US3121954A

US3121954A - Position locating device

Info

Publication number: US3121954A
Application number: US830604A
Authority: US
Inventors: Kenneth W Foster
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 1959-07-30
Filing date: 1959-07-30
Publication date: 1964-02-25
Anticipated expiration: 1981-02-25

Description

Feb. 25, 1964 K. w. FOSTER I 3,121,954

POSITION LOCATING DEVICE Filed July so, 1959 FIG.

FIG. 3

INVENTORI K.W. FOSTER MJMJ HIS ATTORNEY United States Patent Qhlice 3,121,954 Patented Feb. 25, 1%64 3,121,;54 PUSETESN LGCATTNG DEVECE Kenneth W. Foster, Houston, Tern, assignor to Shell Gil tlornpany, a corporation oi Delaware duly fill, 195%, Ser. No. 333.6%

6 t'ilairns. (El. 33 l) This invention pertains to oil well equipment and more particularly to a device for determining the location of a floating vessel with respect to the wellhead of an underwater or offshore oil well.

In the drilling of offshore oil wells two general types of. equipment are used. type of equipment utilizes a fixed platform which is firmly attached to the lloor of the ocean or body of water and the other being a floating platform which is merely anchored over the position in which the well is to be drilled. When using a floating platform it is necessary to accurately locate the platform over tr e site of the vell and maintain it in this position. Even after the floating platform is anchored in position it tends to shift a small amount with relation to the axis of the borehole of the underwater well. This shifting necessitates the bending of the drill string or casing as it is lowered into the borehole which causes considerable difficulty. When the angle between the axis of the drill string and the axis of the borehole becomes too large it is impossible to drill the well due to the inc eased stress placed on the drill string.

in the past various methods and equipment have be n used in an eilort to determine the deviation of the dril i barge or vessel from the desired location. methods utilized complicated electronic gear such as ele tronic fathorneters to locate a triangular target placed on the bottom of the ocean at the location of the wellhead. Also, other types of electronic gear such as television cameras have been used for locating thv wellhead and estimating the deviation of the drilling barge from the desired location. All of these methods are objectionable because they give inaccurate resu ts and utilize complicated electronic gear requires skilled personnel to operate.

Accordingly, the principal object of this invention is to provide a simple means for accurately positioning a floating vessel or drilling barge over an underwater wellhead.

A further object of this invention is to provide a novel system which indicates both the deviation and direction of the deviation of a floating vessel or drilling barge from the axis of an underwater well.

The above objects and advantages of this invention are achieved by providing a guide line connected at one end of the wellhead and at the other end to a tension means on the drilling barge. The tension means on the drilling barge maintains sufficient tension on the guide line to draw it into a substantially straight line. A tiltmeter is secured to the guide line in an oriented position to measure the tilt or deviation of the guide line from a vertical position about two axes at right angles to each other. The measured angular deviations of the guide line from the vertical are converted into electrical signals and used to energize the X and Y axis of an fY-type of plotter. Thus, the exact orientation of the drilling barge from the vertical axis of the well is accurately determined both as to magnitude and direction of displacement.

This invention will be more easily understood by those skilled in the art from the following detailed description of a preferred embodiment when taken in conjunction with the attached drawing in which:

FIGURE 1 is a view of the system attached to a floating drilling barge;

FIGURE 2 is an exploded pictorial view showing the 2 construction of the tiltrneter used in FIGURE 1; and

FIGURE 3 is a schematic drawing illustrating the plotting of the position of the floating drilling barge with relation to the underwater wellhead.

Referring now particularly to FIGURE 1, there is shown a floating vessel or drilling barge it} which is anchored over an underwater wellhead 21 by any desired means (not shown). The drilling barge consists of a supporting barge or floating member 11 and an elevated platform 12 which is supported from the top of the barge 11 by a plurality of columns 13. Mounted on the elevated platform is a derrick or drilling rig 14 which is disposed over openings 15 and 16 in the elevated platform and barge, respectively. The drilling rig and derrick 14 may be a conventional rotary rig used on land for drilling oil wells and the like which is mounted on the elevated platform. In addition, the necessary machinery for operation of the rig may be mounted on the platform of the barge l as is well known in the art of offshore drilling barges.

A suitable wellhead or platform 21 is securely anchored or fastened to the bottom of the body of Water 20 by any desirable means not shown. The wellhead 21 of course contains ecessary auxiliary equipment required in offshore drilling such as automatic shut-down devices and the like. Three guide lines 23, 24 and 25 have their lower ends attached to the top of the wellhead 21 and are led upwardly through the bottom of the elevated platform where they pass over sheaves 25 secured to the underside of the platform 12. The guide lines are oriented on the drilling barge in the same locations as their lower ends occupy on the wellhead. The guide lines 23, 2d and 25 are normally utilized for guiding tools, equipment, drill strings and the like from the bottom of the barge H to the wellhead 21. The free ends of the guide lines are attached to a suitable tensioning means 30 to maintain sufficient tension on the guide lines to draw them into a substantially straight line. The tensioning means may be winches located on the drilling barge with the winches in turn being driven by prime movers through iluid couplings. In this manner the prime movers would maintain a predetermined tension on the guide lines through the slippage oi the fluid coupling. The force required to draw the guide lines into a substantially straight line will vary but a force on the order of 5,000 pounds would be sufiicient under most conditions.

As shown in FlGURE 1, the center line or axis of the drill string is displaced to the right or the of the underwater wellhead 21 with the dotted line 22 representing the axis of the drill string between the barge and the Wellhead. From this represe .tation it will be seen that the drill string must first be bent in one direction as it leaves the lower end of the opening 16 and then bent in the opposite direction as it enters the wellhead Zl. As the drill string rotates these bends will, of course, reverse, thus severely s ressing the tubing forming the drill string.

In order to measure the angle between the guide lines 23, 24 and 25 and the vertical axis or the wellhead iltrneters Eli are attached to one or more or" the guide lines at any convenient location above the surface of the Water. The tiltrneter 31 is designed to measure the angle of deviation of the guide lines from the vertical in two planes which are substantially at right angles to each ther and in addition are parallel to the vertical axis of the wellhead 21.

The detailed construction of the tiltrneters 31 are shown in FEGURE 2 and consist of an outer frame work or cage ll). The outer frame work or cage may assume any desired construction being shown as two end plates 43 which are held in a spaced relation an secured together by four tubular members located at the corners. The tubular members 47 may be fastened to the end plates 48 by any desired means such as welding or the like. A lifting ring 56 is attached to the center of both the upper and lower plates and is utilized for attaching the guide lines to the tiltmeter case 48. Of course, the rings 56 should be attached so that they are aligned with the vertical axis of the tiltmeter in order that the tiltmeter will accurately measure the desired angles.

The tiltmeter proper consists of a substantially sealed case 6% in which there is mounted a gimbal or outer frame 41. The frame 4-1 is secured to the case as any desired means such as welding or the like. While the gimbal frame is shown as being square, of course, a round gimbal frame could also be used if one desired. Mounted within the gimbal frame 41 is the gimbal ring 42 which is pivoted on the gimbal frame 51 along an axis 52 which, for convenience, is designated the north-south axis. Pivoted within the gimbal ring 42 on a shaft is a pendulum rod 44 having a pendulum weight 45' at its lower end. The pendulum rod M- is pivoted at its upper end about an axis 51 which is disposed in the same plane and at right angles to the axis 5'2. The axis 51, for convenience, is designated as the east-west axis. Of course, the pivots for both the gimbal ring 42 and the pendulum shaft 44 should be as free of friction as possible so that the pendulum may move freely in both north-south and east-west directions. Two potentiometers 5t) and 46 are disposed to be actuated by movement of the pendulum about either the east-west or north-south axis, respectively. The potentiometers 46 and fill should be chosen so that they will provide an electrical output signal which is proportional to the angular displacement of the pendulum about the two axes.

The above tiltmeter is mounted in the sealed case 6% to protect it from the weather with the case 60 in turn being securely mounted in the frame or cage 43. When the sealed case 69 is mounted in the frame 4%, care should be taken to orient both axis of the tiltrneter with the frame 40 and the axis of the pendulum with the mounting means used for attaching the guide lines to the frame 40. While the above describes a suitable design for the tiltmeter other well known tiltmeters may be used, the only requirement being that they accurately measure the deviation of the guide lines in two oriented planes. Of course, two tiltmeters could also be used on each guide line with one meter measuring the deviation angle in one plane and the second meter measuring the deviation angle in a plane at right angles to the first plane.

From the above description it will be appreciated that there has been provided a tiltmeter which is capable of measuring the angular deflection of a guide line in two planes which are at right angles to each other. Thus, if the tiltrneter is attached to the guide lines so that the axis of the guide line passes through the axis of the tiltmeter the tiltmeter will accurately measure the angular deflection of the guide line in the two planes. Furthermore, if the axis of the tiltmeter is geographically oriented with the wellhead it will accurately measure the direction and distance that the center line of the drill rig 1 3 has been displaced from the wellhead. Also, through this arrangement the orientation of a vessel may be determined with respect to the position of a reference point on the floor of a body of water, i.e., a wellhead.

Referring now to FIGURE 3, there is shown one means by which the information obtained from the tiltmeter may be utilized to plot the position of the drilling barge. In this figure the two potentiometers 46 and 5% are shown as being powered from a battery 53 which has its negative side connected to a ground 54. The output from the potentiometer 46 which measures the movement in a north-south direction is applied to the Y axis of an XY recorder so that it will move the recording mechanism in a Y direction. The output from the potentiometer 50 which measures the movement in the east-west direction is applied to the X axis of recorder and thus moves the recording mechanism in an X direction. A combination of the two movements will displace the recording element of the recorder to a given location which is shown in FIGURE 3 at 55. if this is the point of the recording of the deflection of the guide line as measured by the tiltmeter it would indicate that the floating vessel is displaced in a north-east direction and that the angular deflection between the center line of the drill rig and the axis of the wellbore is 8 degrees. While the deflection is given as an angular measurement it could easily be recorded as an actual distance if desired. Angular displacements are preferred since the stress on the drill string or other equipment lowered to the wellhead is a function of the angular displacement. Also by recording the location of the floating vessel it) as an angular deflection one need not comensate for varying water depths since the angular deflection of the vessel does not depend upon the water depth while the actual distance the vessel is displaced is a combination of the angular displacement and the water depth. Thus, to measure the actual displacement one would need to compensate the instrument for changing water depths or else calculate the displacement for each read ing. Of course, the information from the tiltmeters disposed on the remaining guide lines must be recorded on a similar XY recorder or recorded on the same LY recorder on a time sharing basis.

While but one embodiment of this invention has been described in detail it is susceptible to many modifications. As explained above, various types of known tiltmcters may be used. Also, while three guide lines are shown one will give usable information although the remainder may be used to check the results. Accordingly, this invention should not be limited to the above-described details but only to its broad spirit and scope.

I claim as my invention:

1. A method for determining the location of a floating vessel with respect to an underwater wellhead comprising: connecting a guide line between the vessel and the wellhead; applying sutficient tension to said guide line to maintain it in a substantially straight line; measuring the angular deflection of said guide line from the vertical in two planes at an angle to each other and determining the angular deflection of said vessel with regard to wellhead through the use of said measured deflections.

2. A system for determining the location of a floating vessel with respect to an underwater wellhead comprising: a guide line having one end secured to said wellhead, the opposite end of said guide line being secured to a tensioning means disposed on the floating vessel, said tensioning means applying suflicient tension to said guide line to maintain it substantially straight; tiltmeter means secured to said guide line and disposed to measure the deflection of said guide line from the vertical in at least two separate planes at a significant angle to each other, and means utilizing said measured deflections to indicate the angular deflection of the vessel from the wellhead.

3. A system for determining the location of a floating vessel with respect to an underwater wellhead comprising: at least two guide lines, each of said guide lines having one end secured to the wellhead, tension means disposed on the floating vessel to maintain sufficient tension on each of said guide lines to draw them into a substantially straight line; a tiltmeter means attached to each of said guide lines, said tiltmeter means being disposed to measure the deflection of each of said guide lines from the vertical in two separate planes at substantially right angles to each other, said tiltmeter means in addition supplying said measurements as electrical signals and plotting means responsive to said electrical signals for plotting the angular deflection of the floating vessel relative to the wellhead.

4. A method for determining the location of a floating vessel with respect to an underwater wellhead comprising:

connecting a guide line between the vessel and the Wellhead; applying sufficient tension to said guide line to maintain it in a substantially straight line; measuring the angular deflection of said guide line from the vertical in two planes at substantially right angles to maintaining said elongated member in a substantially straight line between the vessel and the anchored end of the elongated member vessel with respect to the wellhead through the use of said measured deflections.

5. A method of positioning a floating marine vessel comprising:

anchoring one end of an elongated member to the floor of a body of Water at a position having a predetermined relationship to the desired position of the vessel; securing the other end of the elongated member to the vessel; measuring the angular deflection of the elongated member from a vertical position in two planes at an angle to each other; determining the positioning of said vessel from said measured angular deflections. 6. A method of positioning a floating marine vessel comprising:

anchoring one end of an elongated member to the fioor of a body of Water at a position having a predetermined relationship to the desired position of the vessel;

References Cited in the file of this patent UNITED STATES PATENTS 1,209,102 AnschultZ-Kaempef Dec. 19, 1916 1,401,242 Lavaud Dec. 27, 1921 2,198,523 Adams Apr. 23, 1940 (2,396,453 Windle Mar. 12, 1946 2,569,328 Omberg Sept. 25, 1951 2,650,046 Vanderlip Aug. 25, 1953 2,669,785 Rydzewski 'Feb. 23, 1954 2,809,435 Nicolson Oct. 15, 1957 2,873,075 Mooers et a1. Feb. 10, 1959 3,010,214 Postlewaite Nov. 28, 196- 1

Claims

1. A METHOD FOR DETERMINING THE LOCATION OF A FLOATING VESSEL WITH RESPECT TO AN UNDERWATER WELLHEAD COMPRISING: CONNECTING A GUIDE LINE BETWEEN THE VESSEL AND THE WELLHEAD; APPLYING SUFFICIENT TENSION TO SAID GUIDE LINE TO MAINTAIN IT IN A SUBSTANTIALLY STRAIGHT LINE; MEASURING THE ANGULAR DEFLECTION OF SAID GUIDE LINE FROM THE VERTICAL IN TWO PLANES AT AN ANGLE TO EACH OTHER AND DETERMINING THE ANGULAR DEFLECTION OF SAID VESSEL WITH REGARD TO WELLHEAD THROUGH THE USE OF SAID MEASURED DEFLECTIONS.