CWD Data Analysis & Reporting 2 — Questions and Answers
Question 1: When plotting a well driller's log, which scale is most appropriate for representing formation depths accurately?
- Logarithmic scale
- Linear depth scale (Correct answer)
- Semi-log scale
- Exponential scale
Correct answer: Linear depth scale
A linear depth scale provides uniform spacing per unit depth, making it the standard for driller's logs to accurately represent formation thicknesses.
Question 2: A pumping test shows drawdown stabilizes at 45 feet after 4 hours. What does this indicate?
- The well has failed
- Steady-state conditions have been reached (Correct answer)
- The aquifer is confined
- The pump is malfunctioning
Correct answer: Steady-state conditions have been reached
When drawdown stabilizes, it indicates that the rate of water removed equals the rate of recharge, meaning steady-state conditions have been reached.
Question 3: Which of the following best describes the purpose of a specific capacity calculation?
- Determines total well depth
- Evaluates well yield per unit of drawdown (Correct answer)
- Measures static water level
- Calculates casing diameter
Correct answer: Evaluates well yield per unit of drawdown
Specific capacity (gpm/ft of drawdown) is used to evaluate how efficiently a well produces water relative to the head loss imposed during pumping.
Question 4: What does an E-log (electric log) primarily measure in a borehole?
- Water temperature at depth
- Electrical resistivity and spontaneous potential of formations (Correct answer)
- Pump efficiency over time
- Casing corrosion rates
Correct answer: Electrical resistivity and spontaneous potential of formations
Electric logs measure the resistivity and spontaneous potential of subsurface formations, helping drillers identify lithology and fluid-bearing zones.
Question 5: On a well completion report, the term 'static water level' refers to:
- Water level measured during pumping
- Water level after the pump is shut off and equilibrium is restored (Correct answer)
- Depth to the bottom of the well screen
- The rate of natural recharge
Correct answer: Water level after the pump is shut off and equilibrium is restored
Static water level (SWL) is the depth to water measured when the well is not being pumped and pressure has fully equilibrated.
Question 6: A well log shows alternating layers of clay and sand. How should this be recorded in a formation log?
- Record only the dominant formation type
- Log each distinct layer with its top depth, bottom depth, and description (Correct answer)
- Average the properties of all layers
- Record only layers thicker than 5 feet
Correct answer: Log each distinct layer with its top depth, bottom depth, and description
Each distinct lithologic layer must be individually logged with depth intervals and descriptions to provide an accurate stratigraphic record.
Question 7: Which statistical measure is most useful for identifying outlier water quality readings in a dataset of multiple well samples?
- Mean
- Mode
- Standard deviation (Correct answer)
- Median
Correct answer: Standard deviation
Standard deviation quantifies how spread out values are from the mean, making it ideal for identifying data points that fall unusually far from the average.
CWD Data Analysis & Reporting 2
When plotting a well driller's log, which scale is most appropriate for representing formation depths accurately?