lasio

name	lasio
description	Read, write, and manipulate LAS (Log ASCII Standard) well log files for borehole geophysical and petrophysical data. Use when Claude needs to: (1) Read/parse LAS 1.2 or 2.0 files, (2) Extract well headers or curve data, (3) Convert LAS to DataFrame/CSV/Excel, (4) Create new LAS files from arrays, (5) Modify existing LAS files, (6) Handle problematic or malformed LAS files, (7) Batch process multiple well files.
version	1.0.0
author	Geoscience Skills
license	MIT
tags	["Well Logs","LAS","Petrophysics","Data I/O","Lasio","CWLS","Wireline","Borehole"]
dependencies	["lasio>=0.30"]
complements	["welly","petropy","striplog"]
workflow_role	data-loading

lasio - LAS Well Log Files

Quick Reference

import lasio

# Read
las = lasio.read("well.las")

# Access data
df = las.df()                    # DataFrame (depth as index)
gr = las['GR']                   # Single curve as numpy array
depth = las['DEPT']

# Well info
well_name = las.well['WELL'].value
uwi = las.well['UWI'].value

# Write
las.write('output.las')

Key Classes

Class	Purpose
LASFile	Main container - holds headers, curves, data
CurveItem	Single curve with mnemonic, unit, data array
HeaderItem	Header entry (mnemonic, unit, value, descr)

Essential Operations

Read and Inspect

las = lasio.read("well.las")
print(las.curves.keys())         # Available curves
print(las.well)                  # Well section headers
print(las.version)               # LAS version info

Access Curve Data

# As numpy arrays
gr = las['GR']
depth = las['DEPT']

# With metadata
curve = las.curves['GR']
print(curve.unit, curve.descr)   # 'GAPI', 'Gamma Ray'

Create New LAS

import numpy as np

las = lasio.LASFile()
las.well['WELL'] = lasio.HeaderItem('WELL', value='Test-1')
las.well['UWI'] = lasio.HeaderItem('UWI', value='12345678901234')

depth = np.arange(1000, 2000, 0.5)
las.append_curve('DEPT', depth, unit='M', descr='Depth')
las.append_curve('GR', gr_data, unit='GAPI', descr='Gamma Ray')
las.write('output.las')

Modify Existing

las = lasio.read("well.las")
las.append_curve('GR_NORM', las['GR'] / 150, unit='V/V')
del las.curves['BAD_CURVE']
las.well['WELL'].value = 'New Name'
las.write('modified.las')

Handle Problematic Files

# Ignore header errors
las = lasio.read("messy.las", ignore_header_errors=True)

# Check null value
null_val = las.well['NULL'].value  # Usually -999.25

Null Value Handling

LAS files use a specific null value (typically -999.25). Always check and handle:

import numpy as np
null_val = float(las.well['NULL'].value)
df = las.df().replace(null_val, np.nan)

Batch Processing

from pathlib import Path

for path in Path('wells/').glob('*.las'):
    las = lasio.read(path)
    df = las.df()
    # Process...

When to Use vs Alternatives

Tool	Best For
lasio	Direct LAS file I/O, header manipulation, format conversion
welly	Higher-level well analysis, curve processing, multi-well projects
dlisio	DLIS/RP66 binary format files (not LAS)

Use lasio when you need low-level control over LAS file reading/writing, need to handle malformed files, or want to programmatically build LAS files.

Use welly instead when you need curve processing (despike, normalize), multi-well project management, or formation tops. Welly uses lasio internally.

Use dlisio instead when your data is in DLIS format. DLIS files are binary, support multi-frame data and array logs -- lasio cannot read them.

Common Workflows

Read, QC, and export well log data

- [ ] Read LAS file with `lasio.read()`, handle encoding if needed
- [ ] Inspect curves: `las.curves.keys()` and well headers
- [ ] Replace null values: `df.replace(null_val, np.nan)`
- [ ] Validate depth range and sample interval
- [ ] Check for missing curves or anomalous values
- [ ] Export to DataFrame with `las.df()` or write cleaned LAS

Common Issues

Issue	Solution
Encoding errors	lasio.read(f, encoding='latin-1')
Missing curves	Check las.curves.keys() first
Header errors	Use ignore_header_errors=True
Wrong null value	Check las.well['NULL'].value

References

• Curve Mnemonics - Standard curve names and units
• Troubleshooting - Common problems and solutions
• LAS File Structure - Detailed format specification

Scripts

• scripts/validate_las.py - Validate LAS file format
• scripts/las_to_csv.py - Convert LAS to CSV
• scripts/merge_curves.py - Merge curves from multiple files