Study On The Hydraulics And Technology Of Lifting Cuttings In Riser Of Deepwater Drilling

During the deepwater drilling, the lifting rate of the mud would decrease obviously when the mud flowing from casing annulus to riser annulus which cross section area is larger than the former's,that decrease can result with failure to satisfied the requirement of deepwater drilling.After research and analyze the technology of mud-lift home and abroad,and research the theories of cutting movement relate to straight well and riser, we develop two new process to resolve the problems of lifting cuttings in riser,one is the flowing mud into riser from booster for Improve the efficiency of lifting cuttings.the other is inject mud into riser from the subsea mud pump.Both the two process can improve capacity in riser and ensure that remain the original mud circulation system basically unchanged,to improve the up hole velocity in riser for satisfy the request of lifting cuttings.Five rectrained conditions for lifting cuttings of big diameter riser in deepwater drilling was advanced by analyses, the operation and computation technics process of lifting cuttings in big diameter riser in deepwater drilling was workout in allusion to the above two assistant lifting cuttings methods. And base on the consideration of wellbore stability, shaft safety and some other factors, the criteria turn on the booster pump or not was presented. The computation method of displacement and some other parameters of subsea mud pump was advanced and the relevant computation software was compiled to satisfy the request of lifting cuttings.The result from the calculation software was used to bring the preparation of lifting cuttings' parameters optimization results showed that: Mud density and viscosity increase are conducive to improving the efficiency of carrying rocks in riser, mud density increased at the same time improve the bottom-hole pressure; cuttings smaller diameter, the more cuttings there is in favor of the lifting cuttings. Larger diameter riser generally require booster line (subsea mud pump) to support lifting cuttings.