BOREHOLE YIELD ESTIMATION FROM ELECTRICAL RESISTIVITY MEASUREMENTS – A CASE STUDY OF GARU TEMPANE AND BAWKU WEST DISTRICTS, UPPER EAST REGION, GHANA By Albert Acheampong (BSc. Geological Engineering) A thesis submitted to the Department of Geological Engineering, Kwame Nkrumah University of Science and Technology in partial fulfilment of requirements for the award of the degree of MASTER OF SCIENCE IN GEOPHYSICAL ENGINEERING MAY 2017 CERTIFICATION I hereby declare that this submission is my own work and that, to the best of my knowledge and belief, it contains no material previously published or written by another person nor material which to a substantial extent has been accepted for the award of any other degree or diploma at Kwame Nkrumah University of Science and Technology, Kumasi or any other educational institution, except where due acknowledgement is made in the thesis. Albert Acheampong (PG2334714) ……………….. ……............. Name of Student and ID Signature Date Certified by: Dr. F. Owusu-Nimo ..................................... ........................ Name of Supervisor Signature Date Certified by: Prof. S. K. Y. Gawu ................................ ........................ Name of Head of Department Signature Date ii ABSTRACT Electrical resistivity survey has proven to be an effective tool for groundwater exploration and has been widely embraced to help reduce the drilling of unsuccessful wells. Currently, information from electrical resistivity survey is often used in locating points for drilling, but it does not give indication of the yield of the borehole. The lack of this information therefore sometimes results in the drilling of dry and marginal wells. This study therefore looks at the possibility of using resistivity data, which is readily available from electrical resistivity surveys for groundwater exploration, for estimating the yield of yet to be drilled borehole. The study was limited to the Garu Tempane and Bawku West districts. Secondary data on vertical electrical sounding (VES) and drill logs for 49 boreholes in the selected districts were used. The thicknesses, apparent resistivities, longitudinal conductance and transverse resistance of the various subsurface layers of the boreholes were determined from drill logs and VES data. Correlations between borehole yields and the third layer apparent resistivity, longitudinal conductance and transverse resistance were then investigated to develop regression models for estimation of the borehole yields. The results showed that the third layer is fractured and contributes significantly to borehole yields in the area; hence the fractured subsurface layer is of primary interest to be considered in groundwater exploration and estimating potential borehole yield from VES data. The results obtained further indicated that apparent resistivity, longitudinal conductance and transverse resistance had good exponential and positive linear relationships with borehole yield. iii TABLE OF CONTENTS CERTIFICATION ......................................................................................................II ABSTRACT ............................................................................................................... III TABLE OF CONTENTS .......................................................................................... IV LIST OF FIGURES .................................................................................................. VI LIST OF TABLES ................................................................................................. VIII LIST OF ABBREVIATIONS AND ACRONYMS ................................................ IX ACKNOWLEDGEMENTS ........................................................................................ X CHAPTER 1: INTRODUCTION ............................................................................... 1 Background ................................................................................................................ 1 1.2 Research Objective......................................................................................... 2 1.3 Scope of the thesis .......................................................................................... 2 CHAPTER 2: LITERATURE REVIEW ................................................................... 4 2.1 Groundwater Storage, Yield and Flow in Basement Complex rocks ............ 4 2.2 Electrical Resistivity Survey .......................................................................... 5 2.2.1 Electrode Configurations ......................................................................... 7 2.2.2 Vertical Electrical Sounding (VES) ....................................................... 10 2.3 Electrical Resistivity and Groundwater Yield.............................................. 11 2.4 Study Area Description ................................................................................ 13 2.4.1 Location and Size ................................................................................... 13 2.4.2 Topography, Drainage and Vegetation .................................................. 13 2.4.3 Geology and Soil .................................................................................... 14 2.4.4 Groundwater Availability and Potential................................................. 15 CHAPTER 3: MATERIALS AND METHODS ..................................................... 17 3.1 Study Area .................................................................................................... 17 3.2 Data Collection............................................................................................. 17 3.3 Vertical Electrical Sounding ........................................................................ 18 3.4 Borehole Drill logs ....................................................................................... 20 3.5 Determination of Layer Thicknesses ........................................................... 21 3.6 Assigning Apparent Resistivity Values to Layer Thicknesses .................... 22 3.7 Computation of Longitudinal Conductance and Transverse Resistance...... 22 3.8 Developing Regression Models and Testing its Reliability ......................... 23 CHAPTER 4: RESULTS AND DISCUSSION ....................................................... 24 4.1 Layer Thicknesses ........................................................................................ 24 4.2 Assigning Resistivity Values to Layer Thicknesses .................................... 25 4.3 Computation of Longitudinal Conductance and Transverse Resistance...... 26 4.4 Developing Regression Models ................................................................... 30 iv 4.4.1 Using Subsurface Layers from 33 Drill Logs for Garu Tempane .......... 30 4.4.2 Using Subsurface Layers from 33 VES for Garu Tempane ................... 32 4.4.3 Using Subsurface Layers from 25 VES for Garu Tempane ................... 34 4.4.4 Using Subsurface Layers from VES for Bawku West ........................... 38 4.4.5 Testing Reliability of Regression Models .............................................. 40 CHAPTER 5: CONCLUSIONS AND RECOMMENDATIONS .......................... 47 5.1 Conclusions .................................................................................................. 47 5.2 Recommendations ........................................................................................ 48 REFERENCES ........................................................................................................... 49 APPENDICES ............................................................................................................ 53 v LIST OF FIGURES Figure 1: Electrode arrays for resistivity surveys .......................................................... 9 Figure 2: Groundwater potential zones within Ghana ................................................. 16 Figure 3: Map showing study area with drilled boreholes ........................................... 17 Figure 4: Dipole-Dipole field data sheet ...................................................................... 19 Figure 5: Sample Borehole drill log ............................................................................. 21 Figure 6: VES plot for Karateshie ................................................................................ 25 Figure 7: Assigned Apparent Resistivity Values to Layers for Karateshie ................. 26 Figure 8: Yield vrs Apparent Resistivity from 33 Drill logs ....................................... 31 Figure 9: Yield vrs Longitudinal Conductance from 33 Drill logs .............................. 31 Figure 10: Yield vrs Transverse resistance from 33 Drill logs .................................... 32 Figure 11: Yield vrs Apparent Resistivity from 33 VES data ..................................... 33 Figure 12: Yield vrs Longitudinal Conductance 33 VES data ..................................... 33 Figure 13: Yield vrs Transverse Resistance from 33 VES data ................................... 34 Figure 14: Yield vrs Apparent Resistivity from 25 VES data ..................................... 35 Figure 15: Yield vrs Longitudinal Conductance from 25 VES data ............................ 35 Figure 16: Yield vrs Transverse Resistance from 25 VES data ................................... 36 Figure 17: Yield vrs Apparent Resistivity from 25 Drill logs ..................................... 36 Figure 18: Yield vrs Longitudinal Conductance from 25 Drill logs ...........................