Effects of the geothermal water based muds on the drilling performance

Geothermal drilling is usually carried out on the fractured and cracked volcanic areas having high temperature conditions. Because of this situation leading to lost of circulation and decomposition of mud requires a vast amount of water to prepare mud. Fresh water using to prepare mud is desired to be provide from the nearest location of drilling site in terms of benefit/cost. Otherwise, drilling engineers use geothermal spring water to prepare mud from the surface or well near the drilling location. Although there have been many studies about the drilling muds prepared with fresh waters, the geothermal spring waters and their effects on the drilling performance have not been investigated. To this end, first of all, 1 sample of distilled water and 8 sample of geothermal spring water were used to prepare mud samples according to API standards. Then, the viscosity, filtration, gel strength, cake thickness, pH and density of these samples were measured depending on ambient conditions and elevated temperature. In addition, the rheological model to be used in predicting the rheological behavior of the formulated muds was analyzed statistically and the cutting carrying indexes and the minimum anulus velocity required for effective well cleaning of samples were evaluated in terms of drilling performances at ambient conditions and elevated temperature. As a result, it was observed that the muds prepared with geothermal spring waters have lower viscosity and lower yield point and higher water loss than fresh water based muds. On the other hand, when the relationships between the shear rate and the shear rate of the samples are plotted for 6 different temperature conditions (77, 122, 167, 212, 257 and 302 (°F)), the relationship between shear stress and shear of the fluid is shown by the Herschel-Bulkley model which a combination of Bingham plastic and power law models at relatively low temperatures (77-212 (°F) range). However, some mud samples behaved as non-Newtonian fluid that is without yield point at higher temperatures. Also, it is seen that muds prepared with geothermal spring waters have lower carrying capacity than the muds containing fresh water in terms of cutting carrying indexes. Moreover, muds prepared with geothermal spring waters require higher velocity of annulus for effective well cleaning. Consequently, based on this study, it was concluded that the muds prepared with geothermal spring waters have a lower drilling performance compared to muds prepared fresh water sources.