Heavy Oil Science Centre - Overburden

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Drilling Problems and Drilling Operations

If a tool is lost or the drill string breaks, the obstruction in the well is called junk or fish. It cannot be drilled through. Special grabbing tools are used to retrieve the junk in a process called fishing. In extreme cases, explosives can be used to blow up the junk and then the pieces can be retrieved with a magnet.

Some reservoir rocks can be damaged by forcing drilling mud into them. This can be caused by using too heavy an overbalance while drilling. The drilling mud clogs the pores or causes chemical or physical changes in the rock. This decreases the rock's permeability near the well bore. Formation damage prevents or reduces production from the reservoir rock when the well is completed.

Lost circulation occurs when a very porous and permeable formation is encountered in the subsurface. The drilling mud flows into the formation without building up a filter cake. During lost circulation, more mud is being pumped down the well than is flowing back up.

In the past, drillers solved lost-circulation problems by buying all the leather they could locally. They shredded the leather into fine pieces and pumped it down the well. The shredded leather got into the pore spaces of the lost-circulation formation and swelled up, closing off the formation and solving the problem. Today, service companies sell inexpensive fine-grained, fibrous materials such as mica flakes, ground pecan hulls, sugar cane hulls, shredded cellophane, and even shredded paper money to solve lost-circulation problems.

An unexpected pressure in the subsurface can cause a blowout. The overbalance is lost and the fluids flow out of the subsurface rocks into the well in what is called a kick. As the water, gas, or oil flows into the well, it mixes with the drilling mud, causing it to become even lighter and exert less pressure on the bottom of the well. The diluted drilling mud is called gas cut, salt-water cut, or oil cut. The blowout preventers are immediately thrown to close the hole. The kick can be dangerous if it is caused by flammable natural gas or poisonous hydrogen sulfide gas. Sometimes the blowout occurs so fast that the drillers do not have time to throw the blowout preventers, and the results are disastrous. Slides and cables are located on the rig to evacuate the crew in such an emergency. If the blowout preventers are thrown in time, heavier drilling mud is pumped into the well through a choke manifold to circulate the kick out.

A kick and possible blowout is detected by several different methods during drilling. As subsurface fluids enter the well during a kick, more fluids will be flowing out of the well than are circulating into the well. The sudden increase of fluid flow out of the well or rise of fluid level in the mud pit is detected by instruments. The drilling mud can also be continuously monitored for sudden changes in weight, temperature, or electrical resistivity that would indicate the mud is being cut by subsurface fluids.

A blowout can also be caused by raising the drill string out of the well. The drill string displaces a volume of drilling mud in the well. As the drill string is raised, the level of drilling mud falls in the well and the pressure is decreased on the bottom of the well. If the level of the drilling mud is not maintained in the well, overbalance could be lost and a blowout could occur.

Sometimes, the problem is simply getting to and from the drill/well site, as the picture below illustrates. Note the technological innovation as the tractor, holds the winch truck, which winches the perforating truck out of the (surface) mud, and the cat which holds the front of the perforating truck on the road.

Drilling Operation

Operating a drilling rig is very expensive. Because of this, the rig is run 24 hours a day. Three 8-hour shifts or two 12-hour shifts of workers operate the rig.

The drilling contractor is the company that supplies the rig. The operator is the company that organizes and finances the drilling and selects the drill site. The operator has a company representative at the drill site to protect their interests. Service and supply companies are the various companies that supply specialized tools and services needed during the drilling operations.

The "tool pusher" is the drilling company's top representative at the drill site. The tool pusher supervises the drilling operations and usually lives at the drill site 24 hours a day. Each morning the tool pusher compiles the results of the past 24 hours of drilling into a daily drilling or morning report. The report is phoned back to the drilling superintendent at the contractor's office. The report includes the depths, footage drilled, supplies used, and other drilling and geological data.

A driller is in charge of each shift. Drillers operate the drilling machinery from a drilling console on the derrick floor. The derrick operator is second in command of each tour. The derrick operator climbs to the monkeyboard, a platform near the top of the derrick, to handle the pipe during tripping in and out, and is also in charge of the drilling mud and pumps. On the derrick floor will be two to four roughnecks (rotary or floor helpers), depending on the size of the rig. They handle and maintain the drilling equipment. One person is hired to maintain the engines.

These are just some of the people, and some of the problems they have, in recovering me, Crudey, the heavy oil drop. Once they find me, there is lots of work to be done yet. I’ll tell you more about these problems in Completions and Workovers.