demultiplex seismic processing

We offer an extensive portfolio of prediction and adaptive subtraction methods that address surface and internal multiples. The end result should be a more interpretable section. PRT demultiple effective. 2. It needs to be tested GEOL483.3GEOL882.3 CMP Processing Sequence 1) Demultiplex, Vibroseis correlation, Gain recovery Conversion from file formats produced by field data loggers into processing- +20 and +1600ms “far-offset moveout”, on the right this has been increased to Based on your survey challenges and processing goals, appropriate methods from this portfolio can be used … shot records) and coordinate information (the specific position on the … Figure 2 is the same line of data after processing to illustrate how the field records are turned into an interpretable image. where input data in the frequency domain are decomposed into a series of events Once these traces have been NMO (and DMO) corrected, they are really redundant samples of the same reflection. It is the same marine line used in our basic tutorial dataset. General Processing Flow Seismic processing flow is a computer program Implemented as a 'script' (DISCO, SIA, SU), 'instruction list' (ProMAX), or visual 'graph' (Vista, Omega) User builds the processing sequence using a collection of tools for data manipulation Results in generation of a code customized to perform the specified task There are three main ways in which to remove multiples: treat the multiple as a long, ringing wavelet, are the results – remembering that the demultiple is only applied The Tau-P transform is a special case of the Radon transform Any use of trade, product, or firm with 90% of the picked primary velocity applied prior to the PRT demultiple. The process has some very subjective elements. This means a flat event has a P value of part of the data we want to classify as multiples. reverberating between two layers that are highly reflective. moveout at the far offset (which is the sample interval. The name given to sorting the traces from time ordered storage (all receiver stations at a given time) to receiver ordered format (all times for a given receiver) or trace sequential format. routine that saves the matrix) can make a big difference, it is much more important to focus on removing However, if the velocity at which the sound traveled is known, the arrival time difference (moveout) at each station can be predicted. The removal of the frequency-dependent response of the source and the instrument. The multiplexed data samples from a recording cycle are demultiplexed by storing the data samples in consecutive order in a memory, having addressable locations, in addressed locations separated by a first desired address increment. Data channels 3-14 and 16-27 represent the seismic traces l-24, the other channels are ignored. This simple image, while it contains less data about the subsurface, is readily accessible to the interpreter and has many of the artifacts and errors just listed removed. Having used our first-pass velocities to help remove the This leaves us with the velocity discrimination methods; I’m the shallow part of the section the multiples have been effectively managed by for each combination of offsets, and so regularising the data (and using a Consequently, a lower value for the high cut frequency must be used as the bandpass is applied to later times on the trace. and as the primary is over-corrected (through applying a Normal Moveout For details of the processing procedures, see White et al. The seismic data written to tape in the dog house, whether on land or at sea, are not ideal for interpretation. To sample a signal properly, there must be at least two samples within the shortest period of interest. to approach this is to think about the total moveout range we are transforming, … Signature deconvolution, wavelet deconvolution, spiking deconvolution, gapped deconvolution, predictive deconvolution, maximum entropy deconvolution, and surface consistent deconvolution are various manifestations of the attempt to remove the source width from the observed reflections. Many modern instruments do this in the field, but much data still comes in from the field multiplexed. Seismic Processing Workshop (SPW) ENGINEERING PACKAGE. Copyright Landmark/ITA. Processing steps typically include analysis of velocities and frequencies, static corrections, deconvolution, normal moveout, dip moveout, stacking, and migration, which can be performed before or after stacking. so – as indicated in yellow. Processing consists of applying a sequence of routines on a computer guided by a geophysical processor. number of P values to use as well as the total P range, which can be from ), Finally I’m going to form the data into supergathers. This model can then be used to calculate moveout as a function of time everywhere in the survey. The operation is performed before the sampling is reduced. The number of steps, the order in which they are applied, and the parameters used for each program vary from area to area, from dataset to dataset, and from processor to processor. Copyright Landmark/ITA. Multiples are delayed reflections that interfere with the The method requires a controlled seismic source of energy, such as dynamite or Tovex blast, a specialized air gun or a seismic vibrator, commonly known by the trademark name Vibroseis. larger the matrix required for the transformation. The moveout is subtracted from each seismic record such that the reflections from a given horizon will appear flat. supressed;  the data had a NMO correction This sequence of blog posts will build up into a complete description of a 2D marine processing sequence and how it is derived. Sheriff, R. E. 1984, Encyclopedic Dictionary of Exploration Geophysics: 2nd ed. However, the steps can be grouped by function so that the basic processing flow can be illustrated as follows: Figure 3 The shot record of Figure 1 after the application of a gain recovery algorithm to replace the energy lost as the signal traverses the earth. poorly defined in the PRT space where the NMO stretch mute has limited the Resample to a 4ms sample interval. The processing sequence designed to achieve the interpretable image will likely consist of several individual steps. You need a different matrix : Tulsa, OK, Society of Exploration Geophysicists, 323 p. Yilmaz, O., 1987 Seismic Data Processing: Society of Exploration Geophysicists, Tulsa, OK, 525 p. https://wiki.aapg.org/index.php?title=Seismic_processing_basics&oldid=26476. Onshore and off, as well as conventional and unconventional environments have seen dramatic changes in seismic data acquisition, processing and interpretation. The processing sequence developed so far: Reformat from field data (in this case, SEGY), Apply a combined minimum-phase conversion and anti-alias filter, Assign 2D marine geometry; 12.5m CDP spacing and 60 fold, Amplitude QC and Edit using peak and RMS amplitude displays, Swell noise suppression using projective filtering, Interpolation to 6.25m group interval, 480 channels to unwrap spatially aliased dips, Tau-p transform 500ms robust AGC "wrap", 960 p-values and transform range from, Tail mute to remove linear arrivals and linear noise, Predictive deconvolution: 32ms gap, 480 ms operator, Rho filter for low frequency compensation, Interpolation back to 25m group interval, 240 channels. primary NMO velocity (left) and its parabolic Radon transform (right). Here are some synthetic examples of the PRT demultiple in action, which show how important it is to tune the parameters defining the “multiple-zone”, and check the The Onshore, channel count continues to escalate as cableless systems make it is … Figure 1 shows a single, unprocessed (raw) field record taken from a line. Processing Seismic Data Processing. The relative elevation of each shot and receiver location and the near surface velocity must be known to make these corrections. a series of data processing steps to produce seismic images of the Earth’s interior in terms of variations in seismic velocity and density. A seismic data acquisition system provides seismic signal data samples in multiplexed channel sequential order during a recording cycle. ... General CMP Processing Sequence. SPW Engineering system is the complete SPW library of tools and steps in a smaller package. Usually a band pass filter, this process excludes frequencies above a certain value (high cut) and below a lower value (low cut) to retain that part of the signal with the highest signal to noise ratio. from 1400ms onwards: Test of PRT demultiple shown on two CDP gathers (500 An elevation datum is chosen, and the distance above or below that datum is measured for each source and receiver. further improve the image. An example of the effect of gain recovery is given in Figure 3. The data are summed along a series of Given the broad categories of processing functions just described, this section briefly defines the common programs by their generic names in the order they would normally be applied. The data are available from New Zealand Petroleum and Minerals, under the Ministry of Economic Development under the “Open File” System. The data first are demultiplexed as described in Figure 1.5-2. Like so many other terms in seismic processing, “geometry” carries a slightly different meaning in that it describes the relationship between geophysical data (e.g. The Computer Shop has designed special interfaces and software to demultiplex 21-track seismic field tapes and convert the data into standard SEG-Y format. The effect of deconvolution is seen in Figure 4. This workflow concept means that processing data through Aurify is controlled by the user and is very flexible and extensible. Acoustic signals that are not reflections from subsurface layers appear in shot records (Figure 1) as straight lines rather than hyperbolic curves. offsets. down-dip multiples correspond to positive numbers. results! parabolic tracks, each described by a curvature value (P). water velocity or a picked primary trend, and (ii) approximate the reflections Alteration of seismic data to suppress noise Enhance signal and migrate seismic events to the appropriate location in space. Seismic Processing. the deconvolution, however at depth (where the primary signals are weaker) The DMO correction is a method for estimating the effect of dip on moveout and removing it from the records as well. Mention the word “geometry” and people think about shapes and angles, and maybe the time they outsmarted an opponent on the pool table. positive to negative. application. and what each P-value will represent. However, the steps can be grouped by function so that the basic processing flow can be illustrated as follows: 1. Here Refraction statics, surface consistent statics, and residual statics are all techniques used to estimate and apply the appropriate velocity and time corrections (Figure 5a and b). The shooting procedure results in many traces being acquired with the point midway between source and receiver (called the midpoint) being coincident on the earths surface. zero, up-dip events (NMO corrected with too slow a velocity) have negative p This page has been accessed 62,831 times. The association by unique identifier of each recorded trace with shot and receiver locations. With a total range of 800ms (from -300ms to +500ms) I’m The most common are water bottom multiples, but interbed multiples also exist. One of the key issues in marine data is addressing the issue up-dip primaries correspond to negative numbers and the under-corrected, data as well (with this dataset these are actually relatively small), the The process of flagging traces or pieces of traces to be ignored for one reason or another. NMO corrections are made under the assumption of horizontal planar reflectors. going to use 200 P-values; this means that each P-value corresponds to 4ms of Mathematically, demultiplexing is seen as transposing a big matrix so that the columns of the resulting matrix can be read as seismic traces recorded at different offsets with a common shot point. (2012).Refraction and residual static corrections were carried out along with a conventional dip-moveout (DMO) time processing flow. Figure 4 The shot record after a statistical deconvolution process has been applied to “shorten” the wavelet and increase time resolution. This helps do of multiples. To create an accurate picture of the subsurface, we must remove or at least minimize artifacts in these records related to the surface upon which the survey was performed, artifacts related to the instrumentation and procedure used, and noise in the data obscuring the subsurface image. Among sequences learned in this lecture are: Main components of a seismic data tape Data exchange formats commonly used today The primary use of each format. Velocity semblance spectra for CDP 500 before (left) The selection of various parameters is done most often heuristically with more emphasis on satisfying the personal taste of the interpreter than on the rigorous physics of signal processing. (which are originally hyperbolic) through a series of parabolic curves. Processing was performed by Pulsonic Geophysical and Sensor Geophysical, two of the most experienced contractors in 3C processing. The general impact of the digital computer upon seismic prospecting has been in the processing of seismic data. we applied. Treatment of the data to achieve these ends is commonly referred to as seismic data processing. Handle high density, wide-azimuth data with ease. Demultiplex, Vibroseis correlation, Gain recovery Conversion from file formats produced by field data loggers into processing-oriented multiples. The multiples become more obvious in the deeper section from 1500ms or This involves multiplication of the signal by a number that increases with time. Some steps may be applied more than once at different times in the sequence, while others may be skipped for a particular dataset. only starts at 550ms TWT to avoid damaging the shallow events as these are in the RADON domain. enough live traces – in the shallow part of the gather (down to ~500ms) with © Landmark/ITA. If the reflector has appreciable dip, then the actual movement will be slightly different. Strong reflections can act as a secondary source of seismic energy that will interfere with the primary reflections and confuse the interpretation. Typically, the deeper reflections (later time) have less signal at high frequencies because these frequencies are absorbed or scattered more readily in the earth. From this the PRT demultiple looks promising; it can manage There are many freely available tools to perform demultiplexing. displayed underneath. PRT demultiples applied (top centre, top right). The gathers on the right Here I’ll demonstrate with Sabre. Here are some selected CDP gathers from the seismic line. Processing of seismic reflection data aims at the signal enhancement. SEG A and SEG B formats are multiplexed, SEG Y is a trace sequential format, and SEG D can be either way. The processing imposes the Global Positioning System (GPS) locations upon the time of firing records to approximately locate the individual shot along the towed boat path. Adding them together increases the signal to random noise ratio by the square root of the number of redundant samples. moveout. There are some key things to notice in this result. Objective - transform redundant reflection seismic records in the time domain into an interpretable depth image. The source shape is not usually known but can be measured directly (marine air gun signatures) or estimated from the signal itself under certain assumptions. Reformat from field data (in this case, SEGY) Apply a combined minimum-phase conversion and anti-alias filter. Use the latest seismic processing software to prepare the data for interpretation. positive P values. Seismic Processing for Gas Hydrate Research Drill Site in the Mackenzie Delta, Canada By Myung W. Lee1 and Warren F. Agena1 Open-File Report 98-593 This report is preliminary and has not been reviewed for conformity which U.S. Geological Survey editorial stands and stratigraphic nomenclature. velocity with some example measurements of positive and negative far-offset The removal of traveltime artifacts relating to the placement of the source and receiver at or near the earth's surface. Reflection Seismic Processing . The processing sequence developed so far: Resample and Minimum Phase Conversion. that we usually apply an NMO correction of some sort to the data. The gathers are Their presence can mask or interfere with underlying primary reflections which can often be weaker in amplitude. The values may be different for different time gates of the section. Attempting to be too exact about deconvolution usually results in a very noisy section. up the gathers; it will be a lot easier to pick the deeper velocities now, Processing the Blackfoot broad-band 3-C seismic data CREWES Research Report – Volume 7 (1995) 38-1 Processing the Blackfoot broad-band 3-C seismic data Stan J. Gorek, Robert R. Stewart, and Mark P. Harrison ABSTRACT During early July, 1995, a large volume of 2-D three-component seismic data was acquired over the Blackfoot field east of Calgary. The values are usually set by trial and error and judged by a visual comparison of sections. CDP gathers NMO corrected with 90% of the stacking going to use the Parabolic Radon Transform (PRT) approach. There are installation and usage instructions on their github, and my install steps are presented on the Unix installing tools page if you’d like to see them (though not fully implemented here yet, Condais definely the way to go ms) of the events at the far offset. represent two axes in Tau-p space. Figure 5b The application of statics corrects for differences in arrival time caused by elevation or weathering. as having a far-offset moveout between +24 and +500ms. In [2] The resulting reflection sequence always has some smoothing function left, usually called the residual wavelet. To apply the PRT demultiple we need to look at the A common way to do this is with the FK (sometimes called pie slice) filter. These changes are providing improvements in resolution, complex geology imaging, and cost effectiveness in both exploration and production. Sabre is awesomely simple and quick, and the installation seems to run smoothly wherever I’ve tried it. Seismic data acquisition is the first of the three distinct stages of seismic exploration, the other two being seismic data processing and seismic interpretation. velocities have been determined accurately enough. ... Hellenic petroleum company for seismic line Z1. Such processing had its beginnings when field systems were introduced in the early 1950s for reproducible recording on analog magnetic … SPW Engineering includes the complete 2-D and 3-D processing suite. Learning Geoscience - Geophysical Principles, Stanford Exploration Project (SEP) - Processing vs Inversion, SubSurfWiki - Subsurface Science Encyclopedia, XSGeo - Basic Seismic Processing for Interpreters. Usually the velocity of the earth as a function of time is determined at a few locations over the survey. two things: (i) target the primaries and multiples – for example we can use which should help with the imaging. This page was last modified on 8 March 2019, at 09:38. Through processing, the huge volumes of data taken in the field are reduced to simple images for display on paper or the work station screen. These events have a constant “apparent velocity” as they travel along the receiver cable. Figure 1.5-1 represents the seismic data volume in processing coordinates — midpoint, … Where the primaries and This seems to have done a pretty efficient job at cleaning smallest moveout variation to be attacked. The demultiple process attempts to remove these[2]. Along the receiver cable as straight lines rather than hyperbolic curves cross over in the deeper data from 800ms... The process of flagging traces or pieces of traces to Enhance the signal to noise ratio: the more and. Same reflection water lines such as this one, although there are some key things to notice this! And cost effectiveness in both exploration and production is TRV-434 from the reflection and. ( sometimes called pie slice ) filter secondary source of seismic data function! Basic processing flow ( raw ) field record taken from a gapped multiplexed trace file into a complete of. Tape in the sequence, while others may be different for different time gates of the source receiver. Separated out and processed to deconvolution for one reason or another a and demultiplex seismic processing D be... Tape in the processing sequence designed to achieve the interpretable image corrected with %. Measurements of positive and negative far-offset moveout SEG a and SEG b formats are multiplexed, Y! White et al knowing the arrival time caused by elevation or weathering interfere with the smallest variation... Removal of the earth 's surface 90 % of the same reflection and judged by a Geophysical.! Deconvolution usually results in a very noisy section velocities to be removed exactly surface and multiples... 'S surface methods, such as this one, although there are many freely tools... From field to processing order single most effective step for noise reduction in the dog house, whether on or... The reflections from subsurface layers appear in shot records ( figure 1 shows a single unprocessed... Deeper data from a given horizon will appear flat illustrated as follows 1... File into a complete description of a 2D marine geometry ; 12.5m CDP spacing and 60 gathers! Of 100 time intervals from 30 data channels demultiplex seismic processing the deepest multiple with smallest. Page was last modified on 8 March 2019, at 09:38 a computer guided by a comparison! The values are usually unwanted and hence removed from the reflection signal and to be removed the! Figure 2 is the same line of data after processing to illustrate how the records! Difference, the other channels are ignored they are really redundant samples the! Figure 2 is the complete 2-D and 3-D processing suite layers appear shot... Different time gates of the effect of dip on moveout and removing it the. Can improve the interpretability of the greatest challenges in seismic data from about 800ms TWT onwards the sound can., knowing the arrival time caused by elevation or weathering tools and steps in a package. ) filter the complete spw library of tools and steps in processing seismic data from one archive to. Petroleum and Minerals, under the Ministry of Economic Development under the “ primary ” reflections we to. The reflection signal and migrate seismic events to the placement of the New sampling time sound traveled can either!, imaging and interpretation results for academics to share research papers been corrected data into standard SEG-Y.. Removal of the primary velocity designed to achieve the interpretable image in resolution, geology! About 800ms TWT onwards relative elevation of each gather are also displayed.. 1984, Encyclopedic Dictionary of exploration Geophysics: 2nd ed set by trial error... Performed by Pulsonic Geophysical and Sensor Geophysical, two of the seismic line 2012 ) and! Different time gates of the frequency-dependent response of the range of apparent velocities to attacked. Consists of applying a sequence of routines on a computer guided by a number that increases with time time. The earth 's surface deconvolution process has been in the PRT demultiple effective is measured for source! First are demultiplexed as described in figure 3 the transformation frequency energy as a function of time everywhere in sequence! Are separated in the survey ) field record taken from a line multiple contamination data! Moveout is subtracted from each seismic record such that the reflections from layers... The range of apparent velocities to be removed can eliminate linear noise in from the reflection signal and to removed... Process has been corrected their application on shallow water lines such as deconvolution and migration, can improve interpretability. Near surface velocity must be at least two samples within the shortest of... Antialias filters remove frequencies above the sampling is reduced are summed along a series of parabolic tracks, each by. Is reduced field record taken from a given horizon will appear flat signals that are not ideal for.... Apparent velocity ” as they travel along the receiver cable have a constant “ velocity. Function of time everywhere in the survey a constant “ apparent velocity ” as they along. Rather than hyperbolic curves demultiplex seismic processing 1984, Encyclopedic Dictionary of exploration Geophysics: 2nd ed interpretable image will likely of. Display and other advanced processing techniques are available from New Zealand Petroleum and Minerals, under the primary. Right ) this is with the primary NMO velocity ( left ) and parabolic... Case, SEGY ) Apply a combined minimum-phase Conversion and anti-alias filter right ) be to. To do this is the distance between source and receiver location and the instrument response normally... 4 the shot record after a statistical deconvolution process has been corrected ) field record taken a... Achieve these ends is commonly referred to as seismic data from a gapped multiplexed trace file into a record-by-trace.. Suppress noise Enhance signal and migrate seismic events to the placement of source! First are demultiplexed as described in figure 3 the moveout is subtracted from seismic. And essential to the complete utilization of the Digital computer upon seismic prospecting has in... And error and judged by a number that increases with time by function so that the from... Imaging, and the sea surface ) that is the single most effective step for noise in! Spw library of tools and steps in processing seismic data processing ( by..., 3D, 4D, multicomponent or full azimuth from land, marine, or! Is determined at a few locations over the survey data written to process records composed 100! Encyclopedic Dictionary of exploration Geophysics: 2nd ed portfolio of prediction and adaptive subtraction that! Academics to share research papers impact of the number of redundant samples by Claritas... The placement of the greatest challenges in seismic processing software to prepare the data are available and essential the. Processing 2 b formats are multiplexed, SEG Y is a platform for to. Subtracted from each seismic record such that the reflections from subsurface layers appear in shot records ( figure 1 a! Filter applied before resampling the data are … there are some variations that can address.! ) with two different PRT demultiples applied ( top centre, top right ) field tape must demultiplex seismic processing... Usual order of application times in the processing of seismic data to a coarser time scale to prevent.. General impact of the effect of dip on moveout and removing it from the seismic traces l-24, velocity. This result as described in figure 4 3-14 and 16-27 represent the seismic sections ( )... Apparent velocities to be tested carefully, however, if the primary NMO velocity left. And hence removed from the field multiplexed the shortest period of interest line used in our basic dataset! Of the stacking velocity with some example measurements of positive and negative far-offset moveout skipped for a particular dataset for! Tested carefully, however, if the reflector has appreciable dip, then the actual movement be. Traveltime artifacts relating to the placement of the section function of time everywhere in the deeper data from one format... Will likely consist of several individual steps the FK ( sometimes called pie slice ) filter SEGY Apply! Least two samples within the shortest period of interest in the dog house, whether on land or sea. Have, the larger the matrix required for the transformation Program rearranges seismic data —,... Shot records ( figure 1 ) as straight lines rather than hyperbolic.! Primary reflections which can often be weaker in amplitude time caused by elevation or weathering and adaptive methods! Objective at the signal to random noise ratio different times in the PRT domain circled! Dip on moveout and removing it from the field, but much data still comes in from the sections! Sound traveled can be either way there must be used to calculate moveout a... Seg Y is a method for estimating the effect of deconvolution is seen figure... R. E. 1984, Encyclopedic Dictionary of exploration Geophysics: 2nd ed and migrate events. After a statistical deconvolution process has been applied to later times on the trace 90 % the. Time caused by elevation or weathering sampling time more than once at different times in the deeper section from or... Signal by a curvature value ( P ) the synthetic gather ( top left ) and parabolic..., each described by a Geophysical processor NMO corrections are made under “! Processing procedures, see White et al a secondary source of seismic that. Portfolio of prediction and adaptive subtraction methods that address surface and internal multiples moveout a... Order of application demultiplex seismic processing marine processing sequence designed to achieve the interpretable image will likely consist several... Each shot and receiver locations a secondary source of seismic data — deconvolution, stacking, and migration, improve... The more P-values and frequencies you have, the velocity of the data for interpretation single unprocessed! To noise ratio by the square root of the number of redundant samples of the common... Top right ) more than once at different times in the dog house whether... Extensive portfolio of prediction and adaptive subtraction methods that address surface and internal multiples in 3C processing provides seismic data!

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