Note: Descriptions are shown in the official language in which they were submitted.
CA 02867463 2014-10-14
CATASTROPHIC HIT INDICATOR FOR CATCHER IN PLUNGER
GAS/FLUID LIFT SYSTEM FOR WELL OPERATIONS
BACKGROUND OF THE INVENTION
Producing oil and gas wells sometimes produce water as well as
hydrocarbons from formation. If the height of the produced water column in the
wellbore is sufficient, it will exert pressure on the formation which can
exceed the
formation's pressure, and thus inhibit further production. To overcome this,
the
water is sometimes removed from the well by a plunger lift system. A plunger
deployed in the well's bore drops to near bottom hole into the water column,
where it forms a piston between the formation's production pressure below and
the water above. Gas produced below the plunger forces it and the water above
it toward the surface, where the water can be removed and the pressure on the
formation from the water column can be reduced. This function is performed
cyclically, typically without intervention by the operator,
The plunger may develop quite a bit of velocity in its upward travel,
so in most plunger lift systems, a 'catcher' is deployed in the lubricator at
the top
of the well's casing above surface. These lubricator/catchers are used to seal
the
top of the well's bore from atmosphere so that produced hydrocarbons and water
can be collected from the casing below the catcher, and can provide both
access
to the wellbore, and a means for capturing the plunger at the upper end of its
stroke where it can be removed for inspection, repair or replacement.
The lubricator/catcher may be provided with a spring or shock
absorber system as well as a plunger-capture system, to protect the wellbore's
sealed top from damage from by a hard hit from the plunger. Hard hits by a
plunger can cause damage to the well's casing, surface equipment and/or the
plunger itself. Since the well is unattended in operation, generally, such
damage
may not be obvious or immediately apparent.
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SUMMARY' OF THE INVENTION
In this invention, a component is added to a typical lubricator which
includes a coil spring above a striker block, a piston above the striker
block, the
piston sealed but moveable within the bore of the lubricator, above the piston
another spring or set of spring washers, a space, and above the space a thin
membrane or wall in a top nut or seal at the top of the lubricator. If the
plunger
reaches the lubricator's top end with sufficient force, it will compress the
coil
spring and move the striker block to push the piston upward within the bore of
the
lubricator, the piston will compress the second spring or set of spring
washers,
and the top end of the piston, which is preferably pointed, will pierce the
membrane or wall in the top of the lubricator. The lubricator will remained
sealed
because the piston is sealed within the bore of the subassembly within the
lubricator, but the top nut or seal will be pierced, providing an obvious,
externally
observable, indication of the fact that at least one "heavy hit" has been made
by
the plunger to the lubricator and top-hole equipment. The spring compression
forces can be designed so that the indication provided is indicative of forces
which have exceeded a predetermined level of force. In this way, preventive or
repair maintenance can be done by the operator prior to the plunger system
failing due to absorption of too many heavy hits, or too much force from the
plunger. The types of failure that heavy hits from plungers can cause include
(but
are not limited to) stretching of threaded components which weakens their
strength and effectiveness as seals, or degradation of sealing elements.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a cutaway drawing of the striker block, coil spring and
piston/cylinder/cap of the invention.
Figure 2 is an exploded view of the striker block, coil spring, spring
housing, piston, Belleville disc springs, and cap of the invention
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Figure 3 is a cross-sectional view of a lubricator assembly showing
the placement of the subassembly of the invention at the top end of the
lubricator.
Figures 4a and 4b are, respectively, a side elevation and a cross-
sectional depiction of the elements shown in Figure 1.
A parts list with numerical indicators is also shown, which numerals
are indicated on each of the figures.
DETAILED DESCRIPTION
This invention provides a catastrophic or heavy-hit indicator
subassembly for a lubricator in a plunger-lift system for oil and gas
production
wells.
The lubricator shown in Fig.3 in its entirety, is provided with a heavy
hit indicator subassembly, shown in Fig. 1, to be assembled within a mating
cavity formed at the top of the lubricator, the cavity in communication with
the
bore of the lubricator and the well's bore, permitting a plunger of the lift
system to
enter the cavity if sufficient force is applied to the plunger in the lift
system.
In an embodiment, the subassembly comprises a striker block 5 at
the bottom end of a compression spring 8 which may be a coil spring, the
compression spring 8 surrounding a hit indicator spring housing 1. The housing
1 is surrounded by the upper end of the coil spring 8, and the housing 1
includes
in its inner part a cylinder la. The cylinder is open at its top and its
bottom ends.
The cylinder 1 has a bottom opening which is large enough to permit the lower
end of a piston 3 to pass through the opening, which may be sealed by
positioning an elastic o-ring 6 between the piston's lower end extention 3a
and
the housing 1 cylinder's bottom opening.
Midway along the piston 3 is a feature which provides a stop 3b,
above which the piston's upper end 3c continues as a smaller-diameter
cylinder,
on which a number of Belleville washer springs 4 are stacked. Above the
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washers 4:and surrounding the upper tip of the piston, which may be pointed, a
cap 2 is provided, attached with a seal 7 to the housing 1 at its upper end
(the
housing 1). The cap 2 is visible to an observer from outside of the lubricator
through a port in the upper portion of the lubricator assembly (#).
When a plunger of they lift system is forced with sufficient energy to
strike the lubricator and the heavy hit subassembly, the following will occur.
The plunger strikes the striker block 5, pushing it upward within the
lubricator, compressing coil spring 8 and moving a sufficient distance and
with
sufficient force, the striker block 5 will in turn strike the lower end of the
piston 3a
and force it upwards within the cylinder la to compress the Belleville spring
discs
4, and if sufficient force is supplied by the plunger to the subassembly, the
Belleville spring discs 4 will compress sufficiently that the pointed end of
the
piston 3c will pierce the indicator cap 3.
When the indicator cap 3 is pierced, it will be deformed such that an
observer from outside of the lubricator can see that there has been a heavy
hit,
and can determine that the lubricator and top-hole equipment may require
servicing or inspection.
The springs may be chosen to have characteristics such as a
particular designed force to compress, to tailor the subassembly to indicate
hits
of specific characteristics (such as minimum force required to deform the
cap).
In the preceding description, for purposes of explanation, numerous
details are set out in order to provide a thorough understanding of the
embodiments of the invention and how it is meant to work. However, it will be
apparent to one skilled in the art that these specific details are not
required in
order to practice the invention as claimed. The above descriptions are
intended
to be examples only. Alterations, modifications, and variations can be
effected to
the particular embodiments by those of skill in the art without departing from
the
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scope of the invention, which is defined by the claims of the patent flowing
from
the specification.
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