CA2081624A1 - System for the control and monitoring of surface or subsea hydrocarbon production - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The present invention relates to a system for the control and monitoring of surface or subsea hydrocarbon production, comprising production equipment to which is supplied hydraulic power and electrical power and signals for the control of valves, etc. and the monitoring of signals from sensors, etc., respectively, said hydraulic power and electrical power and signals being supplied from a fixed or floating monitoring installation, said system supplying power to the subsea electronics units via signal cables which enable several signals to be transmitted simultaneously via the same conductor or pair of conductors. Further the number of selector switches is reduced by arranging the switches in a matrix relative to the solenoid valves to which electrical power shall be supplied.

Description

WO 91/16523 PCltNO91/00043 - A SYSTEM FOR THE CONTROL AND MONITORING OF SURFACE OR SUBSEA
HYDROCARBON PRODUCTION

Field of the invention The present invention relates to a system for the control and monitoring o surface or subsea hydrocarbon production, comprlsing production equipment to which is supplied hydraulic power and electrical power and signals for the control of valves etc. and the monitoring of signals from sensors etc., respect'ively, said hydraulic power and electrical power and signals being supplied from a fixed or floating monitoring installation.

More specifically the invention relates to special signal and power transmission methods for usage in both subsea and surface located control and/or monitoring systems.
Backaround of the invention ..
'Today's methods require either separate wires for signal and power transmission or only one wire for transmission of both signal and power simultaneously.

The common denominator for these two techniques is that they are expensive and the electronic equipment becomes complex, i,e. expensive due to the extensive wiring required, and complex due to the filter units and other hardware electron-ic units required to accomplish such a system.

Disclosure of the invention --. .
In order~to minimize the noise in the system which requires extensive filtering, signal and power are being transmitted :'~''in'`séries,~i.e`;-signal:and~power are~sent~'at-alternatë times : which is indeed one of the advantages~with;this'invention. ' W O 91/16523 PC~r/NO91/00043 In this way the reliability of the signal/data transmission process will be improved as the number of components and the complexity of hardware is substantially reduces. The power -, transmission method requires a device for storage of energy which comprises a part of the system. The energy transfer --efficiency will be further increased by sending the power as square waves. Such a power storing device which is in fact an accumulator when loaded, greatly improves the utilization of the power in the system. The latter is also another significant advantage with the present signal/power transmission method.

In conventional systems there is one electric switch per function to connect current to e.g. a solenoid which controls a hydraulic val~e. Typically, such a system will require four switches per control valve and approximately 40 switches to control the valves on a subsea Xmas tree (satellite well). In the present system these switches are arranged in a matrix such that the number of switches are reduced (depending on the number of switches required), and the space requirements are substantially reduced compared to conventional systems. Further advantages with the described system are increased reliability by the reduced number of failure sources, whilst the functionality is still main-tained.

Further advantages and features of the present inventionwill appear from the following detailed description and the appended claims.
Brief disclosure of the drawinqs Fig. 1 is a sketch illustrating a subsea oil production installation and a control and monitoring installation having-hydraulic and electrical-connections therebetween.

r, Fig.-2_illustrates,in more detail thezequipment associated ith therinstalla~tion shown in Fig ~.?1. t,....~

f . .

W O 91/16523 PC~r/NO91/00043 Fig. 3 is a diagram illustrating the use of filters in connection with the power suply to the equipment.

Fig. 4A is a power/signal scematic diagram of a conventional system of signal/power frequency multiplexing.

Fig. 4B is a power/signal scematic diagram of an embodiment of the present signal/power time multiplexinq technique.

Fig. S illustrates an embodiment of a solenoid arrangement and switch arrangement in matrix format.

Detailed disclosure of embodiments For the purpose of recovering oil and gas accumulations offshore it is at times necessary to drill wells and install wells and/or other production equipment 1a on the seafloor 1b, see Fig. The control of valves 5 etc. and the monitor-ing of signals from sensors 4 etc. is performed from a control room 2. The control room 2 is usually manned and situated either at a nearby fixed or floating platform 2a onshore. Under many conditions, in particular at medium and large water depths, the power to operate the subsea valves 5 will be supplied through hydraulic fluids under pressure. The hydraulic energy is supplied through one or more hoses or pipes 3. A control unit 1 is positioned locally at the subsea installation 1a to distribute pressure to or from actuators 13 which control the valves The aontrol unit 1 also receives, magnifies and codes signals from the subsea installation 1a and transfer these to the control room 2. The control unit 1 receives control signals from-the control room 2 through a cable 3a which contains electrical conductors.
: . .. . ~ . .
Control systems of the described type consist of a surface .. . ., ., . , . ., ., - .. . . . . .. ~ .. ..
- part~and a subsea part connected by cables, see Fig. 2.
'Thers'ubs~ea''rpar~C1a~-cont-a?ins a~ control unit~iiwhich has an hydraulic'section~ and'~an electricai'i ~ection.- Thëi W O 91/16523 P ~ /N O91/00043 hydraulic energy is supplied to the hydraulic section 6 where the hydraulic pressure is distributed to the different actuators 13 by opening and closing hydraulic valves. The hydraulic valves are operated by electromagnets (hereafter referred to as solenoids) which are supplied by electrical signals from the electrical section.

The usual approach for the control of subsea production equipment is to supply hydraulic energy and electrical energy and signals to the subsea installation through separate conduits. These conduits may be bundled in.a single electro-hydraulic cable or in two or more separate cables.

Further, it is usual to have separate cables for the operation of each actuator.

Finally, it is usual to have separate supply for each solenoid valve for electro-magnetically operated hydraulic valves.

The disadvantage of such systems is that a large number of cables or cables with multiple conduits are expensive. In addition, the subsea installation becomes large and the power consumption grows, which also influences the costs.
Finally the number of switches required in the subsea unit is large~ something which increases the number of possible sources of failure and consequently reduces the system reliability.
The present invention provides a combination of three aspects which used together result in considerable ad-vantages relative to the control of subsea hydrocarbon production wells or other subsea production equipment. The 35 advantages.involve reduced.space.requirements, reduced weight of.the equipment, and.a simpler.and less.expensive *ontrol.system.; ~In~add~tion.jthel,present.inventio~n makes it possi~le to.supply. power ~trlow~rvol-tages... This is an .

WO91/16523 PCTtNO91/00043 advantage, as all usual organic insulation materials tend to get saturated when in use in subsea environment. ~ow voltages can be transmitted even through saturated cables without excessive losses. Low voltages have the further advantages of reducing the risk of corrosion as compared to the usual systems.

Relative to a characteristic asepct of the invention the ~ignals ~or control and monitoring are transmitted through the same cables as the electric power. This is achieved by sending the control signals in certain time intervals. The method is called time multiplexing. In periods when no signal transmission is required an un-interrupted power supply can be maintained. ~he electrical power received by the control unit is stored in an internal condensator. The result is that power pulses of sufficient high effect can be transferred to the solenoid valves, while the power supply through the cable can be transferred over time at a low voltage. The consequence is that the power supply cables become redundant, as all power supply to the subsea electronics may be transmitted through the signal cables~

Another characteristic aspect of the invention is that a pluraily of valves can be controlled via a single pair of conductors by transmitting several signals of different frequencies simultaneously. At the same time, the electric power is supplied on a low frequency. The signals are transmitted by a so-called frequency multiplexing, whilst the power and signals are separated by so-called time multiplexing, whilst.-the power and signals are separated by so-called time multiplexing. This enables several signals to be transmitted simultaneously via the conductor single pair of conductors in addition to the conductor/pair of ,~ ~ conductor'-s ability to supply electric power.

.,,! ; A.thi.rd.characteristic-aspect~of,the~invention~constitute i he,s~ole,noi~d valvesiin~the subsea contrQl-unit1loca~.ed in a imatrix arrange,ment.-irel,a,tive to the;lin,es~-,th,rough.~which-electric power will be supplied.

As appearing from Fig. 2, A control system based on theinvention will comprise a subsea control unit 1 and two main computers 8 located in the control room 2 on the surface. A
cable 15 links the control unit 1 and one of the main computers 8 in the control room 2. The main computer 8 is prov~ded with a lockable panel from which the well actuators can be controlled and from which signal transmitters for pressure and temperature can be recorded. The main computer is also provided with an interface to which a smaller computer of standard type may be connected for control and monitoring of signals via keyboard 8a and visual display unit 9.

The subsea control unit 1 may, according to the invention, comprise an electronic canister 7 containing microprocessc:
based electronics 16 for receiving, conditioning and transmitting signals. Signals from the control room 2 are transmitted via the signal cable 15 to the electronic canister 7 where the microprocessor based electronics interprets the signals in such a way that the electrical power stored in the capasitor 17a is directed to the desired solenoid valve 14 in order for the valve to trigger and open for the provision of hydraulic fluid and pressure.

In the subsea contol unit electronics canister 7, see Fig.
3, the signals from the supplied electronical power are separated using a filter 11 in conjunction with the electronics power supply 9. Such a filter 12 is also located on the surface'unit. The power-is con~erted to direct current and stored in a capacitor 17a.
, .. .. .
The signal cable 15:conducts electric alternating current of a moderate voltage'level, typically 24 volts. ~eferring'to =- Fig~ 4~ possible-format:~fLthe~alternat-i'ng current in the :- -L -cable is,~`a~cordi~ng' t'o~2t~1ë' invefi'tion,~-an'in't-ërval` o~J~ow frequency c^urrent'i13"J A'Jtypical'fre'que'ncy mâ'y'be-50'-Hz.

, .

During signal transmission, the power supply will be switched off and signals 14 transmitted on a somewhat higher frequency. A typical value for frequency transmission may be in the range of 1000 to 1300 Hz.
s The solenoid valves 14 in the subsea control unit 1 are triggered by power pulses to the valves solenoid 19. The transfer of power to the solenoid 18 coils is by electronic switches 17, see Fig. 5, closing the circuit to the coils 18. The connection between solenoids 19 and switches 17 are arranged in the form of a matrix such that two switches must be closed ~n order for the electric circuit to be completed.
Every single solenoid has-two associated switches. The switches 17 are arranged in two groups. One of the solenoids leads 1-n corresponds to a first group of switches 1n-1nm. The other lead corresponds to the second group column of switches 1m-1nm. In this way only one selected pair of switches will close the circuit to one particular solenoid valve and to this only. The arrangement will reduce the necessary number of switches.

In Fig. 5 there is also illustrated a typical sole~oid arrengement, i.e. a solenoid 19 connected between a positive column driver and a negative row driver, with zn arc suppressor diode connected therebetween.

Summarv Above there has been disclosed a system for the control and monitoring of especially subsea hydrocarbon production systems. Such production systems are remotely operated from the surface. The invention provides the following advantages:
. . .
By the use of the present invention the need for separate power supply cables is eliminated. The power is supplied through the signal cables.

Several simultaneously signals may be transmitted through the same conductor by the use of frequency multiplexing.
Electric power may be transmitted through the same cables by the use of time multiplexing as compared to the signals.
S -.
The number of selector switches is reduced due to a matrix arrangement relative to the solenoid valves to which the power is to be supplied.

The present invention is different from other known techniques by the fact the the three above aspects are present simultaneously and are used for the control of especially subsea wells.

.. .

Claims (9)

1. A system for the control and monitoring of surface or subsea hydrocarbon production, comprising production equipment (1a) to which is supplied hydraulic power and electrical power and signals for the control of valves etc.
and the monitoring of signals from sensors etc., respective-ly, said hydraulic power and electrical power and signals being supplied from a fixed or floating monitoring instal-lation (2a), c h a r a c t e r i z e d i n that the electrical power is supplied to the subsea production equipment via the same conductor (15) or conductors as the electric signals.

2. A system as claimed in claim 1, c h a r c t e r i z e d i n that the supply of electric power and electric signals takes place by a time multiplex-ing system, i.e. in that electric signals (14) and power (13) are sent at alternative times.

3. A system as claimed in claim 1 or 2, c h a r a c t e r i z e d i n that the electric power is transmitted as substantially rectangular or square waves 13, for example of a frequency of 50 Hz, and that the signal transmission (14) has a higher frequency, for example in the range of 1000 - 1300 Hz.

4. A system as claimed in claim 1 - 3, c h a r a c t e r i z e d i n that the electric power (13) which is supplied to the production equipment is stored therein in an accumulator (17), possibly after having been converted to direct current.

5. A system as claimed in claim 1 - 4, c h a r a c t e r i z e d i n that the electrical signals (14) are separated from the supplied electric power by means of a filter (11) housed in the subsea equipment (1a), and that a corresponding filter (12) is used on the monitoring installation (2a).

6. A system as claimed in claim 1 - 5, c h a r a c t e r i z e d i n that the subsea equipment comprises a plurality of valves (14) which are controlled by switch operated solenoids (19) , and that the switches and solenoids (19) are arranged in a matrix.

7. A system as claimed in claim 6, c h a r a c t e r i z e d i n that the switches (1n, 1m) are arranged in two groups, for example in a negative driver group (1-1n) and a positive driver group (1-1m), respec-tively, such that each switch in the negative driver group has a common negative lead with an associated row (1n - nm) of valve solenoids (18), and such that each switch in the positive driver group has a common positive lead with an associated column (1m - nm) of valve solenoids.

8. A system as claimed in claim 6 or 7, c h a r a c t e r i z e d i n that the switch (17) is a relay or a solid state element, for example a transistor or similar.

9. A system as claimed in claim 6, 7 or 8, k a r a k t e r i s e r t v e d in that several valves are controlled via a single pair of conductors by transmit-ting several signals of different frequency simultaneously.