Well Failure Analysis & Forensics
Investigating why wells fail — root cause analysis, forensic procedures, and prevention strategies.
Failure Statistics
Approximately 10-20% of newly drilled water wells fail to meet design expectations within 5 years. Understanding failure modes enables prevention and early intervention.
| Failure Mode | Frequency | Typical Cause | Prevention |
|---|---|---|---|
| Low yield | 15-25% | Poor siting, inadequate testing | Geophysical survey, test holes |
| Sand pumping | 10-20% | Incorrect screen/slot size, poor development | Proper design, thorough development |
| Water quality failure | 5-15% | Surface contamination, inadequate sealing | Proper grouting, setback distances |
| Pump failure | 20-30% | Undersized, poor installation, power issues | Proper sizing, surge protection |
| Casing failure | 5-10% | Corrosion, poor material selection | Material compatibility, cathodic protection |
| Screen blockage | 10-15% | Encrustation, biofouling, corrosion | Water treatment, periodic maintenance |
Forensic Investigation Procedures
Step 1: Document the Evidence
- Construction records: Drilling logs, casing schedule, screen specs, development records
- Operating history: Pump test data, production records, water level measurements
- Maintenance history: Rehabilitation treatments, pump replacements, repairs
- Water quality history: All test results over the life of the well
- Adjacent wells: Data from neighboring wells — regional aquifer behavior
Step 2: Visual Inspection
- Camera survey: Downhole video — inspect casing, screen, and borehole condition
- Geophysical logging: Caliper (casing condition), gamma (formation), temperature (water entry)
- Wellhead inspection: Seal condition, surface drainage, contamination sources
- Pump inspection: Motor condition, impeller wear, electrical connections
Step 3: Performance Testing
- Step-drawdown test: Determine well losses and efficiency — compare to original test
- Specific capacity: Q/s — compare to original value (decline indicates deterioration)
- Pump performance test: Verify pump operates on its curve — check for wear
- Water quality sampling: Comprehensive analysis — compare to original and standards
Step 4: Root Cause Analysis
- Fishbone (Ishikawa) diagram: Map all potential causes into categories — geology, design, construction, operation, maintenance
- 5-Why analysis: Ask "why" repeatedly — trace back to fundamental cause
- Pareto analysis: 80% of failures from 20% of causes — focus on primary drivers
- Timeline analysis: Plot performance metrics over time — identify when decline began
Common Failure Case Studies
Case: Sand Pumping After 2 Years
- Symptoms: Progressive sand increase in pumped water — pump damage
- Investigation: Camera shows screen intact but slot size too large for formation
- Root cause: No grain size analysis before screen selection — used stock screen
- Resolution: Installed gravel pack — cost $8,000
- Prevention: Always conduct sieve analysis — select screen slot for 50-60% of formation d₁₀
Case: Yield Decline 40% Over 5 Years
- Symptoms: Specific capacity declined from 5 to 3 L/s/m
- Investigation: Camera shows heavy iron oxide encrustation on screen
- Root cause: High iron content water + dissolved oxygen = rapid encrustation
- Resolution: Acid treatment + surge development — restored 90% of original yield
Prevention: Annual monitoring, biannual chlorination for iron-rich water
Case: Contamination After Drilling Nearby
- Symptoms: Bacteria and nitrates appear in well 6 months after new well drilled 20 m away
- Investigation: New well has inadequate grouting — surface water travels along borehole
- Root cause: New well drilled without proper sanitary seal — no regulatory oversight
- Resolution: New well re-grouted to surface — contamination resolved in 3 months
- Prevention: Proper setback distances, grouting requirements, driller licensing
Prevention Strategies
- Proper siting: Geophysical surveys, test holes — reduce dry hole risk from 20% to 5%
- Design review: Independent review of well design before construction
- Quality assurance: Owner's representative on-site during construction
- Baseline documentation: Complete records at construction — benchmark for future comparison
- Preventive maintenance: Regular inspection, testing, and rehabilitation schedule
- Performance monitoring: Track specific capacity, water levels, water quality over time
Cost of Prevention vs Failure
Geophysical survey: $2,000-5,000. Test hole: $3,000-5,000. QA inspector: $500-1,000/day. Failed well: $10,000-30,000 to re-drill. Contamination remediation: $20,000-200,000. Prevention investment typically returns 5-10× in avoided failures.