API RP 45
Recommended Practice for Analysis of Oil-field Waters
|Publication Date:||1 November 1965|
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. Except for the usual delays in committee activities, this committee has been active since its inception. 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 three sections:
Section 1 - General Information
Section 2 - Methods for the Determination of Major Constituents
Section 3 - Methods for the Determination of Accessory Constituents
Section 1 contains information that should be of interest to all associated with 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. These procedures were not evaluated by the committee, but are used by one or more of the committee members.
The committee believes more work should be done on the accessory constituents. There are three reasons why this work was not attempted: 1, the original assignment was limited to the procedures for determining the major constituents; 2, special equipment is required for some of these procedures; and 3, the general interest in certain determinations was questioned. The committee assignment has been completed and any additional work on this subject would require a new assignment.
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 study 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 items that influence the accuracy and reliability of these data.