Well Configuration & Completion
- Environment: UK North Sea, fixed offshore platform
- Function: Oil producer, mature depletion drive
- Artificial Lift: Gas lift through A-annulus (4.2 MMscf/d)
- Tubing: 4.5 in production tubing, packer ~2,700 m MD
- Casing: 9 5/8 in production, 13 3/8 in intermediate
- Barriers: SCSSV (passing but degrading trend), Tree valves (passing)
Core Integrity Concern
Since 2022, B-annulus has changed from negligible pressure to repeatable sustained pressure with measurable rebuild after bleed-down. Behaviour accelerated during 2026.
- Hydrocarbon indication in prior annulus sample (inconclusive source).
- Correlation with higher A-annulus/gas-lift pressure.
- Deteriorating but still passing SCSSV leak-test trend.
- Overdue integrity surveillance (fingerprint sample).
- Data-quality conflicts (gauge vs transmitter).
B-Annulus Pressure History (2019–2026)
Recent Hourly Pressures (Aug–Sept 2026)
SCSSV Leak Test Trend
Data Quality & Overdue Surveillance
| ID | Issue | Severity | Impact |
|---|
Shift Log & Event Extract
| Date | Role | Comment |
|---|
Configuration Control: Current vs Superseded Limits
| Parameter | WI-ENV-P17-REV4 (Current) | WI-ENV-P17-REV2 (Superseded) | Decision Rule |
|---|---|---|---|
| B-annulus MAASP | 70 barg | 85 barg | Use REV4 REV2 superseded 01 July 2026 |
| B-annulus Action Level | ≥ 40 barg OR rebuild > 25 barg/24h | N/A | Immediate escalation & restriction |
| B-annulus Warning Level | ≥ 15 barg sustained OR rebuild > 10 barg/48h | N/A | Enhanced surveillance & review |
Current Compliance Status
| Parameter | Current Value | Warning | Action | MAASP | Status |
|---|---|---|---|---|---|
| B-annulus Pressure | ~29.6 barg | ≥ 15 barg | ≥ 40 barg | 70 barg | WARNING |
| B-annulus Rebuild Rate | ~16 barg/36h (Sept 5 test) | > 10 barg/48h | > 25 barg/24h | N/A | WARNING |
| A-annulus Pressure | ~108 barg | > 120 barg | > 140 barg | 165 barg | NORMAL |
| C-annulus Pressure | ~0.3 barg | > 3 barg | > 10 barg | 30 barg | NORMAL |
| Surveillance Compliance | Fingerprint overdue | Quarterly required | N/A | N/A | NON-COMPLIANT |
Scenario Analysis & What-If Testing
Select a scenario to evaluate its impact on evidence, uncertainty, integrity constraints, and the operational decision.
Scenario: Increase Production / Choke (+10%)
Would increase THP and flowline pressure. May increase gas lift demand (A-annulus). If leak path is rate-dependent (FM-02/03), B-annulus rebuild will accelerate, providing diagnostic evidence. If stable, weakens rate-dependent hypotheses. Currently uncertain due to overdue fingerprint.
BLOCKED Violates IR-P17-2026-04. Cannot approve until B-annulus source is identified and gauge disagreement resolved. Production opportunity does not override unresolved integrity constraints.
Scenario: Increase Gas Lift Rate
Increases A-annulus pressure. If FM-01 (A/B seal leak) is active, higher A pressure will drive more gas into B-annulus, accelerating B-annulus buildup. This would be a useful diagnostic step test but carries risk of approaching Action levels.
BLOCKED Restriction limits gas lift to ≤ 4.3 MMscf/d. Current rate is 4.2 MMscf/d. Cannot increase without WI approval.
Scenario: Reduce Production Rate
Reduces THP and flowline pressure. Event E012 (Sept 12) showed that reducing rate slowed B-annulus rebuild but did not eliminate it. This suggests the leak/source is not purely rate-dependent, or there is a trapped pressure component.
VALID DIAGNOSTIC Already performed. Confirms that rate reduction alone will not resolve the B-annulus anomaly. Integrity investigation still required. Does not change current restriction status.
Scenario: Shut-In Well
Stops production, reduces THP. B-annulus may stabilize if source is production-dependent. However, shut-in does NOT repair a leaking barrier. Trapped pressure or thermal effects might still cause B-annulus rise. C-annulus would be monitored for cross-contamination.
NOT REQUIRED YET B-annulus is ~29.6 barg, well below MAASP (70 barg) and Action level (40 barg). Shut-in is a last resort if barriers degrade further or limits are approached. Current disposition allows continued flowing under restriction.
Scenario: Controlled B-annulus Bleed & Rebuild
Confirms active leak/source and measures rebuild rate. Last test (Sept 5, BR2026-02) showed rebuild to 18.1 barg in 36h. This confirms the anomaly is genuine and not just instrumentation drift. Provides critical data for hypothesis testing.
MAINTAIN SURVEILLANCE Monthly bleed/rebuild is required while source is unresolved. Next test due early October. If next rebuild exceeds 25 barg/24h, triggers immediate escalation to Action level.
Scenario: Resolve Conflicting Instruments (DQ02)
Local gauge reads 31.0 barg, transmitter reads 27.1 barg. Disagreement of ~4 barg. Neither is automatically preferred. If local gauge is correct, B-annulus is closer to Warning/Action thresholds. Resolving this reduces uncertainty and improves decision confidence.
REQUIRES ACTION Offshore Operations must verify local gauge calibration and transmitter loop. Until resolved, must assume worst-case (higher pressure) for safety. Does not lift production restriction.
Scenario: Complete Overdue Surveillance (Fingerprint)
Fingerprint sample will determine if B-annulus gas is lift gas (supports FM-01) or produced fluid (supports FM-02/03). This is the single most critical piece of missing evidence to narrow down the failure mechanism.
CRITICAL ACTION Sample is overdue since 01 Sept (DQ06). Must be obtained immediately. Until analyzed, source attribution remains unresolved, and production increase cannot be justified.
Scenario: SCSSV Fails Acceptance Test
Current leak rate is 0.44 L/min (limit 0.50). If it fails, the primary subsurface isolation barrier is compromised. This would trigger immediate escalation per IR-P17-2026-04 ("new evidence of a second degraded barrier element").
ESCALATE & RESTRICT Would require immediate well shut-in or intensive intervention planning. Production restriction would become absolute. Triggers formal well integrity review.
Operational Disposition & Recommendation
The well remains inside absolute pressure limits (MAASP), but the B-annulus anomaly is unresolved, surveillance is overdue, and data quality conflicts exist. Production Engineering's request for +10% choke (E014) cannot be approved until integrity constraints are satisfied. A production opportunity does not override unresolved integrity constraints.
Barrier & Integrity Implication
- Primary Containment: SCSSV and tree valves are functional but SCSSV shows degradation trend. Tubing and packer integrity not disproved but unconfirmed.
- Secondary Containment: B-annulus sustained pressure indicates loss of secondary containment margin. Source (lift gas vs produced fluid) unknown.
- Cumulative Concern: Deteriorating SCSSV trend + unresolved B-annulus source + overdue surveillance = reduced overall well integrity confidence.
Required Actions & Diagnostics
| Priority | Action | Owner | Trigger/Deadline |
|---|---|---|---|
| Critical | Obtain and analyze B-annulus fingerprint sample | Well Integrity Engineer | Overdue since 01 Sept |
| High | Resolve B-annulus gauge vs transmitter disagreement | Offshore Operations | Within 7 days |
| High | Perform monthly B-annulus bleed/rebuild test | Well Integrity Engineer | Early October 2026 |
| Medium | Review SCSSV maintenance/replacement plan | Wells/Operations | Before next 6-monthly test |
Escalation Triggers
The following conditions require immediate escalation and production restriction:
- B-annulus pressure ≥ 40 barg OR rebuild > 25 barg in 24h.
- C-annulus pressure > 3 barg sustained or correlated rise with B.
- Fingerprint sample confirms produced fluid (indicates casing/tubing leak).
- SCSSV fails acceptance test (leak > 0.50 L/min).
- New evidence of a second degraded barrier element.
- Unexplained data quality issues preventing safe operation assessment.
Conditions to Change Decision
The restriction on production increase may be lifted only if:
- Fingerprint sample confirms gas is lift gas (supports FM-01) AND rebuild rate is stable/understood.
- Instrument disagreement is resolved and confirmed B-annulus is safely below Warning thresholds.
- SCSSV leak trend stabilizes or valve is replaced.
- Formal Well Integrity Engineer approval is granted based on updated risk assessment.
Note: Even if B-annulus is below MAASP, this does not prove acceptable integrity. Trend, source, rebuild, barrier status, and surveillance completeness remain relevant.