Oil and Gas at Your Door? (2005 Edition) - Earthworks

Oil and Gas Development and Impacts
1. EXPLORATION
Only after minerals have been leased (or permission obtained from mineral owners) may an
individual or company go out onto the land to explore for oil and gas deposits.
Remote sensing techniques, such as photography, radar, infrared images, and microwave frequency
receivers, are used to identify potential production areas and predict the likelihood of
significant reserves. 33 Geophysical exploration is the attempt to physically locate oil or gas-bearing
geological structures. The mostly widely used technique in on-shore geophysical exploration
is the seismic test. 34
Seismic Exploration
Seismic tests are based on the fact that acoustic or seismic waves will travel through, bend,
absorb, and reflect differently off of various layers of subsurface rock. Seismic waves can be
generated in several ways:
1. by blasting dynamite from a hole drilled several hundred feet in the ground;
2. by dropping a heavy weight, known as a thumper, from a truck (called a thumper truck)
onto hard ground surfaces such as paved roads. This technique is known as land vibroseis,
and it is typically used near populated areas and in sensitive environmental areas
where explosions are not desirable; 35 or
3. by shaking the ground with a device known as a vibrasizer.
Seismic waves travel downward and outward, and
are reflected back at different rates and
strengths, depending upon the underground
structures encountered. The strength and timing
of the reflected signals are measured at the surface
by geophones, which are connected to a line
laid along a predetermined course. The line is
connected to a machine that records the signals.
In the 1990s, geologists began using high-powered
computers that could analyze much
greater numbers of seismic signals and display
them on three-dimensional (3-D) maps. To
increase the detail and accuracy of these 3-D
maps, the seismic lines and geophones are
spaced more closely together, which means that
land disturbance also increases. 36
FIGURE I-2. SEISMIC EXPLORATION
30-ton thumper trucks leave lasting impressions on the
surface.
Seismic Exploration—Issues and Impacts
• Survey stakes for mapping out the exploration area should be wooden, and not wire pin
flags, because farming activities like making silage or hay can shred the wire flags. The
resultant metal bits can kill livestock that eat the feed. Also, all stakes and markers should
be removed after exploration is completed, because livestock and wildlife can die from
eating ribbons or flags. 37
• Seismic lines will destroy vegetation and may cause erosion, which could lead to sediment
entering surface waters. 38
• 3-D tests tend to cause greater surface disturbance and companies use your land for
longer periods of time than with two-dimensional surveys.
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