ADVANTAGES AND DISADVANTAGES OF THE REFRACTION

AND REFLECTION METHODS

SIBT-E-HASSAN BUTT

2012-2014

OUTLINE

Seismic methods Refraction methods Advantages Disadvantages Reflection method Advantages Disadvantages Conclusions

SEISMIC METHODS

Seismic reflection and refraction is the principal seismic method by which the petroleum industry explores hydrocarbon-trapping structures in sedimentary basins.

Both the seismic techniques have specific advantages and disadvantages when compared to each other and when compared to other geophysical techniques.

For these reasons, different industries apply these techniques to differing degrees.

REFRACTION METHODS

The refraction of elastic waves on passing between formations of rock having different seismic velocities

ADVANTAGES

Refraction observations generally employ fewer source and receiver locations and are thus relatively cheap to acquire.

Little processing is done on refraction observations with the exception of trace scaling or filtering to help in the process of picking the arrival times of the initial ground motion.

Because such a small portion of the recorded ground motion is used, developing models and interpretations is no more difficult than our previous efforts with other geophysical surveys.

DISADVANTAGES

Refraction seismic observations require relatively large source-receiver offsets (distances between the source and where the ground motion is recorded, the receiver).

Refraction seismic only works if the speed at which motions propagate through the Earth increases with depth.

Refraction seismic observations are generally interpreted in terms of layers. These layers can have dip and topography.

DISADVANTAGES

Refraction seismic observations only use the arrival time of the initial ground motion at different distances from the source (i.e., offsets).

A model for the subsurface is constructed by attempting to reproduce the observed arrival times.

REFLECTION METHODS

The reflection of elastic waves at boundaries between different rock formations, especially as a technique for prospecting or research.

ADVANTAGES

Reflection seismic observations are collected at small source-receiver offsets.

Reflection seismic methods can work no matter how the speed at which motions propagate through the Earth varies with depth.

Reflection seismic observations can be more readily interpreted in terms of complex geology.

ADVANTAGES

Reflection seismic observations use the entire reflected wavefield (i.e., the time-history of ground motion at different distances between the source and the receiver).

The subsurface is directly imaged from the acquired observations.

DISADVANTAGES

Because many source and receiver locations must be used to produce meaningful images of the Earth's subsurface, reflection seismic observations can be expensive to acquire.

Reflection seismic processing can be very computer intensive, requiring sophisticated computer hardware and a relatively high-level of expertise. Thus, the processing of reflection seismic observations is relatively expensive.

DISADVANTAGES

Because of the overwhelming amount of data collected, the possible complications imposed by the propagation of ground motion through a complex earth, and the complications imposed by some of the necessary simplifications required by the data processing schemes, interpretations of the reflection seismic observations require more sophistication and knowledge of the process.

CONCLUSION

Environmental and engineering concerns generally opt for performing refraction surveys.

Reflection surveys are extensively used in oil industry. In situations where both could be applied, seismic

reflection generally has better resolution, but is considerably more expensive

In other cases (e.g. very deep/small targets) only reflection can be expected to work.

Where boreholes or wells are accessible, neither refraction, nor reflection may be recommended in favor of seismic tomography

Reflection technique potentially generates, interpretable observations over complex geologic structures.

QUESTIONS?