Research On Hydraulic Fracture Based On Scattering Wave Migration

With the development of unconventional oil and gas,hydraulic fracturing technology has gradually become one of the important methods in engineering technology.The microseismic events generated by fracturing may be recorded by seismic stations placed in the surface or underground monitoring wells,and the evaluation of the fracturing effect and range during the fracturing process is based on microseismic monitoring methods.It is still a challenge to accurately characterize the fracture zones created by hydraulic fracturing through microseismic event localizations.This is because some of the detected events may be incomplete due to the associated low signal to noise ratio.And somestimes the fracture develops well in some fracturing stages,no micro-seismic events will occur,and even if artificial fractures are formed,it is possible to reclosed at the end of the hydraulic fracturing process,and no effective fracturing can be formed.As a result,the spatial distribution of microseismic events may not well represent the fractured zones created by hydraulic fracturing.Therefore,in this study,we use a method of reverse time migration to image the fracture zones by using microseismic waveforms from some microseismic events.This is based on the hydraulic fractures filled with proppants and other fracture fluids that can act as strong scatterers for seismic waves.For multi-stage hydraulic fracturing,the recorded waveforms from microseismic events caused by the later stages may be scattered by fractured zones from the previous stages.Through the reverse time migration method of microseismic wave recording in the recent production stage,it is possible to determine the strong scattering region of the fracture created in the previous stages and image it.We use a comprehensive model with different two-dimensional downhole microseismic monitoring systems and microseismic events to analyze the relationship between hydraulic fractures,microseismic waveforms and reverse timemigration imaging to study the feasibility of this method and the imaging principle.Simulation experiments have shown that the location of the fractured zone can be illuminated by partial microseismic events,which can provide reliable information for estimating hydraulic fracturing effects.Compared with the conventional location-based hydraulic fracture assessment method,the method used in this paper does not emphasize the dependence on the detected events integrity and accurate events location.The monitoring of a limited number of microseismic events can provide the necessary parameters for characterizing the fracture distribution.For simplicity,we use a two-dimensional model to illustrate the concept about microseismic scattering wave imaging of fracture zone,but this method can also adapt to the three-dimensional model and the actual situation in the future.It can complementcan the conventional stimulated reservoir volume estimation method based on microseismic event localization,and provides a more reliable basis for the evaluation of fracturing effects and engineering design.