Preparing for LNG Production
Once a successful well has been drilled and commercial quantities of natural gas have been confirmed through appraisal activities, the development phase can begin. Development generally includes preparing wells for production. Because the natural gas found in Mozambique’s Offshore Area 1 is approximately 40 kilometers offshore and in water depths of approximately 1,600 meters, specially engineered equipment is required to produce, gather, process and transport the natural gas to the onshore facilities for processing.
The well is “completed” by lowering a steel pipe, called casing, into the drilled hole and cementing it in place. Next, the pipe is perforated in the targeted zone in order to establish a flow path with the natural gas-bearing rock. A second steel pipe called tubing is lowered in the well that enables the natural gas to flow a distance of 2,500 meters to the seabed.
At the seabed, the natural gas is gathered into subsea manifold systems from multiple wells. From this point, the natural gas enters a pipeline for transportation to the onshore LNG facility. The underwater systems are designed with subsea controls to regulate flow from the wells and provide a safe, reliable means for shutdown.
Processing & Liquefaction
The onshore Mozambique LNG facility will receive, pre-treat and liquefy the natural gas. During pre-treatment, the natural gas will flow through a series of pipes and vessels designed to remove water and hydrocarbon liquids along with any impurities to ensure high-quality natural gas.
After the natural gas is treated and conditioned, the gas stream is routed to a liquefaction ‘train’ where it will undergo multiple stages of refrigeration. Cooling the gas to approximately -160°C, the gas condenses into a clear, colorless and non-toxic liquid. The liquefaction process reduces the volume of the gas by 600 times, making storage and transportation easier.
Once liquefied, the LNG is delivered into large, specially designed, sealed, non-pressurized tanks where it is stored, at -160⁰C, until it is ready to be shipped. All tanks for the Mozambique LNG project will be of full-containment design based on industry specification standards. Full-containment tanks typically feature a primary liquid containment, open-top inner tank and a pre-stressed concrete outer tank. The primary tank is constructed of 9% nickel steel, which provides excellent strength and toughness at cryogenic temperatures.
The outer concrete tank shell provides primary vapor containment and secondary liquid containment. As a back-up source of containment, the outer tank will contain the liquid and also provide for a safe, controlled release of the vapor, if necessary.
Storage facilities are equipped with advanced safety systems to monitor pressures and provide early detection of potential issues and rapidly activate emergency shutdown if warranted.
The LNG will then be delivered from specially designed storage tanks through insulated pipelines to a nearby jetty for loading into purpose-built LNG ships.
LNG Shipping / Transport
From the storage tanks, LNG will be transported through insulated pipelines to a nearby export jetty where it will be loaded into purpose-built LNG vessels.
LNG ships come in various sizes, shapes and designs. There is no “one size fits all.” Ship size is optimized project-by-project. One of the key features of the specially designed, double-hulled vessels is their insulated containment tanks that maintain the LNG in a liquid state for sea voyages to markets and consumers around the world.
Once the LNG is loaded onto a LNG ship, the vessel maintains the LNG in liquid state for delivery to markets around the world. The LNG ship essentially acts as the “pipeline” for delivery to other markets around the globe.
One-way voyage times from Mozambique to terminals in northern India might take 7 days, whereas a LNG cargo delivery to certain Japanese markets would be approximately 17 days in duration. When the LNG ship reaches its final destination, the LNG is offloaded at the buyer’s re-gasification terminal. The LNG is transferred into storage tanks and then undergoes vaporization, a process that heats the LNG to convert it back into natural gas. The clean-burning natural gas is then delivered to the intended end-users for energy supplies.
When the LNG reaches its intended market, the liquid is re-gasified into a clean-burning and environmentally preferred energy choice.