Single Riser With Two Wellheads

This invention relates generally to drilling wells, and more particularly to an apparatus for drilling two wells in a single conductor.

A typical offshore well installation comprises a single conductor in a single well. If necessary, several wells may be located side by side in a template. Multiple wells may also be drilled within a single conductor pipe. One example of such an installation utilized a conductor with a diameter the size of a leg of a drilling platform and contained up to 12 wells. That installation utilized a guide member lowered on a riser into the conductor. The guide member had slots for each well along its periphery. U.S. Pat. No. 5,458,199 shows two wells in a conductor with a guide member at the lower end of the conductor, but an improved guide means is desirable.

A guidance system comprising two guide tubes is lowered into a well with a conductor. The guide tubes are connected together by partitions which are about 100 feet apart and divide the conductor into two halves. Each partition comprises two symmetrically formed, semi-cylindrical sections facing in opposite directions. The guide tubes are supported by a plate at the upper end of the conductor. The operator lowers a string of drill pipe into the conductor to drill a first smaller diameter well at the bottom of the conductor. After drilling to the desired depth, the operator runs a first string of casing down the conductor and through the new well bore. The casing is located on one side of each partition and cemented in place. The operator then lowers the drill pipe down the other side of the partitions and repeats the drilling and casing of a second well. After each well is cased, the operator pumps cement down one of the guide tubes to cement the interior of the lower end of the conductor.

FIG. 1 is sectional top view of a partition of the guidance system in a conductor taken along the line 1--1 in FIG. 2.

FIG. 2 is a fragmented side view of the guidance system shown installed in a conductor pipe with one string of casing and is constructed in accordance with the invention.

FIG. 3 is a sectional top view of the mounting plate taken along the line 3--3 in FIG. 2.

FIG. 4 is a schematic drawing of the guidance system shown in a conductor pipe during the initial installation phase.

FIG. 5 is a schematic drawing of the guidance system of FIG. 4 showing a first well being drilled.

FIG. 6 is a schematic drawing of the guidance system of FIG. 4 showing a first completed well.

FIG. 7 is a schematic drawing of two completed wells in a single conductor after the guidance system has been removed.

Referring to FIG. 2, a large diameter string of conductor 11 with a longitudinal axis 22 is installed in a well 12 to a first depth. Conductor 11 is a steel pipe, typically 36 inches in diameter. Conductor 11 normally extends from a drilling platform at sea level downward to the sea floor and may extend several hundred feet into the earth. A guidance system 14 comprising two guide tubes 13 and 15 is lowered into conductor 11. In the preferred embodiment, guide tubes 13 and 15 consist of five inch diameter tubing. Guide tubes 13 and 15 are connected together by a plurality of partitions 17 which are preferably bolted to guide tubes 13 and 15. Partitions 17 are about 100 feet apart, and as shown in FIG. 1, have outer edges or webs 18 that extend out to the bore of conductor 11, thereby dividing conductor 11 into two halves. Webs 18 have an outer dimension that is transverse to longitudinal axis 22 that is approximately equal to the inner diameter of conductor 11. Each partition 17 comprises two symmetrically formed, semi-cylindrical sections 20 facing in opposite directions. The axes of section 20 and guide tubes 13 and 15 are located 90 degrees apart from each other relative to longitudinal axis 22 of conductor 11.

Referring to FIG. 4, guide tubes 13 and 15 are secured to a conventional drilling rig elevator 22 and lowered into conductor 11. Approximately every 100 feet, elevator 22 stops lowering guide tubes 13 and 15 so that a partition 17 may be fastened to them. Elevator 22 resumes lowering the assembly into conductor 11 and repeats the sequence until the first depth of well 12 is reached by guide tubes 13 and 15. Referring to FIGS. 2 and 3, the upper ends of guide tubes 13 and 15 are then landed in a plate 19 which is mounted to the upper end of conductor 11 and elevator 22 is removed. Plate 19 also has two holes 21 and 23 of larger diameter for two strings of casing.

A conventional drilling diverter (not shown) is installed on plate 19. Referring to FIG. 5, a string of drill pipe 25 is run through the diverter and hole 21. Drill pipe 25 is used to drill a first smaller diameter well from the lower end of the bore of well 12 containing conductor 11 to a desired depth. Circulation will be up conductor 11 and the diverter. Hole 23 will be plugged off. Referring to FIG. 6, a first string of casing 29 is run through hole 21, down conductor 11, and through the new well bore before it is cemented in place. Casing 29 is located on one side of guide tubes 13 and 15 and partitions 17. The upper end of casing 29 lands in plate 19. Repeating the sequence, drill pipe 25 is then lowered through the diverter, hole 23 and down the other side of guide tubes 13, 15 and partitions 17 to drill a second well bore. As shown in FIG. 7, drill pipe 25 is removed and a second string of casing 31 is cemented in its place. Casing 31 lands in hole 23 of plate 19. After both strings of casing 29, 31 are in place, the interior of the lower end of conductor 11 is plugged off by pumping cement from pump 33 (FIG. 6) down one of guide tubes 13, 15. When the wells are complete, casing strings 29 and 31 extend upward to the surface and wellhead housings 39 and 41 are mounted to each casing 29, 31, respectively. A cement plug 35 will be located at the bottom of conductor 11. The guidance assembly comprising guide tubes 13, 15 and partitions 17 remain in conductor 11.

The invention has several advantages. The invention provides a guidance system for sequentially guiding a drill string to drill two wells in a single conductor bore. The invention also provides means for separating the casings for the two wells during completion of the wells.

While the invention has been shown in only one of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention.