Geoscience Reference
In-Depth Information
DELINEATION OF WATER BEARING FRACTURES IN
BORE WELLS BY EC LOGS
V. K. SAXENA
∗
,N.C.MONDALandV.S.SINGH
National Geophysical Research Institute, Hyderabad 500 007, India
∗
vks 9020010@yahoo.co.in
The mostly geological and geophysical techniques are in practice for the delin-
eation of water bearing fractures in the hard rock areas. The attempt has been
made to develop some technique, which may be simple, more informative and
also cost effective as well as give groundwater quality information. Electrical
conductivity measurements were conducted in a large number of shallow bore
wells (experimental) in hard rock areas. Electrical conductivity logs were car-
ried out in three different locations of India: (1) Maheswaram: nine shallow bore
wells in a granitic aquifers (2) Wailpally: four shallow bore wells in a granitic
aquifers and (3) Sadras: four shallow bore wells in a charnokite aquifers. The
observations were made at short interval of about 1 m from water table (narrow
spacing wherever required) till the bottom of the bore wells. It is observed that
EC have shown remarkable changes, which suggests the probability of water
bearing fractures in the bore wells. In addition, the results of EC logs were
compared with the results of various known geological and geophysical tech-
niques. The results of EC logs are in good agreement with the results obtained
by litholog profiles, inflow measurements,
λ
-logs, resistivity logs etc. Thus EC
log technique is considered to be a new technique for the delineation of water
bearing fractures in hard rock areas.
1. Introduction
In the study of the hydrology of fractured rocks, knowledge of the fracture
properties is essential. Surface observations may be useful, but the more
relevant observations are those made at the depths of interest. Lee devel-
oped a technique, for locating the contaminated groundwater discharge by
mapping, variations in EC of bottom sediment and used in shallow surface
water in an artificially created seepage area of a small shallow lake.
1
,
2
EC
of water usually uses to get broad picture of TDS of water.
3
,
4
EC is also
use to test the suitability of water for different purposes such as drink-
ing, irrigation and various types of industrial applications etc. Most such
measurements are made through boreholes or underground openings. In
the case of borehole, various methods of determining fracture properties
have been used.
5
-
7
For example, a down hole televiewer can be used to
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