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Lab 6: Static Corrections

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Seismic reflection data in different traces are not always lying on a hyperbole for a horizontal reflector. Reflected data have certain displacement due to the different length of ray paths. Static displacements can be caused by topographic conditions (difference in elevation), weathered/unconsolidated layer; slow velocity, different borehole/gun and cable depth, tidal wave as well as water layer effect.  Figure 1: Topographic and weathered layer effect of seismic survey Thus, static corrections are applied to seismic data in order to compensate for various effects on the data such as those related to near surface, variations in elevations, weathering, and reference to a datum. By applying static corrections, we aim to determine the reflection time assuming the existence of a flat surface plane with no weathering layer.  These corrections include: 1. Elevation static correction, which accounts for variable elevations of the sources and receivers. 2. Residual static co
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Lab 5: Sorting, Velocity Analysis, Stacking

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After performing various seismic data processing steps such as data quality control, frequency filtering and deconvolution on the east Texas real seismic data, the objective of today's lab session is to display the true image of the subsurface which required compressing the seismic data to infer a first approximation for such image. This includes :  1. Sorting the shot gathered data into common mid-point gathers (CMP) 2. Picking appropiate stacking velocities and applying accordingly normal move-out corrections (NMO).  3. Stacking all the CMPs such as average each CMP to form stacked CMP and then concatenate all stacked CMP traces together.  1. Common Midpoint Sorting  Figure 1: CMP Sorting  Seismic data acquisition with multifold coverage is done in shot-receiver ( s, g ) coordinates.  Figure 1  depicts the geometry of a CMP gather and raypaths associated with a flat reflector. Note that CDP gather is equivalent to a CMP gather only when reflectors are hor
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Lab 4: Seismic Deconvolution

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The aim of seismic deconvolution is to increase the vertical resolution of the data by compressing the source wavelet (to a zero-phase spike, if possible) This is known as spiking deconvolution. Not only that, seismic deconvolution also aims to attenuate noise such as multiples elimination. For this, we need to define the seismic convolution model.   To perform spiking deconvolution, we need to set 3 parameters namely: a) Auto-correlation window (w) b) Filter length (N) c) Percent pre-whitening  1. Call and display for seismic shot gather no. 4-6 as shown in figure below before applying spiking deconvolution.  Figure 1 Figure 2: Shot gathers:4,5 and 6 before applying spiking deconvolution 2. Performing Auto-correlation Figure 3: Auto-correlograms of shot gather number 4,5 and 6. 3. Applying spiking deconvolution The aim of spiking deconvolution is to compress the source wavelet into zero-phase spike of zero width.
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Lab 3: Seismic Noise Attenuation

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The objective of the lab session today is to remove unwanted energy which has two main categories; a) random noise or coherent energy which are the disturbance in seismic data which lack phase coherency between adjacent traces & b) coherent noise which shows consistent phase from trace to trace. Since it is impossible to remove all noise, we are trying to improve the signal-to-noise ratio (SNR) as much as possible. In short, noise can be considered as anything other than the desired signal. Noise in seismic records is variable in both time and space . Poor seismic records = SNR ratios < 1.  1. Load Seismic Data (Shot number 1 – 18) before gain  Figure 1: Seismic Data Information Figure 2: Shot number 1-18 (before gain applied) Figure 3: Shot number 1-18 (after gain applied) Seismic data after gain is saved as: SeismicData_B_Gain.  2. Loading QC-ed real seismic data of shot number 10 .  Figures 5, 6 and 7 are showing the ground roll
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Lab 2: Seismic Data QC

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The objective of this lab session is to ensure that data is accurate to obtain an accurate seismic image of subsurface structures. There are a few quality control (QC) steps which includes:    De-multiplexing    Reformatting    Setup of field geometry    Trace editing   Gain application    Application of field statics      This lab will focus on step 4 and 5 which are the trace editing and gain application.             1.        View shot number 11-14                        Figure 1: Wiggle shot for shot 11-14 before muting
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Lab 1: Examine Seismic Data

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The objective of this lab session it to look at the seismic header which contains the basic information of the seismic survey and tabulation of parameter used to acquire the data. The format the we receive is usually in SEG-Y.            1.    Examining the data set  ü Load data into matlab; SeismicData_B.mat ü It will view two main information; a) the original data is stored in variable D & b) the header value is stored in variable H ü Result :  2. Header Information  ü Call for header ü Extract geometrical information such as the source coordinate (sx and sy) and receiver coordinate (gx and gy), the source elevation (gz) and others ü Result :                                        Figure 1: The number of traces per shot Figure 2: The source elevation profile for each  Figure 3: The stacking chart plot of the seismic data 1              3.  Displaying seismic data                  Two
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INTRODUCTION

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I am Nur Khalisa Binti Abdul Hamid (20381). Welcome to my blog Mr. Halim! Hope you like it! For our lab assignment, as a student who is taking Geophysics as a major, we are expected to go through every lab module and understand the concept of processing the seismic data from the very beginning until the migration process. The software that we use is called the MATLAB which lately, has been an increasingly popular tool in earth sciences. It has been used for finite element modeling, processing of seismic data, analyzing satellite imagery, and for the generation of digital elevation models from satellite data. The objective of this lab is to explore the functions of MATLAB, familiarize with seismic coding language, as well as to u nderstand how to use basic MATLAB functions and plotting commands on data vector which relates to the subject we are taking ; Seismic Data Processing.  Common procedures to streamline seismic data processing include: 1. Working wi
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