Forward simulation method of strain rate for helical wound fiber DAS

Distributed Acoustic Sensing (DAS) technology has been widely applied in the field of geophysical exploration. Conventional straight fiber can only acquire vibration information of the axial component of the fiber. By winding fiber vibration information from other directions can be captured, though it also leads to strain rate response characteristics of helical wound fiber DAS becoming more complex. This study focuses on the forward modeling of strain rate for helical wound fiber DAS, constructing the geometric model of the helical wound fiber, establishing a mapping between the three-component particle vibration signals and the strain rate response of helical wound fiber. By incorporating the DAS scattering mechanism, a mathematical expression for the strain rate of helical wound fiber DAS is derived that accounts for gauge-length effects, forming a forward modeling method and workflow of strain rate for helical wound fiber. Numerical simulations demonstrate that the strain rate record of helical wound fiber DAS has the characteristics of periodicity and similarity. Quantitative analysis confirms that the DAS gauge length and the winding angle of fiber have a greater influence on the strain rate for helical wound fiber DAS than the rotation angle and winding radius of the fiber. The forward modeling method in this paper clarifies the vibration signal characteristics of helical wound fiber DAS, providing a basis for the determination and optimization of key parameters during signal acquisition of helical wound fiber DAS, laying a theoretical foundation for directly utilizing DAS signals in data processing and inversion imaging.