Searching for Natural Gas

Companies typically perform seismic studies to learn about formations most likely to hold recoverable natural gas, and may drill exploratory wells to confirm the results of these studies.

Seismic Studies

Companies can make educated guesses about which tracts of land within a field hold recoverable natural gas. Before making large financial investments, however, they typically perform seismic studies that help in characterizing the size, shape, and depth of the formations most likely to hold recoverable natural gas. The use of 3-D seismic technology to image subsurface rocks increases geologic knowledge, improves drilling accuracy, and lowers risks in exploration.

Seismic studies involve the detonation of explosive charges to create vibrations and sound waves that move through underground formations. The sound waves are subsequently reflected back to surface receptors. Some of the elements in a seismic study include:

• A preliminary line survey,
  
  
• Acquisition of necessary permits,
  
  
• Selection and marking of shot-hole locations,
  
  
• Necessary clearing of vegetation,
  
  
• Shot-hole drilling (typically 20 feet deep),
  
  
• Implantation of an explosive charge (generally one pound of dynamite), and
  
  
• Detonation and backfill of shot-hole.

When conducting a seismic study, contractors utilize trucks and helicopters to move equipment into the field and collect data. Geophysical receptor instruments are used to measure the patterns followed by the reflected sound waves as they travel to receptors. Computer algorithms help to interpret the shape and characteristics of underground formations. The size and scope of a seismic survey depends on depth, objective, lease position, available funds, and the complexity of the subsurface geology. The pattern in which sources and receptors are laid out is used to optimize the way sound waves hit the receptors. Modern techniques using multiple sound wave frequencies can be used to determine reservoir properties such as porosity, permeability, saturation, stress, and pore pressure.

Seismic Study Click to enlarge

Exploratory Wells

Company geologists use the results of the seismic studies to predict the optimal locations for siting the wells. In areas with previously established production, production wells can be drilled directly. However, in some cases, before embarking on a full-scale drilling program, the companies may drill one or a few exploratory wells that are used to confirm whether the targeted formations hold economically viable resources.

Drilling an exploratory well involves essentially the same process as drilling a production well. The production well drilling process is described in the next section.

FOR MORE INFORMATION:

• Technologies that can minimize the environmental impacts of seismic studies.
  
  
• Regulatory requirements associated with seismic studies.