Which type of log is used to locate the top of the gravel packed section and detect voids in gravel packs?

Which type of log is used to locate the top of the gravel packed section and detect voids in gravel packs?

• A. Unfocused gamma ray logs
• B. Focused gamma ray logs
• C. Neutron logs
• D. Sonic logs

Answer: (A)

Unfocused gamma-ray logging uses natural gamma radiation from rocks measured with a broad vertical response, which makes it well suited to spotting changes in lithology along the borehole. In a gravel-packed completion, the gravel pack around the screen represents a different lithology and density than the surrounding formation, so the gamma signal changes where the pack begins and ends. This broad, integrated response helps you locate the top of the gravel-packed interval as you move down the well. Voids within the gravel pack interrupt the solid material and alter the local environment, producing noticeable anomalies in the gamma signal over the affected interval, which the unfocused log can reveal more clearly than a highly collimated (focused) instrument. Focused gamma-ray logs are more sensitive to borehole effects and small-scale, localized changes, while neutron and sonic logs serve different purposes (neutron for hydrogen content and porosity, sonic for mechanical continuity) and are not as direct for marking the gravel-pack boundary and identifying voids.

Unfocused gamma-ray logging uses natural gamma radiation from rocks measured with a broad vertical response, which makes it well suited to spotting changes in lithology along the borehole. In a gravel-packed completion, the gravel pack around the screen represents a different lithology and density than the surrounding formation, so the gamma signal changes where the pack begins and ends. This broad, integrated response helps you locate the top of the gravel-packed interval as you move down the well. Voids within the gravel pack interrupt the solid material and alter the local environment, producing noticeable anomalies in the gamma signal over the affected interval, which the unfocused log can reveal more clearly than a highly collimated (focused) instrument. Focused gamma-ray logs are more sensitive to borehole effects and small-scale, localized changes, while neutron and sonic logs serve different purposes (neutron for hydrogen content and porosity, sonic for mechanical continuity) and are not as direct for marking the gravel-pack boundary and identifying voids.