PGS Geophysical AS

Methods and apparatus are described for performing a 4D monitor marine seismic survey that repeats a previous survey. A number of sources may be used during the 4D monitor survey that differs from a number of sources that were used during the previous survey. Shot points from the previous survey are repeated by the 4D monitor survey, and additional shot points may be produced during the 4D monitor survey that were not produced during the previous survey. Embodiments enable efficiency and data quality improvements to be captured during 4D survey processes, while preserving repeatability.

A system and method controls impulsive source activations in a blended acquisition marine seismic survey. A component of the system generates a sequence of dither values deterministically and stores the sequence of dither values, or source activation indicators derived therefrom, in a non-transitory medium readable by a control system operable to execute shot points during the survey responsive to the values stored in the medium. According to some embodiments, generating the dither values comprises iteratively selecting from a fixed set of candidate dither values to produce a candidate sequence of dither values. The selecting is based on evaluating one or more quantitative measures of randomness and one or more quantitative measures of separation exhibited by at least a portion of the candidate sequence of dither values. Generated sequences improve deblending results by reducing coherence exhibited by the dither values in the sequences.

A marine streamer includes: an optical fiber disposed along a length of the streamer; a light source; and light analysis equipment, wherein: the length is at least 20 km, a diameter of the streamer is no more than 25 mm, the optical fiber, light source, and light analysis equipment are configured to provide a receiver sampling density of at least 1 per meter, and the streamer is configured to be towed nominally horizontally through a body of water. A method of marine surveying includes: towing a streamer spread at a first depth of 10 m to 30 m with a survey vessel; and towing Distributed Acoustic Sensing (DAS) streamers at a second depth of greater than 30 m. A method includes: acquiring long-offset data with sensors distributed along the DAS streamers.

A long-offset acquisition system includes a source vessel; a signal source coupled to the source vessel; and a long-offset streamer coupled to a survey vessel and including an aft-most receiver, an offset of the aft-most receiver being at least 12 km. A long-offset acquisition method includes towing a signal source with a source vessel; towing a first long-offset streamer with a survey vessel; and acquiring data with receivers of the first long-offset streamer. A long-offset acquisition method includes towing a signal source with a first survey vessel; towing a long-offset streamer with a second survey vessel, the long-offset streamer having a plurality of receivers; actuating the signal source while an offset between the signal source and at least one of the plurality of receivers is at least 15 km; and acquiring data with receivers of the long-offset streamer.

One or more first sensors may be configured to sense seismic signals and one or more second sensors may be configured to sense electromagnetic crosstalk signals. The second sensors are not responsive to the seismic signals. The data from the first and second sensors may be recorded as first data and second data, respectively. The first data may be modified based on the second data to remove the electromagnetic crosstalk noise form the seismic data.

Methods and systems described herein are directed to determining properties of a subterranean formation using an acoustic wave-equation in terms of a velocity model and a vector reflectivity model of the subterranean formation. The acoustic wave equation may be used with simultaneous inversion to simultaneously build velocity and pre-stack reflectivity in the form of angle gathers of a subterranean formation. The velocity and angle gathers may be employed for quantitative interpretation. The velocity and vector reflectivity may be employed to determine relative impedance and relative density of the subterranean formation for prospectivity assessment. The acoustic wave equation may extend into the angle domain to build angle gathers of the subterranean formation with enhanced resolution and amplitude fidelity. The velocity, angle gathers, and vector reflectivity reveal the structure and lithology of features of the subterranean formation and may reveal the presence of oil and natural gas reservoirs.

A method and apparatus includes: towing a first source with a source vessel; towing a second source with a survey vessel, the survey vessel following the source vessel by at least 5 km; towing a streamer spread at a first depth with the survey vessel; and towing a pair of long-offset streamers at a second depth and following the source vessel by at least 5 km, wherein: the first depth is 10 m to 30 m, and the second depth is greater than 30 m. A method and apparatus includes: towing a first source with a source vessel; towing a second source with a survey vessel, the first source and the second source being separated by at least 5 km; towing a streamer spread at a first depth with the survey vessel; towing a pair of long-offset streamers at a second depth, wherein: the first depth is between 10 m and 30 m, and the second depth is greater than 30 m; acquiring long-offset data with long-offset sensors distributed along the long-offset streamers; and constructing a velocity model with the long-offset data. A method and apparatus includes: towing a first plurality of streamers at a first depth of 10 m to 30 m; receiving first signals generated by a first source with the first plurality of streamers; towing a second plurality of streamers at a second depth of greater than 30 m; while receiving the first signals, receiving second signals generated by a second source with the second plurality of streamers; wherein: the first source and the second source are separated by at least 5 km, the second signals represent long-offset data, and a forward-most receiver on each of the second plurality of streamers has a same inline offset from the first source as a forward-most receiver on each of the first plurality of streamers.

Embodiments generally relates to marine geophysical surveying. More particularly, the present disclosure relates to treatment of geophysical equipment with medetomidine compounds for reduction of marine growth. A method may comprise combining at least a medetomidine compound and a wax to form a mixture; and forming an outer layer disposed on a marine geophysical equipment, wherein the outer layer comprises the mixture of the medetomidine compound and the wax.

A proposed geometrical distribution for a first non-impulsive source and a second non-impulsive source of a source array can be received. A near-field-to-notional computation can be performed for the proposed geometrical distribution to yield a respective computed notional output of the first and second non-impulsive sources. Whether the computed notional output of the first non-impulsive source has a first amount of residue greater than a threshold amount of residue can be determined. Whether the computed notional output of the second non-impulsive source has a second amount of residue greater than the threshold amount of residue can be determined. An indication whether either of the first or second amounts of residue is less than or equal to the threshold amount of residue can be provided.

Processes and systems for imaging a subterranean formation using continuously recorded seismic data obtained during a marine seismic geophysical survey of the subterranean formation are described herein. The processes and systems compute upgoing pressure data at stationary-receiver locations, and low-frequency noise attenuation processes and systems are applied to the upgoing pressure wavefield data to obtain low-frequency noise attenuated upgoing pressure wavefield data. An image of the subterranean formation, or data indicative thereof, may be generated using the low-frequency noise attenuated upgoing pressure wavefield data at stationary-receiver locations.