US3469820A

US3469820A - Drill pipe stabilizing apparatus

Info

Publication number: US3469820A
Application number: US651194A
Authority: US
Inventors: Edward E Horton
Original assignee: Ocean Science and Engineering Inc
Current assignee: Ocean Science and Engineering Inc
Priority date: 1967-07-05
Filing date: 1967-07-05
Publication date: 1969-09-30
Anticipated expiration: 1986-09-30

Description

p 30, 1969 E. HORTON 3,469,820

DRILL PIPE STABILIZING APPARATUS Filed July 5, 1967 5 Shectx-Sheet 1 INVENTOR EDWARD E HORTON Sept. 30, 1969 E. E. HORTON DRILL PIPE STABILIZING APPARATUS 5 Sheets-$heet 1'.

Filed July 5. 1967 Sept. 30, 1969 a. E. HCRTON 3,469,

DRILL PIPE smsxmzmc APPARATUS Filed July 5, 1967 5 Sheets-Sheet Z 5a i l 1 v PUMP 44 54 44 \C lqo POSITION SIGNAL SIGNAL MIXER 1 22 I SIGNAL -102 2a GAIN v as v CHANGE SIGNAL M98 /2 96 SIGN FIG. 6

p 30, 1969 E. E. HORTON 3,469,820

DRILL PIPE STABILiZING APPARATUS Filed July 5, 1967 5 Sheets-Sheet 4 PRIOR ART I PRIOR ART Sept. 30, 1969 E. E. HORTON 3,469,820

DRILL PIPE STABILIZING APPARATUS Filed July 5, 1967 5 Sheets-Sheet s United States Patent US. Cl. 254-172 7 Claims ABSTRACT OF THE DISCLOSURE A construction for use in an offshore drilling operation for maintaining the vertical location of a drill pipe stable with respect to the ocean floor even though its floating support platform is subject to wave action. The drill pipe is supported by cables depending from a traveling crown block which is in turn primarily supported with respect to the platform by a plurality of pressurized air cylinders and secondarily by a plurality of hydraulic cylinders. The hydraulic cylinders are double acting and provide motive power synchronized with ship heave to move the crown block relative to the platform so it remains stationary relative to the ocean floor. The synchronization power is controlled by a travel detecting accelerometer.

This invention relates to apparatus for stabilizing the tension and compression forces acting on a drill pipe suspended from a floating vessel during an offshore drilling operation. The art of conducting drilling operations from ships and stations at points over the bed of the ocean has become increasingly active in recent years. When the drilling is commenced at great depths, it is impractical to stabilize the drilling platform with members extending to the ocean floor. Such drilling stations or platforms therefor are subject to the wave actions of the sea. Although certain measures are available to reduce the effect of this wave action through ship design and buoy systems, the principal effect of this wave action is always present. Such heaving action causes the drill pipe and drill bit to be alternately pulled upwardly from the drilling area as the platform rises and dashes the bit against the bottom of the boring as the platform drops. This invention provides apparatus for mounting the drill pipe to the platform in a manner to maintain stability with respect to the ocean floor by substantially isolating the wave action from the drill pipe.

A principal object of the invention is to provide a crown block support means for the drill pipe which means includes apparatus causing the crown block to remain relatively fixed with respect to the ocean floor as its mounting platform heaves.

Another object of the invention is to provide a crown block supporting means which utilizes pressurized air as a primary support means and hydraulic fluid as both a secondary support means and a power means.

A further object of the invention is to provide a crown supporting means block which quickly compensates for wave action through a hydraulic power system controlled by an accelerometer detector which anticipates this wave action.

A still further object of the invention is to provide a sheave support system for a cable supported crown block having minimum sheave rotation when corrective motions are necessary.

Another object of the invention is to provide a crown block which is adjustable to proportionately compensate for only a segment of platform heave when the wave action is so severe that it cannot be fully compensated because of physical limitations in the supporting derrick.

These and other objects of the invention will become more apparent to those skilled in the art by reference to the following detailed description when viewed in light of the accompanying drawings, wherein:

FIGURE 1 is a front elevational view of the invention;

FIGURE 2 is a side elevational view of the invention;

FIGURE 3 is a perspective view of the crown block assembly;

FIGURE 4 is a front elevational view of the crown block assembly;

FIGURE 5 is a schematic of the crown block air and hydraulic system;

FIGURE 6 is a schematic of the crown block control system;

FIGURES 7a and 7b are a schematic of a prior art sheave support system in different positions;

FIGURES 7c and 7d are a schematic of the instant sheave support system in two different positions, and

FIGURES 8a, b and c are diagrammatic elevational views of the ship in three different positions.

Referring now to the drawings, wherein like numerals indicate like parts, the numeral 10 indicates a ship or other fioatable platform which has a derrick l2 rigidly mounted on its deck. The derrick is of a type which is well known in the art and has a water table platform 14 at its upper end and a working board 16 therebelow. The derrick is used to support a drill string 18 by means of a travel block 20 and a crown block assembly 22 over and through which pass the cables or lines 23-. In order to prevent twisting of the lines 23, outwardly extending

arms

24 and 24 are provided to slidably engage a pair of guide rails 26 and 26'.

Assembly 22 is located within a derrick superstructure 28 and is supported by the water table platform 14. The superstructure comprises a framework 30 having vertical legs 32 which are rigidly braced by diagonal beams 34. The crown block assembly 22 includes a pair of opposed horizontal bars 36 which rotatably support a plurality of crown block sheaves 38. The assembly 22 is supported within the framework by a plurality of vertically disposed air pistons 41. A plurality of rollers 40 are mounted on the assembly and engage the inner corners of the legs 32 to thus permit relative movement between the assembly 22 and the framework 30.

The pistons 41 have their rods 42 secured to cross bars 36 and their cylindrical portions 46 to the table 14 via pins 47. The air cylinders are communicated to pressurized air storage tanks or flasks 50 located on the working board 16 by air pressure lines 48. The pressurized air provides a resilient means of supporting the major portion of the crown block load. In addition to its weight, the load includes the suspended drill string 18.

The crown block assembly is further supported by a plurality of double acting hydraulic jacks 54. First rods 52 of the jack are slidably received through the upper end of cylinders 56 and are secured to bar 36 by pin connections 47. The base of cylinders 56 are connected to water table 14 also by pin connectors although the lower ends of cylinders 56 have balance rods 52', which are not connected to any part of the apparatus. The hydraulic jacks can move the assembly to any selected position intermediate the vertical length of framework 30.

The double acting hydraulic pistons 54 are used not only as a secondary support means for taking up load difference not taken up by the air pistons 44 but primarily provide the means for moving the crown block in compensating synchronization with the vertical motion of the ship. It is advantageous to use a double-acting, double-ended jack with the expansion chambers interconnected since the displaced volume of fluid from the contrasting side of the cylinder will equal the increase in volume expanding chamber. As best seen in FIGURE 5, opposite ends of the cylinder 56 are communicated by hydraulic lines 58, 58' to a variable displacement pump 60.

In the event of a sudden change in crown block load due to a sudden break in the drill string or fracture in either the air or hydraulic systems, a dash pot 62 (FIG- URE 4) is provided on the work table with its dash pot rod 64 secured to the bar 36. Although not shown, the interior of the dash pot cylinder is grooved to allow adequate velocity of the crown block at the middle of its vertical movement and controlled deceleration at the end of it. A spring biased relief valve 66 (FIGURE 5) will operate upon a sudden load change to pass fluid to the low pressure side of the hydraulic system and thus simultaneously transfer the load to the dash pots 62. During normal operation, the dash pots are passive and have a negligible effect.

As briefly mentioned above, the line 23 passes about the crown sheaves 38. As best seen in FIGURES 3 and 4, an idler sheave 68 is rotatably supported between rigid web plates 70. The idler sheave 68 supports the dead line portiton 72 of the line 23. An idler sheave 74 is similarly disposed on the opposite end of the work table 14 between the web plates 76 and supports the fast line portion 78 of the line 23. A schematic of the instant sheave support system is shown in FIGURES 7c and 7d and discloses that the dead line 72 is secured to the derrick floor while the fast line 78 passes around a fast sheave 80 on the derrick floor and thence to a draw works drum (not shown) which maintains a constant preselected tension therein. The purpose of the idler sheaves is to minimize rotation of the traveling block sheaves and the crown block sheaves to thus reduce line and sheave wear. In FIGURES 7a and 7b, a sheave support system is shown without the idler sheaves. It can be seen when the ship moves down from the FIG- URE 7a to the FIGURE 7b position, the compensating vertical movement of the crown block causes a relatively large partial rotation of the crown and travel sheaves. The sheave support system (FIGURES 7c and 7d) utilizes the idler sheaves disposed on the water table at an elevation substantially equal to the midpoint of the crown sheaves vertical movement limits. The portion of the dead line and the fast line between the idler sheave and crown sheave are indicated by the numerals 72 and 78' respectively. When the ship moves from the FIGURE 70 to the FIGURE 7d position the idler sheaves move downwardly with the ship while the crown sheaves are compensated upwardly. The

line portions

72 and 78 are thus moved out of their substantially horizontal positions to provide a component of the increased dead line and fast line legths. In other words, in FIGURE 7d, the increase in distance between the derrick floor and the crown sheaves is supplied partly by a swinging movement of the dead line and fast line portions 72' and 78' and partially by longitudinal lengthening of the dead and

fast lines

72, 78 whereas in FIGURE 7b, the increase in distance is wholly supplied by a longitudinal lengthening of the dead and

fast lines

72, 78.

From the foregoing discussion, it is apparent that the reduced rotation of the crown and travel sheaves gained by the use of idler sheaves will result in minimum line and sheave wear. It is also seen that since the dead line and fast line come off of the crown sheaves on the horizontal, their loads are not supported by the air and hydraulic pistons of the crown block assembly.

For effective operation the speed of crown block compensation must be synchronized vw'th the speed of the ships heave 14. For these purposes a control system as shown in FIGURE 6 is provided. An accelerometer 82 on the crown block 22 senses vertical motion and transmits an electric signal to a servo valve 84. The signal will be positive or negative depending on the direction of the vertical movement. The servo controls the output of a hydraulic accumulator 86 and directs it 4 through either of the lines or 90' to the valve 88 to determine flow of the pump 60 through one of the two lines 58, 58'.

Drift of the crown block from its mid position is prevented by the use of a conventional electrical signal device wherein a displacement signal is originated at 94. The said displacement signal is proportional to the distance the crown block is from the mid-point and acts as a small override to keep the crown block centered.

During heavy seas, the ship heave motion may exceed the allowable travel of the crown block and it is therefore desirable to compensate for only a portion of the heave. To accomplish this, .a second accelerometer 96 is provided on the water table. The signal from the second accelerometer has its sign reversed at 98. The water table signal is thus subtracted from the crown block signal at a signal mixer 100 and the difference will then go to the servo valve 84. The amplification of the water table signal takes place at 102 and is adjustable by the operator. If the absolute values of the two signals are equal, no compensation takes place. If, for example, the water table signal is set at 80 percent of the crown block signal, the crown block is compensated only to 20 percent.

The operating principles are best seen in FIGURES 8a, 8b and 80 which depict compensation of the crown block location during different stages of ship hea-ve. The movements discussed will relate to movements relative to the sea floor unless otherwise specified.

During a mean position as shown in FIGURE 8a, the crown block 22 with its hook load is supported near its mid-point in the framework 30' by the air pistons 44 and the hydraulic jacks 54. As long as the ship is stationary, the crown block will be stationary also. As the ship heaves upwardly to the FIGURE 8b position, the inertial force of the load supported by the air pistons 44 will resist upward movement and cause air compression in the cylinders 46. The natural resistance to upward movement, however, is lessened by the increasing pressure of the air, and the crown block will begin an upward travel. The accelerometer 82 (FIGURE 6) will sense this travel and cause hydraulic fluid to flow into upper chambers of cylinders 56 to maintain the crown block stationary. Similarly, when the ship moves downwardly to the FIGURE 80 position, any tendency of the crown block to move downwardly is sensed :by the accelerometer 84 and hydraulic fluid is pumped to the lower chambers of the cylinders 56.

What has been set forth above is intended primarily as exemplary to enable those skilled in the art in the practice of the invention.

What is new and therefore desired to be protected by Letters Patent of the United States is:

1. Apparatus for maintaining a substantially fixed vertical location of a drill pipe with respect to a bore through the sea floor underlying a body of water and which drill pipe is supported by a cable network suspended from a framework mounted on a floating platform overlying said bore, wherein the improvement comprises:

a sheave assembly mounted for vertical slidable movement in said framework,

resilient support means between said framework and said assembly normally supporting said assembly intermediate the vertical length of said framework,

a vertically disposed expansion jack having one end connected to said framework and its other end connect-ed to said assembly, said jack having first and second expansion chambers,

a source of pressurized fluid having a conduit system leading to said first and second expansion chambers, and

control means causing said first chamber to expand and said second chamber to contract when said platform moves toward the sea floor and causing said second chamber to expand and said first chamber to contract when said platform moves away from said sea floor.

2. The invention described in claim 1 wherein said control means comprises an accelerometer movement sensing means which emanates an electric signal when a vertical movement is sensed between said assembly and said sea floor,

and hydraulic valve means responsive to said signal for communicating one of said chambers to said source upon receiving said signal.

3. The invention as described in claim 2 wherein said accelerometer movement sensing means comprises an accelerometer resiliently mounted on said assembly for detecting a relative vertical movement between said assembly and said bore,

said accelerometer emanating a positive or a negative electric signal depending upon the direction of said movement,

a servo valve connected to said accelerometer having an input and first and second outputs, a hydraulic accumulator on one side of said valve and a hydraulic pump on the other side of said valve,

said valve communicating fluid from said accumulator to said pump through one of said outputs in re sponse to said positive electric signal and through the other of said outputs in response to said negative electric signal,

whereby the output of said pump is directed to said first chamber when said signal is positive and to said second chamber when said signal is negative.

4. The invention as described in claim 1 wherein said resilient support means comprises at least one air cylinder mounted on said framework, a piston slidably received within said cylinder, and forming an air chamber there with, a piston rod connected at one end to said piston and at the other end to said assembly, and means to provide a preselected pressure in said air chamber.

5. The invention as described in claim 2 including a second accelerometer provided on said platform which emanates a second electric signal when a vertical movement is sensed between said platform and said sea floor,

an amplifier connected to said second accelerometer,

a signal mixer connected between said first accelerometer and said amplifier, said second accelerometer being connected to said signal mixer through said amplifier,

means for reversing the sign of said second electric signal whereby the second electric signal is subtracted from the first electric signal at said signal mixer whereby only a portion of said relative vertical movement between said assembly and said sea floor will be compensated.

6. The invention as described in claim 1 wherein said sheave assembly comprises:

a plurality of rotatable axially aligned crown sheaves mounted for vertical slidable movement in said framework;

a plurality of rotatable axially aligned travel sheaves vertically spaced from said crown sheaves,

said travel sheaves lesser in quantity than said crown sheaves by one,

first and second idler sheaves rotatably mounted on said framework at an elevation substantially corresponding to the midpoint of said crown sheaves vertical travel range,

a cable having one end rigidly secured to a fixed point on said platform,

tension means mounted on said platform connected to the other end of said cable for maintaining a constant tension in said cable,

said cable extending from said fixed point over said first idler sheave, alternately and successively around each of said crown sheaves and said travel sheaves and over said second idler sheave to said tension means.

7. The invention as described in claim 6 wherein said tension means comprises a cable payout drum.

References Cited UNITED STATES PATENTS 1,928,958 10/1933 Young 254-190 2,961,216 11/1960 Blair 254-172 3,276,746 10/1966 Berne 254-172 3,309,065 3/1967 Prudhomme 254-172 EVON C. BLUNK, Primary Examiner HARVEY C. HORNSBY, Assistant Examiner U.S. Cl. X.R.