Abstract
Viscosity changes of hectorite slurry and drilling mud water under hydrothermal condition were observed by using stirring autoclave coupled with torque meter. Semi-quantitative values of viscosity were estimated on the basis of an empirical liner function between share rate and torque of a standard fluid.
Viscosity of the drilling mud water changed slightly in the range from room temperature to 220 °C, suggesting moderate characteristics for high temperature mud water. But its viscosity depleted suddenly above 220 °C, which indicates that two phase separation was occured due to alteration of the mud water. Viscosity of the hectorite slurry increased in the ranging from 120 °C to 180 °C, which corresponds to the crystallization temperature of hectorite. However, its viscosity decreased above 180 °C after crystallization of hectorite. These facts indicate that two phase separation, composing from crystallized hectorite and residual solution, was occurred in the temperature range up to 180°C.
Hectorite slurry is one of possible agents for plugging fractures in geothermal reservoir to prevent lost circulation. The equipment developed here and estimation method of viscosity are applicable to evaluate plugging process of hectorite slurry in a geothermal reservoir.
