Abstract: A drum unit for an intervention string for a well includes a drum with a radius for the intervention string, arranged in a structural frame and rotatable by a motor, the drum being arranged translating along a drum axis and driven by a translation motor, for controlled winding of the intervention string onto the drum relative to a first, fixed guide in the structural frame. A compensator includes a guide arch, the guide arch being displaceable in a direction orthogonal to the drum axis using a force device at the structural frame. The intervention string runs between the guide arch and the first fixed guide to or from a first end of the guide arch to the drum. The intervention string runs via a second, opposite end of the guide arch via a second, fixed guide at the structural frame, to or from the well.