Patent Application
20070137865
The field of this invention is mechanisms that can trigger one or more downhole tools that employ a time delay from the point of actuation to allow coordination of operations downhole.
Downhole tools are delivered on strings to proper positions in the wellbore. In the case of packers an inner string is used to set the packer when the proper depth is reached. It is at times desirable to set downhole tools in a particular sequence. Bottom up has been a way to set a series of external casing packers on a casing string.
One type of actuating mechanism that has been used in the past is to take advantage of hydrostatic pressure available in the wellbore to set a downhole tool like a sliding sleeve or a packer, for example. These hydrostatically actuated mechanisms were still triggered by an inner string that shifted a sleeve, for example, to allow the hydrostatic pressure access to an actuating piston. An example of the prior design of such a triggering mechanism that was actuated by hydrostatic pressure is illustrated in
The reason for the valve 12 is to allow time for proper positioning of the downhole tool, such as a packer, before the hydrostatic pressure sets it. Since the exact trigger depth cannot be a certainty, the past designs have employed valves such as 12 in conjunction with an inner string to operate said valves when the proper placement was assured. However, running another string to set one or more downhole tools such as packers was time consuming and therefore expensive. Additionally, once the sliding sleeve that functioned as valve 12 was actuated, there was no delay and the downhole tool set immediately from hydrostatic pressure. The present invention provides a solution to the cost of the running of the inner string by a creating a delay incorporated into the prior trigger designs that allow time to ensure proper placement before the tool is set and yet removes the need for running an inner string or the like to initiate the setting sequence. Multiple mechanisms can be employed with different delay times built in to trigger devices in a particular order. These and other advantages of the present invention will be more apparent to those skilled in the art from a review of the description of the preferred embodiment, the drawings and the claims below, which define the scope of he invention.
A setting mechanism is made to respond to hydrostatic pressure. Upon reaching a predetermined depth corresponding to a given pressure, a pilot piston is shifted to allow well fluids to bypass a first set of piston seals and reach a second set. A shear pin that held the pilot piston in position is broken as the hydrostatic pressure increases with greater depth attained. However, the shifting of the pilot piston does not cause the main piston in the assembly to set the downhole tool. The action of the well fluids on the secondary seal set on the pilot piston eventually fail the second seal set allowing hydrostatic pressure to bypass them and actuate the main piston that will set the downhole tool. Raising the tool from the wellbore allows the spring acting on the pilot piston to seal in a bore to isolate hydrostatic pressure from the operating piston.
In the present invention the valve 12 of the prior art
At a certain depth the hydrostatic pressure in the well overcomes the spring 56 and the shear pin 52 to shift body 34 to the right, as shown in
Those skilled in the art will appreciate that spring 56 stays compressed after shear pin 52 is broken from hydrostatic pressure. During the time delay that is provided from the removal or disintegration of seals 40 from exposure to well fluids, an opportunity exists to raise the mandrel 10 in which case the hydrostatic force could be reduced to a point where spring 56 could be strong enough to shift the body 34 back to the
Alternatively, body 34 can just have seals 36 on it while seals 40 can be on an independent body or alternatively they can comprise a plug in the bore that leads to passage 14.
It is within the scope of the invention to sequentially set a variety of downhole devices using multiple assemblies with a different time constraint on how long it takes for seals 40 to stop functioning once exposed to well fluids. Independently or in conjunction with the disintegration time of seals 40 the strength of spring 56 and shear pin 52 can also be manipulated to obtain the required sequence of operating downhole tools or a series of packers or combinations of different tools such as packers and sliding sleeve valves, for example.
Those skilled in the art will appreciate that an inner string is not necessary using the present invention. This allows substantial savings in time and expense. Similarly, straddle tools are not needed as are commonly used to set external casing packers. Instead, a casing string, for example can simply be lowered into position and the casing packers can set in a preferred sequence, generally from bottom to top. Each packer, of course would have an assembly as depicted in the figures using the valve design discussed in detail with regard to
The device illustrated initiates the setting sequence on reaching a range of depth yet provides the ability to more precisely position the downhole tool before the trigger mechanism actuates it. Alternatively it offers the possibility of raising the device to prevent actuation during the delay period that starts automatically on getting to a certain depth. The device can be triggered by hydrostatic pressure or applied well pressure or combinations of both. With different delay times sequential tool actuation in a desired order can be achieved. The trigger actions required for the prior designs such as an inner string, dropping a ball on a seat, or pressuring the tubing or annulus is no longer required as the device can begin the setting sequence simply by going to a sufficient depth in the wellbore.
The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below.
