Data processing: vehicles – navigation – and relative location – Navigation – Employing position determining equipment
Reexamination Certificate
2000-03-31
2001-08-21
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Navigation
Employing position determining equipment
C405S195100, C175S005000, C175S007000, C114S14400A, C114S264000, C166S352000
Reexamination Certificate
active
06278937
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to a method and apparatus for controlling the position of a floating rig, particularly, to a method and apparatus for controlling the position of a floating rig joining a rig and a well head positioned on the sea bottom by an excavation riser.
Where there a floating rig operating in deep water having a depth exceeding 1,000 meters, it is necessary to hold upright an excavation riser joining the rig and a well head positioned in the sea bottom. Used nowadays for this holding operation is a dynamic positioning system (DPS) for holding the excavation riser at a predetermined position by using thrusters or a combination of thrusters and a propulsion system. In this case, the information on the position of the rig is obtained from signals supplied from acoustic equipment or artificial satellites for performing a desired control. What should be noted in this case is that, if the information on the position of the rig ceases to be received, it is impossible to perform control to maintain the position. What should also be noted is that, if the marine weather conditions are aggravated, the acoustic signal looses its reliability and Differential Global Positionig System (DGPS) signal supplied from the artificial satellite tends to be interrupted. Such being the situation, employed in general is a system in which the position information is obtained by at least three sensor systems and by at least two kinds of sensors differing from each other in the principle of measurement.
Where the water depth is not larger than 300 meters, the anchor at the sea bottom and the floating rig are joined to each other by a wire (taut wire). In the position control of the rig in such a low water depth, the angle of inclination of the wire is changed by the movement of the rig. Therefore, the rig position is maintained by operating the system according to a signal recieved representing a change in the angle of inclination. The tension of the wire is adjusted if necessary.
However, in a sea having a water depth exceeding 1,000 meters, the wire joining the floating rig and the sea bottom is drifted by a current, making it impossible to control effectively the rig position. Also, a system, in which the rig position is controlled by receiving a signal representing the angle of inclination at the lower end of the riser, is employed in place of the wire. In this system, however, it is said to be impossible to perform an effective positioning control in a deep sea having a water depth exceeding 1,000 meters.
Further, the actual operation carried out is such that the angles of inclination at the upper and lower ends of the riser are perceived visually by the operator and the control target position of DPS is determined manually by the operator.
Still further, a shaft of an excavation drill is housed inside the excavation riser, making it necessary to diminish the angle of inclination of the riser to prevent the riser and the excavation drill shaft from interfering with each other. In the conventional apparatus, however, the position is not controlled depending on the angle of inclination of the riser, making it impossible to perform simply the control to maintain the position, and the control is dependent on the degree of skill of the operator.
SUMMARY OF THE INVENTION
An object of the present invention, which has been achieved in view of the situation described above, is to provide a system that permits a floating rig to be automatically held at a position optimum to the riser, even if a position signal of the floating rig is not available, provided that the angles of inclination of the upper and lower ends of the riser can be detected.
To achieve the object, the present invention is directed to a method of controlling the rig position using an excavation riser. The method of the invention makes it possible to estimate accurately the rig position based on the angles of inclination at the upper and lower ends of a riser such that the rig position can be held based on only the information of the angles of inclination at the upper and lower ends of the riser. A neural network is used for calculating the position correcting amount of the floating rig in the direction in which the angles of inclination at the upper and lower ends of the riser are diminished.
To be more specific, the first embodiment of the present invention is directed to a method of controlling the position of a floating rig, in which the floating rig is joined to the well head at the sea bottom by an excavation riser. The position of the floating rig can then be corrected by thrusters, or a combination of thrusters and a propulsion system, wherein a neural network is allowed to learn in advance the position information of the floating rig in relation to the behaving characteristics of the excavation riser, such that the angles of inclination at the upper and lower ends of the excavation riser are detected and supplied to the neural network to allow the neural network to output information for correcting of the present position of the floating rig, by driving the floating rig based on the correcting information from a present position of the rig to a position where the angles of inclination at the upper and lower ends of the riser are diminished. Thus, controlling the position of the floating rig at the position where the angles of inclination at the upper and lower ends of the riser are diminished is achieved.
The second embodiment of the present invention is directed to a method of controlling the position of a floating rig, in which the floating rig is joined to the well head at the sea bottom by an excavation riser and the position of the floating rig can be corrected by thrusters, or a combination of thrusters and a propulsion system, wherein a deviation in the rig position is calculated based on position information supplied from the means for detecting the position of the rig. Again, a neural network is allowed to learn in advance the position information of the floating rig in relation to the behaving characteristics of the excavation riser to output the information for correcting amount the target position by supplying the information on detected angles of inclination at the upper and lower ends of the excavation riser to the neural network, and driving the thrusters, or a combination of the thrusters and a propulsion system, to perform correction of the rig position while diminishing the angle of inclination of the excavation riser.
Further, the third embodiment of the present invention is directed to a method of controlling the position of a floating rig, in which the floating rig is joined to the well head at the sea bottom by an excavation riser and the position of the floating rig can be corrected by thrusters, or a combination of thrusters and a propulsion system, wherein a neural network is allowed to learn in advance the position information of the floating rig in relation to the behaving characteristics of the excavation riser. The angles of inclination at the upper and lower ends of the excavation riser are detected and the information on the detected angles is supplied to the neural network, thereby allowing the neural network to output the information on the correcting amount of the target position of the floating rig, estimating the position of the floating rig based on the received information, obtaining a deviation between the estimated position and the target position, and driving the thrusters or a combination of the thrusters and a propulsion system, to perform correction of the rig position while diminishing the angle of inclination of the excavation riser.
The present invention also provides an apparatus for controlling the position of a floating rig, in which the floating rig is joined to the well head at the sea bottom by an excavation riser and the position of the floating rig can be corrected by thrusters, or a combination of thrusters and a propulsion system. The position control apparatus comprises a target position deviation calcul
Ishida Shigeki
Tanaka Susumu
Cuchlinski Jr. William A.
Mitsui Engineering & Shipbuilding Co. Ltd.
Oliff & Berridg,e PLC
To Tuan C
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