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Cable Drilling

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Cable drilling, also known as percussion drilling, is a method of drilling that involves percussive or repeated penetration of a drill bit to rock or other hard surface in order to create a hole. Cable tool drilling dates back as far as 4,000 years and was traditionally used for boring well holes for brine, and later, oil.

Cable tool drilling is a slow process due to the nature of the tools and components involved. One of the earliest and most common methods of drilling, the first modern wells, including those in the Lloydminster area, were drill by this method.

Cable tool drilling can also be referred to as pounder, percussive, spudder, or walking beam drilling. The hoisting and lowering of a heavy string of drilling tools into a borehole characterizes this type of drilling. The borehole is made deeper by the repeated penetration of a drill bit as it makes contact with the rock and crushes it into small fragments.


[edit] History

[edit] Early Use

Cable tool drilling was one of the first methods used to drill a borehole. It is said to have been in existence for the past 4,000 years, originating in China. Traditionally, cable tools constructed from bamboo were used to drill for brine. It is said that depths up to 3,000 feet (914 m) have been recorded. Cable drills were used for projects such as drilling boreholes in the search for shallow oil and gas wells in the Alps. The cable tool as it is known today was invented in 1825.[1]

The cable drill gets its name from a material known as manila hemp rope, which was used to suspend wooden rods and drill tools when it was first used. Manila was used to hoist the string of the tool up and down a spring pole or walking beam. The bit, made of a blunt chiseled end, repeatedly chipped against the rock in a consistent manner to produce cuttings and expose a hole.

Eventually, multiple strand steel rope and wire rope replaced the manila and wooden rods, and the process of drilling for brine expanded in regions throughout the world, notably in the U.S. from the 1800s onward.

Brine was drilled with cable tool drills that would bore small circular holes down as far as 1,000 feet (305 m) using the spring-pole method, which involved digging water wells more than 2,000 feet (610 m) deep.

The drilling of the first spring pole well in the U.S. began in 1806 and was completed three years later by two brothers, David and Joseph Ruffner, off the bank of the Kanawha River in Charleston, West Virginia. The Ruffners drilled about 58 feet (18 m) deep, 40 feet (12.2 m) of which consisted of bedrock. The first salt well in America was successful and the brothers became pioneers in drilling. They used a method that involved tubing the well with a wooden pipe in an attempt to prevent weak salt water from mixing with the brine. Their method led to the eventual boom in the salt industry and the use of spring-pole drilling that would eventually be used for retrieving oil.

Drilling for brine grew to become an industry in and of itself throughout many parts of the U.S, such as Salina, New York; Tarentum, Pennsylvania; Kanawha, West Virginia; and Duck Creek, Ohio. By the time oil drilling had evolved into a booming industry, the methodology of drilling had already been predetermined by previous methods, particularly cable tool drilling. [2]

[edit] Oil Drilling

The first commercial oil well in North America took place in Petrolia, Ontario in 1858. Not surprisingly, the oil was drilled by cable tool rig. One of the early cable tool rigs involved an 82-foot (25-m) high wooden derrick mounted on several huge timber logs. The legs of the derrick measured two by 12 inches (5.1 by 30.1 cm) and were positioned to form a right angle. Horizontal girts and diagonal struts were bolted to the legs of the derrick and three cable reels were wound using steel cable up and down the crown block shives. Of all the cables used, one was for drilling the line, one was for the bailer, and the last was for hoisting and lowering the casing. Power was also generated by a steam engine positioned in close proximity to the derrick.

Mounted on a band wheel, the derrick was located relatively close to a bailer, which was used to bail out the cuttings and water debris. A Sampson post arranged in the upright position was also used. Mounted on a platform with the derrick, the post lay horizontally and was attached by a hinge to a walking beam. The walking beam was used to hold a clamping device that dipped the drilling to the tools. The drill bit, comprised simply of a steel weight with a point, was hoisted above the well by a cable.

The band wheel (on the end of the walking beam) was cranked to make the wheel turn—an action which raised and lowered a pitman, rocking the beam up and down and resulting in a "teeter-totter" raising and lowering of the drill tool. Constant repetition of this movement resulted in the penetration of the steel drill bit to the formation, and a hole would be bored. [3]

[edit] Process

A cable tool drill uses the following components to operate a drilling rig:

  • A drilling cable for lifting and turning tools, as well as controlling the motion of the tools
  • A swivel socket to connect the cable to the tools and enable  cable to unwind
  • A drill stem that provides weight and guides the bit in the direction of desired drilling
  • A drill bit that is responsible for penetrating and crushing the rock

The cable tool drill rig comprises all the components to a varying degree. In addition, the driller may also include a drilling jar, a device that prevents the tools from jamming. The jars, however, do not make up the drilling process themselves; rather, they simply make the process somewhat easier.

Before the operation of the cable tool is to commence, the drilling machine must be synchronized with the gravitational fall of the tools in order for the rock to be sufficiently drilled. By synchronizing the speed of the engine with the fall of the tools and the stretch of the cable, the rock is penetrated at a speed that is both safe and effective.

A driller might also use a shock absorber in order to provide the system with resilience. The shock absorber rebounds the tools slightly after it strikes the rock.

The process begins by driving the casing to the top of the drill stem with a hammering action provided by the drive clamps. The clamp’s surface acts as a hammer face and allows the case to use it as a weight. After the casing is lowered, the bit is inserted and water is ejected to create slurry so the cuttings produced can be removed. At this point, a bailer may be used to remove the cuttings.

From day to day, the driller continues the process by determining the depth to which the hole has already been drilled. This is accomplished by lowering the drill bit slowly to the bottom of the hole. Once the bottom is reached, the driller makes note of the position on the cable line and begins hoisting and lowering the line, allowing the bit to drill further. All the while, the driller is continually letting a little bit of slack into the line to lower the drill order to continue the process.[4]

When the bottom of the hole is full of debris, water, and rock bits, a bailer is lowered into the well and cleans the area of the rock. The bailer is then removed and the bit is lowered down further. The process of lowering the bailer for the removal of rock trash is typically carried out about every three feet (0.9 m) or so. Bailers operate via a cable line separate from the drilling line.

There are different types of bailers and the selection of the most suitable one depends primarily on the project. For example, the dart valve bailer is best suited for the collection of well-mixed cuttings.

Another essential component of the rig is the driving case. This is where the force of the drive clamp is provided. At a certain point, the driller must lower a casing into the well. A casing is a calf wheel mounted inside the derrick that is used to operate a traveling block.[5]

Water is commonly used in this process to mix or loosen particles of rock at the bottom of the borehole. Water is usually added to the mix when enough slurry has accumulated to warrant its use. Otherwise, the driller might find that it is reducing the effectiveness of the cable tool drill.

[edit] Advantages and Disadvantages

There are several advantages and disadvantages with cable tool drilling. The advantages include cheap maintenance and good fuel efficiency. Due to the nature of cable tool rigs, the machine can often be performed by a single person.

The disadvantages revolve around the productivity and efficiency of this method. Because of the nature of the machine, it does not penetrate the rock at the rate that other methods might. The formation type also determines efficiency, and cable tool drilling is more effective for some formations than others.[6]

[edit] References

  1. Drilling History. NTL World. 2008-10-12.
  2. Cable Drilling. Petroleum History Org. 2008-10-12.
  3. Cable. Lloydminster Heavy Oil. 2008-10-12.
  4. Drilling Methods. Well Drilling school. 2008-10-20.
  5. Cable. Lloydminster Heavy Oil. 2008-10-12.
  6. Drilling Methods. Well Drilling school. 2008-10-20.