During the drilling process of coalbed methane wells, complex and changeable stratigraphic conditions are often encountered, such as pebble layers, weathered and fractured zones, fissures and caves, and soft strata. These complex strata bring many challenges to drilling operations, such as hole wall collapse, blockage, plugging, and difficult-to-form holes, which seriously restrict drilling efficiency and safety. To solve these problems, down-the-hole hammer and casing drilling technologies came into being and showed significant advantages. With its high drilling speed, high efficiency, high hole formation rate, and good safety, this technology shows strong potential in drilling complex formations. Applying down-the-hole hammer and casing drilling technology can not only effectively reduce the complex procedures in drilling construction and quickly pass through complex formations but also significantly improve the drilling efficiency and reduce production costs, becoming an essential method in the coal bed methane well drilling.
Overview of down-the-hole hammer and casing drilling technology
Down-the-hole hammer and casing drilling technology is an advanced technology that can adapt to drilling in various soft and complex formations. It uses a down-the-hole hammer to drive the center drill bit to perform high-frequency impact and cutting and follows the casing to protect the hole wall. It enables rapid and safe passage through complex formations. This technology has the advantages of fast drilling speed, high efficiency, high hole formation rate, and high construction safety, making it the preferred solution for drilling in complex formations.
System composition
- Down-the-hole hammer: as a power source, it is driven by flushing fluid to form rotary drilling with impact load.
- Center drill bit: connected to the down-the-hole hammer, it directly acts on the formation for cutting.
- Casing combined external bit: connected to the center bit through a slot, it drives the casing to follow up and realize the protection of the hole wall.
- Casing tube: this casing follows up with the external drill bit during the drilling process, protecting the wall and isolating the lost formation.
Working principle
During drilling, the down-the-hole hammer is connected to the center drill bit and driven by flushing fluid to form a rotary drilling with impact load. The casing combined external bit is connected to the center drill bit through a spline. Driven by the center drill bit, the footage is achieved through impact and cutting, and the outer drill bit rotates through the slot to prevent the following casing from rotating. The characteristics of hard rock with high brittleness, low shear strength, and low impact resistance improve the drilling efficiency of the down-the-hole hammer. The casing follows the external drill bit to protect the hole wall. After completing the casing drilling, the drill pipe, DTH hammer, and center drill bit can be removed by turning the drill pipe at a slight angle. The casing stays in the well, eliminating the need to remove the drill and install the casing after the conventional drilling work is finished.
Technical advantages
Efficient drilling
DTH hammer and casing drilling technology improves efficiency through high-frequency impact and cutting effects. Compared to traditional mud drilling methods, this technology enables faster drilling and achieves higher footage. According to actual application data, the daily footage of down-the-hole hammer and casing drilling can reach 180-200 meters, which is 2-3 times that of conventional drilling, significantly improving drilling efficiency.
High safety
Drilling in complex formations, hole wall collapse, and buried drilling are frequent safety issues. The down-the-hole hammer and casing drilling technology protects the hole wall by promptly following up the casing. It reduces the risk of hole wall collapse and buried drill. At the same time, this technology reduces the drilling and running casing, further improving safety during the construction process.
Strong adaptability
This technology has strong adaptability and can cope with various complex stratigraphic structures, providing a strong guarantee for drilling operations of coalbed methane wells. Whether it’s a soft formation or a formation with severe leakage, down-the-hole hammer, and casing drilling technology can achieve rapid and secure drilling.
Good environmental benefits
Traditional mud drilling methods use large amounts of mud, which not only causes groundwater contamination but also increases water consumption. The down-the-hole hammer and casing drilling technology reduces the use of mud, has no pollution to groundwater, and consumes less water, which is in line with the concept of modern green drilling.
Remarkable economic benefits
The application of down-the-hole hammer and casing drilling technology not only improves drilling efficiency but also reduces production costs. By reducing material usage and construction time, this technology significantly lowers direct and indirect economic costs. According to actual case comparisons, the consumption of plugging materials and drilling time for wells using the down-the-hole hammer and casing drilling technology are much lower than those of conventional drilling, bringing significant economic benefits.
Conclusion
The application of down-the-hole hammer and casing drilling technology in coalbed methane wells has shown significant advantages and broad application prospects. Its high efficiency, speed, and safety not only effectively solves the problems of hole wall collapse, blockage, plugging, and difficulty in hole formation encountered by traditional drilling methods in complex formations but also dramatically improves the drilling efficiency and hole formation rate and reduces the production cost. As the technology continues to mature and be promoted and applied, it is believed that down-the-hole hammer and casing drilling technology will play a more vital role in the field of coalbed methane exploration and development, promoting the industry to develop in a more efficient, environmentally friendly, and safer direction.
