Water based muds (WBM) provide an eco-friendly and cost effective way out for drilling a petroleum well without using oil based muds. WBM may cause some problems when a water sensitive formation (such as shale) is encountered during drilling. The infiltration of water from mud causes formation minerals to dissolve that may lead to formation damage. Fluid loss also alters the rheological properties of mud which is highly undesirable hence fluid loss should be minimum.
Present study aims to experimentally investigate the effect of CuO and ZnO nanoparticles in presence of poly(4-styrenesulfonic acid-co-maleic acid) sodium salt (PSSM) as a fluid loss control agent for WBM at high pressure-high temperature (HPHT) conditions. Base mud containing hydroxyethyl cellulose was mixed with 1.0 w/v% of PSSM and varying concentrations of either nanoparticle (0.25, 0.50, 0.75 and 1.00 w/v%). The resulting drilling fluid formulations were examined by using viscometer, high temperature ageing cell in roller oven, API filter press, HPHT filter press and capillary suction timer. Zeta potential of nanoparticles in water with and without PSSM was measured using particle size analyser. Filter cake formed by API filtration tests were analysed by field emission scanning electron microscope (FESEM). Ageing experiments were also performed at 230°F for 16 hours and HPHT filtration tests were conducted at 300°F.
Experimental studies have shown that the addition of CuO decreased the rheological parameters such as apparent viscosity, plastic viscosity and yield point by 10 to 15% before hot rolling of drilling fluid. After hot rolling, the rheological parameter for mud containing CuO were reduced, but as the concentration of nanoparticle increased, the rheological properties improved. Effect of CuO was more pronounced as compared to ZnO nanoparticles on fluid loss. The addition of 1.0 w/v% PSSM in base mud reduced LPLT fluid loss to ~64%. API fluid loss of PSSM containing mud was further reduced by ~12% on addition of only 1.0 w/v% of CuO. At 1.0 w/v% concentration of ZnO, API filtrate of base mud reduced by ~8%. HPHT filtrate loss for mud having 1.0 w/v% PSSM was 14.6 mL in 30 minutes at 300°F. Addition of nanoparticles further reduced HPHT filtration loss by 15 to 20%. FESEM images of filter cakes suggested that there were complex structures of polymer chains covering the pores of filter cake, and the network was further blocked by the nanoparticle clusters, therefore inhibiting the passage of fluid through it.
The results obtained from this experimental work have shown that the efficiency of polymer as fluid loss reducer has improved due to the addition of nanoparticles, especially with CuO. The novel combination of CuO nanoparticles with poly(4-styrenesulfonic acid-co-maleic acid) sodium salt can further be explored and engineered to develop an efficient fluid loss reducing formulation for water based mud.