Offshore natural gas hydrate harvesting system

Abstract

The purpose of this project is to design a system that will allow for production of methane gas from a deep-sea Methane Hydrate Harvester. A satellite host system was chosen in a feasibility report, released in September of 2011, where several concepts were economically and technically evaluated. The satellite host system is comprised of four subsea harvesters that will be deployed to search for and harvest the ocean’s naturally occurring thermogenic methane hydrates. The system will be located in the Gulf of Mexico where there is an active source of methane available for formation and accumulation of hydrates. The focus of the project was the design and stress analysis of the subsea riser, harvesters, and subsea manifold. Each harvester will travel above the seafloor where the top 6 inches of seafloor will be fluidized with warm water jets. Fluidization will allow for the dissociation of methane from the natural hydrate formations. The riser will provide a conduit from the harvesting units to the topside processing and storage vessel, modeled after currently available CNG FPSO hull configuration. The process is modeled after a patented process authored by Dr. Ken Hall (Texas A&M) and Todd Willman (National Thermodynamic Laboratory). Use of time domain, frequency domain, static, and quasi-static, finite element modeling, as well as, time domain hydrodynamic panel diffraction modeling was conducted to design the system components. Ship to shore transport was also analyzed using Freeport’s LNG facility as a delivery point.