What are the procedures for mud logging in drilling?

At-a-Glance: Practical, end-to-end mud logging procedures from rig-up through reporting, focused on accurate lag, representative cuttings, reliable gas data, and real-time alerts to reduce non-productive time and support well control. Key KPIs: data uptime, lag error, gas system calibration drift, sample quality, and response time to events.

I. Objective & KPIs

• I.1 Objective: Provide continuous surface monitoring of drilling parameters, circulating system, cuttings, and formation gas to inform drilling decisions, flag hazards early (kick/losses/instability), and deliver high-quality formation descriptions.
• I.2 Scope: Rig-up, calibration, lag modeling, cuttings sampling/description, gas extraction/analysis, real-time monitoring/alerts, QA/QC, reporting, and data handover.
• I.3 Primary KPIs:
  • Data uptime: = 98% of drilling time.
  • Lag error: = ±2 minutes or = ±10 m MD (estimated) once stabilized.
  • Gas system calibration drift: = ±5% of span for total gas; = ±10% for chromatograph components.
  • Sample interval compliance: = 95% on-time collection at programmed footage/time.
  • Alert response time: = 2 minutes to acknowledge and trend anomalies (trip gas, connection gas, torque/ROP changes).
  • Shaker capture efficiency (visual): = 90% retained on primary shakers for target size fraction.
  • Reporting quality: No critical QA/QC flags; daily log delivered by agreed cut-off.

II. Critical Parameters & Target Ranges

II.1 Key Calculations

• Annular velocity: \( AV\;[\mathrm{ft/min}] = \dfrac{24.5 \, Q\;[\mathrm{bpm}]}{A_a\;[\mathrm{in^2}]} \), where \( A_a = \dfrac{\pi}{4}\,(D_h^2 - D_{od}^2) \)
• Annular volume (per length): \( V_a\;[\mathrm{bbl/ft}] = \dfrac{A_a\;[\mathrm{in^2}] \times 0.0002909\;[\mathrm{bbl/in^3}] \times 12\;[\mathrm{in/ft}]}{1} \)
• Total annular volume (section): \( V_{ann}\;[\mathrm{bbl}] = \sum (V_a \times \Delta L) \) across each drillstring/BHA diameter and hole size
• Lag time: \( t_{lag}\;[\mathrm{min}] = \dfrac{V_{ann}\;[\mathrm{bbl}]}{Q\;[\mathrm{bpm}]} \)
• Lag depth correction: \( MD_{sample} = MD_{bit} - (ROP\;[\mathrm{ft/hr}] \times t_{lag}\;[\mathrm{hr}]) \)
• Pump stroke conversion: \( Q\;[\mathrm{bpm}] = \dfrac{SPM \times V_{st}\;[\mathrm{bbl/stroke}]}{1} \)
• Gas ratio examples: Wetness \( W = \dfrac{C2+C3}{C1+C2+C3} \), Balance \( B = \dfrac{\sqrt{C2 \times C4}}{C3} \), Character \( C = \dfrac{C1}{C1+C2} \)

III. Step-by-Step Procedure / Workflow

III.1 Pre-Spud: Planning & Rig-Up

• 3.1.1 Planning (estimated baseline):
  • Review well program: trajectory, hole sizes, mud system, expected pore pressure/FG, target formations, coring/geo-stops.
  • Define logging program: sample intervals, show evaluation criteria, gas alarm thresholds, reporting templates, data handover format.
  • Compute initial lag model using expected BHA/hole sizes and planned flow rates; preload into EDR.
• 3.1.2 Rig-up & Interfaces:
  • Install gas trap/degasser at active flow line, sample line to total gas detector and gas chromatograph; route lines away from heat and pinch points.
  • Mount sensors: flow-out, pump strokes, standpipe, pit volume totalizer (PVT), hookload/block height, torque/ROP via EDR interface.
  • Calibrate depth: zero at rotary table, verify block height encoder, cross-check with driller’s depth and pipe tallies.
  • Verify power, UPS, and data backup; set automatic data buffering in case of EDR dropouts.
• 3.1.3 Gas System Calibration:
  • Leak test all fittings; pressure test sample lines (low-pressure) to ensure integrity.
  • Calibrate total gas (TCD/IR) with zero gas and span mix; document response factors.
  • Calibrate GC (C1–C5 or up to C6+) with certified mix; set cycle time and integration parameters.
  • Perform bump check pre-tour; document drift vs. previous spans.

III.2 Establish Baselines & Lag

• 3.2.1 Baseline Runs:
  • During pre-spud circulation, record baseline TG and component levels; verify noise floor and stability.
  • Record PVT stability and flow-out signal; confirm no false positives at connections.
• 3.2.2 Initial Lag Synchronization:
  • Compute \( V_{ann} \) from actual BHA and hole; set \( t_{lag} \) using current Q.
  • Tag lag using a slug or dye pill if permitted; align bit depth to first arrival at shakers to verify model.
  • Update lag table for trip speeds and flow-rate changes; activate dynamic lag in EDR.

III.3 While Drilling: Continuous Monitoring

• 3.3.1 Real-Time Streams: Track ROP, WOB, torque, SPP, flow-in/out, PVT, gas (TG and C1–C5), pit trends, ECD (if available).
• 3.3.2 Event Alerts: Configure alarms for connection gas, trip gas, unexpected increase in TG or C1/C2 ratios, pit gains/losses = 2–5 bbl, flow-out deviation = 10–15% from flow-in, torque/drag anomalies, and ROP step-changes.
• 3.3.3 Depth Control: Hourly check of MD vs. block position; correct drift immediately; mark connections properly for accurate lag alignment.

III.4 Cuttings Sampling & Description

• 3.4.1 Collection: At programmed intervals, collect at shakers after lag time; avoid cross-contamination; segregate top/bottom decks if multi-screen.
• 3.4.2 Washing: Gently wash with appropriate solvent/water depending on mud type; avoid over-washing oil-based mud (OBM) cuttings to not remove oil stain.
• 3.4.3 Screening & Picking: Use sieves to standardize size fraction; remove cavings; record percent cavings vs. cuttings.
• 3.4.4 Description: Record lithology percentages, grain size, color (Munsell if used), texture, cement, porosity indications, hydrocarbon shows (cut/bleed/fluorescence under UV), and comments on drilling aggressiveness.
• 3.4.5 Preservation: Bag/label samples with MD, TVD (if available), date/time, interval, and analyst; maintain chain of custody.

III.5 Gas Extraction & Analysis

• 3.5.1 Trap Optimization: Set trap depth and agitation per flow rate; tune airflow to maximize SNR without foaming or entrainment.
• 3.5.2 Total Gas: Continuously record TG; filter with short moving average for de-noising; preserve raw data.
• 3.5.3 Chromatography: Run C1–C5; calculate ratios (Wetness, Balance, Character); flag thermogenic vs. biogenic signatures; observe heavy-end lag relative to TG spikes.
• 3.5.4 Show Validation: Correlate TG and ratios with lithology, ROP, torque, and ECD changes; distinguish liberation artifacts (e.g., swab/surge) from true shows.

III.6 Trips, Connections, and Special Operations

• 3.6.1 Connections: Tag connection gas; compare to baseline; investigate if sustained/ratcheting upward pattern develops.
• 3.6.2 Trips: Record trip gas; adjust lag for trip speed; if significant TG increase without corresponding cuttings, assess influx risk with driller and mud engineer.
• 3.6.3 Circulation Pills/LCM: Annotate; expect TG dampening in OBM and spuriously high readings from aeration; temporarily adjust interpretation thresholds.
• 3.6.4 Coring/Testing: Follow program-specific sampling; keep detailed annotations to separate core-induced artifacts.

III.7 QA/QC & Reporting

• 3.7.1 QA/QC: Daily gas system spans; cross-plot TG vs. C1; verify depth-lag by marker beds or tracers; reconcile PVT to theoretical volumes.
• 3.7.2 Daily Reports: Deliver lithology logs, gas curves, events timeline, and narrative; include KPI dashboard (uptime, calibration drift, lag error, alarm counts).
• 3.7.3 End-of-Section/Well: Summaries of formation tops, show intervals with ratios, operational events, and recommendations.

IV. Risk & Mitigation (HSE, Reliability, Redundancy)

• IV.1 H2S/LEL Exposure: Continuous fixed and portable gas monitors; daily bump tests; evacuation and SCBA drills; place gas sampling discharge outside enclosed spaces.
• IV.2 Electrical/Fire: Explosion-proof equipment in classified zones; route cables overhead; proper grounding; no hot work near gas trap.
• IV.3 Well-Control Indications Missed: Multiple alarm paths (visual/audible/EDR); alarm latching; mandatory call-out protocol to driller/company rep for any pit gain/gas surge.
• IV.4 Data Loss/Drift: UPS on logging unit; mirrored storage and automatic backups; dual sensors for critical channels where possible; calibration logs signed each tour.
• IV.5 Sample Mislabeling/Contamination: Two-person verification on labels; color-coded bags; wash protocol with clean trays; avoid cross-sample tools.
• IV.6 Mechanical Damage to Trap/Lines: Guarding around flow line equipment; pressure-relief on sample lines; periodic inspection each tour.
• IV.7 Ergonomics/Exposure: Heat/cold stress plan; PPE for UV use and solvents; safe posture at shakers; hand protection against screens.

V. Optimization Levers

• V.1 Dynamic Lag Model: Auto-update \( t_{lag} \) with real-time Q, AV, and cuttings transport state; validate using event markers to keep lag error = ±2 minutes.
• V.2 Signal Processing: Apply adaptive filtering and derivative alarms on TG and C1–C5 to highlight subtle shows; use envelope detection for connection gas.
• V.3 Multi-Source Correlation: Overlay ROP/torque/SPP with gas/lithology; flag mismatches suggesting recycling, bit wear, or borehole instability.
• V.4 Sampling Strategy: Increase sample density near casing shoes, overpressure markers, and reservoir targets; implement spot samples when TG deviates > 3s.
• V.5 Trap Efficiency Tuning: Optimize trap depth/airflow vs. mud rheology and cuttings load; document efficiency adjustments to interpret gas amplitudes consistently.
• V.6 Preventive Maintenance: Tour-based checklist for sensors, screens, and pumps; replace wear items proactively to keep data uptime = 98%.
• V.7 Event Libraries: Maintain a playbook of pattern-recognition signatures (kick precursor, borehole breathing, bit balling) to accelerate decision support.

VI. Verification & Monitoring Plan

• VI.1 Routine Checks:
  • Per tour: gas span/bump, depth zero, sensor sanity checks, UPS status.
  • Hourly: lag validation, flow-in/out delta check, PVT reconciliation, trap airflow reading.
  • Daily: KPI dashboard issue log; calibration drift trend; data backup verification.
• VI.2 Acceptance Criteria:
  • No missing intervals; sample coverage = 95% of drilled footage.
  • Lag alignment confirmed by at least two independent markers per hole section.
  • Gas system drift within limits; any exceedance triggers re-span and annotation.
• VI.3 Handover & Archiving:
  • Deliver final mud log (LAS/DLIS/PDF as specified), sample inventory, calibration certificates, KPI summary, and event register.
  • Archive raw and processed data with metadata for post-well analysis.