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drag of the drill pipe in the hole, and the inertia of the drillstring itself. During

wire-line operations (such as logging or testing) there usually is not enough drag

and inertial force to cause the compensator to stroke. In these instances, the

additional force is provided by a sensing line. The sensing line is run over a sheave

hung from the hook and is connected to the drilling riser at one end, attached to the

derrick floor at the other end. Tension is then applied to the line by adjusting the
compensator system operating pressure. Wire-line operations may then be

performed, free from vessel heave (fig. 6.26).

Figure 6.25 – Motion compensator force diagram

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