Deepwater drilling problems

Abstract

Several problems encountered in the deepwater makes it very difficult in terms of accessibility for drilling. In this work, the major problems in the deepwater are identified, and discussed from different perspectives. Discussion of the deepwater environment provides a good basis in determining how this environment contributes to deepwater problems and the extent of the problems encountered. Two major categories of problems in deepwater are considered. The first category is the problems associated with drilling facilities while the second are those associated with operations. The former includes: modular offshore drilling units (MODU), the risers and tension leg platforms; while the latter includes hydrate problems, loss of risers, cuttings transport in the annulus and well control problems. Possible solutions were recommended for some of these problems. The calculations and analysis in this work focused on deepwater problems due to riser loss, and this served as good basis to evaluate the integrity of the formation and that of the riser when riser mud loss due to riser disconnect is experienced in the deepwater. To achieve this, two parameters were defined and used: riser margin (in terms of pressure difference) for evaluation of formation integrity and critical sea water hydrostatic pressure for evaluation of riser integrity. The critical sea water hydrostatic pressure is equivalent to the collapse pressure of the riser, and its relationship with bust pressure of the riser was established under the deepwater condition. It is suggested that these values are compared with API pressure ratings for safe operating conditions in the deepwater.