US3486343A - Platform for drilling wells at water locations - Google Patents

Description

Dec. 3G, 1969 R. G. GiBsoN ETAL PLATFORM FOR DRILLING WELLS AT WATER LOCATIONS 3 Sheets-Sheet l Filed Sept, l5, 1966 I N VEN TOR` Dec. 30, 1969 R. 3. GIBSON ETAL PLATFORM FOR DRILLING WELLS AT WATER LOCATIONS 3 Sheets-Sheet 2 Filed Sep. l5, 1966 De.30,1969 RGQBSON ETAL 3,486,343

PLATFORM FOR DRILLING WELLS AT WATER LOCATIONS Filed Sept, l5, 1966 3 Sheets-Sheet 5 United States Patent O 3,486,343 PLATFRM FOR DRILLING WELLS AT WATER LOCATIONS Robert G. Gibson, Mbeya, Tanzania, and Delbert B. Johnson, John G. Mackin, Jr., and James C. Sti-as, Houston, Tex., assignors to Brown & Root, Inc., Houston, Tex.

Filed Sept. 15, 1966, Ser. No. 579,662 Int. Cl. E021] l7/02; E04b 1/34; E04c 3/36 US. Cl. 61-465 6 Claims ABSTRACT F THE DISCLOSURE A drilling platform is disclosed that is adapted to be floated to and sunk at an offshore location. The platform includes two spaced-apart pontoons at the base for floating it to an offshore location and for engaging the ocean lloor when the platform is sunk. An upright central column composed of spaced-apart concentric shells is located between the pontoons to extend above the surface of the water when the platform is sunk. The column is supported between the pontoons by diagonal braces, which are connected between the column and the pontoons so as to be completely below expected ice iloes when the platform is sunk. An X-shaped truss support is located on the top of the column for supporting an operations deck. The pontoons include separate Water compartments, which may be filled with water to adjust the orientation of the platform as it floats or to sink the platform until the pontoons are seated on the ocean floor. The ends of the pontoons are connected by cross braces, which are positioned with their longitudinal axes above the longitudinal axes of the pontoons sufciently for the braces to be above the surface of the water when the pontoons are floating. When the platform is sunk, piles are passed through openings in the end of the pontoons into the bottom to secure the structure against lateral movement on the ocean bottom. One or more surface holes are drilled into the ground below the platform through the center column. Surface casing is placed in the holes and cemented to the ground and to the center column. Thereafter, any increase in the vertical load of the platform is transferred to the ground through the surface casing, rather than through the pontoons.

This invention relates to improvements in drilling platforms for drilling oil and gas wells in inundated areas and refers more particularly to such platforms from which a plurality of wells will be drilled and completed which remains as a permanent part of the installation of the completed wells.

The platform of the instant invention is particularly adapted for use under severe conditions wherein the drilling platform will be subjected to extremely heavy lateral loads.

In certain Northern areas now being drilled, as for example, the Cook Inlet area of Alaska, very severe weather conditions exist. Probably the most serious hazard is occasioned by ice iloes being propelled by very rapid current due to tides, etc. For example, in the Cook Inlet area the tides may vary by as much as thirty feet or more and tremendous quantities of ice are carried by the current created by the rising and falling tides. An obstacle, such as a drilling platform, may back up extremely large quantities of the ice, subjecting it to enormous lateral loads. Also, large quantities of the ice may be carried at a relatively high speed and come in contact with the drilling platform delivering a tremendous impact. Such lateral loads may come from unpredictable compass directions.

In addition, due to the relatively inaccessible location of such areas from industrial and supply centers, the drilling platform must house a self-contained supply of materials used in drilling as well as the housing facilities for the men and one or more drilling derricks. Therefore, the drilling platform should be such that it may be constructed in an industrial area and then floated as a ship to the point of use where it can then be sunk and securely attached to the underwater floor. The base of the platform should therefore be able to serve not only as a ship but also secure the drilling platform stably in location so as to resist lateral loads to which the structure is subjected in use. This is in addition to supporting the tremendous load of the supplies, drilling rig, etc. used in the drilling oeprations.

An object of this invention is to provide a drilling platform for use in such areas that may be readily floated to location.

Another object is to provide such a drilling platform in which the pontoon system serves adequately as a ship with no undue resistance to movement in the water and provides a very strong truss-like base for resisting lateral impacts and loads when the structure is located and anchored to the underwater lloor.

Another object is to provide such a drilling platform wherein the vertical load due to the drilling equipment and supplies is carried by columnar support, the structural members of which largely are provided by the conductor pipe or casing used in drilling the plurality of wells and which also serve as a part of the pile system for anchoring the structure to the underwater floor.

Another object is to provide a columnar support for the drilling platform and its associated equipment which is adapted to have substantially equal strength for resisting impacts applied thereto from any point of the compass.

Another object is to provide a drilling platform which may employ a plurality of columnar supports in tandem.

Another object is to provide a drilling platform supported on a vertical columnar support in which a novel X-shaped support member located at the upper portion of the columnar support provides the cantilever support for the deck of the structure.

Another object is to provide a means for pumping liquid from the compartments of the pontoon-like base thereof by means of a pump located in the lower portion of the columnar section of the structure.

Other and further objects of the invention will appear from the specification and the drawings.

In the drawings, which are to be vread in conjunction herewith, and which illustrate a preferred embodiment of the invention:

FIG. l is a side elevational view of a structure embodying the invention;

FIG. 2 is an elevational view of the structure shown in FIG. l but taken at thereto;

FIG. 3 is a plan view of the structure shown in FIGS. l and 2, taken just below the drilling deck and the support therefor;

FIG. 4 is a plan view of the upper deck and illustrates in dotted lines in plan the X-shaped truss support for the deck;

FIG. 5 is a schematic illustration of a typical piping arrangement which may be employed in conjunction with the various compartments of the structure shown in the preceding figures; and

FIG. 6 is a view, upon an enlarged scale, of a stiffener and conductor guide used between the shells of the vertical column illustrated in the preceding figures.

Referring to the drawings, the structure comprises a vertical columnar or central section 10 at the upper end 3 of which is located a two-level deck 11a and 11b. The structure has a base 12 composed of two parallel pontoons 13 with suitable bracing between the base `and the columnar part which will be hereinafter more fully described.

The base 12 serves both to oat the structure as it is being towed to location from a place of fabrication and to support the structure, primarily against lateral loads, when it is secured to an underwater iloor in operation.

The base comprises the two parallel pontoons 13 and suitable bracing both as spacers between the pontoons and between the pontoons and the vertical columnar section. The preferred bracing is such as to provide a series of trusses and also to provide very little resistance to towing of the vessel through water. For example, in FIG. 3, it is seen that the four diagonal braces 14 provide, with the pontoon sections between the joints of the diagonal braces and the pontoon sections, two triangular geometric gures. Also, when considered in conjunction with the spacers or braces 1S which join the ends of the pontoon, triangular geometric gures are also provided. Likewise, triangular geometrical figures are provided when the diagonal braces 14 are considered in conjunction with the braces 16 as illustrated in FIG. 2. The braces 16 extend between the ends of the pontoon and lower end of the vertical columnar section. The triangles are completed by the portion of the verticle columnar section which joins the inner ends of braces 14 and 16. Thus, this preferred arrangement of braces provides an extremely stable st-ructure for the amount of material employed.

By reference to FIG. 1 it will be noted that tthe upper ends of diagonal braces 14 are located Well below the means low water level. This distance should be such as to provide a water depth that will adequately accommodate any vessels that might be used in servicing the structure and also to be beneath the lower portion of any ice iioes that -might engage the structure. The particular elevations given in FIG. 1 are exemplary of those that might be encountered at some particular location but should not be considered as limiting in any way.

The forward end of the pontoons 13 may be tapered as at 13a to facilitate movement of the structure through water when being towed. In this connection it is to be noted that the longitudinal axis or centerline of braces 15 is located above the longitudinal axis of the pontoon 13. With this arrangement they are located principally above the water level when the structure is being towed. While the braces 16 are not located above the water level in the embodiment illustrated, they are positioned on a diagonal relative to the path of travel of the structure and thereby offer less resistance to ow of the device than would the braces 15 were they completely submerged due to their positioning.

Each of the pontoons is provided at each end with a stiffened section, of large-r diameter than the central portion of the pontoons. These stiffened sections are provided with a plurality of openings in which are secured pile jackets 17. These jackets are sealed to the openings so that they are water-tight. Once the device is towed to position and sunk until the pontoons rest on the underwater floor, piles are driven through the jackets to anchor the device to the oor.

In the particular embodiment illustrated, an illustrative example of the maximum diameter of the pontoon sections is 24'. The smaller diameter section of the pontoons may for example be in the neighborhood of 20 diameter. 'I'he pile jackets may have a diameter of approximately 48 through which 36 piles may be driven. Typically, these piles may be driven as much as from 50 to 65 or more penetration. The diagonal braces 14 may be in the order of l5 diameter and horizontal braces 15 of approximately 7 in diameter. The diagonal braces 16, may also be of approximately 7 in diameter. The above dimensions are merely illustrative and are not t9 be read in a limiting sense.

In order to stabilize the structure during towing, a bulkhead is utilized between the enlarged sections of each or" pontoons 13 and the intermediate narrow sections. These enlarged sections may be connected with each other in such a way that uid may be transferred from either or" the large sections on either of the pontoons to the other to thus counteract list or tipping tendencies of the structure due to wave action, wind action, current action, etc.

Reference is made to FIG. 5 for schematic disclosure of the lines for supplying water to and exhausing water from these pontoon compartments. It will be noted that sea cocks are provided for selectively ooding any of the sections of the pontoons. These are remotely controlled valves located adjacent the low side of the pontoon sections. In accordance with standard practice the valves are actually located internally of the pontoons so as to not be knocked off by obstacles. Lines 19 and 20 are provided for pumping water into each of these sections as illustrated. However, during towing of the vessel they may be used to force air into the end compartment so as to eject water through the sea cocks 18 or, to transfer water from one end to the other of the pontoon through the lines 21 and 22. Each of the end sections is provided with a vent line as shown at 23, 24, 25 and 26. These vents are valve controlled individually, so that they may be individually opened or closed to effectuate transfer of liquid or filling of the pontoon section as required. Valved lines 27 and 28 connect corresponding end compartments of the two pontoons for transferring liquid from one end to the other under the influence of compressed air introduced through lines 19 and 20. All of the valves shown, as well as the sea cock, are remotely controlled, solenoid valves which can be controlled from a panel may be used for this purpose, as will be well understood by those skilled in the art.

The vertical section or column of the structure comprises two concentric shells 27 and 28 and these two shells extend from the lower end of the columnar portion to its upper end where they connect to the box girder 29. This box girder is X-shaped when viewed in plan, as illustrated in FIG. 4. It of course provides the cantilever support for the deck. The X-shape of the box girder distributes the supports for the deck so that the span of the deck between support points is minimized, whereby the strength of the supports for the deck and the box girder, per unit of weight, is increased over use of parallel box girders.

The lower end of the columnar portion may be closed off and sealed, and near the lower end, an inverted dishshaped bafiie or partition 30 may be secured to the inner shell. This ba-le should be just below the junction of the inner ends of the diagonal braces 14 with the vertical column.

, At suitable intervals along the length of the vertical section, stiffeners and conductor guides may be employed as illustrated in FIG. 6'. The stiifeners are provided by rings 31 Welded to the inner and outer shells 27 and 2S, respectively. These rings 31 have a series of openings 32. In each opening 32 is secured a conductor guide made up of a flared portion 33 and a cylindrical skirt 34. The number of openings and of conductor guides will correspond to the number of Wells that are to be drilled from this platform. Similar openings and conductor guides will be provided in the partition 30 but the skirts of the conductor guides in the partition Will preferably extend from the partition 30 through the lower closure in the event the lower end of the column is closed. These openings of course will correspond in arrangement to the openings shown in the central portion within the inner shell as shown in FIG. 3.

The conductor guides are for the purpose of guiding conductor pipe through the Vertical column after the structure has been located and sunk. The conductor pipe will be utilized as surface casing in the wells that are drilled and will be set in the well bores at whatever depth is indicated by the drilling operations. Further, these conductor pipes may be cemented in place in accordance with usual well cementing practices and the drilling operations conducted through them. By use of deviation drilling techniques the wells diverge downwardly so as to develop the desired drilling pattern.

After the conductor pipes are in place, the interior between the inner and outer shells 27 and 28, may be filled with grout to further stabilize the structure. With this arrangement it is apparent that the conductor pipe serves not only for the purpose of conducting the drilling operations therethrough, but also support a major portion of the vertical load of the drilling platform. For this reason the primary function of the base section 12 is to support the device against lateral stresses tending to tilt or tip the structure.

For a large drilling structure in accordance with this invention, the outershell may be of a diameter of approximately 28'. The spacing between the inner and outer shells, as contemplated, may be approximately 3. The bore through the typical conductor guide may be in the order of 2. The dimensions are, of course, merely illustrative, and are not intended as limitations.

The deck is supported by and mounted on the X-shaped box girder 29. It may comprise a two-level deck as shown at 11a and 11b with suitable bracing for supporting the upper deck from the lower deck. With this arrangement much of the drilling equipment may be located on the lower deck, such as the mud pumps, the mud mix tanks, production surge tanks, a tool room, water pumps, separators, shipping pumps, gas scrubbcrs, DC and AC generators, heat units, air compressors and a control room. On the upper level, mud tanks, fuel tanks, and portable water tanks may be located along with tanks for bulk cement and the active drilling mud tank and the appurtenant equipment. The drilling derrick may be mounted upon the upper level and the living quarters may be divided between the two levels. It is contemplated that a heliport may be mounted above the living quarters.

As an example, the deck may be 120' x 120' square or may be circular, oval or oblong in shape.

In the present embodiment, the vertical columnar portion is illustrated as circular in cross-section but it is contemplated that it may be ovoid in cross-section or formed in the shape of either a three or four leaf clover, in crosssection, by utilizing a series of circular sectors joined together at their edges for the purpose. In any event, the support for the drilling deck is a single central column having substantially the same strength against impact coming from any direction of the compass.

To give an illustrative relative size for the upper deck and the base, it is contemplated that if the upper deck is a square having a dimension of 120 that the base should be substantially square and have a dimension of approximately 150' to the side.

While the purpose of the base is to provide support for the drilling platform, nevertheless, due to the size of the components that make up the structure, considerable storage capacity is available. In conducting drilling operations, a supply of fresh water for drilling is required and provision must be made for this where the device is used in salt water locations. The diagonal braces provide a good and readily usable facility for this purpose. Or drilling fuel could be stored in this manner.

In order to utilize the diagonal braces for this purpose, a sump is provided near the lower end of the vertical column as illustrated at 35 in FIGS. 5 and 2. This sump has pipes connected with each of the diagonal braces 14. These pipes are illustrated at 36 and as illustrated may extend through the diagonal braces 16, to the pontoons, and thence to the lower end of the diagonal braces 14. These lines 36 are preferably controlled by remotely controlled valves. A conduit 37 extends from the lower portion of the sump to the surface. Centrally of the conduit 37 is a pump shaft 38 which connects to a downhole pump 39 that communicates with the interior of the sump and discharges through the conduit 37.

In order that liquid ymay be put into and withdrawn from the diagonal braces 14, each of the braces is equipped with a pipe 40 which communicates with the surface. These may serve as vents when the pump 39 is forcing liquid from the diagonal braces to the surface. These lines may be utilized as fill lines with lines 36 venting, when the diagonal braces 14 are filled with liquids. Obviously, the location of the sump 35 should be near the lower extremities o-f the diagonal braces 14 as far as relative horizontal position is concerned.

It is ordinarily preferable during drilling operations and during the production of the wells to maintain the pontoons 13 full of water corresponding to that in which the device is submerged. This adds to the weight of the structure and lends greatly to the stability. Nevertheless, it is contemplated that if during initial operations when the lirst well has been completed, it is desirable to use the pontoons for storage for crude oil pending the completion of a pipeline to the well, this may be done. The vent lines 23 may be utilized for injecting crude oil into the pontoons, the oil being pumped through these vent lines with the line 19 and line 20 providing vents for the displacement of any water in these tanks. In order to recover the crude oil, the vents 23 are opened and serve as outlets for the oil as water is pumped through lines 19 and 20 into the pontoons. Of course a single line 19 could be used for this purpose but the utilization of two lines increases the fill rates.

It is contemplated that water for lines 19 and 20 may be supplied by the re water pumps normally available on such a drilling structure for forcing sea lwater into the oil storage below the oil water interface.

It is believed that the operation of the equipment is apparent from the foregoing description. The device when constructed, is oated to a point of installation being towed by barges or the like. During this operation the buoyancy of the structure ymay be modied, as previously explained, by controlling the amount of water in either end compartment of pontoons 13. By proper adjustment any list of the vessel may be countered to trim the vessel. The towing is facilitated because the braces 15 are basically out of the water during the towing operation andI also are relatively small in diameter. While the braces 16 usually will be under the water level at least to some extent, due to their diagonal arrangement relative to the path of travel of the structure, they offer minimal resistance to towing of the structure. The vessel may be towed to location and anchored, prior to the deck being placed thereon.

When the device has been towed to the desired operational location it is sunk by opening the sea cocks to ll the pontoons and for that .matter the various braces may be filled with the surrounding water. By controlling the rate of ooding, the rate of descent may be controlled. When in place on the'underwater floor, the piles may be driven through the pile guides carried by the pontoon ends to securely anchor the structure in place. Then conductor pipe may be sunk through the various openings and guides therefor in the vertical section. These conductor pipes may be securely cemented in place at depths ranging from in the neighborhood of as little as 50 to 300' or more below the lower end of the vertical column. When the space between the inner and outer shell not occupied by the conductor pipes and stiffeners, is lled with cement, or grout, the structure is extremely sturdy and the major portion of the vertical load is carried directly by the conductor pipes to the sub-strata formations. Due to the heights of the drilling platform above the diagonal braces, a downhole pump arrangement has been arranged by which water may be ejected from the diagonal braces in a convenient and novel manner.

It will be seen that the ends and objects of the invention have been accomplished. A structure has been provided which may be utilized for the drilling of a plurality of wells which may thereafter be produced from this single platform. The platform is particularly adapted for use in cold climates, and under severe conditions of lateral loading. The arrangement is such that no twists are imposed on the structure due to loading from ice floes and various impacts because of the single central columnar support. The arrangement is such that it lends itself well to tandem utilization rwith a single enlarged base and a plurality of columnar structures if more well locations are required, than are conveniently provided for by a single vertical column. Nevertheless the columns do not have to be structurally tied together whereby loading of one would impart a twist of the other in the event of ice floes or other severe lateral loads.

From the foregoing, it Iwill be seen that this invention is one weH adapted to attain all of the ends and objects hereinabove set forth, together with other advantages which are obvious and which are inherent to the apparatus.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.

vAs many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

The invention having been described, what is claimed 1. A drilling platform adapted to be floated to an offshore location and sunk to support an operations deck from which a plurality of offshore wells can be drilled, comprising, in combination: a base section including first and second spaced apart parallel hollow pontoons including watertight compartments into which water may be introduced to adjust the orientation of the platform as it oats and to sink the platform when over the desired location, and tubular spacers connected between the pontoons having a diameter smaller than the diameter of the pontoons and located with their longitudinal axes above the longitudinal axes of the pontoons suiciently to be above the surface of the water, when the pontoons are floating on the surface, to permit relatively unobstructed movement of the platform on the surface of the water, an upright column disposed between and at substantially equal distances from said pontoons, said column having at least a portion of its interior adapted to communicate with such operations deck and a well bore, means attached to the upper end of the column to support an operations deck for supporting at least one drilling rig, and a plurality of tubular braces extending diagonally between the column and the pontoons and connected to the pontoons adjacent their ends and to the column at an intermediate position Well below the anticipated low water level Where the platform is sunk, said diagonal braces being positioned to support the upright column and the load thereon when the platform is oating and during the initial stages of any drilling operations, a conduit that extends throughout a major length of the upright column and communicates at its lower end with the interior of at least some compartments of the base and tubular braces, and a pump located at the lower end of the conduit for pumping uid therefrom through the conduit.

2. A drilling platform sunk at `an offshore location to permit the dn'lling of a plurality of offshore wells, comprising, in combination: an operations deck for supporting at least one rig for drilling a well, a single upright column supporting said deck above the surface of the water, at least one string of casing extending from said deck, through the column and parallel to the length of said column, and into the ground beneath the drilling platform, means securing said casing to the column and the ground, and a buoyant base section being ballastable and deballastable and having sufficient buoyancy when deballasted to float near the surface of the water while supporting the colunms in an upright iposition, said base section being ballasted so as to be seated on the ocean floor and connected to and supporting said upright column, said operations deck, and the load imposed thereon during the installation of said casing after which a major part of the increases in weight on the operations deck subsequent to the securing of said casing to the ground will be transferred to the ground by said casing.

3. The platform of claim 2 in which the casing extends through the interior of said column.

4. The platform of claim 2 in which the column comprises spaced-apart concentric shells and a plurality of guides secured in circumferentially-spaced relation in the space between the shells through which wells may be drilled into the ground below the platform.

S. A drilling platform sunk at an offshore location to permit the drilling of a plurality of offshore wells, comprising, in combination; an operations deck for supporting at least one rig for drilling a well, a vertical column supporting said deck above the surface of the water, at least one string of casing extending from said deck, parallel to the length of said column, and into the ground beneath the drilling platform, means securing said casing to the column and the ground, and a base including at least two spaced apart hollow portions into which liquid can be introduced to sink the platform, said base seated on the ocean Hoor and connected to and supporting said column, said operations deck, and the load imposed thereon during the installation of said casing after which substantially all of the increase in weight on the operations deck subsequent to the securing of said casing to the ground will be transferred to the ground by said casing.

6. The drilling platform of claim 5 further provided with a plurality of guides extending through each end of the pontoons for receiving piles for anchoring the platform against lateral movement.

References Cited UNITED STATES PATENTS 2,033,689 3/1936 Dawson 52-73 2,938,352 5/1960 Knapp et al. 6146.5 3,104,531 9/1963 MCCammon 6l-46.5 3,128,604 4/1964v Sandberg 61-46.5 3,145,538 8/1964 Young 61-46 3,209,544 10/1965 Borrmann 6l-46.5 3,246,476 4/1966 Wolff 61-465 3,315,473 4/1967 Hauber et al.` 6l-46.5 3,364,684 1/1968 Sandberg 61-46 FOREIGN PATENTS 510,916 12/1920 France.

JACOB SHAPIR, Primary Examiner lU.s.'c1. x.R. Y 52 ,73, 721 4 v

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