Wells – Processes – Producing the well
Reexamination Certificate
2000-05-01
2001-07-17
Dang, Hoang (Department: 3672)
Wells
Processes
Producing the well
C166S177700, C166S242100, C166S369000
Reexamination Certificate
active
06260628
ABSTRACT:
FIELD OF THE INVENTION
The following invention relates to a use in connection with transport or flow through a production tubing string in a petroleum well of gas and liquid from a petroleum reservoir with low pressure, where the flowing fluid comprises a substantial liquid part and a less gas contribution, which gas mostly flows or bubbles past or through the liquid in the production tubing.
BACKGROUND OF THE INVENTION
In other words, it can be said that the present invention relates mainly to the type of petroleum wells which may be termed an oil producer, such oil producer producing mainly oil and some gas. This is different from petroleum wells (reservoirs) which are termed gas producers, which gas producers often also produce some liquid, for example in the form of condensate and water. By such a liquid production (in a gas well) and low pressure in the reservoir, such a well could, however, gradually “drown”, and the need for gas lift may be required. Thus, the present invention also relates to gas lift for gas wells.
Most petroleum producers (wells) will have a characterization somewhat between these extremes (liquid with some gas—gas with some liquid), the liquid parts here being considered as having reasonably low viscosity.
When an oil producer (with some gas included) gradually looses its productivity by falling reservoir pressure (and lowest practical receiving pressure above ground), the pressure head in the production tubing will gradually balance the reservoir pressure. Production will then stop and the liquid level in the well will gradually come to rest below ground level.
Gas which is still released from the oil production tubing and in the zone close to the perforation, will bubble up through the production string, and then without effectively contributing to the reduction of pressure head.
It is in connection with this type of wells that the present invention has been developed.
By such oil producing wells also the residual gas will gradually be terminated, and in order to prevent such wells from “dying” it is common to introduce gas lift to reduce the pressure head resistance.
However, the present invention is to the fact of utilizing the previously ineffective gas bubbles flowing through or bubbling past the liquid in a production tubing string, and then in a surprising and new manner.
PRIOR ART
From prior art there should be mentioned applicant's NO-C-146.826 relating to the evening out of multi-phase flow by means of static mixing elements.
Further, there are known static mixing devices in a well from CA-C-1.300.002 and U.S. Pat. No. 4.832.127, but in these cases steam and water, respectively, are introduced in order to improve the well productivity.
COMPARISON WITH PRIOR ART
It is previously known from applicant's NO patent 146.826 to use static mixing elements in rising pipes, but then in connection with a different type of application, namely a typical petroleum platform riser pipe, in which slugging flow may occur. The static mixing elements are then mounted in order to even out or prevent the development of such flow slugging, and the used mixing elements must in this connection be regarded as energy damping or friction stimulating elements, which contributes in dampening the excessive or pulsing energy giving rise to said “slugging”. In other words, the flow pattern is transferred from “slugging” to “mist flow” due to the changed hydraulic conditions introduced by the mixing elements.
In contrary to such a use in order to avoid “slugging”, one has in connection with oil producing reservoir found that even if the mixing elements in their basic design are to be regarded as friction elements, they can surprisingly be used as liquid lifters for petroleum wells which produce substantially only liquid, which in turn is too heavy to lift itself.
Without such mixing elements the few gas bubbles which appear in the production tubing string, will only be greater and greater the further up they rise, which is to the fact that they become more and more ineffective as regards their lifting contribution. By using static mixing elements in that type of production reservoir which is the case here, it has surprisingly been found that the otherwise by-bubbling or through-bubbling gas will be finely distributed with such a fineness in the dominating liquid volume, that there is obtained a lower pressure head and thereby a stimulating lifting effect for the resulting liquid/gas-mixture. Consequently, according to the invention, an instruction of how the gas bubble energy can be channelled or converted into an energy stimulating result is obtained.
Likewise, by introducing, according to the invention, a string of mixing elements in the production piping string, the need for gas lift will be reduced because there is achieved a lower mean pressure head, and then at a lower total gas flow rate. By only introducing a string having such mixing elements in a production well of the stated art, before the well is completely dead, it will thus be possible to increase the lifetime of the well until, sooner or later, it is necessary to introduce additional gas lift. For gas wells having low pressure and liquid production, wherein gas lift is installed, the requirement for lifting gas will also be reduced by the introduction of a string of mixing elements.
BRIEF DESCRIPTION OF THE INVENTION
The present invention provides not only an instruction for a specific field of application, but also the unexpected utilization of “useless” large bubbles in the form of distributed “small bubble carriers”. This involves providing the liquid and the gas to have an effective mean density which in character tends towards a single-phase flow.
It is important to recognize in the present case, that the introduction of mixing elements in a production tubing, wherein productivity is satisfactory will not contribute to a further improvement of the productivity, but rather a reduction due to the increased fall in pressure. Nevertheless, one has in connection with the present invention surprisingly found that the introduction of the mixing elements in a well at falling reservoir pressure, wherein the pressure head in the production tubing gradually evens out the reservoir pressure, will involve the exact opposite result, i.e. such “reduction elements” will operate in a completely opposite manner, namely to reduce the pressure head resistance and stimulate lifting effect for the liquid dominating liquid/gas-mixture.
Thus, especially when the production is unable to operate alone and the flow is low and the pressure head is low, the use of static mixing elements will give a positive stimulating effect by the distribution of gas in liquid.
Further features and advantages of the present invention will appear from the following description taken in conjunction with the appending drawings, as well as from the further attached patent claims.
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patent: 5452765 (1995-09-01), Blanchard et al.
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patent: 5547021 (1996-08-01), Raden
patent: 1300002 (1992-05-01), None
patent: 146826 (1982-09-01), None
Dang Hoang
Frommer William S.
Frommer & Lawrence & Haug LLP
LandOfFree
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