Study On Application Technology Of CAN Type Wellhead For Marine Hydrate Trial Production

This paper is based on the major science projects of CNPC “Engineering basis and key technology of gas hydrate production test in sea area”-“Wellhead and sand control equipment and safety key technology for gas hydrate production test”(ZD2019-184-004)、National Key R&D Program “Marine Hydrate Drilling,Completion and Safety Monitoring Technology”(2016YFC0304005).According to the test production project of natural gas hydrate in China’s sea area,combined with the geological parameters of the overlying soil layer of hydrate in the South China Sea,the surface well construction technology of suction anchor in marine hydrate drilling and the stability of suction anchor wellhead system are systematically studied.Some progress has been made in the following aspects: penetration design method of CAN,loadbearing performance analysis method of CAN,vertical bearing capacity evaluation method of suction anchor wellhead system and load-bearing performance analysis method of suction anchor wellhead system,which can provide theoretical basis and technical support for surface well construction and wellhead technology of hydrate production test in South China Sea.The main research progress is summarized as follows:1.Study on design method of CAN penetration installationBased on the characteristics of overlying soil of hydrate deposits in the South China Sea,study the quantitative characterization of shallow soil parameters and self weight penetration depth of CAN,analyze the theoretical calculation method of negative pressure penetration resistance of CAN,put forward the prediction model of self weight penetration depth and negative pressure interval of suction anchor suitable for South China Sea soil conditions,establishe the prediction process of negative pressure interval of suction anchor in negative pressure penetration stage,and form the design method of suction anchor installation.2.Numerical analysis of underpressure penetration and bearing capacity of CANThe CAN underpressure penetration FEA model is established to calculate the required negative pressure at different penetration depths,verify the design method of CAN penetration installation,and check the structural strength under negative pressure;A CAN-soil coupling analysis model is established according to the cementing conditions of surface casing hanging at wellhead.The vertical and horizontal bearing capacity of CAN is analyzed to reveal the failure mode of foundation bearing,and the ultimate bearing capacity analysis method of CAN is formed.3.Load bearing capacity evaluation method of CAN type wellhead systemThe construction technology and operation process of CAN surface well construction are analyzed to determine the dangerous working conditions.Based on the vertical bearing capacity calculation method of suction anchor and surface casing,the vertical bearing capacity mechanical model of CAN type hydrate production test wellhead is established.Combined with the vertical load of wellhead,the function of vertical stability evaluation of CAN type wellhead system is proposed.Considering the spatial random characteristics of soil parameters and base on the interval model,the load bearing capacity evaluation method of CAN type wellhead is formed.4.Study on bearing characteristics of CAN type wellhead systemBased on the surface well construction technology of CAN,the wellbore structure of suction anchor type horizontal well is proposed.The CAN type wellhead system-soil coupling analysis model is established to evaluate the vertical stability of CAN type wellhead system under production conditions.The lateral stability of CAN type wellhead system is analyzed under different influence factors such as wellhead load,wellhead mud height and so on.At the same time,a conventional wellhead system model with the same size is established to quantitatively evaluate the improvement effect of lateral bearing capacity of CAN type wellhead system.