Study and Application of Additives for Synthetic Fluids with GTL as the Base Fluid

To improve the high temperature rheology and filtration property of the synthetic base drilling fluid using gas-to-liquid (GTL) oil as the base fluid, an organophilic clay having superior gel properties and an environmentally friendly filter loss reducer made from natural humic acid, have been developed. A GTL base drilling fluid was formulated with the organophilic clay, the modified humic acid, a primary emulsifier and secondary emulsifier previously developed. The organophilic clay, DR-GEL, was made by intercalating dihexadecyl dimethyl ammonium chloride into the crystal layers of a purified sodium montmorillonite, and had good gel performance in GTL (percentage of colloid particles to 98%), high viscosity and gel strength (3 Pa), and good high temperature stability (it functioned at 220℃)in laboratory experiments. The filter loss reducer, DR-FCLA, was made by modification of purified humic acid with dihexadecyl dimethyl ammonium chloride and diethylene triamine. DR-FCLA greatly reduced the HTHP filter loss, helped make the drilling fluid emulsified better and improved the rheology of drilling fluid. It functioned at high temperatures up to 230℃. The synthetic drilling fluid made with these additives had densities ranging in 1.6-2.3 g/cm³, good rheology (AV=27-61 mPa·s, YP=6-9 Pa) at temperatures ranging in 120-200℃, high electrical stability (ES>800 V), and HTHP filter loss <2.5 mL. This synthetic drilling fluid has been successfully used in Sumatra, Indonesia to drill the well NEB Basement-1 in Block Jabung. The properties of the drilling fluid remained stable for 40 days at bottom hole temperatures higher than 180℃. Difficulties in maintaining the suspension and cuttings carrying capacity of drilling fluid have been solved since then.