Preparation, investigation and corrosion mechanism of novel thermally stable high-density compound phosphate-based drill-in fluids for HTHP applications

Abstract

Based the requirements of completion operation for drill-in fluids with high-density, solid free, low damage and low toxicity, the novel thermally stable high-density compound phosphate-based drill-in fluids with 1.80, 1.70 and 1.60 g/cm3 were prepared by using weighting agent compound phosphate and other additives, such as solubilizer, deoxidizer and corrosion inhibitor. Then, the compositions of drill-in fluids with 1.80, 1.70 and 1.60 g/cm3 were optimized depend on the single factor experiment method. In addition, the general performances of drill-in fluids, such as solid-free characteristics, density stability, pH stability and environmental compatibility, were further studied. Moreover, the thermal stability of drill-in fluids was investigated in the temperatures range of −10 to 180 ℃, simultaneously, the viscosity was tested at different temperatures, besides, the formation water compatibility and reservoir protection performances were studied. Finally, the corrosion behavior and mechanism of drill-in fluids were studied through SEM and XRD depends on the microstructure and phase analysis of corrosion products. The results show that the novel thermally stable high-density compound phosphate-based drill-in fluids have potential HTHP application value, meanwhile, it suggests that the compound phosphate as a green environment-friendly weighting agent, which can be used as an alternative for preparing high-density drill-in fluids.