Pumps – Motor driven – Fluid motor
Reexamination Certificate
1998-06-09
2001-03-20
Wayner, William (Department: 3744)
Pumps
Motor driven
Fluid motor
C417S401000
Reexamination Certificate
active
06203289
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a hydraulic pumping system particularly for pumping fluids at low pressure and in particular for pumping petroleum fluids at the bottom of a well.
2. Description of the Prior Art
Various methods and devices are used in the field of hydrocarbon production for pumping low-pressure fluids.
Classical hydraulic pumping by jet or piston type bottom-hole pumps requires, for example:
either lifting the drive fluid mixed with the product through the annular gap between the casing and the tubing, or through the central tubing, depending on the method of hydraulic circulation chosen. The drive fluid is, for example, the water in the deposit or a degassed, processed crude that may contain additives and/or solvents, avoiding problems of fouling, emulsion, or rusting. One of the drawbacks of this method is that the mixture of drive liquid and product fluid can lead to cross-pollution of these two fluids. This option demands a voluminous and expensive processing facility at the surface to filter and recycle the drive fluid;
or using a well completion with an extra tubing for lifting the expanded drive fluid, which is an expensive and complex option when reduced to practice.
The present invention injects and recovers the drive fluid through one and the same pipe, alternating the drive fluid injection and removal phases in regular cycles. Using two different bottom/surface hydraulic links for the drive fluid and the pumped fluid prevents mixing of the drive fluid and product fluid during the pumping operation.
To implement the suction phase of the bottom-hole pump, the pressure generated at the bottom by the drive fluid is reduced so that it is below the well pressure at right angles to the pump suction.
Various methods have been described in the prior art for producing this pressure drop.
A first solution, described for example in U.S. Pat. Nos. 2,519,679, 3,941,510 and 4,405,891, consists of using a light drive fluid such as a liquid or a gas.
However, the use of low-density liquids (liquefied butane or propane, alcohol, etc.) does not produce a sufficient pressure for classical applications. The use of gas (natural gas or nitrogen) has the drawback of requiring substantial compression work with each cycle, leading to a very low energy efficiency and a very slow cycling rate.
A second solution, referred to for example in U.S. Pat. Nos. 2,180,366, 3,420,183, and 4,616,974, consists of assisting the suction phase of the pump by having the column of drive fluid and column of pumped fluid (assumed to be a liquid monophase) work alternately. This solution requires complicated machinery at the bottom and at the surface, comprising an assembly of check valves, pistons, and cylinders with different cross sections. This technique, which enables any drive fluid such as water to be used, is in this case well-suited for pumping water. On the other hand, production of crude with free gas, which represents a general application case of oil production, would require considerably increasing the volume of drive fluid transferred with each cycle to assist lifting the product by compressing the product gas, thus considerably limiting energy efficiency and production rate. Fitting a gas separator, whose efficiency is imperfect, to the suction end of the bottom-hole pump would complicate completion of the well without entirely eliminating this drawback.
Finally, a third solution, as described in U.S. Pat. Nos. 2,555,613 or 4,013,385, consists of using a mechanical or pneumatic spring directly applying an upward return force to the piston of a classical piston-type bottom-hole hydraulic pump. This solution faces the great difficulty of installing a long, powerful spring, which is necessary for substantially reducing the hydrostatic load produced by the drive fluid column, in a small-diameter space. The force P to be applied to resist this column must meet the condition:
F>
(&rgr;
M
gh−P
suc
)
S
where:
&rgr;
M
is the density of the drive fluid,
g represents the local gravity constant (approximately 9.8 m/s
2
)
h is the pump depth
P
suc
is the suction pressure of the fluid in the deposit,
S is the section of the bottom-hole hydraulic pump piston.
The force P thus calculated would frequently exceed 1000 kg.
SUMMARY OF THE INVENTION
The present invention is a hydraulic pumping system that solves the problems referred to in the prior art while minimizing investment outlay and the cost of treating fluids at the surface.
The invention relates to a hydraulic alternating volumetric system for pumping fluids at low pressure comprising at least one pumping enclosure, said enclosure comprising at least one pipe for introducing the fluid to be pumped and at least one pipe for discharging the pumped fluid.
The pumping enclosure is provided with a pipe for introducing an auxiliary fluid such as a drive fluid and pressure-reducer for reducing the pressure of said drive fluid transmitted to the fluid to be pumped.
The pressure reducer together with the inside wall of the pumping enclosure can form a space which is reduced to a low pressure or a vacuum.
The invention can include means for preserving the vacuum in this space, said means comprising a vacuum-preserving check valve.
It is also possible to use an elastic seal to complement this valve, said seal being disposed such that it traps a small quantity of liquid in the evacuated space.
In this way, it is possible to maintain the vacuum or low pressure during operation, and the pressure reducer can carry out its function fully throughout the travel of the pressure reducer for as long as the system is operating.
It can also comprise a return connected to said pressure reducer.
According to one embodiment, the pumping enclosure has two parts, a first part and a second part, said parts being connected by a pipe, and:
the first part or drive part has the pressure-reducer and can be provided with means for introducing drive fluid, with the drive fluid also playing the role of buffer fluid,
the second part has for example a means playing the role of a piston and defining two variable-size chambers, one of the chambers being in communication with the pumped fluid introduction and a discharge and the other communicating with the drive fluid introduction pipe.
According to this arrangement, the free piston is controlled hydraulically by the drive fluid or buffer fluid.
The pressure reducer can have at least a first piston P
1
with a section S
1
and a second piston P
2
with a section S
2
, the first and the second piston being disposed essentially along the same axis, and with the ratio S
2
/S
1
between the sections being between 1 and 10 and preferably between 2 and 3.
Ignoring friction of the piston seals, the hydrostatic pressure thus transmitted to the pump comprising for example a free piston is reduced by a factor of S
2
/S
1
.
The pump function can also be formed by a deformable flexible membrane disposed essentially along the length of the pump or by a double membrane or, according to another embodiment, by one or more extensible membranes inflated and folded alternately to create, in the pump body, the changes in chamber volume necessary for the suction and discharge phases.
The pumping operations can be carried out using a device that controls and generates pressure cycles modulated at the surface. The drive fluid is for example a classical hydraulic oil or carefully filtered gas oil, or possibly water treated to prevent corrosion.
The pumping system according to the invention applies particularly well to bottom pumping of a petroleum-type effluent or possibly water from water-bearing deposits.
With respect to the hydraulic pumping systems according to the prior art, the present invention offers in particular the following advantages:
the system is simple to build and operate,
the check valves can advantageously be disposed at the upper part of the pump to favor initial expulsion of the free gas in the discharge phase of the pump, which improves pumping efficiency,
the dead vo
Castel Yvon
Corteville Jacques
Antonelli Terry Stout & Kraus LLP
Institut Francais du Pe'trole
Wayner William
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