Vertical Electrical Sounding for the Investigation of Clay Deposit in Orerokpe, Delta State

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1 Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) (): 665 Scholarlink Research Institute Journals, (ISSN: 76) jeteas.scholarlinkresearch.org Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) (): 665 (ISSN: 76) Vertical Electrical Sounding for the Investigation of Deposit in Orerokpe, Delta State Egbai, J. C Department of Physics, Delta State University, Abraka, Nigeria. Abstract The location of clay was investigated in Orerokpe, Okpe Local Government Area of Delta State using vertical electrical sounding (VES). The research is aimed at fining the quantity of clay deposits in orerokpe for local and industrial purposes. Applying the Schlumberger configuration, VES were carried out in ten selected locations. Data were collected and interpreted firstly by curve matching and computer iterated techniques. The curve identified for the four locations is the type ρ > ρ < ρ with the various resistivities and layer thicknesses. Spontaneous potential (SP) log and Driller s log methods were used to collect data from boreholes drilled around VES locations and the results compared with VES. The results show that the average clay thickness for Orerokpe is about.m. This shows high correlation between the VES, SP logs and driller s log results. Keywords: clay deposits, vertical electrical soundings, driller s log, spontaneous potential log, geoelectric section I TRODUCTIO is widely found and distributed in Nigeria. owever, it is not always found in sufficient quantity or suitable quality for modern industrial purposes. occurs as sedimentary clay, primary clay produced produced by chemical weathering of the parent rock or as secondary clay transported from their point of origin (Kogbe, 989). Very many clay deposits have been reported from all parts of Nigeria. In Nigeria, clay deposits are mined locally by the local inhabitants for making pottery and crude bricks. Commercial production of clay started fully in Nigeria in 96 when it was produced for use as a drilling mud in the oil industry. As a result of the usefulness of clay both at home and industries, this research becomes necessary at determining the existence and quantities of clay deposits in and around Orerokpe in Okpe Local Government Area of Delta State. Nigeria is heavily endowed with mineral resources. What is most urgently needed is to fully investigate and exploit these minerals and also identify the markets for the products. It is hoped that when these are done, not only will Nigeria s foreign exchange earnings improve but will be able to provide jobs in the mineral industries for her teeming unemployed citizens. falls within the group of solid minerals that have not been fully harnessed in Nigeria (Kogbe. 989). The electrical resistivity technique is best adapted for determining depth and resistivity of layered rock structures, sedimentary beds and acquified depth because its liability and accuracy (Okwueze and Ezeanyin, 985). 6 The electrical resistivity method is commonly used in engineering site investigation. Useful It is relevant in depth to bedrock determination, structural mapping, determination of nature of superficial deposits etc (Early and Dyer, 99; Lucius and Bisdorf, 995; Bisdorf 996). The method has been very useful in the mapping of salt water interface in many different hydrogeologic settings (Olorunfemi 985 and Zohdy et al 99). Further references on this research can be seen from the work of the following: Adepelumi et al, 8; Akpoborie et al, ; Atakpo and Akpoborie, 8; Ayolabe, 5; Oladapo et al, and Omosuyi et al, 8, Okolie et al, 8. TEORY The theoretical background of this research is taken from the work of Egbai (997). The basis of all resistivity prospecting with direct current can be written in the differential equation σ ij V = () where σ = conductivity while the subscripts i and j may be any of the X, Y, or Z directions in a rectangular coordinate system, V= scalar potential. Equation () reduces to Laplace s equation in an isotropic case where conductivity at a point in the ground is independent of direction. V = () Equation () is used to solve for the potential at the surface of the earth at a distance r from the current source. Resistivity theory and interpretation have long been biased toward an earth model of horizontal, homogeneous and isotropic layers. This is because of

2 Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) (): 665 (ISSN: 76) the high approximation to the real earth especially in ground water environment and due to natural mechanism of sedimentation. Enhrenburg and Watson (9) pursued the concept of optical analogy and developed a solution for any number of layers of fixed thickness, h. This restriction on thickness ensures that the positions of current images I, are readily predictable. The surface potential was formulated as Iρ = + Q V ( ) () r π r n= ( r + h ) where the first four terms for Q are Q = k Q = ( k) k+ kq Q = ( k) ( k) k+ ( k k k) Q + kq Q = ( k) ( k) ( k) k+ ( k k k k k) Q + ( k k k+ kk ) Q + kq The complexity increases with the number of layers. k is known as the reflection coefficient (or factor). For multiple boundaries, it is generalized to ρ i+ ρ i k = () ρ i+ + ρ i Stefanesco, et al (9) by applying separation of variables to Laplace s equation in cylindrical coordinates, arrived at a general solution for the potential at the surface of an nlayer earth having arbitrary resisitivities and thicknesses. Iρ ( ) = V r + θ n( λ) J ( λr) dλ (5) π r n= where J is the zeroorder Bessel function of the first kind and θ n, called the kernel function, is a function of the thicknesses and reflection coefficients for an assumed earth model, ρ is the resistivity of the first layer and V ( r) is the potential at the surface of the earth at a distance r from the current (I) source. For and layer models, the kernel function is given by: θ θ ( λ) ( λ) k exp = k exp = + k k ( λh) ( λh) k exp( λh) + k exp λ( h + h) exp( λh ) k exp( λh ) k exp{ λ( h + h )} By differentiating equation (5), the Schlumberger apparent resistivity over an nlayer earth becomes. ( ) = + ρ r ρ r λθ ( λ) J ( λ r) dλ (6) n n where J is the first order Bessel function of the first kind. The evaluation of the integral in equation (6) has been done in a number of ways. One of the more important approaches is to write the kernel function as a ratio of polynomials (Flathe, 955b). Ghosh (97b) introduced a novel approach to the problem of computing sounding curves for stratified models by starting with the formula of Stefanesco, et al (9). Applying equation (6) and expressing it as ρ a ( r) = r λ T( λ) J ( λ r) dλ (7) Where T( λ) = ρ { + θ n( λ) } The function T ( λ) is called the resistivity because it is defined by a ankel transformation ( λ ) = r ρ ( r) J ( r) T a λ Equation (7) is a convolution integral. It is possible to dr determine a linear digital filter ( b ), which converts resistivity transform samples into apparent resistivity values for theoretical models. ρ = b () i a T m i i The method is very accurate, fast and simple in operation and has small computer storage requirements. In addition, depths are no longer restricted to integral multiples and may take any arbitrary values. LOCATIO Orerokpe lies within latitude 5 o 6 and 5 o North and longitude 5 o and 5 o East. It is the headquarter of Okpe Local Government Area of Delta State, and has an area of about 9.7sq.km. Figure, shows the map of the study area and locations of the Vertical Electrical Sounding (VES). Warri Stud y are a Loc 9 ew Eku Warri Roa d Loc Loc 6 Loc 8 Lo c L oc Ore rokpe Tow n Loc Loc 7 Ovu Loc Old Eku Warri Road m 5m km Locations of VES F ig. : M ap of study area showing VES locations Eku Ju nction Loc 5 6

3 Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) (): 665 (ISSN: 76) EXPERIME TAL WORK The Abem Terrameter SAS B manufactured in Sweden was used for taking surface resistivity sounding as well as Spontaneous Potential (SP) logging. The Schlumberger array was used for data acquisition because of deeper penetration and is very good in providing information about variation in formations with depth. By increasing the separation of the current electrodes, the depth penetrated by the current lines increases. For full current penetration to be achieved to a depth Z, the total current electrodes spread, L= Z ( Z = L ). A total of vertical electrical soundings were carried out in different locations at Orerokpe. The total current electrode spread is about m in the area. The spontaneous potential, (SP) logging method was utilized for logging nearby boreholes within the areas of survey. Driller s log was equally used to ascertain the quantity of clay within the area of survey. Fig. : Orerokpe Location Field Measurement By Egbai, J. C., Field Data Interpretation By Egbai, J. C., DATA ACQUISITIO A D A ALYSIS The apparent resistivity values obtained from the geoelectric survey were plotted on a loglog graph against corresponding current electrode separation. The VES were quantitatively interpreted by partial curve matching to obtain the true resistivity and thickness of the subsurface layers. The result of the curve matching were used for computer iteration using the Resist Software (Vander Velpeb, 988). The results of the vertical electrical sounding were presented as geoelectric section as shown in table Fig. : Orerokpe Location Field measurement by Egbai, J. C., Field data interpretation by Egbai, J. C., Fig. : Orerokpe Location Field measurement by Egbai, J. C., Field data interpretation by Egbai, J. C., 6 Fig. 5: Orerokpe Location Field measurement by Egbai, J. C., Field data interpretation by Egbai, J. C.,

4 Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) (): 665 (ISSN: 76) Table. Geoelectric section of the surveyed locations VES Geoelectric LAYERS Resistivity (Ωm) Thickness (m) Depth (m) Lithology Curve type.8 Latarite. ρ > ρ < ρ Fine sand Shale sand White sharp sand White sharp sand Coarse sand Gravel Surface soil Fine sand Gravel Fine sand Coarse sand Gravel Surface soil ey sand Coarse sand ey sand Medium sand Surface soil Fine sand ρ > ρ < ρ ρ > ρ < ρ ρ > ρ < ρ KA ρ < ρ > ρ < ρ Q ρ > ρ < ρ > ρ KA ρ < ρ > ρ < ρ KA ρ < ρ > ρ < ρ A ρ > ρ < ρ < ρ A ρ < ρ < ρ RESULTS A D DISCUSSIO The observed sounding curves for the ten locations show that of type (ρ > ρ < ρ ), KA type (ρ < ρ > ρ < ρ ), Q type (ρ > ρ < ρ > ρ ), A type (ρ > ρ < ρ < ρ ) and A type (ρ < ρ < ρ ) and some of the curves are as shown in figures 6 Locations,, and are of type with the first layer resistivity ranging from 5.6Ωm to a maximum of 7.Ωm with thickness varying from.8m to.7m. This layer is of the surface soil and lateritic in nature while the second layer is of a lower resistivity ranging from 7.6Ωm to 56.Ωm with thickness varying from 5.m to 8.8m. The lithology is made of clay. Locations 5, 7 and 8 are of KA type curve with first layer resistivity varying from 5.6Ωm to.ωm 6 while the thickness varies from.8m to.m with lithology made of surface soil and laterite. Location 5 has high resistivity of 9. Ωm with thickness of.m at the second layer. This layer is made of coarse sand. Location 7 has resistivity of 86.8 Ωm with thickness of 9.m at the second layer. It is made of fine sand. Location 8 has lower resistivity of 5.Ωm at the second layer with layer thickness of 7.5m. This is made of clayed sand. Locations 5 and 8 have very low resistivities of.ωm and 8.9Ωm at the third layer with thickness of.m and.6m respectively. Location 7 has high resistivity of 6.5Ωm made of coarse sand at the third layer with thickness of.5m. This location is free of clay with fourth layer made of gravel. Location 6 is of the Q type curve, it has resistivity of 99.Ωm with layer thickness of.m. This layer is made of surface soil. The second layer is made of clay with resistivity of

5 Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) (): 665 (ISSN: 76).Ωm and thickness of.m while the third layer has very high resistivity of 887.Ωm and thickness 8.8m made of fine sand. The fourth layer is made of gravel with resistivity of 85.Ωm. Location 9 is of the A type curve. The resistivity of the first layer is.ωm with.9m thickness made of laterite. The second layer is of a very low resistivity of 6.8Ωm and thickness.m is made of clay while the third layer is of resistivity 68.Ωm and thickness.m made of clayey sand. The fourth layer has resistivity of 58.Ωm made of medium sand. Location is of the A type curve. The resistivity of the first layer is.ω with thickness of.7m and made of surface soil. The second layer has resistivity of.ωm made of clay of thickness.m while the third layer has resistivity of 96.9Ωm made of fine sand. The spontaneous potential log of some locations shows a negative value for clay. Low negative potential is indicative of the presence of shale or clay. The driller s log as well as the spontaneous potential (SP) logs of the various locations is indicative of the presence of clay in large quantities in Oreropke and its environs. These are shown in figure 6. There exist high correlation between the vertical electrical sounding (VES) survey, the SP log and the driller s log. CO CLUSIO The three methods (VES, SP log and driller s log) employed for the investigation of clay in Oreropke were very efficient and reliable. The results are very well correlated. Location 5 and 9 have very low thickness of clay of.m and.m respectively while Depth (m) 8mV 5mV Depth (m) 8mV 5mV Driller s log and SP log for Loc. 8 Driller s log and SP log for Loc. Depth (m) 8mV 5mV Depth (m) 8mV 5mV 7 7 White Sharp Sand Shale Driller s log and SP log for Loc. Driller s log and SP log for Loc. Coarse Sand mixed with Fig. 6: Driller s log and SP log for some locations (Egbai, ) 6

6 Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) (): 665 (ISSN: 76) location 7 has no clay reserve. Apart from these three locations, other seven locations have very high thickness of clay with location having the highest quantity of clay reserve of about.m thick. Considering the result of these seven locations, one can say with certainty that Oreropke has a large quantity of clay for both domestic and industrial purposes. REFERE CES Adepelymi, A. A., Ako B. D., Ajayi, T.R., Afolabi, O. and Omotoso, E.J. (8). Delineation of saltwater intrusion into the freshwater aquifer of Lekki Peninsula, Lagos, Nigeria. Environ Geol, SpringerVerleg, DOI.7/s589. Akpoborie, I.A., Ekakitie O.A, and EtuEfeotor, J.O. (987) The Occurrence and Economic Potential of Clean Sand Deposits of the Niger Delta Journal of African Earth Sciences, 6 (), pp Atakpo, E.A. and Akpoborie, A.I (8). Geoelectric mapping of Amukpe area of Delta State, Nigeria. Nigeria Journal of science and Environment. 7, pp 78 Ayolabi, E.A and (5) Geoelectric Evaluation of Groundwater Potential: A case Study of Alagba Primary School, Akure Southwest Nigeria. Journal Geological Society of India. 66: 995. Bisdorf, R.J. 996, Schlumberger soundings at the Norman landfill, Norman, Oklahoma, U.S. Geological Survey openfile report pp Early, K. R. and Dyer, K. R, 99, The use of resistivity survey in foundation site underlain by karst dolomite. Geotechnique, No., pp 8. Egbai, J.C. 997, Correlation between resistivity survey and well logging in Delta State. Phd. Thesis submitted to Edo State University, Ekpoma p. 9 Ehrenburg, D. O. and Watson, R. T. (9): Mathematical theory of electrical flow in stratified media with horizontal, homogeneous and isotropic layers. Trans American Institute of Mining Engineering and Geophysical Prospecting, Vol. 97, pp.. Kogbe, C. A. (989): Statistics of mineral production in Nigeria (968 to 986) and the contribution of the mineral industry to the Nigerian economy. Geology of Nigeria edited by C. A. Kogbe. Rock view Nig. Ltd Jos. Pp8557. Lucius, J. E and Bisdorf R. J., 995. Sult of geophysical investigations near the Norman, Oklahoma, municipal land fill, 995: U. S Geological Survey open file report 95 85, l5pp Okolie, E.C., Egbai J.C. and Oseji, J.O (8). Comparative investigation strata and groundwater distributions in Orerokpe and Ovu, Delta State using Schlumberger Array. Nig. J. of Sc and Environ. Vol. 7 pp Okwueze, E.E and Ezeanyin, M.V.I (985) Vertical electrical sounding (VES) method in laterite regions and in Ironrich glaciated areas. Nigeria journal of Mining and Geology. (Nos.&): 998. Oladapo, M.I, Mohammed, M.Z, Adeoye, O.O and Adetola, B.A. (). Geoelectical investigatiom of the Ondo State ousing Corporation Estate, Ijapo Akure, Southwestern. Nigeria. Journal of mining and geology (I), pp 8. Omosuyi, G.O., Ojo, J.S., and Olorunfemi, M.O.(8). Geoelectric Sounding to Delineate Shallow Aquifers in the Coastal Plan Sands of Okitipupa Area, Southwestern Nigeria. The Pacific Journal of Science and Technology, 9(),pp Stefanesco, S., Schlumberger, C. and Schlumberger, M., (9): Sur la distribution electrigue potentialle author d une prise de terre pontuells dans un terrain a couches horizontals, homogene et isotropes J. de physique et le Radium, Series 7, Vol. pp.. Vander Velpen, B.P.A, 988, Resist Version. M.Sc. Research Project ITC,Deft, Netherlands. Zohdy, A.A.R., P. Martin, and R.J. Bisdorf, 99. A Study of Seawater Intrusion using DirectCurrent Soundings in the Southeastern part of the Oxnard plain, California. U.S. Geological Survey open file report. 95, pp. Flathe,. (955): A practical method of calculating geoelectric model graphs for horizontally stratified media. Geophical Prospecting Vol., pp Ghosh, D. P. (97b): Inverse filter coefficients for the computation apparent restivity standard curves for a horizontally stratified earth. Geophysical Prospecting, Vol. 9, No., pp