Study On The Interaction Mechanism Between Deep-water Drilling Riser And Production Riser

When using the TLP or SPAR platform for deep water oil and gas production or drilling,the drilling riser and production risers are always placed in compacted arrangement because of the limited space.In this case,the interference between risers is obvious which will decrease the safe clearance and eventually imply a potential for collision between structures.The interference effect will be strongly enlarged by the increasing water depth,threatening the safety of platform,the normal drilling operation and the sustainable exploitation of offshore oil and gas.A new wake model is established by using Goldstein second-order approximation method to predict the wake velocity profile of upstream marine riser which is always in the region of critical or super-critical Reynolds number.As concluded in this thesis,there are some limilations when applied the traditional wake modes to marine riser analysis,such as they can not provide high accuracy results in the very near wake and near wake simultaneously,or some of them can not be used to calculate the lift loads,or some are hard to use beacause of their complex model coefficients.In contrast,the new wake model established in this paper is proved to be more accurate and stable,which broadens the application scope of theoretical wake models,and more inline with the actual application requirements on site.According to different working conditions of normal operation and riser installation,the corresponding static interference mechanical analysis model of deepwater drilling riser-production riser system is established respectively,and the iterative solution is carried out by using the finite difference method.The influence of some key factors like wake model,water depth,top tension coefficient,initial clearance,tial vurrent velocity,wind current velocity to the properties of static interference are systematically studied.The study results imply that ignoring the interference effect will erroneously overestimate the calculation results of the static deformation of downstream riser and increase the risk of collision;properly increasing the top tension and initial clearance can effectively reduce the interference effect;increasing the top tension and reducing the weight of the suspension can effectively widen the safety window for drilling riser installation operation.The two dimensional real size deepwater drilling riser and production riser(or four array production riser cluster)coupling vibration dynamic model is respectively established by the second development of CFD software which contains using the overset mesh technology and writing fluid-structure interaction(FSI)solution program through UDF window of Fl UENT platform.Some important conclusions are summarized by this thesis,for example,the interference effect will increase the vibration amplitude of the downstream riser,widen its frequency lock interval,and may also induce “secondary lock” phenomenon;the central driiling riser will be affected by the surrounding riser clusters at the same time,which make it behave differently compared with the isolated riser or the tandem arranged riser;the bottom row of the production risers is most affected by the interference effect,whose vibration amplitude are significantly expanded and they will enter the vibration lcok interval in advance.There are always some limitations of the traditional vibrating suppression technologies,for example,some of them will increase the drag force on the riser body,or some will make the riser body overloaded,or some are struggling with the costs.This thesis theoretically analyzes the application of the Nonlinear Energy Sinks(NES)technology to the riser interference vibrating suppression.Case study shows that the response vibration amplitude of drilling riser and production riser can both be significantly reduced by using small mass NES devices,the suppression effect is good.