Vertical Stabilization of the Drill

The seabed clamp can also serve as a reentry base (Zuidberg, 1979). In the rare case that a drill bit is worn or tools have been lost downhole and cannot be fished out of the drill string, the drill string can be pulled back for inspection and, subsequently, along the guidelines of the seabed clamp, a new drill string can be inserted into the same hole. 

The last method of heave compensation, the downhole anchor (Zuidberg and Windle, 1980) or inflatable packer, is now rarely used to stabilize the drill string because seabed clamps came into general use several years ago. 

Typically, 15-20 min is required to take a sample or perform a test using modern carrier tool equipment. This time includes both lowering and retrieving the carrier tool. 

5 Samplers Operated in Motion-Uncompensated Drill String 

Several investigators have quantified the effects offshore wireline percussion sampling has on shear strength and other soil properties. For example, Emrich (1971) compared shear 

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