the invention relates to an improved method for injecting and transporting small particles in a natural porous medium . the method is characterized in that , in a first step , the porous medium is conditioned by means of an aqueous solution containing a hydrocarbonaceous compound , polymers or surface - active agents , in a second step , a plug of suspended particles is injected in the aqueous medium containing at least one hydrocarbonaceous compound , polymer or surface - active agent and , in a third step , the plug of particles is pushed by an appropriate aqueous medium . the method is particularly useful for implantation of bacteria in a porous medium .