Hydroxyethyl cellulose (HEC) is widely used in water-base drilling fluid as tackifier because of its good fluidity, stability, prop-carrying capacity, and good reservoir protection, while it has insufficient rheological property under higher temperature. In order to make use of its advantages and improve thermal stability, an innovative method that HEC was dissolved in the emulsion was proposed. Research indicated that compared with traditional water solution, the oil-water emulsion as solution could effectively improve the rheological properties and thermal stability. The oil-water ratio has an obvious effect on rheological properties. Firstly, with the decrease in the oil-water ratio, the apparent viscosity and shear stress were decreased; secondly, under constant oil-water ratio or temperature, the larger the shear rate, the lower the apparent viscosity, and the greater the shear strength; lastly under extremely low shear rate, HEC emulsion’s viscosity peaked at more than 50000 mPa·s, which can effectively solve the problem of sand carrying difficulty and being easy to form sand bed in horizontal well and high angle hole. In addition, the emulsifying stability was degradative with the increase in the oil-water ratio. The degradation was not obvious when the oil-water ratio was less than 30 : 70. On the contrary, the performance deteriorated drastically when the oil-water ratio was greater than 30 : 70. The separator liquid was more than 2 cm and was even about 1/3 when the oil-water was 50 : 50. On the basis of analysis of the experimental results, we can see that oil-water emulsion could effectively improve the rheological stability and thermal stability of HEC and the optimal oil-water ratio was 30 : 70. This study provided a new thought for application of HEC or other polymers in drilling fluid.
Evaporation of oil-water emulsion drops when heated at high temperature