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GenerateTraces

By Jeffrey Reed,2014-05-27 15:08
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GenerateTraces

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     Generate Traces (GENERATE_TRACES)

     Abstract

     Basic traces are created and output in shot gathers. The number of traces within these shots, and the number of shots, are user specified. The output trace headers contain sufficient literals so that other SFMs can add more literals (notably GEOM_NOMINAL_LAYOUT and other geometry SFMs). The output sample interval, trace length, and simple sample amplitudes can also be specified.

     NOTICE Copyright protection as an unpublished work is claimed by WesternGeco. The work was created in 2008. Should publication of the work occur, the following notice shall apply. " 2008 Westerngeco". This work contains valuable tradesecrets; disclosure without written authorization is prohibited.

     November 2008 - WesternGeco

     GENERATE_TRACES

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     Generate Traces

     Contents

     1.0 Technical Discussion 1.1 1.2 1.3 1.4 2.0 Concept Example Emulation of Marine Acquisition Example Geometry Database and UKOOA File Generation Some Details About the Output From This SFM

     Inputs and Outputs 2.1 Outputs

     3.0

     Literal Summary 3.1 3.2 Inputs 3.1.1 STANDARD_INPUT Port Outputs 3.2.1 STANDARD_OUTPUT Port

     4.0 5.0

     Parameter Set Summary Setup Parameters 5.1 5.2 5.3 5.4 5.5 5.6 General Shot Numbering Gun Array Numbering Cable Numbering Channel Numbering Sample Values

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     1.0 Technical Discussion

     1.0 Technical Discussion

     1.1 Concept

     Many Omega SFMs contain powerful analysis and testing options and outputs. Many Omega jobs can also be designed specifically for analysis and testing. A problem that frequently occurs is that these SFMs and jobs require seismic traces and gathers with particular sample

    intervals, length, geometry, and other factors; but no such seismic data is conveniently available. This SFM alleviates this problem by allowing the generation of simple traces in shot gathers. The output trace headers contain sufficient literals so that other SFMs can add more literals (notably GEOM_NOMINAL_LAYOUT and other geometry SFMs as well as TRACE_HEADER_MODIFY, TEXT_TO_TRC_HEADER and similar SFMs). The output trace sample values can be updated by other SFMs (notably TOOLKIT for spikes and noise). Inverse hyperbolic NMO, filters, statics, mutes, and other processes can be used to emulate actual seismic acquisition. The following two sections contain examples.

     1.2 Example Emulation of Marine Acquisition

     The Omega job shown in this example generates shot gathers that emulate marine streamer cable seismic acquisition (results from first cable of first shot are plotted on right). Traces with ??spikes?? are created by this SFM. The headers of these traces are updated with geometry information (a normal setup of GEOM_NOMINAL_LAYOUT except for the use of its Nominal Coordinates parameter set). Noise is added and the traces are filtered. Notice that MOVEOUT is setup to perform Inverse Moveout (the spikes started out at constant times in each generated trace). The resulting traces emulate some aspects of actual seismic acquisition (this could be called basic forward modelling, however, the term forward modelling usually implies more sophisticated techniques).

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     1.0 Technical Discussion

     1.3 Example Geometry Database and UKOOA File Generation

     The Omega job shown in this example generates a marine geometry database (cables and the last few shot locations are plotted on the right). The geometry database is then used to output a UKOOA file (the beginning of that file is displayed below).

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     1.0 Technical Discussion

     1.4 Some Details About the Output From This SFM

     In the output IDheader the DATA_DESC is set to SHOT GATHER, and, in the output trace header literal DEFINED_SUBSET is generated. This means that level 2 end-of-gather flags are produced at the end of each cable (also known as ??subsurface line processing?? flags). Level 1 end-of-gather flags are produced at the end of each shot, of course.

    In the output IDheader the SORT_LITERAL list is set to IDENT_NUM, FLD_CABLE_NUM, and FIELD_CHANNEL_NUM. Their SORT_DIRECTION is set to INCREASING unless you specify their increment negative. In the output IDheader the RMS_AMPLITUDE value is set to 2000 and UNITS_OF_DISTANCE value is set to METERS. These values have no consequence in this SFM but are accessed by default so often in other SFMs that it is better to create them. The output trace literal START_TIME is set to the time of the first sample (which is your specified earliest time plus one sample interval). The output trace literal STACK_WORD is set to 1. At least one output sample is always created (by default it has a value of 0.01).

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     2.0 Inputs and Outputs

     2.0 Inputs and Outputs

     2.1 Outputs

     Standard Output (Required) STANDARD_OUTPUT

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     3.0 Literal Summary

     3.0 Literal Summary

     3.1 Inputs

     3.1.1 STANDARD_INPUT Port

     Identification Header Trace Header

     3.2 Outputs

     3.2.1 STANDARD_OUTPUT Port

     Identification Header

     LITERAL DATA_DESC SORT_LITERAL SORT_DIRECTION MAX_GATHER_MULT MAX_CABLE_NUM MAX_TRACE_NUM RMS_AMPLITUDE SAMP_INT EARLIEST_TIME MAX_REFLECT_TIME CLIENT_NAME LINE_NAME AREA_NAME UNITS_OF_DISTANCE DESCRIPTION Data Set Description Sort Literal Sort Direction Maximum Gather Multiplicity Maximum Cable Number Maximum Trace Number RMS Amplitude Sample Interval Earliest Time Maximum Reflection Time Client Name Line Name Area Name Units of Distance

     Trace Header

     LITERAL SHOTPOINT_NUM IDENT_NUM SOURCE_CODE DEFINED_SUBSET DESCRIPTION Shot Point Number Ident Number Source Gun Array Code Number Defined Subset Number

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     Generate Traces LITERAL FLD_CABLE_NUM FIELD_CHANNEL_NUM TRACE_NUM STACK_WORD START_TIME LTRSAM TIME_SHIFT_ALIGNMENT DESCRIPTION Field Cable Number Field Channel Number Trace Number Stack Word Start Time Length of Trace in Samples Time Shift Alignment

     3.0 Literal Summary

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     4.0 Parameter Set Summary

     4.0 Parameter Set Summary

     Parameter Set Name Geophysical Language GENERAL NUM_SHOTS NUM_GUN_ARRAYS CABLES_PER_SHOT CHANNELS_PER_CABLE SHOT_NUMBERING FIRST_IDENT IDENT_INC FIRST_SHOTPOINT SHOTPOINT_INC GUN_NUMBERING FIRST_GUN_ARRAY GUN_ARRAY_INC CABLE_NUMBERING FIRST_CABLE CABLE_INC CHANNEL_NUMBERING FIRST_CHANNEL CHANNEL_INC FIRST_TRACE TRACE_INC SAMPLE_VALUES SAMPLE_INT EARLIEST_TIME MAX_REFLECT_TIME BASE_AMP TABLE TIME AMP Parameter Set Title Parameter Title General Number of Shots Number of Source Gun Arrays Number of Cables Per Shot Number of Channels Per Cable Shot Numbering First Ident Number Ident Increment First Shotpoint Number Shotpoint Increment Gun Array Numbering First Gun Array Number Gun Array Increment Cable Numbering First Cable Number Cable Increment Channel Numbering First Channel Number Channel Increment First Trace Number Trace Number Increment Sample Values Sample Interval Earliest Time Shift Alignment Maximum Reflection Time Fill Samples With This Base Amplitude Trace Amplitude Table Time Spike Amplitude Status Required

     Optional

     Optional

     Optional

     Optional

     Optional

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     5.0 Setup Parameters

     5.0 Setup Parameters

     5.1 General

     PARAMETERS:

     NUM_SHOTS Number of Shots Number of shot gathers to output. This parameter controls the number of values of literals IDENT_NUM and SHOTPOINT_NUM. By default the first output shot has an IDENT_NUM and

    SHOTPOINT_NUM of 1, and both increment by 1 for subsequent shots. The initial value and increment can be altered via the Shot Numbering parameter set. Optional: Type: Trace-varying: Multi-valued: Default: NUM_GUN_ARRAYS Number of Source Gun Arrays The number of source gun arrays. For typical port-starboard marine shooting this value should be 2. For land or OBC/seabed this value is usually inconsequential. This parameter controls the number of values of literal SOURCE_CODE. By default, the first shot is given a SOURCE_CODE of 1 and each subsequent shot increments by 1 for the number of shots specified here, then the SOURCE_CODE resets to 1 and repeats. The initial value and increment can be altered via the Gun Numbering parameter set. Optional: Type: Trace-varying: Multi-valued: Default: No integer No No 2 No integer No No 10

     GENERAL

     (Status: Required, Type: standard)

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     Generate Traces CABLES_PER_SHOT Number of Cables Per Shot

     5.0 Setup Parameters

     The number of cables. This parameter controls the number of values of literal FLD_CABLE_NUM in the output shot gathers. By default each shot has FLD_CABLE_NUMs that start at 1 and increment by 1 until the value of this parameter. The initial value and increment can be altered via the Cable Numbering parameter set. Optional: Type: Trace-varying: Multi-valued: Default: CHANNELS_PER_CABLE Number of Channels Per Cable Number of channels per cable. This parameter controls the number of values of literals FIELD_CHANNEL_NUM and TRACE_NUM. By default the FIELD_CHANNEL_NUMs start at 1 and increment by 1 within the output shots (continuously from the first cable to the last cable) and the TRACE_NUMs start at 1 and increment by 1 within each cable of the output shots. The initial values and increments can be altered via the Channel Numbering parameter set. Optional: Type: Trace-varying: Multi-valued: Default: No integer No No 500 No integer No No 8

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     5.0 Setup Parameters

     5.2 Shot Numbering

     PARAMETERS:

     FIRST_IDENT First Ident Number First Ident Number. Optional: Type: Trace-varying: Multi-valued: Default: IDENT_INC Ident Increment Ident Number Increment. Optional: Type: Trace-varying: Multi-valued:

    Constraint: Default: FIRST_SHOTPOINT First Shotpoint Number First Shotpoint Number. Optional: Type: Trace-varying: Multi-valued: Default: No number No No 1.0 No integer No No param()!=0 1 No integer No No 1

     SHOT_NUMBERING

     (Status: Optional, Type: standard)

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     Generate Traces SHOTPOINT_INC Shotpoint Increment Shotpoint Number Increment. Optional: Type: Trace-varying: Multi-valued: Default: No number No No 1.0

     5.0 Setup Parameters

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     5.0 Setup Parameters

     5.3 Gun Array Numbering

     PARAMETERS:

     FIRST_GUN_ARRAY First Gun Array Number First Gun Array Number. Optional: Type: Trace-varying: Multi-valued: Default: GUN_ARRAY_INC Gun Array Increment Gun Array Number Increment. Optional: Type: Trace-varying: Multi-valued: Default: No integer No No 1 No integer No No 1

     GUN_NUMBERING

     (Status: Optional, Type: standard)

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     5.0 Setup Parameters

     5.4 Cable Numbering

     PARAMETERS:

     FIRST_CABLE First Cable Number

     CABLE_NUMBERING

     (Status: Optional, Type: standard)

     First Cable Number. Cable numbers start at this value within each shot. Optional: Type: Trace-varying: Multi-valued: Default: CABLE_INC Cable Increment Cable Number Increment. Optional: Type: Trace-varying: Multi-valued: Default: No integer No No 1 No integer No No 1

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     5.0 Setup Parameters

     5.5 Channel Numbering

     PARAMETERS:

     FIRST_CHANNEL First Channel Number

     CHANNEL_NUMBERING

     (Status: Optional, Type: standard)

     First Channel Number. Channel numbers start at this value within each shot and increment continuously for the entire set of traces within each shot. Optional: Type: Trace-varying: Multi-valued: Default: CHANNEL_INC Channel Increment Channel Number Increment. Optional: Type: Trace-varying: Multi-valued: Default: FIRST_TRACE First Trace Number First Trace Number. Trace numbers start at this value on every cable within each shot. Optional: Type: Trace-varying: Multi-valued: Default: No integer No No 1 No integer No No 1 No integer No No 1

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     Generate Traces TRACE_INC Trace Number Increment Trace Number Increment. Optional: Type: Trace-varying: Multi-valued: Default: No integer No No 1

     5.0 Setup Parameters

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     5.0 Setup Parameters

     5.6 Sample Values

     General Information

     SAMPLE_VALUES

     (Status: Optional, Type: standard)

     This parameter set is not permitted when the input port is connected.

     PARAMETERS:

     SAMPLE_INT Sample Interval Sample interval. Optional: Type: Trace-varying: Multi-valued: Constraint: Default: EARLIEST_TIME Earliest Time Shift Alignment Earliest time shift alignment. This value must be a multiple of the Sample Interval. Note: The output START_TIME literal is set to this value plus one sample interval. Optional: Type: Trace-varying: Multi-valued: Default: No integer No No 0 No integer No No param()>0 4

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     Generate Traces MAX_REFLECT_TIME Maximum Reflection Time

     5.0 Setup Parameters

     Length of traces in time. This value must be a multiple of the Sample Interval and must be at least one sample interval greater than the Earliest Time (this SFM always produces at least one output sample). Optional: Type: Trace-varying: Multi-valued: Constraint: Default: No integer No No param()>=param("EARLIEST_TIME")+param("SAMPLE_INT") 4

     BASE_AMP Fill Samples With This Base Amplitude Base amplitude for output samples. All odd sample numbers are initialized with this amplitude, all even sample numbers are initialized with this amplitude multipled by -1. A value of zero is permitted but it should be considered that many seismic processing SFMs search for mute zones (particularly at the top and bottom of traces). Traces with all zero samples or just a few isolated non-zero samples may not produce the expected output or realistic run-time estimates. Optional: Type: Trace-varying: Multi-valued: Default: TABLE Trace Amplitude Table Table containing times and amplitudes. Optional: No No number No No 0.01

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     Generate Traces TIME Time

     5.0 Setup Parameters

     This is the time (in milliseconds) to place an amplitude value in the output traces. This value must correspond exactly to the time of some sample. The default (NOT_USED) means sample amplitudes are set only according to parameter Fill Samples With This Base Amplitude. Optional: Type: Trace-varying: Multi-valued: Constraint: Default: AMP Spike Amplitude This is the amplitude. Optional: Type: Trace-varying: Multi-valued: Default: No number No No 1000 No integer No No param()>=param("EARLIEST_TIME")+param("SAMPLE_INT") &&

    param()<=param("MAX_REFLECT_TIME") NOT_USED

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