Surface driven well pump

Abstract

Oil is recovered from a borehole using a pump using a surface driven high rotary speed pump. In one aspect, the pump is a centrifugal pump, operated at speeds in excess of 3400 rpm. The pump is located in a downhole position, within a production zone of a wellbore. A drive rod extends from a wellhead, downwardly through the wellbore, where it is received in engagement with the impeller of the pump. A dampening element is disposed in conjunction with the rod to reduce the physical excursion of the rod and thus enable high-speed rotation of the rod with minimal risk of excursion related failure of the rod or wellbore.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] Embodiments of the present invention generally relate to the field of fluid extraction from bore holes. More particularly the present invention relates to artificial lifting devices and methodologies for retrieving fluids, such as crude oil, from bores where the fluid does not have sufficient hydrostatic pressure to rise to the surface of the earth of its own accord. More particularly still, the present invention relates to the field of recovery of such fluids, where the fluid temperature of the fluids in the wellbore exceeds the temperature at which the sealing materials in the pump rapidly deteriorate, to the point of failure. [0003] 2. Description of the Related Art [0004] The recovery of fluids such as oil and other hydrocarbons from bore holes, where the fluid pressure in the bore hole is insufficient to cause the fluid to naturally rise to the earths' surface, is typically accomplished by the pumping of fluid ...

AI Technical Summary

Benefits of technology

[0013] In one embodiment, a centrifugal pump, having at least one rotary component, is driven from a wellhead or other remote location. The drive mechanism includes a drive rod, which extends from a surface driven motor to a downhole location, and a damping member configured to reduce oscillations or other vibrations in the driving rod, and thereby prevent disabling vibration or whirling of the drive rod and / or interference between the rod and fluid recovery tube which would otherwise lead to the failure of one or the other. Furthermore, the invention enables the full torque and power input of the remotely positioned motor to drive the pump, without the need to position the motor downhole or to provide intermediate reduction and step up gear boxes.

[0014] In a preferred embodiment, the rod is extended through a damping sleeve, between which is disposed a dampening medium. Preferably this dampening medium is a lubricating material, such as an oil, which serves to both absorb energy from the turning rod, particularly energy created by lateral vibration, mass non-uniformity or other source of induced energy, as well as provide a pliable medium between the rod and sleeve which forms a physical barrier there between, to prevent or at least significantly reduce the interfering contact between the rotating rod and the sleeve through which it extends.

Problems solved by technology

Several methodologies are known to provide this pumping action, each with its own limitations.

These pumps are most effective for pumping medium to light clean oil but they lose efficiency as the oil viscosity increases, and they experience rapid wear if the pumped fluids contain abrasive media.

One issue encountered with progressive cavity pumps is degradation of the pump components at high temperatures.

The material used for effectively forming this seal, typically nitrile rubber, encounters temperature-based resiliency breakdown if the ambient to which the material is exposed exceeds approximately 250 degrees F. Thus, in fields with naturally occurring high downhole temperatures and in fields where steam injection is used to free heavy oil, such as tar sand, from the formation, the temperature of the oil will often exceed the 250 degree F. threshold, and rapid pump degradation will occur.

Although other sealing materials have been used to form the rotor-to-pump seal, they are compromises in terms of either performance or cost, and thus have received limited success in the marketplace.

In high temperature pumping applications such as those mentioned above, the temperature of the well plus the normal temperature rise of an electric motor tends to cause thermal breakdown of the electrical insulation, causing failure of the motor or the wiring.

As a result, the use of this artificial lift method is limited to wells having a moderate temperature.

Although there is the possibility of driving such pumps from the surface, through a rod rotating about its longitudinal axis, the applicability of such an arrangement is limited by the tendency of the rod to whip or whirl as it is rotated at the 3000 to 4000 rpm's necessary to drive a centrifugal pump.

This whirling phenomenon is caused by imbalances in the drive rod, by twist and relax effects as the rod is spun, and by natural vibrations occurring as the harmonic natural frequency of the rod is approached.

As a result, surface driven centrifugal pumps are limited to very shallow fluid recovery applications, typically below 500 feet deep.

This technique suffers from poor system energy efficiency and the need for extensive equipment at the surface, the cost of which typically exceeds the value of the oil which may be recovered.

Jet pumping is less effective with viscous fluids than with lighter fluids because it is more difficult for a venturi effect to pull viscous fluids into the jet pump mixing tube, and the mixing tube must be substantially longer to accomplish adequate fluid mixing in the pump.

This technique suffers from the fact that uniform mixing of the gas with the fluid in the production tubing is more difficult to achieve in viscous fluids.

Gas-assisted lifting is further limited by the fact that it depends upon there being adequate pressure in the reservoir to lift the hydrostatic column of reduced density fluid to the surface.

Images