Abstract: In drilling and production operations, formation damage may occur when the drilling fluid is incompatible with sensitive components in a reservoir. In this paper, the interaction between high pH fluids and the Carboniferous Donghe sandstone reservoir in the Tarim Basin is investigated. Combined with core-flood tests for sensitivity evaluation, petrographical analyses were made on more than 200 samples from the reservoir. The results indicate that the higher the PH of the fluids, the severe the formation damage is. High PH fluids not only cause dispersion/movement of the clay, but also result in partial dissolution/precipitation of certain minerals, leading to drastic decrease in permeability. In addition, the level of formation damage involving alkali sensitivity is also related to the salinity and velocity of the test fluid.

Key words: Formation damage, Well completion fluids, Clay minerals, Alkali sencitivity, Tarim basin, Alkali sensitivity