Eb. Dussan et Fm. Auzerais, BUOYANCY-INDUCED FLOW IN POROUS-MEDIA GENERATED NEAR A DRILLED OIL-WELL .1. THE ACCUMULATION OF FILTRATE AT A HORIZONTAL IMPERMEABLE BOUNDARY, Journal of Fluid Mechanics, 254, 1993, pp. 283-311
A substantial amount of drilling fluid can invade a permeable bed duri
ng the drilling of an oil well. The presence of this fluid, often refe
rred to as filtrate, can greatly influence the performance of instrume
nts lowered into the wellbore for the purpose of locating these permea
ble beds. The invaded filtrate can also substantially alter the physic
al properties of the porous rock. For these reasons, it is of great in
terest to known where the filtrate goes upon entering the bed. The obj
ective of this study is to quantify the influence of the difference in
density between the filtrate and the naturally occurring formation fl
uid on the shape of the filtrate front as the filtrate invades the for
mation. This type of phenomenon is often referred to as buoyancy or gr
avity segregation. In this study, Part 1, we determine the behaviour o
f the filtrate as it accumulates (and spreads out) at a horizontal imp
ermeable barrier within the formation. This is a combined theoretical
and experimental study in which an X-ray CT scanner is extensively use
d to determine the appropriateness and limitations of the simplifying
assumptions used in the theory. In Part 2, the flow of the invading fi
ltrate within the entire bed will be presented. The problem addressed
in Part 1 may be viewed from the broader, more fundamental, perspectiv
e, as a well-defined model fluid mechanics problem for flow in porous
media. One fundamental issue infrequently addressed concerns the conse
quence on the dynamics of the fluids of heterogeneities, always presen
t to some degree, in consolidated porous solids. The X-ray CT scanner
enables the assessment of the appropriateness of modelling such porous
solids as spatially homogeneous, a very popular assumption. This stud
y also addresses the limitation of the small-slope approximation when
a fluid-fluid interface occurs in a porous solid, an approximation whi
ch has enjoyed great success in free-surface fluid mechanics problems
when no porous media is present.