Page 564 - Air and Gas Drilling Manual

11-2 Air and Gas Drilling Manual
rig development over the past three decades is the top head rotary drive. This is a
hydraulically actuated device. A prime mover on the rig floor operates a hydraulic
pump which pumps hydraulic fluid through hoses to a hydraulic motor (the reverse
of a pump). The hydraulic motor is the rotating element of the top head rotary drive
(see Chapter 1 for more discussion). The top head rotary drive is located on the drill
rig mast and moves up and down on the mast in a track attached to the mast. The
movement of the top head rotary drive can be actuated hydraulically or by a direct
mechanical device such as a chain drive mechanism. This development was first
introduced on small rotary drilling rigs that were capable of drilling only shallow
wells (see Figure 1-3 for a typical example). Since this introduction, the
hydraulically actuated rotary device technology has been adapted for use on many
new drilling rig designs that have greater depth directional capabilities.
Drill String and Casing Rotation Rigs
Figure 11-1 shows a typical dual rotary drilling rig. These very unique rotary
drilling rig designs utilize hydraulically actuated rotary drives that can rotate both
the drill pipe and the casing that is driven and advanced simultaneously with the
advance of the drill string. This innovation allows these drilling rigs to drill
shallow highly fractured, incompetent, unstable rock formations.

Figure 11-1: Dual rotary drilling rig used for shallow drilling (courtesy of Foremost
Industries Incorporated).