Gilsonite in Drilling Fluids Explained

Drilling fluid, or “mud”, does many jobs: it carries cuttings to the surface, cools the bit, balances formation pressure and supports the wellbore. Gilsonite is one of the most effective natural additives for helping mud do these jobs, especially in shale and high-temperature wells.

How gilsonite works in mud

Gilsonite particles are deformable at downhole temperature. As mud filtrate tries to flow into the formation, gilsonite particles move with it, soften slightly and plug pores and micro-fractures. This builds a thin, low-permeability filter cake and reduces the amount of fluid lost into the rock.

Main benefits

• Fluid loss control – lower HPHT filtrate volumes.
• Shale stabilization – sealing micro-fractures reduces pressure transmission into shale.
• Wellbore stability – less sloughing and caving.
• Lubricity – reduced torque and drag.
• Reduced differential sticking – thin, slick filter cake.

Water-based and oil-based muds

Untreated gilsonite works well in oil-based and synthetic-based muds. In water-based muds, it is often used together with surfactants or in the form of sulphonated asphalt, which disperses in water.

Typical dosage

2–8 lb/bbl depending on formation and fluid loss target. Add slowly through the hopper during circulation.

Choosing a grade

Where gilsonite fits in a mud programme

Signs you may need gilsonite

• Rising HPHT fluid loss at higher temperatures
• Cavings and tight hole in shale
• High torque and drag in deviated sections

Select a softening point close to the expected bottom-hole temperature. Our drilling fluid grade gilsonite is milled to around 200 mesh for easy mixing. For more detail, read selecting gilsonite softening point for wells.