A one-way milling teeth run in circle while cutting the cement column,so the drilling plug operation can be completed.

it is concluded that the technology of using two times of string to do it has much advantages,during drilling plug,are having less cement scraps and being reverse circulated making big drilling scraps to full down for their weights that provides a new solution to sweep cement dangling plug testing in big cased well for the future.

The oil layer reformation measure is frequent when the development of a field enters the mid-and-late part stage,meets drilling plug construction frequently.