Ship-based CO2 Injection into Subseabed Geological Formations Using a Flexible Riser Pipe Pickup System

Abstract

This report presents details of one aspect, namely, the flexible riser pipe pickup system, of a proposed ship-based carbon dioxide capture and storage (CCS) method. The liquefied CO2 (LCO2) to be sequestered is directly injected into subseabed geological formations through a flexible riser pipe using injection facilities contained onboard an LCO2 carrier ship. The flexible riser pipe remains on the seabed, one end attached to the injection wellhead, until the other end is hoisted up and connected to the (dynamic positioning system (DPS)-controlled) LCO2 carrier ship arriving at the ocean injection site. This proposed system has various advantages over the use of stationary sea surface structures for ship mooring and CO2 injection: i) no need for stationary sea surface structures, e.g., ship-mooring-buoy or platform; ii) simplifies ship handling, especially in rougher sea states; and iii) the flexible riser pipe can remain on the seabed in rough seas. Details of a pickup buoy system for retrieving the riser from the seabed and the structure of the flexible riser pipe are presented in this paper. The riser pickup system consists basically of shipboard equipment such as a coupling valve, crane, winches and A-frame and offshore equipment such as a pickup buoy, pickup float, messenger line, sinker and pickup wire rope. The flexible riser pipe, outer diameter of 309mm, was designed with due consideration of the stresses encountered with repeated retrievals from the seabed.