A Novel Method for Determining Geophone Orientations From Zero-Offset VSP Data Constrained by Scalar Field

Abstract

In vertical seismic profile (VSP) acquisition, the orientation of the three-component geophones in a borehole is often not aligned due to random rotation of the wireline receiver array. Knowing the geophone orientation is crucial for rotating the waveforms back to the position where the geophones are assumed to be aligned. This procedure is critical in three-component VSP data processing as it provides the correct wavefields for subsequent VSP data imaging and inversion. For zero-offset or near zero-offset VSP measurements, the direct P-wave propagates nearly vertically, and the horizontal geophones receive only a small fraction of the direct P-wave energy. The first-arrival in the horizontal component data is often of low signal-to-noise ratio (SNR). As a result, it is difficult to apply conventional first-arrival–based methods for obtaining accurate geophone orientations. On the other hand, a seismic event comprising individual waveform would achieve maximum correlation if all corresponding geophones are aligned. The geometric characteristics, that is, the slope and continuity of a seismic event in the vector wavefield are the same with those of the modules of the vector wavefield. The latter, also known as the scalar wavefield, can be used for scanning geophone orientations based on waveform correlation. In this study, we propose to use the scalar field to extract the slope of seismic events. The orientation of the individual geophone was calculated with the constraint of the slope. We use both synthetic and field data to demonstrate the effectiveness and applicability of the proposed method. The results show that the new method can provide wavefields of horizontal component VSP data with much higher accuracy and resolution.

Receiver orientation and event back-azimuth estimation for downhole microseismic monitoring using a probabilistic method based on P-wave polarization

“…By assuming that the polarization direction of the P-wave of the microseismic event coincides with its propagation direction, receiver orientation can be accomplished by performing polarization analysis using available calibration shots (e.g., perforation shots, string shots, ball-drop events, or vibroseis sources at the surface) to derive P-wave propagation direction, which can then be utilized to rotate the horizontal components to the correct direction (Nakamura et al, 1987;Menanno et al, 2013;Lagos and Velis, 2019;Huo et al, 2021). In addition to P-waves, Rayleigh waves have also been employed for receiver orientation (Niu and Li, 2011;Zha et al, 2013;Wang et al, 2016;Xu et al, 2018;Ensing and van Wijk, 2019;Takagi et al, 2019;Son et al, 2022;Yang et al, 2022). Receiver misorientations are defined as the deviations between the empirical and true back azimuths, and the relative-angle method by measuring the relative azimuth angle between receiver pairs is another strategy (Zeng and McMechan, 2006;Grigoli et al, 2012;Zhu et al, 2018;Ojo et al, 2019;Huo et al, 2021).…”