Abstract:
A system for handling liquified natural gas (LNG) wherein (a) the LNG is delivered into a subterranean formation such that the LNG absorbs heat energy from the subterranean formation and is thereby converted to a gas product and (b) the gas is then produced from the subterranean formation. The subterranean formation is preferably a depleted offshore gas formation having an offshore production platform which is modified to receive LNG from marine transport vessels which are unloaded at an offshore receiving station.

Description:
FIELD OF THE INVENTION 
     The present invention relates to systems for importing, storing, and vaporizing liquified natural gas (LNG). 
     BACKGROUND OF THE INVENTION 
     There currently exist only about four import terminal facilities in the United States for receiving LNG. At these facilities, the LNG is unloaded from LNG tankers and stored in land-based, insulated tanks. From these tanks the LNG is typically pumped through a heated vaporizing system for delivery as a gas to a gas pipeline distribution system. 
     Natural gas prices are currently increasing rapidly due to inability to meet demand. Unfortunately, the LNG import terminals existing in the United States are presently operating at capacity. New import terminals of the type currently used in the United States cost hundreds of millions of dollars to build. Moreover, it is very difficult and expensive to find and acquire permissible sites for such facilities. Besides the space needed for the import tanks, pumps, vaporizers, etc., large impoundment safety areas must also be provided around all above-ground LNG storage and handling vessels and equipment. LNG import facilities also consume large amounts of fuel gas and/or electrical energy for pumping the LNG from storage and vaporizing the material for delivery to gas distribution systems. 
     Thus, a need presently exists for LNG import, storage, vaporization, and delivery systems which are more energy efficient and are less difficult and expensive to site and build. In view of the urgent need for additional import capacity in the United States, the new import, storage and delivery facilities will also preferably be able to be placed in operation very quickly. 
     SUMMARY OF THE INVENTION 
     The present invention satisfies the needs and alleviates the problems discussed hereinabove. The inventive system can generally be used for receiving, storing, vaporizing, and delivering LNG from any source. The inventive system is particularly well-suited for receiving LNG from tankers, ships, or any other types of marine transport vessels. 
     In one aspect, the present invention provides a method of handling liquified natural gas (LNG) comprising the steps of: (a) delivering the LNG in a liquid state into a subterranean formation such that the LNG absorbs heat energy from the subterranean formation which converts the LNG to a gas product in the subterranean formation and (b) producing the gas product from the subterranean formation. 
     The subterranean formation will preferably be a gas formation which has been substantially depleted. The conversion of the LNG to gas in the subterranean formation will preferably increase the formation pressure sufficiently at least for producing the gas from the formation. Once produced from the formation, the gas will preferably be conducted to a desired delivery point. Examples of typical delivery points could include, but are not limited to, gas pipeline systems or gas-burning facilities. 
     In another aspect, the present invention provides a method of handling LNG comprising the steps of (a) unloading the LNG from a marine transport vessel at an offshore receiving station and (b) delivering the LNG into an offshore subterranean formation such that the LNG absorbs heat energy from the formation which converts the LNG to a gas product. The offshore subterranean formation will preferably have at least one well extending into the formation via which the LNG is delivered in step (b). The method preferably further comprises the steps of: (c) producing the gas product from the offshore formation; and (d) conducting the gas product to a land-based receiving point. The conversion of the LNG to gas in step (b) will preferably increase the pressure of the offshore subterranean gas formation such that the formation pressure is sufficient at least for producing the gas from the formation. 
     In yet another aspect, the present invention provides an apparatus for handling LNG. The inventive apparatus preferably comprises: an offshore receiving station for receiving LNG from a marine transport vessel; an offshore gas production platform for producing gas from a subterranean gas formation, the subterranean gas formation having at least one well extending thereinto; means for delivering the LNG received from the marine transport vessel into the well; and means for conducting gas from the offshore subterranean gas formation to a land-based receiving point. 
     Further objects, features and advantages of the present invention will be apparent to those skilled in the art upon examining the accompanying drawings and upon reading the following description of the preferred embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The drawing schematically illustrates an embodiment 2 of an offshore handling system provided by the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The inventive system can receive LNG from substantially any source and can utilize substantially any subterranean formation capable of containing and transferring geothermal energy to the LNG material. For example, in one alternative to the embodiment depicted in the Drawing, the subterranean formation could be either a land-based or an offshore formation located near an existing LNG import terminal. In such case, the inventive system could optionally use the tanker unloading facilities already existing at the terminal and would significantly supplement the terminal&#39;s storage and vaporization capacity. 
     The subterranean formation used in the inventive system will preferably be an existing gas formation and/or will preferably be a formation which has been at least substantially depleted. The subterranean formation will most preferably be an existing offshore gas formation. 
     The Drawing illustrates a particularly preferred embodiment 2 of the inventive system. Inventive system  2  preferably utilizes an existing offshore gas formation  4  equipped with: an offshore gas production platform  6 ; at least one well (preferably a plurality of wells)  8  and/or  9  extending into formation  4 ; and a gas production/sales line or other conduit  10  extending from production platform  6  to a land-based receiving point  12 . 
     Land-based receiving point  12  can be any type of onshore gas distribution or gas using facility. The land-based receiving point  12  will typically be a gas pipeline distribution system. 
     In the inventive system, LNGA in a liquid state will preferably be pumped into the offshore formation  4  via one or more of wells  8 . As the LNG flows into and floods formation  4 , the LNG absorbs geothermal energy from formation  4  such that the LNG vaporizes and the pressure within formation  4  increases. The resulting vaporized gas product can be held and stored in formation  4  until needed. In addition, the vaporization of the LNG will preferably at least provide sufficient pressure in formation  4  for producing the gas from formation  4  via one or more of the wells  8  and/or  9 . The increased formation pressure can in some cases be sufficient for delivering the gas to land-based receiving point  12  via sales line  10 . However, if necessary, one or more compressors or other pumping systems can be installed on-shore and/or on the offshore platform  6  for boosting the flow of gas to receiving point  12 . 
     Offshore platform  6 , wells  8  and  9 , and sales line  10  will preferably be existing structures which were previously used for producing and delivering natural formation gas from offshore formation  4 . The metallurgy of the casing or pipe in the particular existing well(s)  8  selected for use in injecting the LNG into formation  4  may need to be upgraded for handling cryogenic fluid. In addition, these well(s)  8  can optionally be fractured, if desired, in order to increase the rate at which the LNG can be pumped into formation  4 , thus expediting the unloading of LNG vessels  16 . 
     The inventive system  2  will preferably include a plurality of wells  8  and  9  so that one or more wells  8  can be used for delivering LNG into formation  4  and one or more other wells  9  can be used for producing the vaporized gas product from the formation. In such cases, only those wells  8  which are used for delivering the LNG into formation  4  will typically require any modification. As will be understood by those skilled in the art, existing offshore units used for producing natural gas can, in some cases, include as many as two dozen or more wells  8  and  9 . 
     The wells  8  used for LNG injection and the wells  9  used for gas production will preferably be selected to optimize flow and heat transfer throughout formation  4 . For example, the LNG could be injected via a plurality of outer wells  8  with the gas product being withdrawn via one or more centrally located wells  9 , or vice versa. Alternatively, all of the material could be caused to flow across the entire formation  4  by injecting LNG into one end or side of the formation and recovering the gas product from the opposite end or side thereof. 
     Inventive system  2  also preferably comprises: an offshore receiving station  14  for unloading and receiving LNG from a tanker, ship, or any other marine transport vessel  16 ; one or more pipes or other conduits  18  for delivering the LNG from offshore receiving station  14  to well(s)  8 ; and, if needed, one or more pumps  20 , preferably positioned on platform  6 , for pumping the LNG into wells  8 . 
     Offshore receiving station  14  can be any type of facility or system used for unloading LNG from transport vessels. By way of example, but not by way of limitation, receiving station  14  can comprise a boom  22  as depicted in the drawing (preferably a pivotable and/or retractable boom) provided on offshore platform  6  and having one or more cryogenic hoses  24  which can be extended from boom  22  to vessel  16 . Alternatively, a typical swivel jointed pipe system (e.g., a Chicsan arm) could be extended from platform  6  to vessel  16 . As will be appreciated by those skilled in the art, systems such as these will readily accommodate changing tides and unsteady seas. 
     As will also be understood by those skilled in the art, typical LNG vessels  16  will be equipped with pumps sufficient for offloading their cargo into the receiving system. Depending upon the particular well(s)  8  and formation  4  in question, the pumps on vessels  16  might also be sufficient for pumping the LNG into the formation. 
     The present invention thus provides a low cost, highly energy efficient system for importing, storing, delivering, and vaporizing LNG. The inventive system can also be located and built very quickly and at costs which are much lower than those of current types of LNG import facilities, particularly when offshore formations already having existing production platforms, wells, and other production and delivery equipment are used. 
     Thus, the present invention is well adapted to carry out the objects and attain the ends and advantages mentioned above as well as those inherent therein. While presently preferred embodiments have been described for purposes of this disclosure, numerous changes and modifications will be apparent to those skilled in the art. Such changes and modifications are encompassed within the spirit of this invention as defined by the appended claims.