Microscopic Observations of Oil Displacement in Water-Wet and Oil-Wet Systems

Abstract

This paper was prepared for the 46th Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in New Orleans, La., Oct. 3–6, 1971. 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 request 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 discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines. Abstract Laboratory studies of the behavior of crude oil and brine in a waterflood were conducted using micromodels packed with graded sand. Flow mechanisms and residual oil patterns were observed and photographed through a microscope. The wettability of the micromodels, which possessed many of the over-all characteristics of reservoir rocks, ranged from strongly water wet to strongly oil wet. Observations of waterflooding showed that each fluid moves through individual networks of interconnected pores during the period of oil production. The size of trapped oil pockets production. The size of trapped oil pockets behind the water front depends upon the wettability of the system. The rapid development and growth of water fingers ahead of the front resulted in early water breakthrough in the oil-wet systems. The length of these fingers ahead of the front depended upon the wettability of the system. When additives were used to stimulate residual oil production, three distinctly different types of residual-oil flow mechanisms were observed. These can be described as slug flow, globular flow, and extraction. Sandstone cores were used to determine quantitatively the effect of wettability on oil displacement and relative permeability. The results of these tests of different wettability systems are in good agreement with visual observations of the micromodels. Strongly water-wet systems produce more oil and have better displacement efficiency than oil-wet systems. Introduction The USBM has long recognized the need for more knowledge about the mechanics of fluid flow within the pore spaces of reservoir rocks. This knowledge is necessary for development of new and improved methods of oil recovery. Waterflooding is the main process used for the secondary recovery of oil, and wettability has long been recognized as an important factor in this process. The importance of the relative wetting tendencies of oils to production and techniques for measuring wettability have been discussed by many researchers. Micromodels have been used to observe and study fluid-flow behavior during simulated waterfloods. Chatenever described flow mechanisms and residual oil patterns in a model using-glass and/or Lucite beads with water and filtered crude oil. (Reference to specific brands is made for identification only and does not imply endorsement by USBM.) Mattax and Kyte used a network of interconnecting capillary grooves etched into a flat glass plate to observe more closely the behavior of water and refined oil at the interface. Morris and Wieland used a glass bead model with water and a highly refined kerosene to study the effect of varying the wettability. In this research, micromodels packed with clean graded sand were used with centrifuged crude oil and simulated brine.