During workover of the slant holes, after the casing is removed out of the upper hole, hole collapse frequently occurs in the shale formation, causing stuck pipe and downhole tools, and impacting the normal workover operation.

The key factors in sidetracking well profile design are inter-well distance and well course.

The application of the off-angle drilling workover technique enabled the casing sheered wells, whose casing were damaged in formations of deep depth and were difficult to be repaired, resumed their production.

Performance and pressure distribution on blade of highly skewed propellers by using unsteady lifting surface theory;