Plugs are usually used to close or seal lower portions of a wellbore. Such bridging or plugging operations are often employed, for example, to seal a lower portion of the well for a fracking operation, when a lower zone in the well has ceased to be productive, where the wellbore has been drilled into a porous formation, or for any other reason where it may be desired to plug or close-off a lower zone and produce from or pressurize a higher zone in the well. To close off a higher zone in a wellbore from a lower zone in a wellbore a plug is positioned in the wellbore at a point adjacent the top of the zone to be sealed.
Generally, the plug is set by applying a force in the front of the plug and a force on the rear of the plug that compresses the plug to force slips and elastomer into contact with the wellbore. A plug may be run into the well on the end of a tubular, wireline, tractor, or other means. Unfortunately, on occasion the plug will run into an obstruction within the wellbore. With weight on the rear of the plug and an obstruction preventing the front of the plug from moving further into the wellbore it was possible for a plug to become prematurely set within the wellbore.
In a current embodiment the plug the present invention allows for the plug to be connected to the surface by a center mandrel. The center mandrel is attached to the plug only at the front end of the plug and the front end of the mandrel. Generally, the center mandrel will be connected to the plug by shear device, preferably shear threads. By connecting the mandrel to the plug only at the nose of the plug the body of the plug is drawn into the well behind the nose so that should the plug encounter an obstruction within the wellbore force applied to the plug on its leading nose via the center mandrel is applied only to the nose of the plug in order to overcome the instruction and without applying a load to the rear of the plug which would otherwise cause the plug to prematurely set.
An additional feature of the present embodiment is that the rear of the plug the mandrel passes through a seat. The mandrel incorporates a shoulder that interfaces with the seat such that the shoulder interfacing with the seat at the rear of the plug and mandrel connected to the front of the plug allows the plug to be assembled so that the mandrel holds the various components of the plug together until the plug is set.
Upon setting the mandrel is generally removed from the plug on some instances the mandrel may be allowed to remain in place. In order to remove the mandrel from the plug additional force is applied to the mandrel in excess of the force that was required to set plug in the first instance. The additional force applied to the mandrel causes the shear device such as shear screws, shear pins, or shear threads to release allowing the mandrel to be removed from the plug.
With mandrel removed fluid may flow through the plug through the cavity created through the center bore the plug when the mandrel was removed. In some embodiments a chamber is provided through the interior of the plug adjacent to the mandrel. With the mandrel in place the chamber is isolated from fluid within the wellbore. However, with the mandrel removed the chamber is now in contact with fluid within the wellbore. The chamber may contain one or more chemicals. The chemicals may be markers, salts, biocides, paraffin inhibitors, or any other chemical that may be useful downhole. In a particular embodiment a salt may be provided to accelerate the degradation or dissolution of certain compounds. In other embodiments the chamber may be provided with an electronics package. Such an electronics package to be used to determine the pressure, temperature, salinity, oil/water ratio, or other downhole information.
In certain embodiments the seat provided at the rear of the plug may be utilized such that a ball, wiper, or other obturator may be allowed to seal upon the seat to prevent fluid flow from the surface through the plug.
The description that follows includes exemplary apparatus, methods, techniques, or instruction sequences that embody techniques of the inventive subject matter. However, it is understood that the described embodiments may be practiced without these specific details.
With the center mandrel 12 threaded into plug nose 20 and in position through the center through bore 15 in plug body 14 compartment 17 is isolated from wellbore fluid by O rings 19 and 21. Plug 10 is generally run into the wellbore attached to the tubular via socket 40 at the rear end 42 of center mandrel 12.
Plural instances may be provided for components, operations or structures described herein as a single instance. In general, structures and functionality presented as separate components in the exemplary configurations may be implemented as a combined structure or component. Similarly, structures and functionality presented as a single component may be implemented as separate components. These and other variations, modifications, additions, and improvements may fall within the scope of the inventive subject matter.
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Number | Date | Country | |
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20190323315 A1 | Oct 2019 | US |