Abstract

One of the main goals of enhanced oil recovery (EOR) is to achieve maximum oil recovery. The occurrences Of dispersion of miscible displacement cause not to obtain the hundred percent recovery at one pore volume of the injected fluids. This dispersion phenomena is Junction of pore size distribution and the properties of the displacement fluids. In this work different miscible displacement tests has been conducted experimentally on artificial porous media and real porous media (Berea sand-stone). The experimental results show that the shape of S-curve of the miscible displacement are reverse of pore size distribution of the media. The results of the tests are also confirmed by computer modelling. This work shows that the miscible displacement test is a tool to characterize the flow distribution of a porous medium which should be considered in EOR assessment.

Introduction

The theory of mass transport by dispersion in flow through porous media has become a basic consideration in many scientific and engineering applications. The theory is essential to several disciplines such as chemical, engineering, soil mechanics, geology, and petroleum engineering. Dispersion is of great importance to petroleum engineers, because the phenomenon is incorporated in mathematical models governing the miscible oil recovery processes. these models predict and estimate the rate of miscible injection fluids, as well as predicting the volumetric sweep efficiency of oil reservoir with respect to space and time.

Most mathematical models of miscible displacements in porous media are based on the assumed applicability of Fick's Law of molecular diffusion for describing dispersion. The molecular diffusion coefficient of Fick's Law is used to describe the spreading ofa solute as it moves through porous media, but has been relabelled the "dispersion coefficient". This coefficient tends to be the most difficult parameter to determine for miscible flooding models. It has traditionally been assumed to be linearly correlated with the mean flow velocity, with the resultant constant of proportionality termed the dispersivity (Perkins and Johnston, 1963)1. The dispersivity is believed to be a characteristic of the porous media and, according to Freeze and Cherry (1979)3, is the most elusive of the solute transport parameters.

Despite the practical importance of understanding the dispersion of miscible displacement fluids in reservoir 2oil, there are currently no methods to confidently predict the magnitude of dispersion at a given unstudied chemical oil recovery field.

This study was conducted to empirically develop a description of hydrodynamic dispersion in porous media that is independent of the questionable assumption ofapplicability of Fick's Law of molecular diffusion. In order to examine this hypotheses it was necessary to employ a method which would measure dispersion, independent of applying any existing Fickian solute transport model. Hence, the spreading of the miscible displacement breakthrough curve about one pore volume of displacement was used as the measure of dispersion.

EXPERIMENTAL APPARATUS

The experimental apparatus used for this study was designed to isolate and study dispersion phenomena in relation to flow velocity, porous media properties in one dimension. In order to isolate the dispersion phenomena, several interfering processes had to be eliminated.

This content is only available via PDF.
You can access this article if you purchase or spend a download.