Wells – Processes – With indicating – testing – measuring or locating
Reexamination Certificate
2001-07-23
2002-12-24
Neuder, William P. (Department: 3672)
Wells
Processes
With indicating, testing, measuring or locating
C166S369000, C166S068500, C166S105000
Reexamination Certificate
active
06497281
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to improvements in downhole production pumps and operating systems therefor for use in pumping fluids from boreholes and especially an oil well production system for stripper wells wherein crude oil is removed from the borehole as fast as it comes into the well.
Marginal oil wells, also called stripper wells, are usually uneconomical for the major oil companies to operate because the labor and pumping costs are close to the revenue from the hydrocarbon sales. Every day many of these unprofitable stripper wells are being shut in, plugged, and abandoned. But there is a type of oil field hand that loves to get possession of these marginal wells because he has the where-with-all to scrounge up enough equipment to maintain and operate these wells at a small profit.
Many of these stripper wells in the U.S.A. produce only about 10 barrels or less, of hydrocarbons/day. These wells are important to the U.S. economy, especially during times of political unrest when they become vital to our national defense. After all, just one days production at a rate of 10 barrels, or 440 gal, of oil/day will operate a small auto several thousand miles after the crude oil has been refined into fuel.
Accordingly, it is desirable to make available novel oil well production equipment that is relatively inexpensive and can be assembled from mostly commercially available material and thereby increase the profit gleaned from a stripper well. Additionally, the novel equipment should be easy to work on and have low cost maintenance and operation. Further, the novel equipment should operate the well in such a manner that the production rate can be increased from marginal to profitable. When all of these and several other desirable attributes are considered, it is easy to see that they add up to a novel well production system that provides the unexpected result of changing an unprofitable situation into one that is profitable.
Most oil wells in West Texas are produced by a pump-jack unit that reciprocates a bottom hole pump. The pump-jack usually operates cyclically for time intervals selected to avoid reaching a pump-off condition which starts a destructive condition known as fluid pounding, or gas lock. This situation is evidenced by the hundreds of issued US Patents which address this problem. One simply never pumps-off a well.
Fluid pounding is encountered when a pump-off condition is reached due to the attempt to remove downhole fluid from the borehole faster than it can accumulate. This introduces compressible gas into the variable chamber of the downhole pump, causing the plunger to accelerate and “pound” the bottom of the pump as the liquid supported by the plunger impacts the stationary valve assembly at the bottom of the pump barrel. Fluid pounding is destructive for it can result in accelerated wear and tear on the entire production equipment. Therefore, in most reciprocating downhole production pumps, a lot of consideration is given to avoiding a pump-off condition of the downhole pump.
Contrary to the prior art method of producing a well, the production system of the present invention is operated in a continually pumped-off condition by removing the formation fluid from the bottom of the well just as fast as it enters through the casing perforations of the borehole, thereby reducing the hydrostatic pressure against the pay zone to a minimum. This allows the oil bearing formation to produce at its maximum, but at the same time it is bound to ingest compressible gas into the bottom of the pump barrel, where it would be expected to cause fluid pounding, especially if provision is not made to avoid this occurrence. Accordingly, a purpose of this invention is the provision of a novel downhole pump and system that can accommodate the pumping of mixed hydrocarbon fluids (gas and liquid) and thereby change the problem of encountering a pump-off condition into an asset, while avoiding the dangers of fluid pounding. This is achieved in accordance with the present invention by the provision of a downhole pump assembly having a very long barrel that lifts both gas and liquid uphole every up-stroke of the pump plunger so that the pump chamber does not accumulate compressible fluids therewithin, but instead exhausts all gases along with the liquid each upstroke of the pump.
In addition to avoiding fluid pounding, this novel feature of this invention also has the unexpected advantage of enhancing pumping efficiency by using the gas expelled from the pump into the production tubing to provide additional lifting power in the manner similar to a well that uses a gas or air lift to produce liquid therefrom. Hence, gas that flows into the pump apparatus of this disclosure is slowly exhausted from the top of the variable chamber each upstroke of the pump plunger, and consequently there is no means by which the gas from a previous stroke can accumulate in the pump barrel for another stroke because the gas is removed from the pump apparatus at the end of each upstroke. Accordingly, fluid pounding is never encountered.
Further, the exceedingly long stroking pump plunger, together with the unusually slow time interval of the upstroke each cycle of operation, provides the necessary time delay for any gas that flows into the pump chamber to separate from the fluid and accumulate at the top of the barrel. During the slow plunger up-stroke the accumulated gas is slowly expelled from the pump variable chamber and enters the bottom of the production string at a very slow rate, which reduces the density of the contents of the tubing.
During the upstroke, the slow traveling pump plunger is acting against a constant lifting force and therefore does not accelerate significantly due to the differences in design between the system of this invention and the prior art production pumps, as will be more fully appreciated later on as this disclosure is more fully digested. Stated differently, there is not enough plunger speed and built-in inertia force in the present system as compared to the massive rotating parts of a prior art pumpjack operation to effect fluid pounding. Further, the low pumping speed of this novel cyclic operation along with the low bottom hole pressure at the perforations prevents accumulation of gases within the pump barrel for more than one cycle of operation, and this is a situation in which fluid pounding cannot be brought about.
Another novel feature of this disclosure is the provision of a method which reduces the oil/water ratio to a minimum by skimming the oil from above the oil/water interface of the formation fluid accumulated in the bottom of the well. The amount of water produced can be reduced until the desired crude production is achieved, or the desired oil/water ratio is achieved.
Other advantages of this disclosure over rod type downhole pumps is that the downhole production pump apparatus claimed herein can be pulled from the tubing by using the operating cable for reeling the lifting cable uphole until the pump apparatus surfaces. Then the entire pump apparatus can be serviced, as required, with change out of desired parts, and thereafter run back downhole into the borehole by unspooling the cable. Both method and apparatus that achieves the above desirable results are the subject of this invention and for which patent protection is sought.
In the prior art, it is noted that Coberly, U.S. Pat. No. 1,970,596, discloses a cable actuated long stroke pumping mechanism having a cable drum that includes a mechanical speed and switching control means associated therewith. The cable drum is rotated such that it accelerates the rate of travel of the plunger at the end of each stroke.
Mayer, et al, U.S. Pat. No. 4,761,120, measures a load on the rod string to provide automatic shutdown of a pumping unit.
London, et al, U.S. Pat. No. 5,372,482, controls the filling of a well pumping device by an arrangement in which the motor current is measured and compared to rod position using a computer to process the signals.
McKee, U.S. Pat. No. 4,973,226 disclos
Bates Marcus L.
Neuder William P.
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