Wells – Processes – Producing the well
Reexamination Certificate
2000-01-31
2001-10-09
Bagnell, David (Department: 3672)
Wells
Processes
Producing the well
C166S105600, C166S163000, C166S263000, C166S401000
Reexamination Certificate
active
06298918
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the operation of petroleum wells which require an artificial lift system. More particularly it applies to low-productivity conventional or offshore wells and offers an advantageous alternative to mechanical pumping or other known methods based on continuous gas injection.
BACKGROUND OF THE INVENTION
The various artificial lift methods which may be used for the production of petroleum in non-flowing wells or for increasing the productivity of wells in general, depending on local conditions, may present a number of drawbacks.
PRIOR ART
In non-flowing conventional wells with low productivity levels, mechanical pumping systems or gas-lift-type systems are frequently used.
Lifting the petroleum, contained in a reservoir, up to the surface is possible only if there is a minimum pressure over the petroleum at the bottom of the well. One method used to assist lifting is known as “gas lift” which comprises the injection of gas, under controlled conditions, into the annulus defined between the production column and the well casing. By means of this artificial lift method gas is continuously injected, passing through one or more valves known as gas-lift valves, from the surface to the production zone where it mixes with the oil, thereby lowering the density of the oil and facilitating its lifting to the surface.
An embodiment of this method is disclosed in U.S. Pat. No. 4,392,532, which relates to the location and the spacing of the gas-lift valves, and in U.S. Pat. No. 4,711,306, which proposes the injection of pressurized gas and liquid.
Artificial lifting by means of the gas-lift system is suitable only in wells which are draining reservoirs in which there is still a reasonable amount of static pressure such that, after injection of the propulsion gas, the pressure of the fluid at the bottom is higher than a minimum value sufficient to lift the oil/gas mixture to the surface.
Brazilian application PI 9303715-5 offers an alternative to a conventional gas-lift system. According to this application a drilled or already existing well which is blind, for example because the lower zones have been abandoned, is supplied below the perforation region. It is thus possible to obtain a column of oil over the entry of the production piping with sufficient height, after it has been gasified, to allow the lifting of the oil from the bottom of the well to the surface. The propulsion gas is brought to the production column through a second column installed in the well. Two possible embodiments are offered for achieving the object of the invention.
The mechanical systems may be of the “progressive cavity pump” (PCP) or “constant flow pump” (piston and shaft) type. Although efficient in that they allow satisfactory utilization of the oil reservoirs they exhibit, principally in wells where there is a high concentration of aggressive fluids, a high incidence of mechanical problems. Under these conditions, broken shafts, worn pump pistons, etc. are common occurrences, giving rise to the need for frequent intervention for the purposes of maintenance. Such interventions are generally fairly expensive, since they require the use of probes, and also jeopardize production targets.
Furthermore, after a certain stage in the depletion of reservoirs, gas-lift systems show a substantial reduction in efficiency.
OBJECTS OF THE INVENTION
It is a principal object of this invention to offer an improvement over the above prior art in not using moving parts, and thereby reducing maintenance costs and the need for shutting down production.
In addition, it is a further object of the invention to provide a system which, when compared with gas lift or with the system described in our Brazilian Patent Application PI 9303715-5 (now granted), will produce a greater pressure differential when the storage chamber is depressurized, thereby allowing greater utilization of the reservoir.
It is a further object of the invention to provide a system which applies equally to offshore wells, where gases are frequently present and can cause problems for mechanical systems but do not present any drawback regarding a pneumatic system. Depending on the well conditions, the efficiency of mechanical pumping will not always be guaranteed.
SUMMARY OF THE INVENTION
The invention relates to a pneumatic petroleum lift system for application in wells with low productivity levels. Basically, it consists in the cyclic pressurization and depressurization of a storage chamber, located in the lower part of the well, by means of the injection and release of gas, thereby forcing the petroleum which has accumulated there to be lifted via the production column. When the storage chamber is depressurized, the gas may be routed to the upper part of the production column where, by means of the provision of an auxiliary lift columns, the fluid lift conditions are improved. With a view to reducing the volume of gas required for operation of the system, a few adaptations are made to the geometry of the columns, creating, for example, an annular space of small volume, where said injection takes place. A control subsystem is responsible for timing the operating cycle. Depressurization of the bottom of the well, during part of the operating cycle of the system, improves the conditions of recovery of petroleum from the reservoir.
REFERENCES:
patent: 3106170 (1963-10-01), Gray
patent: 3797968 (1974-03-01), Elfarr
patent: 3894583 (1975-07-01), Morgan
patent: 3941511 (1976-03-01), Morgan
patent: 4392532 (1983-07-01), Raggio
patent: 4427345 (1984-01-01), Blann et al.
patent: 4711306 (1987-12-01), Bobo
patent: 9303715-5 (1995-04-01), None
De Oliveira Francisco Alberto Cerqueira
Franco Zadson De Almeida
Bagnell David
Nixon & Vanderhye PC
Petroleo Brasileiro S.A.--Petrobras
Walker Zakiya
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