| CPC E21B 33/12 (2013.01) [E21B 34/06 (2013.01)] | 35 Claims |

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1. A wellbore plug for use in the bore of an oil and gas well, where the wellbore plug comprises:
a bore;
a first stop in the bore of the wellbore plug;
a second stop in the bore of the wellbore plug;
a sealing element surrounding the bore of the wellbore plug and positioned entirely between the first stop and the second stop such that there is no overlap between the sealing element and the first stop and the second stop, whereby the sealing element prevents contents in the bore of the oil and gas well from traveling between the sealing element and a wall of the bore of the oil and gas well when the wellbore plug is mounted in the bore of the oil and gas well; and
a shuttle valve mounted in the bore of the wellbore plug to travel between the first stop and the second stop, whereby the shuttle valve is stopped by the first stop when pressure in the bore of the wellbore plug below the shuttle valve is greater than pressure in the bore of the wellbore plug above the shuttle valve, and whereby the shuttle valve is stopped by the second stop when pressure in the bore of the wellbore plug above the shuttle valve is greater than pressure in the bore of the wellbore plug below the shuttle valve.
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