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Date: 2015-10-07; view: 657.

Unit 6. Drilling the Surface Hole

C. Discussion

Topics:

1. Functions and properties of a drilling fluid.

2. Field tests on drilling fluids.

3. Composition of water-based and oil-based muds.

After the rathole crew prepared the initial 15 metres of the hole, the rig crew is ready to begin drilling the first part of the hole. They make up the bit on the end of the first drill collar, and they lower both bit and drill collar into the conductor hole. They make up enough collars and drill pipe to lower the bit to bottom. On a rig using a rotary table and kelly, the driller then picks up the kelly out of the rathole where it has been waiting. Crew members then stab and make up the kelly onto the topmost joint of drill pipe sticking up out of the rotary table. The slips suspend this joint (and the entire drill string) in the rotary table.

With the kelly made up, the driller starts the mud pump, lowers the kelly drive bushing to engage the master bushing. The driller actuates the rotary table to begin rotating the drill stem and bit. The driller gradually releases the drawworks brake, and the rotating bit touches bottom and begins making hole.

Using an instrument called the "weight indicator," the driller moni­tors the amount of weight put on the bit by the drill collars. After the bit drills about 9 metres, which is about the length of a joint of drill pipe, crew members must add a new joint of pipe to drill deeper. At this point, crew members say that the "kelly is drilled down," meaning that the bit has made enough hole so that the top of the kelly is very near the kelly drive bushing.

With the kelly (or the joint of drill pipe on top-drive rigs) drilled down, the driller stops rotating, picks up (hoists) the drill string, and stops the mud pump. The floorhands are ready to make a connection - that is, they are ready to add (connect) a new joint of drill pipe to the drill string so that the bit can drill another 30 feet or so.

To make a connection the driller picks up the drill string high enough for the kelly to clear the rotary table - that is, the driller uses the drawworks to hoist the traveling block, hook, and swivel up into the derrick or mast so that the first joint of drill pipe is exposed in the opening in the rotary table.

With the kelly clear of the rotary table, the floorhands set the slips around the joint of drill pipe to suspend the drill string in the hole. They then latch two big wrenches called "tongs" on the kelly joint and the tool joint of the joint of drill pipe. A tong pullline - a length of strong wire rope - runs from the end of the tongs to the breakout cathead on the drawworks. The driller engages the automatic cathead, and it starts pulling on the line with tremendous force. The pulling force on the tongs breaks out (loosens) the threaded joint of the kelly and drill pipe. Once the joint is loosened, the driller engages a kelly spinner, which is a special air motor mounted near the top of the kelly. The kelly spinner rapidly turns or spins the kelly to back it out (unscrew it) from the drill pipe joint.

With the kelly backed out of the drill pipe's tool joint, crew members swing the kelly over to the mousehole, that lined hole in the rig floor the crew prepared when they rigged up. Earlier, crew members placed a joint of drill pipe into the mousehole so that it would be ready to add to the drill string.

They stab the kelly into the joint in the mousehole, and the driller spins up the kelly into the joint using the kelly spinner. Crew members grab the tongs, latch them onto the kelly and pipe, and buck up (tighten) the joint to final tightness. Next, the driller uses the drawworks to raise the kelly and attached joint out of the mousehole. The crew stabs the end of the new joint into the joint suspended by the slips in the rotary table, and, using a spinning wrench and the tongs, they thread the joints together and buck them up to final tightness. Finally, the driller lifts up the kelly and attached string a small amount, the crew removes the slips), and the driller lowers the newly added joint and kelly until the kelly drive bushing engages the master bushing. The driller starts the pump, begins rotating, and lowers the bit back to bottom to continue making hole. Crew members make a connection each time the kelly is drilled down - each time the bit makes about 30 feet of hole. Near the surface, where the drilling is usually easy, they may make several connections while they are on tour.

At a predetermined depth, perhaps as shallow as a few hundred feet (metres) to as deep as two or three thousand feet (metres), drilling stops. Drilling stops because crew members drill this first part of the hole - the surface hole - only deep enough to get past soft, sticky formations, gravel beds, freshwater-bearing formations, and the like that lie relatively near the surface. At this point, crew members remove (trip out) the drill string and bit from the hole. They trip out the drill string and bit so that they can run casing into the hole.