The present disclosure relates to methods of controlling a microbial level in an aqueous fluid or a solid component used in an oilfield operation or a pre- or post-production process associated with wellbore production, the method comprising: measuring a microbial parameter of the aqueous fluid； and subsequently using the measured microbial parameter to decide on an appropriate antimicrobial treatment. These proposals also relate to methods further including monitoring of a microbial parameter in such a fluid or on such a solid component over a period of time. The methods and aspects of the present disclosure may be applied in any oilfield operation or a pre- or post-production process associated with wellbore production.
