Although, the depth of invasion is controllable to a certain degree by designing the drilling fluids on the basis of concentration and particle size of the bridging material and of the pore sizes of the reservoir rock, the invasion of solids and filtrate, and corresponding formation damage are inherent to drilling fluid. Therefore, the reservoir drilling fluid should be designed to generate saline inhibitive filtrate which would not swell the clay envelop in and around the payzone particles and would not react with the formation fluid to form insoluble precipitate. In this study, the potassium chloride (KCl), choline chloride and polyol have been taken as the clay inhibiting agent of reservoir drilling fluid. To investigate the inhibition characteristics of these materials, the bentonite (smectite) clay and the shale have been taken as the swelling agent. Although, the KCl (5%) is found very effective to inhibit the swelling of smectite (damaging) type of clay, due to its negative environmental impact, non-suitability for stabilizing kaolinitic shale and scarcity; the nontoxic, environment friendly and substantially available choline chloride and polyol have been tested and found very effective as clay hydration suppressant at much lower concentration (i.e. 2.5% of each) compared to KCl.
