steadfastasart/geoscience-skills/geostatspy

GeostatsPy - Geostatistical Analysis

Quick Reference

import geostatspy.GSLIB as GSLIB
import geostatspy.geostats as geostats
import pandas as pd
df = pd.read_csv('data.csv')
df['npor'], tvpor, tnspor = geostats.nscore(df, 'porosity')  # Transform
lag, gamma, npairs = geostats.gamv(df, 'X', 'Y', 'npor',      # Variogram
    tmin=-9999, tmax=9999, xlag=50, xltol=25, nlag=15,
    azm=0, atol=22.5, bandwh=9999, bandwd=9999)
vario = GSLIB.make_variogram(nug=0.0, nst=1, it1=1, cc1=1.0,  # Model
                              azi1=0, hmaj1=300, hmin1=300)
est, var = geostats.kb2d(df, 'X', 'Y', 'npor', ..., vario=vario)  # Krige

Key Functions

Common Operations

1. Normal Score Transform

df['npor'], tvpor, tnspor = geostats.nscore(df, 'porosity')
original = geostats.backtr(nscore_data, tvpor, tnspor, zmin=0, zmax=0.3)

2. Experimental Variogram

lag, gamma, npairs = geostats.gamv(
    df, 'X', 'Y', 'npor',
    tmin=-9999, tmax=9999,    # Trimming limits
    xlag=50, xltol=25,        # Lag distance, tolerance
    nlag=15, azm=0, atol=22.5, bandwh=9999, bandwd=9999)

3. Variogram Model

# Types: 1=spherical, 2=exponential, 3=gaussian
vario = GSLIB.make_variogram(
    nug=0.0, nst=1,            # Nugget, number of structures
    it1=1, cc1=1.0,            # Type, sill contribution
    azi1=0, hmaj1=300, hmin1=300)  # Azimuth, major/minor range

4. Kriging (kb2d)

est, var = geostats.kb2d(
    df, 'X', 'Y', 'npor', tmin=-9999, tmax=9999,
    nx=50, xmn=25, xsiz=50,    # Grid X: ncells, origin, size
    ny=50, ymn=25, ysiz=50,    # Grid Y
    nxdis=1, nydis=1, ndmin=1, ndmax=10,
    radius=500, ktype=0, skmean=0.0, vario=vario)  # ktype: 0=simple, 1=ordinary

5. Sequential Gaussian Simulation

sim = geostats.sgsim(
    df, 'X', 'Y', 'npor', wcol=-1, scol=-1,
    tmin=-9999, tmax=9999, itrans=0,
    ismooth=0, dession=0, dmession=0,
    zmin=-4, zmax=4, ltail=1, ltpar=0, utail=1, utpar=0,
    nsim=1, nx=50, xmn=25, xsiz=50, ny=50, ymn=25, ysiz=50,
    nz=1, zmn=0, zsiz=1, seed=73073,
    ndmin=1, ndmax=10, nodmax=10, radius=500, radius1=500,
    sang1=0, sang2=0, sang3=0, mxctx=10, mxcty=10, mxctz=1,
    ktype=0, vario=vario)

6. Declustering

wts, cell_size, ncut = geostats.declus(
    df, 'X', 'Y', 'porosity', iminmax=1, noff=10, ncell=20, cmin=10, cmax=500)
declustered_mean = np.average(df['porosity'], weights=wts)

Variogram Models

Key Parameters

When to Use vs Alternatives

Choose GeostatsPy when: You need GSLIB-compatible workflows in Python, especially for sequential simulation (SGSIM/SISIM), declustering, or if you are familiar with GSLIB parameter conventions. Best for reservoir characterization workflows.

Choose scikit-gstat when: You prefer a modern scikit-learn-style API for variogram analysis and kriging, with better integration into Python data science workflows.

Choose pykrige when: You only need kriging interpolation (no simulation) and want universal kriging with external drift or regression kriging capabilities.

Common Workflows

Variogram Analysis and Kriging Interpolation

• [ ] Load spatial data into a pandas DataFrame
• [ ] Explore data with GSLIB.locmap() and GSLIB.hist()
• [ ] Check for clustering and decluster with geostats.declus() if needed
• [ ] Apply normal score transform with geostats.nscore()
• [ ] Compute experimental variogram with geostats.gamv() (isotropic first)
• [ ] Check directional variograms for anisotropy (azimuths 0, 45, 90, 135)
• [ ] Fit variogram model with GSLIB.make_variogram()
• [ ] Overlay model on experimental variogram to verify fit
• [ ] Run kriging with geostats.kb2d() (ktype=1 for ordinary)
• [ ] Run SGSIM for uncertainty quantification (50-100 realizations)
• [ ] Back-transform results with geostats.backtr()
• [ ] Validate with cross-validation or holdout data

Common Issues

Tips

1. Always transform to normal scores - Most methods assume Gaussian
2. Start isotropic - Add anisotropy only if justified by directional variograms
3. Check variogram pairs - Ensure enough pairs at each lag
4. Multiple realizations - Use 50-100+ for uncertainty quantification
5. Back-transform last - Apply to final results only

References

• [GSLIB Programs](references/gslib_programs.md) - GSLIB program reference
• [Simulation Methods](references/simulation_methods.md) - SGSIM, SISIM, and other methods

Scripts

• [scripts/kriging_example.py](scripts/kriging_example.py) - Complete kriging workflow