Planning Controlled Source Seismic Projects
Here’s a list of things PI’s should do when planning a controlled source experiment.
Early planning (proposal stage)
It is important to plan how the survey to be conducted, based on project objectives. Most experienced PI’s understand that improper planning can lead to injury, cost overruns, data loss and missing project objectives to name a few. Generally, most people underestimate the time and effort required to properly plan/conduct an experiment.
1) Identify the target and depth to be imaged. Identify the imaging method, reflection or refraction/tomography. What level of redundancy is desired? These factors help determine the size and number of sources needed.
2) Identify the near-surface geology. Near-surface geology is a relative term, but it controls the source method required and the source coupling. For example, if a Pn arrival is desired the shot size can vary between a few hundred kilograms to a few thousand kilograms depending on coupling and therefore near-surface geology. Also, different sources are applicable in situations, such as the accessibility of an area and the sensitivities of the environment.
3) Once 1) and 2) above are determined the SSF can identify if it can provide the sources and what supplies and/or outside contracting will be needed. The SSF will begin to get quotes for supplies, drilling, or vibrators as needed to begin costing out the PI’s proposal. PI’s should realize that not all drilling methods, explosive types or even vibrators are available everywhere. Often compromises are made on these items. At this point the SSF will have a cost estimate for the PI, this will be in the form of a cost proposal.
Preparation for acquisition (funded stage): Firm quotes and permitting
4) Once the proposal is funded another set of quotes for supplies, drilling, or vibrators is obtained because the time line becomes much more defined and earlier quotes are likely only good for 30 or 90 days.
5) Field work begins with the selection shot points and determination of the exact survey location. At this point permitting can begin. Many landowners are sensitive to liability and for this reason the SSF carries a $1M commercial general liability policy. This policy is carried specifically to obtain permits, it is not carried to manage risk. Risk management is done through procedural methods and the SSF will rigorously enforce those procedures.
Acquisition using sources
6) Safety is the number one concern during data acquisition phase of project. Because the SSF is a government research organization we are exempt from many state and federal regulations, however we coordinate our activities with state and county fire marshals, state oil and gas commissions, state geological surveys and 811 call-before-you-dig services to ensure that our activities are being performed safely and in an approved manner.
Because most of our instrumentation timing is traced to UTC, our sources are also traced to UTC.
7) Finally, damage sometimes occurs during geophysical surveys, shotholes collapse and vehicles leave ruts, these damages must be repaired by the permit holder as specified in the permit. The SSF usually does this, although sometimes we request help from PI’s.