QUANTITATIVE ANALYSIS BASICS
With the advent of modern, inexpensive, multi-function, programmable calculators, pocket computers, and desktop micro-computers, chartbook methods are quickly disappearing. Charts are occasionally referred to when working in complex lithology, where the pattern or position of points on the chart or graph may be helpful. Even this can be quantified by appropriate equations.
Algebra from various Chapters can be merged together and coded in calculator or computer language to give customized programs for the individual user. Once recorded and documented, they can be carried on the job as readily as a chartbook, and they are much more convenient and powerful. Most chartbooks do not handle shale corrections, so they are now inappropriate for very many oil and gas reservoirs.
For fast, practical analysis, preprogrammed methods for the calculator or computer are essential. Spreadsheet software , commercial petrophysical packages, and in-house software has replaced the chartbook. Unfortunately, many of these systems are delivered pretty "naked"; you will probably have to code numerous equations into the package yourself.
These are provided in later sections of this Handbook and are "computer-ready". They do not need to be derived, translated, or heavily modified to be used in virtually all computers with Basic, Fortran, or similar computer languages or interpreters. This may have made the equations a little harder to read, but easier to use.
Not all methods outlined in this handbook, or elsewhere, apply in every instance. Nor is there time or data available to try every method on a particular zone. How to select a reasonable method is described in appropriate sections of each Chapter.
Most user defined equation interpreters require that you distinguish between a log curve and a parameter - read your software documentation manual to see how this is done and adapt the algorithms in this Handbook appropriately.
The layout of all algorithms in this book has been specially designed to allow a text editor or language interpreter program to convert the information into a working program. This has been achieved by using a very brief pseudo-programming language with few keywords, and yet it retains many components of the English language to increase readability.
More than one algorithm may appear under a single Chapter subheading. Conversely some Chapter subheadings may contain no algorithm.
The algorithms are written in a pseudo computer language using structural programming style. The key words are:
keyword follows the algorithm line number, and only one keyword
can be on a line. For example:
more complicated IF statement might use several lines:
Using this style eliminates the need for the END IF statement and allows one to read the program in English without difficulty. It also lends itself to automatic translation into Excel, Basic or Fortran by a simple interpreter program or the Find/Replace function of a word processor. Some language interpreters will insist that the complete IF..THEN..ELSE be on one program line. Some care is required to keep the AND and OR statements sorted out when you convert this pseudo-code. Some languages will insist on different punctuation or parentheses to compile correctly. Read your language manuals carefully to determine what you need to do to translate the algorithms.
An example will illustrate this point more clearly:
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