Inter-tandem pump intake

[0002] This invention relates to a submersible pump assembly having a downhole hydrocyclone separator (DHS). In particular, the invention relates to a submersible pump apparatus for use in a well containing a mixture of hydrocarbons wherein the submersible pump assembly pumps lighter fluids or oils to the surface and injects heavier fluids or water into the well.

[0003] When receiving oil from oil wells containing a mixture of hydrocarbons and water, it is desirable to separate the hydrocarbons from the water and reinject the water either above or below the producing zone. Apparatus and methods have been proposed that make it possible to separate hydrocarbons from water and to reinject the water.

[0004] U.S. Pat. No. 5,456,837 to Peachey teaches a method of downhole cyclone oil/water separation that utilizes a cyclone separator. The cyclone separator includes a separation chamber, wherein liquids of differing densities are separated. The separator has at least one mixed liquids inlet through which liquids pass into the separation chamber, a first outlet for liquids of a first density range to pass out of the separation chamber and a second outlet for liquids of a second density range to pass out of the separation chamber. Although Peachey teaches the use of multiple separators inside of a separation chamber, Peachy does not teach a method wherein liquids are separated multiple times to facilitate more complete separation.

[0005] A difficulty with using a single separator is that some formations need disposal water to contain very low concentrations of oil. Otherwise, the ability of some injection formations to accept the disposal fluid is reduced.

[0006] An assembly is provided for use in a well containing a mixture of hydrocarbons and water wherein the assembly utilizes multiple separators to separate hydrocarbons from the mixture. The assembly of the invention injects heavier fluids such as water into the well and pumps lighter fluids such as hydrocarbons to the surface. The assembly includes a first pump section having a production fluid intake for receiving a mixture of oil and water from a production zone and an outlet. The assembly also includes a second pump section having an outlet and an intake that is connected to the outlet of the first pump section. A first separator is provided having an inlet connected to the outlet of the second pump section for receiving and separating the oil and water. The first separator additionally has an oil outlet for discharging oil to flow to the surface. The first separator also includes a water outlet. A second separator is provided that has an inlet connected to the water outlet for further separating oil from the water and a purer water outlet for discharging water into an injection zone. The second separator also has a less pure water outlet connected to the intake of the second pump section for passing the less pure water back through the first and second separators.

[0007] FIG. 1 is a schematic view of the assembly of the invention.

[0008] FIG. 2 is an elevation view of the assembly depicted in FIG. 1.

[0009] Referring to FIGS. 1 and 2, shown is an assembly designated generally 10, for use in a well 12 containing a mixture of hydrocarbons and water within well casing 13. Assembly 10 is designed to separate hydrocarbons from a mixture of well fluids in well 12. Assembly 10 injects the separated heavier fluids into an injection zone 14 of well 12 and pumps the separated lighter fluids, such as oil, to surface 16. Preferably, assembly 10 is positioned below producing zone 18. The assembly 10 includes an upper pump or third pump section 20 preferably connected to a lower end of production tubing 21 for pumping relatively lighter fluids represented by arrow 22, such as oil, to surface 16. Upper pump 20 is connected to oil bypass tube 23. The upper pump 20 is typically separated from an electrical motor 24 by a seal section 26 as is commonly known in the art.

[0010] A tandem pump or lower pump 28 is positioned below upper pump 20 and is preferably separated from motor 24 by seal section 30 which may be the same type as seal section 26. Tandem pump 28 is also a centrifical pump and is preferably constructed of first pump section or upper tandem pump section 32 having a well fluid intake or production fluid intake 34 and a second section or lower tandem pump section 36 separated from first pump section 32 by an inter-tandem intake 38. Well fluid intake 34 is on an upper end of first pump section 32. An outlet 29 of first pump section 32 is on a lower end of the first pump section 32. Outlet 40 of second pump section 36 is on a lower end of second pump section 36 and feeds downhole separator 41. Motor 24 drives upper pump 20 and first pump section 32 and second pump section 36 of tandem pump 28.

[0011] The location of inter-tandem intake 38 is determined by an amount of intake pressure required at the overflow side of the downhole hydrocyclone separator (DHS) 41.

[0012] Preferably, a first downhole separator section 42 is positioned below second pump section 36 of tandem pump 28. First downhole separator section 42 is designed to separate well fluid into relatively lighter fluids, such as oil, and relatively heavier fluids, such as water. Downhole separator 42 is preferably a vortex type referred to as a hydrocyclone. First downhole separator section 42 has an oil outlet 43 connected to oil bypass tube 23 which transfers at least a portion of the lighter oil/water to the surface via upper pump or third pump section 20 in the preferred embodiment. First downhole separator section 42 has a discharge 44 leading to a second downhole separator section 45. Although first downhole separator section 42 is quite efficient, a small percentage of oil will be present in the water discharged through discharge 44. The second downhole separator section 45 is also a hydrocyclone separator like the first downhole separator section 42 and operates in the same manner. Second downhole separator section 45 separates the water received via discharge 44 from the first downhole separator section 42 into purer water, represented by arrow 47, and injected via purer water outlet 48 into an injection zone 14 of the well 12. Second downhole separator section 45 has a less pure outlet or lighter fluid discharge 49 connected to recycle tube 50 to return fluid back to tandem pump 28 for transferring the recycled light fluids back to first downhole separator section 42 for further separation.

[0013] It is necessary for proper pressure ratios to exist between the pressure (P1) at the water discharge 44 of the first downhole separator section 42 or pressure at the inlet of the second downhole separator section 45, the pressure (P3) at the less pure outlet 49 of the second separator section 45, and the pressure (P2) at the purer water outlet 48 of the second separator section 45. The proper pressure ratios are obtained by the location of placement of inter-tandem intake 38. The proper pressure ratio is (P1-P3)/(P1-P2) equals 1.7 to 4. Preferably, the ratio is approximately 2.

[0014] Preferably, assembly 10 is positioned within well 12 and is separated from the injection zone 14 by packer 52 to prevent the purer water or separated final heavy fluid 47 from mixing with the unseparated well fluid.

[0015] In practice, assembly 10 utilizes a method of injecting water and producing oil in a well that includes separating the well fluid into relatively heavier fluid and relatively lighter fluid 22 with a downhole separator 41. The relatively lighter fluid 22 is transferred to surface 16 with upper pump or third pump section 20. At least a portion of the relatively heavier fluid is injected into injection zone 14 in well 12. At least a portion of the relatively heavier fluid is recycled through the downhole separator 41 and reseparated into purer water or separated final heavy fluid 47 for injection into injection zone 14. The unpure water from second separator section 45 is recycled by pumping the fluid through recycle tube 50 to inter-tandem intake 38 positioned between first pump section or upper tandem pump section 32 and second pump section or lower tandem pump section 36. The lighter fluid recycled through recycle tube 50 is then pumped by second pump section 36 to downhole separator 41 for additional separation.

[0016] There are several advantages to the invention. By adding a second downhole separator section, a more complete separation of hydrocarbons and water may be accomplished. Therefore, purer water may be injected back into the well. The injection of water of greater purity reduces clogging of the injection zone by the injection fluid. Feeding the lighter fluid overflow of the second separator section back to the tandem pump at an intermediate point allows the proper pressure ratios to be achieved for the second separator section.

[0017] While the invention has been shown in only one of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes without departing from the scope of the invention.