LogSimulator User Manual

Theory of Electromagnetic Well Logging

Table of Contents

Introduction ......................................................................................................................................2

Use of Program ..................................................................................................................................3

Default Tools and Formations ................................................................................................................... 4

Edit Tools and Formations ........................................................................................................................ 6

Create Tools/Formations .......................................................................................................................... 9

Run Simulation ................................................................................................................................ 10

Tool and formation combination ............................................................................................................ 10

Simulation Results ................................................................................................................................... 10

Display Settings ....................................................................................................................................... 14

Introduction

This software package is a companion of Liu’s Book “Theory of Electromagnetic Well Logging”. It is

intended for the reader and students to practice some of the theory described in the book. However,

the software package can also be used to help the data interpretation of the logging data. The logging

tools used in this software is limited to electrical logging tools only, not including tools based on other

physics.

LogSimulator simulates tool responses in a formation. In this program, 3 types of logging tools are

included:

1. Induction

2. Laterolog

3. Logging while drilling resistivity

All these three tools measure formation resistivity, or its reciprocal, conductivity.

A basic Induction tool has a transmitter coils and a receiver coils. The transmitter coil is fed by an

alternating current source, and induces eddy current loops by generating magnetic field in the

formations. These current loops in turn induce EMF in the receiver coils in the same way, and the

induced EMF is directly proportional to the formation conductivity. Induction tool is best used in

resistive drilling fluids, e.g. oil-based mud. Detailed induction tool theory used in this software is given in

Chapters 2 and 7 of the book.

A Laterolog tool uses electrodes to send currents into the formation. By controlling the currents from

these nodes and keeping them in a focus condition, the tool will have greater depth of investigations.

Laterolog tool is best used with low resistive drilling fluids. The laterolog tools are described in Chapter

15 of the book.

LWD resistivity tools usually use three coils, one transmitter and two receivers. It uses high frequency

signals propagating in the formation to measure the resistivity of the formation. Two receivers are used

to compensate the measurements and cancel out uncertainty from electrical devices or environments.

The LWD principle is given in Chapter 2 and 4 in the book.

Geology structures of the Earth can be very complicated. In this program, 3 types of formations are

considered:

1. Isotropic 1D

2. Cylindrical 1D

3. Anisotropic 2D

An Isotropic 1D formation is a vertically layered formation, with each layer has different

electromagnetic properties, e.g. resistivity, permittivity (epsilon), and permeability (mu).

A Cylinder 1D formation is a zoned formation, each zone is a cylinder around the borehole with different

radius. Each zone has its electromagnetic properties, e.g. resistivity, permittivity (epsilon), and

permeability (mu).

An Anisotropic 2D formation has 2 levels of structures. The first level is a layered formation, each layer

has both horizontal (Rh) and vertical (Rv) resistivity, and a number of zones. Each zone has different

radius, and may have different horizontal (Rh) and vertical (Rv) resistivity.

Use of the Program

The software interface is shown in Figure A-1. Use of the program is very straightforward, simply choose

a tool and a formation, and then click Run.

Figure A-1. The interface of the LogSimulator

On the left-hand side, the software interface displays tool and formation. The results of the simulation

are displayed on the right, together with the formation resistivity for comparison. The names of the tool

and formation selected are displayed on the status bar at the bottom of the interface.

Default Tools and Formations

For user’s convenience, program has implemented a few default tools and formations.

There are 6 default tools, each type has 2 tools as shown in Figure A-2.

Figure A-2 The tool selection dialog box

There are also 3 default formations as shown in Figure A-3:

6STAIRS: Isotropic 1D

CYL3: Cylinder 1D

2D: Anisotropic 2D

Figure A-3 Built-in formations

Edit Tools and Formations

To edit a built-in tool or formation, first click Select Tool/Formation from menu. On Select

Tool/Formation dialog, click Edit button, Edit Tool/Formation dialog opens (see below). Make any

changes, click OK to save changes and back to selection dialog. You may also click Save to File to save

edited tool/formation as shown in Figure A-4. The following is an Mwd tool Edit dialog:

Figure A-4 Example of tool parameter editing

On the top left are 3 parameters: Name (Tool), Tool ID, and Number of channels, to which user may

make changes. Every time the Number of channels is changed, the list items in the Channel dropdown

list below will change accordingly. For example, if user changes the Number of channels to 3, the list

items in the Channel dropdown list will be 1, 2, and 3.

In the middle are the TX/RX parameters in every channel. To make changes to these parameters in any

channel, user must first select that channel, make any changes, and then click Apply button to save

changes to that channel. If you forget clicking Apply button, all changes to that channel will be lost.

Clicking OK saves the top left 3 parameters, and won’t save TX/RX parameters specified in each channel.

Figure A-5 is an example of editing an Anisotropic 2D formation.

Figure A-5 An example of editing a formation

On the top left, there are 4 parameters: Name (tool), Borehole radius, Mud resistivity, and Number of

layers, to which user may make changes. Every time the Number of layers are changed, the list items in

the Layer dropdown list below will change accordingly. For example, if user changes the Number of

layers to 3, the list items in the Layer dropdown list will be 1, 2, and 3.

The middle left are the parameters for all layers. Here are 3 rules must be followed:

1. The number of rows in this Layer table must match the Number of layers specified above.

2. The Start depth on the first row must be 0.

3. The start depths in the first column must be increasing.

In the middle right are the zone parameters in every layer. To make changes to the zone parameters in

any layer, user must first select that layer from the Layer dropdown list, make any changes, and then

click Apply button to save changes to zone parameters in that layer. If you forget clicking Apply button,

all changes to zone parameters in that layer will be lost. Clicking OK only saves the top left 4 parameters.

The zone table rule must be followed in the Zone table:

The number of rows in this Zone table must match the number of Zones of that layer specified in

the left Layer table.

Create Tools/Formations

From Tool/Formation menu, select New and the type of Tool/Formation to open Create specific

Tool/Formation dialog. Because using the same dialog as in editing, all functions in Edit

Tools/Formations apply here. There are 2 differences between creating and editing modes:

1. There is an Open from File button, with which user may load the corresponding tool/formation

previously saved.

2. The tool/formation created will be appended in the corresponding tool/formation list as user

clicks OK button. It’s suggested that the name of created be different from those already exist in

the list.

Run Simulation

Tool and formation combination

As described previously, there are 3 types of tools and 3 types of formations. Not all types of tools can

be run simulation with all types of formations.

An Induction tool can be run with either Isotropic 1D or Cylinder 1D formations, but can’t run with any

Anisotropic 2D formation;

A Laterolog tool can be only run with Anisotropic 2D formations;

An MWD tool can be only run with Isotropic 1D formations.

Simulation Results

As an Induction tool run with an Isotropic 1D formation, it usually turns out one resistivity curve. The

default depth range is calculated based on the formation thickness plus 20 feet in the last layer. The

curve with the formation’s name is the resistivity curve of the formation. Figure A-6 is an example of the

simulation result.

Figure A-6 An example of the simulation result.

When an Induction tool runs with a Cylinder 1D formation, the result will be a single number shown on

the dialog in Figure A-7.

Figure A-7. The dialog displaying results of the induction tool response in a cylindrically-layered

formation.

When a Laterolog tool runs with an Anisotropic 2D formation, the result is a single resistivity curve. The

default depth range is calculated based on the formation thickness plus 20 feet in the last layer. The

curve with the formation’s name is the Rv curve of the formation as shown in Figure A-8.

Figure A-8. The laterolog tool response in a two-D anisotropic formation

When an MWD tool runs with an Isotropic 1D formation, the result is 2*N curves, where N is the

number of channels, and each channel has 2 curves: apparent phase and attenuation resistivity. The

default depth range is calculated based on the formation thickness plus 20 feet in the last layer. The

curve with the formation’s name is the apparent resistivity curve of the formation as shown in Figure A-

9.

Figure A-9. The simulation results of a LWD resistivity tool.

Display Settings

To make changes to the display settings, right click mouse on the plots, and then click Plot Property …,

the Plot Property dialog opens (Figure A-10).

Figure A-10. The display window

On the General panel (Figure A-10), user may change the display ranges, fonts, and major and minor

grids, etc. On the Curve panel (Figure A-11), which applies to the result plot only, user may change the

line color and width of a curve selected.

Figure A-11. Curve display options

To change the display ranges of the depth, user may also use pan and zoom feature. To pan, press and

hold the CTRL key, use the left mouse button to move the depth ranges; to zoom, press and hold the

SHIFT key, use the mouse wheel to zoom in/out the depth ranges.