| 摘要 |
A piston tractor system can include at least two piston assemblies which sealingly engage a wellbore, and a pump which transfers fluid between an annulus isolated between the piston assemblies, and another annulus. A method of operating a piston tractor system can include sealingly engaging at least two piston assemblies with a wellbore, grippingly engaging one piston assembly with the wellbore, and then pumping a fluid from an annulus formed between the piston assemblies, while the other piston assembly is secured to a tubular string, thereby biasing the tubular string to displace through the first piston assembly. A method of advancing a tubular string through a wellbore can include sealingly engaging piston assemblies with the wellbore, each of the piston assemblies including a gripping device which selectively grips the wellbore, and one piston assembly including another gripping device which selectively grips the tubular string.
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