The Effect of Drilling Fluid and Temperature on the Cement-Rock Interaction in Geothermal Wells

Abstract

The current study has investigated the interactions between well cements and one of the most common types of rocks found in geothermal environments, under hydrothermal conditions. Holes were drilled in blocks of ignimbrite rock and API class G cement with 0, 20 and 40% added silica flour, was poured into the cavities. The whole assemblage was autoclaved, under typical geothermal conditions at 150° and 300°C for 28 days. The results show that chemical reactions occur in the intertransition zone, which are dependent on both drilling fluid and temperature. The use of bentonite as a drilling fluid and the exposure to higher temperatures (300°C) when compared to 150°C, seem to exacerbate the reactions occurring in the ITZ. Consequently, there is formation of new crystalline products, which have worse performance when the physical bonding between the cement and the rock is considered. The effect of other variables such as CO2 exposure, the hydrothermal alteration of the rock and the curing time are currently being investigated within this research project.