Hydraulic and earth engineering – Marine structure or fabrication thereof
Reexamination Certificate
2001-03-27
2004-11-16
Kreck, John (Department: 3673)
Hydraulic and earth engineering
Marine structure or fabrication thereof
C405S210000, C166S350000, C114S230130
Reexamination Certificate
active
06817809
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
The invention relates generally to offshore oil production and, more particularly, to offshore oil storage that can be used for deepwater applications.
2. Background Art
A major factor in determining whether or not to exploit an offshore oil and gas field is the feasibility of handling and transporting the hydrocarbons to market once they are produced. Generally, hydrocarbons produced offshore must be transported to land-based facilities for subsequent processing and distribution. Temporary storage may be provided at the offshore production site for holding limited quantities of hydrocarbons produced and awaiting transport to shore. In some cases, equipment is also provided at the offshore production site for separating and/or treating the produced hydrocarbons prior to storing and transporting them to shore.
In the case of an offshore production facility located relatively close to shore, hydrocarbons produced may be feasibly transported to shore through a pipeline system extending from the offshore site (e.g., offshore platform or subsea wells) to the shore along the ocean floor or seabed. This type of pipeline system is typically preferred, when feasible, because it permits the constant flow of hydrocarbons to shore regardless of the weather or other adverse conditions.
However, in some parts of the world, the use of a seabed pipeline system for transporting hydrocarbons to shore may result in expensive pipeline tariffs.
For offshore facilities located a great distance from shore, construction of a pipeline to shore is typically not practicable. In these cases, floating vessels, known as tankers, are used to transport hydrocarbons to shore. Tankers are specially designed vessels which have liquid hydrocarbon storage (or holding) facilities, typically, in the hull of the vessel. In the case of crude oil production, water, vapor, and other impurities are typically removed from the oil prior to offloading the oil onto tankers for transport. In some cases, tankers include additional equipment for separating and treating crude oil prior to storage and transport.
Because tankers float on the water surface, their operations are largely dependent upon surface conditions, such as wind, wave, and current conditions. Thus, tankers are typically not operated during severe or unfavorable conditions. Additionally, operation of a particular tanker may be interrupted periodically for maintenance and repairs. Due to the large expense associated with maintaining tankers, tankers may also be shared among several offshore sites. As a result, long delay periods may occur between tanker availability for a particular site. Therefore, it is desirable to have storage facilities available at the offshore site to avoid the need to “shut-in” (or halt) production due to tanker unavailability. Additionally, offshore storage may be desired to allow for continuous production operations, independent of tanker hook-up and disconnect operations, as discussed below.
Examples of existing offshore production and storage systems used for deepwater applications are illustrated in FIG.
1
and in
FIGS. 2A-2D
.
FIG. 1
shows one example of a production platform
2
used in a deepwater application. This platform
2
includes processing and storage equipment
4
for separating and treating crude oil collected from subsea wells
6
and storing a limited quantity of the processed oil when transport is not available. Because the surface area and weight carrying capacity of the production platform
2
is extremely limited, storage facilities provided on a platform
2
are limited in size and, thus, inadequate for handling large quantities of hydrocarbons which may be produced during periods of shuttle tanker or other hydrocarbon transport unavailability.
FIG. 2A
shows a floating production, storage, and offloading (FPSO) system
10
which comprises a tanker
11
specially equipped to function as an offshore production facility. The FPSO tanker
11
is permanently moored at the offshore site and connects to the subsea wells or subsea production gathering system
14
through one or more flowlines
18
connected to the production inlet
16
of the FPSO tanker
11
. During production operations, produced hydrocarbons are received, directly or indirectly, from the subsea wells
14
. Once on the FPSO tanker
11
, hydrocarbons are processed and temporarily stored. Hydrocarbons stored on the FPSO tanker
11
are periodically transferred onto a shuffle tanker
12
temporarily positioned in the vicinity of the FPSO tanker
11
during the transfer. Because FPSO systems
10
comprise surface vessels, they are susceptible to severe weather conditions, during which production must be interrupted and the flowlines
16
leading to the FPSO tanker
11
disconnected. Furthermore, positioning of the shuttle tanker
12
close to the FPSO tanker
11
for hydrocarbon transfer is typically limited to relatively calm weather conditions. As a result, the storage space on the FPSO system
10
may become full and production may have to be halted until a shuttle tanker
12
for offloading is provided.
FIG. 2B
shows one example of a floating storage and offloading (FSO) system
20
, which is a pure form of ship-based storage without production facilities on board. Using this type of storage system, produced hydrocarbons from a production platform
22
are transferred to an FSO vessel
26
via a flowline (not shown) extending from the production platform
22
to the FSO system
20
. Hydrocarbons transferred to the FSO vessel
26
are stored, typically in the hull of the FSO vessel
26
. From the FSO vessel
26
, produced hydrocarbons are periodically offloaded onto a shuttle tanker
24
for transport to shore. As in the case of the FPSO system
10
discussed above with reference to
FIG. 2A
, production operations which depend upon an FSO system
20
for storage may be susceptible to production interruptions due to severe weather conditions. Also, during periods when a shuttle tanker
24
is not available for offloading the storage facility on the FSO vessel
26
, it may become fall requiring interruption of production until a shuttle tanker
24
is available.
FIG. 2C
is an illustration of a direct shuttle loading (DSL) system
30
. In a DSL system
30
hydrocarbons produced from subsea wells
33
are collected at an offshore production gathering system, in this case a production platform
32
, and directly offloaded onto a shuttle tanker
34
,
38
when available, through a flowline
36
. For the DSL system shown in
FIG. 2C
, hydrocarbons are loaded onto one shuttle tanker
34
for transport to shore while another shuttle tanker
38
waits nearby for subsequent offloading after the first tanker
34
is fall and en route to shore. Like other tanker-based storage systems described above, production operations which use DSL systems
30
are susceptible to interruptions in production due to severe weather conditions and periods of shuttle tanker unavailability. Additionally, the use of a DSL system
30
may require operation of a larger shuttle tanker fleet because the presence of at least one shuttle tanker
34
,
38
is required at substantially all times in order for production operations to continue. Further, in cases where no temporary storage is provided at the production site, hydrocarbon production will be interrupted every time a shuttle tanker
34
,
38
is connected or disconnected for offloading and transport.
Production platforms have also been developed to integrate oil storage into the hull
44
of a platform, such as a SPAR platform
40
as shown in FIG.
2
D. However, in cases involving significant production volumes, this storage is not adequate during periods of tanker unavailability. Thus, frequent tanker hook-ups to the platform
40
will still be required. In such cases, even a system comprising a platform
40
with integral storage is still too dependent upon the presence of a shuttle tanker
42
.
Other offshore storage systems for deepwater applications may also include sma
Chan Jack H-C.
Choi Michael S.
Tuturea David P.
ConocoPhillips Company
Kreck John
Osha & May L.L.P.
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