION 
     This invention refers to an arrangement for hydrocarbon extraction in wells using progressive cavity pumps, and more in particular it relates to an oil extraction tubing arrangement developed in order to reduce its wearing out as a result of friction and corrosion in field wells in which progressive cavity pumps or “PCP” are used. 
     PRIOR ART AND ADVANTAGES OF THE INVENTION 
     Within prior art as to this matter, it is worth mentioning that usually in hydrocarbon extraction field wells, power transmission from the surface engine to the bottom pumps “progressive cavity pumps” type, or PCP, is carried out by means of one or more metal rods or bars which rotate inside the metal tubing. As the production well depth may be of several hundred meters or over one thousand meters, it is impossible to avoid certain contact and friction between the tubing and the rods rotating inside it. The progressive cavity pump uses the oil which it pumps from the bottom of the well as a lubricant between the surfaces which suffer this friction, i.e. between the internal face of the tubing and the external face of the rods which rotate along its inside. One of the disadvantages arising from the friction between the bottom pump driving rods and the tubing appears as oil fields grow old, as the secondary recovery process increases the percentage of water in the “water-oil” mixture reaching amounts over 95%, bringing about poor lubrication and, in many cases, a combined situation of tubing wearing out due to friction and corrosion. As a consequence of the reiterated friction between rods and tubing the protective boundary layer breaks up—this layer is formed by the building up of a thin deposit of the hydrocarbon present in water and/or by the artificial injection of certain film coating product used as non-corrosive, should this latter method be used—causing tubing corrosion and wearing out. Therefore, it is extremely important to solve this serious problem as it causes considerable economic losses, clearly enough, as exploitation processes at oil fields must be interrupted until tubings are repaired or replaced. 
     With the aim of solving the above mentioned problems, the arrangement subject matter of this invention has been developed, it allows to considerably reduce the tubings&#39; “wearing out-corrosion-wearing out” combined problem, as it shall be explained below in the “how to put it into practice” proposal. 
     SUMMARY OF THE INVENTION 
     The purpose of this invention is to provide an arrangement for hydrocarbon extraction in wells using progressive cavity pumps, this arrangement was developed with the aim of reducing wearing out as a result of friction and corrosion in conventional tubings used in field wells in which the extraction of fluids is carried out by means of progressive cavity pumps. This arrangement consists of a rotating tube located inside a fixed tube placed along the well casing. The rotating tube carries the fluid from the bottom of the well to the surface. Between the rotating tube and the fixed tube there is an “O” ring-type space into which an anti-friction lubricant is injected between the external face of the rotating tube and the internal face of the fixed tube. The bottom end of the rotating tube has a section with holes which allow fluids to flow into it and it is connected to the progressive cavity pump by means of a rod, its top end is connected to a production outlet and to its propelling motor mechanism. The upper section of the fixed tube is connected to an anti-friction lubricant injection pipe in the space left between the rotating tube and the fixed tube. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding and clarity of the purpose of this invention, it has been illustrated in several drawings which represent it according to the preferred ways in which to carry it out, all of them should be taken as examples, that is: 
         FIG. 1  outlines a typical example of a conventional arrangement for hydrocarbon extraction in wells using progressive cavity pumps. 
         FIG. 2  outlines the arrangement for hydrocarbon extraction in wells using progressive cavity pumps, subject matter of this invention. 
         FIGS. 3 to 6  respectively show the blown up details A, B, C and D of the arrangement shown in  FIG. 2 . 
     
    
    
     It is worth mentioning that in  FIG. 1 , corresponding to the prior art, and in the following figures in which this invention is illustrated the same or equivalent parts are indicated with the same reference numbers in both cases. 
     DETAILED DESCRIPTION 
       FIG. 1  shows that the illustrated example of a conventional pumping arrangement consists of a casing  1 , with a wellhead outlet  2 , which holds inside a tubing  3 , which carries the fluid from the bottom of the well to the surface, formed by a succession of sections  4  connected among them by joints  5 . Between the casing  1  and the tubing  3  there is a longitudinally defined “O” ring-type space  13 . The upper section  4  of the tubing  3  which projects itself from the wellhead at the field&#39;s land T surface has a production outlet  6 , through which the first of a succession of rods  8  connected among them by joints  9  passes as well as through a stuffing box  7 , the last rod  8  at the tubing&#39;s lower section  4  is connected to a bottom PCP pump  10 . In order to drive the rotating movement of the group of rods  8 , and consequently to drive the pump  10 , the upper rod  8  is connected to an electric engine  11  by means of a belt-and-pulley transmission mechanism  12 . 
     As it has already been stated, the pump  10  uses the oil which it pumps from the bottom of the well as a lubricant between the surfaces subject to friction, i.e. between the internal face of the tubing  3  and the external face of the rods  8  which rotate along its inside. As oil fields grow old the percentage of water present in the “water-oil” mixture increases, thus lubrication becomes poor causing the tubing&#39;s wearing out as a result of friction and corrosion until the protective boundary layer, formed as a consequence of the building up of a thin deposit of the hydrocarbon present in water, breaks up. 
     In  FIG. 2  the way in which this invention solves the problem of the wearing out of the pumping rods due to friction and their resulting corrosion is shown. As a matter of fact, the herein proposed arrangement, aimed at solving such problems, consists of a rotating tube  14  located inside a fixed tube  15 , between which a space is left which serves as a lubricant oil container, as it can be seen in  FIG. 3 , detailed under reference A in this  FIG. 2 . For the injection of the lubricant oil, the top end of the fixed tube  15  is connected to a pipe  22  which can be accessed from land T surface. 
     In the preferred way of carrying it out which is described and drawn, tubing  14  has a 2 3/8 -inch section and tubing  15  has a 2 7/8 -inch section, which is enough to achieve the necessary lubrication in order to avoid the wearing out of tube  14  as a result of friction with tube  15 . That is to say, the invention comprises a casing with the necessary length to transform the well into a giant bearing which shall operate protected by the layer of lubricant oil which is injected from the outside. In this way, the tubing&#39;s internal wearing out, as a result of rods&#39; friction, and the accelerated tubing&#39;s corrosion, as it occurs in conventional arrangements, are avoided. 
     Tube  15  is made up of a succession of sections connected by means of joints  5 , as shown in  FIG. 4  corresponding to detail B in  FIG. 2 . Tube  14  is made up of a succession of sections connected by means of joints  16 , as shown in  FIG. 5  corresponding to detail C pointed out in  FIG. 2 . 
     The upper section of tube  14  has a diameter reduction  17  from where it is connected to a pipe  18  with an articulated joint or “swivel” which ends at the production outlet  6 . The lower section of tube  14  shows an end defined by a tube  19  with holes through which the fluid extracted by the pump  10  flows, said pump is connected to such lower section of tube  14  by means of a rod  20 . In  FIG. 6  tube  19  is enlarged and is indicated in  FIG. 2  under reference D, where its holes  19  can be clearly seen. 
     Tube  14  transmits output power and carries 100% of the fluid extracted from the bottom of the well to the surface along its inside. The oil film  21  between both tubes  14  and  15  (see figure detail) prevents tube  15  internal corrosion and tube  14  external corrosion. In addition, a paint coating on the internal face of tube  14 , which carries the fluid, contributes to prevent internal corrosion caused by it. The only modification on tube  14  consists in the structure of the threaded joint  16 , by adapting the connecting nipple (see detail C in  FIG. 5 ) which allows to link both tubes without modifying their external diameter. 
     In summary, the arrangement, subject matter of this invention, basically consists of the use of two tubes,  14  and  15 , API standard manufacturing, of 2 3/8 -inch and 2 7/8 -inch respectively, which jointly form a “hydraulic bearing” from the surface to the bottom of the well, which can be lubricated by filling the “O” ring space between both tubes with clean oil and with the desired viscosity, for example SAE  10 . This lubricant prevents corrosion and attenuates the wearing out between both tubes  14  and  15 . This arrangement also allows the flowing of all the fluid produced along the inside of tube  14  with no internal moving parts, thus allowing the application of a paint coating in its inside in order to avoid internal corrosion. Also, a similar arrangement could be arranged with tubes holding different diameters, for example 1.42-inch internal diameter, 1.88-inch external diameter within a 2 3/8 -inch internal diameter tube, or in other diameters, obtaining the same and before mentioned “hydraulic bearing” effect. 
     In this way important advantages are achieved as compared to already known and used arrangements, such as:
         By increasing the contact area between the two frictioning surfaces, contact pressure decreases. This contact pressure causes wearing out, thus having less contact pressure results in less wearing out (“hydraulic bearing” effect).   It allows to reduce the number of revolutions per minute of the rotating tube  14  which transmits power, as it bears higher torsion for holding a bigger diameter than the rods in conventional arrangements, giving it a greater moment of inertia, thus allowing a reduction in the number of friction cycles originated by the rotation frequency for the same power applied, since by transmitting higher torque it is able to rotate at a slower speed resulting in a lower number of wear-out cycles.   It allows to add an artificial lubricant, chosen by the user, between both frictioning surfaces, i.e. between tubes  14  and  15 .   It allows to do without rods inside the tube which carries production towards the surface, thus being able to apply paint to prevent corrosion on its internal face.