Three-dimensional seismic response mechanism of straight and helically wound optical fibers
Distributed Acoustic Sensing(DAS)measures axial strain or strain rate,and straight optical fibers re-ceive a single component signal and are insensitive to the response of waves incident perpendicularly to the fiber.Helically wound optical fibers can receive multi-component signals,which can solve the problem of insensitive response.Firstly,the theoretical axial strain rate responses of P-wave,SV,and SH waves of straight optical fi-bers and helically wound optical fibers with winding angles of 35.3° and 54.7° are analyzed.Secondly,the axial strain rate response is simulated using the three-dimensional elastic finite difference method.Finally,DAS is deployed on the surface,horizontal wells,and vertical wells,and the seismic responses of straight optical fibers and helically wound optical fibers with winding angles of 35.3° and 54.7° are simulated using uniform models,double layer models,and southwest shale gas models.The axial strain rate response of DAS is compared with the velocity z component and pressure component of conventional detectors.The results show that:① Straight optical fibers receive single component information,but the response of waves received in the direction perpen-dicular to the optical fiber is weak,while helically wound optical fibers receive multi-component information,so the response of waves received in the direction perpendicular to the optical fiber is strong;②there is no S wave response in the helically wound optical fiber seismic record with a winding angle of 35.3°,and its waveform is similar to the pressure component of a conventional detector.The acoustic equation can be used for imaging.
万方数据
维普
