Method and apparatus for communicating with a device located in a borehole

Abstract

A method of communication comprising: providing a string of a plurality of connected components (), one or more vessels running along the string to form a continuous fluid path (); incorporating a device () into the string so that the device is in communication with the fluid path; inserting the string into a borehole () so that the device is located below a surface into which the borehole is formed and the fluid path extends from the surface to the device; providing a pressure sensor at the surface, adapted to sense the pressure of the fluid in the fluid path; filling it with a pressurized fluid; over a communication period, venting fluid, under the control of the device, from the fluid path () to an exterior of the string () at the device on occasions, so that the resulting decrease in pressure in the fluid in the fluid path can be detected by the pressure sensor; and during the communication period introducing fluid into the fluid path at a rate below 30 gallons/minute [0.113 m3/minute].