Wells – Packers or plugs – Controllable passage through packer
Patent
1991-01-09
1992-03-31
Dang, Hoang C.
Wells
Packers or plugs
Controllable passage through packer
166192, 166324, 166332, 166385, E21B 3312, E21B 3414
Patent
active
050999192
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to logging plugs for use in oil, gas and other wells.
To ascertain parameters of well operations such as pressure, temperature and flow rate one or more logging tools are run down the well on a logging or slick line cable, which will subsequently be referred to by the further alternative term wireline. As many of these parameters must be measured while the pressure in the perforation zone is different from that obtaining in the upper part of the well down which the logging tool is run, it is necessary for the wireline to be passed through a logging plug which maintains a good, but not perfect seal, with the wire, and which is itself sealable within a nipple incorporated in production tubing, by-pass tubing or the well casing.
Considerations arising from a typical employment of a conventional logging plug will now be discussed with reference to the accompanying diagrammatic drawings in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a vertical section through a length of an oil well including a perforated zone, and a logging plug, electric submersible pump (ESP) and by-pass system installed therein with the pump running;
FIG. 2 corresponds to FIG. 1 and shows pressures obtaining after the pump has been switched off;
FIG. 3 corresponds to FIGS. 1 and 2 illustrates a stage in the removal of the logging plug; and
FIG. 4 is a detail illustrating circulation in the absence of a logging plug.
FIG. 5 is an enlarged longitudinal cross-sectional view of the logging plug.
As shown in FIG. 1 a well casing 10 has a perforated zone 12 through which oil flows from a reservoir 14 as indicated by the arrows 16. From the bottom of a production string 18 is suspended a Y-crossover tool 20 from which depends an electric submersible pump 22 with the interposition of a pump sub 24 containing a non-return valve 26. From the tool 20 there also depends a length of by-pass tubing 28 formed with a nipple 30 in which a conventional logging plug 32 is sealed; slidably passing through the plug 32 but in effective sealing engagement therewith is a wireline 34 from which a logging tool 36 for measuring well parameters is suspended.
In FIG. 1 the pressure obtaining within the well casing is denoted P.sub.2 and the pressure on the outlet side of the pump 22 which is higher than P.sub.2, as P.sub.1. There is thus a differential pressure P.sub.1 -P.sub.2, defined as .DELTA.P.sub.1, acting downwardly on the logging plug 32. As this differential pressure holds the plug firmly in place, it must be substantially eliminated to allow the logging plug to be removed, and the tools withdrawn. However, equalization of pressure cannot be achieved simply by switching off the pump 22 due to the action of the non-return valve 26, as will now be explained with reference to FIG. 2.
When the pump 22 is switched off the pressure below the check valve 26 will increase until it equals the static reservoir pressure P.sub.3. P.sub.3 is greater than running pump intake (flowing well bore) pressure P.sub.2 but less than pump discharge pressure P.sub.1 which still obtains above check valve 26. The pressure differential holding the plug 32 in place will now be P.sub.1 -P.sub.3, defined as .DELTA.P.sub.2, and the force exerted on the plug 32 will be .DELTA.P.sub.2 .times.(cross-sectional area of plug 32).
In current practice the pressure differential is equalized simply by relying on leakage past the wireline 34, as indicated by the arrows 38 in FIG. 3, where there is not, as previously mentioned, a perfect seal. However, it can take considerable time for such equalization to occur, and P.sub.1 to equal P.sub.3, thus allowing the logging plug 32 to be withdrawn, withdrawal being effected by abutment with the tool 36 as shown in FIG. 3.
FIG. 4 illustrates the situation if it were attempted to run a logging tool through a by-pass system without isolation. As before the intake pressure of pump 22 is designated P.sub.2 and the discharge pressure P.sub.1, the pressure differential P.sub.1 -P.sub.2 being defined as .
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patent: 4307783 (1981-12-01), Lanmon, II
patent: 4392377 (1983-07-01), Rankin
patent: 4729429 (1988-03-01), Wittrisch
patent: 4804042 (1989-02-01), Knight et al.
Barcia Hugo M.
Schneider John L.
Dang Hoang C.
Reynolds Florence U.
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