Effect of Floodwater Salinity on Recovery Of Oil from Cores Containing Clays
Authors: Bernard George G. 
Published: December 2007

American Institute of Mining, Metallurgical and Petroleum Engineers, Inc.

This paper was prepared for the 38th Annual California Regional Meeting of the Society of Petroleum Engineers of AIME, to be held in Los Angeles, Calif., Oct. 26–27, 1967. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon requested to the Editor of the appropriate journal, provided agreement to give proper credit is made.

Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers Office. Such discussions may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

The objective of this study was to investigate the relative effectiveness of fresh and salt waters in flooding oil from cores containing clays. Both synthetic and natural water-sensitive cores were flooded with waters of various salinities.

In general, it appears that water sensitive cores will produce more oil with a freshwater flood than 'with a brine flood. However, the fresh-water flood is accompanied by a lowering of permeability and the development of a relatively high pressure drop. If the freshwater flood does not develop a high pressure drop, then no additional oil is produced.

Introduction

Oil reservoirs are often composed of sands containing various amounts of clays. Certain of these clays possess a dual nature in that they are essentially unaffected by salt water, but are greatly affected by fresh water. The effect of clays on flow of liquids in rocks has been discussed widely in the literature.

Johnston has indicated that clays are important in the oil recovery process because they occur as small particles adjacent to the sand grains, where they usually contact water. Whereas clays are relatively inert to oil, they sometimes show extreme reactivity to water.

Fancher, Lewis and Barnes found that the permeability of certain oil sands is affected by hydration of clays.

In 1945, Johnston and Beeson presented data on the permeability of 1,200 samples of oil sandstones. They showed that the permeability of about 70 percent of the samples decreased on contacting fresh water.

Many other investigators have shown that salinity has a great effect on permeability of cores containing clays. While most of this work is concerned with permeability variations, only one study apparently has been made to determine if clay hydration affects oil recovery.

The idea that clay hydration could affect oil recovery seemed plausible after considering the mechanics of the process. Petrographic studies by Morris, Anne and Gates have shown that the clays occur in the pore spaces, attached to the sand grains. When these clays hydrate and swell, the pore space available to liquids probably decreases.