CWD Data Analysis & Reporting 3 — Questions and Answers
Question 1: A time-drawdown graph plotted on semi-log paper shows a straight line. This pattern is characteristic of:
- Unconfined aquifer with delayed yield
- Confined aquifer under Theis conditions (Correct answer)
- Boundary effects from a nearby stream
- Well development in progress
Correct answer: Confined aquifer under Theis conditions
Under Theis conditions, a confined aquifer produces a straight line on a semi-log time-drawdown plot, which is the basis for the Cooper-Jacob analytical method.
Question 2: What information does a gamma-ray log provide during borehole geophysical logging?
- Measures fluid velocity in the borehole
- Indicates clay/shale content by detecting natural radioactivity (Correct answer)
- Records formation temperature gradient
- Determines water pH at each depth
Correct answer: Indicates clay/shale content by detecting natural radioactivity
Gamma-ray logs measure natural radioactivity from potassium, uranium, and thorium, which is concentrated in clay minerals and shales, helping distinguish them from cleaner sands and carbonates.
Question 3: When documenting well construction, the gravel pack interval should be recorded as:
- Total weight of gravel used only
- Top and bottom depths, grain size specifications, and volume placed (Correct answer)
- Only the screen interval length
- Diameter of the gravel pack zone
Correct answer: Top and bottom depths, grain size specifications, and volume placed
Complete gravel pack documentation requires recording the depth interval, grain size (e.g., 10/20 mesh), and volume placed to verify design specifications were met.
Question 4: During a step-drawdown test, what is the primary data being collected?
- Temperature changes at each pumping rate
- Drawdown at successively increasing pumping rates (Correct answer)
- Casing diameter at each depth
- Formation color changes over time
Correct answer: Drawdown at successively increasing pumping rates
A step-drawdown test measures water level drawdown at multiple increasing pumping rates to evaluate well efficiency and identify well losses versus aquifer losses.
Question 5: A driller notices the drill cuttings change from gray shale to white quartz sand at 180 feet. How should this be noted on the field log?
- Note the change at the next 10-foot interval
- Record the formation change at exactly 180 feet with descriptions of both formations (Correct answer)
- Wait until coring confirms the boundary before recording
- Record only the new formation without noting the previous one
Correct answer: Record the formation change at exactly 180 feet with descriptions of both formations
Formation contacts should be logged at the precise depth they are encountered, with descriptions of both the overlying and underlying formations to create an accurate stratigraphic record.
Question 6: Transmissivity (T) in an aquifer is calculated as:
- Hydraulic conductivity divided by aquifer thickness
- Hydraulic conductivity multiplied by aquifer saturated thickness (Correct answer)
- Storativity divided by aquifer thickness
- Pumping rate divided by drawdown
Correct answer: Hydraulic conductivity multiplied by aquifer saturated thickness
Transmissivity equals hydraulic conductivity (K) times the saturated thickness (b) of the aquifer, representing the aquifer's ability to transmit water across its full saturated depth.
Question 7: Which report element is legally required on a well completion report in most U.S. states?
- Driller's license number and signature (Correct answer)
- Name of the well owner's spouse
- Brand of drilling fluid used
- Drilling contractor's profit margin
Correct answer: Driller's license number and signature
Most state well completion report regulations require the licensed driller's number and signature to verify that work was performed by a qualified, licensed professional.
CWD Data Analysis & Reporting 3
A time-drawdown graph plotted on semi-log paper shows a straight line.
This pattern is characteristic of: