What is casing drilling?

What is casing drilling?

Casing drilling refers to using casing pipe instead of drill pipe to apply torque and drilling pressure to the drill bit to achieve drill bit rotation and drilling. The entire drilling process no longer uses drill pipes, drill collars, etc. The drill bit is fished out using a wire rope to achieve drill bit lifting and lowering in the casing, that is, the drill bit can be replaced without lifting the drill. It reduces accidents such as drilling and blowouts, and drill stuck, improves drilling safety, and reduces drilling costs.

Development history:
As early as the 1950s, some people envisioned using casing instead of drill pipe to complete drilling operations, but due to the limitations of technology and equipment conditions at the time, it was difficult to realize this idea. In the 1990s, due to the great development of new technologies, new materials, and electronic technologies, the continuous development of oil extraction technology was promoted, and a large number of new drilling processes, new tools, and new equipment emerged. Casing drilling technology was once again proposed. In 1996, the Canadian Texco Company drilled the first casing drilling test well. The well was a test site well, using 9 5/8″ casing was drilled 150 meters. By the end of 2000, Texco had completed more than 20 development wells using casing drilling technology, achieving good economic benefits.

Performance characteristics:

Casing drilling has obvious advantages over conventional drill pipe drilling. It is a technical revolution in drilling engineering and can bring huge economic benefits to oilfield operators. Casing drilling has the following characteristics:

1. Casing drilling uses standard oil well casing, and allows drilling and casing operations to be carried out simultaneously;
2. The bottom hole drill assembly is installed at the lower end of the casing column and can be quickly removed through the inside of the casing with a wire rope. During the removal process, the mud can be kept in continuous circulation;
3. The entire drilling process In the process of drilling, the casing is kept straight to the bottom of the well to improve the well control;
4. The casing is drilled into the formation in one direction only and is not pulled out again. Unless it is confirmed to be a dry well after drilling, the last section of the casing string may need to be pulled out;
5. Casing drilling can use many existing drilling technologies, such as directional drilling, cementing, logging, coring and well testing;
6. The main difference between the application of these technologies and the original ones is that they no longer rely on drill pipes, but rely on wire ropes to replace drill bits;
7. Casing drilling uses standard oilfield casing. The difference is that the casing coupling or thread needs to be improved to provide the torque required for drilling; Tesco used the thread (Hydrill 511 Premium Thread) when drilling the first test well, and the coupling used the modified reinforced coupling (Modified Buttress Coupling).

Advantages of casing drilling:

1. Reduce the time of drilling. Using wire rope to replace the drill bit is about 5-10 times faster than using the traditional drill pipe to drill;
2. Save the cost of purchasing, transportation, inspection, maintenance and replacement of drill pipes and drill collars;
3. Because there is always casing in the wellbore, there is no pumping effect on the wellbore when the drill pipe is pulled up, so the well control condition is improved;
4. The pumping effect and pressure pulsation caused by pulling up the drill pipe are eliminated;
5. When the drill bit is pulled up with wire rope, the continuous circulation of mud can be maintained, which can prevent the accumulation of drill cuttings and reduce the occurrence of well kicks;

6. Improve the annular return speed and the cleaning of the wellbore. When pumping mud into the casing, its inner diameter is larger than the drill pipe, which reduces the hydraulic loss, thereby reducing the equipped power of the drilling rig mud pump. When the mud returns from the annular space between the casing and the well wall, the annular area is reduced, which increases the return speed and improves the removal of drill cuttings;

7. The size of the drilling rig can be reduced, the structure of the drilling rig can be simplified, and the cost of the drilling rig can be reduced. The reasons are as follows:
(1) The improvement of hydraulic parameters reduces the demand for the power of the drilling rig mud pump.
(2) The second-layer platform and the drill pipe box for discharging drill pipes can be eliminated.
(3) Drill pipes are no longer used.

(4) Casing drilling is based on a single casing, and it is no longer necessary to use a stand drilling method similar to double or three drill pipes. Therefore, the height of the derrick can be reduced and the weight of the base can be reduced. For deep well drilling rigs, the structure and weight of the derrick and base of a drilling rig based on a single drilling rig are much simpler than those based on stand drilling.

8. The drilling rig is lighter and easier to move and operate. The amount of labor and costs will be reduced.
9. According to Tesco's calculations, drilling a 10,000-foot well can save about 30% of drilling time.

Scope of application of casing drilling:

Casing drilling is suitable for oil fields with relatively stable burial depth of oil layers: Since casing drilling is completed directly after cementing and then perforating for oil production, there is no logging technology to measure the reservoir depth and evaluate the reservoir development. Therefore, the oil layer development and burial depth must be stable, so that the depth design of casing drilling is guaranteed.

Applicable to areas with stable development and small formation inclination: Since there is inevitably well inclination during casing drilling, the result of well inclination is that there is a difference between the completed well depth and the vertical depth. The greater the well inclination, the greater the difference. The size of the formation inclination, the development of cracks, faults, etc., play an important role in the influence of well inclination. Therefore, the formation inclination in the design casing drilling area should be small, and the cracks and faults should be undeveloped or underdeveloped, which is conducive to the control of well inclination in casing drilling.

Read more: Types of drilling casing pipe or Specifications and dimensions of drilling casing