Seismic Surveys

Seismogram

Seismic. When most people hear this term they usually associate it with earthquakes. While seismic is indeed associated with earthquakes, man-made seismic is associated with earth science as well as the search for oil.

Two of the most critical components of drilling the Niobrara formation is knowing exactly where your target formation is beneath the ground, and to what degree, and in what orientation, the naturally occurring formation fractures exist.

Luckily this information is available through Seismic technology, specifically 3C Seismic. 3C Seismic is defined as a type of multi-component seismic data acquired in a land, marine, or borehole environment by using three orthogonally oriented geophones or accelerometers. 3C is particularly appropriate when the addition of a hydrophone (the basis for 4C seismic data) adds no value to the measurement, as for example, on land. This technique allows determination of both the type of wave and its direction of propagation.

So in the event you are not a geophysicist let me interpret! Basically, a 3 axis (horizontal x, horizontal y, and vertical z) geophone measures vibrations (acoustic energy) that are propagated into the ground and the energy returns to the geophone are processed via computer to measure the return times of the introduced energy and to compute the location of underground rock strata based on the processed reflections of those sounds. Its kinda like a sonogram for the earth.

Thumper Truck

In the olden days acoustic energy was introduced with seismic charges containing high explosives. Today, especially in inhabited areas, it is preferable and probably required, to use Vibroseis trucks also known as “Thumper” trucks to introduce the acoustic energy into the ground.

3c Geophone

Remember its the geophones that collect all the readings. When a survey is conducted the geophones are aligned in survey grids to measure the areas being explored.

This may very well happen in your neighborhood, so  don’t be surprised to see this happen on your

Geophone Connecting Wire

Geophone connection wire – Image Courtesy Geokinetics

local road or in a nearby farmers field. As a landowner, you may even be asked for permission for a string of geophones to be placed on your property for a short duration of time while the survey is being conducted. (Usually a small fee is offered for access to your property) It is of course the choice of the land surface owner to either grant or deny access.

Look for a crew with survey stakes and a line of orange  geophones connected with orange wire lying nearby in some field.

Seismic Recording Truck – Image Courtesy Geokinetics

The data is collected by a recording truck for initial processing and storage. After collection the survey data will be more heavily processed at a data processing center with sophisticated algorithms and software to determine and interpret what that data shows. What are the outputs of such a survey?

The final output of a 3-c seismic survey is a detailed 3 dimensional picture of the subsurface strata. From this picture the drillers will know exactly where the oil bearing strata is, and how it is oriented. The resolution of a survey of this type should also give indications of subsurface fracturing within the reservoir as well as any subsurface faults that may exist. The results of the analysis of this data will give project geologists and geophysicists the necessary information to precisely locate the drill pad and how to steer the drill bit on the horizontal leg of the well so the well bore stays within the targeted zone.

Seismic Survey Animation

 

 

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