Patent Application
20120073800
The invention relates to electrical submersible pumps. More particularly, the invention relates to replacing one or more pump stages with a spacer, or pump shaft bearing support, for fine tuning a pump's lift capacity to more closely match well capacity.
Electrical submersible pumps (ESP) are used to artificially lift well fluid from deep underground. Primarily, ESPs are used to pump oil, typically as part of an oil and water mix, from deep wells at high pressures. ESPs are driven by long tubular, high horsepower, electric inductance motors that typically run at speeds of approximately 3,500 rpm. A common type of pump used in an ESP is a pump generally known as a centrifugal pump. Centrifugal pumps are made up of six (6) primary components. The major components are the housing, shaft, head, base, impeller and diffuser. The impeller and diffuser, when paired together, are referred to as stages.
Pumps are designed, manufactured and marketed by stage and series. The term “stage” reflects stage variation or the number of stages in a pump. “Stage” is a term used to communicate accurately the amount of fluid a pump can lift in a day. A common daily rate of lift is described in barrels per day. For example “D50” refers to a pump with an impeller and diffuser combination, i.e., stage, that is able to lift 50 gallons per hour under specific power requirements, rpm and well fluid levels. Therefore, pump stages are an important consideration when sizing an ESP for a well.
“Series” is a term that directly relates to a pump's outside diameter (O.D.) and indirectly to a well casing inside diameter (I.D.). Pumps are designed, manufactured and sold in many different series so that pumps may be easily sized to fit into a well casing and to allow room for the pump's housing and for power cable clearance. Common series in the industry are 300, 400, 500, 675 and so on. A 500 series pump will fit into a well casing I.D of 6.50 inches. An incorrectly sized pump runs the risk of getting stuck in the casing.
The larger the series number and the larger the stage number and amount of stages, the more fluid a pump can lift in a given time period. The amount of fluid that a pump can lift in a given time period is referred to as lift capacity. However, the lift capability of a pump is not only dependent on pump diameter, pump size and number of stages, but it is ultimately tied to the capability of a well to produce fluid.
A well will produce only the quantity of fluid that is released from a well formation under the surface. Wells are logged and evaluated to determine their ability to produce fluid, known as capacity. Capacity is important for two reasons. First, lifting more fluid than the well can produce will run a pump dry and irreparably damage the pump. Second, to maximize profits, production and efficiency, a pump needs to lift exactly the amount of fluid that a well will provide. Therefore, sizing the pump is critical.
In the past, pump manufactures were only able to get close to providing a pump with the amount of stages to exactly match lift with well capacity. This is due to limitations imposed by commonly available housing lengths and stage configurations.
Several methods have been utilized to match pump lift capacity with well capacity. One way to size a pump is to tie pumps together, i.e., a tandem pump, so that the stages add up closely to the requirements. A disadvantage with this solution is that the use of tandem pumps is a costly solution to the customer.
Another way to avoid pumping off or under pumping a well is to control the speed (rpm) of a pump with a variable speed drive (VSD). The flow rate of the pump can be controlled by a VSD. The VSD actively monitors the fluid discharge rates to increase or decrease the pump's speed. A disadvantage associated with the use of VSDs is that VSDs are relatively expensive and costly to operate, thus costing the customer more.
Therefore, it is desirable to provide a low cost method of matching pump lift components with well capacity. The pump lift capacity of a pump can be modified by the replacement of one or more stages with a shaft bearing support of the invention.
By adding the shaft bearing support of the invention, a given housing can be used with the exact number of stages required to effectively pump fluid out of a well, which allows for a well to be pumped without running the well dry and without leaving any fluid below. This invention will maximize profits and efficiency while minimizing wear and tear on the equipment.
The shaft bearing support of the invention is made up of several features. The outside diameter of the shaft bearing support is an outer ring that fits inside a pump housing. Webs connect the outer ring to an inner ring, which defines an inside diameter of the shaft bearing support. Therefore, the inner ring is fixed relative to the outside diameter ring. Both the outer and inner rings have a sufficient width and depth to be mechanically sound. The inner ring of the shaft bearing support has an inner diameter (ID) that is large enough to allow the pump shaft to pass therethrough and to accommodate a fluid bearing between the pump shaft and the ID of the inner ring. The webs of the shaft bearing support define a volume or void between each web so that pumped fluid can move through the voids defined by the pump shaft bearing support with minimal obstruction or frictional loss.
One or more compression tubes may be located adjacent to the shaft bearing support. The orientation and configuration of the compression tubes relative to the shaft bearing support to the stage can vary. The compression tubes may be located toward the head, they can be toward the base, or they can be anywhere in between. A common orientation is to locate a first compression tube adjacent to the head, then locate a first side of the shaft bearing support adjacent to the first compression tube. A second compression tube may then be located adjacent to a second side of the shaft bearing support.
Referring now to
Pump unit 20 further includes a housing 26. A pump base 28 (
ESP unit 18 additionally may be provided with gas separator 40 (
Referring now to
In a preferred embodiment, shaft bearing support 48 is preferably a cast part made from Ni-resist and then machined to exact specifications. Webs 54 may be oriented perpendicularly to a central axis 53 of shaft bearing support 48, e.g., webs 54a. Alternatively, webs 54 may be tapered, e.g., 54b (
Referring back to
In use, a lift capacity of ESP unit 18 may be modified by replacing one or more stages 38, preferably 8 to 10 stages 38, of pump unit 20 with spacer assembly 46, such as a spacer assembly made up of shaft bearing support 48, first compression tube 55, and possibly second compression tube 58. Multiple spacer assemblies 46 can be located within housing 26, e.g., multiple spacer assemblies 46 may be placed end to end. Other spacer assembly configurations may also be utilized that support pump shaft 32 and occupy space surrounding a length of pump shaft 32. By fine tuning the lift capacity of ESP unit 18 in this manner, the lift capacity may be made to more closely match the well capacity of well 10.
Thus, the present invention is well adapted to carry out the objectives and attain the ends and advantages mentioned above as well as those inherent therein. While presently preferred embodiments have been described for purposes of this disclosure, numerous changes and modifications will be apparent to those of ordinary skill in the art. Such changes and modifications are encompassed within the spirit of this invention as defined by the claims.
