Abstract: A system is disclosed for removing a periodic interfering signal from an electrical signal which may also include a data signal such as a seismic signal. A digital representation of the interfering signal, comprising a series of digital words, is generated and a nulling signal formed from this digital signal is subtracted from said electrical signal. The amplitude difference between said electrical signal and the nulling signal is determined and the digital words comprising the digital representation of the interfering signal are changed by a function of the difference between said electrical signal and said nulling signal, to reduce said difference.

Abstract: This invention is a control system for a hydraulic vibrator that permits the injection into the ground of seismic signals having pseudo-random code patterns or other broad band signals. Feedback for controlling vibrator operation is taken from the coupling plate. At low frequencies, the feedback is proportional to coupling plate position and at higher frequencies, the feedback is proportional to the coupling plate velocity.

Abstract: A monochromatic interference signal is removed from seismic data records by transmitting into the earth a seismic signal having a null component in its power spectrum at substantially the frequency of the interference signal. When cross-correlation techniques are used to determine subsurface characteristics, the cross-correlation product of the detected signal with the transmitted signal will contain a substantially zero component at the frequency of the interference signal.

Abstract: In a variable frequency seismic vibrator including an earth coupling plate, means for generating a reaction impedance, and an energy source for generating reciprocating movement of the coupling plate relative to the reaction impedance, the reaction impedance is generated by a reaction mass and a spring of variable stiffness which couples the reaction mass to the vibrator. As the frequency of vibration changes, the stiffness of the spring is automatically adjusted so that the impedance of the spring resonates with the impedance of the mass to maximize the reaction impedance, thereby increasing the operating efficiency of the vibrator.

Abstract: In a subsurface formation, where shaliness affects the results of typical electrical well logging measurements, partial water and partial hydrocarbon saturations are determined from measurements of dielectric constant. The relation between dielectric constant and conductivity due to shaliness in a partially water saturated formation and a relation defining dielectric constant change as a function of partial water saturation are used to determine partial water saturation and partial hydrocarbon saturation of said formation.

Abstract: A system for performing wellbore telemetry operations wherein a communication link between a subsurface location in a well and the location substantially at the surface is established and maintained through electromagnetic coupling between two insulated electric conductors. The first conductor is electrically coupled to a transmitter, normally located at the subsurface location, and extends upwardly in the well. The second conductor is electrically coupled to a receiver, normally at the surface location, and extends down into the well. Normally, the two conductors will overlap along a substantial portion of the lengths thereof. As the well is drilled deeper and the drill string is lengthened, the transmitter and the first conductor follow the progression of the wellbore into the earth, thereby reducing the overlap between the first and second conductors. When the two conductors cease to overlap, the second conductor may be lengthened to re-establish the overlap.

Abstract: Apparatus and method for drilling a well into a submerged bottom from a floating drilling vessel while employing a riser pipe having positive buoyancy is disclosed. The riser pipe extends between the vessel and the well and is comprised of an upper and a lower section. Means are connected to the lower section for imparting a buoyant force to it of sufficient magnitude to render it positively buoyant. Means are provided extending between the submerged bottom and the upper end of the positively buoyant riser section for restraining the lower section against upward movement. The upper section of the riser pipe may be disconnected from the lower section so that the vessel may abandon the well site. The lower riser section is left self-standing, connected to the wellhead.

Abstract: Apparatus is described for eliminating monochromatic interfering frequency components of seismic signals detected during the course of seismic exploration comprising an electrical circuit for producing a monochromatic nulling signal that has the same frequency as the interfering signal. The monochromatic nulling signal is produced by generating a truncated triangular wave having the same period as the interfering signal and filtering the truncated triangular wave to remove all components thereof except those having the period of the interfering signal. Circuit means are provided for controlling the amount of truncation of the truncated triangular wave, and for controlling the time phase thereof. The filtered signal is combined with the geophone signal in such a manner that the filtered signal at least partially cancels out the interfering component of the seismic signal.