Geolog6.6 Loglan Programming Tutorial

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Geolog 6.6 Loglan Programming Tutorial

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Contents Introduction to Geolog's Loglan Programmin Programming g Tutorial Tutorial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Prerequisites Prerequisites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Document Document Conventions Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Tutorial Tutorial Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Loglan Overview Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 What is Loglan? Loglan? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Create a New Program Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Getting Started. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

The Loglan Loglan Environment Environment.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 The Loglan Loglan Program Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Loglan Program Program Developme Development nt Interface Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Starting Starting Loglan. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Loglan Variables Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

The Module Module Launcher Launcher Interface Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Overview Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Single Well Processing Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Multiwell Multiwell Processing Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

How to Write Write a Program Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Make a Plan Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Make the Code Code Maintainabl Maintainable e. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Make the Code Code Robust Robust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Remain Logical Logical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Re-Use Existing Existing Code Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

41 41 42 42 42

Loglan Language Language Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Program Program Structure Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Source File File Format Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Types of Statement Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Loglan Functions Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

43 44 44 49

Arrays in Loglan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 Overview Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

Log Constants Constants.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 Overview Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

External Functions Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

Geolog 6.6 - Loglan Programming Tutorial

01 / 2006

1

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Introduction to Geolog's Loglan Programming Tutorial Welcome to Paradigm’s Geolog Loglan Programming tutorial. This tutorial teachs you to develop log processing modules to perform your own processing algorithms on your Geolog data. These modules will be fully integrated integrated into the Geolog6 environment, and will function function in exactly the same way as any other module in Geolog6. Ge olog6. The tutorial guides you through: • a simple simple example example to give give you a feel for for how Loglan works works • the general general structure structure of a Loglan Loglan program program and the the program develop development ment interfa interface ce • Logl Loglan an vari variab able les s • the Module Module Launch Launcher er inte interfa rface ce • an introduc introduction tion to general general programming programming principles principles • specific specific detai details ls of the synta syntax x of the the Loglan Loglan language language A number of exercises are included throughout to demonstrate concepts concepts and to allow you to check your progress.

Prerequisites Basic familiarity with the Geolog6 environment is the only prerequisite for this course, although some prior experience with programming concepts would be helpful. Geolog’s online help for Loglan also provides further information.

Document Conventions In this document, all INPUT to the computer is in Bold Courier New , while all OUTPUT from the computer is in Courier New, but not bold.


Introduction 1

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Tutorial Data The following additional files (files not supplied with software) are used in this tutorial: DATA:

stars_master.unl nuke.asc sonic.asc

LAYOUTS: LOGLAN:

REPORTS:

SECTIONS: ./examples/ans*.lls and ans*.info c_extern.c extern_c.lls and extern_c.info launcher.lls and launcher.info validation.lls and validation.info

PLOTS:


SPECS:

WELLS:

atlas botein capella deneb

Introduction 2

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Loglan Overview What is Loglan? Loglan (an acronym for Log ging Language) is Geolog’s log processing language and provides the Software Development Kit for Geolog. Loglan is a programming language especially suited to log processing and its syntax is similar to that of C, but it is reasonably intuitive so familiarity with C is no great advantage for learning Loglan. It does help if you have a programming background, if only because it makes you realise how unintelligent computers are, in that they will do exactly and only what they are told to do! Loglan is fully integrated into the Geolog environment. There is a Graphical User Interface (GUI) for creating and modifying Loglan programs, and, as far as Geolog is concerned, a Loglan program is no different from any other module. When you compile your Loglan program, it is first translated into the C programming language; then it is compiled and linked to produce an executable program. To create and edit Loglan programs, you need to have an ANSI C compiler installed on your computer. The default compiler used is the one provided by the hardware vendor for Unix, and Visual C++ for Windows.


Loglan Overview 3

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Create a New Program Procedure In this section, you are introduced to the Loglan programming interface, and you will: • create a simple program for use in Geolog’s Well application.

Exercise 1

Getting Started Before getting into the details of the language, we will perform a simple exercise to demonstrate how easy it is to write and run a Loglan program (do not worry if you do not understand exactly what is happening—the details will be covered later). The program will calculate porosity from sonic according to the algorithm of Raymer, Hunt and Gardner (SPWLA, 1980), valid for porosities of less than 0.37, using the formula:

φ

= – α –

α

2

∆t ma

+ ------------ – 1

∆t

Eq. [1]

and

α

∆t m

= ------------ – 1 2 ∆t

Eq. [2]

fl

where:

α

is the porosity to be calculated

t ma

is the matrix ∆t t in µs/ft

t fl

is the fluid ∆t t in µs/ft

t

is the value of the sonic log in µs/ft

To start the program development interface

1.

Start Geolog and open the STARS project.

2.

Start the Well application.


Create a New Program 4

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3.

Open the BOTEIN well.

4.

On the Well menu, select General > Loglan... to open the Loglan development interface mui_loglan and present its base window.

Menu Bar Toolbar

Status Bar Message Area Figure 1: Blank Loglan Window

5.

Select Loglan > New to display the Loglan Properties dialog box (see Figure 2).



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Figure 2:Loglan Properties Dialog Box

6.

In the "Program" field, enter the program name rhg_por.

7.

In the "Description" field, enter Raymer-Hunt-Gardner Porosity .

8.

Do not enter a layout name. This field allows you to specify a layout to be opened automatically when the Loglan program is executed.

9.

Leave Hide insensitive arguments as toggled ON. This means insensitive arguments wil not be displayed when the program is run in Geolog’s Module Launcher (the SHOW INSENS checkbox will be toggled OFF in the Module Launcher).

10. Click OK open the Loglan window ready for program creation.



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Figure 3: Loglan Window Ready for the New rhg_por Program

The Loglan window contains three tabs; Input/Output, Source and Description.

Input/Output Tab - Inserting Variables The program variables and the interface displayed when the program is executed are defined here. This information is saved as .info when the loglan is saved. The next step is to define the variables required by our program: • an input sonic log, DT • two input constants, DT_MA and DT_FL, for the matrix and fluid delta t • an output porosity log which we will call PHIE_RHG • another output porosity log limited to the range, zero to one, which we will call PHIE • a temporary (local) variable alpha You can insert variables with a mode of input, input/output, and output, and Lo cal variables. In this example, you will insert six rows on the Input/Output tab for variables DT,DT_FL, DT_MAS, PHIE_RHG, PHIE, and alpha.



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11. Select Edit > Insert (or press Insert on the keyboard) to display the Insert Row window. 12. Enter DT (for the sonic log) as the Name, set the Location to Log and the Mode to Input, and click OK. 13. Repeat steps 11. and 12. using the data provided in the following table. NAME

LOCATION

MODE

DT_FL

Interval

Input/Output

DT_MA

Interval

Input/Output

PHIE_RHG

Log

Output

PHIE

Log

Output

Local

"greyed out"

This is set to Input-Output so that when the program is run, the value we enter is saved and then used as the default next time the program is run. The reason we make this an interval value rather than a constant is that the value is interval related. If we are not processing intervals, the value will be obtained from and saved as a well constant; otherwise, a log in the interval set will be used.

This is a copy of the PHIE_RHG curve limited between zero and one.

ALPHA Local variables are used within the program for "local" processing, and are not input or output.

Specifying units

A default list of applicable units is generated if the Name is defined in the loginfo file (e.g., if the log name used is DEPTH, a list of valid length units, such as metres, centimetres, millimetres, is generated). 14. In the Input/Output tab, ensure the units for DT_FL, DT_MA, and DT are set to µs/f and the units for PHIE and PHIE_RHG as v/v (volume ratio).



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Specifying default values

15. The following values are used as the defaults when the program is run if values cannot be obtained from the constants or interval information: Default value for:

use:

DT_FL

189

DT_MA

55.5

The following specifies the default curve names for the output logs, which will be placed into the output set when the program is executed. Default value for:

use:

PHIE_RHG

PHIE_RHG

PHIE

PHIE

Specifying comments

16. Edit the Comments as shown in Figure 4:

Figure 4: Completed Input / Output Tab of Loglan Program

Source Tab - Entering the Code The actual Loglan code for the program is typed into the Source tab.



To indent text, press the Spacebar or Ctrl+Tab.



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17. Click the Source Tab and enter the code as shown in Figure 5 using the following guidelines: — Instructions which are to be executed for each frame of data must be entered within the dowhile get_frame ()…enddo loop. Instructions before or after this loop are executed only once. — As the variable alpha is a local variable and is constant throughout the well or interval, it does not need to be recalculated for every frame. Therefore, it can be placed BEFORE the dowhile get_frame ()…enddo loop.



To toggle off the Arguments table click the

icon.

Argument Table

Figure 5: Code for Loglan Program Entered in Source Tab

Description Tab - Entering Program Documentation 18. Click the Description Tab and type in the description as shown in Figure 7.



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Figure 6: Description Tab

19. Select Loglan > Save. This creates two files in the loglan directory in the local project area: rhg_por.lls which contains the source code and rhg_por.info which contains descriptive information about the loglan, as well as information on how to control the variables displayed in Geolog’s Module Launcher. 20. Compile the program by selecting Tools > Compile. If your program compiles successfully, the message Loglan program <./loglan/rhg_por.lls> compiled ok is displayed

in the Message area at the bottom of the Loglan window. The program can be run in the same way as any Geolog-supplied program. Executing the program

21. Close the Loglan application and return to Geolog’s Well application. 22. In Well, select General > Module... to invoke Geolog’s Module Launcher and open the File Select dialog box.



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Figure 7: Geolog’s Module Launcher

23. Select the rhg_por.info module to open the Loglan program you have just created (see Figure 8).



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Figure 8: rhg_por Module Displayed in Geolog’s Module Launcher

24. Click Start to execute your Loglan program.

Note If you are running with metric units, the values displayed for DT_MA and DT_FL are in µs/m, but they are passed to your Loglan program in µs/f.



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The Loglan Environment Procedure The Loglan environment has three components —the Loglan program, the Loglan development interface mui_loglan, and the Module Launcher. In this section, you will learn about the Loglan program. The Loglan development interface mui_loglan is covered in "Loglan Program Development Interface" on Page 17, and the Module Launcher, a component of both Geolog’s Well and Project applications, is covered in "The Module Launcher Interface" on Page 31.

The Loglan Program A compiled Loglan program actually comprises three files: • the source code file, identified by the .lls (loglan source) suffix • the module information file (identified by the .info suffix) • the executable file created when the Loglan program is compiled (no suffix on Unix, .exe on Windows).

Loglan Source File The source file consists of a header section with the program description as entered in the Description tab (see Figure 6 on Page 11) of mui_loglan, then a list of the variables used by the program, followed by the executable code. Using the program created in Exercise 1, the source file rhg_por.lls contains: PROGRAM: RHG_POR

Raymer-Hunt-Gardner Porosity

/*------------------------------------------------------------/*start_doc /*This program calculates the Raymer Hunt Gardner /*porosity using the equation: /* /*Porosity = -alpha - SQRT ( alpha**2 + DT_MA/DT -1) /* /*where: /* /*alpha = DT_MA/(2*DT_FL) -1 /* /*end_doc /*-------------------------------------------------------------


The Loglan Environment 14

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INPUT

DT_FL DT_MA

US/F US/F

DT

US/F

/* /* INTERVALS -------------/* /* Delta T Matrix /* Delta T Fluid /* /* LOGS ------------------/* /* Sonic log

LOCAL alpha

/* Temporary

OUTPUT

DT_FL DT_MA

US/F US/F

PHIE_RHG PHIE

V/V V/V

/* /* INTERVALS -------------/* /* Delta T Matrix /* Delta T Fluid /* /* LOGS ------------------/* /* Limited porosity /* Raw proosity

START: /* Calculate the constant before looping through the data. alpha = DT_MA / ( 2 * DT_FL ) -1 /* Now loop through the data calculating the porosity. dowhile GET_FRAME () /* Skip calculation if value is missing. if ( DT == MISSING ) then goto finish endif PHIE_RHG = -alpha - SQRT ( alpha**2 + DT_MA / DT -1 ) /* Apply limit. PHIE = LIMIT ( PHIE_RHG, 0, 1 ) finish: call PUT_FRAME () enddo end Geolog 6.6 - Loglan Programming Tutorial


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TIP Generally, source files are edited using the Loglan program development interface (Loglan window) but it is quite easy to edit them using your favourite editor. If you want to edit source files using a text editor other than the Loglan window, you should be very careful when changing anything before the START: label. Variables should be inserted, deleted and modified only through the Loglan window, since changes to these require the .info file to be changed—this process is handled automatically by mui_loglan.

Module Information File The module information file, identified by the .info suffix, is a Geolog specification file which controls the appearance of the module, including default values and logs, comments, data validation and the visibility of variables in the Module Launcher window, when invoked from Geolog’s Well or Project applications. This file should not be changed except through the Loglan window.

Executable File This file has no suffix under Unix, and a suffix of .exe under Windows; it is created by the Loglan compilation procedure. All of these files are stored in the loglan directory of the local project. If they are to be made available to your entire company, they can be copied to your site/ loglan directory. It is good practice to create programs with names that describe what they are designed to do.



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Loglan Program Development Interface Procedure In this section, you will learn the various methods for starting the Loglan development interface (Loglan window) and the components of the interface are covered in detail. You will: • Practice using most of the commands available in the Loglan window. • Edit a program which demonstrates validation string usage. For the remainder of this manual, the "Loglan program development  interface" will be referred to as the "Loglan window".

Starting Loglan The Loglan window can be opened using several different methods: • From Geolog’s Project or Well application menu, select General > Loglan... OR • From Geolog’s Launcher Bar, click on the Loglan Applications > Loglan.

button or select

OR • At a Unix prompt, enter geolog6 mui_loglan. The Loglan window is fully documented in Geolog’s Loglan online help d ocumentation, so the main points will be mentioned only briefly here. Loglan operation is quite intuitive.

Exercise 1 1.

If you do not have a Loglan window already open, open one now so that you can try out the commands as they are explained.

Create a New Loglan Program 2.

Select Loglan > New from the menu to create a new Loglan program.

Open an Existing Loglan Program 3.

Select Loglan > Open to open and edit an existing Loglan program.


Loglan Program Development Interface 17

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Save a Loglan Program 4.

Select Loglan > Save to save the currently open program. NOTE, however, that this command does not create a new executable; to do that you have to use the Compile command.

Save a Loglan with a Different Name 5.

Select Loglan > Save As... to save the currently open program under a different name.

Run Command 6.

Select Loglan > Run... to execute an external program or command.

Delete a Loglan Program 7.

To delete an existing program which is no longer required, select Loglan > Delete... All the files associated with the program (the source, information, and executable files) will be deleted.

Exit the Loglan Window 8.

Select Loglan > Exit. If any of your loglans have not been saved, you are prompted to Save or Discard the open Loglan program, or Cancel the Exit command.

Edit Menu • Undo

Only available when a row has been removed in the Input/Output tab.

• Insert

Used for inserting rows in the Input/Output tab in which program inputs and outputs are defined.

• Find

Select to open the Find dialog box. If you have the Input/ Output tab selected, the Quick Find dialog is displayed; if you have the Source or Description tab selected, the Loglan Find dialog box is displayed.

• Sort

Sorts Input/Output variables by location.

• Sort By Name

Sorts Input/Output variables by location and name.

• Properties...

Display/modify details of the program's name, description and documentation.



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• Externals...

Specify the path names for included files and directories, external libraries and directories, external objects, and the Linker used to load the compiled program. Loglan programs are converted to C language and compiled to produce an executable module. This requires a C compiler in your environment. The environment variable MIN_CC defines the C compiler to be used.

• Code...

Start the editor specified by the environment variable MIN_EDITOR to edit the Loglan code. If a compile error has previously occurred, the editor will be started pointing to the line containing the first error. The editor must start up in a new window, and the mui_loglan window is blocked until the editor exits. If no editor is specified by the environment variable, "xterm vi" is used. Emacs (usually /usr/local/bin/emacs) is a good choice.

• Description...

Used to enter a detailed description (program documentation or users’ guide) via the editor specified by the environment variable MIN_EDITOR.

• Input/Output Table Click the Table Menu icon to display editing functions for the Input/Output tab (see Figure 9).



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Figure 9: Table Menu

Tools Menu The commands on the Tools menu perform the tasks described below: • Compile

Compiles the program. Error messages are displayed in the message area of the Loglan window. Requires an ANSI-C compiler. Windows 2000/XP requires Microsoft Visual C++ version 4, 5 or 6. The installation path cannot contain spaces (except for the "Program Files" section).

• Site Install

After compiling the loglan, select this option to install the program to the Site area to make it available to all users.

• Function Maintenance Select this option to create/modify user defined functions.

View Menu • Functions Table


Select this option to toggle the display of a Functions list.


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• Arguments Table

Use this option to toggle the display of the Arguments table while viewing the Source tab.

• Compile Output

Use this option to toggle the display of the compilation output window on the Source tab.

Loglan Variables As mentioned previously, a Loglan program consists of basically two parts: • the variables or data on which the program operates, and • the code, or instructions, executed by the program. Variables in Loglan have a number of attributes, most of them displayed in the Input/Output tab of the Loglan window. These include the name, location, mode, units, default, comment, validation and visibility of the variable.

Variable attributes

Location

A variable's location defines its source and destination, and may be one of: • Parameter This is generally used for input data which is not well or interval dependent. It is usually more convenient to use a constant instead. • Constant This is used for data which is not interval dependent. For Input or In/Out variables, the value used for a constant will be obtained from the well header constant with the same name as the variable. If no such constant exists, the default value specified in the Loglan program is used. For Output or In/Out variables, it will be stored as a well header constant when the Loglan program is executed. Geolog 6.6 - Loglan Programming Tutorial


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• Log Constant These variables must have a name of the form _, where is the name of a log header constant such as UNITS, MAX, MEAN, etc. (see the Loglan online help for further information), and is the name of a log used in the program. • Interval Interval variables are similar to constants, except that values will be obtained from and stored in a log in the current interval set. If you are not using interval processing, well header constants will be used. These are used for data whose values are interval dependent. • Log This is used for variables whose values vary for each frame (i.e., for log data). • Local For variables used only within the Loglan program, usually as temporary variables to hold intermediate results. Local variables are n ot stored in the .info file, so are never displayed in the Module Launcher window. Mode

A variable's mode defines the way in which it is processed by the Module Launcher. It must be one of: • Input For variables which are read by the Loglan module but are not to be written back to the well. • In/Out For variables which are used both as input for the Loglan module and output to the well after the module has executed. Often, this mode is used for constants and interval parameters so that the values used for an analysis will be stored in the well and used as defaults next time the Loglan module is run. • Output For variables which are calculated by the Loglan module and are to be stored in the well. Name

Valid names must start with an alphabetic character, and the other characters must be alphabetic, numeric, or the underscore character. The name may be no longer than 32 characters for input or output variables, while the limit for local variables is 63 characters. A name may not end with an underscore followed by a number, as this could be confused with a version number.



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There are a number of names which cannot be used: • words which are reserved in the Loglan language itself (such as endif); • those reserved in the C language (such as case); • those whose names conflict with standard functions used by the C language. There is a complete list of these in the Loglan online help documentation, but you do not really need to know the list, as the compile step will report any transgressions. Names of the form _ should be avoided, since these may be confused with Log Constants (see "Log Constants" on Page 66). It is good programming practice to use meaningful names: this makes it easier for others to understand what is going on if they need to look at the code. Type

Variables can be of type Alpha, Numeric (Integer, Real, or Double), or Logical. • Alpha Alpha variables have an alpha string value and are defined using the following syntax: Log Name

Type

Comment

Log

alpha*num

/* General case

The units alpha*num specify the maximum number of characters which may be assigned to the variable. Any characters beyond num will be truncated. The default length (if the "*num" is omitted) is 4. The maximum length is 72 for INPUT/OUTPUT variables and 1024 for LOCAL variables. • Numeric Any variable which is not declared Alpha or Logical is numeric. The units can be any valid units defined for the variable in the unit category specified in the variable's loginfo definition. • Logical Logical variables have the values TRUE or FALSE and are useful for flags, switches or toggles. Unit

For a unit to be valid, the variable to which it applies must be defined in a log information (loginfo.loginfo) file, and the unit must exist in the unit category for that variable. It is usually easiest to use the List Select dialog box. Note: Units cannot be specified for Local Variables.



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The way the units are used depends on whether the variable is input or output (for In/Out, both apply). • Input variables If you specify valid units for an input variable then, when the Loglan program executes, its data will be passed in those units, irrespective of the units in which the data is held in the well and displayed, provided the units in the well are valid. If either the Loglan units or the data units are invalid (or blank), then no unit conversion can be performed by the Module Launcher and an error will be reported unless the Loglan units are blank. For character variables, the data will be truncated (if the Loglan length is less than that of the data in the well), or padded with spaces (if the Loglan length is longer). If no units are specified for a numeric variable, the Loglan program will receive the data in the units in which the data is stored in the well. The log constant UNITS_ can be used to access these units. This is often useful when reporting data. • Output variables If you specify valid units for an output variable, these will be used only if the preferred units for the variable are blank; otherwise, the data will be stored in (after conversion to) the preferred units. If the units in the Loglan program are blank, the variable is assumed to be in the preferred units. For character variables, the length specified in the Loglan program will be used only if the variable does not already exist in the well; if it does already exist, the length will not be changed and the data will be truncated or padded with spaces, as required. Default

The interpretation of the default depends on both the variable's location and its mode (see "Location" on Page 21 and "Mode" on Page 22).

Terminology In the descriptions below: Launcher default means the value displayed in the Module Launcher (and used by the Loglan program when it is executed). Loglan default is the value specified as the default in the Input/Output section of the Loglan window. Note that the following discussion implies that there is no defaults file for the module; the use of a defaults file is explained in "Notes on Saving" on Page 38. Geolog 6.6 - Loglan Programming Tutorial


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Log constants are not included in this discussion since they do not appear in the Module Launcher window. • For local variables the Loglan default is ignored. These variables do not appear on the Module Launcher window. • For input logs the Launcher default is a log with the same name as the input variable. The Loglan default is used only if the log with the same name as the variable cannot be found. If the variable is numeric, and the Loglan default is numeric, the Loglan default will be used as a constant value of the input log for all frames processed by the program. If the variable is numeric, and the Loglan default is a name, then, if a log of that name exists, it will be used as input to the Loglan program; otherwise, the Loglan default is ignored. If the variable is o f type character (alpha), the Loglan default will be used as the name of a log if that log exists; otherwise, it will be used as a constant value. • For input constants the Launcher default is the value of the well header constant with the same name as the input constant. The Loglan default will be used if its type (i.e., numeric or alpha) matches the type of the constant, and if the constant with the same name as the input variable does not exist in the well. If the types do not match, the Loglan default is ignored. • For input interval constants the Launcher default is the value of the log (in the interval set) with the same name as the variable, for the current interval. If that log does not exist, or if interval processing is not enabled, the Launcher default is the value of a well constant with the same name as the variable. If that does not exist, then the Loglan default will be used if its type (i.e., numeric or alpha) matches the type of the interval constant; if the types do not match, the Loglan default is ignored. • For input parameters the Loglan default will be used if its type matches the type of the parameter; if the types do not match, the Loglan default is ignored. • For output logs the Launcher default (i.e., the name of the log produced by the Loglan program) is the Loglan default, which must be a valid log name. • For output constants and interval constants the Loglan default is ignored. Interval and well constants are always created with the name used in the Loglan program, and the value output by the program. • Output parameters should not be used.



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• For Input/Output logs the Launcher default is a log with the same name as the variable. The Loglan default is used only if the log with the same name as the variable cannot be found, in which case the Loglan default must be a valid log name. • Input/Output constants and interval constants are handled in the same way as input constants and input interval constants, respectively. • Input/Output parameters should not be used. Comment

The comment is displayed on the Module Launcher window and should therefore be meaningful. It is also stored in the well as the comment for any logs or constants created by the Loglan module when it is run. Validation

Validation specified in the Loglan window is applied in the Module Launcher when the value of an entry is changed, and when Start is selected. There are two types of validation—lists and ranges. For strings, only list validation is permitted. The validation is ignored for logical variables. • A range validation is a string of the form lower limit:upper limit , or lower limit

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Visibility

Defines input/output visibility when a Loglan module is executed. If TRUE, the entry is displayed when the program is executed. If FALSE, the entry is not displayed when the program is executed. If the “visible” parameter is a statement in the following form: variable1:[!]value[,value...] and is true (if variable1 has any of the specified values), the parameter is visible and active. If the condition is false, the par ameter is not displayed unless the SHOW INSEN button in the Module Launcher is toggled ON, in which case, it will be inactive (grayed out). Case is ignored when the value is tested. Use of the ! (exclamation mark) reverses the sense of the test. Example: RHO_DSH visibility may be controlled by OPT_PHITYPE:TOTAL. See Figure 10 for an example.



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OPT_SON is set to FALSE and therefore, is not visible in the Module Launcher.

OPT_PHITYPE is not set to TOTAL, and Show Insens is toggled on so RHO_DSH is "grayed out" - visible but inactive.

Figure 10: Examples of Visibility in the Module Launcher

If controlling visibility with a logical (e.g. OPT_COAL), the following syntax must be used: OPT_COAL:YES or OPT_COAL:TRUE or OPT_COAL:1

If more complex control over visibility is required, an expression may be used. This must be a quoted string, and has exactly the same form as a logical expression in Loglan (see "Logical expressions" on Page 45). Geolog 6.6 - Loglan Programming Tutorial


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For example: "FILTER_TYPE<>'EXTERNAL' & FILTER_TYPE<>'KLAUDER' & PHASE_MODE == 'CONSTANT'"

Note that if you are using this form, all literals (character constants) must be quoted using single quotes.

Exercise 2 The objective of this Validation exercise is to test the different kinds of validation available in Loglan programming. 1.

Open the Loglan program, validation.lls, in the Loglan window, and validation.info in the Module Launcher to see the results of the different validation strings used.



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Note that for variable a3, a blank is allowed. The Dropdown List (in the Module Launcher window) contains a blank at the end of the list. Click below the last item in the list to select the blank. 2.

In the Loglan window, insert an Input Constant as follows: — call it BS; — set units to inches; — set the default to 7 inches; — set the value to be between 3.625 and 18 inches; — set visibility to be true when ALPHA_LIST:val2.

3.

Save the changed program—there is no need to compile since we will not be executing the program.

4.

Update the Module Launcher window by selecting Launcher > Module... and reopening the module.

5.

Toggle on Show Insens to view the BS constant.



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The Module Launcher Interface Procedure In this section, you are introduced to the components of the Module Launcher interface and you: • practice using the various components of the Module Launcher.

Overview The Module Launcher is a component of both Geolog’s Project and Well applications and multiwell analysis is carried out within both of these applications. In Well, several wells can be loaded into memory, processed, and the changes saved to the database or discarded, as required. You should use the Well application where only a few wells need to be open at one time. Where a large numbers of wells are to be processed simultaneously, use the Project application, as the wells are not stored in memory, and data is immediately processed and saved to the database. We discuss the Well interface first using "Single Well Processing" below, and then examine the additional facilities in the Project interface (see "Multiwell Processing" on Page 40). The Module Launcher window is exactly the same for a Loglan program as it is for any module which is part of Geolog. A user defined module is opened by selecting General > Module... from the menu, and specific modules are opened directly by selecting the relevant menu command (e.g. General > Evaluate).

Single Well Processing Exercise 1 1.

If it is not already running, start the Well application and open the BOTEIN well.

2.

Select General > Module... to open the Module Launcher and the File Select dialog box (see Figure 11).


The Module Launcher Interface 31

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Figure 11: File Select dialog box - Opening a Module

3.

Enter or locate the required file—for this exercise, open launcher.info. See "Using Geolog" in the online help documentation for further information on using the File Select dialog box.

4.

Click OK. This causes the .info file to be read and the module arguments will be displayed in the Parameters section of the window (see Figure 12).



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Sampling Log

Set Processing Limits

Input / Output Sets

Parameters section

Figure 12: Components of the Module Launcher

Input Set The set displayed is either the set specified for the module, or, if not specified, the default set specified for the application (select Well > Default Set...). Logs to be processed by the module come from this set, unless otherwise specified. For instance, in Figure 12, if COR.DT is entered, the DT log from the COR set is used, rather than the DT log from the WIRE set. 5.

To change, click on the Set Select sets, or enter a set name in the field.

icon to select from a list of available

 Parameters were reset to the defaults for the module. This no longer occurs. In previous versions of Geolog, when the Input Set was changed, all To reset the Parameter defaults, select Launcher > Reopen.

Output Set The set displayed is either the set specified for the module, or, if not specified, the default set specified for the application (select Well > Default Set...). Logs to be processed by the module are written to this set, unless otherwise specified. For instance, in Figure 12, if COR.PHIE is entered, the PHIE log from the COR set is used, rather than the PHIE log from the WIRE set). If the set specified does not exist, it is created.



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6.

To change, click on the Set Select sets, or enter a set name in the field.

icon to select from a list of available

 ALPHA input parameter called SET_IN or SET_OUT and use the required To specifiy an Input Set or an Output Set for a Loglan prgram, create an set name as the default.

Sampling Log 7.

Click on the Log Select icon to display a Log Select dialog box and select the name of the log which will control the sampling (i.e., the data frames) of the input data to be passed to the module. If this field is left blank, the input/output sample rate is determined by the input set’s reference (e.g. depth) or, if no input set is specified, by the first input log.

Set Processing Limits 8.

Click the Set Processing Limits button to open the Datum dialog box to specify whether interval processing is to be used (and, if so, which intervals are to be processed), or the range of reference values to be processed.

Parameters Section The Parameters section is a table displaying all the visible arguments used by the module (log constants are never displayed because they are automatically derived from the associated logs). colors

The colors in the table depend on both the Mode and the Location of the module parameters. Data displayed with a colored background is read-only. The Value column (white background) can be edited. The Location, Mode, Comment, Unit and Name columns come from the variable definitions in the Loglan program, and are described in "Loglan Variables" on Page 21. If interval processing has been selected (either by clicking on the Set Processing Limits... button or selecting Well > Datum... from the menu), there is a Value column for each selected interval, and the column heading is the interval name rather than "Value". Also, the location for the variable "INTERVAL_IN_OUT" changes from "Constant" to "Interval", and the color of that line changes.



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special module parameters

There are a few variables which are handled in a special manner by the Module Launcher; these are SET_IN, SET_OUT, and INTERVAL. If your prog ram uses SET_IN or SET_OUT as a parameter, or INTERVAL as an interval constant, these do not appear on the Module Launcher window but are automatically passed to your program with the appropriate value(s). A constant named WELL also automatically receives a value.

Data Entry and Execution Quick Entry

For small modules, it is quicker to enter/select values directly in the Value column fields. For large modules, the Quick Entry option opens a dialog box which enables you to quickly cycle through and select the required values for the Value column(s) in the Parameters section of the the Input/Output tab. To use Quick Entry for multiple intervals 1.

In the Well application, select Launcher > Module and select Launcher.info.

2.

Set the processing limits to Interval, the interval log to tops.tops , and select MALABAR FM and THORLEY FM as the intervals.

3.

For multiple value columns, where applicable, toggle the ALL column on (see Figure 13), to enable simultaneous multiple entries for a value entered.

4.

Click in a Value field.

5.

Select Edit > Quick Entry to display the Quick Entry dialog box (see Figure 13).



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ALL column

Figure 13: Using Quick Entry to enter values in Values column(s)

6.

In the Quick Entry dialog box: — double click the required value in the List field to enter the value in the Value column and go to the next editable cell.

OR — select a value and then click Apply or press ENTER to enter the value in the Value column and go to the next editable cell.

 otherwise, editing continues to the right.

If the ALL column is available and toggled ON, editing continues down

• where there are no values in the List field, click in the Selection field and enter a value, then press ENTER or click Apply to enter the value. • to skip a field, press ENTER or use the Next button. • to finish editing or cancel the operation, click Close.



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Launcher Menu The Launcher menu options are used to manage modules. TOOLBAR

MENU ITEM Module...

DESCRIPTION Opens the File Select dialog box to locate and select a module. A module can also be opened by: • Selecting a relevant menu item (e.g. General > Evaluate); • OR, selecting General > Module... in a Geolog application to open the Module Launcher and File Select dialog box; • OR, selecting A p p l i c a t i o n n a m e > Run... (e.g. Well > Run...) and entering the command applicationname_module in the Run dialog box. An empty Module Launcher window is displayed—select Launcher > Module... to open a module. If you know the name of the module you wish to open, in the Run dialog box enter applicationname _module module=modulename For example: well_module module=tp_calc

Reopen

If and when required, use this function to reload the defaults for the currently open module. If a defaults file exists, it will be reloaded. Note: The manual function, Launcher > Reopen, replaces the automatic function in previous versions of Geolog where, when the Input Set was changed, the Parameter defaults for the module were automatically reloaded.

Close

Closes the Module Launcher window. Note that if you have not saved the specifications currently entered, they will be permanently removed (see "Launcher > Save As" below).

Well... Use to specify the well(s) to process. Not available/applicable in all Well Previous multiwell processing applications. Well Next Datum

Use to specify datum to use for the currently active view.

Start

Select to start execution of the module.

Cancel

Some functions run a series of modules and/or other processes. Use the Cancel option to cancel the operation before or after execution of any process in the series. The entire operation will be cancelled and the Module Launcher window cleared. The function can then be restarted, or the Module Launcher closed. Note the Module Launcher is also cleared after a series of processes have been run.



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TOOLBAR

MENU ITEM

DESCRIPTION

Note: When one of the three commands listed below is selected, the Filter field in the File Select dialog box defaults to *. (where is the name of the currently open module) therefore, if you wish to find/save/delete a file with a different extension, you must change the filter. Restore...

Restore previously saved or executed specifications for the module. When the File Select Dialog Box opens, select your saved file (see Save As below) or "previous.". Geolog automatically saves the last specifications used when the module was run in a file called previous. (located in the project's specs directory). Therefore, when you select the Restore command to retrieve your saved specifications, you will see files similar to the following:

previous.tp_evaluate specifications when last executed mysettings.tp_evalute specifications you have saved Use the Restore Previous icon to quickly reload (Files Select dialog box is not opened) the last specifications run.Note that the "previous" file is always REPLACED, so specifications are only those relevant to the last execution. Save As...

Save the specifications you have entered in the currently open module. See "Notes on Saving" below for further information.

Delete...

Opens the File Select Dialog Box to locate and permanently delete files containing previously saved specifications.

Module Help

Opens a separate window that displays the Detailed Description (see Figure 2 on Page 6) from the .info file for the module documentation for this m odule. You can also click the button.

Edit > Undo/Redo

If this option is selected after the module has executed, the changes resulting from the execution of the module will be undone. Clicking it again undoes the effect of the "Undo".

Notes on Saving When saving specifications, if you do not enter a file name extension, the module name is used as the extension. If you do enter an extension, the information will be saved with the file name and extension you specify, but that file will NOT be automatically displayed when you select Restore (you need to change the Filter to locate the file).



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When the values for a module are first displayed, the Module L auncher checks to see if a defaults. specification exists. If it does, the values in that specification will be automatically restored. So, if you save your values w ith the name defaults, the information will subsequently be automatically restored whenever you run the module. This is useful if you want to always use the same values.

Warning The saved data contains interval information. If your p rocessing limits (i.e., intervals) are different from those which were applied when you performed the save, the results may not be exactly what you expect. If the data was saved without intervals, and restored with interval processing enabled, every interval will receive the same value. As well, when you select Launcher > Reopen to reload the parameters, the defaults file is used, not the original defaults for the module.

Exercise 2 1.

Select General > Loglan... and open the Loglan program, launcher.lls, in the Loglan window (launcher.info should still be open in the Module Launcher, as well).

2.

Use this Loglan program to experiment with different modes of processing (i.e. interval and depth range).

3.

Open a Text view (Well > View > Text) to check the results.

Experiment with the Undo/Redo, Save and Restore functions.



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Multiwell Processing When in Geolog’s Well or Project application with more than one well open to be processed, the window displayed when you select General > Module... has an additional column in the Parameters section of the Input/Output tab.

Extra column Figure 14: Multiwell Processing - Loglan Program Displayed in Module Launcher

The additional column after the Name column specifies the source for the parameter; "S" for "screen", "W" to indicate the information must come from the well (the well is not processed if the value cannot be obtained), or "P" to indicate the value is to be obtained from the well, if possible, otherwise the screen value is used. Multiwell processing is beyond the scope of this tutorial, and is covered in detail in the Deterministic Petrophysics tutorial.



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How to Write a Program Procedure In this section of the tutorial, we will look at some general programming principles to help you get your Loglan programs written and working as quickly as possible.

Make a Plan The most important part of writing a program is to have a plan showing how the program will operate. It does not need to be "formal": a written description of the steps involved is often adequate, though sometimes a flowchart can be helpful if the program is complicated and involves a nu mber of different paths, depending on the data. It is often easiest to start off w ith a very high level plan, and then fill in the details later. The important point is that you have at least some kind of plan as a starting point.

Make the Code Maintainable A program is almost never be perfect on the first attempt as problems may occur, or enhancements may be requested. It is very important to make the maintenance and enhancement procedures as straightforward as possible, and the best way to ensure this is to document your code. This means using meaningful names for your variables, adding comments as often as possible, and making sure that the program header explains what the program is intended to do. It is often worthwhile to keep some form of revision history. The Description tab (see Figure 6 on Page 11) is a facility within Loglan to place a documentation section in the header that allows other users or programmers investigating the Loglan program to know what the program is supposed to be doing, and how it is doing it. It cannot be stressed enough that the more documentation exists within a program, the easier it is for other users to understand the processes used. Another important consideration is to make your code easy to follow. It is all very well to do really neat, clever things, but when you or someone else needs to modify the code some months later, practices like these can lead to frustration, errors and wasted time. Generally speaking, efficiency is nowhere near as important as maintainability. If your site has any standards for coding, documentation, or variable naming conventions, adhering to these makes it easier for others to maintain your code.


How to Write a Program 41

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Make the Code Robust Protecting your code against bad data and inexperienced users is also important. If there is something wrong, display an error message. Failure to do so can lead to wasted time on the part of the user in trying to track down the cause of erroneous results. If you are thorough in ensuring that your data is valid, you can also prevent the user from having to call the programmer to sort out these problems.

Remain Logical When a program does not work, and resists all your best efforts to make it work, it is easy to become desperate and frustrated. It is important to tackle the problem in a logical, analytical way, working through the code by hand. If necessary, use debugging display statements to report what the pr ogram is doing.

Re-Use Existing Code Often, problems related to the one you are trying to solve will have been tackled before. Looking through existing code is an efficient way of learning how to go about solving your own problem, as well as providing an insight as to how the Loglan language can be used. The Loglan programs included in the Geolog distribution would often be a good place to start. Generally speaking, these programs are well documented and well written, and provide worthwhile examples of good programming techniques.


How to Write a Program 42

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Loglan Language Syntax Procedure This section deals with the details of the language itself. You should also have access to the Loglan online help documentation, as this tutorial contains only general information to guide you on what to look for in the documentation. You will: • Create a program to calculate and display porosity. • Create an interactive user input program. • Create several programs to read or write to external files. • Create a program to analyze data on an interval basis across multiple wells. • Create a program using data from frames other than the current one.

Program Structure The first section of any Loglan program is the declaration section, which is used to declare the variables used by the program. It is maintained by mui_loglan (using the Input/Output tab of the Loglan window), and it should not be otherwise modified. The next logical section is the program code section, containing the instructions to be executed by the program when it runs. This may be logically subdivided into: • the initialisation section, which contains code which does not need to be executed for each data frame; this code pr ecedes the program's "dowhile GET_FRAME" loop. • the processing section, which contains the code to be executed for each data frame. Then follows the end section, which consists only of the keyword end and tells the Loglan processor that the end of the code has been reached. It is required only if the program contains subroutines. When the end statement is executed, the Loglan program terminates. Optionally, there may be a subroutines section containing segments of code which may be executed from within the processing section. See "Subroutines" on Page 48 for further information.


Loglan Language Syntax 43

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Source File Format Continuation character

Generally, the Loglan source contains one command or statement per line. If a statement is long, it may be split over more than one line by terminating every line but the last with the continuation character , ~ (tilde). Statement separator

More than one statement may be placed on a line by using the statement separator character , ; (semicolon). Comment

A comment, preceded by the comment specifier, /* (forward slash and star), may appear either on a line by itself or at the end of a statement. Blank lines

Blank lines are ignored but may be used to logically group sections of code. Case

Case, except in character constants, is ignored. Conventionally, local variables are lowercase while all other variables are uppercase, but you are free to use no case or your own convention.

Types of Statement Loglan has three fundamental types of statement: • assignment statements

used to assign a value to a variable.

• control statements

change the normal sequential flow of a program; among other things, they may be used to either conditionally or repeatedly execute groups of statements.

• function call statements

executes a Loglan provided function.

We will deal with each of these types in turn.



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Assignment Statements An assignment statement has the form: variable = expression

where variable is any variable defined in your Loglan program, and expression is a combination of variables, constants, function calls and operators, whose result is a single value. A function call in an expression consists of the function name, an opening round bracket, the function argument (or arguments, separated by commas), and a closing round bracket. For example: ATAN ( 5, 10 ). Details of the functions available in Loglan are covered in "Loglan Functions" on Page 49. Expressions

An expression in Loglan has two attributes, a type and a value. The type of an expression may be numeric, alphanumeric or character, or logical; these are the same types which are defined for variables. The type of an expression is determined by the types of the variables and constants it contains; in genera l, all the variables in an expression must be of the same type, and the expression in an assignment statement must have the same type as the variable to which it is being assigned. Numeric expressions Numeric expressions can contain numeric variables (e.g. depth), numeric constants (e.g. 3.14159), or functions returning a nu meric value (e.g. SQRT), combined with numeric operators. The operators and their order of precedence are described in "Operators" under the "Program Syntax" section of the Loglan online help documentation. Note that operators of equal precedence are evaluated from left to right; thus 5/2*4 evaluates to 8. This is because when all the components of an expression are integers, the expression will be evaluated using integer arithmetic, so 5/2 = 2. If you want the evaluation performed using real values, add a decimal point at least one of the numbers. Character expressions Like numeric expressions, character expressions can contain character variables, character constants (e.g. 'Hello'), or functions returning a character value (e.g. UPCASE), combined with character operators. The only character operator is the concatenation operator, //. Logical expressions Logical expressions contain logical variables, logical constants (e.g. TRUE), logical functions (e.g. MISS), and logical operators such as NOT, AND, and OR. Additionally, logical expressions may contain other types of variables combined with relational operators such as < (less than), <> (not equal to), etc. Geolog 6.6 - Loglan Programming Tutorial


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Constants Constants, like variables and expressions, come in 3 flavours: numeric, character, and logical. Numeric constants are just numbers, such as 5 or 1.234. Additionally, Loglan has pre-defined numeric constants such as PI, MISSING, and TOP_DATA. A character constant consists of a sequence of characters enclosed in single quotes, such as 'Here is an example'. There are two logical constants, TRUE and FALSE.

Control Statements Normally, statements in a Loglan program are executed sequentially. Control statements are used to alter this flow. if statement

The if statement lets you conditionally execute other statements. Its basic form is: if ( logical-expression ) then statements endif

This statement will cause the statements following the "if" to be executed if the logical expression evaluates to TRUE. The brackets around the logical expression are optional. You may optionally have one or more elseif statements, optionally followed by an else statement. For example: if ( OPT_GR == 'LINEAR' ) then VSH_GR

= v

elseif ( OPT_GR == 'STIEBER1' ) then VSH_GR

= v / ( 3.0 - 2.0 * v )

elseif ( OPT_GR == 'LARINOV1' ) then VSH_GR

= 0.33 * (( 2.0 ** ( 2.0 * v )) - 1.0 )

else DISPLAY_ERROR ( 'Invalid option: ' // OPT_GR ) endif

for statement

The for statement is used to repeatedly execute a g roup of statements. Its form is: for = to [by ] do statements endfor Geolog 6.6 - Loglan Programming Tutorial


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This statement will execute the statements in the body of the loop, varying the loop variable from the initial value to the final value, incrementing the loop variable by the step after each iteration. If the "by step" is omitted, a value of 1 is assumed. The loop is pre-tested. This means that the loop is not executed if the value of the loop variable is greater than the final value. The step may be negative. For example: sum = 0 for i = 1 to 20 do sum = sum + i endfor

do until statement

This is a post tested loop which executes a group of statements until the termination condition evaluates to TRUE. Its format is: do until

See "Program Control" under the "Program Syntax" section of the Loglan online help documentation for an example. dowhile statement

The dowhile statement dowhile statement has the form: dowhile statements enddo

It is more or less the opposite of the do until statement: until statement: the condition is tested before the statements in the body are executed, and the loop continues to execute until the condition evaluates to FALSE. goto statement

The goto statement has the form: goto

where label-name is label-name is a name (the validity rules are the same as for variables) which appears elsewhere in the program as a label, label, consisting of the label name immediately immediately followe followed d by a colon (:). This command causes execution flow to be transferred to the statement following the label. It can be useful for skipping sections of the program, if an error occurs.



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Function Call Statements A function call statement is is used to execute an internal Loglan function. This may be done in one of two ways. The first method is to use the function name in place of a variable name, with the arguments to the function (separated by commas if the function has more than one argument) in round brackets after the function name. If the function has no arguments, you must use () after the function name. The second method is to use the call command call command before the function name, followed by the arguments as before; in this case, the function result is ignored. This will be more fully described in "Loglan Functi Functions" ons" on Page Page 49. 49.

Subroutines A subroutine is a block of code which may be called called from (often multiple places) within a Loglan program. It is often preferred to inline code to make the program more modular and easier to understand, or to eliminate duplication of the subroutine code if it is to be executed from more than one place in your program. Subroutines are coded after the end statement end statement within the Loglan program (the end statement end statement causes the Loglan program to terminate execution), and are executed by the perform command. perform command. A subroutine begins with a label, label, which is the name of the subroutine used in the perform command. perform command. A label consists label consists of a name (the validity rules are the same as for variables) followed by a colon (:). Then follow the instructions to be executed in the subroutine, including one or more return commands. return commands. The return command return command causes execution to transfer to the command immediately following the perform command perform command which caused the subroutine to be called. For example: perform sub1 end sub1: return

would execute the expressions up to the perform command, perform command, then transfer execution to subroutine sub1, sub1, and then jump back to the line following the perform statement.



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Loglan Functions Much of the power of the Loglan language comes from the wide variety of functions supported by the language. These a re all described in the "Functions" section of the Loglan online help documentation. In this tutorial, we will discuss only the more important ones. All Loglan functions return a result, result, but often the result is ignored (for example put_frame). put_frame). The case of the function name is not significant. Spaces around the parentheses, as well as between the arguments, are ignored.

 text variable, while "numeric" is used for a numeric variable, and logical for

In the examples which follow, the word "text’ is used to indicate an alpha or

a logical variable.

Display Functions At any time during the execution execution of a Loglan program, you can display display messages in the Message area at the bottom of Geolog’s Well or Project application windows. These messages could be results of calculations, status comments, variable input values, or any other text. The Loglan functions in this category are: DISPLAY_MESSAGE DISPLAY_MESSAGE ( 'Text for Display' )

and DISPLAY_ERROR ( 'Error message' )

The argument can be either a quoted string (as in the examples above), or an alpha variable or expression. Both functions display their argument in the Message area of the window. In addition, the second function causes the Loglan program to abort with an error condition. It is useful if you want the program to abort if, for example, the input data is invalid. A few further examples: e xamples: DISPLAY_MESSAGE DISPLAY_MESSAGE ( 'Processing interval ' // INTERVAL ) call DISPLAY_ERROR ( 'Invalid option: ' // option )

Note that the call can call can be omitted. In the first example, if INTERVAL was defined as an interval constant, it would automatically contain the name of the interval being processed, if you are processing intervals (otherwise, it will be blank). If you want to display the value of a numeric variable, you will first need to convert its value to text using one of the functions described in "Conversion Functions" on Page age 50. 50. For example: DISPLAY_MESSAGE DISPLAY_MESSAGE ( 'Value of SW: ' // NUMSTR ( SW ) )



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Conversion Functions This group of functions converts character to numeric variables and vice versa. These include: NUMSTR function Converts a numeric variable to a string (text), using a fixed precision of 13 digits. The syntax for this is: text = NUMSTR ( numeric )

CONVERT function Similar to the NUMSTR function, except that it provides two additional facilities. Firstly, you can control the number of character positions (field width) as well as the number of decimal places to be used. Secondly, you can add additional text to the resulting text string. text = convert ( format, numeric )

where format is a text literal or variable which defines how the numeric variable is to be converted. It consists of text which is copied to the function result, and a field code enclosed in curly brackets. The value of the numeric, formatted according to the field code, replaces the field code in the function result. The field code has the form Nw.d, where "w" is the number of characters to be used, and "d" specifies the number of decimal places. For example: CONVERT ( 'The value of Sw is:{N8.3}', sw )

would produce the string "The value of Sw is:    0.134" (where " " represents a space) if the value of sw was 0.134234455. As a further example, if you have variables DEPTH, RHOB and NPHI with values of 5200, 2.56, and 0.176 respectively, then CONVERT ( '{N8.3}', DEPTH ) // ~ CONVERT ( '{N8.3}', RHOB )

// ~

CONVERT ( '{N8.3}', NPHI )

would produce "5200.000   2.560   0.176". STRNUM function Converts a string to a number: text = STRNUM ( '1.23456' )



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Exercise 1

 suggestions. Also, the flow of the program is indicated by comments.

In this and the other exercises which follow, the variables listed are only Example solutions can be found in the /loglan/examples subdirectory.

• In this exercise, you will write a program to display the average value of porosity for a well. • The program is to calculate a simple value of density porosity and display the average for the well to the Message area of the Well application. Use the formula porosity = ( RHOma - RHOB ) / ( RHO ma - RHOfl ).

Program: DISP_POR Input variables: RHO_MA (Constant, G/CC) (Validation Range 1.5 - 3.5) RHO_FL (Constant, G/CC) (Validation Range 0.5 - 1.2) RHOB (Log)

Local variables: poro, count, sum

Program steps: /* Initialise variables. /* Loop through the data.

/* Calculate porosity, increment sums. /* End loop.

/* Calculate average. /* Display the calculated average.

REMEMBER: all INPUT to the computer is in Bold Courier New , while all  OUTPUT from the computer is in Courier New, but not bold (i.e., the code for the comments listed above which are NOT bold are automatically created by mui_loglan).

ASK Functions ASK are used to obtain interactive user input. They are most often used when the input required depends on the parameters passed to the program—otherwise, it would be much more efficient to get the required values by using module parameters. For these functions to work, the environment variable MIN_DIALOGS must be set to TRUE, otherwise, the default value is returned. If you are not sure how to do this, contact your Geolog administrator. Geolog 6.6 - Loglan Programming Tutorial


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In the normal case, a popup window appears into which the user enters the required value. There are three functions involved—one each for text, numeric, and logical values; these are ASKS, ASKN, and ASKL, respectively. They all have the same syntax: result = ASKx ( prompt, default )

where prompt is a literal or text variable containing the prompt to be displayed, and default is the value (which must be of the appropriate type) to be used if the user does not enter a value. For example: rho_ma = ASKN ( 'Enter value of Rho Matrix:', 2.65 )

or, exactly equivalently: string = 'Enter value of Rho Matrix:' rho_ma = 2.65 rho_ma = ASKN ( string, rho_ma )

Exercise 2 • In this exercise, you will create an "interactive" program. • The program will calculate Sw using the Archie formula sw=SQRT(rw/(rt*phi**m)) and display the result in the feedback window. • Because the program requires no input or output parameters, all variables will be local. • The program should ask for, and display, a username (merely so we can demonstrate ASKS), and should iterate, if required.



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Program: ASK_SW Local variables: rw, m, phi, rt, sw, name (ALPHA*16), again (LOGICAL)

Program steps: /* Initialize logical variable. /* Ask for the user's name. /* Start the iteration loop. /* Get the values for the variables. /* Calculate the water saturation. /* Display the results. /* Ask the user whether to run again.

File Access Functions In addition to accessing data from the Geolog database, Loglan programs can access external files for both input and output. Text files can be both read and written by a Loglan program, allowing you to perform data manipulation as well as loading or unloading data. In this section of the tutorial, we will discuss the functions involved in opening and closing external files, and those which facilitate reading and storing data in those files. File Opening

To access a text file in a Loglan program, it must first be opened: logical = FOPEN ( mode, filename, index )

where: mode

is the action that is to be performed on the file—'read' opens an existing file for reading; 'owrite' overwrites an existing file or creates a new one for writing; and 'awrite' either appends to an existing file, or creates a new file if the named file does not exist.

filename

is the name of the file to be opened, either a literal (quoted string), or a text variable.

index

is a number (or the name of a numeric variable). This index is used to read from or write to the file. Up to 40 files may be opened at any one time within a Loglan program, so it is possible to read and write many files simultaneously.



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The function returns TRUE if the file was successfully opened. Possible causes of failure are: • an invalid file name • a non-existent file opened for read • a non-existent directory • a protection failure It is good practice to test the result of the FOPEN call so your program can take the appropriate action if it fails: if ( ^ FOPEN ( 'read', filename, 1 ) ) then DISPLAY_ERROR ( 'Failed to open file ' // filename ) endif

This checks if the file can be opened for reading, and aborts the program with an error message if the file cannot be opened; otherwise, the file is opened and the index 1 is associated with it.

File Closing When your Loglan processing has finished processing a file, it must be closed using the FCLOSE function: FCLOSE ( index )

where index is the file index with which was opened by FOPEN.

Reading from a File External files are always read sequentially; the next line from the file is returned by the FREAD function: text = FREAD ( index )

where index is the number used in the FOPEN call. If no more data remains to be read from the file, the string EOF is returned—if you want to detect end-of-file, you must test for this result. This is a common way of processing a file: record = FREAD ( 1 ) dowhile ( record <> 'EOF' ) record = FREAD ( 1 ) enddo



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Processing the Data Read from a File Because FREAD returns a single character string, you usually need to do some work to extract the data from this string. The method used depends on how the data is stored in the file. If it is in fixed columns, it is most efficient to use the SUBSTRING function. If the data is not stored this w ay, or if you want to take the easy way out, use the TOKEN function: text = TOKEN ( string, index )

where string contains the text from which a token is to be extracted, and index is the number of the token to be extracted. A token is a string of characters delimited by one or more spaces. The function draws a blank if there are fewer then index characters in the passed string. For example, if the variable record contained "a b ab 123.456", then numeric = STRNUM ( TOKEN ( record, 4 ) )

would assign 123.456 to the variable numeric . To retrieve data from fixed positions in a record, use the SUBSTRING function: text = SUBSTRING ( string, start, length )

where string contains the text from which the substring is to be extracted, start is the position of the first character to be extracted, and length is the number of characters to be extracted from the string. For example: SUBSTRING ( '1234567890', 3, 6 )

would return the text 3456. Other functions which are useful for manipulating text in buffers are INDEX and TRIM (see "String Related" under "Functions" in the Loglan online help documentation).

Writing to a File The FWRITE function is used to write a buffer of data to a file opened for write. Its format is: logical = FWRITE ( index, buffer )

where buffer contains the text to be written to the file, and index is the number used in the FOPEN call. The function returns TRUE unless an error occurred.



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Exercise 3 By now you should have enough knowledge to complete an exercise to process a text file containing log data and load it into Geolog. • In this exercise, you will write a program to read data from a fixed-column format file. • The file to be loaded is in your data subdirectory and is named nuke.asc. The data contains GR, DRHO, RHOB and NPHI curves in the following fixed-column format: DEPTH 5100.000 5100.500 5101.000 5101.500 5102.000 5102.500

GR 61.155 60.522 58.631 54.852 51.073 50.139

DRHO -0.022 -0.018 -0.012 -0.002 0.008 0.010

RHOB 2.452 2.445 2.437 2.425 2.414 2.421

NPHI 0.268 0.262 0.253 0.238 0.223 0.213

As you can see, the file has a header line and then data lines each containing 5 values in fixed fields each 10 character positions long. • In this exercise, the data will be read one line at a time using the FREAD function, and the resulting text string split into the separate numbers to be used as data using the SUBSTRING function. • Note that, because there are no input logs, you will not require the dowhile get_frame loop. • It is VERY important to specify units for the output logs, otherwise, they will be assumed to be in your preferred units when they are written to the Geolog database.

Program: READ_COL Input variable: FILENAME (Alpha*32) (PARAMETER)

Output variables: DEPTH (FEET) (LOG) GR (GAPI) (LOG) DRHO (G/C3) (LOG) RHOB (G/C3) (LOG) NPHI (V/V) (LOG)

Local variable: buffer (Alpha*80) Geolog 6.6 - Loglan Programming Tutorial


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Program steps: /* Open the input file, checking for errors. /* Read (and ignore) the header line. /* Read first line of data /* Loop through all the remaining records. /* Decode the fields in the current record. /* Write the data to Geolog. /* Read the next record. /* Close the input file.

Exercise 4 • In this exercise, you write a program to read data from a space or tab delimited file. • This exercise is similar to the previous one, except that the file to be processed is space or tab delimited rather than in fixed columns. This means that instead of using the SUBSTRING function, we will u se TOKEN. Note that we could have used TOKEN in the pr evious exercise, but it is much less efficient. • The file to be loaded is ./data/sonic.asc, which contains: #

DEPTH

DT

5100.000

98.9480

5100.500

99.5305

LLD

LLS

4.08 4.19

3.01 3.07

5101.000 99.7355

4.39

3.18

5101.500

4.72

3.36

99.3742

GR 61.1547 60.5218 58.6305 54.8517

As you can see, the columns are not aligned as they were in the previous exercise, so it would be very difficult to specify start and length numbers for each variable; hence, we have to use the TOKEN function. • As in the preceding example, it is VERY important to specify units for the output logs, otherwise, they will be assumed to be in your preferred units when they are written to the Geolog database.

Program: LOADER2 Input variable: FILENAME (Alpha*32) (PARAMETER) Geolog 6.6 - Loglan Programming Tutorial


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Output variables: DEPTH (LOG), DT (LOG), LLD (LOG), LLS (LOG), GR (LOG)

Local variable: buffer (ALPHA*100)

Program steps: /* Open the input file, checking for errors. /* Read (and ignore) the header line. /* Read first line of data /* Loop through all the remaining records. /* Decode the fields in the current record. /* Write the data to Geolog. /* Read the next record. /* Close the input file.

Note the program steps are exactly the same as those for the previous example.

Exercise 5 • In this exercise, you create a program which writes data to a text file (data from the Geolog database will be written to a text file). • Writing to text files has to be done one line at a time, so the buffer to be output first has to be assembled (unless, of course, you want to output the values one per line). This is done by concatenating the data values which have first been converted from numeric to text using the NUMSTR or CONVERT functions.

Program: UNLOAD1 Requirements: Your Loglan program will create a text file with header lines containing: LINE1:

the well name

LINE2:

x location

LINE3:

y location

LINE4:

the porosity constants RHO_MA and RHO_FL

LINE5:

the log names

LINE6:

and then, for each data frame, a line containing the depth, RHOB, and the calculated porosity PHIE



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See the example below. EXAMPLE: Well: X_LOCATION: Y_LOCATION: RHO Matrix: RHO Fluid: DEPTH

RHOB

PHIE

In the example above, the items in angle brackets are replaced by values passed to your program. The format for the lines containing the data values for depth, etc., is to be a field width of 10, with 3 decimal places. The porosity PHIE is calculated using: PHIE = ( RHO_MA - RHOB ) / ( RHO_MA - RHO_FL )

The calculated porosity, as well as the other module parameters (RHO_MA, etc.), are to be written back to the Geolog database. The program will be passed a file name without a directory, but the output file is to be created in the data subdirectory. Input variables: FILENAME (ALPHA*32) (PARAMETER) WELL (ALPHA*16) (CONSTANT) X_LOCATION (DOUBLE) (CONSTANT) Y_LOCATION (DOUBLE) (CONSTANT) RHOB (K/M3) (LOG)

Input/Output variables: RHO_MA (K/M3) (INTERVAL) RHO_FL (K/M3)(INTERVAL)

Output variable: PHIE

(V/V) (LOG)

Local variables: outfile (ALPHA*32) repline (ALPHA*80)



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Program steps: /* Create full pathname of the output file. /* Open the output file. /* Write the first three lines of header data. /* Write porosity constants. /* Start per-frame loop. /* Calculate porosity. /* Assemble output line. /* Output data to text file and database. /* Close the output file.

Interval and Multiwell Processing Functions When a Loglan program executes, it is passed the data for one interval (if you are processing intervals) and for one well ( if you are processing multiple wells), although local variables are initialized only once. Sometimes, you need to be able to identify whether you are starting a complete run, a new well, or a new interval (e.g. if you want to calculate an average for an entire project or well). Loglan has a number of functions to facilitate this: START () FINISH ()

These functions return a logical result which indicates that the current data is either the first or last to be passed to your Loglan program. WELL_START () WELL_FINISH ()

These functions allow you to identify whether the current da ta is the first or last for a well. If you are processing only a single well (using mui_well), these functions will return TRUE only once (at the start and end of processing). If you are processing multiple wells (using mui_project), the functions will return TRUE at the start and end of each well. INTERVAL_START () INTERVAL_FINISH ()

These functions return TRUE when the first or last frame for an interval is being processed. If you are not processing on a n interval basis, they are equivalent to WELL_START and WELL_FINISH. You would normally use these functions only within the dowhile GET_FRAME loop, since the code before this loop is executed at the start of an interval and the code after the loop at the end.



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Exercise 6 • In this exercise, you write a program to calculate Well and Interval Average values for Porosity. • This exercise is designed to demonstrate the use of the WELL_START and INTERVAL_START functions to initialize variables at the beginning of the well and at each interval change. Values of density porosity are to be calculated, and then averages output to a text file as a report. • Use wells ATLAS, BOTEIN, CAPELLA and DENEB to test your loglan program.

Program: PHI_AVG_RPT Input variables: FILENAME (ALPHA*32) (PARAMETER) WELL (ALPHA*32) (CONSTANT) RHOB (G/C3) (LOG) INTERVAL (ALPHA*32) (INTERVAL)

Input/Output variables: RHO_MA (G/C3) (INTERVAL) RHO_FL (G/C3) (INTERVAL)

Output variables: PHIE (V/V) (LOG)

Local variables: wcount wsum icount isum



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Program steps: /* Initialize well totals. /* Initialize interval totals. /* Open text file for output if first time. /* Start looping through the data. /* Calculate porosity if RHOB is present. /* Increment interval totals. /* Increment well totals. /* At interval end write average porosity. /* At well end, write well average porosity. /* At the very end, close the text file.

Frame Positioning Functions All of the previous exercises have assumed that the process to be carried out is done on a depth-by-depth basis, so any calculations are only written to a single depth with inputs from that depth and that depth alone. If a program needs to input data from surrounding frames, then positioning within the data stream must be undertaken. This is carried out using the POS_FRAME function, which has the syntax: logical = POS_FRAME ( frame_number )

where frames are numbered sequentially from the first depth point to the last depth point, starting at 1.

Exercise 7 • In this exercise, you will create a program to calculate a 5-point moving average of the GR log. • The exercise is designed to demonstrate the use of data from frames other than the current one. The program should input the GR curve, count the number of frames, and then position itself frame by frame. At every depth it should read the GR values from the 2 frames on either side of the current frame, and output an average value.

Program: MAV_GR Input variables: GR (GAPI) (LOG)



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Output variables: GR_MAV (GAPI) (LOG)

Local variables: count frame i n sum

/* /* /* /* /*

Number of frames in average. Current frame number. Loop variable. Number of frames in data. Sum of GR values.

Program steps: /* Get the number of frames. /* Loop through the data again. /* Compute average over window. /* Calculate value of output log.



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Arrays in Loglan Procedure In this section, using arrays in Loglan is explained, and you: • Create an array program to sort GR data and derive the 5th and 95th percentiles of the GR.

Overview Loglan supports the use of one dimensional arrays. The size of an array is specified in mui_loglan by specifying the number of elements in the array in square brackets after the name: VARIABLE_NAME[array size]

For example, if a variable called arraylog is to have 2000 elements, it would be declared as arraylog[2000]. The first element of a n array has a subscript of one. References to elements of an array use the same syntax (i.e., variable[subscript]). The first element of the above array would be arraylog[1].

Exercise 1 • In this exercise, you create a program which uses an array to 'bubble sort' GR data, and use this to derive percentiles for use in Vshale calculations. • The exercise is designed to demonstrate the use of arrays, and also to show the bubble sort algorithm. The GR data is read into an array and then sorted using a bubble sort procedure. This is then used to derive the 5th and 95th percentiles of the GR, which are stored into the database as GR Matrix and GR Shale, respectively. • The algorithm for a bubble sort is as follows: for i = 1 to n - 1 do for j = i + 1 to n do if ( data[i] > data[j] ) then temp = data[j] data[j] = data[i] data[i] = temp endif endfor endfor

This sorts array data, containing n elements, into ascending order. Geolog 6.6 - Loglan Programming Tutorial

Arrays in Loglan 64

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Program: PERCENTILE Input variable: GR (GAPI) (LOG)

Output variables: GR_MA (GAPI) (CONSTANT) GR_SH (GAPI) (CONSTANT)

Local variables: n i, j data[5000] temp

/* /* /* /*

Frame count. Loop variables. Stored GR values. Temporary.

Program steps: /* Store GR values. /* Check if room in array. /* Sort GR values. /* Calculate the constants.


Arrays in Loglan 65

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Log Constants Procedure This section is a brief overview of using Lo glan to access log constants. You will: • Create a program to convert NPHI from decimal to percent if the mean of NPHI < 1.

Overview A Loglan program can access log constants for both input and output. They are defined in mui_loglan using, for example, Insert…Input…Log Constant. Log constants have names of the form constant_logname, where constant is the name of the required constant and logname is the name of a log (which must have been previously defined). The available constants include: NAME, MEAN, MIN, MAX, STDDEV, TOP, BOTTOM, and UNITS (see "Declaration Section" under "Program Syntax" in the Loglan online help documentation for a full list). Note that the value of most output log constants is ignored, since these are nor mally calculated automatically by the Geolog database. Log constants are never displayed in the Module Launcher window, as they are always automatically derived from the corresponding log.

Exercise 1 • In this exercise, you will write a program to convert NPHI from decimal to percent if the mean of NPHI < 1. • The exercise shows the use of Log header constants to determine whether a log has a mean of less than 1, and multiplies it by 100 if it does. This is (or should be) a somewhat artificial example, since, if proper procedures have been followed, the NPHI log should have its units specified, and if we specified units in our Loglan program, the data would be automatically converted to these units. • Also, it is important that, for this exercise, the output log not exist in the loginfo file, otherwise, the results would be automatically converted to your preferred units.

Program: NPHI_PC Input variables: NPHI (no units) (LOG) MEAN_NPHI(no units) (LOG CONSTANT)


Log Constants 66

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Output variable: NEW_NPHI (%) (LOG)

Program steps: /* Calculate conversion factor. /* Check mean of nphi log. /* Start looping through data. /* Convert. /* Write to Geolog database.


Log Constants 67

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External Functions Procedure External C and Fortran functions can be called from within a Loglan program. Because the Loglan program is converted to C, it is easier if the external function is also written in this language, although Fortran may also be called if the argument passing mechanism is compatible. Because Loglan does not allow unknown external functions to be called directly, it is necessary to enter into C mode in order to make the function call. This is done using the following syntax: .cc_begin Variable = user_function (arg1,arg2...) .cc_end

Exercise 1 The "CPUTIME Example" on Page 69 is a Loglan programme that calls a C function named c_cputime. The variable CPUTIME_C is the Loglan variable that is passed to the function, modified by the function and then passed back to Loglan to be written to the Geolog database. You have a copy of this example—compile and run it, and then view the results. You may also look at the external C function which is located in the /loglan directory and called c_extern.c


External Functions 68

Geolog6.6 Loglan Programming Tutorial

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