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 parameter is determined by the Waxman-Smits model that the standard Archie equation does not account for?
Answer: Clay conductivity contribution to measured resistivity
The Waxman-Smits model accounts for the additional electrical conductivity contributed by clay-bound water and exchange cations on clay surfaces, which Archie's equation ignores.
What is the main advantage of Logging While Drilling (LWD) over wireline logging?
Answer: Measurements taken before significant invasion and borehole deterioration
LWD acquires data immediately after bit penetration, before substantial mud filtrate invasion alters formation fluid distribution and before borehole wall degradation.
A formation with a photoelectric factor (PE) of approximately 4.65 is most likely composed of:
Answer: Limestone (calcite)
Calcite (limestone) has a PE value of approximately 5.08, and dolomite is about 3.14; a PE near 4.65 is characteristic of limestone or a limestone-dominated mixture.
In nuclear magnetic resonance (NMR) logging, the T2 cutoff is used to distinguish:
Answer: Bound (irreducible) water from free (producible) fluids
The T2 cutoff separates short T2 signals (clay-bound and capillary-bound water) from longer T2 signals representing moveable fluids like free water and hydrocarbons.
The dual water model for shaly sands treats clay-bound water as having:
Answer: Zero salinity (effectively fresh)
The dual water model treats clay-bound water as essentially fresh (zero salinity) because cations balance the charge, making it behave like distilled water electrically.
Which log combination best differentiates dolomite from limestone in a carbonate section?
Answer: Neutron-density crossplot and PE curve
The neutron-density crossplot positions and PE values clearly distinguish dolomite (PE ≈ 3.14) from limestone (PE ≈ 5.08) and can resolve mixed mineralogies.
Formation water resistivity (Rw) can be estimated from logs using the SP log equation when the mud filtrate resistivity (Rmf) is known and the formation is:
Answer: 100% water-saturated and permeable
The SP-derived Rw estimate requires a clean, water-saturated permeable bed so the SP deflection reflects only the electrochemical potential driven by the Rmf/Rw salinity contrast.