Solid-Free Flexible Colloidal Completion Fluid with Variable Density for Gas Well Completion in High-Temperature and High-Pressure Reservoirs: Experimental Study and Pilot Test

Summary Despite the increasing contribution of renewables to global energy, fossil fuels such as oil and gas still play an important role in energy supply. The development of deep and ultradeep oil and gas reservoirs has become more urgent. Typically, the ultrahigh-temperature and high-pressure (HTHP) environment is a big challenge. Solid-free brine is often used as a weighting component of high-density well completion fluid in the process of well operation, but the large amount of free water can easily cause water blocking damage to the reservoir. Therefore, there is an urgent need to develop a high-density completion fluid system that can be used in HTHP reservoir environments with little free water. In this paper, based on the theory of dispersion, degradation, viscosity extraction, and viscosity stabilization of polymer flexible colloidal particles in brines, an ultrahigh-temperature (180°C)-resistant, solid-free flexible colloidal completion fluid (SFCCF) with variable density and low corrosion was prepared. It breaks through the classical Flory’s water absorption theory. The phosphate brine was selected as the weighting base fluid of SFCCF, and the flexible colloidal particles were saturated with the phosphate brine to improve the density of SFCCF, as well as to reduce free water to lower the potential of water blocking damage. The results show that the dynamic viscosity of SFCCF is adjustable and ranges from 27 to 690 mPa·s, and the density is adjustable in the range of 1 to 1.8 g/cm3. SFCCF is a typical pseudoplastic fluid with shear dilution property, which is the result of the network destruction and the shear deformation of the flexible colloidal particles. The pump rate vs. dynamic viscosity curve is drawn. Under the pump rate of 50 to 800 L/min, the dynamic viscosity of SFCCF (1.2 to 1.7 g/cm3) is less than 40 mPa·s. In addition, SFCCF is viscosity stable for at least 4 days at 180°C and has excellent clay swelling resistance and reservoir fluid compatibility. Finally, SFCCF provides good reservoir protection and rock carrying capabilities and has the advantage of low cost. The successful application of SFCCF in a high-pressure gas well in the East China Sea is summarized, and some recommendations are proposed. The developed SFCCF can significantly reduce water blocking damage in HTHP well operations, providing a new avenue for HTHP well completions.