
Citation
Rampnouxi, N., Broquet, P. and J. Maniai (1993). Hydraulic
characterization of a fissured calcareous formation in FrancheComté (France). Rev.
Sci. Eau, 6 (1) : 322. [article in french]
Original title : Caractérisation hydraulique d'un massif calcaire
fissuré de FrancheComté (France).
Full
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Abstracts
An experimental site in fissured calcareous media has been
analysed in the upper jurassic of the Loue valley. A tore of some 30 metres
has been drilled and analysed by different laboratory techniques (porosity,
permeahility, ultrasonic speed, quantification ol the fissuration) and in the
field (hydraulic injection tests between shutters, sonic and density diagraphics
data). The rock volumes have been explored at the surface by the refraction
sesmic method.
ln the tore the fissures are distributed according to four families :
 subvertical stylolitic fractures, the horizontal pealo; of which denote the
maximum compressive direction of the original tectonic stresses,
 mineralized crevices with calcitic filling, closed fissures,
 opened fractures which induced the hydraulical quality of limestones.
The total porosity of the limestones is characterized by homogeneous values
(front 2 to 6 %) and three differents familles of porosity o and the average
diameter d_{m} (0.00310 0.27µm) of the accessible apertures
in the matrix :
 family 1 : 0.003 µm < d_{m} < 0.018 µm, 1.05 % < ø < 2.14
% in relation with intergranular spacing in the cementic phase. The clay in
the basal part of the tore indures a great reduction of this kind of porosity,
 family 2 : 0.044 µm < d_{m} < 0.11 µm, 0.49 % < ø <4.39
% in liaison with intergranular spacing between the carbonatic figurative elements
(biociasts, Iithoclasts, oolithes and microorganisms),
 family 3 : 0.14 µm < d_{m} < 0.27 µm, 0.28 % < ø < 3.13
% in relation with the increasing of the sizes of the figurative elements.
A good agreement between permeability k and porosity ø is observed (k=3.4
10^{5}  ø^{496} in darcy nuits).
Three diagraphic
investigations has been carried out with gammagamma measurements (bulk density),
with gammaray
measurements (clay
content) and with acoustic compensated measurements (sonic waves speed). The
bulk density log is uniform (2.5 to 2.7 g/cm^{3}), the gammaray log is increasing
down the hole (21 to 29 m) whereas the clay content rises.
The acoustic log records the total wave signal chat can be traduced by two
computed logs :
 speed propagation of the S waves (Vs speed) and P waves (Vp speed) with ihe
ratio Vp/Vs,
 Poisson coefficients and Young modulus.
The principal results suggest the existence of a liaison between hydraulic
parameters and the fissuration of the calcareous formation where three levels
of fracturation are observed (from 11 to 12 m, from 16 to 18 m and from 19
to 20m).
The permeability values of the limestone matrix cores ara relatively homogeneous
(1 to 19 10^{5} darcy) with a decrease in the 23 to 27 m section of
the borehole where a clayed cernent is detected. The hydraulic conductivity
of the fractured
zone, as determined by means of hydraulic injection tests between shutters
leads to values of 1.10^{6} to 8.10^{6} m/s (# 0.1 to
0.8 darcy). Five zones have been choses for the hydraulic tests in liaison
with
different parts
of the
bore hole. The high values ot permeability k are in accordance with the
high le index values of the open fractured zones.
A tirst local calibration function is proposed :
lc=7.13 Log k + 51
A pour relation connects the laboratory and field results because the elementary
volume is increasing from cubic centimeters to some cubic matera. The homogeneity
and the isotropy of matrix is disturbed hy the fissures (shut or open).
The matrix medium is continuous on the laboratory scate and discontinuous
in the field. The ultrasonic investigation confirms the liaison between
the high
values of the sonic P waves speed and the principal regional direction ot
tectonical stress. The total acoustic recording yields the knowledge of the
S and P waves
speeds of in correlation with subvertical fractures when the speed value
variations are numerus.
Three fracture zones are distinguished between 11 to 12 m, 17 to 18 m and
19 to 20 m. The lc index obtained from the sonic log must be used cautiously
aller correction in the true clayed zones. In these zones the values of the
le index
are above 10 without waler flowing in the bore hale alter hydraulic testing.
We propose the use of a corrective chart C (lc) to correct for the clay
effect and a new corrected index lc  C (lc) is more reliable.
An adjusted statistical graphical chart is proposed with the following expression
: C (lc) = ß • X with
= 1.84
and ß = 0.088 (valid only for limestones) and X : lite clay index
obtained from the gammaray measurements. The le
index
values histogram localizes the permeable zones of limestones with
hydreulically active open fractures.
Measurement of the speed variation of P sesmic waves on the bottom of the
quarry by the means of the refraction method leads to a good agreement between
the
maximum speed anisotropy direction and the major fracture direction (N 120°N
140°) which is perpendicular to the minimum anisotropy sesmic speed direction
(N 40° N 50°). The open fractures direction measured on the core
is adjoining about N 135°N 145° when the direction of maximum anisotropy
in the quarry is near N 140°.
Keywords
Limestone, fissure, refraction sesmic, gammara y, sonic, permeability,
porosity, le index.
Corresponding author
Rampnouxi, N., Université de FrancheComté, Laboratoire de
Géologie Structurale et Appliquée, Place Leclerc, 25000 Besançon,
France
 