FIELD

The embodiments described herein relate to the collection of natural gas for transportation from remote reserves and, more particularly, to systems and methods that utilize modularized storage and process equipment configured for floating service vessels, platforms, and transport vessels to yield a total solution to the specific needs of a supply chain, enabling rapid economic development of remote reserves to be realized by a means not afforded by liquid natural gas (LNG) or compressed natural gas (CNG) systems, in particular reserves of a size deemed “stranded” or “remote” by the natural gas industry.

BACKGROUND INFORMATION

Natural gas is primarily moved by pipelines on land. Where it is impractical or prohibitively expensive to move the product by pipeline, LNG shipping systems have provided a solution above a certain threshold of reserve size. With the increasingly expensive implementation of LNG systems being answered by economies of scale of larger and larger facilities, the industry has moved away from a capability to service the smaller and most abundant reserves. Many of these reserves are remotely located and have not been economic to exploit using LNG systems. A backlash of land based environmental and safety issues in recent years has also led to counter innovations in floating LNG (FLNG) production facilities, and on board deepwater re-gasification and offloading processing trains and storage being fitted to some vessels—all at additional capital cost. Finding savings from simplification of the LNG transportation/processing cycle by turning to related pressurized LNG (PLNG) technology also has yet to materialize in the industry.

For LNG systems40as shown inFIG. 2, the raw natural gas stream from the gas field12enters a LNG production plant42where it is first necessary to pre-treat the natural gas stream to remove impurities such as CO2, H2S and other sulfur compounds, Nitrogen and water. By removing these impurities, solids cannot be formed as the gas is refrigerated. Thereafter, the heavier ends, being C2+ hydrocarbons, are removed under cryogenic conditions of −265 F and atmospheric pressure. The resulting LNG is made up of mostly (at least 90%) methane, while the C2+ and NGLs require a separate handling and transportation system. LNG production plants42require high upfront capital in the order of billions of dollars for commercial scale operations, and are for the most part land based. These plants also require cryogenic temperature storage facilities43from where the LNG is pumped on board LNG carriers44arriving at adjacent docking points.

The LNG carriers44are specially constructed cryogenic gas carriers that transport17the liquid natural gas product at a density of 600 times that of natural gas at atmospheric conditions. A fleet shuttle service of LNG carriers44is run to LNG receiving and processing terminals46at the market end of the sea route, which typically require cryogenic temperature storage facilities45. These terminals46receive the LNG, store and reheat it to atmospheric temperatures prior to compressing and cooling47it to the entry pressure of the transmission pipelines26and then injecting48the natural gas into the transmission pipelines26that deliver natural gas to market.

Recent work by the industry seeks to improve delivery capabilities by introducing floating LNG liquefaction plants and storage at the gas field and installing on board regasification equipment on LNG carriers for offloading gas offshore to nearby market locations that have opposed land based LNG receiving and processing terminals. To further reduce energy consumption by simplification of process needs, the use of pressurized LNG (PLNG) is once again under review by the industry for improvement of economics in an era of steeply rising costs for the LNG industry as a whole.

The advent of CNG transportation systems, to cater to the needs of a world market of increasing demand, has led to many proposals in the past decade. However, during this same time period there has only been one small system placed into full commercial service on a meaningful scale. CNG systems inherently battle design codes that regulate wall thicknesses of their containment systems with respect to operating pressures. The higher the pressure, the better the density of the stored gas with diminishing returns—however, the limitations of “mass of gas-to-mass of containment material” have forced the industry to look in other directions for economic improvements on the capital tied up in CNG containment and process equipment.

Work discussed in U.S. Pat. No. 6,655,155 (Bishop) is an example of the direction sought to improve cargo (gas) mass-to-containment mass ratio. In Bishop, increasing pressure is recognized as having limitations and the concepts of decreasing temperature and moving the gas into a dense phase state (as described in prior art by others) while avoiding the liquid phase of the gas is suggested by Bishop to be beneficial.

For CNG systems50, as shown inFIG. 3, a less stringent processing system, again seeking better economics, is typically used to primarily remove water, CO2and H2S (when present) from the raw gas received from the gas field12to yield streams of a pipeline quality natural gas and marketable natural gas liquids (NGLs). On leaving the processing plant, the natural gas stream is compressed and cooled/chilled53before being loaded on board a CNG vessel54. Various modes of loading CNG into containment vessels or tanks, including the use of displacement fluids, are typically employed. Bishop suggests pure glycol or methanol as suitable displacement fluids according to temperature needs.

During marine transportation17of the CNG, the CNG containment tanks aboard the CNG transport vessel54typically operate at temperatures as low as −30 F and at pressures from 1400 psig to 3600 psig. (Packaging of small amounts of natural gas for vehicle fuel resorts to pressures in the region of 10,000 psig to attain practical storage volumes). In general, designs proposed for commercial bulk transport are intended to carry the product at densities from 200 to 250 times the densities of the gas at atmospheric conditions. Under conditions of low temperature and high pressure a density approaching 300 times the atmospheric value is possible with accompanying higher energy requirements for compression and cooling, along with the requirement of even thicker walls for the containment vessels.

Unloading the CNG at receiving terminals requires a variety of solutions to ensure the product is completely evacuated or transferred from the containment vessels. These evacuation solutions range from the elegant use of displacement fluids57, with or without pigging, to equilibrium blow-down56, and to using energy consuming suction compressors55for final evacuation. Heat (along with NGL extraction58if required) has to be added to compensate for initial expansion cooling of the natural gas, and compression cooling59is then provided for injection24into the transmission pipelines26or storage vessels25if required.

Yet, the improved cargo density of CNG returns described in Bishop still do not meet those attainable with the combination of lower process energy for a liquid state storage method as outlined in U.S. Published Patent Application No. 2006/0042273 for a methodology to both create and store a liquid phase mix of natural gas and light hydrocarbon solvent, which is incorporated herein by reference. The liquid phase mix of natural gas and light hydrocarbon solvent is referred to hereafter as compressed gas liquid (CGL) product.

However, current solutions or services for natural gas production and transmission to market tend to be one size fits all and tend not to afford economic development of remote or stranded gas reserves. Accordingly, it is desirable to provide systems and methods that facilitate economic development of remote or stranded reserves to be realized by a means not afforded by liquid natural gas (LNG) or compressed natural gas (CNG) systems.

SUMMARY

Provided herein are exemplary embodiments directed to systems and methods that utilize modularized storage and process equipment scalably configurable for floating service vessels, platforms, and transport vessels to yield a total solution to the specific needs of a supply chain, enabling rapid economic development of remote reserves to be realized by a means not afforded by liquid natural gas (LNG) or compressed natural gas (CNG) systems, in particular reserves of a size deemed “stranded” or “remote” by the natural gas industry. The systems and methods described herein provide a full value chain to the reserve owner with one business model that covers the raw production gas processing, conditioning, transporting and delivering to market pipeline quality gas or fractionated products—unlike that of LNG and CNG. Moreover, the systems and methods described herein enable raw production gas to be loaded, processed, conditioned, transported (in liquid form) and delivered as pipeline quality natural gas or fractionated products at the market as well as providing complimentary natural gas service to sources presently linked to LNG (liquid natural gas) systems. It can also service on demand the needs of the industry to transport NGLs.

The disclosed embodiments provide a scalable means of receiving raw production or semi-conditioned gas, conditioning, CGL production and transporting this CGL product to a market where pipeline quality gas or fractionated products are delivered in a manner utilizing less energy than either CNG or LNG systems and giving a better ratio of cargo-mass to containment-mass for the natural gas component than that offered by CNG systems.

Other systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description.

