Monitoring strain in downhole tubulars by measuring transmit time of acoustic signals along the wall of the tubular

摘要

A method of monitoring the strain in a downhole tubular A (e.g. casing string in an oil, gas or water well) comprises measuring the time of travel of a signal (e.g. acoustic signal) from a signal transmitter B to one or more signal receivers C, D through the wall of the downhole tubular. The distance travelled by the signal is calculated from the transit time. When the tubular is under tension the distance will increase, but when the tubular is in compression the distance will decrease. Also disclosed is a method of identifying a flow regime, a method of detecting sand in a fluid flow, a method of identifying localised events and a method of determining flow velocity.