Resistivity Software

Software for the one, two, or three dimensional modeling of resistivity data.

1-D Modeling: IX1D (Win) - 1-D Direct Current (DC) Resitivity & IP Inversion Software

Supports most DC resistivity arrays, including: Wenner, Schlumberger Dipole-dipole Pole-dipole and Pole-pole arrays. Supports Resistivity only or Resistivity with IP measurements in terms of PFE, chargeability in msec or phase in mrad. Capability to read in a resistivity well log from a flat ASCII file.

IX1D - 1D Inversion Software

IX1D is a 1-D Direct Current (DC) resistivity and Induced Polarization (IP) inversion program with the following features:

• Supports Most DC resistivity arrays, including: Wenner, Schlumberger Dipole-dipole Pole-dipole and Pole-pole arrays.
• Supports Resistivity only or Resistivity with IP measurements in terms of PFE, Chargeability in msec or Phase in mrad.
• IX1D has the capability to read in a resistivity well log from a flat ASCII file and the user can interactively reduce the log to several discreet layers by fitting straight line segments to the cumulative conductance in the log. The resulting model can be copies to the model in the current data set for further modeling.

• Creation of data by spreadsheet entry
• Import of data or models from flat ASCII files
• Models are entered from the keyboard as either Depth models or Layer Thicknes
• Layer boundary elevations are shown and calculated relative to surface elevations.
• The Model Entry dialog box allows for dynamic column and row manipulations to make model entry more convenient.
• Fix Flags allows the user to fix parameters for the inversion calculations. Either the layer thickness (or depth) and/or the resistivity can be fixed in the inversion process.
• Forward and inverse model calculations can be carried out using buttons on the model entry dialog. Models can be inverted using either the layer depth or layer thickness.
• Graphics are presented as the Sounding data on the left hand side with the model on the right hand side. Interactive property sheets allows for user configuration of displayed data. For DC and IP data, the model can be displayed on the same axes as the data.
• Menu commands and toolbar buttons are available for estimating a layered model (DC and IP data only), estimating a smooth model or analyzing equivalence of the layered model.
• Smooth models are generated by starting with as many layers as there are data points. Thicknesses are automatically generated from the spacing or frequency data and the model begins with a homogeneous earth (all layers set to the average resistivity found in the data). Inversion can be Ridge Regression or Occam's inversion.
• The display can be set to show the layered model, smooth model, equivalence analysis or any combination of these three. The model(s) can also be shown on the same graph as the data, in which case the spacing axis doubles as a depth axis.
• The model and data plots can be zoomed by dragging the mouse across the display with the left button depressed. This feature can be switched on and off by clicking on the Zoom menu command in the View menu or by clicking on the Zoom tool bar icon.
• Axes labels as well as axis sizes can be edited under View Properties. Grid lines, including major and minor, for the Data and Model axes can be switched on and off under the View Grid menu subchoices. Axes can be auto-scaled from the model and data by selecting the View Unzoom menu command.
• Data, Layered models and Smooth models can be exported to ASCII files.
• Graphics can be exported as DXF, CGM or WMF file formats.
• Tool bar buttons are provided for the most-used menu commands, including New Sounding or Model, Open and Import data, Save, Print, Edit Data or Model, Zoom status, Unzoom, model display selection, Forward, Inverse and Equivalence Analysis calculations, and Estimation of Layered or Smooth models.

Model entry Dialog Box

Axes Label Properties

Resistivity Well log show with layered model interpretation

Default Graphics Screen

2-D Modeling: RES2DINV, 2-D Resistivity & IP Inversion Software

For Windows 95/98/2000/NT

The RES2DINV program uses the smoothness-constrained least-squares method inversion technique to produce a 2D model of the subsurface from the apparent resistivity data alone. It is completely automatic and the user does not even have to supply a starting model. This program has been optimised for the inversion of large data sets. The use of available memory is optimised so as to reduce the computer time by minimising disk swapping. On a Pentium based microcomputer, the inversion of a single pseudosection is usually completed within minutes. Four different techniques for topographic modelling are available in this program. Together with the free 2D forward modeling program RES2DMOD, it forms a complete 2D resistivity forward modeling and inversion package.

The program will automatically choose the optimum inversion parameters for a particular data set. However, the parameters which affects the inversion process can be modified by the user. Three different variations of the least-squares method are provided; a very fast quasi-Newton method, a slower but more accurate Gauss-Newton method, and a moderately fast hybrid technique which incorporates the advantages of the quasi-Newton and Gauss-Newton methods. The smoothing filter can be adjusted to emphasize resistivity variations in the vertical or horizontal directions. Two different variations of the smoothness constrained least-squares method are provided; one optimised for areas where the subsurface resistivity varies in a smooth manner (such as chemical plumes), and another optimised for areas with sharp boundaries (such as massive ore bodies). A robust data inversion option is also available to reduce the effect of noisy data points. Resistivity information from borehole and other sources can also be included to constrain the inversion process.

• Supports on land, underwater and cross-borehole surveys
• Supports the Wenner, Wenner-Schlumberger, pole-pole, pole-dipole, inline dipole-dipole, equatorial dipole-dipole and non-conventional arrays.
• Supports exact and approximate least-squares optimisation methods
• Supports smooth and sharp constrasts inversions
• Supports up to 2000 electrodes

3-D Modeling: RES3DINV, 3-D Resistivity & IP Inversion Software

For Windows 3.1, 95 and NT

In areas where the geological structures are approximately two-dimensional (2D), conventional 2D electrical imaging surveys have been successfully used. The main limitation of such surveys s probably the assumption of a 2D structure. In areas with complex structures, there is no substitute for a fully 3D survey. This program is designed to invert data collected from E-SCAN (Li and Oldenburg 1992) type of surveys where the electrodes are arranged in a rectangular grid. The arrays which are most commonly used for 3D surveys are the pole-pole, pole-dipole and dipole-dipole. Other arrays probably do not provide sufficient horizontal coverage to fully map the area of interest.

The RES3DINV program uses the smoothness-constrained least-squares inversion technique to produce a 3D model of the subsurface from the apparent resistivity data alone. It is completely automatic and the user does not even have to supply a starting model. This program has been optimised for the inversion of large data sets. The use of available memory is optimised so as to reduce the computer time by minimising disk swapping. A Pentium Pro or Pentium II based microcomputer with at least 64 megabytes RAM and a 3.2 gigabyte hard-disk is recommended.

Depending on the size of the survey grid and the number of field measurements, as well as the speed of the computer system used, the inversion of a single 3D data set can take anywhere from a few minutes to more than 12 hours! Topographic corrections can also be carried out with this program by using a distorted finite-element grid such that the surface of the gird matches the topography.

The program will automatically choose the optimum inversion parameters for a particular data set. However, the parameters which affects the inversion process can be modified by the user. Three different variations of the least-squares method are provided; a very fast quasi-Newton method, a slower but more accurate Gauss-Newton method, and a moderately fast hybrid technique which incorporates the advantages of the quasi-Newton and Gauss-Newton methods. Two different variations of the smoothness constrained least-squares method are provided; one optimised to reduce the difference between the calculated and measured apparent resistivity values, the other which guaranties models with smooth resistivity variations even with noisy data sets.

An example of the results obtained from an electrical imaging survey in an area with a complex subsurface geology is shown in Figure 1. This survey was carried out at Lernacken in Southern Sweden over a closed sludge deposit (Dahlin and Bernstone 1997). A resistivity survey using a grid of 21 by 17 electrodes with a 5 metres spacing between adjacent electrodes was carried out. The pole-pole array was used. The former sludge ponds containing highly contaminated ground water show up as low resistivity zones in the top two layers. This was confirmed by chemical analysis of samples. The low resistivity areas in the bottom two layers are due to saline water from a nearby sea.

As RES3DINV is a Windows based program, all graphics cards and printers with a Windows driver are automatically supported. It has been tested for graphics modes with a maximum resolution of 1600 by 1200 pixels and 256 colours.

X2IPI Tool box for 2D DC and DC-IP measurements

Overview of the X2IPI tool box

X2IPI allows to perform 5 main tasks with data of multielectrode measuruments:

• To prepare and to modify protocols files [*.seq or *.org] files needed for multielectrode measurements with SYSCAL® or SAS4000/SAS1000 equipments
  • prepare protocol file for the next types of array:
    
    • Pole-Dipole (forward and reverse)
    • Half Wenner
    • Wenner alpha
    • Wenner beta
    • Wenner-Schlumberger
    • Dipole-dipole
  • Modifying electrodes unit spacing
  • Removing a faulty electrode
  • Removing measurement lines
  • Preparing a “Roll along” [*.seq, *.up, *.dwn] files
  • Changing the numbers of the MULTINODE® used in a [*seq] file, i.e. the hard reference numbers of the electrodes

• To work with field data files from SYSCAL® or SAS4000/SAS1000 equipments and in Res2dInv format:
  • visualization of data,
  • trim outlier measurements,
  • merge data files,
  • remove a faulty electrode,
  • input topography;
• To remove "geological noise" linked to near-surface inhomogeneities;
• To prepare input files with the convenient formats for interpretation softwares (including new general format for Res2dInv);
• To work with results of 2D inversion by Res2dInv.