SPE Well Completions and Stimulation 3 — Questions and Answers
Question 1: What is the purpose of an acid pre-flush stage in a matrix acidizing job?
- To dissolve carbonate minerals and prepare the formation for main acid (Correct answer)
- To neutralize formation water salinity
- To hydrate the acid before injection
- To set the packer before treatment
Correct answer: To dissolve carbonate minerals and prepare the formation for main acid
An acid pre-flush removes carbonate minerals and cleans the near-wellbore area before the main acid system is injected.
Question 2: Which completion method is most commonly used in deepwater subsea wells?
- Surface wellhead with Christmas tree
- Subsea tree with wet completion (Correct answer)
- Openhole with no tubing
- Beam pump with sucker rods
Correct answer: Subsea tree with wet completion
Deepwater subsea wells use subsea trees (horizontal or vertical) installed on the wellhead at the seafloor, enabling wet completions.
Question 3: What is 'proppant embedment' in hydraulic fracturing?
- Proppant settling to the bottom of the fracture
- Proppant grains being pressed into soft formation rock, reducing fracture width (Correct answer)
- Proppant dissolving in fracture fluid
- Proppant bridging at the perforations
Correct answer: Proppant grains being pressed into soft formation rock, reducing fracture width
Embedment occurs when proppant grains press into soft or weak formation rock under closure stress, reducing the effective propped fracture width.
Question 4: What diagnostic test uses the pressure decline after a small-volume injection to determine fracture closure pressure?
- Extended leak-off test (XLOT)
- Mini-frac (or DFIT — Diagnostic Fracture Injection Test) (Correct answer)
- Step-rate test
- Pressure buildup test
Correct answer: Mini-frac (or DFIT — Diagnostic Fracture Injection Test)
A DFIT (or mini-frac) analyzes the pressure decline after a small injection to determine closure pressure, permeability, and reservoir pressure.
Question 5: What does a negative skin value indicate about a well?
- The well has severe formation damage
- The well is producing below its natural potential
- The well has been stimulated beyond its natural productivity (Correct answer)
- The well requires immediate workover
Correct answer: The well has been stimulated beyond its natural productivity
Negative skin indicates enhanced near-wellbore flow, such as that created by hydraulic fracturing or acid stimulation.
Question 6: In coiled tubing operations, what limits the maximum depth of coiled tubing deployment?
- Formation temperature and pressure
- Coiled tubing weight, friction, and helical buckling (Correct answer)
- The number of perforations in the casing
- Wellhead equipment pressure rating
Correct answer: Coiled tubing weight, friction, and helical buckling
Helical buckling of coiled tubing under compressive load, combined with friction forces, limits how deep coiled tubing can be pushed in a well.
Question 7: Which parameter is used to describe the efficiency of a hydraulic fracture treatment?
- Fracture gradient
- Fluid efficiency (ratio of fracture volume to total fluid injected) (Correct answer)
- Proppant concentration in lbm/gal
- Fracture initiation pressure
Correct answer: Fluid efficiency (ratio of fracture volume to total fluid injected)
Fluid efficiency is the ratio of the final fracture volume to total fluid pumped, accounting for fluid lost to leak-off.
SPE Well Completions and Stimulation 3
What is the purpose of an acid pre-flush stage in a matrix acidizing job?