Abstract Conventional drilling fluids usually contain various polymers, which are the main cause of formation damage. A biological method, which could efficiently reduce this type of damage, was developed. Several halotolerant and thermotolerant microorganisms were isolated and their ability to degrade polymers was tested. Specifically formulated bacterial package proved to be very effective in minimizing starch, xanthan and cellulose-based skin damage when added to drilling mud. The result of experiments showed the usefulness of using the microorganisms for the degradation of polymers and for removal of mud from the pore space. It had been demonstrated that bacterial strains are particularly fitted for degradation of polymers and mud filtrate cake.