Vista Seismic Processing Series Of Narrow

As the seismic wavefront travels outward from the source, it not only gets weaker (as a result of energy conservation), but also causes reflections from a larger and larger area. (Consider light from a flashlight or ripples on a pond.) All of these reflections are recorded at the receiver location as a single sum without regard to the origin of the reflection except for time of travel.

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.

Treatment of the data to achieve these ends is commonly referred to as seismic data processing.

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.

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.

Figure 1 shows a single, unprocessed (raw) field record taken from a line.

Figure 2 is the same line of data after processing to illustrate how the field records are turned into an interpretable image.

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.

However, the steps can be grouped by function so that the basic processing flow can be illustrated as follows.

The proper assignment of these geometrical properties is fundamental to all that follows.

As computers move into the field, more of this work will be done at the dog house.

Differences in traveltime related to elevation and other surface conditions at the shot or receiver are removed, as are the timing peculiarities of the field apparatus.

Where organized (nonrandom) noise is recognized, one usually tries to determine the origin of this noise to better predict how it will manifest in the signal and hence derive the most efficient filter to remove it.

Redundant samples of the same subsurface location that occur in a predictable fashion as a result of the multichannel recording technique are summed together to reduce random noise in a process called stacking.

Ideally, we should be able to determine the time of a reflection absolutely and achieve infinite resolution.

First, the signal sent into the earth is not infinitely short.

If more than one interface is encountered within the width (in time) of the source pulse, the responses will interfere and the reflection received at the surface will be a complex sum of all the reflections created.

One can think of the source pulse as a running sum over the ideal reflection sequence.

Second, the hydrophone or geophone receiver and the seismic recording device each have a characteristic response time, that is, they take time to react to any signal such that a pulse is smeared or averaged over a time wider than the pulse itself.

Reflections occurring at shorter intervals than this characteristic time will be summed together.

Finally, the earth is not perfectly elastic so smearing of the signal occurs through the natural mechanism of transmission in the earth.

The mathematical process used to compute the result of such interactions is called convolution.

Reversing the process is called deconvolution.

If one knows the response time of the instrument and receivers (hydrophones or geophones) used, one can calculate the summing function that has been applied to the signal and can remove it or deconvolve it from the seismic records.

Vista Seismic Processing Series Of Narrow

Similarly, the source pulse or wavelet and the nonelastic properties of the earth can be removed using the process of deconvolution in an attempt to eliminate all time-averaging effects and turn the seismogram into a series of narrow reflections with greater resolution in time.

As the seismic wavefront travels outward from the source, it not only gets weaker (as a result of energy conservation), but also causes reflections from a larger and larger area.

Consider light from a flashlight or ripples on a pond.) All of these reflections are recorded at the receiver location as a single sum without regard to the origin of the reflection except for time of travel.