Study of the Mixing Process in The Displacement of Miscible Fluids
Authors: Iffly R. , Leduc J. 
Published: December 2007

This paper was prepared for the European Regional Meeting of the Society of Petroleum Engineers of AIME, to be held in Milan, Italy, April 4–6, 1968. 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
To study the efficiency of the miscible gas injection project in the Hassi-Messaoud field, Algeria, many laboratory experiments have been performed to determine the laws of evolution of the mixing zone separating both fluids. The displacement of actual reservoir fluids in long columns packed with an artificial porous medium, and the displacement of simulating fluids in short columns of reservoir rock have been studied experimentally. The results obtained have been combined by observing the displacement of the simulating fluids in the long columns previously used. The experimental techniques and apparatus are described, and the main results are presented. In particular, the composition of the mixing zone is given and its length expressed as a function of the distance traveled, of the displacement velocity and of the characteristics of the porous medium.

Introduction
Presented here are the main results of the studies that were conducted on the mixing phenomena accompanying the displacement by miscible gas of reservoir fluids in the Hassi-Messaoud field, Algeria. By "mixing phenomena" are meant all the mechanisms directly or indirectly contributing to the formation of a mixing zone between oil and gas, namely molecular diffusion, kinematic dispersion, more or less rapid formation of fluid miscibility, microscopic heterogeneity of medium, and fingering.
By means of numerous experiments, precise information could be derived about the growth of this mixing zone for a one-dimensional displacement in macroscopically homogeneous media. Gravity effects were ignored. The results of these experiments were extended, by calculations, to a two-dimensional displacement presenting the same kinematic characteristics as the real displacement. Studies conducted at the same time to take into account the macroscopic heterogeneity and gravity effects are beyond the scope of the present paper.
When this study was started in 1963, an extensive literature already was available on mixing conditions of fluids of equal density and viscosity, instantaneously and totally miscible with each other, during displacement in homogeneous and unconsolidated porous media. A few papers were devoted to the influence on mixing of the viscosity ratio or of the difference of fluid density.