US Patent 7124817 Method of treating a hydrocarbon bearing formation

A method of treating a hydrocarbon-bearing measure such as an oil-bearing rock formation (13). The method comprises: injecting water containing a source of vitamins, phosphates and an electron acceptor such as nitrate into the formation at first location (10) and allowing anaerobic bacteria, which are either already present in the formation (13) or which are introduced simultaneously to multiply using the oil as their main carbon source. This establishes a biomass layer (16) which acts to dissociate the oil from the rock formation (13). The dissociated oil is removed via an outlet (15). The vitamins are supplied by means of a controlled-release medium.