HALCYON P-17 Well Integrity Decision Workbench

Well Configuration & Operating Limits

Well Identity

Parameter	Value
Well Name	HALCYON P-17
Location	UK North Sea, Fixed Offshore Platform
Function	Oil Producer (Mature, Depletion Drive)
First Production	2019
Artificial Lift	Gas Lift via A-annulus

Completion Schematic

                    PRODUCTION TREE
              +------------------------+
 Production ->| Master / Wing / Choke  |----> Flowline
              +-----------+------------+
                          |
                     Wellhead seals
          C annulus ------|---------------- 13 3/8" casing
          B annulus ------|---------------- 9 5/8" casing
          A annulus ------|---------------- 4.5" tubing
                          |
                        SCSSV
                          |
                  Gas-lift mandrels  <---- gas injected via A annulus
                          |
                    Production tubing
                          |
                  Production packer
                    (~2700 m MD)

Operating Limits & MAASP

Parameter	Current Value	Limit	Status
A-annulus Pressure	110 barg	200 barg (MAASP)	Normal
B-annulus Pressure	30 barg	50 barg (MAASP)	Critical
C-annulus Pressure	0 barg	0 barg	Normal
Tubing Pressure	170 barg	180 barg	Normal
Casing Pressure	140 barg	150 barg	Normal
SCSSV Leak Rate	0.31 L/min	0.5 L/min	Warning

Data Quality & Trustworthiness

Review data quality issues before using evidence for decision-making.

Data Quality Register

Parameter	Issue	Severity	Impact	Status
B-annulus Pressure Sensor	Drifting	High	May underreport pressure	Open
Gas-Lift Flow Meter	Calibration due	Medium	Uncertainty in gas-lift rate	Open
C-annulus Pressure Sensor	No recent test	High	Unknown integrity status	Open

Surveillance Status

Surveillance Item	Last Performed	Next Due	Status
B-annulus Pressure Check	2026-09-20	Daily	OK
SCSSV Leak Test	2026-04-22	2026-10-22	Due Soon
Gas-Lift Valve Inspection	2026-07-10	2026-10-10	OK
C-annulus Pressure Test	2025-12-01	2026-06-01	Overdue
Wellhead Inspection	2025-09-01	2026-09-01	Overdue

Anomaly Detection

Identify meaningful changes, degradation, and abnormal behavior.

B-annulus Pressure Trend (Recent Hourly Data)

SCSSV Leak Rate Trend

Gas-Lift Rate vs. B-annulus Pressure

Key Anomalies

Parameter	Normal Range	Current Value	Trend	Concern Level
B-annulus Pressure	< 10 barg	30 barg	Rising rapidly	Critical
SCSSV Leak Rate	< 0.5 L/min	0.31 L/min	Increasing	Warning
Bleed-Down Test Rebuild Time	< 60 min	120 min	Slowing	Critical

Compare Measurements Against Limits

Compare current measurements against approved operating limits and MAASP.

Pressure vs. MAASP

Historical Trends (Monthly Data)

Interpret Observations

Distinguish normal from abnormal behavior for this well configuration.

Normal Behavior

A-annulus Pressure: ~100-110 barg (gas-lift operations).
C-annulus Pressure: 0 barg (atmospheric).
SCSSV Leak Rate: < 0.5 L/min (passing).

Abnormal Behavior

B-annulus Pressure: Rising to 30 barg (exceeds 10 barg threshold).
SCSSV Leak Rate: Increasing trend (0.12 → 0.31 L/min).
Bleed-Down Test: Slow rebuild (120 min vs. < 60 min expected).

Hypothesis Assessment

Present multiple plausible integrity hypotheses with supporting and contradicting evidence.

🔹 Hypothesis 1: Gas Migration into B-annulus

Description: Gas is migrating from the reservoir or A-annulus into the B-annulus.

Evidence For:

B-annulus pressure rising rapidly (5 → 30 barg).
Slow bleed-down rebuild (120 min vs. < 60 min).
No fluid detected in B-annulus (consistent with gas migration).

Evidence Against:

No direct evidence of gas source (e.g., no A-annulus pressure spike).

Confidence: High

Evidence Still Required:

B-annulus gas composition analysis.
C-annulus pressure test (to rule out casing leak).

🔹 Hypothesis 2: SCSSV Degradation

Description: The SCSSV is degrading, leading to increased leak rates.

Evidence For:

SCSSV leak rate increasing (0.12 → 0.31 L/min).
Previous failure in 2025 (0.6 L/min, repaired).

Evidence Against:

Leak rate still below 0.5 L/min limit.
No direct link to B-annulus pressure rise.

Confidence: Medium

Evidence Still Required:

SCSSV internal inspection.
Pressure test across SCSSV.

🔹 Hypothesis 3: Gas-Lift Valve Failure

Description: A gas-lift valve is failing, causing gas to leak into the B-annulus.

Evidence For:

Gas-lift valve malfunction in 2026-07-10.
Gas-lift rate increased by 20% → B-annulus pressure rose to 15 barg.

Evidence Against:

No direct evidence of valve leakage.
B-annulus pressure rise predates gas-lift rate increase.

Confidence: Medium

Evidence Still Required:

Gas-lift valve pressure tests.
Inspection of gas-lift mandrels.

Barrier Assessment

Assess the condition of primary, secondary, and tertiary barriers.

Barrier Status

Barrier	Elements	Condition	Risk	Implications
Primary Barrier	SCSSV + Production Tubing	Degrading	Medium	SCSSV leak rate increasing; tubing intact.
Secondary Barrier	Production Casing + Wellhead Seals	Compromised	High	B-annulus pressure > 10 barg; potential loss of secondary barrier if pressure exceeds MAASP (50 barg).
Tertiary Barrier	Intermediate Casing	Unknown	High	No recent C-annulus pressure test; integrity uncertain.

Cumulative Integrity Concerns

B-annulus Pressure: Critical (30 barg, approaching MAASP of 50 barg).
SCSSV Leak Rate: Warning (0.31 L/min, approaching limit of 0.5 L/min).
Bleed-Down Test: Critical (slow rebuild suggests B-annulus leakage).
Missing Surveillance: Critical (C-annulus test and wellhead inspection overdue).

Assess Risk

Evaluate the risk of continued operations and potential failure scenarios.

Risk Matrix

Scenario	Likelihood	Consequence	Risk Level	Mitigation
B-annulus pressure exceeds MAASP (50 barg)	Medium	Catastrophic (loss of secondary barrier)	High	Shut in well if B-annulus pressure > 30 barg.
SCSSV leak rate exceeds 0.5 L/min	Medium	Severe (loss of primary barrier)	High	Monitor SCSSV leak rate; plan intervention if trend continues.
Gas-lift valve fails, causing uncontrolled gas injection	Low	Severe (A-annulus overpressure)	Medium	Inspect gas-lift valves; monitor A-annulus pressure.

Operational Decision

Evaluate production vs. integrity trade-offs and determine the operational disposition.

Current Recommendation

Do NOT increase production.

Rationale: B-annulus pressure is already at 30 barg (critical threshold). Increasing production could exacerbate the pressure rise and risk exceeding the MAASP of 50 barg.

Production vs. Integrity Trade-offs

Action	Production Impact	Integrity Impact	Recommendation
Increase production/choke	↑ Oil rate	↑ B-annulus pressure (high risk)	❌ Not Recommended
Increase gas-lift rate/pressure	↑ Oil rate	↑ B-annulus pressure (high risk)	❌ Not Recommended
Reduce production rate	↓ Oil rate	↓ B-annulus pressure (low risk)	✅ Recommended
Shut in well	↓ Oil rate (0)	↓ B-annulus pressure (safe)	⚠️ Consider if pressure continues to rise
Controlled B-annulus bleed-down/rebuild test	No impact	Diagnostic (low risk)	✅ Recommended

Operational Disposition

Current Disposition: Enhanced Surveillance + Restrict Production

Conditions to Change Decision:

If B-annulus pressure > 30 barg → Shut in well.
If SCSSV leak rate > 0.5 L/min → Shut in well.
If Bleed-down test passes → Continue monitoring.
If C-annulus pressure test passes → Reassess tertiary barrier.

Actions Required

Define restrictions, diagnostics, approvals, surveillance, or intervention actions.

Immediate Actions

Shut in well if B-annulus pressure exceeds 30 barg.
Conduct controlled B-annulus bleed-down/rebuild test to assess leakage.
Inspect SCSSV for degradation (leak rate: 0.31 L/min).
Inspect gas-lift valves for potential leakage.
Calibrate B-annulus pressure sensor (currently drifting).

Surveillance Actions

Daily B-annulus pressure checks (threshold: > 10 barg → investigate).
Perform C-annulus pressure test (overdue since 2026-06-01).
Conduct wellhead inspection (overdue since 2026-09-01).
Monitor SCSSV leak rate (next test due: 2026-10-22).

Approval Requirements

Engineering review required before any production increase.
Management approval required for well shut-in.

Verification

Verify conclusions and trace reasoning back to source evidence.

Key Conclusions & Evidence

Conclusion	Evidence	Source
B-annulus pressure is critically high.	B-annulus pressure = 30 barg (threshold: > 10 barg).	`recent_hourly_2026-08-20_to_2026-09-20.csv`, `shift_log_extract.csv`
SCSSV is degrading.	Leak rate increased from 0.12 L/min (2024) to 0.31 L/min (2026).	`valve_test_history.csv`
Bleed-down test suggests B-annulus leakage.	Rebuild time = 120 min (expected: < 60 min).	`bleed_rebuild_tests.csv`
Gas-lift rate increase correlates with B-annulus pressure rise.	Gas-lift rate +20% → B-annulus pressure rose to 15 barg.	`shift_log_extract.csv`

Assumptions & Uncertainties

Assumption	Uncertainty	Impact
B-annulus pressure rise is not due to tubing leak.	No fluid detected in B-annulus.	Low
SCSSV is still functional despite increasing leak rate.	Leak rate still below 0.5 L/min limit.	Medium
B-annulus pressure sensor is drifting (underreporting).	Actual pressure may be higher than measured.	High
C-annulus integrity is unknown.	No recent pressure test.	High

Lessons Learned & Next Steps

Document lessons learned and define next steps for continuous improvement.

Lessons Learned

B-annulus pressure monitoring is critical: Early detection of rising pressure could have prevented the current situation.
SCSSV degradation must be addressed proactively: Increasing leak rates should trigger immediate inspection.
Surveillance gaps can hide integrity issues: Overdue C-annulus tests and wellhead inspections may have missed early signs of failure.
Gas-lift changes can impact integrity: Production changes (e.g., gas-lift rate increases) must be evaluated for integrity risks.

Next Steps

Implement real-time B-annulus pressure monitoring with alerts for thresholds (10 barg, 30 barg).
Schedule regular SCSSV inspections (e.g., quarterly) to catch degradation early.
Conduct a root cause analysis for the B-annulus pressure rise.
Update the surveillance plan to include more frequent C-annulus and wellhead inspections.
Review gas-lift operations to ensure they do not compromise integrity.