Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) 3 (2): 326-329
© Scholarlink Research Institute Journals, 2012 (ISSN: 2141-7016)
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Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) 3(2):326-329 (ISSN: 2141-7016)
Geophysical Study of Sandstone Properties
At Ozalla Area of Edo State, Nigeria
Ezomo F.O
Department of Physics, Faculty of Physical Sciences,
University of Benin, P.M.B. 1154,
Ugbowo, Benin City, Nigeria
Corresponding Author: Ezomo F.O
___________________________________________________________________________
Abstract
The occurrence of sandstone deposit in Ozalla village area of Edo state, Nigeria was detected geophysically by
using vertical electrical sounding (VES) techniques of electrical resistivity method. The urgent need to prospect
for sandstone deposit in the area became imperative in order to arrest youth restiveness in the area by way of
setting up chemical industry that rely on sandstone as raw material for its manufacture purposes. The
prospected sandstone properties include its thickness depth below sea level and types of rock above it. Twelve
(12) fairly distributed VES in three (3) different regions, employing six (6) points per decade were carried out
by using the commercially available terrameter equipment to justify the operation of collecting, apparent
resistivity data. The resulting apparent resistivity data was interpreted by using the IP12WIN software utilizing
computer iteration. The result of the geophysical survey showed that sandstone deposits were intercepted at
depths varying from about 0.45m to 82.00m while the thicknesses varied from about 0.40m to 45.00m. The
resistivity of the sandstone deposit varied from about 200.00hm – m to 21000.0 ohm – m. Area of probable
sandstone deposits have been identified for future mining, of industries, foundation, operation and drilling.
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Keywords: sandstone deposit, Ozalla, Edo State, geophysically, urgent, imperative, youth restiveness
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INTRODUCTION
pores. But as the sand turns into rock, the cement can
Geophysical exploration is usually conducted to
fill in these pores making the sandstone, less porous
detect and locate significant accumulation of
and less able to allow water to move through the rock
sandstone deposit, limestone deposit, clay deposit,
(Ezomo and Ifedili, 2007). In fact sandstone is a very
oil, natural gas and other minerals including ground
porous rock as rocks go and is the ideal rock for
water which are very valuable in the world economy
groundwater. Hence sandstone will house substantial
(Ezomo and Ifedili 2004). The use of sandstone in
aquifer and is also the best oil reservoir because
chemical industry for
flooring, wall covering,
petroleum is a fluid that primarily flows through
making fireplaces and exterior cladding in sea-shore
sandstone (Ezomo and Ifedili, 2007). It has a high
buildings had greatly aided many developed and
mechanical strength and is resistant to air, saline
developing nations of the world e.g. Nigeria, China,
water, acids, alkalies, corrosion and weathering
Spain, Brazil, U.S.A e.t.c (Ezomo, and Ifedili, 2006).
(internet information 2011).
Sandstone in the form of brickstone can be used for
building uses, like the Khmer temple in Cambodia.
Geologically, Ozalla is underlained by sedimentary
(Internet information, 2011). Sandstone is a very
rocks which are of ages between paleocene to recent
common sedimentary rock and perhaps the best
which is in concordance with the Bande Ameki
known sedimentary rock usually composed of sand. It
formation of the area consisting of the lithologies
is formed in many environments. Just about
clay, shales, sandstones, limestones, sands (Reyman
anywhere there is water, whether frozen or not, in a
1965).
river or ocean, there is a probability to form
sandstone. Even where there is no water as in a
This research paper tends to estimate the thickness of
desert, there is sandstone formation under foot
sandstone deposit and its depth below sea level in
(internet information 2011).
Ozalla village area of Edo state using geophysical
method with the intention of providing detailed
Sandstone is formed by the cementation of sand
documentation of known sandstone deposit and
grains such that any deposit of sand can lithify to
recommend possible set up of an industry/factory in
sandstone. The cementing agents also affect the
the area that rely on sandstone for manufacture
porosity of sandstone. When the initial sandstone is
purposes. Ozalla is at a distance of about 75km from
first deposited, there are lots of open spaces or pores.
Benin City main town and lies approximately
Water, for instance, flows through sand due to all the
between longitude 50 45’E and 60 05’E and also
326
Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) 3(2):326-329 (ISSN: 2141-7016)
between latitude 60 45’ N and 70 00’N (information
centre, 2008).
EXPERIMENTAL WORK
The experimental work behind the discussed
theoretical analysis have been documented in the
author’s previous research work (Ezomo and
Ifedili,2004 – 2007) Twelve (12) vertical electrical
sounding (VES) fairly distributed using the signal
averaging system (SAS) 300 terrameter and its 2000
booster for deeper penetration were conducted. The
operational efficiency of the SAS equipment have
been documented in previous research work of the
author (Ezomo, Ifedili, and Akujieze 2004 – 2011)
THEORETICAL ANALYSIS
There are different types of electrical resistivity
theoretical approaches based on electrodes array for
interpreting resistivity data. The techniques of data
interpretation used involved seeking a solution to the
inverse problem namely the determination of
subsurface apparent resistivity distribution from
surface measurements. (Ezomo and Ifedili 2004 –
2007). There is a function called Kernel function that
represents a very good solution to the inverse
problem. It describes the apparent resistivity
measurement in terms of subsurface lithological
variation with depths. The function assumes the earth
to be locally horizontally stratified, inhomogeneous
and isotropic layers, and unlike apparent resistivity
function, it does not depend on electrode
configuration. It cannot be measured in the field but
has to be obtained from the transformation of
measured apparent resistivities. The Kernel function
utilized in this work have been documented in
previous research work (Ezomo and Akujieze 2011)
such that:
Where
T(λ)
the
kernel
function
is
given
RESULTS AND DISCUSSION
The graph of apparent resistivity ( ) was then
plotted against Schlumberger semi current electrode
separation (AB/2).
This curved produced the
computer iterated sounding curves shown in typical
figures 1-3 by using IP12WIN software for
interpretation and its associated lithologies shown in
typical table 1-3. The lithologies or rock types of the
different layers were confirmed by using nearby
borehole / driller’s log of the area (Ozalla borehole
log, 2000). For the purpose of generating the earth’s
model or various lithologies, borehole driller’s log of
the area is usually integrated with standard table of
electrical resistivities (Okwueze and Akpotu, 1979)
because it is possible for different rock types to have
the same range of resistivities which usually make
electrical resistivities data ambiguous to interpret.
By integrating the resistivity results with the bore
hole/driller’s log, resistivity interpretation for typical
VES stations 1-3 lithologies, shown in typical tables
1-3 were obtained.
as
J1 represents Bessel function of first order, first kind
and T (λ) is the transformed resistivity data.
However, when the earth is approximately composed
of horizontally stratified isotropic and homogeneous
media such that the change of resistivity is a function
of depth, the Schlumberger array is the most widely
used array and may provide useful information in
solving subsurface geophysical problems. A vital
aspect of the Schlumberger is the less sensitivity of
the array to the effect of near surface lateral
heterogeneities and easy recognition of their effects
(Ezomo and Ifedili 2004 – 2007).
It is pertinent to state categorically that sandstones
exist in all the typical station of the area. In typical
VES station one (1), sandstones occurred at depth of
about 82.26m below sea level with a thickness of
about 45.00m. In typical VES station two (2),
sandstones occurred at a depth of about 35.47um
below sea level, with a thickness of about 8.50m;
Sandstone is also present in typical VES station three
(3) with a depth of about 10.20m below sea level and
of thickness 4.95m.
In electrical resistivity prospecting, four electrodes
are usually earthed along a straight line in the order
AMNB, where A and B are the current electrodes, M
and N, the potential electrodes. The calculated
A close examination of all the VES stations revealed
that sandstone deposit in typical VES station one (1)
is the thickest. Sandstone can therefore be explored
and exploited in this region commercially which will
then boost the economy of Edo state in particular and
Nigeria in general.
apparent resistivity ( a) according to Schlumberger
array condition of AB ≥ 5MN is
AB = Current electrodes spacing in metres
MN = Potential electrodes spacing in meters
V = Potential difference in Volts
I = Electric current in Amperes,
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Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) 3(2):326-329 (ISSN: 2141-7016)
Typical Table 1: Inferred Lithology for Typical VES Station 1
Layer
1
2
3
4
Resistivity
(ohm-m)
92.00
1450.00
222.69
10550.00
Thickness (m)
Cum. Thick.(m)
0.45
26.52
8.50
Infinity
0.45
26.97
35.47
Infinity
Inferred lithology
Clays
Shales
Sandstones
Sandstones
Typical Figure 1; iterated sounding curve for VES Station 1
Typical Table 2: Inferred Lithology For Typical VES Station 2
Layer
Resistivity
(ohm-m)
Thickness (m)
Cum. Thick.(m)
Inferred lithology
1
92.00
0.45
0.45
Clays
2
1450.00
26.52
26.97
Shales
3
222.69
8.50
35.47
Sandstones
4
10550.00
Infinity
Infinity
Sandstones
Typical Figure 2; iterated sounding curve for
VES Station 2
AB/2 (meters)
Typical Table 3: Inferred Lithology for Typical VES Station 3
Layer
1
2
3
4
5
Resistivity (ohm.m)
100.00
2919.45
500.67
32.31
3403.44
Thickness (m)
1.45
3.80
4.95
12.65
Infinity
Typical Figure 3; iterated sounding curve for VES Station 3
328
Cum. Thickness (m)
1.45
5.25
10.20
22.85
Infinity
Inferred Lithology
Clays
Sandstones
Sandstones
Sands
Limestones
Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) 3(2):326-329 (ISSN: 2141-7016)
CONCLUSION
From the geophysical survey results, sandstone
deposit were intercepted in all VES stations, at depths
below sea level varying from about 0.45m to 82.00m
with thicknesses varying from about 0.40m to
45.00m. The resistivities of the sandstone deposit
varied from about 200.0 ohm-m to 21000.0 ohm-m.
Since sandstones deposit occurred in all the typical
VES stations with the thickest deposit occurring in
typical VES station one (1), Ozalla Village is
therefore rich in sandstone deposit and hence
industry/ factory that uses sandstone as its major raw
material can be cited in the area to create job
opportunity for the citizen of the area and thereby
drastically reducing or curbing youth restiveness in
the area. This will however go a long way in
improving the economy of Edo state in particular and
Nigeria in general. Geophysical exploration methods
utilizing vertical electrical sounding (VES) has
proved useful and successful in studying the
properties of sandstone deposit in Ozalla Village
Area of Edo State, Nigeria.
Ezomo, F.O (2010): Geophysical survey as a useful
instrument for determining subsurface lithology in
Igara, Edo state, Nigeria. Journ. of the Nig. Asssoci.
of Math phy. 17(1), 403-408.
Ezomo, F.O (2010) ‘Schlumberger array as a useful
tool for determining aquifers in Agbor Area of Delta
State. World Journ of Bio- Tech. 11(1), 1662-1667.
Ozalla bore-hole driller’s log (2000): Ozalla borehole/ driller’s log. Courtesy of geo. Nigeria limited in
Ozalla, Edo State, Nigeria.
Okwueze, E.E and AKPOTU, N. (1979): Standard
table for approximate ranges of electrical resistivity
of rocks and soil, Calabar, Nigeria.
APPENDIX
Friday
O.
Ezomo
graduated
with
B.Sc
(Hons.)
in
Applied
Physics from University
of Benin, Benin City,
Nigeria in 1989. M.Sc and
Ph.D
(exploration
geophysics) from the same
University in 1992 and
2003 respectively under
the watchful eyes of
Professor S.O. Ifedili of
the blessed memory. He is
presently a Senior Lecturer in the Department of
Physics in the same University. He has about 40
research papers in various local, national, and
international journals. His research areas include
prospecting for aquifer and allied minerals in various
regions/areas.
REFERENCES
Ezomo, F.O and Ifedili, S.O (2004): Ground water
exploration in Ekpoma and its environs. by electrical
resistivity method. Published Ph.D thesis, physics
Dept, university of Benin, Benin City, Nigeria.
Ezomo, F.O And Ifedili, S.O (2006): Schlumberger
array of vertical electrical sounding (VES) as a useful
tool for determining water bearing formation in
Iruekpen, Edo state, Nigeria. African Journ. Of Sci,
9(1), 2195-2203
Information
from
internet,
geology.com/rock/sandstones
(2011):
www.
Ezomo, F.O and Ifedili, S.O (2007): VES as a useful
instrument for investigating aquifers existence in
EGUARE-EGORO, Edo state. Journ. of the Nig
association of math. Phy 11(1), 597 - 604
Reymen, M.A (1965): Aspect of the geology of
Nigeria, Ibadan University Press, Ibadan, Nigeria.
Information centre, (2006): Palm House, Sapele road,
Benin City, Nigeria – introducing Ozalla Village.
Ezomo, F.O and Akujieze, C.N (2009): Geophysical
determination of buried structural features at
Ovbiogie Village, Edo State, Nigeria. Journ of the
Nig. Association of math phy. 14(1), 177-180
Ezomo, F.O and Akujieze, C.N (2010): Geophysical
investigation of ground water in Agbor area of Delta
state, Nigeria. Journ of the Nig. Associ. Of math
physics, 16(1), 597-602.
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