Patent Application
20170256159
The invention relates to a method and system for suppressing nuisance alarms of a Floating Production, Storage and Offloading (FPSO) surveillance system due to oscillating liquid level variations in FPSO crude oil and/or other liquid storage tanks resulting from oscillating motions of the FPSO unit during severe weather conditions.
FPSO surveillance systems are available from vendors, such as Moxa Inc. (URL:
http://www.moxa.com/application/Alarm-to-Video_Monitoring_for_Offshore_Oil_Gas_FPSO.htm) and may be part of a Distributed Control System (DCS) used for integrated control of FPSO crude oil production, storage, treatment and offloading operations.
FPSO surveillance systems may comprise liquid level monitoring equipment which monitor a liquid level in FPSO crude oil and/or other liquid storage tanks and alarm FPSO operators if the liquid level changes rapidly and the speed of change exceed a preset threshold, for example due to a liquid leak or due to an excessive liquid influx into the FPSO storage tanks, for example due to pressure fluctuations in the FPSO risers and/or associated oil and/or gas production wells.
During severe weather conditions the FPSO unit will make oscillating motions due to wave and/or wind impact, which may induce waves in the FPSO crude oil and/or other liquid storage tanks, which may generate an excessive amount of nuisance alarms of the FPSO surveillance system.
There is a need for an improved FPSO surveillance system, which does not generate an excessive amount of nuisance alarms during severe weather conditions.
In accordance with the invention there is provided a method for suppressing nuisance alarms of a Floating Production, Storage and Offloading (FPSO) surveillance system due to oscillating liquid level variations in a FPSO storage tank during severe weather conditions, the method comprising:
In accordance with the invention there is furthermore provided a Floating Production, Storage and Offloading (FPSO) surveillance system comprising:
Optionally, the oscillating motion monitoring system comprises a tilt meter that is configured to identify a maximum FPSO inclination angle θ resulting from the oscillating motions of the FPSO unit;
The FPSO surveillance system may be part of a Distributed Control System (DCS) that monitors and manages well effluent transfer and storage at the FPSO unit, and which DCS may comprise an acoustic and/or visual alarm system that alerts FPSO operating staff about potentially unsafe liquid level variations in the FPSO storage tank and the DCS comprises an alarm threshold that suppresses nuisance acoustic and/or visual alarms if the monitored liquid level variations do not exceed the estimated liquid level variations due to the monitored oscillating motions. The well effluents may comprise a multiphase mixture of crude oil, condensates, water and/or natural gas, which is at least partially separated at the FPSO unit and stored in at least one FPSO storage tank.
The FPSO unit may comprise an elongate turret moored floating vessel equipped with an FPSO tilt meter that is configured to identify an aggregated maximum inclination angle e resulting from aggregated oscillating rolling, pitching and yawing motions of the elongate turret moored floating vessel during severe weather conditions.
Furthermore, the system according to the invention may comprise a computer readable medium, which, when connected to a computer, induces the computer to execute the method according to the invention. These and other features, embodiments and advantages of the method and system according to the invention are described in the accompanying claims, abstract and the following detailed description of non-limiting embodiments depicted in the accompanying drawings, in which description reference numerals are used which refer to corresponding reference numerals that are depicted in the drawings.
Similar reference numerals in different figures denote the same or similar objects. Objects and other features depicted in the figures and/or described in this specification, abstract and/or claims may be combined in different ways by a person skilled in the art.
The FPSO unit 1 is connected to subsea oil and/or gas production wells (not shown) by subsea flowlines (not shown) that are connected to a flexible riser assembly 5.
Crude oil and/or gas produced from the subsea wells may be separated and/or otherwise treated at the FPSO unit 1 and temporarily stored in one or more FPSO crude oil and/or other liquid storage tanks 6 that may extend along at least a substantial part of the length and width of the hull of the FPSO unit 1.
From time to time crude oil export tankers (not shown) may be moored alongside or behind the FPSO unit and unload crude oil from the storage tanks 6 via a crude oil offloading hose 8.
The crude oil and/or other liquid level in the FPSO storage tanks 6 will therefore cyclically rise and fall and will be monitored by a FPSO surveillance system 7 that may be part of a Distributed Control System (DCS) that assist FPSO operators and other staff to monitor, safeguard and manage the overall production, performance, integrity and safety of the FPSO operations.
For this purpose the FPSO surveillance system 7 comprises level gauges that monitor the liquid level in the FPSO storage tanks 6 and that give an alarm if the liquid level changes rapidly, for example due to a pressure surge in the wells and/or production risers 5 and/or due to a damage or rupture of a production riser 5 and/or offloading hose (not shown).
The upper part of
For the elongate FPSO unit 1 shown in
During severe weather conditions sea waves will initiate significant oscillating rolling motion of the FPSO unit 1, which will also initiate significant waves of the crude oil and/or other liquid in the FPSO storage tanks 6.
The lower horizontal line 22 in
In the FPSO surveillance system 7 according to the invention generation of nuisance alarms due to wave action in the FPSO tanks 6 during severe weather conditions is suppressed by inducing the FPSO surveillance system 7 to monitor the oscillating tilt angle θ of the FPSO unit at least due to the sway action about the longitudinal axis X and to suppress nuisance alarms of the liquid level gauge or gauges if the liquid level variations ΔH in the FPSO storage tanks do not exceed (W/2)*sin θ, or in other words by formula:
Δ≦H(W/2)*sin θ,
wherein:
It will be understood that the above formula may be provided with an empirically determined correction co-efficient and that the FPSO surveillance system 7 and method according to the invention will effectively suppress nuisance alarms that are solely due to wave action of the liquid stored in the FPSO storage tanks 6 without reducing the sensitivity of the FPSO surveillance system 7 for rapid liquid level changes in the FPSO storage tanks 6 due to leaks and/or pressure surges.
The FPSO unit 1 may be equipped with one or more storage tanks 6 for storage of crude oil, water, condensates, fuel and/or other liquids, which may each be equipped with liquid level gauges and alarms for exceptional liquid level variations.
If the FPSO unit 1 is relatively short then also pitching motions may be significant and taken into account in addition to the swaying motions. In such case the FPSO surveillance system may monitor a maximum aggregated tilt angle θa, which is an accumulation of the maximum sway angle θs and a maximum pitch angle θp and in such case the width W of the FPSO storage tank or tanks 6 may be measured in a vertical plane in which the aggregated tilt angle θa resides.
It will be understood that the FPSO unit 1 may be moored in a sea, lake, ocean and that a skilled person may make various modifications and alterations to the FPSO surveillance method and system according to the invention as described in the foregoing detailed description of depicted embodiments and shown in the associated drawings without exercising inventive skills.
Therefore, the system and method according to the present invention are well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the present invention. While compositions and methods are described in terms of “comprising,” “containing,” or “including” various components or steps, the compositions and methods can also “consist essentially of” or “consist of” the various components and steps. All numbers and ranges disclosed above may vary by some amount. Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range is specifically disclosed. In particular, every range of values (of the form, “from about a to about b,” or, equivalently, “from approximately a to b,” or, equivalently, “from approximately a-b”) disclosed herein is to be understood to set forth every number and range encompassed within the broader range of values. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. Moreover, the indefinite articles “a” or “an”, as used in the claims, are defined herein to mean one or more than one of the element that it introduces. If there is any conflict in the usages of a word or term in this specification and one or more patent or other documents that may cited herein by reference, the definitions that are consistent with this specification should be adopted.
| Number | Date | Country | Kind |
|---|---|---|---|
| 14182835.0 | Aug 2014 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2015/069722 | 8/28/2015 | WO | 00 |
