API RP 45
Recommended Practice for Analysis of Oil-Field Waters
|Publication Date:||1 July 1981|
The oil industry has used water analyses for many years for formation identification, compatibility studies, water-quality control, and evaluation of pollution problems. The users of these data have assumed the values to be reliable. Unfortunately, data collected from a multiplicity of sources may not have the required reliability, and unless the quality of such data can be verified, its use for comparative purposes is not recommended.
This lack of agreement between laboratories is understandable when all Phases of the subject are considered. 1. The methods used to analyze oil-field waters were developed by modifying the procedures used to analyze fresh water. Individual laboratories have further modified these procedures to suit their particular need. 2. Comparison of analytical data or procedures is difficult because standard samples of synthetic brines are not readily available from commercial sources. 3. Data are used for many different purposes with quality requirements ranging from very accurate to reasonable estimates. Laboratories usually produce the quality of data their clients require. 4. The availability of equipment and quality of personnel has a decided influence on the quality of analytical data.
The increase in secondary-recovery projects, interest in water quality, and the continued interest in formation identification has resulted in more emphasis being placed on water analyses. The interest in these data should have been accompanied by a similar interest in accuracy and reliability, but this phase of the problem has been neglected.
A cooperative study by 20 laboratories proved there was a serious need for more reliable water-analysis data. This study resulted in the formation of the API Study Committee on Analysis of Oil-field Waters in the spring of 1958. The work of this study committee was published in 1965 as API Recommended Practice for Analysis of Oil-field Waters (Tentative). Additional work was recommended; and, in 1966, the Subcommittee on Analysis of Oilfield Waters was formed to complete this work. The results of this study are presented here in a form the committee believes will be useful to the industry. No claim is made for originality nor has the subject been exhausted.
The report has been divided into four sections:
Section 1 - General Information
Section 2 - Methods for the Determination of Major Constituents
Section 3 - Methods for the Determination of Accessory Constituents
Section 4 - Spectroscopic Methods
Section 1 contains general information about obtaining, reporting, and using water analyses. Section 2 contains the methods used in routine water analysis. Section 3 contains procedures which often are not routine, and have been included for convenience. Section 4 contains spectroscopic procedures that are of interest to laboratories equipped to use these methods. The procedures in Sections 3 and 4 were not evaluated by the committee as a whole, but were evaluated and recommended by the committee members using these procedures.
Several procedures have been included because of the current interest in water pollution. The committee believed this would serve two purposes: 1, to provide procedures that are known to be reliable; and 2, to call attention to the accuracy of these procedures. Hopefully, general acceptance of these procedures by all interested parties would provide a reliable basis for the evaluation and resolution of pollution problems.
It is the hope of the committee that the information presented in this recommended practice will serve a useful purpose and, as a result of this effort, the overall reliability of analytical data will be improved. The work of the committee proved accurate water analyses can only be obtained from reliable methods in the hands of competent analysts. The remainder of this section is devoted to a discussion of the terms that influence the accuracy and reliability of these data.