WO2009124372A2

WO2009124372A2 - Integrated method of obtaining lng and cng and energy conformity thereof, flexible integrated system for carrying out said method and uses of cng obtained by said method

Info

Publication number: WO2009124372A2
Application number: PCT/BR2009/000099
Authority: WO
Inventors: Gilvan Couceiro D' Amorim; Paul Louis Poulallion
Original assignee: International Finance Consultant Ltda.
Priority date: 2008-04-10
Filing date: 2009-04-13
Publication date: 2009-10-15
Also published as: WO2009124372A3; BRPI0800985A2

Abstract

The present invention refers to a method for collecting, decontaminating, removing water, compression and cooling and removal of condensable fractions of natural gas from an offshore source to transfer the gas to the surface and connection to a vesselplant of the invention or from an on-shore source accessible by river or sea, said method being characterized by useing the accumulated energy in the compression of gas for liquefraction thereof. The invention also includes a flexible integrated system with a collection and treatment capacity of up to 600.000 Sm3/day of natural gas compression (2) of the treated gas, storage (3) of the compressed gas, transport and delivery of the gas and its compressed fractions in liquid state, comprising (a) a small vessel (1), preferably of the catamaran type, equipped with (i) means coupling to the feeding pipeline of natural gas decontamination (ii) unit (5) for removing H2S and other contaminants present in the natural gas collected; (iii) dehydration (6) to remove water present in the decontaminated gas; (iv) at least a compressor set (2) and heat exchanger (3) to carry out the compression steps necessary for removing the condensable fractions of gas and cooling of the dehydrated, decontaminated gas and (v) containers (3) to store the compressed gas and tanks, preferably installed on the lower deck, to store the condensed fractions.

Description

INTEGRATED METHOD OF OBTAINING LNG AND CNG AND ENERGY

CONFORMITY THEREOF, FLEXIBLE INTEGRATED SYSTEM FOR CARRYING

OUT SAID METHOD AND USES OF CNG OBTAINED BY SAID METHOD

Field of the Invention The present invention refers to a method for collecting, decontamination, removing water, compression and cooling and removal of condensable fractions of natural gas from an offshore source, be it an FPSO fixed rig {"Floating Production, Storage and Offloading") or even a well or a sub sea separation system having equipment to transfer the gas to the surface and connection to the plant-vessel of the invention or from an on-shore source accessible by river or sea, said method being characterized by using the accumulated energy in the compression of the gas for liquefaction.

The invention also includes a flexible integrated system with a collection and treatment capacity of up to 600.000 Sm³/day of natural gas produced offshore or onshore, compression of the treated gas, storage of the compressed gas, transport and delivery of the gas and its condensable fractions in liquid state, comprising (a) a small vessel, preferably of the catamaran type, equipped with (i) coupling means to the feeding pipeline of natural gas produced offshore or on-shore; (ii) unit to remove H₂S and other contaminants present in the natural gas collected; (iii) unit to remove the water present in the decontaminated gas; (iv) at least a compressor and heat exchanger set to carry out the compression steps needed to remove the condensable fractions of _# the gas and cooling of the dehydrated, decontaminated gas and (v) containers to store the compressed gas and tanks, preferably installed on the lower deck, to store the condensed fractions.

Background of the Invention

In oil exploration operations, natural gas, which is produced during the prolonged tests or in anticipated production systems, is usually burned.

Additionally, low production on-shore wells are often abandoned due to their unattractive capacity from the- business point of view.

The same type of waste also occurs, sometimes, in oil production operations with associated natural gas by virtue of the high costs both for making it available in the consumption centers, generally situated far away from the source, but also because of the high investment needed to construct and maintain natural gas pipelines, which makes its exploration unfeasible.

This energy waste is all the more problematic because the burning of natural gas also contributes to global warming, a phenomenon that is becoming increasingly important in government policy planning, especially relating to the use of energy and to the environment.

Another matter to be considered in the offshore exploration of natural gas is safety, which is always one of the most rigorous points not only in concession contracts to exploit and transport oil, derivates and other fuels by sea, but also the security requirement in handling dangerous and/or inflammable cargoes at the delivery sites, either on the coast or offshore.

The known methods of sea transport of natural gas are: (a) underwater pipelines; (b) transport of natural liquefied gas (LNG) in tankers and (c) transport of compressed natural gas (CNG) in containers located on the deck of ocean-going tankers . Each of these methods has its advantages and drawbacks, particularly relating to safety and financial investment. The first method (underwater pipeline) is unfeasible at depths exceeding 300m or when the capacity or time availability is not assured. The second, transport of LNG, also involves high investments relating to the capacity of said transport, both to liquefy the natural gas and to transport it and vaporize it. The drawback of the third method is essentially its economic unfeasibility because it requires large transport capacity for intercontinental distances and, therefore, requires large scale projects. In the case of LNG, proposals to reduce the transport costs of natural gas, from its source up to delivery point, involve the substitution of underwater pipelines by LNG transport tankers and that include units necessary to carry out some steps of liquefaction or re-gasification of natural gas . Some examples of these kinds of vessels are described in documents US 6003603, US 5025860, WO 2004/00638, US 2005/0005615, GB 1560733 and US 2005/0042035. Additionally, there have been various proposals to reduce the drawbacks of the method of CNG sea transport, from the collection of natural gas to the storage of CNG and availability at the delivery point. For example, patent US 7155918 describes a system for processing and transport of compressed natural gas comprising: (a) a separator to receive the gas with high energy content from a feeding pipeline and produce gas with pressurized high energy content, a liquid of natural gas and a condensate; (b) a decontaminating unit connected to the separator to receive the saturated gas and remove the impurities from the saturated gas; (c) a dehydration unit connected to the decontaminating unit to receive the decontaminated gas and remove the water therefrom, producing a pressurized, dry gas; (d) a cooling unit connected to the dehydration unit to received the pressurized gas and cool it from ambient temperature to a temperature varying between about -62 ^aC and about -84 ^aC forming a two-phase gas comprising a vapor phase and a liquid phase; (e) at least a storage element located on a tanker, said storage element connected to the cooling unit and to the separator, receiving the two-phase gas, the liquid of the natural gas and the condensate, keeping these three components at a pressure varying between 800 psi (5,515.8 kPa) and 1200 psi (8,273.7 kPa) , and said element comprising an insulating layer between an inner wall and an outer wall; and (f) the tanker being adapted to transport the storage element storage at a distance varying between 500 and 2,500 nautical miles, and the vapor phase of the compressed gas is used as fuel to move the tanker. The system described in patent US 7155918 has three drawbacks, namely: (i) the tanker is used merely to transport the compressed natural gas, making use of at least a good part of same as fuel, (ii) the maintenance of such low temperatures (between about -62²C and about -84²C) requires considerable energy consumption and (iii) thermal insulation to avoid overweight due to the high pressure- type reservoirs which besides causing energy waste and significantly high costs with the reinforcement of the recipients, requires complex control in keeping the pressure and initial temperature conditions in balance.

The processing of oil and natural gas in tankers destined for the transport of the end or semi-final products have been considered as an alternative to avoid environmental problems with plants located on land such as, for example, for the synthesis of ammonia. These refinery- vessels or plant-vessels have been known for some time, such as those described in documents GB 1492550 and GB 1475813. One of the major problems of these plant-vessels is their maneuverability in relation to offshore production rigs or other offshore natural gas exploration structures. The stability of this kind of vessel is also a critical point to be considered in the investment applied in the manufacture of such structures that often need to withstand extreme climactic and maritime conditions. Documents US 6688248 and DE 3733321, for example, propose catamaran-type vessels which can be used in the transport of unassembled rigs, with the aim of maximizing the stability of the vessel carrying a considerable weight.

Catamaran-type vessels are also used in the processing of natural gas. Document SE 8305632 describes a vessel of this kind, having greater stability than single-hull, the catamaran being anchored over a gas well that provides the supply. The catamaran carries a plant that includes a reformer (18) for the processing of natural gas. Although this vessel has advantages for the reforming of natural gas, there are other difficulties to be overcome such as, for example, the inclusion of various types of equipments, when the aim is to obtain CNG. Additionally, no product storage means are provided for in the vessel itself.

Another matter to be solved is the storage of CNG in a safe manner, economically feasible, with lower dead weight (weight of empty containers) and ease of offloading at delivery point. For example, documents US 7273391, US 7240498 and US 7240499 propose cylinder or sphere-shaped, CNG storage elements with double wall and intermediary insulating layer to enable the maintenance of very low temperatures, at around -80²C, said storage elements being disposed in relation to the overlapping in the tanker deck, also being provided with mooring and fixing structure of said storage elements and to the deck of the tanker. These elements, requiring the maintenance of low temperatures, financially burden the transport of natural gas, thus reducing the economic feasibility of offshore exploration of natural gas . Another CNG storage proposal is set forth in document US 2007/014636, which provides a single structure forming cylindrical bodies for the storage of CNG on tankers. Besides requiring an individualized size for each vessel size, this kind of structure hinders the offloading of the CNG at the delivery point, especially if it is the end user.

The state of the art described above clearly shows that a system is not yet available that uses the energy conserved in the compression of natural gas, carried out in a small and highly mobile vessel, and in the transport of compressed gas at high pressure, so that, on land, products other than CNG can be obtained, the LNG directly and also to reduce the energy consumption in the liquefaction of the compressed gas carried out on land.

Summary of the Invention The present invention aims to provide a system and method for collection, decontamination, dehydration, compression, storage and transport of compressed natural gas at high pressure, produced offshore or on-shore in low production well fields, all operations being carried out on board of a small vessel with high maneuverability, mobility and stability, for example, a vessel of the catamaran type. More than this, especially, the invention provides a system and method to maximize the use of the accumulated energy in the compressed gas at high pressure to obtain, directly, the LNG product and to carry out the liquefaction, on land, of said compressed gas .

A first embodiment of the invention relates to an integrated method of obtaining LNG and CNG and energy conformity there'of, said method comprising the steps of: (a) collection of natural gas from an a source offshore or on-shore (coastal) and storage of said gas in reservoirs, located on board a vessel, for processing; (b) decontamination of said gas for producing a stream of gas free of contaminants; (c) dehydration of the stream of natural gas decontaminated for producing a stream of dry natural gas; (d) at least a compression step of said stream of dry natural gas; (e) at least a cooling step of said compressed natural gas for producing a stream of compressed natural gas at a temperature of up to about 30²C upon entry to CNG storage cylinders; (f) storage of said compressed natural gas and cooled in cylinders disposed in at least a container; (g) transport of at least a container from the offshore or on-shore production point to the delivery point of the compressed natural gas and (h) offloading of the compressed natural gas from at least a container, and all steps of said method are carried out on board a small vessel and that the offloading of said compressed natural gas is carried out so as to maximize the use of the accumulated energy in the compression of the natural gas, enable LNG to be obtained directly and also the application of said accumulated energy in the subsequent processing of the CNG, especially in the liquefaction carried out on land.

In a second embodiment, the method of the invention includes the steps (a) up to (f) of the first embodiment and at least a part of the CNG is destined for: (i) generation of energy for said plant and for movement of said small vessel, for example, of the catamaran type,- (ii) start-up of production or resumption of natural gas production, by means of gas-lift, in wells that have been shut down and do not have other economically feasible gas sources; (iii) operation of rig or other offshore structures; or, also, preferably, (iv) liquefaction of the natural gas on land.

In a third embodiment, a flexible integrated system is provided comprising: (a) a feeding terminal of crude natural gas produced offshore or on-shore; (b) a small vessel, for example, of the catamaran type, with connecting means to the feeding terminal of said natural gas , and having at least a reservoir for storing said gas for processing, and said vessel has a plant comprising (i) a decontaminating unit of crude natural gas for producing a stream of gas free of contaminants; (ii) a dehydration unit to remove water from the decontaminated natural gas for producing a stream of dry natural gas; (iii) at least a compressor and heat exchanger set to compress and cool the dry natural gas, up to a temperature of up to about 30²C upon entry to compressed gas storage reservoirs or cylinders, to obtain a stream of compressed natural gas;

(iv) a set comprising condensate compressors for each compression step, suitable pumps and tanks for the temporary storage of the condensed fractions; (v) at least a compressed gas reservoir storage container or cylinders; and (vi) means of offloading the compressed natural gas from said compressed gas reservoir storage container or cylinders in said at least a container at the delivery point so as to maximize the use of the accumulated energy in the compression of said natural gas to obtain CNG products, especially LNG; and (c) delivery point of compressed natural gas selected from the group consisting of land storage park and offshore production structure.

A fourth embodiment of the invention refers to a system similar to the system of the first embodiment, in which are, additionally, provided means of using the compressed natural gas stored in at least a container to: (i) generate energy for said treatment and compression plant and for movement of said catamaran-type vessel; (ii) start-up of production or resumption of production by means of gas-lift at wells that have been shut down and have no other source of economically feasible gas; (iii) operation of rig or other offshore structures; or, also, (iv) liquefaction of the natural gas on land, whereby optimizing the use of the energy potential of the high pressure of the CNG transported.

A fifth embodiment of the invention refers to the use of CNG produced by the method of the invention in the liquefaction of CNG on land; in the generation of energy for said plant and for movement of said small vessel, for example, of the catamaran type; the start-up of production or resumption of production of natural gas at wells that have been shut down and have no other source of gas economically feasible gas,- in the operation of the rig or other offshore structures. More preferably, the present invention refers to the use of CNG produced by the method of the invention in the liquefaction of said CNG using at least part of the accumulated energy in the compression of the natural gas carried out on board a small vessel, for example, of the catamaran type.

Brief Description of the Drawings Figure 1 shows a top view of a small plant-vessel, for example, of the catamaran type, of the present invention.

Figure 2 depicts the approximation of the vessel of the catamaran type of the invention, in dynamic positioning mode, the submerged buoy for collection of the gas conductor, wherein: (A) shows the approximation itself and,

(B) shows the fast engagement/disengagement connection.

Figure 3 depicts the versatility of the system of the invention in which a small vessel, for example, of the catamaran type can be connected to the natural gas production rig to carry out any of three kinds of operation: (a) collection of the natural gas to be treated; (b) delivery of compressed natural gas to the rig using already existing pipeline, and (c) delivery of pressurized gas for gas-lift operations. Figure 4 depicts one of the embodiments of the invention showing a small vessel, for example, of the catamaran type in a natural gas collection operation from an FPSO structure.

Figure 5 depicts the embodiment of the system of the invention in which the delivery of the compressed natural gas transported in the catamaran-type vessel of the invention is performed on land with maximization of the use of the accumulated energy in the gas compression. Figure 6 shows a comparison between the method of the present invention in which the compression of gas is carried out at a pressure in the range between 10,000 and 27,000 kPa, generating accumulated energy capable of producing, at least partially, LNG directly, and the method of the state of the art, in which the compression is made at 4,000 kPa, meaning LNG cannot be obtained directly.

Figure 7 depicts, schematically, the versatility of collecting natural gas from different structures and using the CNG produced on the plant-vessel.

Figure 8 depicts a comparison of the method of the present invention, in which there is a maximization of the use of the accumulated energy in the compression of gas for direct (partial) generation of LNG and for processing CNG in other applications, including, preferably liquefaction, and the various conventional methods , three modes being shown, in which it is not possible to produce LNG directly.

Figure 9 shows the method flowchart of the present invention from offshore or on-shore extraction to storage and storage for delivery on land or to maritime installations .

Detailed Description of the Invention

The system of the present invention is fundamentally based on the use of a vessel that offers the best conditions of maneuverability, mobility and stability for collection, from an offshore or on-shore source in fields with low production wells, preferably offshore, of natural gas, said vessel being equipped with (i) a treatment unit for inhibiting or removing the adverse effects of the corrosive or dangerous components that are present in the natural gas collected, (ii) a dehydration unit for removing the water that accompanies the natural gas collected offshore, (iii) a compression and condensable removal set, including heat exchangers, condensate compressors (for example, gas scrubbers) , pumps and tanks for storing condensates and (iv) special recipients (compressed gas storage reservoirs, for example, cylinders) for storage of the compressed natural gas at high pressure. The compressed natural gas, stored in special recipients, is transported at high pressure for offloading at the delivery point, where it is also possible to deliver the condensed fractions that are stored in the tanks, preferably installed on the lower deck of the small vessel, for example, a catamaran. In one of the preferred embodiments, the delivery point is located at land stations that temporarily accumulate the compressed gas for subsequent transfer to the consumption centers, either in CNG transport vehicles, or in transport or distribution gas pipelines, or, also, especially preferred, the compressed gas stored at high pressure in the reservoirs (for example, cylinders) is processed so as to maximize the use of part of the accumulated energy in the compression of gas for direct LNG production, and the other part of the accumulated energy is used, both in the CNG transport and/or storage on land, and preferably for obtaining LNG.

Figure 1 shows the system of the present invention comprising the gas catamaran (1) carrying a natural gas treatment plant produced offshore or on-shore that includes: (a) various sets of compressors (2), which can be driven by any suitable energy source, such as, for example, driven by gas or electric motors; (b) various sets of containers (3) where the reservoirs are located, for example, CNG storage cylinders; (c) supply device (4) of gas to be treated; (d) decontaminating unit (5) to remove any contaminant present in the gas collected, for example, removal of H₂S; (e) dehydration unit (6) of the gas from which H₂S was removed; (f) inter-phase heat exchangers (7), refrigerated with a suitable cooling means, for example, sea water or atmospheric air, preferably sea water; (g) condensate compressors (8) and (h) at least a connection (9) , preferably at least two, for the offloading of gas, located in any suitable site on the vessel, for example, portside, starboard or other suitable site.

Offshore collection can be seen in Figures 2, 3 and 4. Alternatively, the collection can occur¹ on-shore from fields, accessible by sea or river, with low production natural gas wells and whose commercial exploration by conventional methods is prohibitive. In either alternative, offshore or on-shore, one of the main characteristics that ensures the feasibility of natural gas exploration, impractical until the advent of the present invention, is the use of a small vessel, for example, of the catamaran type, that has greater maneuverability, mobility and stability, in the collection, on-board processing of the natural gas, compression of processed gas and transport of compressed natural gas up to the delivery point. Another main characteristic of the invention, and which will be explained in detail ahead, is the maximization of use of the accumulated energy in the compression of gas, both in obtaining LNG directly, as in sending the CNG for storage, distribution or liquefaction, the latter destination being preferred in the use of the accumulated energy in the compression of gas.

In Figure 2, the offshore collection of natural gas is carried out with the vessel (1) situated on the supply well. Figure 2 shows the approximation of the gas catamaran in dynamic positioning mode in relation to the submerged buoy to collect the gas conductor, wherein: (A) shows the approximation of the vessel to the submerged buoy (10) and the drawing up of the flexible gas conductor pipe (11) and in (B) the flexible pipe (11) drawn up is connected to a quick engagement/disengagement system (12), being kept in dynamic positioning so as to receive the gas or to transfer the gas in mooring mode at the submerged buoy which is kept in position thanks to the anchoring cable (13) .

The drawing up and connection of floating oversleeves or flexible pipes with surface buoy can be carried out in a similar way, with the catamaran kept in dynamic positioning mode. Figure 3 shows another embodiment of the invention according to which the offshore collection is performed from a rig of natural gas (14) , with the vessel (1) moored to the rig, and the gas is transferred by flexible pipe or oversleeve (15) . In Figure 3 it is possible to visualize the versatility of the system of the invention in which the gas catamaran, connected to the natural gas production rig, can carry out any of three kinds of operations: (a) collection of the natural gas to be treated; (b) delivery of compressed natural gas to the rig connected to a gas pipeline destined for the transfer of the gas collected by the gas catamaran to an installation situation on land and

(c) delivery of pressurized gas for gas-lift use in the rig operation requiring gas for the start-up of production at shut down oil wells .

Collection of Natural Gas at Offshore Installations

The collection of natural gas is carried out at a pressure never less than 6 bar (600 kPa) , up to a maximum pressure of 270 bar (27,000 kPa) , when the gas is collected directly from gas wells not associated to oil, at offshore installations without prior separation on board the rigs. The prior separation is carried out when the gas produced is associated to oil. The transfer of gas is processed by means of a special connection with double blockage, one being internal for the gas under pressure and one external acting as protection for the mechanisms against the effects of the sea action and to avoid any gas leakage, said connection having a quick engagement/disengagement device, including automatic blockage valve, which, coupled to a flexible pipe, floating oversleeve or other suitable means, from an FPSO, production rig, or surface structure linked to one or more underwater wells, or even any other offshore or on-shore support structure, enables the link between the source of natural gas and the vessel of the catamaran type of the invention, while the latter remains moored to said structure.

As shown in Figures 2, 3 and 4, in operation, the collection unit works as follows : after the flexible pipe or oversleeve (11, 15, 17), located on the offshore production structure, for example, submerged buoy (10) , rig

(14) or FPSO structure (16) is connected to the vessel (1) , a blockage valve, located at the end of the flexible pipe or oversleeve, is open to allow the transfer of natural gas from the source of supply to the provisional storage of the natural gas on the vessel for subsequent treatment. Preferably, the blockage valve is a double-sphere valve having fast engagement, for example, "quick connect- disconnect" to connect the flexible pipe or oversleeve (11, 15, 17) in the line of receiving the gas on the catamaran and, additionally, with the possibility of quick disconnection in the event of an emergency. Once the transfer operation is concluded, that is, when the gas transferred reaching provisional storage capacity in the vessel, or, if applicable, before reaching this capacity, the disconnection operation begins. Upon disconnection, firstly, the blockage valve that is part of the transfer pipe is closed, allowing safe disconnection of the fast engagement/disengagement pipe (5, 7) and the subsequent unmooring of the vessel (1) .

Treatment of Natural Gas on Board the Catamaran-Type Vessel All the natural gas stored on board is submitted to treatment for decontamination, that is, elimination of the corrosive or dangerous components, in the decontaminating unit (5) to form a stream of decontaminated natural gas. The types of impurities that frequently occur in natural gas produced offshore are CO₂, H₂S and a set of these contaminants. Examples of decontamination units include amine contact device, catalytic bed, scrubber-type reactor or a set of these devices .

Dehydration of Natural Gas Treated on Board the Catamaran- Type Vessel

The system of the present invention includes a dehydration unit (6) which is connected to the decontaminating unit (5) , receiving the decontaminated gas to remove the water. The dehydration unit (6) can be any one selected, for example, from types of dry bed adsorption, glycol contact towers, molecular membrane units or a set of these units, or, also, any suitable kind that is well-known to persons skilled in the art of treating natural gas .

Compression and Cooling of Natural Gas Natural Treated and Dehydrated and CGN Storage on Board Catamaran-Type Vessel

The natural gas treated for decontamination and dehydration is compressed on board the vessel (1) of the invention and separated from the condensable fractions, including remaining water, for subsequent storage in gas reservoirs at high pressure, preferably in the range of 100 to 270 bar (10,000 to 27,000 kPa) , and more preferably, from 250 to 270 bar (25,000 to 27,000 kPa) . The compressor or compressors can be driven by electric motor (s) or by motor means using the natural gas collected, or a set of these two types, and said compressor (s) sized for operating conditions (compression of the natural gas received at a pressure not less than 600 kPa to a pressure in the range of 10,000 to 27,000, preferably from 25,000 to 27,000 kPa) and being sufficiently flexible for being adapted to the different gas handling possibilities. Between two successive compressions and after the last compression, the gas is cooled, preferably by way of heat exchangers using a suitable cooling means, for example, sea water or atmospheric air, preferably sea water. These heat exchangers are widely known in the state of the art and a person skilled in the art can select the suitable type and size for the levels of pressure and temperature desired.

In the same way, the condensate compressors are sized to operate on board and are sufficiently robust so as to withstand the movements if the floating vessel of the present invention.

Lastly, the compressed gas up to a final pressure of 10,000-27,000 kPa, more preferably 25,000-27,000 kPa, is stored in at least a container, preferably a set of containers, in which the high pressure compressed gas reservoirs are housed (for example, high pressure cylinders) , preferably stored vertically. The reservoirs are preferably elongated cylindrical shape and are made of material resistant to this level of pressure, to fire and to corrosive substances. Examples of such materials are: carbon fiber, basalt fiber and polymers. Preferably, the high pressure reservoirs/cylinders are made of materials with high mechanical resistance and to the chemical attack of products present in the natural gas and, additionally, having reduced weight as a way of lowering the dead weight in the vessel without unnecessarily raising its center of gravity.

The reservoirs /cylinders of the set are equipped with blockage valves and duly arranged so as to enable loading and offloading of the natural gas in selective cascade or from all the containers at the same time, if so desired.

The selectivity of the arrangement of the reservoirs for loading and offloading can be carried out by local control or by distance command from a central control room. Accordingly, the natural gas collected and stored in reservoirs /cylinders at high pressure (up to 270 atm, approximately 27,357 kPa) is delivered at land storage and commercialization installations, situated at distances of up to 1,000 nautical miles, where the gas can be: (a) partially liquefied using the accumulated energy in the compression carried out on board the vessel, (b) totally or partially commercialized in the form of LNG and in the form of natural liquefied gas or compressed for residential, commercial, industrial or vehicle use, or, also, (c) used in the generation of energy at thermo-electric plants or as raw materials or energy supplies for industry or also transferred to transport or distribution gas pipelines. Alternatively, the gas collected, decontaminated and dehydrated, after being compressed and stored in the reservoirs /cylinders and stored in the containers, can be transported to offshore installations nearby that have no gas pipelines for receiving the gas collected or perform gas-lift operations, in wells that have been shut down and have no other source of economically feasible gas .

Offloading the CNG from the Catamaran-Type Vessel

As mentioned previously, one of the main advantages of the method and system of the present invention is the maximization of the use of the accumulated energy in the compression carried out on board the small vessel, for example, of the catamaran type. This maximization is enabled by the high pressure used in the compression of the gas, in the range of 10,000 to 27,000 kPa. This level of pressure allows that, in the offloading operation, the compressed gas directly into a liquefaction system, part of said gas is liquefied by the action of the cold generated by the Joule effect that occurs on expansion of the other part of the gas (residual fraction) which is directed for storage or to the gas pipeline, for example.

Besides this major advantage of the method and system of the present invention, at high pressure used in the compression of gas on board the vessel (catamaran, for example) , it also contributes to reduce the energy expenditures in the liquefaction of the compressed gas to be carried out on land installations, when the CNG is destined to produce liquefied gas. Figure 5 shows, schematically, the different destinations of CNG produced in the vessel, namely: (a) for storage and subsequent transport in the form of CNG; (b) for expansion and cooling, and a part is liquefied and sent for storage as LNG or transport as LNG and the other part, in the form of gas, is sent to other destinations, such as gas pipelines, industries, thermo-electric plants, etc.

Figure 6 helps to understand the difference of the method and system of the invention in comparison with the state of the art. In the system and method of the invention, the accumulated energy in the compression of the gas at high pressure is used in the liquefaction, at land installations, of the compressed gas in which part of this gas, in the liquefaction with direct cooling, is directly liquefied and the other part of said gas is still at a sufficiently high pressure to reduce the energy expenditure with liquefaction significantly. In the installations and conventional methods (liquefaction with indirect, closed- cycle cooling) , in which the compressed gas is at a significantly lower pressure (4,000 kPa) , and besides not having direct production of liquefied gas, it is still necessary to use energy to carry out the compression of the mixture of gases.

In short, the system of the invention enables the CNG obtained by compression at high pressure to be transported in the catamaran-type vessel (1) and to be delivered on land, so as to maximize the energy use of said compression for the destinations of said CNG, especially for liquefaction. Also as shown in Figure 5, the same land terminal provides for the delivery of the condensates withdrawn in the gas compression method for storage and subsequent transport . CNG offloading is carried out by offloading of the CNG into the reservoirs and/or liquefaction unit through swivel arms, high pressure flexible pipes or by suitable offloading arms .

For quick offloading from the reservoirs /containers on board, specific compressors installed themselves are used to compress the gas for storage in the containers, or also the pumping of appropriate liquid, for example, oil, inside the cylinder-shaped reservoirs /containers in a liquid piston formation procedure, according to which the liquid fills the space previously occupied by the gas and forces the stored gas out, under high pressure.

In the offloading method using the liquid piston method, the drop in pressure will be decreased during transfer, allowing the optimization of land storage and the use of accumulated energy in an associated method of gas liquefaction or for other purposes .

The natural gas can also be off-loaded offshore in natural gas production units or other structures linked by ducts to run-off systems . Figure 7 shows as different sources of natural gas, as gas processing steps on board the small vessel and the various destination possibilities of the CNG produced on the catamaran, both land and offshore. Especially, when the gas is off-loaded on land, it is preferably sent to a liquefaction unit in which the use of the accumulated energy in the compression enables a significant reduction in energy consumption to obtain LNG. Figure 8 is particularly illustrative of the energy savings obtained by the method and system of the present invention when compared to the conventional methods and installations represented, in the Figure, such as routes a, b and c. Indeed, the high pressure, in which compressed gas is found on board the small vessel that is part of the system of the invention, enables the liquefaction for the production of LNG and/or storage of the CNG (CNG lung) with a much lower energy consumption than that used in conventional methods, for example, routes a, b and c represented in Figure 8. This energy use not only increases the profitability of the CNG liquefaction method but contributes to guarantee the formation of strategic stocks that ensure the feasibility of continuous supply of LNG, independent of traditional sources of LNG. Alternatively, the CNG off-loaded from the catamaran- type vessel can be sent to a gas pipeline or to a storage park composed of high pressure storage recipients (CNG lung) , or pipes underground or situated on the surface, with sufficient capacity to store all the gas transported, from the offshore installations, said recipients or pipelines being suited to the variations in demand.

The reservoirs located in the storage park of the compressed natural gas receive the gas off-loaded in cascade, the product being stored at different pressures to increase the efficiency of the system and save energy. Besides the reservoirs for the natural gas, the park is also provided with compression equipments and measuring instruments to assist in the transfer of gas or in the loading of this fuel into compressed natural gas transport vehicles .

When the composition of the gas so allows, a potential alternative is the direct offloading of the CNG into distribution systems, done in an equipment of the "City Gate" type having a pressure regulator device and rate gauge .

When different specifications need to be met, the natural gas can be submitted, in the storage park, to additional dew point adjustment treatments, removal of H₂S and/or remaining CO₂, or, also, removal of any condensates that arise during processing of offloading and subsequent operations .

All operations, that is, collection, treatment (decontamination) , removing water, compression, storage and offloading of compressed natural gas and of the condensables, are carried out on board the catamaran-type vessel of the invention, and the control of these operations is made individually at the unit carrying out each operation or in an integrated manner from a central control room. The liquids and condensates separated during the method of obtaining CNG are stored in specific reservoirs (tanks situated preferably on the lower deck of the vessel) for subsequent offloading on land or on the rig itself or support structure of the collection of gas from the supply source.

Due to its greater mobility, maneuverability and stability, a catamaran-type vessel of the invention can also be displaced to a delivery point in which it is used as a supply source of natural gas, as auxiliary fuel or in gas-lift operations, in the start-up of production or resumption of production, for example, at wells that have been shut down and have no other source of economically feasible gas .

Figure 9 shows, in a block diagram, an equivalent scheme to that of Figure 7 which helps understand the magnitude of the advantages of the system and method of the present invention in comparison with methods and installations of the state of the art.

All publications and patent applications mentioned in the description are indicative of the level of those persons skilled in the art to which the invention refers . All publications and patent applications are hereby incorporated as references in the same extent as if each individual publication or each patent application were specifically and individually indicated to be incorporated as a reference.

Although the preceding invention has been described in certain details by means of illustrations and examples for the purpose of clarity and understanding, it will be obvious that certain changes and modifications can be made within the scope of the claims accompanying this description.

Claims

1. Integrated method of obtaining LNG and CNG and energy conformity thereof, said method comprising the steps of:

(a) collection of the natural gas from an offshore or on-shore source and storage of said gas in reservoirs, located on board a vessel, for processing;

(b) decontamination of said gas for producing a stream of gas free of contaminants;

(c) dehydration of the stream of decontaminated natural gas for producing a stream of dry natural gas;

(d) at least a compression step of said stream of dry natural gas ;

(e) at least a cooling step of said compressed natural gas for producing a stream of compressed natural gas at a temperature of up to about 30²C upon entry to CNG storage cylinders;

(f) storage of said compressed natural gas and cooled in said cylinders disposed in at least a container;

(g) transport of at least a container from the offshore or on-shore production point to the delivery point of the compressed natural gas; and

(h) offloading of compressed natural gas from at least a container, wherein all the steps of said method are carried out on board a small vessel and the offloading of said compressed natural gas is carried out so as to maximize the use of the accumulated energy in the compression of the natural gas to obtain LNG in the liquefaction carried out on land.

2. Method according to claim 1 wherein a source from which the natural gas is collected is an offshore source.

3. Method according to claim 1 wherein a small vessel is of the catamaran type.

4. Method according to claim 1 wherein said collection of natural gas is carried out at a pressure not less than 600 kPa.

5. Method according to claim 1 wherein said decontamination of natural gas provides a removal of contaminants selected from the group consisting of CO₂, H₂S and combinations thereof.

6. Method according to claim 1 wherein said dehydration of the stream of natural gas decontaminated is carried out by a method selected from the group consisting of dry bed adsorption, contact with glycol, passage of the stream of gas containing water by molecular membrane and combinations thereof .

7. Method according to claim 1 wherein said at least a compression step compresses the decontaminated, dry natural gas up to a pressure in the range of 10,000 to 27,000 kPa.

8. Method according to claim 1 wherein said at least a cooling step up to a temperature of up to about 30^aC upon entry of said CNG storage cylinders is carried out between two steps of compression and after the final compression.

9. Method according to claim 1 wherein said at least a cooling step is carried out with a cooling means selected from the group consisting of sea water and atmospheric air.

10. Method according to claim 1 wherein said offloading of the compressed natural gas is carried out such that the accumulated energy in the compression carried out on board the small vessel is used in liquefaction of the gas carried out on land.

11. Method according to claim 10 wherein part of the compressed natural gas is liquefied directly, during said offloading, by using said accumulated energy.

12. Method according to claim 10 wherein said offloading of the natural gas is by pumping an appropriate fluid inside the cylinder.

13. Integrated method of obtaining LNG and CNG and energy conformity thereof, wherein said method comprising the steps of:

(a) collection of natural gas from an offshore or onshore source and storage of said gas in reservoirs, located on board a vessel, for processing;

(c) dehydration of the stream of natural gas decontaminated for producing a stream of dry natural gas ;

(d) at least a compression step of said stream of dry natural gas ; (e) at least a cooling step of said compressed natural gas for producing a stream of compressed natural gas at a temperature of up to about 30²C upon entry to CNG storage cylinders; (f) storage of said compressed natural gas and cooled in said cylinders disposed in at least a container;

(g) transport of at least a container from the offshore or on-shore production point to the delivery point of the compressed natural gas; and (h) offloading of said compressed natural gas from at least a container, wherein and all the steps of said method are carried out on board a small vessel and at least part of the compressed natural gas produced is used to generate energy for said plant and for movement of said small vessel.

14. Integrated method of obtaining LNG and CNG and energy conformity thereof, wherein said method comprising the steps of:

(a) collection of natural gas from an offshore or on- shore source and storage of said gas in reservoirs, located on board a vessel, for processing;

(d) at least a compression step of said stream of dry natural gas ; (e) at least a cooling step of said compressed natural gas for producing a stream of compressed natural gas at a temperature of up to about 30²C upon entry to CNG storage cylinders; (f) storage of said compressed natural gas in said cylinders disposed in at least a container;

(g) transport of at least a container from the offshore or on-shore production point to the delivery point of the compressed natural gas; and (h) offloading of said compressed natural gas from at least a container, wherein all the steps of said method being carried out on board a small vessel and at least part of the compressed natural gas produced is used in start-up of production or resumption of oil or natural gas production.

15. Integrated method of obtaining LNG and CNG and energy conformity thereof, wherein said method comprising the steps of:

(b) decontamination of said natural gas for producing a stream of gas free of contaminants;

(d) at least a compression step of said stream of dry natural gas; (e) at least a cooling step of said compressed natural gas for producing a stream of compressed natural gas at a temperature of up to about 30^aC upon entry to CNG storage cylinders; (f) storage of said compressed natural gas and cooled in said cylinders disposed in at least a container;

(g) transport of at least a container from the offshore or on-shore production point to the delivery point of the compressed natural gas; and (h) offloading of said compressed natural gas from at least a container, wherein and all the steps of said method are carried out on board a small vessel and at least part of the compressed natural gas produced is used in the operation of the rig or other offshore structures.

16. Flexible integrated system for obtaining LNG and CNG and energy conformity thereof, wherein said system comprising:

(a) a feeding terminal of crude natural gas produced offshore or on-shore;

(b) a small vessel with connecting means to the feeding terminal of said crude natural gas and having at least a reservoir for storing of said gas for processing, and wherein said vessel has a plant comprising: (i) a decontaminating unit of crude natural gas for producing a stream of gas free of contaminants , (ii) a dehydration unit for removing water from the decontaminated natural gas for producing a stream of dry natural gas,

(iii) at least a compressor and heat exchanger set to compress and cool the dry natural gas to obtain a stream of compressed natural gas,

(iv) at least a set of condensate compressors for each step of compression, pumps and tanks suitable for temporary storage of the condensed fractions, (v) at least a container or cylinder storage reservoirs for the compressed natural gas, and

(vi) means of offloading the compressed natural gas from said container or cylinders for storing compressed gas located in said at least a container, using at least part of the accumulated energy in the compression of said natural gas to obtain CNG products, especially LNG; and

(c) delivery point of the compressed natural gas selected from the group consisting of land storage park and offshore production structure.

17. System according to claim 16, wherein at least a part of said accumulated energy is used in the liquefaction unit of the compressed gas .

18. System according to claim 17, wherein at least a part of said accumulated energy is used to obtain liquefied gas directly.

19. System according to claim 16, wherein said feeding terminal of natural gas produced offshore is located on a rig or similar structure.

20. System according to claim 16, wherein said decontaminating unit of the natural gas is a unit for removing contaminants selected from the group consisting of amine contact device, catalytic bed, scrubber-type reactor or set of these devices .

21. System according to claim 16, wherein said dehydration unit is selected from the group consisting of a dry bed adsorption unit, glycol contact towers, molecular membrane units or set of these units.

22. System according to claim 16, wherein said at least a compressor and heat exchanger set carry out the compression of the natural gas received at 600 kPa for a pressure in the range of 10,000 to 27,000 kPa, and cooling is made up to a temperature of about 30^aC upon entry to the reservoirs or cylinders of compressed gas .

23. System according to claim 22, wherein said compressor is driven by electric motor or by natural gas driven motor or by a set of these kinds of motors .

24. System according to claim 22, wherein said heat exchanger is cooled with a cooling means selected from the group including sea water and atmospheric air.

25. System according to claim 16, wherein the said at least a container is of suitable shape and size for housing reservoirs or cylinders containing the compressed natural gas and is made of resistant material that is resistant to pressure in the range of 10,000 to 27,000 kPa, to fire and to corrosive substances .

26. System according to claim 25, wherein said cylinders containing the compressed natural gas are equipped with blockage valves .

27. System according to claim 25, wherein said at least a container is disposed in the vessel so as to allow loading and offloading of the natural gas, from the cylinders, selectively in cascade or from all the cylinders at the same time.

28. System according to claim 25, wherein said material that is resistant to pressure in the range of 10,000 to 27,000 kPa, to fire and to corrosive substances is selected from the group consisting of carbon fiber, fiberglass or polymer .

29. System according to claim 16, wherein the said means of offloading the compressed natural gas to the land reservoirs are swivel arms or flexible high pressure pipes.

30. System according to claim 16, wherein said offloading of compressed natural gas is of the quick offloading type.

31. System according to claim 30, wherein said quick offloading is carried out by the compressors which compress the gas for storing in the cylinders .

32. System according to claim 30, wherein said quick offloading is carried out by liquid piston.

33. System according to claim 16, wherein said delivery point of the compressed natural gas is an offshore production structure.

34. System according to claim 16, wherein said delivery point of the compressed natural gas is a liquefaction unit located on land.

35. System according to claim 32, wherein said delivery point are reservoirs of compressed natural gas, located on land.

36. Use of the compressed gas produced by the method of claim 1, using the system defined in claim 16, wherein is in the production of natural liquefied gas using at least part of the accumulated energy in the compression of the natural gas carried out on board of a small vessel .

37. Use of the compressed gas produced by the method of claim 1, using the system defined in claim 16, wherein is in the generation of energy for decontamination, dehydration and compression plant of natural gas located in a small vessel and in the movement of said vessel.

38. Use of the compressed gas produced by the method of claim 1, using the system defined in claim 16, wherein is in start-up of production or resumption of natural gas production in wells that have been shut down and have no other source of economically feasible gas.

39. Use of the compressed gas produced by the method of claim 1, using the system defined in claim 16, wherein is in the operation of the rig or other offshore structures .