HDD Borehole Pull-In Analysis of Offshore CCS Pipeline

Abstract

Abstract In recent years, with the increasing demand of reducing CO2 emissions, offshore pipeline found its new application in transporting CO2 offshore. Carbon capture and storage (CCS) is an effective method in the fight against climate change. This technology allows CO2 to be “captured” from large sources such as power plants and prevents release of greenhouse gas to the atmosphere. The captured CO2 has to be compressed and then transported to a safe and durable storage location, such as depleted subsea oil reservoirs. The captured CO2 is then locked away deeply under the sea floor so that it cannot escape into the atmosphere and contribute to global warming. To facilitate the connection between an offshore pipeline and an onshore plant, a robust landfall method must be adopted. The benefits of using horizontal direction drilling (HDD) for offshore pipeline landfall include longer durability, potentially lower project cost, less community and environmental disruption, and fewer authorization issues. In this paper, the analysis methods and the results of an HDD pull-in case study are presented. An analytical method for pull-in force is discussed first and then a global finite element (FE) model is developed. In the global model, a 10 km long pipeline is included. The pipeline, the pull wire and HDD borehole are simulated by using beam elements. The tube-to-tube elements are used to simulate the contact between the pipeline/wire and the borehole. The global model is used for both the pull-in and the hang-off analysis. To prevent corrosion of the pipeline in case of the coating damage, circular anodes are installed on the pipeline. In the HDD borehole, the anodes are installed for all the pipe joints. Since the anode pitch is small enough, the anodes are also used as centralisers during pull-in installation. To study of the effect of anodes on pull-in load, a local FE model is also developed. In the local model, a short pipe section and an anode with detailed geometry are included. The pipe and the HDD borehole are modelled using shell elements and the anode is modelled with solid elements. The additional pull-in load caused by the anode is predicted by using the local model. The loads acting on the hang-off structure in different phases are also obtained from the analysis, which are used as design input data for the hang-off structural design. The finite element analysis (FEA) results are compared with the results obtained from the simplified analytic calculation. It is concluded that the results obtained from the proposed FEA method are more accurate and more reliable than those from the simplified methods. In future, the proposed numerical analysis method can be used as reference or go-by for projects with HDD pull-in.