Well Integrity And Barrier Diagnostics

Integrity skill for production, injection, and workover decision support. Use it to frame the problem, screen likely leak paths, and identify which logs or pressure tests are worth running next.

Important: Barrier questions are high-consequence. Do not overstate certainty from a single bleeddown test. Always distinguish between screening diagnosis and formal well-integrity signoff.

Data To Request First

Current well schematic: casing, tubing, packer, perforations, and barrier status
Pressure history for each annulus and tubing
Bleedoff volume, pressure rebuild, and test timing
Cement tops, squeeze history, and cement evaluation logs if available
MIT or pressure test results, leakoff details, and acceptance criteria used
Corrosion history, caliper data, retrieved tubular inspection, and workover history

Workflow

Identify the barrier envelope that should exist.
Classify the pressure behavior: thermal, trapped pressure, SCP, or active communication.
Estimate gas volume or leak severity from bleeddown and rebuild behavior.
Screen the most likely leak path.
Recommend the next discriminating diagnostic, not every possible test.

Module 1 - Annulus Gas Inventory And Bleeddown

def annulus_gas_inventory_scf(pressure_psia, annulus_volume_bbl,
                              temperature_f=100.0, z=1.0):
    """
    Approximate free-gas inventory in standard cubic feet.
    Uses PV/ZT scaling from actual annulus conditions to standard conditions.
    """
    if pressure_psia <= 0 or annulus_volume_bbl <= 0 or z <= 0:
        return None
    v_ft3 = annulus_volume_bbl * 5.615
    t_r = temperature_f + 459.67
    scf = pressure_psia * v_ft3 * 520.0 / (14.7 * z * t_r)
    return scf

def bleeddown_volume_scf(p_initial_psia, p_final_psia, annulus_volume_bbl,
                         temperature_f=100.0, z=1.0):
    """Gas volume released between two annulus pressures."""
    q1 = annulus_gas_inventory_scf(p_initial_psia, annulus_volume_bbl, temperature_f, z)
    q2 = annulus_gas_inventory_scf(p_final_psia, annulus_volume_bbl, temperature_f, z)
    if q1 is None or q2 is None:
        return None
    return max(0.0, q1 - q2)

def pressure_rebuild_rate(p_start_psia, p_end_psia, days):
    """Average annulus pressure rebuild rate."""
    if days <= 0:
        return None
    return (p_end_psia - p_start_psia) / days

Interpretation

Pressure behavior	Likely meaning
Pressure bleeds to zero and stays there	Trapped pressure, low active communication
Pressure bleeds to zero and rebuilds repeatedly	SCP or leak path communication
Pressure tracks temperature / production cycles	Thermal annulus behavior likely
Large bleedoff gas volume from small annulus	Real gas source, not just thermal expansion

Module 2 - Pressure Limits And Barrier Envelope

def maasp_from_shoe(shoe_tvd_ft, fracture_gradient_psi_ft, annulus_fluid_ppg):
    """
    Screening maximum allowable annulus surface pressure from the shoe.
    MAASP = (FG - fluid gradient) * TVD
    fluid gradient = 0.052 * MW(ppg)
    """
    fluid_grad = 0.052 * annulus_fluid_ppg
    return (fracture_gradient_psi_ft - fluid_grad) * shoe_tvd_ft

def safety_factor_to_limit(current_pressure_psi, allowable_pressure_psi):
    """Fraction of pressure limit currently consumed."""
    if allowable_pressure_psi <= 0:
        return None
    return current_pressure_psi / allowable_pressure_psi

Barrier review should answer:

What are the intended primary and secondary barriers right now?
Which annulus is supposed to be isolated?
What is the governing pressure limit: packer, casing, connection, or shoe?
Is the observed pressure inside or outside the design envelope?

Module 3 - Leak Path Screening

Symptom	Likely leak path	Best next discriminator
SCP on A-annulus with stable tubing	Tubing leak or packer leak	Tubing pressure test, noise / temperature log
Multi-annulus pressure communication	Behind-pipe or connection issue	Cement evaluation, pressure communication matrix
Pressure tied to production shut-ins	Tubing-to-annulus communication	Shut-in sequence and gradient comparison
Pressure tied to injection cycles	Injection string or packer leak	Injection falloff and annulus monitoring
Iron, scale, or solids in annulus bleedoff	Corrosion breach or produced-fluid communication	Sample the bleedoff, inspect metallurgy

Module 4 - MIT Interpretation

Use MIT results to answer three separate questions:

Did the pressure test hold according to the stated acceptance criterion?
Does the pressure-hold behavior fit the expected compressibility of the test volume?
If the test failed, does the failure implicate the string, packer, or behind-pipe isolation?

Do not treat "failed MIT" as a full diagnosis. It only narrows the suspect set.

Module 5 - Escalation Logic

Escalate the integrity concern when any of these are true:

Annulus pressure rebuilds rapidly after full bleeddown
Current pressure approaches the controlling MAASP or tubular rating
Two independent barriers cannot be clearly identified
Sampled annulus fluid shows hydrocarbons, produced water, or corrosion solids unexpectedly
Pressure communication spans multiple annuli or changes with nearby operations

Output Format

When using this skill, structure the answer as:

Intended barrier envelope
Pressure behavior classification
Most likely leak path or failure mode
Pressure limit comparison
Highest-value next diagnostic or workover action

Integration Points

Use api-well-standards for casing, tubing, and cement design context.
Use pnge:tubing-design for tubing movement, seal assembly, and packer force effects.
Use pnge:flow-assurance and pnge:production-chemistry when corrosion or deposits are implicated.
Use pnge:materials-fracture-mechanics when crack growth or fatigue is part of the failure hypothesis.

well-integrity-barriers