GB2559149A

GB2559149A - Offshore CO2 transport system

Info

Publication number: GB2559149A
Application number: GB1701325.1A
Authority: GB
Inventors: Mainza De Koeijer Gelein
Original assignee: Statoil Petroleum ASA
Current assignee: Equinor Energy AS
Priority date: 2017-01-26
Filing date: 2017-01-26
Publication date: 2018-08-01
Anticipated expiration: 2037-01-26
Also published as: GB2559149B; GB201701325D0

Abstract

An apparatus 100; 200 and method 300; 400; 500 for offshore transport of CO2 are provided. The method includes transporting at least one transfer tank containing CO2 130; 140; 150; 230; 240; 250 to an offshore installation 110; 210 on a floating vessel 120, 220, conveying the transfer tank(s) to the offshore installation and coupling the transfer tank(s) to a CO2 inlet for emptying the transfer tank(s) of CO2 while away from the floating vessel. The floating vessel is free to return to shore and come back with further transfer tanks while the CO2 is being offloaded at the offshore installation. The floating vessel may be loaded at the offshore installation with empty transfer tanks and/or transfer tanks filled with hydrocarbons for return to shore.

Description

(54) Title of the Invention: Offshore CO2 transport system Abstract Title: Offshore CO2 transport system (57) An apparatus 100; 200 and method 300; 400; 500 for offshore transport of CO₂ are provided. The method includes transporting at least one transfer tank containing CO₂130; 140; 150; 230; 240; 250 to an offshore installation 110; 210 on a floating vessel 120, 220, conveying the transfer tank(s) to the offshore installation and coupling the transfer tank(s) to a CO₂ inlet for emptying the transfer tank(s) of CO₂ while away from the floating vessel. The floating vessel is free to return to shore and come back with further transfer tanks while the CO2 is being offloaded at the offshore installation. The floating vessel may be loaded at the offshore installation with empty transfer tanks and/or transfer tanks filled with hydrocarbons for return to shore.

1/7

100

112

Figure 1

Figure 2

2/7

100

110

102

104

Figure 3

Figure 4

100

Figure 6

4/7

200

Figure 8

5/7

300

6/7

402

400

Bring full CO₂ tank(s) on floating vessel

7/7

500

- 1 OFFSHORE CO₂ TRANSPORT SYSTEM

The present invention relates to an apparatus and method for transporting

CO₂ offshore.

It is known that CO₂ which is captured can be injected underground for storage of CO₂ and/or for Enhanced Oil Recovery. Long-term storage (or sequestration) of CO₂ has been proposed as a way to reduce build-up of greenhouse gases in the atmosphere, and therefore to counter-act global warming and other climate changes that may occur due to such greenhouse gases. CO₂Enhanced Oil Recovery (EOR) is a secondary or tertiary recovery method for oil production.

However, it has been found that the time taken for transporting the CO₂offshore on a tanker towards an offshore installation for injection underground, as well as the time taken for unloading the CO₂, results in an inefficient system. The tanker must remain in place by the offshore installation while the CO₂ is unloaded and injected underground.

One possible solution to this problem is the use of permanent pipeline for piping the CO₂ offshore, without the need for tankers. However, due to the large capital expenditures associated with this equipment, especially when the hydrocarbon well and/or injection well for subsea geological storage is a long way from the shore, it is often not financially viable to achieve. Moreover, ships are more flexible in both timing and location than pipelines.

Consequently, it is desirable to provide a system and method for more efficient transportation of CO₂ offshore.

According to a first aspect of the invention, there is provided a method for offshore transport of CO₂ comprising: providing at least one transfer tank for transport of CO₂; providing an offshore installation with a CO₂ inlet configured for fluid communication with the at least one transfer tank; transporting the at least one transfer tank to the offshore installation using a floating vessel whilst the at least one transfer tank contains CO₂; conveying the at least one transfer tank between the floating vessel and the offshore installation using a transfer device; and coupling the at least one transfer tank to the CO₂ inlet in order that the CO₂ can be emptied from the transfer tank via the CO₂ inlet.

By providing transfer tanks in which CO₂ is transported and subsequently transferred to an offshore installation, the floating vessel is not required to remain

-2by the offshore installation while the CO₂ is emptied from the transfer tanks.

Instead, the floating vessel is free to leave the offshore installation while CO₂ is being emptied from the transfer tanks via the CO₂ inlet of the offshore installation.

In some embodiments, one or more empty transfer tank(s) may be returned to the floating vessel from the offshore installation. The empty transfer tank(s) may be transfer tanks other than the transfer tank(s) brought by the floating vessel. With this arrangement, the waiting time for the floating vessel can be significantly reduced, since all that is required is for the transfer tank(s) containing CO₂ to be removed from the floating vessel and to be replaced with empty transfer tanks. The floating vessel is then free to return to shore with the empty transfer tanks while the transfer tanks containing CO₂ remain at the offshore installation to be emptied in time for the floating vessel’s return.

The transfer tank may also be able to carry hydrocarbons in the form of oil and/or gas on the return journey on the floating vessel, as described in at least some of the below embodiments.

The method may further comprise: fluidly engaging the transfer tank containing CO₂ with the CO₂ inlet; and discharging the CO₂ from the transfer tank therethrough to the offshore installation.

Once the CO₂ leaves the transfer tank, it may be discharged into the offshore installation, whereupon it can be stored and/or used for CO₂ Enhanced Oil Recovery.

The method may further comprise: providing the offshore installation with an engagement pad; and engaging the transfer tank with the engagement pad when it is at the offshore installation.

By engaging the transfer tank with an engagement pad at the offshore installation, a secure means of retaining the transfer tank in place can be achieved.

The offshore installation may be a subsea installation. In this arrangement, there may be no need for long risers, or indeed, for any risers if the offshore installation is at the sea bed. This can help reduce capital expenditures of the system which can be greatly raised due to material cost of long risers.

The method may further comprise: providing the offshore installation with a hydrocarbon outlet configured for fluid communication of hydrocarbons from the offshore installation to at least one transfer tank.

In some embodiments, the hydrocarbon outlet may be separate from the CO₂ inlet, whereas in other embodiments, the hydrocarbon outlet and the CO₂ inlet

-3may be part of the same single connector. In either arrangement, the transfer tank can be filled with hydrocarbons from the offshore installation. This may be done once the CO₂ has been emptied.

The method may further comprise conveying at least one transfer tank containing CO₂ from the floating vessel to the CO₂ inlet of the offshore installation using the transfer device; and conveying at least one transfer tank containing hydrocarbons from the hydrocarbon outlet of the offshore installation to the floating vessel using the transfer device.

With this method, the waiting time for the floating vessel can be significantly reduced, since all that is required is for the transfer tanks containing CO₂ to be removed from the floating vessel and to be replaced with transfer tanks containing hydrocarbons and optionally produced formation water. The floating vessel is then free to return to shore with the transfer tanks containing hydrocarbons while the transfer tanks containing CO₂ remain at the offshore installation to be emptied and the same or another set of transfer tanks may be filled with hydrocarbons in time for the floating vessel’s return.

In some embodiments, the transfer tanks conveyed to the floating vessel may be empty, partially full of hydrocarbons, full of hydrocarbons or a mixture of the above option.

The method may further comprise: concurrently connecting the CO₂ inlet and hydrocarbon outlet to a transfer tank when it is at the offshore installation, such that the transfer tank is to be filled with hydrocarbons; or conveying at least one transfer tank which has been emptied of CO₂ from the CO₂ inlet of the offshore installation to the hydrocarbon outlet of the offshore installation using the transfer device.

In the first option above, the CO₂ inlet and the hydrocarbon outlet can be simultaneously connected to the same transfer tank. This arrangement allows simultaneous emptying of CO₂ and filling with hydrocarbons to take place. This provides additional time savings compared to the second option above, since there is no need to wait for the transfer tank to be emptied of CO₂, and/or to convey the transfer tank after emptying of CO₂, before the transfer tank can be filled with hydrocarbons.

In the second option above, the steps of emptying of CO₂ and filling with hydrocarbons are kept separate and thus a more modular system is achieved. In this arrangement, there is no possibility of conveying a transfer tank which still

-4contains a significant amount of CO₂ from the hydrocarbon outlet back to the floating vessel. This is because the CO₂ would need to have been emptied from the transfer tank before the transfer tank was conveyed from the CO₂ inlet to the separate hydrocarbon outlet for filling with hydrocarbons.

The method may further comprise: providing the at least one transfer tank with a piston for separation of hydrocarbons and CO₂ within the transfer tank; and sliding the piston within the transfer tank, as a moving divider, as quantities of CO₂and/or hydrocarbons vary within the transfer tank.

This arrangement allows the hydrocarbons entering the transfer tank to be kept separate from the CO₂ exiting the transfer tank, if the two flows are occurring at the same time. Additionally, if one of the CO₂ and the hydrocarbons has a higher flow rate, then there will be either a suction force or a pressure force on the piston, which will act to equalize the flow rates.

Alternatively, if the hydrocarbons are to be pumped into the transfer tank after it has been emptied of CO₂, then the piston ensures that any remnant of CO₂does not contaminate the hydrocarbons.

The transfer device may comprise at least one crane. The crane may be at a topside floating location, which avoids the need for long piles to support the crane.

The method may further comprise providing the transfer device and/or the floating vessel with a power supply.

The method may further comprise providing compressors and/or pumps for transferring CO₂ and/or hydrocarbons to or from the at least one transfer tank.

This arrangement allows faster flow of CO₂ and hydrocarbons out of and into the transfer tank respectively.

According to a second aspect of the invention, there is provided an apparatus for offshore transport of CO₂ comprising: at least one transfer tank for transport of CO₂; an offshore installation comprising a CO₂ inlet configured for fluid communication with the at least one transfer tank to receive CO₂; a floating vessel configured to transport the at least one transfer tank to the offshore installation whilst the at least one transfer tank contains CO₂; and a transfer device for conveying the at least one transfer tank between the floating vessel and the offshore installation so that the at least one transfer tank can be coupled to the CO₂inlet in order that the CO₂ can be emptied from the transfer tank via the CO₂ inlet.

-5As CO₂ is transported in transfer tanks which are subsequently transferred to an offshore installation, the floating vessel is not required to remain by the offshore installation while the CO₂ is emptied from the transfer tanks. Instead, the floating vessel is free to leave the offshore installation while CO₂ is being emptied from the transfer tanks via the CO₂ inlet of the offshore installation.

In some embodiments, one or more empty transfer tank(s) may be returned to the floating vessel from the offshore installation. The empty transfer tank(s) may be transfer tanks other than the transfer tank(s) brought by the floating vessel. With this arrangement, the waiting time for the floating vessel can be significantly reduced, since all that is required is for the transfer tank(s) containing CO₂ to be removed from the floating vessel and to be replaced with empty transfer tank(s).

The floating vessel is then free to return to shore with the empty transfer tanks while the transfer tanks containing CO₂ remain at the offshore installation to be emptied in time for the floating vessel’s return.

The transfer tank containing CO₂ may be configured to fluidly engage with the CO₂ inlet, and the apparatus may be configured to discharge the CO₂ from the transfer tank through the CO₂ inlet to the offshore installation.

Once the CO₂ leaves the transfer tank, it is discharged into the offshore installation, whereupon it can be stored and/or used for CO₂ Enhanced Oil Recovery.

The offshore installation may further comprise an engagement pad for engaging the transfer tank when it is at the offshore installation. This arrangement provides a secure means of retaining the transfer tank in place can be achieved.

The offshore installation may further comprise a hydrocarbon outlet configured for fluid communication of hydrocarbons from the offshore installation to at least one transfer tank.

-6may be part of the same single connector. In either arrangement, the transfer tank can be filled with hydrocarbons from the offshore installation. This may be done once the CO₂ has been emptied.

The transfer device may be further configured to: convey at least one transfer tank containing CO₂ from the floating vessel to the CO₂ inlet of the offshore installation; and convey at least one transfer tank containing hydrocarbons from the hydrocarbon outlet of the offshore installation to the floating vessel.

With this method, the waiting time for the floating vessel can be significantly reduced, since all that is required is for the transfer tanks containing CO₂ to be removed from the floating vessel and to be replaced with transfer tanks containing hydrocarbons and optionally produced formation water. The floating vessel is then free to return to shore with the transfer tanks containing hydrocarbons while the full transfer tanks remain at the offshore installation to be emptied and the same or another set of transfer tanks may be filled with hydrocarbons in time for the floating vessel’s return.

The CO₂ inlet and hydrocarbon outlet may be concurrently connectable to a transfer tank when it is at the offshore installation, such that the transfer tank is arranged to be filled with hydrocarbons; or the transfer device may be further configured to convey at least one transfer tank which has been emptied of CO₂ from the CO₂ inlet of the offshore installation to the hydrocarbon outlet of the offshore installation.

In the second option above, the steps of emptying of CO₂ and filling with hydrocarbons are kept separate and thus a more modular system is achieved. In this arrangement, there is no possibility of conveying a transfer tank which still contains a significant amount of CO₂ from the hydrocarbon outlet back to the

-7floating vessel. This is because the CO₂ would need to have been emptied from the transfer tank before the transfer tank was conveyed from the CO₂ inlet to the separate hydrocarbon outlet for filling with hydrocarbons.

The at least one transfer tank may comprise a piston for separation of hydrocarbons and CO₂ within the transfer tank, wherein the piston is slideable within the transfer tank, acting as a moving divider as quantities of CO₂ and/or hydrocarbons vary within the transfer tank.

The transfer device and/or the floating vessel may comprise a power supply.

The apparatus may comprise compressors and/or pumps for transferring CO₂ and/or hydrocarbons to or from the at least one transfer tank.

Certain embodiments of the present invention will now be described by way of example only and with reference to the drawings in which:

Figure 1 shows schematically a first CO₂ transfer apparatus at a stage of removing a transfer tank containing CO₂ from a floating vessel using a crane;

Figure 2 shows schematically the apparatus of Figure 1, in which the transfer tank containing CO₂ has been transferred to an engagement pad at the sea bed;

Figure 3 shows schematically the apparatus of Figure 2, in which the transfer tank is engaged with the engagement pad at the sea bed for emptying of CO₂ and the floating vessel has returned to shore;

-8Figure 4 shows schematically the apparatus of Figure 3, in which the floating vessel has returned with a further transfer tank of CO₂ and the crane has removed the empty transfer tank from the engagement pad;

Figure 5 shows schematically the apparatus of Figure 4, in which the empty transfer tank and the transfer tank full of CO₂ have been exchanged using the crane;

Figure 6 shows schematically a second CO₂ transfer apparatus having two engagement pads for emptying a transfer tank of CO₂ and filling a transfer tank with hydrocarbons respectively;

Figure 7 shows schematically the apparatus of Figure 6, in which a floating vessel has brought a transfer tank of CO₂;

Figure 8 shows schematically the apparatus of Figure 7, in which the empty transfer tank has been moved to the hydrocarbon engagement pad, the transfer tank filled with hydrocarbons has been moved to the floating vessel and the transfer tank containing CO₂ on the floating vessel has been transferred to the CO₂engagement pad;

Figure 9 shows a flowchart depicting a first method for transporting CO₂;

Figure 10 shows a flowchart depicting a second method for transporting CO₂; and

Figure 11 shows a flowchart depicting a third method for transporting CO₂.

In the Figures like reference signs denote like features.

A first method 300 for transporting CO₂ is shown, to be read in conjunction with the depicted first apparatus 100 of Figure 1. Figure 1 shows a first apparatus 100 comprising an offshore installation 110 in the sea 102. At the sea bed 104, there is a CO₂ engagement pad 114 which is connected to a CO₂ inlet 116 to an injection well for subsea geological storage. The apparatus 100 comprises a floating vessel 120 which, as shown in step 302 and in Figure 1, has brought a transfer tank containing CO₂ 130 from the shore (not shown) to the offshore installation 110. A crane 112 of the offshore installation 110 operably connects to the transfer tank containing CO₂130 for transfer from the floating vessel 120.

At step 304 and as shown in Figure 2, the crane 112 has transferred the transfer tank 130 to the CO₂ engagement pad 114 for operable connection with the CO₂ inlet 116.

Once the transfer tank 130 has been removed from the floating vessel 120, the floating vessel 120 is free to leave the offshore installation 110 to return to

-9shore. The floating vessel 120 to return to shore and return with a further transfer tank 140 which contains CO₂ (see Figure 4), as shown in step 308. Meanwhile, as shown in step 306, the transfer tank 130 which previously contained CO₂ is emptied via the CO₂ inlet 116.

The next step 310 is shown at Figures 4 and 5. The crane 112 swaps the transfer tanks 130, 140 by transferring the empty transfer tank 130 back onto the floating vessel 120, and by transferring the transfer tank 140 containing CO₂ to the engagement pad 114 operatively connected to the CO₂ inlet 116.

To carry out this operation, the crane may be able to separately lift two transfer tanks at the same time, and/or there may be a temporary holding place for a first transfer tank to be held at the offshore installation whilst a second transfer tank is moved by the crane to free up a space for the first transfer tank at the engagement pad or on the vessel. For example, there may be a “spare” engagement pad. Alternatively, or in addition, the vessel may have multiple spaces in the cargo hold for receiving multiple transfer tanks and it may be used with a spare space in the cargo hold being available during operation of the crane.

Steps 312 and 314 occur at least partially simultaneously. At step 312, the transfer tank 140 is emptied of CO₂, while at step 314 the floating vessel 120 travels to shore with the empty transfer tank 130 and returns with a transfer tank containing CO₂.

The method 300 then repeats loop-wise steps 310, 312 and 314.

A second method 400 is shown in Figure 10, for a second apparatus 200 such as shown in Figures 6-8. As shown in Figure 6, apparatus 200 comprises an offshore installation 210 in the sea 202. At the sea bed 204, there is a CO₂engagement pad 214 which is connected to a CO₂ inlet 216 to an injection well for geological subsea storage, as well as a hydrocarbon engagement pad 217 which is connected to a hydrocarbon outlet 218 from a hydrocarbon production well. The apparatus 200 comprises a floating vessel 220 (see Figures 7 and 8) which, as shown in step 402, brings a transfer tank 230 containing CO₂ from the shore (not shown) to the offshore installation 210. A crane 212 of the offshore installation 210 operably connects to the transfer tank 230 containing CO₂, for transfer from the floating vessel 220.

At step 404, the crane 212 transfers the transfer tank 230 to the CO₂engagement pad 214 for operable connection with the CO₂ inlet 216.

- 10Once the transfer tank 230 has been removed from the floating vessel 220, the floating vessel 220 is free to leave the offshore installation 210 to return to shore. At step 408, the floating vessel 220 travels to shore and return with a further transfer tank 240 which contains CO₂. Meanwhile, as shown in step 406, the transfer tank 230 which previously contained CO₂ is emptied via the CO₂ inlet 216.

The next step 410 involves the crane 212 carrying out two transfers. One transfer is of the empty transfer tank 230 from the CO₂ engagement pad 214 to the hydrocarbon engagement pad 217 for filling with hydrocarbons via the hydrocarbon outlet 218. The other transfer at step 410 is of the transfer tank 240 which contains CO₂ from the floating vessel 220 to the CO₂ engagement pad 214 operatively connected to the CO₂ inlet 216.

Steps 412, 414 and 416 then occur at least partially simultaneously and this is illustrated in Figures 6-7. At step 412 the transfer tank 240 is emptied of CO₂, while at step 413 the empty transfer tank 230 is filled with hydrocarbons. The transfer tank which has been filled with hydrocarbons may also be referred to as a hydrocarbons transfer tank. Meanwhile, at step 416, the floating vessel 220 travels to shore and returns with a transfer tank 250 containing CO₂.

The next step 418 involves the crane 212 carrying out three transfers. A first transfer is of the empty transfer tank 240 from the CO₂ engagement pad 214 to the hydrocarbon engagement pad 217 for filling with hydrocarbons via the hydrocarbon outlet 218. A second transfer at step 418 is of the transfer tank 230 which has been filled with hydrocarbons from the hydrocarbon engagement pad 217 to the floating vessel 220. A third transfer at step 418 is of the transfer tank 250 which contains CO₂ from the floating vessel 220 to the CO₂ engagement pad 214 operatively connected to the CO₂ inlet 216. The arrangement of the transfer tanks 230, 240, 250 before step 418 is shown in Figure 7, while the arrangement of the same after step 418 is shown in Figure 8.

- 11 Steps 420, 422 and 424 occur at least partially simultaneously. At step 420, the transfer tank 250 is emptied of CO₂, at step 422, the empty transfer tank 240 is filled with hydrocarbons, while at step 424 the floating vessel 420 travels to shore with the transfer tank 230 which contains hydrocarbons and returns with a transfer tank which contains CO₂.

The method 400 then repeats loop-wise steps 418, 420, 422 and 424.

A third method 500 is shown in Figure 11, for an apparatus similar to apparatus 200 as shown in Figures 6-8 except that the engagement pads 214, 217 are one and the same. The apparatus comprises an offshore installation in the sea. At the sea bed, there is an engagement pad which is connected both to a CO₂ inlet to a hydrocarbon well or an injection well for subsea geological storage and to a hydrocarbon outlet from a hydrocarbon production well. The apparatus comprises a floating vessel. At step 502, the floating vessel brings a transfer tank containing CO₂ from the shore to the offshore installation. A crane of the offshore installation operably connects to the transfer tank containing CO₂ for transfer from the floating vessel.

At step 504, the crane transfers the transfer tank to the CO₂ engagement pad for operable connection with the CO₂ inlet and the hydrocarbon outlet.

Once the transfer tank containing CO₂ has been removed from the floating vessel, the floating vessel is free to leave the offshore installation to return to shore. At step 508, the floating vessel travels to shore and returns with a further transfer tank which contains CO₂. Meanwhile, as shown in step 506, the transfer tank which previously contained CO₂ is emptied of CO₂ via the CO₂ inlet and filled with hydrocarbons via the hydrocarbon outlet.

The next step 510 involves the crane carrying out two transfers. One transfer is of the transfer tank now filled with hydrocarbons (also referred to herein as a “hydrocarbon transfer tank”) from the engagement pad to the floating vessel. The other transfer at step 510 is of the further transfer tank which contains CO₂from the floating vessel to the engagement pad.

To carry out this operation, the crane may be able to separately lift two transfer tanks at the same time, and/or there may be a temporary holding place for a first transfer tank to be held at the offshore installation whilst a second transfer tank is moved by the crane to free up a space for the first transfer tank at the engagement pad or on the vessel. For example, there may be a “spare” engagement pad. Alternatively, or in addition, the vessel may have multiple spaces

- 12 in the cargo hold for receiving multiple transfer tanks and it may be used with a spare space in the cargo hold being available during operation of the crane.

Steps 512 and 514 then occur at least partially simultaneously. At step 512 the transfer tank is emptied of CO₂ and filled with hydrocarbons. The transfer tank which has been filled with hydrocarbons may also be referred to as a “hydrocarbon transfer tank”. Meanwhile, at step 514, the floating vessel travels to shore with the hydrocarbon transfer tank and returns with a transfer tank containing CO₂.

The method 500 then repeats loop-wise steps 510, 512 and 514.

It should be noted that throughout the above description and in the Figures, although only one transfer tank is depicted and described in each location, multiple transfer tanks are also envisioned as being in one or more of the floating vessel and the engagement pad(s) respectively.

Further, alternatives to the third method include the CO₂ inlet and the hydrocarbon outlet being a single connector which connects to a transfer tank. This may for example be used in series as a CO₂ inlet and then as a hydrocarbon outlet, in order to empty and then fill the transfer tank.

In the apparatus of the first or second methods, it is envisioned that the transfer tank may include a piston for separation of CO₂ and hydrocarbons. This arrangement prevents cross-contamination of any remnant of CO₂ with the incoming hydrocarbons and also prevents egress of hydrocarbons together with the CO₂.

Claims

1. A method for offshore transport of CO2 comprising: providing at least one transfer tank for transport of CO2; providing an offshore installation with a CO2 inlet configured for fluid communication with the at least one transfer tank;

transporting the at least one transfer tank to the offshore installation using a floating vessel whilst the at least one transfer tank contains CO2;

conveying the at least one transfer tank between the floating vessel and the offshore installation using a transfer device; and coupling the at least one transfer tank to the CO2 inlet in order that the CO2 can be emptied from the transfer tank via the CO2 inlet.

2. A method as claimed in claim 1, further comprising:

fluidly engaging the transfer tank containing CO2 with the CO2 inlet; and discharging the CO2 from the transfer tank therethrough to the offshore installation.

3. A method as claimed in claim 1 or 2, further comprising: providing the offshore installation with an engagement pad; and engaging the transfer tank with the engagement pad when it is at the offshore installation.

4. A method as claimed in any of claims 1,2 or 3, wherein the offshore installation is a subsea installation.

5. A method as claimed in any preceding claim, further comprising: providing the offshore installation with a hydrocarbon outlet configured for fluid communication of hydrocarbons from the offshore installation to at least one transfer tank.

6. A method as claimed in claim 5, further comprising:

conveying at least one transfer tank containing CO2 from the floating vessel to the CO2 inlet of the offshore installation using the transfer device; and

- 14conveying at least one transfer tank containing hydrocarbons from the hydrocarbon outlet of the offshore installation to the floating vessel using the transfer device.

7. A method as claimed in claim 6, further comprising:

concurrently connecting the CO2 inlet and hydrocarbon outlet to a transfer tank when it is at the offshore installation, such that the transfer tank is to be filled with hydrocarbons; or conveying at least one transfer tank which has been emptied of CO2 from the CO2 inlet of the offshore installation to the hydrocarbon outlet of the offshore installation using the transfer device.

8. A method as claimed in any of claims 5 to 7, further comprising: providing the at least one transfer tank with a piston for separation of hydrocarbons and CO2 within the transfer tank; and sliding the piston within the transfer tank, as a moving divider, as quantities of CO2 and/or hydrocarbons vary within the transfer tank.

9. A method as claimed in any preceding claim wherein the transfer device comprises at least one crane.

10. A method as claimed in any preceding claim further comprising providing compressors and/or pumps for transferring CO2 and/or hydrocarbons to or from the at least one transfer tank.

11. An apparatus for offshore transport of CO2 comprising: at least one transfer tank for transport of CO2;

an offshore installation comprising a CO2 inlet configured for fluid communication with the at least one transfer tank to receive CO2;

a floating vessel configured to transport the at least one transfer tank to the offshore installation whilst the at least one transfer tank contains CO2; and a transfer device for conveying the at least one transfer tank between the floating vessel and the offshore installation so that the at least one transfer tank can be coupled to the CO2 inlet in order that the CO2 can be emptied from the transfer tank via the CO2 inlet.

- 1512. An apparatus as claimed in claim 11, wherein the transfer tank containing CO2 is configured to fluidly engage with the CO2 inlet, and the apparatus is configured to discharge the CO2 from the transfer tank through the CO2 inlet to the offshore installation.

13. An apparatus as claimed in claim 11 or 12, wherein the offshore installation further comprises an engagement pad for engaging the transfer tank when it is at the offshore installation.

14. An apparatus as claimed in any of claims 11, 12 or 13, wherein the offshore installation is a subsea installation.

15. An apparatus as claimed in any of claims 11 to 14, wherein the offshore installation further comprises a hydrocarbon outlet configured for fluid communication of hydrocarbons from the offshore installation to at least one transfer tank.

16. An apparatus as claimed in claim 15, wherein the transfer device is further configured to:

convey at least one transfer tank containing CO2 from the floating vessel to the CO2 inlet of the offshore installation; and convey at least one transfer tank containing hydrocarbons from the hydrocarbon outlet of the offshore installation to the floating vessel.

17. An apparatus as claimed in claim 16, wherein the CO2 inlet and hydrocarbon outlet are concurrently connectable to a transfer tank when it is at the offshore installation, such that the transfer tank is arranged to be filled with hydrocarbons; or wherein the transfer device is further configured to convey at least one transfer tank which has been emptied of CO2 from the CO2 inlet of the offshore installation to the hydrocarbon outlet of the offshore installation.

18. An apparatus as claimed in any of claims 15 to 17, wherein the at least one transfer tank comprises a piston for separation of hydrocarbons and CO2 within the transfer tank, wherein the piston is slideable within the transfer tank, acting as a

- 16moving divider as quantities of CO2 and/or hydrocarbons vary within the transfer tank.

19. An apparatus as claimed in any of claims 11 to 18, wherein the transfer 5 device comprises at least one crane.

20. An apparatus as claimed in any of claims 11 to 19, further comprising compressors and/or pumps for transferring CO2 and/or hydrocarbons to or from the at least one transfer tank.

Application No: GB1701325.1 Examiner: Mr Richard Nicholls