Abstract: A telemetry system for transmitting data between a downhole location in a wellbore and the surface of a well utilizing an acoustic signal which operates within naturally occurring passbands on a string of pipe have substantially fixed frequency ranges which are related to pipe length and condition.

Abstract: A sub for use in an acoustic telemetry system provides a sound path of low impedance to facilitate the transmission of acoustic signals through a string of pipe positioned in a wellbore. The sub section of pipe includes a tubular receiving member positioned in the bore of a pipe section and spaced from the interior walls thereof. Ports and flow channels are also provided to permit the passage of well fluids through the pipe section when an acoustic instrument is positioned in the tubular receiving member. A lateral shoulder is formed in the interior wall of the receiving member and is arranged to matingly receive a flat portion on the instrument. The abutment of the flat portion of the instrument and the shoulder provides a positive sound path for transmission of longitudinal sound waves from the instrument to the receiver member.

Abstract: Ice is broken with expenditure of less energy by pumping water from beneath the ice and discharging it in large quantities onto the surface of the ice. Breaking stress is provided by the weight of the water and by thermal shock. A conventional ice breaking apparatus can also be run up onto the ice to provide a breaking force in which case friction between the ice and the ice breaking apparatus is lessened by the water.

Abstract: An anchor frozen into an ice sheet is used primarily for propelling arctic vehicles by providing a stationary structure toward which the vehicle can be winched. The anchor includes a band of high tensile strength material formed in a closed, curved configuration for freezing into an ice sheet and attaching the vehicles thereto.

Abstract: Disclosed is an inclinometer particularly adapted for use as a top-hole indicator in drilling operations. The inclinometer employs a ferrofluid in a closed tube; the fluid serves as an angle-sensitive movable core of a differential transformer. The secondary coils of the transformer are wrapped around the tube; the primary coil is wrapped around a core piece or the tube. Equipment is provided for comparing the outputs of the secondary coils to produce an angle signal. A sturdy construction for downhole use is disclosed.