Houston, TX- A typical oil well has a large-diameter casing at its top and progressively smaller diameters as well depth increases. One casing program might call for 400 ft of 30-inch drive pipe supporting the wellhead.
Then would come 20-inch conductor casing, followed by 13-3/8-inch surface casing, 9-5/8-inch casing, and, finally, 7-inch production casing. The wellhead supports the weight of all the casing strings. When completed, this typical well has a "Christmas tree" of valves at the top to control the oil.
Developed by Baker Oil Tools, the Downhole Splitter(TM), permits the drilling of two wells from a single wellhead. Douglas Hall, senior product engineer with Kvaerner National Inc., designed the multi-bore wellhead portion of the equipment. In this system, the 30-inch drive-pipe still supports the wellhead. The splitter mechanism mounts on the bottom of the 20-inch conductor casing.
After the 20-inch casing is lowered to its full depth (a maximum of 10,000 ft), a 9-5/8-inch drilling riser leads to one of the holes in the splitter. Workers cement the 20-inch casing through the drilling riser. Using conventional directional drilling techniques, the operator drills the well to its final depth and installs the 7-inch production liner.
Now, the drilling riser moves to the other side of the 20-inch casing and drilling begins. After drilling the second well and installing the 7-inch liner, the operator removes the 9-5/8-inch drilling riser. Standard tie-back assemblies connect the two wells to the surface. Two independent Christmas tree assemblies complete the two wells.
Douglas Hall has also designed the Surface Splitter(TM) Wellhead System. It accomplishes the same goal of producing two wells on the same wellhead, but without the use of movable downhole tools.
Perhaps the largest savings result from reduced drilling time. "With offshore drilling costing $40,000 to $50,000 per day, the savings add up in a hurry," says Hall. In one example, a single 10,000-ft-deep well required 36 drilling days. A second conventional well would take another 36 days, plus the time needed to skid the rig to the new location. Using a splitter to drill two 10,000-ft wells required 63 days.
Additional details...Contact Joe Johnson, Kvaerner National, Inc., 1255 N. Post Oak Rd., Houston, TX 77055.