Geological investigation using coiled tubing incorporating sensors

A method of deploying a geological investigation assembly to enable data to be transmitted to a receiving station above ground. The assembly consists of a length of coiled tubing having two tubes (20, 80) disposed coaxially and a transmission means for transmitting power or data from a number of sensors/transmitters (33), possibly of acoustic type. The sensors/transmitters (33) are disposed between the inner and outer coaxial tubing (20, 80) or in the flow path within the coiled tubing. There can be a means of penetration present, such as a drill or water jet (30, fig 2a, not shown). The assembly can be used on land or under the sea-bed. When used under the sea-bed the assembly can include a casing (35), which can be left beneath the sea-bed while the coiled tubing is detached.