Abstract: The invention relates to methods of determining whether a wellbore sealing operation has been performed correctly, and to wellbore-lining tubing which facilitates the determination of whether a wellbore sealing operation has been performed correctly. The invention has a utility in determining whether cement has been correctly supplied into an annular region defined between an internal wall of a wellbore and an external surface of a wellbore-lining tubing located in the wellbore, or whether a packer has been properly set to seal such an annular region.

Abstract: A method of communication comprising: providing a string of a plurality of connected components (2,3,5,6,7), one or more vessels running along the string to form a continuous fluid path (13); incorporating a device (3) into the string so that the device is in communication with the fluid path; inserting the string into a borehole (18) 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 pressurised fluid; over a communication period, venting fluid, under the control of the device, from the fluid path (13) to an exterior of the string (17) 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].

Abstract: A downhole assembly includes an apparatus for generating a fluid pressure pulse downhole. A disclosed apparatus for generating a fluid pressure pulse downhole includes an elongate, generally tubular housing defining an internal fluid flow passage and having a housing wall. The apparatus also includes a device for selectively generating a fluid pressure pulse, the device having a cartridge which can be releasably mounted entirely within a space provided in the wall of the tubular housing. The internal fluid flow passage defined by the tubular housing is a primary fluid flow passage. A secondary fluid flow passage has an inlet which communicates with the primary fluid flow passage. The cartridge houses a valve actuable to control fluid flow through the secondary fluid flow passage to selectively generate a fluid pressure pulse. Data relating to a measured downhole parameter or parameters can be transmitted to surface via the pressure pulses.