Research On Dynamic Reliability Of Underwater Oil And Gas Production System

Underwater oil and gas production system is an important production system in offshore oil and gas exploitation.With the development of offshore oil and gas resources to deeper ocean,the requirement for underwater oil and gas production system is increasing.The underwater oil and gas production system in the marine environment is subject to extremely complex environmental loads.If it fails,it will bring huge economic losses to the entire oil and gas field enterprises,and may lead to great envi1onmental problems.Therefore,the reliability of underwater oil and gas production system is particularly important.Therefore,this paper takes the dynamic reliability analysis of-underwater oil and gas production system as the main research topic,and studies the dynamic reliability of underwater oil and gas production system from the perspective of flow and equipment respectively.Firstly,in order to study the dynamic reliability of underwater oil and gas production system,this paper briefly introduces the uncierwater oil and gas production system and its main equipment studied in this paper,and introduces the main location,main failure modes and failure mechanism of failure prone to occur in the flow path,and gives common failure modes of dynamic models.At the same time,the reliability data sources of this paper are given.Secondly,a simplified model of underwater oil and gas production system.i.e.wellbore-pipeline-riser model.is established under the assumption of ideal gas?using constant gas flow.liquid flow and reservoir pressure as boundary conditions.The six-state model in this paper is obtained by using the mass conservation laws of gas and liquid phases in tubing,pipeline and riser sections.The mass fraction and density of gas-liquid two-phase in the pipeline are calculated,and the friction pressure loss of the pipeline is calculated only considering the liquid phase.The average liquid mass fraction of the pipeline is calculated according to the inflow boundary conditions,thus the pipeline model is obtained.According to the ideal gas law,the pressure at the top of the riser is calculated,and the average liquid volume fraction and level in the riser are combined.The friction pressure loss in the riser is calculated by using the same friction coefficient as that in the pipeline with respect to the average mixing velocity and the average density of the mixture,thus the riser model in this paper is obtained.Assuming that the production from reservoir to well is linear,the friction in the well is calculated by combining the average volune fraction of the liquid in the well,the average surface velocity of the liquid and the sarnc triction coefficicnt in front.Pressure loss,thus the wellbore model in this paper is obtained.so far,the How model of the underwater production system in this paper is established.Finally,themodel is validated by OLGA simulation.Then,on the basis of the flow model of the underwater production system,the flow network model of the underwater production system with two wells input is established.The flow network model is established by using the nodes representing the pressure nodes in the network and the paths of representative wells,throttle valves and pipelines,and these nodes and paths are represented by different exponents.Through the constraints of mass conservation,inflow and outflow of flow,pressure drop and so on,the flow network model of the underwater production system is obtained.The network model of underwater production system was established by OLGA to validate the previous model,and the flow analysis was made according to the simulation results.Finally,because the internal reliability of the main production equipment of the underwater production system is not considered in the previous contents,the dynamic model of the main production equipment of the underwater production system is added on the basis of the flow model of the former underwater production system and the flow network model of the underwater production system,and the impact of the erosion and eorrosion of the valve is taken into account,the underwater production system is established.Mixed model of main production equipment.Finally,by using the failure probability,failure maintenance ability and service life of the pipeline network,the dynamic law of the failure probability of the pipeline network increases with the increase of flow rate,deereases with the increase of failure maintenance ability,and increases with the increase of service life is obtained,By summarizing and analyzing the variation law of failure probability,the necessary suggestions and opinions are provided for improving the reliability of underwater production system.