CPG Exploration Techniques & Seismic Interpretation 3

Question 1

What is the primary advantage of 3D seismic surveys over 2D surveys for prospect evaluation?

Accepted Answer

Full spatial sampling eliminates out-of-plane reflections and enables accurate structural mapping

Answer

3D seismic provides full spatial sampling, removing sideswipe and out-of-plane energy that distorts 2D profiles, and enables accurate volumetric structural and stratigraphic mapping.

Question 2

Which exploration method measures variations in the Earth's gravitational field to detect subsurface density contrasts?

Accepted Answer

Gravity surveying

Answer

Gravity surveys detect lateral changes in rock density; salt bodies (low density) produce negative Bouguer anomalies, while dense basement rocks produce positive anomalies.

Question 3

In reflection seismology, what is a 'multiple' reflection?

Accepted Answer

A seismic wave that has reflected more than once before being recorded at the surface

Answer

Multiples are seismic events that have undergone more than one reflection, often between the sea floor and the water surface or between two strong reflectors, and can mimic primary reflections.

Question 4

What does the 'dominant frequency' of a seismic wavelet control in exploration?

Accepted Answer

The vertical resolution of the seismic data, with higher frequency giving finer resolution

Answer

Vertical resolution is approximately λ/4, and since λ = velocity/frequency, higher dominant frequency yields shorter wavelength and finer resolution of thin beds.

Question 5

A CPG candidate is evaluating a prospect mapped as a four-way dip closure on seismic. What additional risk must be assessed that this structural map alone cannot fully address?

Accepted Answer

Seal integrity and the presence of a top seal capable of retaining hydrocarbons

Answer

Structural closure confirms trap geometry but does not prove seal; without an effective top seal, hydrocarbons will migrate through even a perfect four-way closure.

(CPG) Certified Petroleum Geologist Practice Test

(CPG) Certified Petroleum Geologist Practice Test

CPG Exploration Techniques & Seismic Interpretation 3