Pump-down pressure plug

Abstract

A pressure plug system comprising a pressure plug with a tapered section, a receiving landing receptacle having a tapered section with substantially the same tapering angle as tapered section of the pressure plug, and tapering angle being less than the friction angle corresponding to the coefficient of friction between the pressure plug and the landing receptacle. The pressure plug engages the receiving landing receptacle providing reliable seal and locking the plug against landing receptacle preventing axial movement under cycling pressure and rotation of the plug during drillout.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of the preferred embodiments of the invention, reference will now be made to the accompanying drawings in which:

FIG. 1 shows a typical prior art pump-down pressure plug.

FIG. 2 shows a cross-sectional view of a pressure plug in accordance with the present invention.

FIG. 3 shows a cross-sectional view of a pressure plug engaged in a landing receptacle in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2 shows main geometrical features of the pump-down pressure plug 20 according to the present invention. The pressure plug 20 comprises a nose section 10, having a forward end 12 and a rearward end 18. The plug 20 has a conical section of the length L which is tapered towards the front 12 under the tapering angle α. The plug 20 also comprises an optional cylindrical section 15 of a constant diameter D with a pair of external annular grooves in which are disposed a pair of seal rings such as O-rings 16. A pair of rubber cups 14 is disposed on the rod as shown and are abutted against the rearward side of the plug nose 18.

FIG. 3 shows the pressure plug system with the pressure plug 20 being engaged in the landing receptacle 30 having a tapered section 31 under the same angle α as the plug 20, and an optional cylindrical section 32 of a constant diameter. During normal operation the plug 20 is pumped down through the drill pipe until the plug is landed in the landing receptacle 30. Under the applied pressure P_t, a certain interference stress between the plug 20 and the landing receptacle 30 in the tapered section 31 is developed. Then, if the tapering angle α is substantially small, the plug will be locked in the landing receptacle, since it will be so firmly seated in the landing receptacle that there will be considerable frictional resistance to any force tending to remove or rotate the plug relative to the landing receptacle.

In general, in order to achieve locking of the plug in the landing receptacle, the tapering angle, α, should be less than the friction angle corresponding to the coefficient of friction between the plug and the landing receptacle. The friction angle, ρ, is related to the friction coefficient, μ, as:

μ=tan(ρ)

The maximum back pressure, P_b, see FIG. 3, which can be held by the pressure plug 20 after it has been engaged in the landing receptacle 30 by applied pressure P_t can be estimated as:

$P_b=\frac{\tan \left(\rho -a\right)}{\tan \left(\rho +a\right)}·P_t$

For example, if friction coefficient ρ=0.1 and pressure plug tapering angle α=1.5 degrees, the maximum back pressure P_b will be approximately 58% of the pressure P_t applied at the engagement of the pressure plug in the landing receptacle. It was found through experimentation and finite element modeling that pressure plugs with tapering angle α from approximately 0.5 to approximately 6 and preferably from 1 to 3 degrees are most useful.

The ratio of the length, L, to the diameter, D, of the tapered section of the pressure plug, see FIG. 2, should be selected based on the maximum expected pressure, P_t, the yield stresses of the pressure plug and the landing receptacle material, and on the geometry of the landing receptacle. It was found through experimentation and finite element modeling that pressure plugs with L/D ratios of approximately 1 to approximately 6 and preferably of 2 to 4 are most useful.

In this embodiment, pressure plug described above provides both resistance to back pressure and resistance to rotation of the plug relative to the landing receptacle, and creates a metal-to-metal seal between the plug and landing receptacle. However, in cases having the possibility of the tapered area of the plug to be scratched or damaged during pump-down deployment, it is desirable to provide another embodiment with a secondary sealing mechanism. This can be accommodated by incorporating an optional cylindrical section 32, see FIG. 3. The cylindrical section 15 of the plug includes grooves with elastomeric rings 16 adapted to sealingly engage in a cylindrical section of the landing receptacle.

One of the main advantages of the pressure plug system according to present invention compared to conventional pressure plugs is the lack of a slack movement upon cycling of pressure and thus the pressure plug system according to present invention provides a more reliable pressure seal. The other advantage of the pressure plug system according to present invention is its resistance to rotation of the pressure plug during drill-out operations without utilizing locking clutches. Thus, the latching of the plug is more reliable than the latching of conventional anti-rotational plugs.

It should be understood that a pressure plug according to present invention can be made of any suitable material, preferably easily drillable material such as, but not limited to, metal alloys, aluminum, brass, cupper, bronze, phenolic resins, polymeric materials, or reinforced plastics.

The foregoing description and drawings of the invention are explanatory and illustrative thereof, and various changes in sizes, shapes, materials, and arrangements of parts may be made within the scope of the appended claims without departing from the spirit of the invention.

Claims

1. A pressure plug system comprising: a pressure plug comprising a first tapered section with a first tapering angle;a landing receptacle comprising a second tapered section with a second tapering angle substantially equal to the first tapering angle of the first tapered section of the pressure plug;whereby the first tapered section of the pressure plug is adapted to engage in the second tapered section of the landing receptacle; andwhereby the first tapering angle of the pressure plug is less than a friction angle corresponding to a coefficient of friction between the first tapered section of the pressure plug and the second tapered section of the landing receptacle.

2. The pressure plug system of claim 1, wherein the tapering angle is in the range of substantially from 0.5 to 6 degrees.

3. The pressure plug system of claim 1, wherein the tapering angle is in the range of substantially from 1 to 3 degrees.

4. The pressure plug system of claim 1, wherein the ratio of the length to the diameter of the tapered section of the pressure plug is substantially from 1 to 6.

5. The pressure plug system of claim 1, wherein the ratio of the length to the diameter of the tapered section of the pressure plug is substantially from 2 to 4.

6. The pressure plug system of claim 1 comprising a cylindrical section of constant diameter, wherein the cylindrical section of the pressure plug having at least one groove with elastomeric ring adapted to sealingly engage in a cylindrical section of the landing receptacle.

7. The pressure plug system of claim 1 comprising at least one elastic cup extending outwardly and rearwardly.

8. A method of providing a pressure containment comprising: providing a pressure plug system comprising a pressure plug with a tapered section, a receiving landing receptacle having a tapered section with substantially the same tapering angle as said tapered section of the pressure plug, and said tapering angle being less than the friction angle corresponding to the coefficient of friction between the pressure plug and the landing receptacle;pumping said pressure plug down through the drill pipe and landing pressure plug in receiving landing receptacle;applying pressure not less than maximum expected back pressure.

9. The method of providing a pressure containment of claim 8, wherein said applied pressure is approximately twice higher that the expected maximum back pressure.