Abstract This paper describes the results of laboratory investigations into the effect of drilled solids on the drilling rate and drilling performance. Drilling fluid performance and a successful result during drilling operations are characterised by the fluid's properties providing hole cleaning and cutting transport. Various concentrations of bentonite which has the same specific gravity with drilled solids were used to simulate drilling performance. The results were discussed in terms of electric stability (emulsion stability), high-pressure high-temperature (HPHT) including the resultant filter cake, rheological properties of the active fluid Experiments show that the ES drops in half as the drilled solid (bentonite) concentration increases from 0 to 75 lb/bbl. The HPHT FL test produced thicker filter cake and the HPHT FL doubles while the YP quadruples as the bentonite concentration increases. Accumulation of filter cake on the bit or BHA during pull out of hole of a drill string and hole problems are attendant problems associated with inefficient solid control. The use of bentonite to simulate the drilled solid is good agreement with previous works.