Wells – With eduction pump or plunger – With packer or plug
Reexamination Certificate
1998-11-06
2001-03-20
Bagnell, David (Department: 3672)
Wells
With eduction pump or plunger
With packer or plug
C166S105000, C166S266000
Reexamination Certificate
active
06202744
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to separation of fluids having different densities in production fluid streams from underground wells. More particularly, the present invention relates to an apparatus and system for moving the effective pump intakes of a dual pump downhole pump arrangement further from one another using a pair of shrouds surrounding the pumps to facilitate the separation of the fluids, namely water and oil.
BACKGROUND OF THE RELATED ART
Oil and water often exist in the same production zone. Additionally, water is often injected into a production zone to facilitate the flow of oil from the production zone and enhance production. During production of the oil, the oil and water must be separated. The separation may be accomplished in a number of ways such as by using hydrocyclones to separate the oil from the water. Another method allows the oil and water to settle in the casing and separate naturally and uses a pair of pumps, one of which is adapted and positioned to pump water and the other of which is adapted and positioned to pump oil. Typically, the clean water stream is then directed toward injection perforations in another potential production zone or another area of the current production zone.
To effectively produce the oil with the first, upper pump and water with the second, lower pump, the upper pump intake must be positioned above an oil-water interface and the lower pump must be positioned below the oil-water interface. Preferably, the distance between the intakes to the upper and lower pumps is as great as possible to maximize the retention time of the fluids within the casing to allow the fluids to naturally separate from one another due to their different densities. The longer the retention time of the oil and water in the casing before removal, the better the separation.
However, a single motor is typically positioned between the pumps and drives both of the pumps. Using a single motor to drive both of the pumps is advantageous because of the lower equipment cost of using only one motor and because only one power cable is required to power the pumps, as opposed to a two motor system that would require two power cables. However, a disadvantage of using a single motor to power both of the pumps is that the pumps and their intakes must be positioned relatively close together because the allowable space between the motor and the pumps is limited. Therefore, using a one motor system limits the separation of the upper and lower pump intakes from one another and from the oil-water interface and decreases the retention of the fluid in the casing prior to removal by the pumps. Thus, the downhole separation of the fluids using a system with two pump and a single motor is limited and the produced fluid may require substantial additional separation.
Accordingly, there is a need for an apparatus that permits the use of a single motor with a pair of pumps while providing for increased retention time of fluids in the well bore, a greater distance between the pump intakes and between the intakes and the oil-water interface and that provides for better separation of the fluids.
SUMMARY OF THE INVENTION
The present invention generally provides an apparatus for increasing the separation between the pump intakes of a pair of pumps driven by a single motor positioned between the pumps. In general, the apparatus is a fluid communication passageway extending from the pump intake of at least one of the pumps away from the other pump to form an effective pump intake that is further from the other pump. Preferably, each of the pump intakes are connected to a separate communication passageway. More particularly, the apparatus is a shroud surrounding the pump that is connected to the intake end of the pump and extends at least partially over the pump forming a communication passageway therebetween.
A casing that encloses the wellbore includes a production perforation through which production fluids enter. The production fluids typically comprise a mixture of oil and water that must be separated for the oil to be produced. Once in the casing, the differing relative densities of the fluids cause the fluids to separate and form an oil water interface with the oil floating on the water. The longer the fluids are allowed to remain in the casing before removal, the better the separation.
A production string is provided having a production tubing interconnected to a pair of pumps that are both driven by a single motor mounted between the pumps. Each pump includes an intake end, a second end, and an intake port through which the pump receives fluid. The pumps are preferably positioned so that one pump is above the oil-water interface and the other pump is below the oil-water interface and each pump pumps a separate fluid. The greater the distance between the pump intakes and the oil-water interface and between the two pump intakes, the longer the retention time of the fluid in the casing and the better the gravity separation. Preferably, this distance between the pump intakes is at least about sixty feet. However, because both pumps are connected to the same motor, the allowable separation of the pumps is limited.
To increase the effective separation between the pump intakes, the present invention provides at least one fluid communication passageway, having a first end and a second end, that extends from the pump intake of one of the pumps away from the other pump. The first end is proximal the pump intake and the second end is distal the pump intake and defines an inlet orifice. Preferably, the apparatus includes two fluid communication passageways each extending from the pump intake of a separate pump in diverging directions. The inlet orifices of the fluid communication passageways are preferably at least sixty feet from one another.
Another aspect of the invention provides a shroud surrounding one of the pair of pumps and defining an inner fluid passageway therebetween and an outer fluid passageway between the shroud and the casing. The shroud is sealably connected to the production string at a position between the motor and the pump intake of a first pump surrounded by the shroud and extends to a position beyond the pump intake. A second shroud similar to the first shroud surrounds a second pump and is sealably connected to the production string between the motor and the second pump. Preferably, the shrouds are connected to the intake ends of the pumps they surround. Additionally, the shrouds define inlet orifices at their second ends distal the first, sealed ends and the inlet ends of the shrouds are preferably at least about sixty feet from one another.
A further aspect of the invention is a system for separating fluids that incorporates the two pump, single motor design previously described with a shroud surrounding each of the pumps. The shrouds create effective pump intakes increasing the distance between the pump intakes, preferably to at least about sixty feet. This effective separation of the intake ports maximizes the retention time of fluids in the wellbore, thereby assisting and facilitating gravity separation of the fluids.
Another aspect of the invention provides a method for increasing the pump intakes of the pumps that comprises providing a communication passageway from the pump intake of at least one of the pumps that extends away from the other pump to a position distal the other pump. The preferred method provides a communication passageway for each of the pumps and the communication passageways are formed using shrouds that separate the pump intakes, preferably by at least about sixty feet.
An alternate embodiment provides a shroud for a system having two pumps that are each driven by a separate motor
50
. The shrouds
70
facilitate separation of the effective pump intakes
66
from one another. Another alternate embodiment provides a shroud for a single pump driven by a single motor to provide an effective pump intake that is removed from the intake of the pump. Further, the shroud may be utilized to incre
Bagnell David
Baker Hughes Incorporated
Locke Liddell & Sapp LLP
Walker Zakiya
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