Drilling mud is a vital component in the drilling operations of oil, gas, and water wells. It plays multiple roles including pressure control, lubrication, cooling of the drill bit, and preventing borehole collapse. Typically, drilling mud consists of a water- or oil-based fluid, mineral additives (like bentonite), and chemical or polymeric additives. In recent years, researchers have increasingly explored the use of various polymers to enhance mud properties
Polyethylene is a non-polar, water-insoluble thermoplastic polymer with a simple hydrocarbon structure, offering high chemical resistance and thermal stability. Its molecular weight and density vary across types—LDPE, HDPE, and LLDPE—which directly influence its mechanical behavior in drilling environments:
LDPE: Flexible, soft particles, capable of forming dispersed networks in mud.
HDPE: Rigid, high mechanical strength, forms protective layers on borehole walls.
LLDPE: Hybrid properties, suitable for rheology control and permeability reduction.
Due to its insolubility in water, polyethylene is used in mud as suspended particles or emulsions. Its key mechanisms include:
Rheology and Viscosity Enhancement Polyethylene particles act as fillers, increasing viscosity and flow index, aiding in cuttings transport and reducing borehole slippage.
Permeability Reduction and Filter Cake Formation Polyethylene forms semi-permeable physical layers on borehole walls, preventing water intrusion into clay formations, reducing swelling, and enhancing wall stability.
Water Retention and Clay Swelling Control In water-based muds, polyethylene creates dispersed networks that trap excess water, similar to soluble polymers like CMC or PAC, but with superior chemical resistance and thermal durability.
Mechanical Property Improvement Recent studies show that combining polyethylene with nanoparticles (e.g., nanocarbon or mineral nanofillers) enhances shear strength and filter cake integrity, reducing borehole collapse risk.
Despite its advantages, polyethylene use in drilling mud faces several challenges:
Water Insolubility: Requires emulsification or particle size reduction for uniform dispersion.
Excessive Viscosity: May hinder mud flow and pumpability.
Higher Cost: Compared to synthetic polymers, economic use demands optimization of dosage and particle size.
Additive Compatibility: Some chemicals may physically interact with polyethylene, reducing its effectiveness.
Polyethylene, as a non-soluble physical additive in drilling mud, can enhance viscosity, filter cake control, permeability reduction, and borehole stability. However, optimal use requires careful design of particle size, concentration, polyethylene type, and compatibility with other additives. Recent research suggests that polyethylene combined with nanoparticles or used in emulsified form offers a blend of mechanical and environmental benefits, potentially replacing part of the synthetic polymers in water-based drilling muds.