How to conduct well diagnostics using wireline technology?

At-a-Glance: End-to-end wireline well diagnostics plan covering pressure/temperature, PLT, formation testing, and integrity logs with field-proven procedures, target parameters, QC metrics, and risk controls to maximize data quality and minimize NPT.

I. Objective & KPIs

• I.1 Objective: Execute a wireline-based diagnostic campaign to quantify production/injection profile, reservoir pressure and mobility, completion integrity, and flow assurance status, enabling actionable optimization decisions (choke, lift, zonal isolation).
• I.2 Primary KPIs:
  • Data Quality Index (DQI): depth correlation ±0.5 ft; pressure stabilization drift =0.02 psi/s; spinner hysteresis =10%; tool temperature within rating.
  • Coverage: 100% completion interval; all targeted zones tested/logged per program.
  • Operational efficiency: wireline rig-up to rig-down = planned duration; NPT =10% of spread time.
  • Well performance KPIs: updated PI/J-index, zone-by-zone rates (±10%), reservoir pressure (±2%), skin estimate, sample contamination =10% filtrate (estimated).
  • Integrity KPIs: leak detection certainty =95% within 20 ft depth window; CBL/VDL bond index trending vs baseline.
  • HSSE/Emissions: TRIR = 0; pressure control barrier compliance 100%; minimized venting/bleed-offs.

II. Critical Parameters & Target Ranges

III. Step-by-Step Procedure / Workflow / Checklist

III.1 Pre-Job Engineering

• III.1.1 Define scope: PLT (single- or multiphase), memory/real-time P/T, formation tester with sampling, CBL/VDL, caliper, temperature/noise. Prioritize zones and passes.
• III.1.2 Well review: completion schematic, deviation/DLS, restrictions, historical logs, IPR/VLP, expected rates/pressures, scale/asphaltene risk, prior packer/annulus tests.
• III.1.3 Toolstring design: select temperature/pressure ratings, sour-service materials, weakpoint above fish neck, contingency knuckle joints/roller or tractor, telemetry (memory vs surface readout).
• III.1.4 Pressure control: lubricator length = tool length + 10–15%; wireline valve, grease head (for E-line), BOP rams, shear capability, redress kits.
• III.1.5 Programs: logging speeds, station schedule, pass sequence, stabilization criteria, sampling volumes, abort criteria; QA/QC sheets and checklists loaded.
• III.1.6 Calculations: MAWHP, expected hydrostatics, flowing gradients, cable tensions vs deviation and fluid drag, tractor pull, jar settings, ESD setpoints.
• III.1.7 HSE planning: SIMOPS review, sour gas plan, electrical safety, pressure testing plan, evacuation routes, permit to work.

III.2 Mobilization & Rig-Up

• III.2.1 Pressure test PCE: nipple-up per schematic; test each barrier to = test pressure; function-test grease/seals; verify lubricator volume bleed-down path.
• III.2.2 Tool surface tests: electronics burn-in; calibrate sensors (pressure zero/span, spinner threshold, temperature offsets, optical fluid ID).
• III.2.3 Depth system: calibrate depth wheel; encoder verification; install CCL/GR for correlation.

III.3 Baseline & Correlation

• III.3.1 Baseline passes: up/down at slow speed to check noise/drift; record P/T baseline and spinner zero-flow.
• III.3.2 Correlate depth: GR/CCL ties to known markers; lock depth references in program and on real-time display.

III.4 Flowing/Injection PLT (if applicable)

• III.4.1 Surface rate control: set stable rate at surface; record choke, WHP/WHT; avoid transient swings.
• III.4.2 Pass design: multiple passes in both directions at 20–80 ft/min; include stationary points over suspected zones; repeatability check within ±10%.
• III.4.3 Multiphase acquisition: use spinner + holdup (capacitance, optical, density) for phase rates; enable bore/back-pressure regulators for slip mitigation in deviated wells.
• III.4.4 Injection logging: reverse flow identification; adjust spinner orientation; maintain 10–30 ft/min to avoid tool lift-off.
• III.4.5 QC: spinner hysteresis loop test; holdup tool clean/calibrate; check for tool eccentricity using caliper.

III.5 Pressure/Temperature & Build-Up/Drawdown

• III.5.1 Static gradient survey: log P/T at stations every 100–200 ft; identify fluid contacts/leaks from gradient breaks.
• III.5.2 Build-up test: flow at constant rate; shut in downhole if possible; record high-frequency P/T; ensure ?t spans 1–2 log cycles.
• III.5.3 Drawdown test: for injectors or low-perm; apply controlled ?p; monitor sanding risk.

III.6 Formation Testing & Sampling (WFT)

• III.6.1 Station selection: target clean sand via GR/Resistivity/PLT inflow; avoid shale/silt; consider vertical stress for packer sealing.
• III.6.2 Seal and pretest: set packer; conduct mini-drawdown/buildup to estimate mobility; decide sample-go/no-go.
• III.6.3 Sampling: open sample chamber when contamination trend < threshold; capture PVT-representative sample; record volumes/time.
• III.6.4 MDT/Probe safety: limit maximum drawdown to prevent gas breakout, asphaltene precipitation, or fines migration.

III.7 Integrity Logs

• III.7.1 CBL/VDL: evaluate cement bond across critical intervals (Shoe/liner-top/packer); compare to baseline.
• III.7.2 Temperature & spectral noise: scan annuli and behind-pipe paths for crossflow/leaks; confirm with pressure bleed-downs.
• III.7.3 Caliper: identify ID restrictions, scale, or corrosion for workover planning.

III.8 Pull-Out & Demobilization

• III.8.1 Controlled POOH: monitor line tension vs model; avoid sticking points; circulate debris if needed.
• III.8.2 Debrief: on-site quicklook, QC sign-off, preliminary zone allocations; capture lessons learned.

III.9 Quicklook Interpretation (Essential)

• III.9.1 Rate allocation: reconcile PLT total with surface test; apply slip/holdup corrections; iterate until ±10% closure.
• III.9.2 Pressure gradients: detect fluid types/contacts and behind-casing flow from gradient changes and temperature anomalies.
• III.9.3 Integrity: confirm leaks via coincident noise+temp+pressure decay and CBL/VDL indications.

IV. Risks & Mitigation

• IV.1 High pressure/temperature: use tools with =20% rating margin; stage cool-downs to avoid thermal shock; verify elastomer compatibility.
• IV.2 Sour service: NACE-compliant metallurgy; breathing apparatus; continuous H2S monitoring; contingency for emergency rig-down.
• IV.3 Conveyance/stuck tools: pre-model tension/drag; roller-knuckle joints; tractors in high deviation; weakpoint sized below fish neck; jars and fishing plan ready.
• IV.4 Electrical/telemetry failure: redundancy in head electronics; memory backup logging; spare panel/cable head.
• IV.5 Flow-induced error: spinner slippage and eccentricity bias; mitigate with centralizers and multi-pass bidirectional runs.
• IV.6 Sand/scale/asphaltenes: limit drawdown; use screens/filters on tools; pre-flush solvent or scale inhibitor if indicated.
• IV.7 Well control: dual barrier philosophy; test PCE; establish shut-in procedures and verify all valves tagged/operable.
• IV.8 SIMOPS/conflicts: lock-out of conflicting operations; radio silence during critical telemetry if needed.

V. Optimization Levers

• V.1 Real-time analytics: on-the-fly DQI scoring, spinner slip correction, PLT closure vs surface meter, pressure derivative plotting for decision steering.
• V.2 Adaptive program: add stations/passes where anomalies detected; skip low-value stations to stay on schedule.
• V.3 Conveyance choice: tractors/coiled-tubing assist for horizontals; memory tools to reduce rig time when real-time not critical.
• V.4 Debottlenecking: utilize caliper/CBL to target scale removal or recompletion; use WFT mobility/pressure to refine lift settings and candidate zones for stimulation.
• V.5 Maintenance strategy: align diagnostic results with proactive chemical treatment and gas-lift valve changeouts; reduce repeat interventions.

VI. Verification & Monitoring Plan

• VI.1 What to measure:
  • Per run: depth correlation shifts, tool health, P/T drift, spinner calibration checks, contamination indicators.
  • Per zone: inflow/outflow rate, holdup, pressure, temperature anomaly, integrity indicators.
  • Surface: rate, WHP/WHT, choke setting, separator phase rates and GOR/WGR for closure.
• VI.2 Frequency: real-time during operation; daily quicklook; final integrated report within 72 hours with recommended actions.
• VI.3 Acceptance criteria: PLT closure ±10%; pressure repeatability ±2 psi; depth ±0.5 ft; sample contamination =10% (estimated).
• VI.4 Follow-up: implement choke/lift changes; schedule remediation (isolation/perf/acid) per zone diagnostics; plan re-logging cadence 6–12 months or after major interventions.

VII. Key Equations & Quick Calculation Guides

VII.1 Hydrostatics & Gradients

Pressure with depth:

\[ p(z) = p_{\text{ref}} + \int_{z_{\text{ref}}}^{z} \rho(z)\, g \, dz \]

For gas density (real gas):

\[ \rho_g = \frac{p\, M}{Z\, R\, T} \quad ; \quad \frac{dp}{dz} = \rho g \]

VII.2 Productivity/Injectivity

Productivity Index (oil/water):

\[ \text{PI} = \frac{q}{p_r - p_{wf}} \]

Vogel (solution-gas drive oil):

\[ \frac{q}{q_{\max}} = 1 - 0.2\left(\frac{p_{wf}}{p_r}\right) - 0.8\left(\frac{p_{wf}}{p_r}\right)^2 \]

VII.3 PLT Spinner & Phase Rates

Spinner velocity to flow conversion (calibrated constants):

\[ v = k_s \, (N - N_s) \quad ; \quad q_{\text{bulk}} = \frac{v \, A}{f_{\text{slip}}} \]

Phase allocation using holdup (H) and bulk rate (q):

\[ q_o = (1 - H_w - H_g)\, q \quad ; \quad q_w = H_w \, q \quad ; \quad q_g = H_g \, q \]

VII.4 Build-Up Analysis (Horner)

Horner time:

\[ H = \frac{t_p + \Delta t}{\Delta t} \]

Slope (m) of \(p\) vs \(\log H\):

\[ k = \frac{162.6 \, q \, \mu \, B}{m \, h} \]

Skin (radial flow):

\[ s = 1.151 \left[ \frac{p^* - p_{wf}(\Delta t=0)}{m} - \log \left( \frac{k \, t_p}{\phi \, \mu \, c_t \, r_w^2} \right) \right] \]

VII.5 Formation Tester Mobility (WFT) – Spherical Flow

From drawdown/buildup slope \(m\) and geometry constant \(G\) (tool-specific):

\[ \frac{k}{\mu} = \frac{G}{m} \]

Contamination trend tracking (optical): stop sampling when contamination fraction \(C_f \le 0.1\) (target).

VII.6 Leak/Conduit Diagnostics via Temperature

Joule–Thomson effect (qualitative for leak detection):

\[ \Delta T \approx \mu_{JT} \, \Delta p \]

VIII. Practical Tips from Field Operations

• VIII.1 Pass sequencing: always start with low-risk logs (GR/CCL/P/T), then PLT, then integrity; leave WFT/sampling after stabilizing operations.
• VIII.2 Repeatability: insist on repeat passes over key zones; if repeats disagree >10%, fix conveyance bias before proceeding.
• VIII.3 Depth confidence: lock depth at known collars; avoid re-zeroing encoder mid-job; document all corrections.
• VIII.4 Thermal stabilization: hold stations until dP/dt and dT/dt thresholds are met to avoid misinterpretation of transients.
• VIII.5 Horizontal wells: use tractors and centralization; consider array spinners and distributed holdup sensors for cross-sectional coverage.
• VIII.6 Closure with surface: reconcile PLT to separator meters; if mismatch persists, check multiphase slip model and holdup calibration first, not spinner factors.