D5201 - Drilling for gas, oil or minerals

Operational Details
Drilling rigs are generally owned by contractors who sell their services to exploration and production companies. There are many different types of rigs, but as a rule of thumb, the bigger the rig, the deeper it can drill. Rig movers include the use of up to 50 semi-trailer loads of components and equipment that are used in the erection of the drilling platform. The mast, from which the pipe is hung, is rotated on a turning kelly, and dropped into the hole, and by the use of a bit, drills a hole into the earth’s surface to a petroleum or potash producing formation.

Before drilling takes place the rig must be stabilized by using either heavy timbers or concrete. This is due to the tremendous torque resulting from the twisting of the drill stem, which turns the drilling bit. The drilling process itself includes the use of a revolving steel bit that cuts a hole through rock at the bottom of a string of pipe. The bit may be studded with tungsten carbide, or industrial diamonds to penetrate harder rock formations.

Drilling mud is used to lubricate the bit, to remove cuttings and to stabilize the pressure in the hole. The mud, a suspension of chemicals and minerals in water or oil is pumped down the drill pipe. It circulates back to the surface through the space outside the pipe known as the annular space. The mud recirculates after cuttings are removed by a screen called a shale shaker. As the bits penetrates deeper, the crew threads additional pipe onto the top of the drill string. (In some situations, the bit can be turned by a mud motor, which is placed into the hole above the bit at the bottom of the string. It receives its power from the flow of mud.)

Typically each pipe is 9.5 meters long, but may be longer or thicker, depending on the well depth and soil conditions. A rotary table on the rig floor turns the drill string to rotate the bit. When the hole is first begun, a surface hole is frilled to reach a depth of anywhere from 60 to 1200 meters, depending on the well’s depth potential and soil conditions. The crew then pulls the drill string and inserts a steel pipe, called surface casing, which is cemented into place to keep the walls from caving in. It controls the return flow of mud during the drilling and prevents contamination of water deposits.

Blow Our Preventer (BOP) devices are installed on top of the well casing, below the rig flow. BOPs are large valves that help to control the flow of fluid form the well. One type of BOP can seal off the annulus, if the drill pipe is still in the hole. Another can shear off the drill pipe and thus seal off the entire well. A third can seal off the well if pipe is not in the well. If the well is likely to encounter high pressure, all of these BOPs may be used in a BOP stack. After spudding and setting surface casing, the crew resumes drilling. When a bit needs replacing because of wear and tear, or changing rock strata, the crew must pull the entire string of pipe in the hole, unscrew and stack sections beside the derrick. Once the bit is replaced, the entire string is sent back down the hole again. If a string breaks in the hole a specialist is called in to fish out the pieces or obstructions.

When well bits enter a critical zone where sour gas is likely to be encountered additional precautions are taken and breathing apparatuses are worn by those working on the rig. Throughout drilling, a log is kept of the progress. The record includes data about the type, thickness of rock layers, based on the rig geologist’s examination of cuttings from the mud. The rate of penetration is another indicator. Logging instruments may also be attached on a string above the bit to send information continually during drilling. If more information is needed a cylindrical bit may cut a core sample which is analyzed by a geologist or geochemist.

Drill stem tests may be undertaken to determine the potential oil, gas or potash production. This tool has valves and rubber sleeve, called packers, that can be controlled from the surface. First the packers are expanded to isolate the section of the hole to be tested. Next, the valves on the tool are opened, allowing fluids or gas to escape from the formation into the empty drill pipe. This gives a good indication as to the fluids in the formation.

If tests indicate the well is a dry hole, not capable of producing commercial quantities of gas, oil or potash, the drilling crews will plug the well bore with cement and clean up the site. If a well is confirmed for production, the well is capped while the rig is dismantled, which may take the rig crew several days to accomplish, and then a wellhead assembly is attached and finally, an oilfield contractor installs a pumpjack or artificial lift assemble to pump the oil to the surface to be stored or transported to a refinery through a pipeline.

There are many similarities in drilling for gas, oil and potash. However, when potash production is confirmed the recovery methods are different, depending on the amount of the product available and where it is located. For potash mining, there is a need for a drilling rig that has the ability to sink a shaft deep into the earth’s curst. Typically, test or pilot holes are drilled to confirm potential production. This process could lead to deciding on what mining methods would be used to recover the ore, Underground mining or solution recovery are used.

Approximately 60 workers are involved in drilling of one well, however, usually there are only 5 to 7 on site at a time. Several shifts may be used, and typically 3 crews of 5 to 7 workers comprise a working crew that can drill around the clock 7 days a week. Each rig crew consists of tool push, floormen, derrickmen and roughnecks. In addition to handling drill bits and pit, workers operate the drilling fluid circulation system, maintain the equipment, and any other tasks associated with the 24 hour operation of equipment.

SIC Codes
000000374 - Drilling for gas, oil or minerals
000000394 - Diamond drilling