The potential study of ultra-high density heteropolysate solid free brine as well completion fluid for deep reservoir development

The exploration of ultra-high pressure reservoirs is becoming more and more common due to the increasing demand of fossil fuels. It is anticipated that well drilling and completion in ultra-high pressure reservoirs will be the main exploration work in the future. The highest density of cesium formate brine is only 2.42 g/cm3, which cannot be served as the well completion fluid in ultra-high pressure reservoirs. The development of a higher density solid-free completion fluid has become a increasing demand as well as big challenge for ultra-high pressure reservoir exploration. In this paper, heteropolysate solid free brine was first applied to the field of completion fluid, and its density can reach at 2.8 g/cm3 or higher, which makes a breakthrough on the density limit of existing solid-free brines. The physical performance of heteropolysate brine is stable at 1–180 °C, and the mechanism of its dissolution and stability is illustrated. The corrosion rate of fluid is 0.0899 mm/a at 180 °C and the regained permeability recovery for tight cores is about 80%. The heteropolysate brine has the good compatability with formation water and oil and the biotoxicity evaluation shows that the brine is only slightly toxic (EC50 belongs to the range of 1000–25000 mg/L). The cost of heteropolysate brine is generally lower than that of cesium formate brines and it is recyclable. The heteropolysate brine in this study is applicable to both oil and gas reservoir and has the potential to be served as the well completion fluid for the ultra-high pressure reservoir development. •The heteropolysate brine makes a breakthrough on the density limit of existing solid-free brines.•The heteropolysate brine is stable at 1–180 C and low corrosiveness, environment acceptable.•The heteropolysate brine can be used for well completion in the ultra-deep reservoir development.