Carboxymethyl cellulose (CMC) is a polymer compound obtained by chemical modification of natural cellulose and is widely used in many industries. In drilling fluid, carboxymethyl cellulose plays a key role as an important thickener and stabilizer. It improves the efficiency and safety of drilling operations by improving the viscosity and rheological properties of drilling fluid and inhibiting solid phase precipitation.

1. Basic properties of carboxymethyl cellulose

Chemical structure: The molecular structure of carboxymethyl cellulose contains carboxymethyl (-CH2COOH) substituents, which makes its molecules negatively charged and have certain water solubility and hydrophilicity. CMC is obtained by etherifying natural cellulose molecules and replacing part of the hydroxyl (OH) with carboxymethyl groups.

Water solubility: Carboxymethyl cellulose has a high solubility in water and forms a viscous colloidal solution. This property makes it an ideal thickener in drilling fluid, which can enhance the suspension ability and rheological properties of drilling fluid.

Adjustability: CMC’s molecular weight, degree of substitution, solubility and other properties can be adjusted according to demand. This allows it to be selected and optimized according to actual needs in different types of drilling fluids.

2. The role of carboxymethyl cellulose in drilling fluids

Thickening effect: Carboxymethyl cellulose is used as a thickener in drilling fluids to effectively increase the viscosity of the liquid. Higher viscosity helps to suspend and transport cuttings, reduce the deposition of solid particles in the drilling fluid, and prevent clogging of the wellbore. In addition, the thickening effect of CMC can improve the carrying capacity of the drilling fluid and ensure that the drilling fluid can still maintain good rheological properties under high temperature and high pressure conditions.

Rheological property optimization: The rheological properties of drilling fluid directly affect the efficiency and safety of drilling operations. CMC can adjust the rheological curve of the drilling fluid so that it has a suitable yield stress and viscosity to cope with different drilling environments. Its addition can improve the flow characteristics of the drilling fluid downhole, so that the drilling fluid can still maintain a stable flow state when encountering high flow rates or complex geological conditions, and avoid excessive pressure fluctuations.

Inhibit solid phase precipitation: Carboxymethyl cellulose can effectively inhibit the formation of solid phase precipitation in drilling fluid and ensure the stability of drilling fluid. During the drilling process, solid phase precipitation (such as cuttings, mud, etc.) will enter the drilling fluid as the drill bit rotates. CMC helps to keep the solid particles suspended and prevent precipitation by increasing the viscosity and dispersibility of the liquid, thereby maintaining the fluidity of the drilling fluid.

Improve fluidity and reduce drag: In deep wells or high temperature and high pressure wells, when the fluidity of the drilling fluid deteriorates, the addition of CMC can effectively improve its flow performance, reduce the friction resistance of the fluid, and improve drilling efficiency. At the same time, CMC can reduce the evaporation loss of the drilling fluid and reduce the friction between the drill bit and the well wall, reducing energy consumption in drilling operations.

Lubrication: CMC can also play a certain lubricating role, reduce the friction between the drill bit and the well wall, and reduce equipment wear. Especially under high temperature and high pressure and complex geological conditions, the lubrication effect is particularly important.

Well wall stability: CMC can enhance the adhesion of the drilling fluid, so that a thin film is formed on the surface of the well wall to prevent the well wall from collapsing. Especially in soft rocks, clay layers or complex geological conditions that are prone to collapse, this role of CMC is particularly important.

3. Application effect of carboxymethyl cellulose in drilling fluid

Improve drilling efficiency: Since carboxymethyl cellulose can adjust the rheology of drilling fluid, it can still maintain good fluidity and stability under high temperature and high pressure, thereby improving the efficiency of drilling operations and reducing operation time and cost.

Enhance drilling safety: The addition of CMC helps to stabilize the well wall, prevent well wall collapse, and reduce the wear of downhole equipment. At the same time, its thickening effect can improve the carrying capacity of drilling fluid and reduce operational difficulties and safety hazards caused by poor fluidity of drilling fluid.

Wide applicability: Carboxymethyl cellulose can be used in various types of drilling fluids, including water-based drilling fluids, oil-based drilling fluids and synthetic drilling fluids. This makes it widely applicable in different drilling environments.

As an excellent thickener, stabilizer and rheology modifier, the application of carboxymethyl cellulose in drilling fluids is of great significance. It can increase the viscosity of drilling fluid, improve rheological properties, inhibit solid precipitation, reduce friction and enhance well wall stability, thus providing a more efficient and safe working environment for drilling operations. With the advancement of science and technology and the continuous development of drilling technology, the application prospects of carboxymethyl cellulose in drilling fluid will be broader.