Well Log Interpreter

Well Log Interpreter

What this skill does

Parses LAS 2.0/3.0 and DLIS well log files, identifies and normalizes curve mnemonics, computes standard petrophysical properties, picks formation tops, identifies net pay intervals, and generates an interpreted log summary. Flags data quality issues and zones requiring manual review.

When to use

• User uploads or references LAS or DLIS files
• User asks to interpret well logs, compute porosity, or find pay zones
• User needs formation tops picked or updated
• User wants petrophysical properties for a specific interval
• User is building a reservoir summary and needs log-derived inputs

Trigger phrases

• "Interpret this LAS file"
• "Analyze the well logs for this well"
• "Find pay zones in these logs"
• "Compute porosity and water saturation from the log"
• "Pick formation tops from this log"
• "What formations are present in this LAS file?"
• "Calculate net pay for the Eagle Ford interval"
• "Summarize the petrophysical properties for the target zone"

Inputs

• LAS 2.0 or LAS 3.0 file (.las)
• DLIS log container (.dlis)
• Optional: formation top depths from offset wells or geological model
• Optional: fluid contacts (OWC, GOC, GWC)
• Optional: cutoff parameters (GR cutoff, Sw cutoff, porosity cutoff)

Outputs

• Curve inventory: mnemonics, units, depth range, data quality
• Formation top picks with depth in MD and TVD
• Net pay summary per zone (gross, net, N/G ratio)
• Petrophysical properties per zone (Vsh, PHIE, Sw, pay flag)
• Zone-by-zone interpretation summary
• Data quality report (bad hole, rugosity, statistical outliers)
• Quality flags per curve and per zone

Curves interpreted

Input curves (auto-detected by mnemonic alias)

| Curve family | Common mnemonics | |---|---| | Depth | DEPT, DEPTH, MD, TVDSS | | Gamma ray | GR, GRC, SGR, CGR | | Deep resistivity | RT, RD, RILD, RDEEP, ILD | | Density | RHOB, DEN, RHOZ | | Neutron porosity | NPHI, TNPH, CNCF, APLC | | Sonic | DT, DTCO, AC | | Caliper | CAL, CALI, C1, C2 | | Photoelectric | PE, PEF | | Spontaneous potential | SP |

Computed curves (derived outputs)

| Curve | Formula | Units | |---|---|---| | VshGR | (GR - GRclean) / (GRshale - GRclean) | fraction | | PHID | (RHOBma - RHOB) / (RHOBma - RHOBfl) | fraction | | PHIN | Directly from NPHI curve | fraction | | PHIE | (PHID + PHIN) / 2 — Vsh correction applied | fraction | | SwArchie | (a / (Rw × PHIE^m))^(1/n) from Rt | fraction | | pay_flag | 1 if Vsh cutoff | binary |

Default cutoffs (overridable)

| Parameter | Default | Description | |---|---|---| | GRclean | 20 GAPI | Clean sand/carbonate gamma ray | | GRshale | 120 GAPI | Pure shale gamma ray | | Vshcutoff | 0.40 | Maximum shale volume for pay | | PHIEcutoff | 0.06 | Minimum effective porosity for pay | | Swcutoff | 0.60 | Maximum water saturation for pay | | RHOBmatrix | 2.65 g/cc | Quartz sandstone default | | RHOB_fluid | 1.00 g/cc | Fresh water default | | Rw | 0.05 ohm-m | Formation water resistivity | | a | 0.62 | Archie tortuosity factor | | m | 2.15 | Archie cementation exponent | | n | 2.00 | Archie saturation exponent |

All defaults are overridable per zone or for the full well.

Formation top picking logic

1. Compute smoothed GR, density, and resistivity trends
2. Identify significant inflection points or step changes
3. Match inflection depths against user-provided top list or known regional markers
4. Assign confidence score based on sharpness of the transition
5. Flag picks within bad hole intervals (caliper > 2× bit size)

Pay identification

A zone is flagged as pay when all three conditions are met:

• Vsh PHIE_cutoff (sufficient porosity)
• `Sw (bit size + 2 inches) as rugose or washed out. In bad hole:
• Density readings are unreliable
• Neutron readings may be high
• Computed Vsh and porosity should be used with caution
• Mark affected depth ranges in quality flags

Example response

WELL LOG INTERPRETATION — Eagle Ford A12H
══════════════════════════════════════════
Log depth range:  7,500 – 9,200 ft MD
Curves present:   GR, RT, RHOB, NPHI, DT, CAL (6 curves)

FORMATION TOPS PICKED
──────────────────────
Austin Chalk:     7,500 ft MD   (confidence 0.82)
Eagle Ford Shale: 7,840 ft MD   (confidence 0.91)
Buda Limestone:   8,650 ft MD   (confidence 0.87)

NET PAY SUMMARY — Eagle Ford Interval (7,840 – 8,650 ft)
───────────────────────────────────────────────────────
Gross interval:   810 ft
Net pay:          380 ft
N/G ratio:        0.47
Avg Vsh:          0.28
Avg PHIE:         0.09
Avg Sw:           0.42

⚠ Quality flags:
  - Bad hole interval 8,100–8,180 ft (caliper > 12.5 in): density interpretation unreliable
  - NPHI missing below 8,500 ft: porosity computed from density only

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: ttracx
• Source: ttracx/oil-and-gas-claude-skills
• License: MIT

Install and usage instructions live in the source repository linked above.