90% of the earth’s surface is covered by loose and sparse materials. During drilling, the strata formed by these materials usually encounter adverse conditions such as collapse, block dropping, drill sticking, water gushing, and leakage. If not handled properly, it will cause drilling difficulties or accidents in the hole. Using the casing system to bring the casing into the hole wall can effectively prevent the hole wall from collapsing or quicksand filling the borehole during the drilling process. It is suitable for drilling into loose formations and quicksand layers and achieved good construction results, so it has been widely used.
What is a casing system?
The casing system means that the casing tube penetrates with drill bits at the same time. The casing tube provides the enforcement to the hole wall and prevent the hole from collapsing during drilling. It is composed of two parts: the casing and the drill bit.
Working principle of casing system
A considerable part of the geological conditions in mountainous areas is a mixed layer of gravel, clay, and rock, and this kind of unstable rock and soil layer is very easy to collapse the hole wall after lifting the drill and cannot achieve the purpose of putting explosives in the hole. Mountain casing systems are mainly composed of drill pipes, DTH hammers, and outer casing. Among them, the DTH hammer is connected to the inner drill pipe, and the rotation of the inner drill pipe and the DTH hammer is driven by the power unit of the mountain drill, which drives the vibration of the DTH hammer. The upper part of the drill bit at the lower end of the DTH hammer is made into a stepped shape and keyway. When the power unit drives the drill bit to rotate through the inner drill pipe, the outer casing makes vertical movement toward the formation with the inner drill pipe, reducing the resistance vantage of the power unit. When the DTH hammer is rotating and vibrating in the positive direction, it drives the lower end of the outer casing to rotate and follow up together. The outer casing plays the role of fixing the wall of a well, and after dropping the explosive from the center of the casing to the bottom of the well, the outer casing is pulled out by the pipe puller, thus completing the operation process of drilling and drugging once.
Features of casing system
1. It has a wide range of applications and mature construction technology; almost all complex geology that is not easy to form holes can be constructed with casing systems, which can be used for anchoring, pile foundation support, and water well/geothermal well engineering; in addition, it can be used with DTH drills and top hammer drills.
2. Large drilling diameter and deep drilling depth. The maximum drilling diameter is more than 1 meter and the drilling depth can reach hundreds of meters with large construction equipment.
3. Fast drilling speed and good hole quality. Under complex geological conditions, the casting acts as retaining wall support, avoiding jamming and loss of high-pressure gas in rock crevices, improving the slag removal effect and drill bit service life.
4. According to design requirements, the casing can be pulled out and used repeatedly after drilling, or it can be left in the hole without pulling out as an bolt.
Practical application of casing system
Drilling with casing system
Drilling technology is one of the main factors for fast and efficient drilling in casing. It can be said that drilling technology is the most variable factor in the casing, and it is often the most easily overlooked in drilling construction. The drilling method is selected according to the drillability, abrasiveness, and integrity of the rock. Among them, the principle of percussion rotary drilling adopts the conventional drilling method. When using a casing system, the small gauge should be used as much as possible according to the bipolar drilling principle of the rock drilling tools, combined with the special characteristics of casing drilling, taking into account the soft and hard uneven characteristics of the complex strata, and under the premise of ensuring reasonable drilling speed.
Protect the hole wall with the casing system
There are three ways to protect the wall with the casing system: flushing liquid retaining wall, casing retaining wall, and pouring cement slurry retaining wall. After the drilling hole is formed, the flushing fluid immediately seeps into the hole wall stratum. The flushing fluid plays a vital role in the drilling of rock formations. The flushing fluid has low filtration loss and strong wall-building properties, which can effectively protect the stability of the hole wall and prevent the rock drilling tools from scaling and has good performance in carrying rock powder, cleaning the bottom of the hole, and cooling the drill bit.
Coring with casing system
The technical characteristics of mountain drilling in complex rock and soil strata put forward higher requirements on the performance of the flushing fluid. When drilling in rock and soil formations, the drilling speed should be strictly controlled, and low-speed and small-volume drilling should be used to ensure the recovery rate of rock cores. In some cases, dry drilling and coring or reverse circulation coring technology at the bottom of the hole can be used, which makes the casing systems have high drilling efficiency and solve the problem of difficult hole formation in geotechnical strata.
How to choose the appropriate casing system
Choosing the appropriate casing system is of great significance to improving drilling efficiency, reducing costs, and ensuring construction safety. When selecting a casing system, you need to consider the following factors:
- Geological conditions: select an appropriate casing system according to the geological conditions of the drilling area to ensure that the drilling tools can adapt to the formation characteristics and drilling needs.
- Drilling diameter and depth: choosing the appropriate drilling diameter and depth is crucial to ensure that the casing system meets the construction requirements.
- Equipment quality and performance: choose a casing system with reliable quality and stable performance to ensure stability and safety during the construction process.
- Cost-effectiveness: while considering the quality and performance of the equipment, you also need to consider the cost-effectiveness and choose cost-effective casing systems to reduce construction costs.
Conclusion
As an efficient and practical drilling tool, the casing system plays an essential role in many fields. The casing system’s distinctive operational principles and versatile applications render it an indispensable component of underground drilling construction. Selecting the right casing system can enhance drilling efficiency, cut costs, and ensure construction safety. As science and technology progress and engineering demands evolve, casing systems will maintain their crucial role and pursue further advancements through continuous technological innovation.
