Abstract

An experimental study has been conducted to investigate the effects on water flood oil recovery caused by the addition of sodium hydroxide to only a portion of the injected fluid. The results of interfacial tension measurements between the viscous crude oil and water indicate that a low interfacial tension can be achieved at concentrations of sodium hydroxide varying from 0.1 to 7.0 % by weight. The wide range of concentrations is a result of the significant variation in water compositions.

The results of displacement tests involving an artificial sodium chloride brine indicate that a significant increase in recovery can be achieved at concentrations of sodium hydroxide in excess of 0.1% by weight. The results of displacement studies involving varying slug sizes indicated that sodium hydroxide concentrations as low as 0.1% by weight in a slug volume of approximately 40% of the pore volume, resulted in an oil recovery equivalent to that which could be obtained by the continuous injection of a dilute aqueous sodium hydroxide solution of 0.1% or greater by weight in caustic concentration.

The optimum concentration of sodium hydroxide required to significantly reduce the interfacial tension and thus increase the recovery of viscous crude oil over that obtained by pure water flooding is significantly affected by the concentration of the calcium and magnesium ions of the in-situ formation waters and the source waters used for the injection project.

Introduction

For a number of years investigations have been carried out in the Petroleum Engineering Department of the University of Alberta dealing with the effect of various chemicals on the water flood recovery of very viscous crude oils. Most of the early investigations dealt with the addition of chemicals continuously to all of the water injected during the water flood displacement of a crude oil system.

As early as 1952, Preston and Calhoun1 suggested that only a part of the injected water need be treated. The transmission or movement of a surfactant slug through the reservoir was described by the application of the theory of chromatography. However, no experimental evidence was brought forth to support this mechanism.

Jennings et al.2 stated that two assumptions were implicit in the suggestion that a slug could perform as well as continuous injection. Firstly, the time required for the surface active material to be released from the oil from any point in the reservoir had to be less than the time it took for the surfactant bank to pass through that point. Secondly, the released or mobile oil must travel faster than the surfactant or chemically treated bank.

Since slug concentration is directly proportional to the rate of movement of the slug through the reservoir system, it is generally thought that a small high concentration slug would achieve the same results as a large low-concentration slug. Although the complete description and understanding of the mechanism which results in improvement of oil recovery in the presence of certain chemicals is not completely understood, it would appear that in order to achieve the higher recoveries a relatively high-concentration low volume slug would be required.

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