The process of transforming seismic data from a scale of time the domain in which they are acquired to a scale of depth to provide a picture of the structure of the subsurface independent of velocity. The relevant physical properties, namely the thermal conductivity. Depth conversion is an important step of the seismic reflection method, which converts the acoustic wave travel time to actual depth, based on the acoustic velocity of subsurface medium sediments, rocks, water depth conversion integrates several sources of information about the subsurface velocity to derive a threedimensional velocity model. Chen, 2018, datadriven timefrequency analysis of seismic data using nonstationary prony method. To remove structural errors inherent in time migration, it is necessary to convert timemigrated images into the depth domain either by mi grating the original data. This is a case study and gives the practical approach for velocity modeling which can be further utilized for time to depth conversion. Velocity modelling and depth conversion uncertainty analysis of onshore reservoirs in the niger delta basin. In this process, the wells were tied to the seismic in depth with the depth converted seismic using the velocity model, which was generated using the smoothed 30 hz fwi model. Timetodepth conversion and seismic velocity estimation using time. Get an optimal initial model for inversion and accurate uncertainty maps and volumes. Velocity modeling estimages geostatistics for geophysics. In this video you will learn the different methods for depth conversion. Pdf the objective was to build an efficient algorithm 1 to estimate seismic velocity from timemigration velocity, and 2 to convert timemigrated. Hence, we use the dix velocity instead of timemigration velocity as a more convenient input.
Depth conversion is the process by which interpreted seismic horizons and time domain seismic itself are converted from the travel time domain to the depth. Fomel, 2018, fast timetodepth conversion and interval velocity estimation with weak lateral variations. Oil and gas consultant scott mackay is an independent consultant with 35 years of experience. Pdf seismic velocity estimation and time to depth conversion of. Time to depth conversion and uncertainty characterization. Only 3d local geostatistics combined with a geological expertise can feed a velocity model with high resolution 3d heterogeneities, thus leading to minimum depth errors.
Seismic velocity estimation and timetodepth conversion. Panorama technologies chapter 6 prestacktimeanddepth migration prestackmigrationalgorithmsarerelativelysimplevariantsofthepoststack methodologies. A good approach to depth conversion, especially in a complex geological environment, is first to perform a depth migration with a velocity model optimized for structural imaging, second to render the resulting laterally positioned depth image to time using the provelocities, and finally to convert the depthmigrated seismic data now in the. How it works timedepth conversion dug insight 4 user. How are seismic signals from a particular period of time transformed in depth. Pdf summary we address the problem of time to depth conversion of time migrated seismic images and show that the dix velocities. Pdf velocity modelling and depth conversion uncertainty. Geo expro a simple guide to seismic depth conversion ii. It makes use of the twt and depth information from checkshot, calculates velocities at wach checkpoint depth and uses this. A depthtime conversion would be required before inversion of depthdomain seismic data, which would depend on an accurate velocity model and a fine timedepth conversion algorithm. The interpreters guide to depth imaging by scott mackay. The relation between the residual anomalies and the depth of the subterranean masses is examined. Unlimited viewing of the articlechapter pdf and any associated supplements and figures.
In the case of a laterally homogeneous medium, the conversion from time to depth is provided by the classic dix method dix, 1955. A timetodepth velocity conversion can be done by rst applying the dix inversion tccs8. The topic outlines how seismically derived velocities can be used with sparse well control, identifies two methods that can be used when exploration objectives require a reliable depth conversion algorithm, and explains how interval stacking velocity maps are used to extend values obtained from area wells. Velocity interpretation and depth conversion petroleum. Depth conversion and seismic inversion of the scarborough. Pdf timetodepth conversion and seismic velocity estimation. Fast timetodepth conversion and interval velocity estimation in the. In order to create a reservoir model or compute volumetrics, these time interpretations need to be converted to depth and calibrated to well markers. A robust approach to timetodepth conversion and interval velocity. Velocity modeling petrel workflow polynomial equations. Tom wilson, department of geology and geography time seconds 0. Depth conversion of 3d post stack seismic migrated time. A simple linear regression model has to be constructed to translate the seismic data picked in the time domain external drift to a smooth trend model in the depth domain. If such procedures are to be applied after a depth imaging project has been conducted, it is necessary to convert the data to the time domain from the depth domain.
The combination of the interval velocity maps from step c with the depth horizons from step d constitutes the initial model derived from timetodepth conversion. Seismic reflection methods environmental geophysics us epa. The time required for the seismic signal to travel from its source to a reflector and back is known as the twoway travel time, and. To convert from time s to depth ft you must know the velocity of the material. Switch to depth mode in time interpretations and convert time scene to depth, onthefly. Seismic velocities and depth conversion level skill 510 years experience instructor scott mackay mackay consulting corporation, inc. Timedomain processing has a long history in seismic imaging and has always been. In contrast, if you export the volume, it must be actually resampled onto the requested export sample interval. We have met experts in reservoir characterization and geophysics, debated with our consortium partners and, point by point, decided which methodologies and what parameters a user would need to have full control of for the time to depth conversion.
Themes why geophysics uses fourier analysis when earth material properties are constant in any of the cartesian variables t,x,y,z then it is useful to fourier transform ft that variable. Conversion felix obere this presentation includes forwardlooking statements. Time horizons are map migrated to depth one layer at a time, through a developing depth model. A simple guide to the parameters involved in seismic depth conversion a complex but important subject in geophysical seismic processing. Depth conversion, ideally, is an iterative process that begins with proper seismic processing, seismic velocity analysis and study of well data to refine the conversion. Seismic reflection data records the twoway travel time twt to a reflection event from the surface. Function 2nd order polynomial function this is the basic timedepth conversion methodology. This course will teach you how to use velocity information and structural inputs to build a consistent velocity model andor calibrate ones that have been created during seismic data processing. Uncertz consortium time to depth conversion evolved. Depth conversion as well ties in time did not adequately resolve the residuals between the seismic and the wells, an iterative process of well ties in depth was employed. The influence from masses at a greater or lesser depth is almost. A simple guide to seismic depth conversion i geo expro.
Here, i consider the situation of having performed an anisotropic tilted transverse isotropy tti presdm. Actual future conditions including economic conditions, energy demand, and energy supply could differ materially due to changes in technology, the 1 development of new supply sources, political events, demographic changes, and other factors discussed herein and in item 1a of exxonmobils latest. A small mean residual difference indicating an unbiased depth conversion and a low standard deviation meaning the method explains the depth quite well are indications of a. Optimize your timetodepth conversion, at a prospect or a regional scale. Depth conversion is the process by which interpreted seismic horizons and time domain seismic. Qc your velocity data with a variety of velocity qc tools and visualize data from velocity models on seismic sections.
W7 well logs and synthetic seismograms, seismic well calibration 10. Depth penetration of gpr is severely limited by attenuation andor absorption of the transmitted. Residual anomalies and depth estimation geophysics. Therefore, conversion from time to depth is needed for a clear picture of the prospect and the risks involved. Approximating a seismic horizon timedepth conversion using a twovelocity layer approach in seisworks frequently in industry you will want to display a horizon map in depth ft instead of the landmark seisworks default, which is twoway time twt.
Image ray in left the depthdomain can be traced with a source at location x 0 with slowness vector normal to the earth surface. Also, you can visit our facebook page and group at. Timetodepth conversion geological structures are picked from seismic profiles in the time domain. Timetodepth conversion and seismic velocity estimation. Jones abstract many data processing and interpretation procedures are performed on time domain data. The residuals are the difference between the depth predicted by the velocity model using the seismic time at the well marker and the actual depth observed in the well. Traps and prospects conversion to depth complete the. The problem of conversion from timemigration velocity to an interval velocity in depth in the. Each of these options requires converting the time migration velocity to a velocity model in depth. In seismology, the earth does not change with time the ocean does. Seismic velocity estimation and timetodepth conversion of time. The timedepth conversion is exact to the limit of your screen resolution.
Fathometers determine water depth by repeatedly transmitting seismic energy through the water column and recording the arrival time of the reflected energy from the water bottom. Interpret a set of time horizons from an image volume derived from time migration. Relationship between pointshaped scattering body and diffraction hyperbola, kirchhoff migration principle. Abstract contemporary depth imaging projects often require final prestack depthmigrations presdm to be converted to time for comparison to vintage prestack timemigrations prestm, or to facilitate conversion to geological depth through calibration to well and checkshot data. Easily incorporate geophysical and geological interpretations into a single consistent subsurface model.
The timetodepth conversion strategy involves the following steps. A depth variant seismic wavelet extraction method for. Thus, it could be beneficial that we can directly invert the depth migrated seismic data. Dynamically build velocity models by tying your well and seismic data. Ability to view your data in either depth or time domains. A robust approach to timetodepth conversion and interval. The course focuses on intuitive quality controls and quantitative spreadsheet tools to plan and ensure stable depth solutions during the. Geo expro a simple guide to seismic depth conversion i. Hence, as you zoom in closer, it will interpolate the converted data at ever increasing levels of detail. Approximating a seismic horizon timedepth conversion.
1002 1394 934 424 362 916 581 919 936 389 1297 292 167 317 592 364 267 1497 241 616 400 682 1137 1029 213 1019 1002 847 1132 652 719 577 1477 1067 885 556