US 3004612 A
Description (OCR text may contain errors)
Oct. 17, 1961 D. c. KOFAHL SUBMERGED ELEVATED WELL HEAD STRUCTURE Filed Nov. 5, 1956 2 Sheets-Sheet 1 FIG. 2.
R. w 0 y W z 1! Wm 2 w Oct. 17, 1961 D. c. KOFAHL 3,004,612
SUBMERGED ELEVATED WELL HEAD STRUCTURE Filed NOV. 5, 1956 2 Sheets-Sheet 2 INVENTOR. 041 40 6'. 60/5444.
United Stes This invention relates to drilling and production of oil from wells located in an offshore marine location and is particularly directed to improvements in a submerged elevated well head structure and to a method of drilling wells embodying such structure.
Wells in oifshore marine locations are now being drilled from floating vessels, with the rotary drill pipe passing through a well head structure located on the ocean floor. This technique is satisfactory where the water depths are not too great and where it is possible for divers to descend to the position of the well head structure. However, when the water depth exceeds that at which divers can operate readily, the drilling of wells is not feasible by conventional techniques.
It is an object of this invention to elevate the well head structure of a submerged oil well to a depth readily accessible to a deep sea diver and to support the well head structure at that depth. A related object is to support and stabilize the casing of the oil well between the ocean floor and the submerged elevated well head structure. Another object is to provide a rigid supporting structure to stabilize blowout preventers, casing heads and tubing heads at submerged locations considerably above the level of the ocean floor. Other and more detailed objects and advantages will appear hereinafter.
In the drawings:
FIGURE 1 is a side elevation in diagrammatic form showing a submerged elevated well head structure and illustrating a method of drilling the well from a floating vessel and for producing a well into a floating barge. FIGURE 2 is a sectional plan view taken substantially on lines 2-2 as shown in FIGURE 1.
FIGURE 3 is a side elevation on an enlarged scale showing a portion of the apparatus illustrated in FIG- URE 1.
Referring to the drawings, a support structure generally designated 10 includes a plurality of longitudinal tubular elements 11 arranged in the general form of a square, and a central tubular element 12. Horizontal braces 13 and diagonal braces 14 connect the longitudinal elements 11 and 12. Each of the tubular elements 11 and 12 has a clear passageway therethrough to permit insertion and withdrawal of drill tools and to allow circulation during jetting as described below. The tubular elements 11 may be straight or may be slightly bowed as shown in the drawing.
The structure 10 is fabricated on land by conventional methods and transported to the offshore marine location by barge. It is then lowered over the well site by means of a barge and derrick (not shown) and rested on the ocean floor 15. The lower ends 16 of the tubular elements 11 project below the remainder of the structure 10*. Water under pressure is pumped through the interior of the tubular elements 11 to cause a jetting action adjacent the lower ends 16 and thus cause the structure 10 to become embedded in the'ocean floor. The structure 10 is plumbed by selectively jetting the tubular elements 11. When the structure is plumbed so that column 12 is substantially vertical cement is pumped down each of the tubular elements 11 to provide a temporary anchor. The cement passes out through the lower ends 16 and returns upwardly to the level of the ocean floor.
Drill tools are then operated through each of the tubular elements 11 to drill through the loose ocean floor overburden and into consolidated formation. This drilling operation is preferably carried out by means of the apparatus shown in the drawings. The floating barge 17 carries a mast 18 and suitable rotary drilling apparatus 19 for rotating a drill pipe string 20. A bit 21 is carried at the lower end of the drill pipe string 20. A pair of guide cables 22 extend downward from the floating barge 17 and are attached to the upright posts 23 fixed on the submerged platform 24 of the structure 10. Guide cables 22 may be supported from within an access Well provided in the barge 17 and preferably are suspended from a rig floor on which the rotary drilling apparatus 19 may be located. A well head structure generally designated 25 is fixed on one of the tubular elements 11 adjacent the platform 24. This structure 25 includes a blowout preventer assembly 26 mounted on slidable guide tubes 27 loosely received on the posts 23.
A cross head 28 is provided with guide sleeves 29 which slide on the guide cables 22 and this cross head has a central sleeve 30 through which the drill pipe 20 loosely extends. The bit 21 is larger than the opening through the sleeve 30.
When the drill string 21 is lowered from the floating barge 17 the cross head 28 slides down the guide wires 22 and centers the bit 21 for entrance into the upper end 31 of the well head structure 25. Continued downward movement of the drill string 20 causes the bit 21 and drill string to pass axially through the well head assembly 25 and into the tubular element 11. The cement within the element 11 is drilled out and the bit passes downward through the lower ends 16 of the tubular element 11, forming a shaft 32 which is a prolongation of the tubular element 11. Cement is then pumped down the interior of the drill pipe string 20 out through the ports in the bit 21 and back through the shaft 32 to fix the drill pipe within the consolidated formation of the ocean floor. The drill pipe is then disconnected at the top of the platform 24 and serves to function as a reinforced concrete post within the tubular element 11. The same drilling and cementing operations are carried on sequentially with respect to each of the tubular elements 11. By this means the submerged structure 10 is securely anchored to the ocean floor.
The drill tools are then operated through the central column 12 to drill a prolongation shaft and a conductor pipe (not shown) is lowered through the interior of the column 12 and cemented in place. The drill tools are then operated through this conductor pipe to drill the Well. After completion of the drilling of the Well, the well head structure 33 is connected to the upper end of the central column 12 for producing oil from a well. This structure 33 is preferably similar to that disclosed in my copending application Serial No. 620,451, filed November 5, 1956 and employs a housing 34 which forms an enclosure for the tubing head. Well fluid produced through the tubing head passes outward through conduit 35 and flow line 36 to any convenient reservoir such as, for example, the barge 37.
Having fully described my invention, it is to be understood that I do not wish to be limited to the details herein set forth, but my invention is of the full scope of the appended claim.
A submerged well head structure for a well in an oilshore marine location comprising in combination: a wholly submerged support structure having a plurality of tubular elements extending from the lower end to the upper end thereof, the lower ends of certain of the tubular elements extending into the ocean floor, a post fixed within each of the latter said tubular elements further projecting into the ocean floor, whereby the structure is rigidly fixed against movement, a submerged well head device fixed to the upper end of one of the other tubular elements laterally flexible guide means connected with the well head device and extending upwardly for guiding drilling tools into the well head device from a floating vessel at the ocean surface, and means on the floating vessel for rotating the drill tools.
References Cited in the file of this patent UNITED STATES PATENTS Flood et al. .L June 21, 1910 Gross Apr. 1, 1941 Tucker June 27, 1950 Samuelson Mar. 11, 1952 Evans et a1. May 12, 1953 7 Bauer et a1. Oct. 1, 1957 McNeill et al Oct. 1, 1957