Before any activity happens on a lease and sometimes even before a land purchase, seismic surveys are conducted to assess the potential resources existing in an area of interest.

Seismic surveys gather and record patterns of induced sound wave reflections from underground layers of rock to help determine the geological formation of a particular land area, if drilled, will produce resources. Geophysicists use seismic surveys to map underground rock formations and create detailed models of the underlying geologic structure.  These surveys are an important first step in the lifecycle of a well.

In an onshore survey, several lines of sensitive receivers called geophones or “jugs” are laid out by the crew along a grid that has been clearcut, and explosions or vibrations are created at “shot points” on the surface.  The energy is reflected back as seismic waves from several rock layers and is recorded by the geophones. The amount of time for arrival of information indicates depth.  This process is repeated several times.

Although dynamite charges were used traditionally to generate energy waves, contractors now use the mechanical vibroseis method to reduce environmental impact.  Low-impact and helicopter-portable seismic equipment also cut environmental costs significantly and companies work closely with local conservation groups to plan seismic surveys that make maximum use of existing trails.

There are three types of seismic surveys –2D, 3D and 4-D.  Geophysicists interpret the results of the surveys to see if there is enough oil or gas present in the area of interest to justify drilling an exploratory well.  Before a seismic survey is taken, companies have to arrange surface access agreements with landowners directly affected by exploration activities.

As the technology available becomes more sophisticated, new generations of data collection and interpretation evolve.  Today there are three generations of seismic programs.  Each has its own unique data capture requirement, interpretation and data presentation.  Global Positioning System (GPS) technology has been incorporated to allow the data to be tied to specific surface locations.

2-D Programs This is the traditional type of seismic program, whereby data is collected and interpreted.  The data is presented in two-dimensional maps, which does not provide for a good indication of depth or thickness of the potential producing formation.

3-D Programs This is a newer type of program that requires the seismic lines to be set on a narrower grid pattern than the 2-D program.  Therefore, this program is more expensive than the 2-D.  However, the data interpretation allows the results to be presented in three dimensions.  This program provides a sense of the thickness and shape of the potential producing zone.  This technology allowed many operators to go back into fields that were thought to be “drilled out” and find many smaller pools.

4-D Programs This is the newest type of program.  It is basically an enhanced 3-D program that collects data that is more sensitive to the timing of the results collected.  The data interpretation can therefore be even more precise than 3-D, especially with regard to the size, thickness and shape of the potential hydrocarbon formation.

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