Carboxymethyl cellulose (CMC) is a common water-soluble polymer compound widely used in various industrial fields. Especially in drilling and petroleum engineering, CMC plays an important role as a mud additive. Its main functions are to improve the rheological properties of mud, increase the stability of mud, improve lubricity, reduce drill bit wear, etc.

1. Increase the viscosity of mud
The viscosity of mud is crucial for drilling operations. Too low viscosity cannot effectively remove the cuttings generated during drilling, and too high viscosity will affect the fluidity and efficiency of mud. CMC can effectively increase the viscosity of mud by interacting with water molecules through the carboxylmethyl group in its molecular structure. CMC molecules form a network structure in water, which can absorb water and swell and increase the viscosity of the liquid, thereby enhancing the rheological properties of mud. This property is of great significance for removing cuttings and stabilizing the borehole wall during drilling.

2. Thickening and adjusting rheological properties
The rheological properties of mud (including viscosity, fluidity, etc.) are very important for the smooth progress of drilling operations. CMC can significantly increase the plastic viscosity and yield value of mud at a certain concentration, adjust the rheological properties of mud, and ensure that the mud has good fluidity and lubricity during drilling. The increased viscosity helps to reduce the flow resistance of the mud, thereby improving the efficiency of drilling and reducing the wear of the drill bit caused by excessive flow resistance during drilling.

3. Improving the stability of mud
During the drilling process, the stability of the mud is crucial, especially under different geological environments and temperature changes. Due to its good water solubility and stability, CMC can enhance the heat resistance and salt resistance of the mud, so that it can still maintain high performance under different drilling conditions. CMC can form a stable colloidal solution in the mud, prevent the mud from sedimentation, flocculation and other phenomena, and ensure the long-term stability of the mud.

4. Increase the lubricity of mud
During drilling operations, the friction between the drill bit and the formation is inevitable. Excessive friction will increase energy consumption, reduce drilling efficiency, and may even cause equipment damage. CMC can significantly increase the lubricity of mud, reduce the friction coefficient between the drill bit and the borehole wall, reduce the wear of the drill bit, and improve the operational stability during drilling. The improvement of lubricity helps to reduce the risk of well wall collapse during drilling and extend the service life of equipment.

5. Block cracks and control permeability
Under some special drilling conditions, such as encountering high permeability or fractured formations, CMC can effectively block pores and cracks in the formation. CMC molecules have good gelling properties and can form colloids in drilling fluids to reduce the permeability of water in mud. This blocking effect helps prevent water in the mud from entering the groundwater layer or oil and gas layer, reducing pollution and protecting underground resources.

6. Salt resistance and high temperature resistance
In some high-salinity and high-temperature drilling environments, CMC has shown excellent adaptability. The carboxyl groups contained in its molecular structure can effectively combine with water molecules to enhance its solubility and stability in salt water environments. This allows CMC to still play a role in thickening and stabilizing mud in salt water slurries. In addition, CMC also has a certain degree of high temperature resistance and is not easy to decompose in high temperature environments, which helps to maintain the performance of mud in high temperature formations.

7. Environmental protection
With the continuous improvement of environmental protection requirements, many industries are working hard to reduce environmental pollution. In drilling operations, traditional mud additives often contain toxic ingredients, which may have a negative impact on the ecological environment. As a natural product, CMC is derived from plant fibers and can be quickly degraded in water, which has less harm to the environment. Therefore, it is a green and environmentally friendly mud additive. Its non-toxic and degradable properties make it the preferred material in many oil and gas development projects.

8. Synergy with other additives
In practical applications, CMC is often mixed with other mud additives (such as polyacrylamide, bentonite, etc.). CMC can synergize with these additives to further improve the rheology, stability and lubricity of the mud. For example, when CMC is mixed with bentonite, it can enhance the colloidal stability of the mud, avoid the sedimentation of the mud during use, and improve the adaptability of the mud in high temperature and high pressure environments.

Carboxymethyl cellulose (CMC) plays many roles in mud. It can not only increase the viscosity and rheology of the mud, improve the stability and lubricity of the mud, but also improve the environmental protection of the mud, reduce the wear of equipment during drilling, and effectively seal the formation cracks under special geological conditions. As an important drilling mud additive, CMC has excellent performance and broad application prospects, especially in the field of environmental protection and efficient drilling, showing its irreplaceable value.