Hydraulic Oilfield Lift Pump

Abstract

A vertically orientated hydraulically driven oilfield lift pump unit having a simplified hydraulic system. The system uses a pair of single acting hydraulic cylinders in tandem with a pair of double acting hydraulic cylinders interacting with hydraulic accumulators to provide an energy efficient, robust hydraulic system design with a minimum number of components.

Description

[0001]This application claims priority from U.S. provisional patent application Ser. No. 61 / 183,264, filed on Jun. 2, 2009, which is incorporated herein by reference.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]This invention relates to lift pumps suitable for producing hydrocarbons and other liquids from the earth. In particular, this invention is drawn to a very long stroke hydraulically operated lift pump using a combination of single and double acting hydraulic cylinders that are actuated with an energy efficient hydraulic fluid accumulator system.[0004]2. Description of the Related Art[0005]Hydraulically operated Oilfield lift pumping units are well known and have been used in the industry for many years. Typically, these units mimic the non-hydraulic mechanical ‘walking beam’ design similar to the pumping unit 10 illustrated in FIG. 1. These conventional units are more commonly driven directly by electric motors through gear boxes, but many are also hydrauli...

AI Technical Summary

Benefits of technology

[0012]This may also effectively balance the pump motor's load between the upstroke and the downstroke cycles, and may permit use of a prime mover motor or engine to run under a relatively constant load (compared to conventional pumps) regardless of whether in both the upstroke mode and the downstroke mode. Typical load variations may be in the range of 70% to 130% of the average load, but as will be described, these variations may be reduced even more than this, if desired. When compared to other pump units of this type, the load balancing effect of the accumulators allows the use of a motor with a significantly less horsepower rating (or capacity) than the prior art units. Furthermore, the lower peak power consumption may allow for a lower effective electric rate, as in many locations the electric rate is based on, or at least affected, by the peak load instead of the average load.

[0015]During the ‘down’ stroke, the pressurized fluid from the hydraulic power unit is applied only to the ‘rod’ ends of the double acting hydraulic cylinders. The combination of the weight of the load and this hydraulic pressure on the top end of the cylinder causes all the cylinders to retract. This in turn forces the hydraulic fluid on the cap ends of the double acting cylinders back into the accumulators—and therefore filling them. The relative horsepower required for each of the ‘extend’ and ‘retract’ cycles may be changed and / or more nearly equalized by adjusting the pre-charge pressure of the accumulators to account for variations in the average lifting load, permitting usage of the smallest possible engine or motor for the hydraulics. Furthermore, this may also help reduce large load fluctuations, reducing stress on the system. However, because in some instances the actual loading may vary over time, an intermediate pre-charge pressure may be chosen.

Problems solved by technology

Furthermore, the lower peak power consumption may allow for a lower effective electric rate, as in many locations the electric rate is based on, or at least affected, by the peak load instead of the average load.

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