drill bit seismic interferometry with and without pilot signals 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

drill bit signal separation for rvsp using statistical independence drill bit noise and rvsps time and depth migration of seismic data usually is based on velocities estimated from surface measurements the actual velocities which calibrate the depth migrated seismic to the well data are determined after the well is drilled using check shots and vsps by then it may be too late to correct for seismic migration velocity imprecision and impact the well s success the earlier we can obtain such velocity information the more time will be available for reprocessing remigration of either the seismic or any depth maps if necessary it is therefore very useful to determine the velocities to calibrate seismic and well velocities while drilling this allows us to better locate the drill bit in time on the seismic section to redirect the well if necessary and to gather as much further information as possible on the rocks ahead of the bit

acoustic velocity of seismic while drilling swd borehole guided waves borehole guided waves other than the extensional waves traveling through the drillstring can be used as pilot signals to obtain seismic while drilling swd seismograms and information about the drilling conditions this occurs when there is no rotation of the drillstring while drilling and when the contacts between the drillpipe and the borehole wall preclude the propagation of the extensional wave to obtain the velocity of the guided waves we model the compressional wave velocity of drilling mud with different compositions of low and high gravity solids corresponding to a given drilling plan and taking into account the presence of formation cuttings and in situ conditions then we compute the velocities of the tube wave with and without casing and the guided wave traveling in the mud inside the drillstring pipe wave the results indicate the pipe wave constitutes a reliable pilot signal in the absence of drillpipe rotation this allows us to obtain a complete depth reverse vertical seismic pro

using ambient noise seismic interferometry and local and teleseismic earthquakes to determine crustal thickness and moho structure of the northwestern gulf of mexico margin

interface prediction ahead of the excavation front by the tunnel seismic while drilling tswd method predicting geologic interfaces ahead of a tunnel front is of major importance when boring tunnels unexpected variations in ground properties can cause problems for tunnel boring advance and risk for human safety the tunnel seismic while drilling tswd method utilizes noise produced during mechanical excavation to obtain interpretable seismic data this passive method uses accelerometers mounted on the advancing tunnel boring machine reference signals together with seismic sensors located along and outside the tunnel data recorded by fixed sensors are crosscorrelated with the reference signal and sorted by offset similar to reverse vertical seismic profiling crosscorrelated tswd data are processed to extract the reflected wavefield during mechanical excavation of a 950 m tunnel through upper triassic dolomite a survey was performed to predict geologic interfaces faults intersecting the tunnel were observed on seismic tswd data and later were confirmed by geostructural inspection p and s wave i

a blind interpretation of drill bit signals the role of kurtosis in evaluating the quality of vertical seismic profiling vsp drill bit data is investigated the calculations show how kurtosis depends on the dominant frequency bandwidth and phase content of a seismic signal this analysis is applied to synthetic and real common offset and common shot drill bit seismograms to evaluate the prominence and quality of the first arrival and other coherent events high values of kurtosis correspond to an isolated first arrival or to a compressed coherent noise event while low values are typical of low s n distributed ratio traces kurtosis analysis applied to drill bit vsp data while drilling proved to be successful at identifying high quality traces with little interpretational input

seismic while drilling by using tunnel boring machine noise the tunnel boring machine tbm is used extensively to mechanically excavate tunnels to optimize the mechanical drilling and work safely an estimate of the geology to be drilled is necessary we consider using the elastic waves produced by the tbm cutting wheel to obtain seismic while drilling swd information for predicting the geology ahead of the drilling front this method uses accelerometers mounted on the tbm together with geophones located along and outside the tunnel similar to the technique successfully used to drill oil and geothermal wells study of noise and the resolution of the signal produced by the large diameter cutting head shows that nonstationary noise separation can be achieved by locating sensors at the front and rear ends of the tunnel the higher resolution in front of the tbm is limited by pilot delays while the lower lateral resolution is limited by the radial dimension of the tbm analysis of seismic data acquired in a field test shows that p and s wave arrivals have a wide frequency band and high amplitude in seismic traces measured 700 m away from the drilling front in comparison with swd applications in wells tunnel swd technology has the advantage of allowing direct access to the tunnel front which makes it easy to connect the tbm reference sensors for while drilling monitoring this method can be successfully applied without interfering with drilling activity to monitor tunnel excavation continuously reduce risks and optimize drilling

estimation of fracture zone geometry from steady state hydraulic head data using iterative sequential cokriging the hydrogeology of fractured crystalline rock is often controlled by a few highly conductive features such as faults and or fractures zones accurate modeling of fluid flow and transport in these systems requires that the geometry of these conductive features be characterized explicitly a new method for estimating the geometry of these features is presented the method is an extension of the recently developed geostatistical technique of sequential cokriging in this extension the geometry of the fracture zone is iteratively updated until an update increases the discrepancy between the estimated and observed hydraulic heads results from two hypothetical examples demonstrate that the method can accurately estimate the geometry of highly conductive fracture zones

retrieving virtual reflection responses at drill bit positions using seismic interferometry with drill bit noise in 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 non transient 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 drill bit 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 while drilling 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

a comparison of coherency measurement using semblance and multiple signal classification from a seismic while drilling perspective abstracta diamond drill bit is usually considered to be an inadequate seismic vibration source to detect and use weak drill bit generated seismic wavefields in hard rock drilling we compared different coherency measures between a conventional method of semblance and a generalized multiple signal classification music algorithm we tested the detectability and resolution differences between semblance and music with synthetic examples music coherency has the advantage of higher resolution over semblance measurement when the source wavefronts are accurately predicted in addition we applied both methods to detect the coherent moveout of a diamond drill bit signal from a hard rock seismic while drilling experiment at hillside south australia we used the coherent moveout to estimate the overburden velocity around the borehole we also performed interferometry migration using the coherency measurements to image the drill bit position our analysis determined that the direct waves generated from a diamond

the use of drill bit energy as a downhole seismic source a new wellbore seismic technique uses the vibrations produced by a drill bit while drilling as a downhole seismic energy source the technique is described as inverse vsp because the source and receiver positions of conventional vsp are reversed no downhole instrumentation is required to obtain the data and the data recording does not interfere with the drilling process these characteristics offer a method by which borehole seismic data can be acquired processed and interpreted while drilling interchanging the conventional vsp source and receiver positions improves the efficiency of recording multioffset surveys for imaging a 3 d data volume in the borehole vicinity the continuous signals generated by the drill bit are recorded by a pilot sensor attached to the top of the drillstring and by receivers located at selected positions around the borehole the pilot signal is crosscorrelated with the receiver signals to compute traveltimes of the arrivals and to attenuate incoherent noise deconvolution and time shifts of the pilot signal compensate for the effects of propagation from the drill bit to the top of the drillstring by repeating this process for an interval of the well a vsp equivalent data set is generated results from a test well demonstrate that the processed drill bit data are comparable to conventional vsp data

autocorrelogram migration ivspwd test we present the results of applying autocorrelogram migration to inverse vertical seismic while drilling ivspwd profile data collected in the austin chalk formation the seismic reflections were excited by a drill bit moving along a horizontal well at a depth of 2800 m the data were recorded by a receiver array on the surface there were 609 twenty second traces recorded at each of 10 three component stations after preprocessing the traces were autocorrelated and migrated two imaging conditions were examined the ghost reflection imaging condition produced a reflectivity section that agreed with a nearby common depth point section the migration section obtained with a primary reflection imaging condition produced a reflectivity section inferior in quality to that of the ghost image a possible explanation is that the drill bit location was not precisely known which can be shown to induce weak errors in the ghost imaging condition but stronger errors in the primary reflection imaging condition ghos

a new approach to offshore drill bit reverse vertical seismic profiling rvsp seismic while drilling swd is a tool that can be used to optimize drilling at offshore areas and to reduce the related risks different while drilling vertical seismic profiling vsp technologies that use seismic receivers located in fixed positions can be considered for offshore 2 d investigations with short medium offset and in limited water depth we introduce a new approach using conventional towed streamers to extend the offshore swd measurements to large offset 3 d and deepwater applications where conventional technology has limitations this technology may not only replace other swd methods but could also integrate them

positioning drill bit and look ahead events using seismic traveltime data we study seismic traveltime measurements acquired in the borehole including vertical seismic profiling seismic measurements while drilling and drill bit noise generated data these traveltime data are used to assess informative parameters including drill bit position distance to drilling target and parameters of the velocity model first we analyze seismic traveltime data using a simple hyperbolic traveltime equation for rays between surface sampling locations and the drill bit second we describe a model for estimating both the position of the drill bit and the relative distance to geologic interfaces ahead of the bit finally we present a dynamic bayesian strategy for real time prediction of drill bit positions velocity parameters and distances to geologic markers walk away vertical seismic profiling data from the norwegian sea are used to demonstrate our methods for this data set we pick five key reflectors ahead of the drill bit the deepest reflector is estimated to be 207 5 m ahead of

drill bit seismic monitoring while drilling by downhole wired pipe telemetry abstract 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

seismic while drilling by using dual sensors in drill strings drill string waves can be successfully used as reference pilot signals for drill bit seismic while drilling swd purposes the seismic signals obtained by correlating pilot and geophone measurements are disturbed by the drill string reverberations because the pilot waves are reflected at each interface between string sections with different acoustic impedances inverse filtering of these reflections using a reference pilot deconvolution calculated in the presence of additional noise may cause signal distortion to overcome this problem we consider using dual sensor measurements in the drill string to remove the reflections of the drill bit waves in the acquisition phase and to improve pilot deconvolution we measure acceleration and strain of drill string dual fields which have opposite reflection coefficients and in a string of constant elastic properties the same transmission coefficients these quantities are scaled to fit the amplitude of the direct arrivals summed to remove the reflections in the drill string and in the rig and may be deconvolved by einstein deconvolution to characterize the reflection coefficient between the drill bit and the formation synthetic numerical examples and real measurements acquired downhole in a location close to the bit show that upgoing and downgoing drill string pilots can be separated using dual fields and jointly used to improve the swd seismograms

prediction ahead of the bit by using drill bit pilot signals and reverse vertical seismic profiling rvsp surface drillstring axial pilot signals are used to predict reflections ahead of the drill bit we show that part of the drill bit signal propagates downward in the formation reflects upward by a seismic interface and is then transmitted to the drillstring and the surface pilot sensors these reflections are interpreted in drill bit pilot signals by means of a numerical model of the drillstring coupled to the formation at the bit rock contact the result is an additional low cost reverse vsp rvsp in the zero offset approximation these while drilling results are integrated with conventional drill bit rvsp measurements and compared with other geophysical and well results

true amplitude prestack depth migration most current true amplitude migrations correct only for geometric spreading we present a new prestack depth migration method that uses the framework of reverse time migration to compensate for geometric spreading intrinsic q losses and transmission losses geometric spreading is implicitly compensated by full two way wave propagation intrinsic q losses are handled by including a q dependent term in the wave equation transmission losses are compensated based on an estimation of angle dependent reflectivity using a two pass recursive reverse time prestack migration the image condition used is the ratio of receiver source wavefield amplitudes two dimensional tests using synthetic data for a dipping layer model and a salt model show that loss compensating prestack depth migration can produce reliable angle dependent reflection coefficients at the target the reflection coefficient curves are fitted to give least squares estimates of the velocity ratio at the target the main new result is a procedure

energy balance of a drill bit seismic source part 2 drill bit versus conventional seismic sources the radiation properties of a downhole drill bit seismic source are related to the amplitude and frequency of the forces exerted by the working bit the main vibration modes of roller cone and polycrystalline diamond compact pdc bits are investigated under different drilling conditions the analysis includes vibrations produced by teeth indention multilobed patterns bouncing with periodic and random effects single cutter forces stick slip and whirling effects mud pressure modulation forces and bit wear drill bit radiation properties are calculated using the results obtained in part 1 of this paper and are numerically compared to the radiation of conventional vertical seismic profiling vsp sources

characterization of a high transmissivity zone by well test analysis steady state case a method is developed to analyze steady horizontal flow to a well pumped from a confined aquifer composed of two homogeneous zones with contrasting transmissivities zone 1 is laterally unbounded and encloses zone 2 which is elliptical in shape and is several orders of magnitude more transmissive than zone 1 the solution for head is obtained by the boundary integral equation method nonlinear least squares regression is used to estimate the model parameters which include the transmissivity of zone 1 and the location size and orientation of zone 2 the method is applied to a hypothetical aquifer where zone 2 is a long and narrow zone of vertical fractures synthetic data are generated from three different well patterns representing different areal coverage and proximity to the fracture zone when zone 1 of the hypothetical aquifer is homogeneous the method correctly estimates all model parameters when zone 1 is a randomly heterogeneous transmissivity field some parameter estimates especially the length of zone 2 become highly uncertain to reduce uncertainty the pumped well should be close to the fracture zone and surrounding observation wells should cover an area similar in dimension to the length of the fracture zone some prior knowledge of the fracture zone such as that gained from a surface geophysical survey would greatly aid in designing the well test

numerical modeling and interpretation of drillstring waves drill bit seismic and pilot seismograms contain drillstring periodicities from signal and environmental noise sources these coherent components are similar in seismic while drilling correlations and their joint contribution may cause distortions in signal processing numeric modeling of the drillstring transmission line is used to correctly interpret the axial and torsional events with similar propagating modes of signal and noise the reflection coefficients are computed for drillstrings of arbitrary materials and their average mechanical features are related to the axial and torsional group velocities obtained by the dispersion equations fitting of the periodical components in the real seismograms is used to automatically correct the drill bit pilot delays and to estimate the surface and downhole boundary conditions

interferometry by deconvolution part 2 theory for elastic waves and application to drill bit seismic imaging deconvolution interferometry successfully recovers the impulse response between two receivers without the need for an independent estimate of the source function here we extend the method of interferometry by deconvolution to multicomponent data in elastic media as in the acoustic case elastic deconvolution interferometry retrieves only causal scattered waves that propagate between two receivers as if one acts as a pseudosource of the point force type interferometry by deconvolution in elastic media also generates artifacts because of a clamped point boundary condition imposed by the deconvolution process in seismic while drilling swd practice the goal is to determine the subsurface impulse response from drill bit noise records most swd technologies rely on pilot sensors and or models to predict the drill bit source function whose imprint is then removed from the data interferometry by deconvolution is of most use to swd applications in which pilot records are absent or provide unreliable estimates of bit excitation with a numerical swd subsalt example we show that deconvolution interferometry provides an image of the subsurface that cannot be obtained by correlations without an estimate of the source autocorrelation finally we test the use of deconvolution interferometry in processing swd field data acquired at the san andreas fault observatory at depth safod because no pilot records were available for these data deconvolution outperforms correlation in obtaining an interferometric image of the san andreas fault zone at depth

seismic interferometry with a tbm source of transmitted and reflected waves we discuss the use of autocorrelogram interferometry by using noise from the tunnel boring machine tbm the tbm provides seismic signals waves while drilling in a tunnel tswd the tunnel geometry unlike a reverse vertical seismic profile rvsp using a drill bit makes it possible to record the waves reflected from the region between the tunnel face and the projected tunnel exit and those transmitted ahead of the tunnel face we processed the waves recorded at back positions with respect to the tbm in a manner similar to a rvsp data set obtained by conventional reference correlation techniques we processed the waves transmitted ahead of the tbm using autocorrelogram interferometry techniques using these wavefields offers advantages over conventional borehole drill bit vertical seismic profiles vsps the most important advantage is getting reflections from the transmitted front wavefield by utilizing kunetz s equation and reversed time traces the approach also improves the analysis of the trans

seeing coal seam top ahead of the drill bit through seismic while drilling blast damage to the tops of coal seams due to incorrect blast standoff distances is a serious issue costing the industry in australia about one open cut mine for every ten operating mines the current approach for mapping coal seam tops is through drilling and pierce point logging to provide appropriate depth control with accuracy of 0 2 m for blast hole drilling it is typically necessary to drill deep reconnaissance boreholes on a 50 m x 50 m grid well in advance of overburden removal pierce point mapping is expensive and can be inaccurate particularly when the seam is disturbed by rolls faults and other obstacles numerical modelling and prototype field testing are used in this paper to demonstrate the feasibility of two seismic while drillingbased approaches for predicting the approach to the top of coal during blast hole drilling i reverse walk away vertical seismic profiling recording in which the drill bit vibration provides the source signal and the geophones are planted on the surface near the drill rig and ii in seam seismic recording in which channel waves driven by the coupling to the coal of the seismic signal emitted by the approaching drill bit are guided by the seam to geophones located within the seam in nearby or remote boreholes

drill bit displacement source model source performance and drilling parameters the emission properties of a drill bit source and the signature of the drill bit seismograms depend on the dynamic action of the drill bit which in turn is a function of the geological conditions rock properties and drilling parameters in fact drilling is a variable dynamic process in which the vibrations produced by the drill bit are transmitted into the drillstring and formation with a partition of energy determined by the impedances at the bit in this analysis we study drill bit performance and calculate the forces produced by an ideal drill bit to determine the variations in the signal signature and ultimately the conditions of source repeatability as a function of average drilling parameters and signal frequency the model includes near field effects and assumes the drill bit acts as a displacement source producing axial bit forces with relative bit formation displacement and vertical penetration in the formation the analysis shows that the expected bit signature which is equivalent to the ground force in vibroseis depends on average tooth impact area percussion frequency rate of penetration formation strength bit wear and downhole pressure in particular the results show that larger amplitudes of the axial forces are expected at a lower rate of penetration higher formation strength and lower formation pressure

vertical seismic profiling vertical seismic profiling is one of the rapidly developing areas of geophysical technology for exploring in mature basins the measurement basically involves recording the total upgoing and downgoing seismic wave fields propagating through a stratigraphic section by means of geophones clamped to the wall of a drilled well