| CPC E21B 34/10 (2013.01) [E21B 4/02 (2013.01)] | 17 Claims | 

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               1. A method for advancing a tubular conduit into a borehole of an oil and gas well, the method comprising: 
            advancing the tubular conduit into the borehole, wherein the tubular conduit includes a backpressure tool that comprises a vortex-controlled variable flow resistance device; 
                wherein the vortex-controlled variable flow resistance device defines at least one flow path comprising: 
                an inlet and an outlet; 
                  a jet chamber; 
                  first and second input channels diverging from the jet chamber; 
                  a vortex chamber with a central opening continuous with the outlet and having first and second inlet openings, wherein each of the first and second input channels defines a straight flow path from the jet chamber to the first and second inlet openings, respectively, of the vortex chamber, wherein the first and second inlet openings of the vortex chamber are positioned to direct fluid in opposite, tangential paths into the vortex chamber so that fluid entering the first input inlet opening produces a clockwise vortex and fluid entering the second inlet opening produces a counterclockwise vortex; 
                pumping a well fluid through the tubular conduit; and 
                operating the backpressure tool to reduce frictional engagement between the borehole and the tubular conduit. 
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