Geometrical instruments – Indicator of direction of force traversing natural media – Borehole direction or inclination
Reexamination Certificate
1998-12-02
2001-09-18
Gutierrez, Diego (Department: 2859)
Geometrical instruments
Indicator of direction of force traversing natural media
Borehole direction or inclination
Reexamination Certificate
active
06289596
ABSTRACT:
This invention relates to a downhole tool, and in particular but not exclusively to a drift indicator for use in measuring the deviation from the vertical of a drilled hole. The invention also relates to elements of such a downhole tool, and to an arrangement for mounting a pivotable member, and to a biassing arrangement.
Drift indicators are utilised to facilitate drilling operations by providing surface recordings of hole deviation. The tool is generally located in the drill string adjacent the drill bit. One of the most widely used drift indicators currently available is the Teledrift (Trade Mark) tool as supplied by Dies Downhole Drilling Inc, of Oklahoma City, Okla. The tool is provided with a pendulum that moves along a series of graduated stop shoulders within a fluid reservoir, and a signalling plunger that traverses a series of seven annular restrictions to produce pressure pulses in the mud stream. The plunger is biassed upwardly by a spring within the fluid reservoir but during normal drilling operations is pushed to a lower position by the flow of drilling mud over the head of the plunger.
To measure the hole deviation, or drift, the bit is pulled off bottom, rotation of the string is stopped and the mud pump is stopped. The plunger, under the influence of the spring, rises, passing one or more annular restrictions and lifting the pendulum, until the pendulum engages one of the stop shoulders; the smaller the degree of drift, the further the pendulum will travel without engaging a shoulder. If the mud pumps are started once more, the plunger is pushed downwardly past the annular restrictions. As the plunger passes each restriction there is an increase in mud pressure above the plunger and this is detected at the surface, in the form of a mud pressure pulse, the number of pulses indicating the degree of drift; typically, each pulse represents a 0.5 degree deviation from the vertical. The pulses are produced at 10-30 second intervals, and the first pulse usually appears within 10 to 15 seconds of starting the pump.
The mud pressure is measured at a surface chart recorder which is linked to a surface mud line via a is diaphragm and oil-filled hose. The drill operator determines the degree of drift by examining the print-out from the chart recorder, counting the number of pulses detected, and correlating the pulse count with a set of tables supplied with the tool.
It is among the objectives of the embodiments of the present invention to provide improved downhole tools, and also an improved drift indicator.
According to the present invention there is provided a mounting arrangement for a pivotable member, the arrangement comprising first and second members defining respective normally spaced apart first and second surfaces, and a pivot connection between the members including a pivot member connecting the members, the arrangement being such that on the pivot connection being subject to a predetermined load the first and second surfaces engage to limit the load experienced by the pivot member.
In use, the arrangement permits provision of a sensitive pivot connection which does not have to be constructed to withstand high loads which the first and second members may experience. The arrangement may be incorporated in a downhole drift indicator, wherein the first member is a plunger and the second member a pendulum.
Preferably, the pivot connection permits pivoting of the second member relative to the first member, the pivot member defining a pivot surface for supporting the second member. The pivot surface may be of relatively small area, for example a point or line, as the surface will not be subject to high loads and the corresponding force concentration that would result.
Preferably also, the pivot member is linked to the first member via a resilient deformable mounting which deforms under said predetermined load to allow the second member to move relative to the first member and the first and second surfaces to engage. Most preferably, the pivot member is spring mounted.
According to another aspect of the present invention there is provided a downhole drift indicator comprising:
a housing for location in a drill string and defining a passage for drilling fluid;
a restriction body defining a series of flow restrictions in the passage;
a restriction member for cooperating with the flow restrictions to define a restricted flow area when located adjacent a flow restriction, said restriction member being moveable in one direction relative to the housing under the influence of the flow of drilling fluid through the passage, towards a first position;.
return means for biassing the restriction member in the other direction, towards a second position; and
a drift responsive member being moveable relative to the housing and pivotally connected to the restriction member, the pivot connection including a pivot member connecting the restriction member and the drift responsive member, the arrangement being such that on the pivot connection being subject to a predetermined load surfaces of the restriction member and drift responsive member engage to limit the load experienced by the pivot member,
the degree of movement of said drift responsive member in said other direction from a respective first position being related to the inclination of the housing, the arrangement being such that, in use, reducing the flow of drilling fluid through the passage results in movement of said restriction member in said other direction from said first position until arrested by the drift responsive member, and restarting the flow of fluid resulting in movement of said restriction member from the arrested position towards said first position, the reduction in flow area resulting as the restriction member passes each flow restriction producing a pressure pulse in the drilling fluid, which pulse is detectable at the surface, the number of pulses indicating the degree of drift.
Preferably, the restriction member cooperates with the flow restrictions to define a minimal flow area when located adjacent a flow restriction such that, in use, the magnitude of the pulses is such that the pulses may be counted by the operator simply by monitoring an existing drilling fluid pressure gauge at the surface. This obviates the requirement to provide pressure sensors and chart printers, considerably simplifying the monitoring of drift of a hole being drilled.
Preferably also, the flow area defined between the restriction member and an adjacent restriction is no more than 60% of the flow area when the restriction member is spaced from a restriction. Most preferably, the restricted flow area is around 40% of the flow area between pulses.
Preferably also, the drift responsive member is adapted to engage a selected one of a series of graduated engagement members defined by the housing. The engagement members may be in the form of annular or part-annular teeth, and the pivotally mounted drift responsive member may be a pendulum. The pendulum is preferably located within a fluid reservoir, isolated from the drilling fluid. To permit pressure equalisation, to accommodate movement of the restriction member, the reservoir preferably includes a moveable wall, most preferably in the form of a floating piston.
To allow the pulses produced on movement of the restriction member to be more easily detected, it is preferable that damping means is provided for damping the movement of the restriction member and the drift responsive member. Preferably, the damping means only permits movement of the restriction member once a predetermined fluid pressure force is exerted on the restriction member. The damping arrangement may include valve means for limiting fluid flow between parts of the fluid reservoir and such a damping arrangement preferably includes a coiled tube and may also include a check valve.
Preferably also, the return means acts on the restriction member via the fluid reservoir. Most preferably, the return means acts against the floating piston. The return means preferably maintains the fluid reservoir under pressure.
Accordi
Anderson Charles Abernethy
Eddison Alan Martyn
Alston & Bird LLP
Andergauge Limited
Gutierrez Diego
Verbitsky Gail
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