CMC For Oil Drilling

Polyanionic Cellulose (PAC) is commonly used in oil drilling fluids as a viscosifier, fluid loss reducer and shale inhibitor. 

It effectively improves the rheological properties of drilling fluids and helps maintain wellbore stability.

Core Functions and Mechanisms of Action

1. Drilling Fluid Viscosifier

PAC dissolves in water to form a high-viscosity colloid. Through molecular chain entanglement, it increases the apparent viscosity 

and dynamic shear strength of the drilling fluid, enhancing its capacity to carry drill cuttings and preventing cuttings from settling.

It is particularly suitable for high-angle wells, horizontal wells, and other scenarios with high cuttings-carrying requirements. 

Typical addition rates range from 0.1% to 0.5%, which can increase drilling fluid viscosity by 20%–50%.

2. Fluid Loss Reducer

PAC adsorbs onto the surface of clay particles, forming a dense filter cake that reduces the filtration of water from the drilling fluid 

into the formation—protecting the oil and gas reservoir from contamination.

It significantly reduces fluid loss (API filtration rate can be reduced from 15 mL to below 5 mL). 

This is especially effective in sandstone and shale formations that are prone to lost circulation.

3. Shale Inhibitor

The carboxyl groups on the PAC molecular chain adsorb onto the cations on shale surfaces, forming a protective film that inhibits shale hydration, 

swelling, and dispersion—preventing wellbore collapse. In water-sensitive shale formations, PAC is often used in combination with potassium chloride (KCl), 

polyamines, and other additives to reduce shale swelling rates by 40%–60%.