A Test Rig for Jetted Conductors in Soft Clays

Abstract

Abstract This paper describes the design, construction and operation of a test rig for jetted conductors in soft clays. The rig was designed to produce repeatable tests under controlled conditions to evaluate the influence of operational jetting procedures on the conductor performance just after installation and at different periods after installation (set-up effect), underdifferent loading conditions. The test drilling rig consists of two main parts: an isostatic supporting structure and a jetting bottom hole assembly (BHA). All parts were designed to emulate real operational conditions found in offshore drilling rigs on a more manageable scale. A 7" (177.8 mm)OD and 6 m long conductor was used for this purpose and a 3.5" (88.9 mm) commercial drilling motor was fitted inside it. The design was such that several combinations of values of bit stick-out and flow rate are easily obtained in the field. The test rig showed up as a powerful tool for geotechnical research in which the influence of some drilling parameters on the axial and lateral bearing capacity of the conductor, such as: bit stick-out, flow rate and set-up can be evaluated.