Rig Jacking on Soft Soil Foundations: Improvements in Safety and Speed by Monitoring Leg Loads

Abstract

The stability of jack-up rigs with spud-cans, particularly during the jacking-up and preloading operations, has always been critical in soft soil conditions. In the offshore areas opened to prospection in Cameroon, unconsolidated clays and silts are frequent, and therefore the need to conduct these critical operations with maximum safety is of utmost importance. The monitoring of soil reactions at the spud-cans and of structural loads at the jack-houses enabled jacking operations to be conducted safely, in an area where other rigs previously encountered severe difficulties (capsizing). Data recorded by instrumentation have shown that leg maneuvering with soil penetrations of up 40 m (131 ft) may induce dangerous overloads to the structure. The continuous monitoring and control of soil reaction forces and structural loads during drilling ensured the safety of the rig. For jacking-down, the monitoring of the loads was necesary to control the structural stresses induced by the legs pulling out. To the authors’ knowledge, no similar measurements have been reported in the past.