Abstract

Surfactant/polymer and alkaline/surfactant/polymer (ASP) floodings have been mostly used in worldwide oil fields as an effective enhanced-oil-recovery method. The principles of these chemical floodings are to reduce the interfacial tension between oil and flooding solution of alkaline/surfactant.

The spinning drop technique has been used to evaluate the interfacialtension between oil and the solution by measuring the shape of the oil drop inthe flooding solution contained in a capillary tube. Until now, the shape ofthe drop has been measured by micrometer of a microscope. This method, however, often brings on human errors and a great time-loss. In order to eliminate these defects, an automatic measuring system has been newly developed by combining avideo- image analysis, an automatic recording system, and a computer for calculation of the interfacial tension under the spinning drop technique. The features of this system are as follows:

  1. It enables to measure and record the interfacial tension automaticallyfor a long time.

  2. It enables to change the measuring time and the recording interval veryeasily by programming.

  3. It reduces human errors and contributes to laborsaving.

Introduction

In oil industries, the chemical flooding has been actively studied and applied for the enhanced recovery of oil, but a large amount of expensivesurfactant can not be used at present, such as the low-cost age of crude oil. Now, economical methods for the chemical flooding are expected by combining the surfactant with low-cost chemicals, because of the big effect of the surfactanton the recovery of oil. One of the methods is an alkali-chemical flooding, in which the surfactant is combined with an alkali-aqueous solution. The base forselection of the chemical in this case is the interfacial tension between crudeoil and the alkali-solution, and the solution causing lower interfacial tension is preferable.

For the selection of solution, the spinning drop technique is very useful. In this technique, a minute drop of crude oil is injected into the glasscapillary tube filled with a chemical solution, and then the tube is rotated around its longitudinal axis. The interfacial tension between the oil and the solution can be calculated according to the method of Cayias etal.1) by measuring the shape of the oil drop inside the glass tube. Their method uses a microscope to measure the shape of the oil drop.

In this study, a CCD camera is used for the measurement, and the longitudinal and horizontal axes of the image of oil drop on the video are measured by the image analysis. By substituting the measured values into the Cayias' equations, the interfacial tension between the oil and solution is automatically evaluated. Furthermore, this tension has been evaluated for along time by repeating the above-mentioned process automatically? The method developed in this study enables to do the long-term measurement of the interfacial tension without manpower, and further reduces the error caused by the man's fatigue in the method up to now. This paper reports on the measuring system mentioned so far and a few experimental results.

Automatic Measuring System for Interfacial Tension by Spinning Drop Technique

The automatic measuring system for the interfacial tension by the spinning drop test used in this study is shown in Fig.1, where the left-hand side from the vertical dotted line in the middle part corresponds to the spinning-dropmeasuring system heretofore for the interfacial tension. In this system, aglass capillary tube (1), whose inner diameter is 2mm, is filled with chemical solution, and an oil drop is injected into the solution inside the tube by the micro-syringe. Then, this glass tube is rotated around its longitudinal axis by the high-speed belt pulley (2), and lightened by the strobo scope (3).

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