Retrieving virtual reflection responses at drill‐bit positions using seismic interferometry with drill‐bit noise

Abstract

A B S T R A C TIn the field of seismic interferometry, researchers have retrieved surface waves and body waves by cross-correlating recordings of uncorrelated noise sources to extract useful subsurface information. The retrieved wavefields in most applications are between receivers. When the positions of the noise sources are known, inter-source interferometry can be applied to retrieve the wavefields between sources, thus turning sources into virtual receivers. Previous applications of this form of interferometry assume impulsive point sources or transient sources with similar signatures. We investigate the requirements of applying inter-source seismic interferometry using nontransient noise sources with known positions to retrieve reflection responses at those positions and show the results using synthetic drilling noise as source. We show that, if pilot signals (estimates of the drill-bit signals) are not available, it is required that the drill-bit signals are the same and that the phases of the virtual reflections at drillbit positions can be retrieved by deconvolution interferometry or by cross-coherence interferometry. Further, for this case, classic interferometry by cross-correlation can be used if the source power spectrum can be estimated. If pilot signals are available, virtual reflection responses can be obtained by first using standard seismic-whiledrilling processing techniques such as pilot cross-correlation and pilot deconvolution to remove the drill-bit signatures in the data and then applying cross-correlation interferometry. Therefore, provided that pilot signals are reliable, drill-bit data can be redatumed from surface to borehole depths using this inter-source interferometry approach without any velocity information of the medium, and we show that a well-positioned image below the borehole can be obtained using interferometrically redatumed reflection responses with just a simple velocity model. We discuss some of the practical hurdles that restrict the application of the proposed method offshore.

Combination of surface and borehole seismic data for robust target-oriented imaging

“…On the other hand, seismic interferometry (SI, also called Green's function retrieval) is a data-driven technique that can transform the original data into a sort of virtual data, where physical receivers are turned into virtual sources (Bakulin & Calvert 2006) or vice versa (Curtis et al 2009;Liu et al 2016). This makes it an alternative processing technique for certain types of VSP data (Schuster 2009) to image targeted areas that are difficult to image with the original acquisition geometries.…”

Characterization of drilling-related noise and curvelet-based evaluation of seismic-interferometric reflections for imaging of iron-bearing formations in Pilbara, Western Australia

“…Drilling operations, as opposed to conventional industrial AN sources, are mostly occurring in the subsurface and thus can be used advantageously for retrieval of body waves with SI, as recordings from the drilling operations will not be dominated by surface waves (e.g. Liu et al 2016). For a fixed AN source position in the subsurface, the slope of a retrieved reflection event depends on the propagation velocity, depth of the receivers, depth of the reflector and the angles of incidence and reflection (Snieder 2004).…”

“…In contrast to the complicated AN wavefield generated by vehicle movement and mine activity, continuous recordings of borehole drilling are dominated mostly by the repetitive type of arrivals with approximately known source positions (Liu et al 2016). This type of data is often referred to as active noise (e.g.…”

“…This type of data is often referred to as active noise (e.g. Liu et al 2016) and dedicated methods were developed for its processing (e.g. Seismic While Drilling; Rector & Marion 1991;Poletto & Miranda 2004).…”

“…These methods usually require pilot signals to remove the drillinginduced signatures. However, even without a pilot trace, it is possible to retrieve the reflection response from drilling-induced AN using SI (Liu et al 2016;Asgharzadeh et al 2019).…”