Experimental Investigation on the Effect of the Aphron Drilling Fluid in Mitigating Formation Damage of Dawood Bai-Hassan Reservoir

Drilling fluid is one of the crucial parts of the drilling operation and has a significant role in carrying rock cuttings to the surface, stabilizing the wall of the borehole and controlling formation pressure. Most of the depleted reservoirs drilled by water-based drilling fluid are subjected to high overbalance pressures due to the difference in density of drilling fluid compared with the formation fluid. This overbalance pressure creates the lost circulation of mud, pipes sticking and formation damage. Underbalanced drilling can be considered to eliminate the above-mentioned problems. However, it has safety issues and prohibitive in many depleted fields. This study focuses on the development of the Aphrons-based drilling fluid from adding two types of surfactants (City-Termidyl Ammonium Bromide (CTAB) as a stabilizer, and Sodium Dodecyl Benzene Sulfate ( SDBS) as a generator) and xanthan gum (XC) polymer to be used for drilling of Dawood Bai-Hassan Reservoir. (20) samples of Aphrons drilling fluids were formulated at different concentration of xanthan gum (0.2 and 0.4 wt.%), CTAB (0.2 and 0.4 wt.%) and SDBS (0.1 to 1 wt.%). All the developed drilling fluids subjected different experiments of rheological and filtration properties. The obtaining results show that better rheological behavior were obtained with adjusting the concentration of the used additives as 0.4 wt.% xanthan gum, 0.2 wt.% CTAB and 0.4 wt. SDBS when achieved and added to the base drilling fluid. The results showed that (XC) Polymer combination with surfactants (CTAB and SDBS) have a major effect on mud filtration at even under-surface conditions, where it was lowered by 47% at surface ( 20°C, 100 psi) and lowered by 41.67%, 50% at conditions 60 °C, 90 °C (600 psi) temperature respectively. In addition, for maintaining other mud properties such as viscosity, yield point, gel strength and cleaning capacity as well.