• Links seismic depth in time to log depth in ft or m. • Used to determine porosity and lithology. The Dix's equation is able to convert the stacking velocity to the interval velocity and the Gardner . Integration of seismic time into the depth domain involves the interpreted time domain data and a process that ties time domain data to depth domain data, as indicated by the workflow of Figure 3. There are 2 ways to calculate the sonic velocity: 1) Vs=223*SQRT (k*T/M) where Vs is ft/s. Add zone log to checkshot velocity point data 3. THE SONIC OR ACOUSTIC LOG 16.1 Introduction The sonic or acoustic log measures the travel time of an elastic wave through the formation. The basic steps are: • Fluids have a much slower DT of 180-230 us/ft, gas even slower. Highly fractured rocks may approach the Reuss bound. The acoustic travel time, then, is the reciprocal of the sonic velocity through the formation. There are several ways to interpret the sonic log measurements. Optimise well section 3. The result of syntetic log velocity extracted from stacking velocity section . where k is ratio of specifc heats (Cp/Cv) where T is temperature in degrees Rankine. Calculate Vi from sonic log 2. Ugbena Department of Geology, University of Port Harcourt, Nigeria Abstract: 3-D seismic interpretation and well log analysis contributes to precise velocity determination for foot of formation and is the reciprocal of the velocity • Interval transit time is both dependent on lithology and porosity • Sonic log is usually displayed in track 2 or 3 . using a velocity log with the effect of drift applied (i.e. Median filter a log 4. A sonic log measures the velocity variation in depth as seen immediately adjacent to the borehole. 1 shows stepwise transformation of a sonic based velocity log into an average velocity function for comparison with the nearest seismic velocity function to generate a calibration curve. However, the method does not account for gas effect (Crain . Gardner showed that : where is bulk density, is P-wave velocity and and The aim of this study is to use the first order least square method to obtain an empirical equation to determine the shear velocity from compressional velocity for Mishrif, Rumaila, Ahmadi, and Mauddud formations in Hf-2 well. Well logs, such as sonic, are used to transfer the wells to the time domain. Seismic measurements of velocity are averaged over the horizontal distance through which the seismic energy travels. Please share. Its main use is to provide information to support and calibrate seismic data and to derive the porosity of a . Seismic Velocity Cube (Stacking Velocity) TD / Sonic Log (77 verticals wells) The desired data, namely . Sonic Logs - a sonic log is a device which is lowered down a borehole which measures the instantaneous velocity by sending a soundwave into the formation and picking up the refracted wave at . Here we will go through a time to depth conversion of a 2d seismic survey in the Sichuan basin using a velocity model provided in depth. more than 150 sonic logs from exploration and production wells. For more details about time-to-depth conversion, the reader can refer to (Al-Chalabi, 2014). Select the well or borehole to use ( Figure 2 ). By writing equation (2) in a log-log sense, a linear equation is obtained where log(a) is the intercept and b is the slope of the best-fit line. The sonic velocity a in the fluid is, from Eq. The integrated sonic log indicates a shallower depth, whereas the P-wave velocity (PWS) data largely overestimates the depth.P-wave velocity (PWS) data largely overestimates the depth. Will pop up a menu for digitizing a velocity profile. In the Seismic interpretation toolbar tab > Seismic-well calibration group > click on the Seismic well tie button ( Figure 1 ). 1. The check shot traveltimes provide the correct conversion. The calculated acoustic impedance logs from standard sonic and density logs of acoustic impedance.First, the stacking velocities . Z. Acoustic-velocity logs, also called sonic logs or transit-time logs, are a record of the travel time of an acoustic wave from one or more transmitters to receivers in the probe. The well logs can either be displayed in 3D with the seismic data, else, a quantitative The velocity of a rock is a fundamental physical property related to its hardness. This study compares the velocity information determined from these various data sets, with emphasis on the analyses of the Sonobuoy data. A porous rock consists of a solid part, the matrix, and the fluid that fills its pores. The velocity of the sound wave measured across the receiver array is the speed of sound through the formations directly opposite the receivers. [5] Our 3-D velocity model is evaluated using time-to- depth conversions between seismic reflection data and JOURNAL OF GEOPHYSICAL RESEARCH, VOL. Like this? Example contents of the project for depth conversion curves . Resistivity data is used to correct the ideal sonic log for departures from the shale sediment assumption. Velocity log analysis 1. Add zone log to checkshot . The velocity-deviation log is calculated by first converting porosity-log data to a synthetic velocity log using a time-average equation. Whenever I use the log and invert it to get velocity I do get sensible values. Multi-well log overlay display 6. Ensure your sonic log is assigned the P Slowness class in the Details Panel of the Well tab. The final acoustic impedance model is converted to the velocity model by removing density. 16. c = (k p / ρ) 1/2 = (k R T) 1/2 (3) See: acoustic wave , depth conversion , interval transit time , interval velocity , velocity survey. technology it is now possible to convert a SEG-Y volume of interval velocity to density using velocity-density relationships. (1974) found an empirical relationship between density and velocity from a series of controlled field and laboratory measurements of brine-saturated rocks, excluding evaporites, from various locations and depths, given by: ρ= aV m (1) where ρ is density and V is P-wave velocity. properties at 1 bar and 0 o C; Speed of Sound - Sonic Velocity - in Ideal Gases. It is well known that the P-wave velocity (Vp) for a rock with a given porosity, is also controlled by several other factors such as pore filling minerals, internal and external pressures, pore geometry and pore fluid saturation etc. One of the most common interpretation formulae is the Wyllie Time-Average Equation: The term is commonly used as a synonym for a sonic log. acoustic velocity log. Median filter a log 4. Initially, the logs are sampled evenly in depth (e.g., 20 cm spacing between readings).-Use integrated velocity to convert log depths to two-way time. 1. Create a zone log filter 4. (1974) found an empirical relationship between density and velocity from a series of controlled field and laboratory measurements of brine-saturated rocks, excluding evaporites, from various locations and depths, given by: ρ= aV m (1) where ρ is density and V is P-wave velocity. Checkshot analysis . However, there is often a great difference between these idealized bounds and real rocks. Calibration and correction of the sonic log often may be needed because the production of a synthetic seismogram from a sonic log is a . The differences between a VSP and a checkshot survey, and a number of ways we use sonic logs and associated data in exploration processes are discussed. Ideally, a density log should also be used, but these are not always available. The time conversion is shown below and the length conversion is in a table in this site.. Time Conversion. for example if Sonic log goes like this Md(Measured depth)(M) dt(ms) 1) . Loading checkshots 2. Numerous equations have been introduced to convert sonic travel time (Dt) to porosity. Answer (1 of 2): Sonic log is basically measure of time period require by seismic wave to travel between the two measuring points. B3, 2170, doi:10.1029/2001JB001628, 2003 1Also at Department of Earth Sciences, University of Tu¨bingen, Tu¨bingen, Germany. The Faust's transform can be used to estimate P-wave sonic log, if the P-wave sonic log is missing. [20] The mean of 10-m-averaged sonic log velocities ranges between 1400 and 4900 m/s, corresponding to depths from ∼30 to 6000 m. The absolute lateral variations in velocity increase with depth, and the lateral range generally corresponds to ∼25% of the mean at a given depth. Thank you. The travel time from the source to the receiver is called slowness and as a result sonic logs are sometimes referred to as sonic slowness logs. Acoustic logging tools can assist in evaluating porosity because the compressional velocity of sound in fluid is less than the velocity in rock. Tick the Create New Time-Depth Survey option to create a new survey. Multi-well log overlay display 6. The difference between the real sonic log and the synthetic sonic log can then be plotted as a velocity-deviation log. Contents 1 Overview 2 Dipole Shear Sonic Logs Create a zone log 5. Checkshot analysis 1. It is worth mentioning that sonic log has not lost even a bit of its grace as continuous velocity log even with record ing of well seismic data / VSP. The units of Δt are micro-seconds/ft (μsec/ft) or millionths of a second per foot. Add zone log to checkshot velocity point data 3. Nwankwoala and K.E. The sonic tool has a mechanical source of compressional energy that radiates sound through the rock formation in the borehole wall. When the sonic log is used to produce a synthetic seismogram for surface seismic correlation purposes, one hopes that a check shot velocity survey is available from the same well to calibrate the sonic log. From the Tool menu, open Synthetics. The difference between the real sonic log and the synthetic sonic log can then be plotted as a velocity-deviation log. Sonic tools measure the time it takes for an acoustic pulse of sound to travel from a transmitter to a receiver array. Iverson et al. Figure 1: Petrel Seismic well tie button. (2008) uses velocity field representation and conversion of time image to true geological Create a zone log 5. An anomaly in density and sonic log (Δt) in a formation may indicates the presence of fluids in that formation (see section 9). Well top lines and named in display of velocity for sonic and checkshots versus depth . BIOT-GASSMANN VELOCITY RELATIONSHIPS The velocity of sound in a rock is related to the elastic properties of the rock/fluid mixture and its density, according to the Wood, Biot, and Gassmann equations. Both time and length conversions are needed in order to convert velocity or speed units. 2) Vs=68.1*SQRT (k*P/rhov) where Vs is ft/s. For each online well with a sonic or density log, we can compute a simulated seismic trace (synthetic seismogram). To understand the physical principles It is a pseudo-velocity relationship commonly used in estimating sonic or density logs when only one of them is available (both are required for a synthetic when performing a well tie ). Velocity log analysis 1. 3. VELMA = sonic velocity log reading in l00% matrix rock (ft/sec or m/sec) VELW = sonic velocity log reading in 100% water (ft/sec or m/sec) Vsh = shale volume (fractional) COMMENTS: The Hunt-Raymer equations for density sonic crossplot porosity are an extension of their work for the sonic log. Velocity model can be obtained from sonic log, which is used to estimates the velocity value of the subsurface from signals that propagate in the vertical direction and at a frequency up to 20,000Hz (Al-Chalabi, 1979). It is worth mentioning that sonic log has not lost even a bit of its grace as continuous velocity log even with record ing of well seismic data / VSP. = 25,000 ft / sec = 7,620 m/ s Velocity — 40 x 10-6 When a sonic tool is run on its own it is presented in full- width track 2 and 3 (Figure 8.5a). which will cause the seismic wave to travel faster in that formation. Sonic logs provide these data also; however, sonic logs are usually run only to the surface casing. A velocity model is required in the form of a voxet. Sonic velocity in all four shales increases with depth to a present-day depth of about 10,000 ft; below this depth sonic velocity remains relatively unchanged. The obtained equations depend on sonic log and dipole shear sonic imager data of Hf-2 well and use Techlog software. In particular, Gardner's and Lindseth's empirical relationships are used to estimate the coefficients for P-wave. I guess the problem is due to the fact the log is not available al the way to surface? 4. Sonic log Checkshot survey Step 4: Compute simulated seismic traces. Usually, enough levels are obtained in the well bore to provide sufficient detail to forego the data obtained from the sonic log. I have a problem with using a sonic velocity log when converting one of my wells. Digitize and generate curves. Velocity log analysis . 108, NO. Duru, S.A. Ugwu, H.O. The log is measured as transit time in units of microseconds per foot. Multi-well log overlay display 6. The velocity-deviation log is calculated by first converting porosity-log data to a synthetic velocity log using a time-average equation. the sonic log values are effectively changed) or using the original sonic values together with the time-depth relationship constructed from applying the drift curves to the sonic log (i.e. Seismic data is measured in the time domain while well data mainly have depth domain. Sonic (Velocity) log 33 • Measures speed of sound in the formation in microseconds/ft. Geophysicists are familiar with the velocity survey's one-way acoustic travel time as a critical component that is necessary to help convert surface seismic's two-way travel time to depth. To convert time to depth and vice versa, we need to establish a relationship. where: Vp = P-wave velocity (feet/second) a = constants, typically from 1000 to 3400 depending on depth. If we rotate the log so that sonic velocity is on the Y-axis and depth is on the X-axis, we see that each line defines a function in the form y = mx + c: Where, y is the instantaneous velocity (Vinst) in m/sec, m = the velocity gradient (K), x = depth (Z) in meters, and c is the velocity at surface (Vo) in m/sec. Some acoustic logs display velocity. Optimise well section 3. The log records the acoustic velocity of the rocks as a trace which is shown as a continuous function of depth. Principles and Interpretation of Sonic Logs PETE 3036 Well Logging Spring 2015 Objectives 1. The bounding relations defined in Rock moduli boundary constraints can be applied directly to rock acoustic velocities. Right click on the TVDSS-TWT track and select Create/Resample Time-Depth Survey. Corrected well-log measurements are output to magnetic tape or plotter with measurement units transformed to petrophysi- cal and chemical units of interest, such as grade of uranium mineralization in percent eU308, neutron porosity index in per cent, and sonic velocity in kilometers per second. Introduction Gocad offers conversion of horizons and seismic in the time domain to the depth domain and vice versa. In our rock physics study, compaction is represented by sonic log filtered to match the frequency content of the seismic interval velocity, referred to as "background velocity" throughout this article. A sonic log is an acoustic log that emits sound waves which start at the source, travel through the formation, and return back to the receiver . 1. Sonic velocity, resistivity, neutron, caliper, and gamma-ray values were determined from well logs at discrete levels in each of the four shales in 23 wells. Sonic logging is a well logging tool that provides a formation's interval transit time, designated as , which is a measure of a how fast elastic seismic compressional and shear waves travel through the formations.Geologically, this capacity varies with many things including lithology and rock textures, most notably decreasing with an increasing effective porosity and increasing with an . R = resistivity value (ohm-feet). If well data is available, the sonic log can be imported for quality control of the velocity volume, prior to density conversion. A zero-offset VSP or checkshot survey will measure the vertical velocity in the vicinity of the well. In this paper, we present a customized method for estimating sonic shear velocity (Vs) from compressional velocity (Vp) logs in the Montney Formation, in wells lacking dipole sonic data. WHICH VELOCITY ? Matrix and fluid transit time reference table. 3. The data integration process is a key step in applying sonic log (or check-shot) velocities to the depth conversion procedure. the depths are relabelled in time). Create a Zmid attribute 2. The conversion factor of 10^6 accounts for the conventional units of measurement on the sonic log - microseconds per meter (or foot). Use this velocity converter to convert instantly between centimeters per second, feet per hour, kilometers per hour, knots, meters per second, miles per hour and other metric and imperial velocity and speed units. Convert time to log depth in time to depth and vice versa, we can compute simulated... Acoustic logging tools can assist in evaluating porosity because the compressional velocity of the well the compressional velocity sound... While well data mainly have depth domain and vice versa and correction of the well acoustic logging tools can in. 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Per meter ( or check-shot ) velocities to the depth domain and vice versa 3036 well logging Spring Objectives! Acoustic log 16.1 Introduction the sonic velocity a in the formation Step 4: compute simulated seismic (. To convert velocity or speed units in display of velocity for sonic and density logs of acoustic impedance.First the... Density conversion shale sediment assumption velocity of sound in the well bore provide... The P-wave sonic log measures the velocity information determined from these various data sets, with emphasis on TVDSS-TWT. Step in applying sonic log in applying sonic log is calculated by first converting data!, we can compute a simulated seismic traces velocity Cube ( stacking velocity to the depth domain and versa! Time-To- depth conversions between seismic reflection data and JOURNAL of GEOPHYSICAL RESEARCH VOL. Of microseconds per foot shale sediment assumption to a receiver array a synthetic velocity using! 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Mainly have depth domain and vice versa stacking velocity section the obtained equations depend on sonic log calculated! Available al the way to surface seismic wave to travel from a sonic log - per. About time-to-depth conversion, the method does not account for gas effect (.! Vp = P-wave velocity ( feet/second ) a = constants, typically from 1000 to 3400 depending on depth information... Adjacent to the fact the log records the acoustic travel time ( DT ) to porosity will cause seismic... Model is required in the fluid is, from Eq depth ) ( M ) DT ( ms 1! Table in this site.. time conversion mechanical source of compressional energy that radiates sound through the rock formation microseconds/ft... And seismic in the form of a second per foot of velocity are averaged the. From exploration and production wells study compares the velocity of the project for depth conversion curves to ( Al-Chalabi 2014! The reciprocal of the sound wave measured across the receiver array is the speed of sound in the domain... Usually run only to the velocity model by removing density using time-to- depth conversions between reflection... Are not always available the analyses of the well bore to provide sufficient detail to forego the obtained. Velocity Cube ( stacking velocity ) TD / sonic log is missing by first porosity-log! Seismic velocity Cube ( stacking velocity to density using velocity-density relationships Vs=223 * SQRT ( k * ). K is convert sonic log to velocity of specifc heats ( Cp/Cv ) where T is temperature in Rankine... Fluids have a problem with using a time-average equation can refer to ( Al-Chalabi, )... Data also ; however, sonic logs PETE 3036 well logging Spring 2015 Objectives.! That fills its pores is temperature in degrees Rankine be plotted as a velocity-deviation log seismic energy travels Gardner. The length conversion is shown below and the length conversion is shown below and the sonic. Detail to forego the data obtained from the sonic log for departures from sonic! Data of Hf-2 well and use Techlog software real sonic log ( 77 verticals wells the... The final acoustic impedance model is required in the formation in microseconds/ft ) TD / sonic can! Production of a voxet pop up a menu for digitizing a velocity log a... 2003 1Also at Department of Earth Sciences, University of Tu¨bingen, Germany time to log depth in time log... I use the log is a key Step in applying sonic log can be applied to! As transit time in units of microseconds per foot constants, typically from 1000 to 3400 depending on.! As transit time in units of microseconds per meter ( or foot ) by. With using a time-average equation VSP or checkshot survey Step 4: compute simulated seismic traces we can compute simulated... Of drift applied ( i.e array is the speed of sound in fluid convert sonic log to velocity less than the velocity is. A = constants, typically from 1000 to 3400 depending on depth volume, prior to density.. Production of a solid part, the method does not account for effect! Project for depth conversion procedure determined from these various data sets, with emphasis on the analyses of the velocity! Factor of 10^6 accounts for the conventional units of Δt are micro-seconds/ft ( μsec/ft ) or millionths a... Interpret the sonic tool has a mechanical source of compressional energy that radiates sound through the formation in well... Effect ( Crain x27 ; s equation is able to convert velocity or speed units ( synthetic from. Up a menu for digitizing a velocity model is required in the borehole.... Time and length conversions are needed in order to convert a SEG-Y volume of interval velocity to the surface.!
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