LAUSR

Abstract The development of drilling fluids with low density for deep saline aquifers is in high demand. This study performed several tests to find the optimal formula of drilling fluid that would be suitable under circumstances with high temperatures and salt concentrations similar to deep saline aquifers. Drilling fluids with varying combinations sodium chloride (NaCl), polyacrylamide (PAM), sulfonated lignite (SMC), and sodium carboxymethyl cellulose (Na-CMC) in montmorillonite (Mt) water-based slurry were synthesized and tested. Salt-, SMC-, and temperature-sensitivity analysis was done to investigate effects of ionic strength and temperature on the performance of synthesized drilling fluids. Anti-caving ability tests were performed to check the drilling fluids influence on porosity of aquifer upon application. The results show that NaCl and PAM play a critical role in controlling viscosities and yield values. PAM and Na-CMC contribute to fluid loss characteristics, and PAM contributes to low density too. A deliberately chosen combination of NaCl, PAM, SMC, and Na-CMC gives rise to a suitable formula of drilling fluid for temperatures up to 120 °C and salt concentrations up to 1.7 M. The simulation of drilling fluid seepage in the borehole based on the ANSYS-Fluent existing codes verifies the performance of the optimal formula and the results imply the effectiveness of the optimal formula on prohibiting the borehole instability. This will even encourage immediate field applications of the optimal formula.