Patent Publication Number: US-2015071795-A1

Title: Fluid displacement system using gerotor pump

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a system and method for pumping fluids from a subterranean well. 
     Subterranean wells are commonly used for producing fluids such as hydrocarbons and the like from deep underground formations bearing such fluids. In some instances these fluids are sufficiently free-flowing and under sufficient pressure that production through the well to the surface does not need to be assisted. In other instances, the fluids can have an extremely high viscosity, or formation pressure may be too low, or numerous other factors can lead to unsatisfactory flow rates from the well. 
     Various pumping methods have been used to increase flow from wells including sucker-rod pumps, progressing cavity pumps and electric submersible centrifugal pumps. In fact, each of these systems has issues when needed to operate on highly viscous hydrocarbons such as the heavy and extra heavy crude oils which are contained in the Orinoco Oil Belt. 
     The ability of centrifugal pumps to handle fluids is impaired by high viscosity. For surface applications where viscous fluids are to be pumped, centrifugal pumps or rotor-dynamical relatives are disregarded in favor of positive displacement pumps. Nevertheless, centrifugal impellers still have an advantage for downhole use. This advantage consists of the easiness to stack many impellers in a cylindrical housing that fits into oil production casing. This design produces a very long pump (30 ft or more) that must be driven by a powerful electric motor. Electric submersible pumps used in the Orinoco Oil Belt are equipped with motors whose power is in the range of 200 HP to 300 HP. A significant amount of power is wasted due to the low mechanical energy conversion capacity of centrifugal pumps. Thus, there is a need for a more efficient pumping device more suitable for handling viscous oils. 
     Sucker-rod pumps are preferred to produce medium to low flow rates (500 b/d or less). It is possible to achieve larger flow rates but at the expense of using cumbersome, visually unpleasant and expensive surface driving units such as giant walking beams and power cylinders with necessary hydraulic power units. Furthermore, clever as it is, converting rotational motion from prime motor to reciprocating motion to drive the downhole pump implies wasted energy due to incessant acceleration and deceleration of large mechanical parts such as rod strings and surface units. 
     Thus, the need remains for an improved approach to pumping these fluids. The present invention addresses this need. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, the forgoing need has been met. According to the invention, a fluid displacement system and method are provided for producing fluids from a subterranean well, and the system and method are based on the use of gerotor pumps which have been found to be particularly effective at pumping highly viscous hydrocarbons. 
     According to the invention, a fluid displacement system is provided for pumping fluids from a fluid producing subterranean well, which system comprises a well extending from a surface to a subterranean fluid bearing formation, the formation being in fluid communication with the well; and a gerotor pump in the well for pumping fluid from the formation to the surface. Details of the pump are also novel as discussed herein. 
     In further accordance with the invention, a method is provided for pumping a fluid from a well, which method comprises the steps of positioning a well from a surface to a subterranean formation; placing a gerotor pump in the well; and operating the gerotor pump to drive fluids from the subterranean well to the surface. 
     Other advantages and details will appear in the detailed description which follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A detailed description of preferred embodiments of the present inventions follows, with reference to the attached drawings, wherein: 
         FIG. 1  shows a typical well extending from the surface to a subterranean formation and including a gerotor pump according to the present invention; 
         FIG. 2  illustrates basic components of a gerotor assembly in accordance with the present invention; 
         FIG. 3  shows rotors of a gerotor pump within an eccentric ring; 
         FIGS. 4-5  further illustrate the porting disks of a gerotor pump in accordance with the present invention; 
         FIGS. 6-7  illustrate a gerotor pump with two gerotor sets working in series; 
         FIGS. 8-9  illustrate a middle casing for use in a multiple pumping stage gerotor pump according to the invention; 
         FIGS. 10-11  illustrate a middle casing housing two pumping stages to provide a two pumping stage assembly working in parallel; 
         FIG. 12  illustrates a two stage gerotor assembly with bearing carriers; 
         FIGS. 13-14  illustrate the inlet bearing carrier of  FIG. 12 ; 
         FIGS. 15 and 16  illustrate the outlet bearing carrier of  FIG. 12 ; and 
         FIG. 17  is a cross sectional view of a multistage parallel gerotor pump assembly in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The invention relates to a fluid displacement system and method which utilizes gerotor pumps to improve pumping flow rates of heavy and extra heavy crude oils from subterranean wells. 
       FIG. 1  illustrates a subterranean well  1  extending from the surface  2  to a subterranean formation  3 . Formation  3  is typically a permeable formation containing fluids within the void space of the formation, and it is desired to produce these fluids from the formation  3  through well  1  to surface  2 . 
     While useful with a variety of potential different applications, the present invention is particularly well suited for use in producing heavy and extra heavy crude oils such as the heavy crude oil contained in the Orinoco Oil Belt. A typical hydrocarbon from this belt has a viscosity of about 1,000 cP at reservoir temperature (130-140° F.), and this type of fluid is very difficult to pump utilizing conventional sucker-rod pumps, progressing cavity pumps and the like. 
     In accordance with the invention, a gerotor pump  10  is positioned down hole in well  1  and used to enhance flow of heavy and extra heavy crude oils from the wells in accordance with the present invention.  FIG. 1  shows gerotor pump  10  positioned in well  1  at a depth D which may typically be set in the Orinoco Belt at a depth between about 3,000 and about 3,500 feet. The setting depth of this pump is not limited to such values, which can also be greater than 10,000 feet. 
     A gerotor is a positive displacement pumping unit. The name gerotor is derived from “generated rotor”. A gerotor typically consists of an inner and an outer rotor  16 ,  18  ( FIG. 2 ). The inner rotor  16  typically has N teeth and the outer rotor  18  typically has N+1 teeth. Centerlines of outer rotor  16  and inner rotor  18  are parallel and separated by a certain eccentricity in order to be properly assembled. With such mating satisfied, both rotors rotate. The geometry of the two rotors partition the space between them into N different dynamically-changing volumes. During the assembly&#39;s rotation cycle, each of these volumes changes continuously, so any given volume first increases and then decreases. An increase creates a vacuum, and this creates a suction which draws fluid into the space between the rotors. This is where the intake to the pump can be located. As a volume decreases, fluids can be pumped or compressed, and an outlet can be located at this position. The cylindrical geometry of the gerotor pump makes such pumps suitable for building downhole pumps. Also, their movement is rotational, which is advantageous for using rotating prime movers such as electrical motors and hydraulic motors. Moreover, rotational motion can be also delivered from surface using a rotating rod string as a power transmission shaft. 
       FIG. 2  illustrates a gerotor set  12  which is a component of gerotor pump  10 , and shows a shaft  14  upon which is mounted an inner rotor  16 , and about which is engaged an outer rotor  18 . As discussed above, rotation of shaft  14  causes pockets to be expanded and then contracted between the inter-meshed gears or teeth of inner rotor  16  and outer rotor  18 , and with a proper porting, these pockets can be used to pump fluid. This structure is particularly well structured for pumping highly viscous fluids. 
       FIG. 3  shows rotors  16 ,  18  of  FIG. 2  positioned within an eccentric ring  20 . Eccentric ring  20  is a ring which has a gradually increasing and then gradually decreasing wall thickness. Thus, ring  20  defines an inner cylindrical surface which is not concentric with its outer cylindrical surface. Outer rotor  18  is positioned within eccentric ring  20  as shown. When shaft  14  is rotated, inner rotor  16  and outer rotor  18  also rotate within eccentric ring  20 , and the pockets between inter-meshed gears of the rotors  16 ,  18  expand and contract as desired. 
     Ring  20  also serves as a journal bearing for outer rotor  18 . Outer rotor  18  fits into eccentric ring  20  with the necessary space to allow sliding movement while preventing excessive fluid slippage or leakage. 
       FIG. 4  shows set  12  with porting disks  22 ,  24  mounted on either side.  FIG. 4  shows porting disk  22  with an inlet  26 , and inlet  26  is arranged to be aligned with the space between inter-meshed teeth of the rotors where the space expands. In this fashion, the vacuum created between the teeth of the rotors draws fluids through inlet  26  into the vacuum. As the rotors rotate, the fluid becomes trapped at the precise moment when the space defined by the teeth reaches a maximum volume. With further rotation, the space between rotors decreases, and fluid in the space is compressed. The fluids will be expelled from an outlet  28  ( FIG. 5 ) of porting disk  24  at a significantly higher pressure. Outlet  28  is positioned on disk  24  to coincide with the proper location with respect to the gerotor set  12  where fluids should be expelled. 
     In accordance with the invention, to enhance pumping volume and speed, gerotor sets  12  can be assembled in series such that fluid discharged from one gerotor set can then be acted upon by another gerotor set.  FIG. 6  shows a rotor assembly  21  having a first rotor set  12  and a second rotor set  12 ′ arranged for operation in series. The first and second rotor sets  12 ,  12 ′ are separated by a cylinder or porting disk  24 ′ which is positioned such that the discharge from first gerotor set  12  coincides with the vacuum and inlet of the second gerotor set  12 ′. Porting disk  22  is positioned at an inlet end of the assembly. This is also further illustrated in the exploded view of  FIG. 7 . 
     Still considering the embodiment of  FIG. 6 , while the illustrated assembly could itself be an entire pump and have an outlet side porting disk  22 ′ ( FIG. 7 ), the assembly can also be one stage of a multiple stage unit, and in that circumstance can have an interstage porting disk or middle casing at an outlet end. Such a middle casing is further discussed below. 
     It should be appreciated with consideration of the illustration of  FIGS. 6 and 7  that the eccentric ring  20 ,  20 ′ in this embodiment are rotated 180 degrees relative to each other when assembled as shown in  FIGS. 6 and 7 . In this way, the external gears  18 ,  18 ′ acquire the necessary radial placement to generate discharge from the first gerotor set  12  and this discharge is properly aligned with the inlet of the second gerotor set  12 ′ as shaft  14  rotates. This can be seen in  FIG. 7  from considering the position of spaces between teeth of the rotors  16 ,  18  for each rotor set  12 ,  12 ′. 
     The assembly illustrated in  FIGS. 6 and 7  can advantageously be used in multiples to provide a multi-stage system. To this end, for a two stage system, a middle casing  32  is provided and is further illustrated in  FIGS. 8 and 9 . 
     Middle casing  32  has openings  33  to house multiple gerotor sets, and ports to feed fluid to and discharge pumped fluid from each gerotor set or stage.  FIG. 8  shows casing  32  as a cylindrical member having an opening  33  facing each end, each opening being sized to receive a gerotor assembly. Casing  32  has an inlet  34  positioned inwardly from one opening to receive a discharge of fluid from a first gerotor set or pumping stage.  FIG. 9  further illustrates middle casing  32 , and shows an internal passage  36   a  which conducts fluids from inlet  34  to outlet  36 . The passage  36   a  defined between inlet  34  and outlet  36  conducts fluids radially outside of a second pumping stage in the other opening, bypassing it. Also shown in  FIG. 9  is a second stage inlet  38  which can be defined in the cylindrical wall surrounding the opening for the first stage. Fluids enter through inlet  38  and then are conducted radially inwardly through passage  38   b  and discharged through outlet  38   a.  Outlet  38   a  feeds the second pumping stage. The second stage of such a system can therefore be considered to be operating in parallel to the first stage since its pumping action is independent from the first pumping stage, but both fluid rates are summed up. 
       FIG. 10  further illustrates the two stage embodiment in accordance with the present invention, and shows middle casing  32  housing two gerotor steps or stages  35 ,  37  as discussed above.  FIG. 11  further illustrates components of this aspect of the invention.  FIG. 11  is a cross sectional view and shows middle casing  32  with components of the first gerotor pumping stage  35  which receives fluids at the inlet  26  to the stage, and pumps these fluids to inlet  34  of middle casing  32 , through passage  36   a,  and to outlet  36 . In the meantime, additional fluids are drawn into inlet  38  and through passage  38   a  to the radially inwardly located inlet  26 ′ of second pumping stage  37 , and fluids exiting the second pumping stage can then re-join fluids exiting middle casing  32  from the first stage. 
       FIG. 12  illustrates a further aspect of the invention related to bearing carriers  42 ,  42 ′ which can advantageously be positioned on either side of middle casing  32  to support shaft  14 . Bearings housed therein can be bushings or antifriction bearings, depending upon the work load to be handled by the pump. The bearings  44 ,  44 ′ are mounted in bearing carriers  42 ,  44 ′ as shown in  FIG. 12 . Inlet bearings carrier  42  therefore has openings  46 ,  46 ′ which can advantageously be aligned with the inlets to the pumping stages, for example as further illustrated in  FIGS. 13 and 14 . 
     As shown in  FIGS. 13 and 14 , bearing carrier  42  can have two inlets  46 ,  46 ′ which can be radially extended openings formed in one face of the carrier. One inlet  46  can lead to a passage  48  which aligns with the inlet to the first pumping stage, while inlet  46 ′ leads to a passage  48 ′ which aligns with inlet  38  of middle casing  32 . Thus, flow into inlet  46  would be acted upon by the first stage of the pumping unit, while flow through inlet  46 ′ would be acted upon by the second stage.  FIGS. 13 and 14  also further illustrate the bearing bore  50  through which shaft  14  passes, and also illustrates a radially enlarged portion  52  which can house a bearing cover  54  (shown in  FIG. 12 ). 
     From a consideration of  FIGS. 15 and 16  it should be appreciated that the second bearing carrier  42 ′ can be structurally similar or identical to the first bearing carrier  42 , with flow passages properly aligned as shown in  FIG. 12  to carry the discharge from both pumping stages, and to pass this flow to outlets having a shape similar to the inlets illustrated in  FIG. 14 .  FIG. 15  shows bearing carrier  42 ′ from the side which connects to middle casing  32 , and shows inlets  56 ,  56 ′. Considering also  FIG. 16 , inlet  56  leads through a passage  58  to an outlet  60 , while inlet  56 ′ leads through a passage  62  to outlet  60 ′. It should be apparent from  FIGS. 12 and 15  that inlet  56  aligned with the outlet of the second stage, while inlet  56 ′ aligns with outlet  38   a  of middle casing  32 . Outlet  60 ,  60 ′ are radially extending grooves similar in shape to the inlets of inlet bearing carrier  42 . In addition, outlet bearing carrier  42 ′ also has a bearing bore  50 ′ and can be provided with a radially enlarged portion  52 ′ for holding bearing  44 ′, with a bearing cover  54 ′ securing the bearing in place. 
     Turning now to  FIG. 17 , a cross sectional view of an entire assembly of a multi stage pump in accordance with the present invention is illustrated.  FIG. 17  shows middle casing  32  housing first and second pumping stages  35 ,  37 , and having bearing carriers  42 ,  42 ′ connected at each end of middle casing  32 . Shaft  14  passes through both bearing carriers  42 ,  42 ′, middle casing  32  and the first and second pumping stages  35 ,  37 , housed therein. Shaft  14  is rotated by an electric motor (not shown), and this rotation causes the rotors of pumping stages  35 ,  37  to rotate and pump fluid.  FIG. 17  shows the two parallel flow paths for fluid being drawn through the multistage pumping system, and again makes clear that these paths are parallel paths, with one being acted upon by first stage  35  and the other being acted upon by second stage  37 . 
     Inlet and outlet connector sections  64 ,  64 ′ are also shown in  FIG. 17  and would be used to connect the multistage pump unit in accordance with the present invention into or at the end of a production tube for use in increasing flow of fluids from the well and through the tube. 
     As discussed above, gerotor pump  10  in accordance with the present invention operates through rotation being imparted to shaft  14 . Various available structures and methods could be used to impart rotation to shaft  14 . One particularly preferred approach in accordance with the present invention is to use an electric submersible motor  80  ( FIG. 1 ), advantageously incorporated into the structure of pump  10  to cause such rotation as desired. Contrary to suggestions made in prior art documents, an electric submersible motor  80  can be positioned in pump  10  and used in the described manner, even at extreme depths, such as depths greater than 10,000 feet deep in a well drilled to a subterranean formation, and such motors are useful for extended periods of time. 
     Thus, in accordance with the present invention, the driver for the pump is advantageously an electric submersible motor, and it is desirable to position at least one of pump  10  and motor  80 , and preferably both of these components, within well  1  at a depth D between 3,000 and 3,500 feet, and even greater than 10,000 feet as needed. 
     It should be appreciated that the present disclosure has been given in terms of a preferred embodiment. The scope of the invention is not to be viewed as being limited by this embodiment, but rather as being defined by the scope of the appended claims.