Svein Vaage

A Dual-Sensor, Towed Marine Streamer; Its Viable Implementation And Initial Results

In 1947, Roy Paslay, George Pavey and Pershing Wipff invented the towed marine streamer (Lawyer et. al., 2001; Paslay et. al., 1956). Since that time, there have been many improvements in streamer technology. However, one aspect of that technology has remained fixed during the intervening 60 years; the type of seismic detector has remained the hydrophone. As a consequence, every recorded and finally processed reflection wavelet from marine streamers has been accompanied by a ghost reflection from the ocean’s surface. And the resulting filter effect on the recorded data has restricted streamer towing depths to a range of about six to nine meters. In this paper, we report on the successful addition of particle velocity sensors to a new dual-sensor towed marine streamer, and the geophysical improvements and advantages that result.

Modeling of water-gun signatures

A method for calculating the acoustic signal generated by a water gun is presented. The equations describing the shuttle motion and the water jet formation are derived with the assumption that the water is incompressible. The motion of the shuttle is evaluated by assuming adiabatic expansion of the air initially contained in the air chamber of the gun. The formation and dynamics of the water jets emerging from the gun ports are closely connected to the shuttle motion. The combined effect of the water motion through the gun ports and the collapse of a cavity inside the gun nozzle can explain the first part of a water‐gun signature, often referred to as the precursor. The last part of the signature is mainly an impulsive shock wave caused by the collapse of external cavities. It is assumed that the external cavities are formed due to the pressure drop behind each water jet, and that the cavities collapse due to the hydrostatic pressure. The main effect of including interaction between the external cavities ...

Surface Related Multiple Suppression in Dual- sensor Towed Streamer Data

Conventional surface related multiple prediction for towed streamer configuration is flawed by the sea surface level variation and sea surface reflection coefficient fluctuation. Knowledge of the sea surface and reflection coefficient allows approximate correction of the prediction errors. Based on a novel dual-sensor towed streamer acquisition we propose a multiple prediction approach from the down-going vertical velocity field and up-going pressure field. This approach handles the obliquity factor and sea surface variations implicitly and may reduce bad-weather-related acquisition downtime.

Improvements in 3-D marine acquisition using continuous long offset (CLO)

Continuous long offset (CLO) acquisition combines a dual-vessel operation, using only short streamers, with a smart recording technique involving overlapping records (“mother records”). The dual-boat operation effectively doubles the streamer count, thus obtaining very long offset ranges. The mother records reduce cycle time and ensure an acceptable shot-point interval. The extra fold from long offsets roughly compensates for the loss of fold due to the increased shot-point interval.

Surface‐related multiple suppression in dual‐sensor towed‐streamer data

SUMMARY Conventional surface related multiple prediction for towed streamer configuration is flawed by the sea surface level variation and sea surface reflection coefficient fluctuation. Knowledge of the sea surface and reflection coefficient allows approximate correction of the prediction errors. Based on a novel dual-sensor towed streamer acquisition we propose a multiple prediction approach from the down-going vertical velocity field and up-going pressure field. This approach handles the obliquity factor and sea surface variations implicitly and may reduce bad-weather-related acquisition downtime.

Comparison of air‐gun clusters

Measurements of signatures from a variety of airgun cluster configurations have been carried out. The configurations include symmetrical two-gun clusters of Bolt 1500 C airguns, Bolt 1500 C airguns with waveshapekit, symmetrical two gun clusters of Bolt 600 C mounted parallel above each other, asymmetrical two-gun clusters of Bolt 600 C and Sleeve airgun clusters with more than two guns mounted in an in-line configuration. These measurements have been analyzed together with previous measurements reported by Vaage, Strandenes & Zaalberg-Metselaar 1990 [ 11, and give the basis for the following conclusions: regardless of source and gun type i) the optiial gun separation in a symmetrical two-gun cluster is 2.4 times the equilibrium radius of the individual air volumes ii) the improvement in primary/bubble peak amplitude ratio is on the average 2.4 times the ratio for two non interacting guns iii) the loss in peak amplitude at the optimal separation distance is 15% and iv) the corresponding bubble period is increased by 20%. The use of waveshapers reduce the relative improvement in primarylbubble peak amplitude ratio to about 1.5, and the optimal separation distance is close to 2.4 times the air volume above the waveshapers. Asymmetrical two-gun clusters are less effective than symmeuical clusters and give a relative improvement in primary/bubble peak amplitude ratio between 0.9 and 1.6, depending of the airgun volumes involved. The optimal separation distance is close to 2.4 times the equilibrium radius of the average air volume in the cluster. Increasing the number of guns in a symmetrical cluster decreases the optimal separation distance compared to the two-gun case and leads to a substantial reduction in acoustic efficiency as the number of guns increase.