Requirements for solids control in coalbed methane drilling

At present, the drilling methods for ground coalbed methane extraction mainly include conventional vertical wells, cluster wells, and multi-branch horizontal wells in terms of well types. In terms of drilling circulating media, there are mainly two methods: water-based drilling fluid and air drilling.

Characteristics of coal seams
The coal seams are usually referred to as methane gas in coal seams, which mainly exist in the coal seams in an adsorbed state. Its generation mechanism is the process of pressure reduction, analysis, diffusion, and penetration. Coal seams have a dual pore structure, and their mechanical and physical properties are different from those of conventional sandstones. They are shallowly buried, have low pressure, are loose and easily compressible, and have developed endogenous fissures.

Key points of coalbed methane drilling technology
The characteristics of coalbed methane determine the key points of coalbed methane well drilling technology are as follows:

1. The later completion and drainage work requires that the maximum well inclination of coalbed methane wells is not more than 3°, the horizontal displacement of the bottom of the well is less than 20m, and a reasonable drilling tool combination is selected, and the drilling parameters are optimized to ensure the quality of the well body.
2. Use clean water and water mixed drilling fluid, focusing on preventing well collapse and the complex situations caused by well collapse.
3. Establish a reasonable well body structure, speed up drilling speed, and reduce coal seam immersion time.

Requirements for solid control in coalbed methane drilling
Due to the characteristics of coalbed methane drilling, the requirements for the stability of the performance of the drilling fluid and the specific gravity of the drilling fluid are very strict. Coalbed methane drilling has high requirements for drilling solid control, because the drilling fluid can play the following roles in coalbed methane drilling:

1. Clean the bottom of the well and carry rock cuttings. Keep the bottom of the well clean, avoid repeated cutting of the drill bit, reduce wear and improve efficiency.
2. Cool and lubricate the drill bit and drill string. Reduce the temperature of the drill bit, reduce the wear of the drill tool, and increase the service life of the drill tool.
3. Balance the side pressure of the well wall rock, form a filter cake on the well wall, seal and stabilize the well wall. Prevent pollution of the oil and gas layer and well wall collapse.
4. Balance (control) formation pressure. Prevent blowouts, well leakage, and prevent formation fluid from polluting the drilling fluid.
5. Hydraulically break the rock. The high-speed jet formed by the drilling fluid through the nozzle can directly break or assist in breaking the rock.