Tool driving or impacting – Impacting devices – Selective axial direction of impact
Patent
1996-05-17
1998-09-08
Smith, Scott A.
Tool driving or impacting
Impacting devices
Selective axial direction of impact
173137, 173212, 175296, E21B 414
Patent
active
058031820
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a double-acting hydraulic striking tool, especially for use with fishing operations within oil wells.
BACKGROUND OF THE INVENTION
When drilling for oil and gas and with maintenance of production wells, there is a need for picking up objects which either are mounted downhole or which unintentinally have fallen into the well, and a large number of tools for use in socalled fishing operations have been developed. It is sometimes necessary to be capable of loosening objects which have got stuck within the well, and a plurality of tools and methods have been known in order to supply impacts in order to loosen or crush a stuck object. In many cases, it is necessary to be capable of supplying upwardly directed impacts to the object stuck, and, since the access always is from above, it is necessary to fix a grip in the object in order to obtain the purpose.
Gradually, it has become usual to use hydraulic striking tools mounted at the end of a coil pipe and lowered into the well toward the object stuck. Energy is supplied in that liquid is pumped through the striking tool, often such that the liquid circulates in the well. From U.S. Pat. No. 4,462,471 a hydraulic double-acting striking tool is known, giving downwardly directed impacts when subjected to axial pressure load and upwardly directed impacts when subjected to axial tensile load. Thus, the direction of impact may be changed when raising and lowering the coil pipe, at the end thereof the striking'tool is suspended. Striking effect is achieved in that a moving impact mass which is resiliently suspended within the striking tool, is put into oscillations by the flowing liquid and strikes against a part of the tool which is attached to the object to which impacts are to be supplied. A disadvantage of the striking tool known from U.S. Pat. No. 4,462,471 is that the strength of impact can not be adjusted. Another disadvantage is that the striking effect can not be neutralized without stopping the circulation of liquid.
OBJECTS OF THE INVENTION
An object of the invention is to provide a double-acting hydraulic striking tool wherein the striking strength can be adjusted. Further, it is an object that the the direction of striking is easily reversible, and that the striking effect is neutralizable without reducing or stopping the circulation of liquid.
The objects are achieved through features as defined in the following claims.
SUMMARY OF THE INVENTION
The invention's mode of operation is described in the following. The striking effect is obtained in that a movable mass first is accelerated with a force from a tensioned spring and then impinges against a rest. The mass is assigned a piston adapted to be opened and closed in order to let liquid pumped through a supply pipe, respectively pass freely or drive the piston forwardly. When the piston is closed, the piston is moved by the liquid flow, and the spring is tensioned. Thereafter, when the piston opens the through-flow, the spring is released and, upon its return towards the initial position thereof, accelerates the movable mass and the piston returns to initial position. A new sequence starts when the piston again closes through-flow of liquid.
The invention comprises two independent pistons each assigned its moving mass, of which the first piston is adapted to tension the spring in the same direction as the liquid flows, the second piston being adapted to tension the spring in the opposite direction. By letting the first piston be open and then, alternately, opening and closing the second piston, a hammering effect is achieved. The direction of striking can be reversed by letting second piston be open and then, alternately, opening and closing the first piston. By letting both pistons be open, the striking effect is neutralized.
Available impact energy depends on how much the spring is tensioned, and this is determined through the stroke of the pistons, i.e. the distance from the position where a piston closes the through-flow of liquid to the position
REFERENCES:
patent: 3361220 (1968-01-01), Brown
patent: 4462471 (1984-07-01), Hipp
patent: 5025868 (1991-06-01), Wentworth et al.
patent: 5148878 (1992-09-01), Schmidt et al.
patent: 5172771 (1992-12-01), Wilson
Frommer William S.
Gefro Oilfield Services
Smith Scott A.
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