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Seismic-while-drilling (SWD) by drill-bit source has been successfully used in the past few decades and is proven using variable configurations in onshore applications. The method creates a reverse vertical seismic profile (RVSP) data set from surface sensors deployed as arrays in the proximity of the monitored wells. The typical application makes use of rig-pilot reference (pilot) sensors at the top of the drill string and also downhole. This approach provides while-drilling checkshots as well as multioffset RVSP for 2D and 3D imaging around the well and prediction ahead of the bit. For logistical (sensor deployment) and cost (rig time related to technical installation) reasons, the conventional drill-bit SWD application is typically much easier onshore than offshore. We have developed a novel approach that uses a network of passive-monitoring sea-bottom nodes predeployed for microseismic monitoring to simultaneously and effectively record offshore SWD data. We study the results of a pilot test in which we passively monitored the drilling of an appraisal well at the Wisting discovery in the Barents Sea with an ocean-bottom cable deployed temporarily around the drilling rig. The continuous passive recording of vibration signals emitted during the drilling of the well provides the SWD data set, which is treated as an RVSP. The study is performed without rig-pilot signal. The results are compared with legacy data and demonstrate the effectiveness of the approach and point to future applications for real-time monitoring of the drilling progress, in terms of geosteering the drill bit and predicting formation properties ahead of the bit by reflection imaging.

This paper deals with the design, acquisition and processing of vertical seismic profiling data collected in 2016 at the directional Thonex‐01 geothermal well, drilled in 1993 in the Geneva Canton (Switzerland). The aim of the study was to obtain additional information from existing‐abandoned well for downhole geophysical characterization of potential geothermal reservoirs in the Geneva area. The main results obtained by this study allowed an improved subsurface image by multi‐offset acquisitions near and around the deviated well. Specifically we were able to (1) improve the velocity model of the Geneva Basin, which, at present, is only constrained by one unique deep exploration well, located at the south‐west of the basin, far away from the study area; (2) image the transition between the Tertiary Molasse siliciclastic sediments and the Mesozoic carbonates; (3) define an acquisition strategy for future vertical seismic profiling surveys in support of the geothermal exploration campaigns in the area. This study has demonstrated the value of vertical seismic profiling method for the refinement of the subsurface geology at local scale, and its usefulness to assist the planning of second well associated with geothermal doublets.

Distributed acoustic sensing (DAS) using fiber optic cables is an emerging seismic acquisition technology for the oil and gas industry, geothermal resource exploration, and underground fluid-storage monitoring. This technology offers the advantage of improving seismic acquisition by enabling massive arrays for monitoring of seismic wavefields at reduced cost with respect to conventional methods. In general, it is accepted that this method provides acoustic signals comparable with conventional seismic data, however, without the multicomponent directional information typical of geophones. We have developed a modified data extraction method and found that, as a result of the dense spatial distribution of recording points along the optic cable, DAS can provide two linked wavefield components in the axial direction, even when using a single 1D cable line. These signal pairs consist of dual components that are related to native strain rate (or strain) and particle acceleration (or velocity) fields at a given recording location. These dual signals are easily usable for wavefield separation purposes simply performing a trace-by-trace combination by appropriate scaling coefficient. The analysis performed with borehole data from linear and helically wound cables demonstrates the effectiveness of polarity recovery and dual-wavefield separation. We show real examples in which the data can be combined to provide separation of up- and downgoing wavefields. The ratio of the dual components provides information on local slowness properties in the formation.

The knowledge of the Moon subsoil geophysical properties is of great importance, for scientific reasons for the development of the Lunar exploration activities and the envisaged exploitation of its planetary resources. The Moon surface is characterized by the presence of regolith, a powdered material made up of unconsolidated, porous and highly brecciated rock fragments of several different grain sizes and lithologies. Beneath the regolith, a transition zone showing higher acoustic velocities may be present down to the solid bedrock. The bedrock consists of basaltic layers characterized by high seismic velocity and low seismic attenuation. In these conditions, human civil engineering and rover activities, including drilling may be subject to risk due to the lack of knowledge of the complex subsoil properties. Seismic While Drilling is a method used on Earth to support from geophysical point of view the drilling for oil and gas and geothermal exploration. In this application, the characterization of the stratigraphy by vertical seismic profiles in the drilled section, providing seismic images of the to-be-drilled substructures, is obtained using the drill-bit radiated energy. We present the result of a project that studies the adaptation of the method for Lunar drilling purposes, taking into account the specific issues related to the Moon environment and remote communication aspects. The results of a laboratory test conducted in the framework of a European Space Agency project (completed in 2009) with a planetary drill prototype and a simulator of a complete remote system are presented and discussed together with the perspectives for the seismic-while-drilling application for planetary missions.

Drill‐bit seismic while drilling provides reverse vertical seismic profiles with large configurations of surface seismic sensors. This seismic while drilling technique makes it possible to predict the formation changes ahead of the bit and to image 2D and 3D structures without interfering with the drilling activity. The method is based on the recording of reference (pilot) signals which enable us to recognize and process the signal of the downhole drill‐bit source, thus obtaining impulsive seismograms after the crosscorrelation and deconvolution of the pilot signals and the seismic data recorded by surface or crosswell geophones. One issue in the application of this methodology can be the loss of the transmitted energy for the reference signal propagated from the bit to the surface through the drill string, when the pilot signals are recorded at the surface, at the top of the drill string. It is well known that with polycrystalline diamond compact bits, the pilot signal recorded at the surface may be weak and consequently the seismic while drilling results are poor. This may also happen during drilling in the sliding mode without pipe rotation, and in highly deviated or horizontal wells. A solution to improve the drill‐bit seismic while drilling method in these conditions is to record the reference signal in the proximity of the bit source, using downhole near‐bit tools to get good‐quality measurements of the pilot signal. We present drill‐bit seismic while drilling results obtained in a drilling test using wired pipes for high‐rate communication from bottom hole to the surface. The results demonstrate the applicability of this integrated approach as a standard procedure. The advantage of this is to provide real‐time synchronized reverse vertical seismic profiles, as well as high‐resolution and good‐quality data in terms of S/N and high‐frequency content. The method improves the use of the working drill bit as a downhole seismic source with different types of bit and drilling conditions.

We use different interferometry approaches to process the seismic signals generated by a drill-bit source in one well and recorded by seismic receivers located both in a second borehole and at the surface near the source well. We compare the standard interferometry results, obtained by using the raw drill-bit data without a pilot signal, with the new interferometry results obtained by using the drill-bit seismograms correlated with a reference pilot signal. The analysis of the stationary phase shows that the final results have different S/N levels and are affected by the coherent noise in the form of rig arrivals. The interferometry methods are compared by using different deconvolution approaches. The analysis shows that the results agree with the conventional drill-bit seismograms and that using the reference pilot signal improves the quality of the drill-bit wavefields redatumed by the interferometry method.

In this work, we investigate the wavefields and the broadside response of a helical distributed acoustic sensor cable co-located with a hydrophone streamer in a shallow horizontal borehole. We discuss dual-wavefield separation results for selected optical-cable signals recorded with dense receiver spacing. Moreover, we interpret the phase and amplitude differences observed in the HWC and streamer data using sources at different azimuth. The analysis shows how the frequency response for the DAS signal with respect to the corresponding streamer signal changes with azimuth.

We present the results of a multi-offset vertical seismic profile (VSP) acquired in the Grado-1 (North Eastern Italy) geothermal exploration well in the framework of an integrated VSP, seismic and gravimetric survey. The purpose of the VSP survey was to link borehole logs and seismic data, and to calibrate the surface seismic data acquired for imaging purposes in the area surrounding the well. The VSP allowed us to obtain high-resolution seismic information in depth, and to measure the variations of the physical rock properties in the fractured carbonatic formations at lateral positions, by means of multi offset data processing and wavefield analysis including anisotropy and Vp/Vs ratio. The VSP provided additional and robust geophysical information for the numerical estimation of the fluid-dynamic modelling of the geothermal-doublet system. The results have been subsequently used for the location of the second well that will be drilled in the geothermal reservoir.

Summary Distributed acoustic sensors (DAS) using fiber opticcables is an emergingacquisitiontechnologyforO&G industry.It offers the advantage of improvingseismic acquisition by massive monitoring of seismic waves at reduced cost .In this paperwe show that,as a result of the dense spatial distribution o f recording points along the optic cable ,DAS can providetwo fieldcomponents in theaxial direction , even when usinga single one-dimensional line .These signalpairsconsist ofdualcomponents,whicharerelated to strainand particle velocity fields at a given recording location.We show withreal exampleswhere the datacan becombined to provideseparation ofup-and down-going wavefields. T he ratioof the dualcomponents provides informationon localslowness properties inthe formation.

We present the results of a seismic-while-drilling (SWD) survey performed using the working drill-bit as a seismic source to support drilling from a geophysical point of view in a well drilled for geothermal purposes. In this application we perform revers

In this work we present the results of a seismic while drilling (SWD) application using the drill-bit as a seismic source in geothermal wells. The survey was performed in a well drilled in the Nevada desert with the aim of providing geophysical information while drilling and images of the geological structures around the well. We present a summary description of the drill-bit seismic technology adapted for geothermal purposes, and the SWD results obtained along 2D profiles passing through the well. The good-quality seismic-while-drilling results have been subsequently used to obtain images of the well area in the direction normal to the main fault system, with SWD reverse vertical seismic profiling (RVSP) data migration, using seismic interferometry to extend laterally the coverage of the SWD RVSP images. The migrated seismic interferometry results confirm the main trends of the 2D geological model in the geothermal area.

The MOONBIT experiment investigated the capability to obtain structural and stratigraphic information of planetary subsoil using Seismic While Drilling (SWD) - a geophysical technique used for Earth subsoil exploration. The basic concept of SWD uses the drill bit as a seismic in-depth source of seismic waves, recorded by geophones as surface receivers gathering digital seismograms at different depths: signal processing provides seismic images known as Reverse Vertical Seismic Profiling (RVSP). MOONBIT's target medium is the regolith layer on the Moon surface, covering basaltic bedrock. As innovatively RVSP SWD method, a passive Downhole Hammering Mechanism (DHM) actuates the drill bit, which becomes the borehole source of seismic waves. Two main tests were conducted in regolith simulant with buried geophones: the first test characterized the propagation velocity of seismic waves; the second test used a 1.5 m drill over a container. Drill control strategies and robustness towards signal transmission problems of future unmanned Moon drills of missions, Earth remote controlled, were also assessed and simulated with an error generator and a remote supervisor prototype. Test results with consistent seismic signals of good quality and resolution and comparative analysis showed that the DHM drill bit is an adequate source of SWD signals for RVSP planetary purposes and may support steering, drilling planning and scientific investigations.

We analyze the performance of the drill-bit seismic source for near-well investigation purposes. We test two different configurations, crosshole and single-well-imaging (SWI). The crosshole results are used to characterize the high-frequency content and to observe the radiation pattern of the drill bit source. These results are also used to analyze the stability in the signature of the drill-bit signal. We obtain appreciable results up to 350 Hz. The drill-bit data are used for SWI purposes by reference signal analysis in a drilled depth interval of approximately 140 m. The method allows us to detect reflections for prediction of the interfaces to be drilled, and the results are in agreement with other geophysical results and geological evidences.

Vertical Seismic Profiles (VSP) provide an effective tie between well information (as logs and core analysis) and surface seismics, by linking the local geology to the Earth reflectivity. Seismic tomography gets similar benefits from the joint inversion of direct and reflected arrivals, recorded both at the surface and in a well.

Applications of drill-bit seismic has developed since the end of the 80's (Rector and Marion 1991). This technique uses the noise generated by the drill-bit during perforation as seismic energy. The signal is recorded with sensors placed on the rig and witti geophones in the ground; after processing it is possible to use the data in the same way as traditional VSP data (Angeleri et al. 1990).

Multicomponent seismic while-drilling data were analysed in order to define better the different wavefield components and the energy radiation pattern of a tricone drill-bit. A unique cross-hole acquisition scheme from one of ENI-AGIP's special test sites was used. Direct measurements of high quality P- and S-waves allowed the determination of the radial horizontal component (HR) and of the corresponding transverse horizontal component (HT). Subsequently, analysis of the vertical transverse component (T), derived by combining Z and HR. led to the computation of simplified radiation pattern for the SV component of the drill-bit signal. A large time splitting between horizontally and vertically polarized shear waves, influenced by the acquisition geometry and by the geological setting, was analysed. An unconventional SV velocity tomographic reconstruction from the drill-bit signal is also derived and discussed.

Drill-bit seismic while drilling provides reverse VSP, makes it possible to predict the formation changes ahead of the bit, and to image 2D and 3D structures without interference with drilling activity. When the pilot signals used for crosscorrelation with the seismic signals are recorded at the surface, an issue in the application of this methodology may be the loss of the drill-bit-vibration signal during its propagation from the bottom to the surface through the drill string. With PDC bits, as well as during drilling by sliding condition without pipe rotation, and in highly deviated or horizontal wells, the pilot signal recorded at the surface may be weak and consequently the SWD results poor. A solution is to use near-bit downhole tools to get good-quality measurements of the pilot signal. Literature reports examples of SWD with the use of downhole memory systems, from which the data are downloaded after the bit retrieval at the surface. In this paper we present the new results obtained using a drill pipe equipped with a wireline communication system from bottom hole to the surface. The results demonstrate the applicability of this method providing good-quality RVSP data, in terms of S/N and frequency content.