Determining a position of a hydraulic subsea actuator

A method and an apparatus (280) for determining an estimate of a position of a hydraulic subsea actuator (200), wherein the hydraulic subsea actuator (200) has a fluid port (220) fluidly connected to a fluid source (260). The apparatus (280) comprises a hydraulic cylinder (310) connected in series between the fluid source (260) and the fluid port (220) of the hydraulic subsea actuator, and a movable piston (320) arranged in the second hydraulic cylinder (310), a position determining device, arranged to determine a position of the movable piston (320), and a signal processing device (350), arranged to calculate the estimate of the position of the hydraulic subsea actuator based on the position of the movable piston.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to monitoring hydraulic equipment.

More specifically, the invention relates to a method and apparatus for determining an estimate of a position of a hydraulic subsea actuator.

BACKGROUND OF THE INVENTION

Hydraulic actuators are widely used, e.g. in oil and gas industry. In subsea equipment, for instance in a subsea wellhead, a christmas tree, a blow out preventer, a manifold, a tubing string, or a landing string of a subsea oil and/or gas well, hydraulic actuators are frequently used for operating valves, the actuators being located at inaccessible areas. A recurring problem is to monitor the state of such hydraulic subsea actuators, in particular to determine their actuator position. A particular challenge is determining such actuator position without making modifications or adaptations to the hydraulic subsea actuator. In case of a subsea actuator, e.g., a subsea test tree valve actuator, space constraints or other limitations may make it impossible or inconvenient to provide the actuator itself with a position determining device. Also, strict safety constraints and other requirements must be complied with.

Hence, there is a general need in the art for providing a method and an apparatus for determining an estimate of a position of a hydraulic subsea actuator.

SUMMARY OF THE INVENTION

The method and an apparatus for determining an estimate of a position of a hydraulic subsea actuator according to the invention have been are defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a schematic block diagram illustrating a hydraulic subsea actuator100without means for determining the position of the actuator.

The hydraulic actuator100is a hydraulic subsea actuator, e.g. an actuator operating a valve or another moveable element included in a well head, a Christmas tree, a blow out preventer, a manifold, a tubing string, or a landing string of a subsea oil and/or gas well.

The hydraulic subsea actuator100has a first fluid port120connected to a first fluid source160via a first hydraulic control valve140. The hydraulic subsea actuator100also has a second fluid port110connected to a second fluid source150via a second hydraulic control valve130. The first and second fluid ports are arranged at opposite sides of a movable piston in the hydraulic subsea actuator.

In the case of a subsea actuator, e.g., a subsea test tree valve actuator, space constraints or other limitations make it impossible or inconvenient to provide the actuator itself with a position determining device.

In the present disclosure, the position of the actuator may be understood as the position of a piston in the actuator, or a position of an element that moves in correspondence with the piston in the actuator. In the simplest case the position may have only two values, e.g. corresponding to a closed or open position of a valve. Alternatively, the position may take a number of discrete values within a finite set, or the position may be considered as a continuous quantity within a range.

FIG. 2is a schematic block diagram illustrating a hydraulic subsea actuator connected to an apparatus for determining an estimate of the position of the actuator.

The hydraulic subsea actuator200may be a hydraulic subsea valve actuator. The hydraulic subsea actuator200may, e.g., be an actuator operating a valve or another element included in a well head, a Christmas tree, a blow out preventer, a manifold, a tubing string, or a landing string of a subsea oil and/or gas well. The hydraulic subsea actuator200may be linear.

The hydraulic subsea actuator200has a first fluid port220fluidly connected to a first fluid source260via a first hydraulic control valve240. The hydraulic subsea actuator200also has a second fluid port210fluidly connected to a second fluid source250via a second hydraulic control valve230. The first and second fluid ports are arranged at opposite sides of a movable piston in the hydraulic subsea actuator200.

The actuator200has been illustrated with a spring which may be a fail-safe closing spring that drives the actuator to a closed position as a default, e.g. in the case of hydraulic pressure failure. However, the actuator may alternatively be an actuator without such a fail-safe closing spring.

It should be understood that each of the fluid sources260and250may actually operate as a fluid supply or a fluid return, depending on the operating circumstances.

In order to determine an estimate of the position of the hydraulic subsea actuator200, an apparatus280for determining such an estimate is connected in the hydraulic supply line, between a connection242of the first hydraulic control valve240and the first fluid port220of the hydraulic subsea actuator200.

The apparatus280may be connected separately from the hydraulic subsea actuator200.

The apparatus280may be connected remotely from the hydraulic subsea actuator200.

The apparatus280includes a hydraulic cylinder connected in series between the fluid source260, or more particularly the control valve240that is connected to the fluid source260, and the fluid port220of the hydraulic subsea actuator200. A movable piston, arranged in the hydraulic cylinder, will move in the hydraulic cylinder in response to a movement of the hydraulic subsea actuator200. A position determining device290is included in the apparatus280and is arranged to determine a position of the movable piston280. The position determining device290is further communicatively connected to a signal processing device (not shown inFIG. 2) which is arranged to calculate the estimate of the position of the hydraulic subsea actuator200based on the determined position of the movable piston.

Further possible details of the apparatus280will be described with reference toFIGS. 3 and 4.

FIG. 3is a schematic diagram illustrating an embodiment of an apparatus280for determining an estimate of a position of a hydraulic subsea actuator.

The apparatus280comprises a hydraulic cylinder310. The cylinder has a hydraulic connection314which, when the apparatus is operative, is connected to the fluid source260, possibly via the control valve240, in particular the connector242of the control valve240. The hydraulic cylinder also has a hydraulic connection312which, when the apparatus is operative, is connected to the fluid port220of the hydraulic subsea actuator200, as already explained with reference toFIG. 2and the corresponding description above. A piston320is arranged in the second hydraulic cylinder310and is adapted to move along the length of the cylinder310. Since the cylinder310and the cylinder of the hydraulic subsea actuator200and all fluid lines are filled with a substantially incompressible hydraulic fluid, such as hydraulic oil, a change in the position of the hydraulic subsea actuator200will result in the movement of the piston320in the hydraulic cylinder310in the apparatus280.

The hydraulic cylinder310has a cylinder stroke volume which may be substantially equal to or larger than the stroke volume of the hydraulic subsea actuator200.

The apparatus280further comprises a position determining device, arranged to determine a position of the movable piston320, and a signal processing device350. The position determining device is arranged to calculate the estimate of the position of the hydraulic subsea actuator based on the determined position of the movable piston.

The position determining device may, e.g., be arranged to determine the position of the movable piston by the use of electromagnetic position determination. For instance, the position determining device may include a ferromagnetic element and a magnetic switch. In such a case, the electromagnetic position determination may include detecting the position of the magnetic element relative to the magnetic switch. Alternatively, a plurality (e.g., 2, 3, 4 or more) of ferromagnetic elements and/or a plurality (e.g., 2, 3, 4 or more) of magnetic switches may be employed.

As an example, a number of ferromagnetic elements322may be arranged along the length of the piston320, and magnetic switches such as reed switches may be arranged in a protruding rod330, arranged in a central area of the cylinder310, which is adapted to be received by a corresponding bore in the piston320. Alternatively, magnetic switches such as reed switches may be arranged in or outside the wall of the cylinder310.

Numerous alternatives for determining the position of the movable piston exist, including the arrangement and use of optical (e.g., photoelectric), acoustic (e.g., ultrasonic), or capacitive proximity detectors or position sensors. Ferromagnetic elements and magnetic switches such as reed switches may advantageously be used due to their simplicity and reliability, and since they are passive devices.

In an aspect, the position determining device may be arranged to determine a plurality of discrete positions of the movable piston320. In the simplest case, only two positions need to be determined. In such a case, the signal processing device350may be arranged to determine if the hydraulic subsea actuator200is open or closed. The number of determinable positions may however be 3, 4, 5, 6 or higher, depending on the resolution required.

In another aspect, the signal processing device350may be arranged to determine the position of the movable piston320from a continuous range of positions.

The signal processing device350may be arranged to provide the estimate of the position of the hydraulic subsea actuator200as an electrical output signal. The output signal may be digital or analog. For instance, the output signal may be a 4-20 mA analog current signal, where a certain sub-range of the total range 4-20 mA corresponds to a closed actuator position while another sub-range of the total range 4-20 mA corresponds to an open actuator position. Alternatively, the output signal may be provided as a hydraulic or optical signal, or another type of analog, electronic signal, or a digital, electronic signal.

In yet another aspect, the signal processing device350may be configured to calculate the estimate of the position of the hydraulic subsea actuator by multiplying the position of the movable piston320with a predetermined proportionality constant.

The hydraulic subsea actuator200may include an actuator piston which has a first piston area, i.e. its effective piston area, while the movable piston320in the hydraulic cylinder310may have a second piston area, i.e. its effective piston area. The proportionality constant may in such a case be selected (e.g. pre-selected) as the ratio between the second piston area and the first piston area.

In a particular example, the first piston area may be substantially equal to the second piston area. In such a case the proportionality constant will be essentially equal to 1.

In any of the aspects of the apparatus, the movable piston320may be provided with a fluid passage, e.g. a slit or aperture, having an area which is substantially less than the area of the movable piston. As an example, the area of the fluid passage may be in the range of 1/10000- 1/500 of the area of the movable piston. This particular arrangement, or similar arrangement, may allow a slowly varying flow of hydraulic fluid without moving the movable piston320. Such an arrangement may be useful for allowing the apparatus to ignore particularly slow variations in the hydraulic flow, which are often due to temperature variations or temperature gradients between the hydraulic subsea actuator200and the hydraulic cylinder310in the apparatus280.

In another aspect, the apparatus may comprise at least one temperature sensor. As an example, a first temperature sensor may be arranged to measure a temperature at the hydraulic subsea actuator200, while a second temperature sensor may be arranged to measure a temperature at the hydraulic cylinder310. In another aspect, one of these temperatures may be measured while the other may be assumed to have a certain predetermined approximate value. In such a case the signal processing device may be arranged to compensate for a temperature gradient between the hydraulic subsea actuator200and the hydraulic cylinder310by means of a measurement signal provided by such a temperature sensor.

In any of the above aspects of the apparatus, the hydraulic subsea actuator200may be an actuator that controls a valve included in a well head, a christmas tree, a blow out preventer, a manifold, a tubing string, or a landing string of a subsea oil and/or gas well. The apparatus may advantageously be used during a drilling, testing, completion, workover or production phase of the subsea oil and/or gas well.

FIG. 3further illustrates a cylindrical extension portion340axially extending between the hydraulic cylinder310and an encapsulation for the signal processing device350. Another cylindrical extension portion360axially extends between the encapsulation for the signal processing device350and the electrical connector370, which includes electrical connections for supplying the signal processing device350with electrical power and connections for reading out signals provided by the signal processing device350.

FIG. 4is a schematic diagram illustrating a signal processing device350for an apparatus for determining an estimate of a position of a hydraulic subsea actuator.

The signal processing device350comprises a digital bus420, which is operatively connected to a processor, such as a microprocessor,410. The bus420is also operatively connected to a memory440, which may include a volatile working memory portion such as a random access memory portion, which is used for temporarily storing data, and a non-volatile, fixed portion such as a ROM, Flash, EPROM, EEPROM, etc, which may be used for storing processing instructions (computer program instructions) and fixed data.

The bus420is also operatively connected to an input/output device430, which has at least an input460and an output470. Each of the input460and output470may be digital or analog. As an example, the input and output are both analog 4-20 mA current signals. In such a case the input/output device may include an ND converter and a D/A converter, in order to adapt the signal provided to the analog input460to a digital signal to be processed by the processor410, and in order to adapt a digital signal provided by the processor410to an analog output signal at the output470.

A signal representing the position of the piston320in the apparatus may be connected to the input460. A signal representing the estimate of the hydraulic subsea actuator is provided at the output470.

The processing of the signal at the input460, resulting in the signal provided at the output, is performed by the processor410in accordance with processing instructions held in a portion of the memory440. This processing may be performed, as already explained, as the function of the signal processing device350.

The signal processing device350may further comprise, or be connected to, a power supply450which provides electrical power to elements such as the bus420, the processor410, the input/output device430and the memory440, and possibly other elements or devices connected to the bus420.

FIG. 5is a schematic flow chart illustrating principles of a method for determining an estimate of a position of a hydraulic subsea actuator, wherein the hydraulic subsea actuator has a fluid port220connected to a fluid source260, possibly via a hydraulic valve240. The hydraulic subsea actuator200may be a hydraulic subsea valve actuator. The actuator may be a linear hydraulic actuator.

The method starts at the initiating step500.

First, in the connection step510, a hydraulic cylinder310is connected in series between the fluid source and the fluid port of the hydraulic subsea actuator. Also, movable piston320is arranged in the second hydraulic cylinder.

Next, in step520, a position of the movable piston320is determined.

In a possible aspect of the method, the step520of determining the position of the movable piston320may comprise electromagnetic position determination. The electromagnetic position determination may include detecting the position of a magnetic element relative to a magnetic switch.

In another aspect of the method, the step520of determining the position of the movable piston may include determining one of a plurality of discrete positions. In such an aspect, the number of discrete positions may be two, and the step530of calculating the estimate of the position of the hydraulic subsea actuator200may include determining if the hydraulic subsea actuator200is open or closed.

Next, in step530, the estimate of the position of the hydraulic subsea actuator200is calculated, based on the position of the movable piston320.

In an aspect of the method, step530of determining a position of the movable piston320may include determining the position from a continuous range of positions.

In an aspect of the method, the hydraulic subsea actuator has an actuator stroke volume, and the hydraulic cylinder310has a cylinder stroke volume substantially equal to or larger than the actuator stroke volume.

In an aspect of the method, the estimate of the position of the hydraulic subsea actuator is provided as an electrical output signal.

In an aspect of the method, the step530of calculating the estimate of the position of the hydraulic subsea actuator comprises multiplying the position of the movable piston320with a proportionality constant.

In an aspect of the method, the hydraulic subsea actuator200includes an actuator piston that has a first piston area, while the movable piston320has a second piston area. In this case, the proportionality constant may be selected as the ratio between the second piston area and the first piston area. For example, the first piston area may be substantially equal to the second piston area.

In an aspect of the method, the movable piston320may be provided with a fluid passage with an area substantially less than an area of the movable piston320. This will allow slow movements of the hydraulic subsea actuator200without moving the movable piston320.

In an aspect of the method, the step530of calculating the estimate of the position of the hydraulic subsea actuator comprises compensating for a temperature gradient between the hydraulic subsea actuator200and the hydraulic cylinder310by means of a temperature measurement.

The estimate of the position of the hydraulic subsea actuator, calculated in accordance with the present disclosure, may be provided as an output signal in the output signal provision step540.

The method may be terminated at the terminating step590or repeated, as appropriate.

The disclosed method may advantageously be performed during a drilling, testing, completion, workover or production phase of the subsea oil and/or gas well.