Distributed acoustic seismic systems and their perspectives in VSP

Distributed acoustic sensing (DAS) are systems that use optical fiber cable as a sensor for acoustic signals. Coherent laser pulses are launched into the fiber to measure amplitudes and phases of backscatter waves with time. An acoustic signal, which is coupled by friction or pressure to the optical fiber, induces dynamic strain changes along the cable. These strain changes lead to small displacements of the scattering elements and therefore to variations of the relative phases of the backscattered waves. The fiber behaves as a series of interferometers whose output is sensitive to small changes of the strain along its length.
Materials and methods
Comparison seismic data from uniformgeophones and DGS systems.
Сonclusions
DAS systems designed for seismic measurements offer the possibility to record and process this optoelectronic signal in a manner that establishes a linear relationship to thetime dependent local strain. In order to record the ground motion not only in space but also in time, snapshots of the wave field are created,by repeatedly firing laser pulses into the fiber at sampling frequencies much higher than seismic frequencies.
Results
Review of publications about DAS application revealed next points:
• a possibility of obtaining results whichquality identic to original seismograms, obtained with the new and standard receiving stations;
• technology of work is simplified and reduced the cost due to the simultaneous reception of vibrations along the entire length of the cable and eliminating the need to use relocatable on wellbore single or strings of geophones;
• great prospects of new sending systems during conducting univariate observation, 3D acquisitions and other works.