Current methods of determining conductor setting depths are described. These are based on the assumption that existing overburden pressures develop the capability of the foundation to resist hydraulic fracturing. This leads to conservative results and consequently higher installation costs. In an attempt to reduce this conservatism, packer tests have been performed offshore in the St. Joseph field off the coast of Sabah in heavily over-consolidated clays, in order to measure the hydraulic fracture characteristics directly. This paper describes these tests, the equipment used and discusses the results, both in terms of recommendations for a reduction in the site specific conductor setting depths and by comparing them to existing hydraulic fracture theories. Following these tests, conductors at a nearby platform in the St. Joseph field, founded on an essentially similar clay, were installed at reduced depths in line with the recommendations from the packer test results. Conductor installation time was reduced by approximately seven days of jack-up rig time. Proposals for further work are given.
Conductors are required in the drilling of oil and gas wells to prevent the upper portion of the hole from caving in and water from entering and mud from leaving the hole. Offshore, they also protect the well casings from environmental loads. Typically they are 660mm to 762mm in diameter and, from a geotechnical point of view, the minimum setting depth below mudline should satisfy the following requirements: a) The conductor should have sufficient axial bearing capacity, derived from external frictional resistance alone, to transfer self weight and all external vertical loads on the conductor (e. g. blow-out preventors, initial casing hung off) to the soil.
