Identifying the distributed strain sensing (DSS) patterns (signatures) associated with various hydraulic fracture simulations have been the subject of much interest and investigation. Recent efforts have focused on developing a catalogue of signatures for planer hydraulic fractures in an elastic formation. However, in many instances (e.g., geothermal reservoirs and fault motion monitoring) the deformation mode is shear on natural fractures, but the resulting fiber signature has not been studied. In this work we use a 3D poroelastic hydraulic fracture model to obtain strain signatures given by shear deformation of fractures in various orientations with respect to the monitoring well. Three major cases are considered namely, fracture strike is perpendicular to the fiber, the strike is parallel to the fiber, and the fracture strike is at 45 degrees to the fiber. Expected results were obtained with the fracture simulator in all three cases and it was found out that the strain pattern changes when the direction of the shear deformation with respect to the fiber changes. The results in this study will guide Engineers to better understand the strain signatures obtained with the DSS method.
Distributed strain sensing (DSS) is an emerging technology used in unconventional petroleum reservoirs and recently has gained popularity in enhanced geothermal systems (EGS). It is mainly used to monitor propagation of hydraulic fractures and characterize their geometry. It has proven useful in refining such estimates based on microseismic and pressure monitoring.
In the distributed strain sensing (DSS) the linear strain on the fiber at a particular time is recorded. Repeated measurements at close time intervals can be used to create a strain signature. A typical DSS system requires a laser interrogator, which generates and sends a laser signal, detects the backscattered light from the formation and converts it to strain measurements at sensing points. (Liu et al, 2020). The distance between these sensing points is called the gauge length. These backscattered signals provide information about the axial strain along the fiber cable located in the monitoring well. When compared with other downhole sensors such as geophones, DSS provides information over a longer length and also provides real time measurements.
