An Experin1ental Procedure For Following Flood Fronts Visually And Calculating In-Situ Saturation In Opaque Porous Media
Authors: Bennion D.P.W. , Durrani G.H. 
Published: March 2010

In most laboratory experiments in which one fluid is displacing another within porous material it is desirable to be able to calculate the fluid saturations and visually follow the flood front. The object of this study was to determine if X-ray absorption methods could be employed to accomplish this. Unconsolidated and consolidated five-spot models were used. The movement of the flood front was recorded from an image intensifier onto video from by a TV camera. Saturations were obtained by relating light intensity from the video signal to fluid saturation.

Areal sweep efficiencies were determined from photographs at break through and from the zero saturation front of the displacing fluid. These were obtained for mobility ratios of 1.04 to 32. A maximum difference of 2 per cent between the two procedures was obtained. Sweep efficiencies were also compared to those reported in the literature; this showed that at mobility ratios greater than one the sweep efficiency was affected by model size and rock properties.

Introduction

THE OBJECT of this research was to develop a technique for visually following the interface between two fluids in an opaque porous material and also to be able to measure in-situ concentrations of each fluid. The method employed X-rays to penetrate the porous media, and a television-equipped image intensifier to pick up the X-rays which were not absorbed and to display visually the movement of the interface. For the procedure to be effective, one of the two fluids should be a weak absorber of X-rays and the other a strong absorber. The intensity of the unabsorbed X-rays was then used to obtain in-situ fluid concentrations. X-rays have been used by a number of investigators to obtain fluid saturations(1–7). They have also been used to obtain shadowgraphs, which were employed to obtain areal sweep efficiencies (6).

Since the period in which the above work was reported, improvements, which increase the uniformity, of the X-ray output and the sharpness of the image, have been made. Equipment has been developed to record dynamic experiments and to analyze the intensity of the penetrating X-rays. With these developments and improvements, it was felt that X-rays could be used to give both quantitative and qualitative results. This report describes the equipment used and the technique employed, compares the results obtained with published data and suggests ways ill which the method can be employed.

Theory

X-rays are a form of electromagnetic radiation having wave lengths in the approximate range of 10−10 to 10−1 cm. They are produced by bombarding a metal target with a stream of high-energy electrons. These rays are capable of penetrating materials which are opaque to light, yet they have photographic properties similar to those of light. Their penetration ability depends on their wave length; the smaller the wave length, the greater the penetrating power. They penetrate low-density material easier than high-density material.

Planck quantum theory proposed that electromagnetic radiation is emitted in small packets called quanta. Frequently, the term photon rather than quantum is used when dealing with X-rays.