What is a Casing Coupling (Collar)?
Casing Coupling (collar) is a kind of oilfield drilling tool, mainly used for the connection of tubing. The oil pipe coupling mainly solves the problem that the existing coupling is prone to fatigue fracture due to stress concentration.
The end of the oil pipe is connected with the inner wall of the coupling by a tapered thread, and the end of the coupling body is connected with the oil pipe by a flat thread with the same thread and pitch. It has the characteristics of alleviating the stress concentration at the root of the outer thread of the oil pipe connected by a single taper thread, and is not easy to cause fatigue fracture, and the connection effect is good. Effectively prevent oil well pipe string breakage accidents.
The basic point of the casing drilling process, tools and equipment is to cancel the traditional drill pipe and replace the drill pipe with casing pipe. Its mud circulation mode, coupling feeding mode, coring mode, BOP group and various coupling parameters are no different from conventional couplings. During the casing drilling process, the top driving device drives the casing to rotate, and the casing transmits torque to drive the drill bit installed on the tool set at the end of the casing to rotate and drill.
Since there is no lifting column problem in casing coupling products, the height of the drilling rig can be reduced to about 20 meters, and the structure can also be simplified. Since the inner diameter of the drill bit is smaller than that of the casing, it is impossible to drill a hole with a diameter larger than the outer diameter of the casing, so a retractable reamer is additionally mounted on the tool above the drill bit. When the reamer is open in the collar condition, the well can be enlarged. Mud enters through the casing and returns from the annulus between the casing and the wellbore. The bit is secured to the front end of a specially designed tool set that is locked at the end of the casing string and is connected to a winch for raising and lowering the bit via wireline.
When it is time to change the bit, release the locking device and use the winch to lift the tool set through the casing. After replacing the new drill bit, use the winch to send the tool set into the casing and lock it at the end of the casing; the drilling process of the drill bit is also the process of running the casing. The bushings are driven down one by one without any further lifting. Cementing can start after coupling.
Compared with conventional drill pipe couplings, casing coupling products have obvious advantages. This is a technological revolution in coupling engineering that can bring huge economic benefits to oilfield operators. Casing coupling products have the following characteristics:
1. Casing drilling adopts standard oil well casing, and drilling and casing running are carried out at the same time;
2. The bottom hole assembly is installed at the lower end of the casing string, and can be quickly taken out through the casing with a wire rope. The mud can be continuously circulated during the extraction process;
3. During the entire coupling process, keep the casing straight to the bottom of the well to improve well control conditions;
4. The casing only drills into the formation in one direction and will not be pulled out. Unless it is confirmed that the well is dry after coupling, the latter section of casing string can be pulled out;
5. Casing coupling products can follow many existing coupling technologies, such as directional coupling, cementing, logging, coring and well testing;
6. The main difference between the application of these technologies and the original technology is that they no longer rely on drill pipes, but use wire ropes instead of drill bits;
7. Casing coupling products adopt standard oilfield casing. The difference is that the casing joint or thread needs to be modified to provide the torque required by the coupling.
Casing
coupling products are suitable for oil fields with relatively stable buried depths: due to casing
coupling products and direct perforation production after well completion, there is no logging technology to measure reservoir depth and evaluate reservoir development, so reservoir development And buried depth should be stable, so as to ensure the depth design of casing drilling.
Applicable to areas with stable development and small formation dip: due to the inevitable well deviation in the production process of casing collars, the influence of well deviation will lead to the difference between the collar depth and the vertical depth. The greater the well deviation, the greater the difference. Dip, fracture and fault development play an important role in the influence of well deviation. Therefore, the designed casing collar product area should have a small formation dip, and fractures and faults are not developed or developed, which is beneficial to the well deviation control in the casing collar product.
