High-Temperature-Resistant Long-Term Stable Clay-Free Water-Based Drilling Fluids for Deep Well Drilling and Reservoir Protection

Abstract

Under high-temperature and high-pressure conditions, drilling fluids with long-term stability and low formation damage are one of the key technologies for ensuring safe and efficient drilling in deep reservoirs and achieving higher oil and gas production. In this study, a zwitterionic polymer (SPG) with high-temperature resistance was used to maintain dispersion stability and prevent nanoparticle aggregation, ensuring a uniform distribution of solid particles in the system. On this basis, a set of clay-free water-based drilling fluids (HT-CFWBDFs) was developed. The synergistic effect of SPG and nanoparticles improved the rheological properties and controlled fluid loss of HT-CFWBDFs. The HT-CFWBDFs were tolerant of saturation levels of NaCl, CaCl2, and CaBr2. CaCl2-based HT-CFWBDFs with a density of 1.41 g/cm3 could maintain appropriate rheological properties and low fluid loss after aging at 180 °C for 120 h. The HT-CFWBDFs exhibited good resistance to 3% inferior clay and CO2 contamination. They exhibited more stable rheological properties than bentonite-based drilling fluids under the same contaminated conditions. Furthermore, the HT-CFWBDFs exhibited good inhibition and reservoir protection performance. The HT-CFWBDFs have broad application potential as drilling or drill-in fluids in harsh formations and deep reservoirs.