What are the steps in wellhead integrity testing?

Wellhead Integrity Testing — Purpose, Process, Equipment, and Best Practice

Wellhead integrity testing verifies the pressure-containing capability and functional performance of the wellhead and tree assembly as part of the well barrier envelope. It is executed during completion handover, before start-up, after interventions, and at periodic intervals in production operations.

I. High-level purpose and where this fits in the value chain

• I.I Objective: Confirm that the wellhead, tree, and associated valves, seals, gaskets, and connections can contain and control pressure safely within their rated limits, maintaining primary/secondary barriers.
• I.II Value chain position: Completion-to-operations interface; part of the well integrity management system within production operations and HSE assurance.
• I.III When performed: Post-installation, pre-commissioning, post-maintenance/intervention, after abnormal pressure/thermal events, and at scheduled integrity intervals.
• I.IV Scope boundary: Surface wellhead and tree assembly (assumed). Similar principles apply to subsea systems using dedicated test caps and remote tooling (assumption noted).

II. Step-by-step process flow (wellhead integrity test)

• II.I Define test scope and matrix
  • Identify components to test: casing head, tubing head, tree body, master/swab/wing valves, chokes, flanged connections, annulus outlets, VR plug threads.
  • Define barriers: primary (tree + tubing hanger seals), secondary (wellhead seals/VR plugs), and test boundaries per barrier schematic.
  • Set pressures, mediums, and durations: low-pressure leak check and high-pressure hydrostatic test; functional tests for valves.
• II.II Engineering checks and limits
  • Confirm pressure ratings, temperature limits, allowable loads, and maximum test pressure of the weakest component.
  • Verify casing/tubing MAWPs, annulus limits, and any de-rated elements (corrosion, wear).
  • Prepare P&ID/sketch of test configuration with isolation points and vents.
• II.III Permitting and site preparation
  • Issue PTW, perform JSA, set exclusion zone, and conduct toolbox talk on barriers and emergency response.
  • Position spill containment, fire protection, and verify calibration certificates for gauges/recorders.
• II.IV Isolate and secure the well
  • Shut in the well; bleed down to zero. Confirm no trapped pressure in cavities.
  • Install primary isolations: back-pressure valve (BPV) in the tubing hanger profile, valve removal (VR) plugs in master/wing ports as needed.
  • Isolate annuli not under test; verify check valves/chokes bypassed or isolated to prevent masking leaks.
• II.V Install test equipment and fill with test medium
  • Connect calibrated pump, test manifold with relief valve, and high-accuracy gauges/data logger to the test port or test cap.
  • Use clean water treated with corrosion inhibitor/biocide for hydrostatic testing; displace air thoroughly to minimize compressibility.
  • Confirm vents positioned to remove trapped gas; capture returns in a contained tote.
• II.VI Low-pressure (LP) leak check
  • Pressurize slowly to 200–300 psi (estimated typical). Hold 10–15 minutes after temperature stabilization.
  • Inspect flanges, valve packing, body-bonnet, VR plugs, and threaded connections. Soap test gas-exposed joints if applicable.
  • Acceptance: no visible leaks; pressure loss within instrumentation uncertainty (estimated).
• II.VII High-pressure (HP) hydrostatic test
  • Increase in controlled increments (e.g., 25%, 50%, 75%, 100% of target), pausing to bleed trapped gas and allow thermal stabilization.
  • Reach target test pressure per calculated limit (see formulas below). Hold 30–60 minutes or per standard; record continuous pressure/temperature.
  • Valve function: while at pressure, individually stroke and re-seat master, wing, and swab valves to verify sealing (test opposite side as configured).
  • Acceptance (estimated typical): no visible leaks; pressure decay = 5% after stabilization or = 50 psi/h, corrected for temperature. Zero leak-through on closed valves.
• II.VIII Annulus integrity tests
  • Test each accessible annulus (A, B, etc.) separately to its allowable test pressure, isolating other annuli to prevent crossflow.
  • Hold and acceptance criteria per annulus MAWP and barrier design (estimated typical).
• II.IX Depressurize, demobilize, and restore
  • Bleed down to zero through a controlled vent; confirm all cavities at zero pressure.
  • Remove test equipment and temporary plugs in the correct sequence; restore well configuration.
  • Update well integrity records with plots, calibration data, acceptance statements, and any remedial actions.

Key formulas and acceptance basis

• II.X Test pressure selection (choose the lowest safe limit):

  \( P_{test} = \min\left(k \times WP,\; P_{rating},\; P_{weakest},\; P_{reg}\right) \)

  • \( WP \): component working pressure; \( k \): field test factor (estimated 1.10–1.25, per standard/operator);
  • \( P_{rating} \): manufacturer rating; \( P_{weakest} \): limiting element in the test boundary; \( P_{reg} \): regulatory cap.
• II.XI Leak rate from pressure decay (hydrostatic):

  \( Q \approx C_t \, V \, \dfrac{\Delta P}{\Delta t} \)

  • \( Q \): equivalent leak flow rate; \( C_t \): total compressibility of fluid + system (estimated water \( \sim 3.1\times10^{-6}\; \text{psi}^{-1} \) plus hose/compliance); \( V \): test fluid volume; \( \Delta P/\Delta t \): pressure decay rate after temperature stabilization.
• II.XII Temperature correction (qualitative): Apply correction if pressure changes correlate with temperature drift. Stabilize before acceptance.

III. Major equipment/components and functions

• III.I Isolation hardware: Back-pressure valve (BPV), valve removal (VR) plugs, test plugs for tubing hanger profiles.
• III.II Test interface: Test cap/hat or ports on tree/wellhead; high-pressure manifold with relief valve and calibrated bleed.
• III.III Pressure generation: Air-driven or electric hydrostatic pump; fine metering valve for incremental pressurization.
• III.IV Measurement: Digital pressure gauge (0.1% FS or better), deadweight tester (reference), temperature probe, data logger/chart recorder.
• III.V Ancillaries: High-pressure hoses with whip checks, check valves, strainers/filters, spill trays, drip pans, gas detectors (if applicable).
• III.VI Safety: Calibrated reliefs, barriers/exclusion, eyewash/firefighting, communications and ESD interface.

IV. Key performance drivers (efficiency, cost, safety, emissions)

• IV.I Barrier discipline: Clear definition of test boundaries prevents over-pressurizing weak components and reduces rework.
• IV.II Thermal stabilization: Time allowed for temperature equalization minimizes false fails from pressure drift.
• IV.III Instrumentation accuracy: High-accuracy gauges and deadweight references improve pass/fail confidence and shorten holds.
• IV.IV Fluid quality and de-aeration: Air-free, filtered fluid reduces compressibility and noise in pressure traces.
• IV.V Sequencing and documentation: Standardized test matrix and real-time data capture cut downtime and facilitate audits.
• IV.VI Environmental control: Closed-loop fluid handling, minimal venting, and spill prevention reduce emissions and cleanup costs.
• IV.VII Time on well: Efficient rig-up/rig-down and parallel preparation of plugs/ports lower production deferment.

V. Typical challenges/bottlenecks and mitigation

• V.I False pressure decay from temperature drift: Allow adequate soak; monitor temperature; apply corrections; use sunshades or insulation on test lines.
• V.II Trapped gas pockets: Vent high points; orient hoses to avoid gas traps; pressurize in steps with intermediate vents.
• V.III Leaking VR plugs or packing: Inspect threads, replace seals, apply correct torque and thread compound; test each barrier independently.
• V.IV Weak-link overtest risk: Complete a weakest-component analysis; set \( P_{test} \) by the lowest-rated element; install protective blinds or isolate sensitive equipment (e.g., gauges/chokes).
• V.V Instrument error and drift: Use recently calibrated Class A gauges; cross-check with deadweight; zero at ambient; avoid long small-bore lines.
• V.VI Annulus crossflow masking: Isolate annuli; verify check valves; test each annulus separately; observe for offset pressures.
• V.VII Cold weather/freeze: Use antifreeze blends, heat trace, or insulated lines; prevent ice-induced pressure artifacts.
• V.VIII H2S/CO2 corrosion or aged seals: Pre-inspect elastomers; de-rate limits; consider seal replacement prior to test if degradation suspected.

VI. Why this activity matters economically and operationally

• VI.I Safety and compliance: Demonstrates barrier integrity, reducing blowout and release risk and meeting regulatory/insurance obligations.
• VI.II Reliability: Early detection of leaks prevents escalation to workovers and unplanned outages.
• VI.III Cost and uptime: Efficient, right-first-time tests minimize deferment and avoid damage from inadvertent over-pressurization.
• VI.IV Lifecycle integrity: Provides baseline data for trend analysis, supports extension of inspection intervals where justified.