A method of generating geophysical data using at least one source. The method may include the steps of generating a geophysical wavefield with a varying signature using at least one source, wherein the signature is varied in a periodic pattern.

Methods and apparatuses for obtaining and/or processing slip sweep seismic survey data. The methods compute harmonic weight ratios using two types of data: 1) direct survey data where a harmonic sweep does not overlap with the fundamental component of responses of Earth interior and 2) another set of data representative of fundamental component of responses of Earth interior where the harmonic sweep does overlap with the fundamental component of responses of Earth interior. The set of data representative fundamental component of responses of Earth interior can be extracted from ground force measurements or a different sweep. The harmonic weight ratios using ground force measurements at overlapped frequencies may be calibrated with one or more harmonic weight ratios at non-overlapped frequencies.

Received shot gathers are sorted to a common receiver gather. A target three-dimensional (3D) amplitude spectrum of seismic wavefield direct arrivals is computed from synthetic data. A 3D amplitude spectrum of seismic wavefield direct arrivals in field data is computed for each receiver. A matched filter is calculated from the 3D amplitude spectrum of field data to target response and applied to downgoing seismic wavefields separated from the common receiver gather to generate filtered downgoing seismic wavefields. Time-dependent smoothing of the filtered downgoing seismic wavefields is performed to generate smoothed downgoing seismic wavefields. A cross-correlation is calculated between upgoing seismic wavefields separated from the common receiver gather and the smoothed downgoing seismic wavefields.

Methods and apparatus for interferometric seismic imaging and creation of a high-resolution three-dimensional seismic volume in proximity to a wellbore are described. In contrast to current methods that deliver positions of microseismic events using a small fraction of the microseismic wavefield, the present invention provides for the analysis of a full microseismic wavefield. In a preferred embodiment, the method includes creating a planar image slice and/or corridor between the location of one or more microseismic events and one or several sensor arrays to produce a multitude of azimuthally orientated planar image slices and/or corridors. The method further includes adding the planar image slice and/or corridor contributions to create a single three-dimensional volume for analysis and rendering.

A method for attenuating noise in seismic data signals is described wherein seismic signals are transmitted using a pseudo-random frequency sweep signal. Noise is then attenuated from the resulting, acquired seismic data on pre-phase subtraction basis, e.g., before correlating or de-convolving the acquired seismic data. In this way, repetitions associated with, for example, diversity stacking techniques can be avoided.

A method for attenuating noise in seismic data signals is described wherein seismic signals are transmitted using a pseudo-random frequency sweep signal. Noise is then attenuated from the resulting, acquired seismic data on pre-phase subtraction basis, e.g., before correlating or de-convolving the acquired seismic data. In this way, repetitions associated with, for example, diversity stacking techniques can be avoided.

New methods for calculating acquisition illumination are computationally less expensive in comparison with conventional methods. In one such new method, source wavefield propagations are calculated and assigned to corresponding zero-offset receivers. Further, the number of non-zero-offset receivers within the coverage of the shot at the source location is decimated. Such a method is most advantages in reverse time migration, in which all source wavefield propagations are already calculated. The receiver-side illumination for each shot can be obtained by summing up all the source-side illumination with the source located within receiver coverage. All the source-side illumination and receiver-side illumination can be summed up to get the acquisition illumination for the survey. The acquisition illumination can be used to value the acquisition system and to compensate the migration images.

An air gun intended for use in generating seismic energy impulses, i.e. acoustical waves, in a body of water that provides improved performance by adjusting the length of the firing chamber in order to tune the rise time from zero pressure to peak pressure and to increase or decrease the slope of the initial pulse. By selecting the length of the firing chamber, the rise time of the initial pulse is tuned to increase low frequencies and reduce objectionable high frequencies to help in mitigating damage to marine life and the marine environment and to provide greater penetration of the seismic signal through for example basalt and sub-basalt structures.

A technique includes towing at least one seismic source in connection with a survey of a structure; and operating the seismic source(s) to fire shots, where each shot is associated with a frequency sweep. The technique includes varying phases of the frequency sweeps from shot to shot according to a predetermined phase sequence to allow noise in an energy sensed by seismic sensors to be attenuated.

Method for separating signals recorded by a seismic receiver and generated with at least two vibratory seismic sources driven with no listening time. The method includes receiving seismic data that includes data d recorded by the seismic receiver and data related to the first and second vibratory seismic sources; computing a source separation matrix based on the data related to the first and second vibratory seismic sources; calculating first and second earth impulse responses HA and HB corresponding to the two vibratory seismic sources, respectively, based on the data d recorded by the seismic receiver, the data related to the two vibratory seismic sources and the source separation matrix; and separating the signals recorded by the seismic receiver based on the first and second earth impulse responses HA and HB such that signals the two vibratory seismic sources are disentangled.