| CPC E21B 21/08 (2013.01) [E21B 21/106 (2013.01); E21B 33/085 (2013.01); E21B 19/16 (2013.01)] | 19 Claims |

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1. A tripping system for maintaining pressure in an annulus during axial movement of drilling pipe in a well, the system comprising:
a trip tank configure to store drilling fluid, wherein the drilling fluid flows from the annulus to the trip tank, wherein the drilling fluid flows from the trip tank to the annulus;
an active fluid system configured to store the drilling fluid, wherein the active fluid system is sized larger than the trip tank;
an upstream flow measurement device that measures flow of the drilling fluid from the trip tank to the annulus;
a downstream flow measurement device that measures flow of the drilling fluid from the annulus to the trip tank without measuring the flow of the drilling fluid to the active fluid system;
a back pressure device located downstream from the annulus, wherein the back pressure device opens and closes to adjust the pressure on the annulus.
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