Long-term axial capacity of deepwater jetted piles

Jetting is a technique commonly used to install well conductors, which is faster than the conventional drill and cement method. Conductors are designed to support the buoyed weight of the first string of casings (typically, 3–5 days after jetting) and later to provide the lateral stability for the well system against cyclic loading from environmental elements. The axial bearing capacity of a jetted conductor increases with time due to consolidation and thixotropy effects; however, the field data for set-up only extend to about 10 days. Installation of jetted conductors as piles and anchors may be an economic solution for offshore developments. The long-term axial capacity of jetted conductors was investigated through a series of centrifuge modelling and laboratory thixotropy testing. The centrifuge tests simulated jetting installation of four model conductors and measured capacities at set-up times ranging between 10 and 1000 days in a kaolin clay seabed with an undrained shear strength profile similar to that encountered in deepwater Gulf of Mexico. The centrifuge test results were compared to the field data in the Gulf of Mexico. The implications of the centrifuge test results for deepwater Gulf of Mexico conditions are discussed. A method is presented for estimating the long-term axial capacity of jetted conductors in Gulf of Mexico seabed conditions with recommendations for additional studies.