The present disclosure relates to methods of controlling a microbial level inan aqueous fluid or a solid componentused in an oilfield operation or a pre- or post- production process associatedwith wellbore production, the method comprising:measuring a microbial parameter of the aqueous fluid； and subsequently usingthe measured microbial parameter to decide on anappropriate antimicrobial treatment. These proposals also relate to methodsfurther including monitoring of a microbial parameter insuch a fluid or on such a solid component over a period of time. The methodsand aspects of the present disclosure may be applied inany oilfield operation or a pre- or post- production process associated withwellbore production.
