Formation Evaluation and Logging Flashcards
7 cards from real SPE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Formation Evaluation and Logging flashcards as text
Which neutron log measurement is most directly affected by the presence of gas in the formation?
Answer: Decreased neutron porosity reading
Gas has very low hydrogen index compared to water or oil, causing the neutron log to read anomalously low porosity in gas-bearing zones.
What is the primary purpose of a caliper log in formation evaluation?
Answer: Determining borehole diameter and shape
The caliper log measures the diameter of the borehole, identifying washouts, key seats, and zones of good mudcake formation critical for correcting other log measurements.
In a density-neutron crossplot, a gas crossover occurs when:
Answer: Density porosity exceeds neutron porosity
Gas crossover occurs when density porosity reads higher than neutron porosity due to gas having low density and low hydrogen index simultaneously.
The formation factor (F) in Archie's equation relates to which petrophysical property?
Answer: Cementation and tortuosity of pore space
The formation factor F = R0/Rw reflects how the geometry, tortuosity, and cementation of pore channels affect resistivity relative to the pore fluid alone.
Which log is most commonly used to identify fractures in a formation?
Answer: Fullbore Formation MicroImager (FMI)
The FMI (or similar microresistivity imaging logs) produces high-resolution borehole wall images that clearly reveal fracture orientations and apertures.
What does a high spontaneous potential (SP) deflection (toward negative millivolts) typically indicate?
Answer: A permeable, porous sand with fresh formation water
Large negative SP deflections indicate a permeable bed where salinity contrast between mud filtrate and formation water drives a significant electrochemical potential.
Invasion of mud filtrate into a formation primarily affects which logging measurements?
Answer: Shallow and medium resistivity measurements
Mud filtrate invasion affects shallow and medium resistivity measurements most because those tools read within the invaded zone, while deep resistivity reads the virgin formation.