미소진동자료를 이용한 균열대의 영상화를 위한 포인팅벡터 기반 영상조건

Abstract

Hydraulic fracturing has been implemented in enhanced geothermal systems and in developing unconventional reservoirs to increase the permeability of earth media. To improve the safety during the hydraulic fracturing, a method is proposed for imaging pre-existing fractures adjacent to the hydrofractured zones based on observed seismic signals during microseismic monitoring using the Elastic Reverse Time Migration with Source-independent Converted Phase (ERTM SICP) imaging condition. The ERTM SICP imaging condition is more computationally efficient than the conventional ERTM method is, and it can be used to perform migration without the information on the locations of source events. It is therefore appropriate for handling microseismic data. However, because of the difference between P- and S-wave velocities and complex geometry, ERTM SICP imaging condition produces spurious events that can be confused with fractures when it is applied to reflected waves. Based on the idea that the propagation directions of the P- and S-waves at mode converting points are very similar, whereas those in other regions are commonly different, I modified the imaging condition by adding a weighting function calculated from the P- and S- waves and named this modified imaging condition as Poynting vector based imaging condition. The weighting function has different values depending on the angle between the propagation directions of the P- and S-waves. Through 2D and 3D numerical tests, I showed that the modified imaging condition can successfully suppress the linear spurious events that appear in non-mode-converting regions.