Numerical Analysis And Experimental Study On Deepwater Installation Of Offshore Oil And Gas Equipment

The exploration and development of global offshore oil and gas resources has expanded to the deep water and ultra-deep water areas.The installation technology of subsea equipment has become a key link for the development and construction of subsea production systems.The increase of equipment weight and installation water depth proposes new challenges for installation,load control,positioning and environment adapting.In the case of large subsea equipment installation,the cables or risers,installation vessels and equipment compose a coupled system.It will exhibit interactive influences and complex dynamic responses under the environmental loads.Therefore,it is of great significance to study the deep water installation to ensure the safety and low costs of the underwater installation.In this paper,numerical simulations and model tests are conducted to analyze the dynamic responses of installation system in two deep water installation methods selected for subsea oil and gas equipment,namely the drilling riser method and the pendulous installation method(PIM).A semi-submersible drilling platform and a drilling ship and an anchor handling tug supply vessel(AHTS)are selected as the installation vessels to carry out the research.For the high accuracy positioning problem of semi-submersible executing drilling riser method installation with thruster assisted mooring(TAM)system,based on the governing equations of horizontal three degrees-of-freedom(DOFs)motion for semi-submersible platform,a set point chasing control method considering mooring line structural reliability is proposed.In the deep water installation analysis with semi-submersible using TAM system,the set point chasing control method can improve the positioning accuracy and reduce the dynamic responses of mooring lines using the same control parameters,which can improve the safety of mooring lines.In order to study the motion of equipment,heave compensation effect and dynamic response of riser during installation of drilling riser method based on drilling vessel,a mathematical model of vessel/riser/equipment considering dynamic positioning and heave compensation is established,and coupled time-domain numerical analysis is carried out.The results show that in the numerical simulations the dynamic positioning system has effects on the vessel motion,riser tension and equipment motion.It is of practical significance to consider the dynamic positioning and heave compensation.Aiming at the problem of low efficiency in analyzing and calculating the influencing factors of dynamic response of installation system,a dynamic response analysis method of vessel/riser/equipment based on the neural network approximate model is proposed according to the design of experiment and RBF neural network.Under the premise of calculation accuracy,fast and effective analysis of the environmental influence on the heave compensation effect and installation system dynamic response is implemented.By establishing a numerical model of the PIM installation system with DP and heave compensation,the coupled time-domain analysis of the main stages of installation is carried out,and the falling motion of equipment,the shape and load of the installation cable and the vessel motion during the PIM installation are studied.According to the calculation results of ship motion,propeller thrust,cable motion and tension and trajectory and velocity of underwater equipment,the positioning process and compensation effect are analyzed,and the response rules of equipment pendulous motion and cable tension are obtained.On this basis,the influence of environment,equipment and layout on several dynamic response factors of cable and underwater equipment during the PIM installation is studied by sensitivity analysis.To study the equipment motion and installation cable tension,a model test is carried out for PIM installation.By analyzing the equipment motion characteristics in various depths using PIM,the feasibility of simulating equipment motion in actual installation depth based on equipment motion results from relative shallower depth is verified.The model test and concomitant numerical simulation are conducted under the limits of scaling factor and experiment hardware.By comparing the results,the accuracy of the numerical model is verified,which lays a foundation for further research on the process of the PIM installations.In order to study the difference and correlation between the basin test results in the case of limited water depth and the actual deepwater equipment movement,the functional relationship between environmental parameters,initial layout and the dynamic response of underwater equipment and installation cables is established by training RBF neural network.Main control points of the movement or force curve are predicted.The equivalent prediction results of the movement of the actual water depth equipment and the dynamic tension of the installation cable are obtained by the non-linear transformation.The accuracy of the method is verified by comparing with the full-scale model test results in the literature.Finally,the problem that the basin depth restricts the PIM model test is solved.