Determining strain on a well casing

摘要

A system for measuring strain on a well casing 1 includes an optical fibre sensor 8 coupled to the exterior circumference of the casing 1 that senses casing strain along a section of the casing 1. A housing 9 fixed to the casing 1 forms a closed cavity on the outside of the casing 1 along the sensing section and encloses the optical fibre 8 thereby isolating the sensing section from the outside environment. The sensor 8 may include a coil of optical fibre (7, fig 4) bounded by a pair of Bragg gratings (6, fig 4). A method of measuring a microfracture within a casing is also disclosed which involves detecting and analysing acoustics having a frequency of at least 10 kilohertz.