Analysis of information sources in references of the Wikipedia article "钻机" in Chinese language version.
By the time of the Song Dynasty, Chinese craftsmen had invented special tools for digging small-mouth-diameter wells
After the cementing of the casing has been completed, the drilling rig, equipment, and materials are removed from the drill site. A smaller rig, known as a workover rig or completion rig, is moved over the well bore. The smaller rig is used for the remaining completion operations.
By the time of the Song Dynasty, Chinese craftsmen had invented special tools for digging small-mouth-diameter wells
