PAC drilling mud additive

Adjusting PAC Drilling Fluid Formulations for Different Operating Conditions

PAC drilling fluid needs to be optimized based on formation characteristics (salinity, temperature, clay content). In freshwater shallow wells, the PAC dosage is 0.2%-0.5%, using a basic formulation without additional salt tolerance agents; a small amount of starch can be added to reduce filtration loss. In brine/seawater wells, the PAC dosage is 0.5%-0.8%, requiring increased PAC usage (salt tolerance: PAC > CMC), and the addition of 2%-5% NaCl to simulate the formation conditions. Water layer is crucial to prevent swelling of salt-sensitive clay.

In high-temperature deep wells (>120°C), the PAC dosage should be 0.6%-1.0%. High-temperature resistant PAC (such as PAC-LV, low viscosity, high temperature resistance) should be selected and compounded with sulfonated filtration reducers (such as SMP) to improve temperature resistance. In easily collapsing shale wells, the PAC dosage should be 0.4%-0.7%, requiring an increase in KCI dosage to 3%-5%, compounded with 0.2%-0.5% polyquaternium salt to enhance clay stability.
 

Key Precautions During Preparation

There are several precautions to take when dissolving polyanionic cellulose (PAC) powder. It is strictly forbidden to pour PAC directly into still water (as it easily clumps). It must be added slowly while stirring. Avoid mixing with strong acids (pH < 6), as acidic environments will hinder the ionization of PAC carboxyl groups, resulting in loss of thickening and filtration reduction effects. Regarding equipment, the stirring equipment must have sufficient shear force (speed ≥ 1000 r/min) to ensure full extension of the PAC molecular chains. The mixing tank must be clean, avoiding residual oil and salts (such as Ca2+, which will react with PAC carboxyl groups and reduce performance).

For safe operation, Petroleum-grade PAC powder is easily airborne. Operators must wear dust masks. Avoid direct skin contact with chemicals such as NaOH and KC. Wear gloves during operation. Regarding performance stability, the prepared drilling fluid should be used within 24 hours. For long-term storage, it needs to be stirred regularly (to prevent sedimentation of the weighting agent). When using in the field, the performance must be retested and treatment agent added every 100-200 meters of drilling.
 

The core working principle of petroleum drilling grade polyanionic cellulose (PAC) in drilling fluids:

PAC's filtration reduction effect is manifested in the formation of a "thin and dense filter cake" on the wellbore by its molecular chains, preventing water loss from the drilling fluid to the formation and protecting the reservoir (especially oil and gas reservoirs) from contamination. Its thickening and rheological regulation effects are due to the network structure of PAC increasing drilling fluid viscosity and shear stress, ensuring cuttings suspension (avoiding sand settling and stuck pipe), while also maintaining the drilling fluid's cuttings carrying capacity in the annulus.

Its salt and contamination resistance stems from the carboxyl groups in the PAC molecule's strong tolerance to metal ions such as Nat and Ca2+, making it more suitable for saline environments than CMC, reducing the destructive effects of salt contamination on drilling fluid performance.