Whether the hole is in safe state is quite essential in the construction technology of trenchless directional horizontal hole. Many consequences caused by hole wall instability will seriously affect the normal construction of trenchless engineering. It is proved by theory and practice that when the underground excavation passes through the natural cracks in the stratum, the instability issue of the hole wall is serious. It is necessary to select mud with appropriate density to inject into the hole for auxiliary drilling, so as to ensure that no collapse or slurry leakage happens within the hole. In this paper, aiming at the trajectory optimization of trenchless horizontal well in fractured formation, a mechanical model is built, and the optimal drilling direction of horizontal well under specific working conditions is given with the help of programming calculation.
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