Use Of Single-Point Resistance And SP Logging In Groundwater Investigation

Project and Seminar Material for Geology

Use Of Single-Point Resistance And SP Logging In Groundwater Investigation


Abstract


The purpose of this study is to examine the use of single-point resistance and spontaneous potential (SP) logging in groundwater investigation. A total of 134 respondents were selected from the population figure out of which the sample size was determined. The primary source of data collected was mainly a structured questionnaire. Data collected will be analyzed using frequency table, percentage and mean score analysis while the nonparametric statistical test (Chi-square) was used to test the formulated hypothesis using SPSS (statistical package for social sciences). We interpreted that the lowest unit fresh water aquifers in the deepest parts of the boreholes are the best suitable to be screened for groundwater extraction in the Apapa area. The results show that most of the groundwater borehole logs are located in the upper part of the reservoirs, and the depths of these logs range from 220 to 280 m in Tin Can Island and Snake Island, respectively.


Chapter One


Introduction

1.1 Background of the Study

Water is one of the abundant and widely used natural resources available to man. Many communities obtain the water they need from rivers, lakes, or reservoirs, sometime using aqueduct or canals to bring water from distant surface sources. Another source of water lies directly beneath most towns. This resource is groundwater, the water that lies beneath the ground surface. The origin of water is traced to the process of the hydrologic cycle. When rain falls on the land surface as precipitation, more than half of the water returns rather rapidly to the atmosphere by evaporation or transportation from plants. The remainder either flows over the land surface as runoff to streams, rivers, and lakes, or soaks into the ground by infiltration to form groundwater. Rivers stream and lakes make up the surface occurrence while those that sink into the ground make up subsurface occurrence called ground water.

Groundwater is the water that lies beneath the ground surface, filling the pore spaces between grains in bodies of sediment and clastic sedimentary rocks and filling cracks crevices in all types of rocks (Plummer et al 1999). The subsurface zone in which all rocks opening are filled with water is saturated zone. The upper surface of the saturated zone is the water table. Groundwater is unfortunately not evenly distributed everywhere. The distribution of ground water depends on large extent upon the types and depth of occurrences (Oseji, 2010). Ground water in its natural state tends to be relatively free of contaminants in most areas. Because it is a widely used source of drinking water, the contamination of groundwater can be a very serious problem (Plummer et al., 1999). Groundwater can be contaminated by pesticides and herbicides (such as diazion, atarzine DEA and 2, 4, D) applied to agricultural crops Can find their way into groundwater when rain or irrigation water leaches the contaminants downward into the soil; Liquid and solid wastes from septic tanlas, sewage plants and animal. Feedlots and slaughterhouse may contain bacteria viruses, and parasite that can contaminate groundwater.

Ground exploitation sometime often result in failed and abortive borehole because of lack of preliminary geophysical investigation required to map and locate prolific zones within the aquifers (Atakpo et al., 2008). In order to avoid such an occurrence and to increase the probability of drilling successful and sustainable borehole, it becomes pertinent and economically wise to carry out prior geophysical investigation. Borehole electrical resistivity and spontaneous potential method is based on the variable resistance in surface materials to the conduction of electrical current depending on materials to the conduction of electrical current depending on variation in fluid content, density and chemical composition of the composition (Paransis, 1986). Recently other electrical geophysical method such as electro-magmatic induction (EM) and ground penetrating radar (GPR) becomes increasingly popular.

The evaluation of ground-water systems by use of geophysical logs begins with a thorough knowledge of the environmental factors that cause geophysical-log responses. This evaluation also requires an understanding of the relation among geophysical-log responses and rock properties, models, experimentally derived equations, and the principles that govern the responses of logging devices. Established “oil-field” geophysical-log interpretation methods have been applied to the analysis of freshwater aquifers and indicate that interpretations depend on reliable empirical data. The geologist, log analyst, or reservoir engineer needs to be thoroughly familiar with the variables and assumptions applied to the quantitative or qualitative analysis of geophysical logs and to the determination of the interrelation among lithologic properties. All formation evaluations, through the use of geophysical logs, rely on some assumptions, and the finished interpretation is no better than the assumptions and data on which it is based. The limited success of applying oil-field geophysical-log analysis and interpretation methods to freshwater aquifers is, in part, a result of the use of assumptions and principles that do not apply to the analysis of freshwater aquifers. Geophysical-logging equipment developed primarily for shallow-hole logging, such as for water wells and mineral exploration, has become readily available, more reliable, and can be calibrated to the same standards as those developed for oil-well logging. The considerably lower initial investment, relative to oil-well logging equipment, results in lower logging costs.

Most shallow-hole logging equipment has digital capabilities and on-board computer software that provides cross plots and on-location log analysis. These advantages, coupled with the increase in drilling costs, have made logging of freshwater wells more cost effective. The results have been an increase in water-well logging activity and a subsequent increased demand for better interpretation principles as applied to ground-water problems. Oil-well geophysical-log interpretation principles are well established but not directly applicable to hydrologic problems, partly because of differences in the chemistry of solutions that saturate the porous medic.
However, the study tends to examine the use of single-point resistance and SP logging in groundwater investigation.


1.2 Statement of the Problem

Geophysical downhole logging provides in situ information about the physical properties of the rock strata and groundwater. In a hole with limited core recovery or the drill cuttings or samples are of questionable origin, the depth of even significant lithological changes can be uncertain. The geophysical logs give a continuous depth record of formation properties, which clearly identifies the lithological changes with an uncertainty of a few centimeters. This information is of great importance in geological modeling. Geophysical borehole logging generally provides additional information to identify fresh water bearing sands in the subsurface. This information includes lithology of the rocks penetrated by the borehole and nature of the fluid contents. The most useful parameters for this are gamma-radiation, electrical resistivity, acoustic velocity, and caliper. Increasing the number of parameters measured either increases the accuracy of the interpretation due to redundancy or can be used to determine further constituents of the rock. Therefore, this makes correlation of well logs of neighbouring boreholes is possible and the correlation distance depends on the lateral homogeneity of the strata. This study aims to use combine geophysical borehole logs and ditch cutting samples as tools for delineating fresh water aquifers and for borehole designs. The study area is located between longitude 3° 9.51′ and latitude 6° 26.22′ with an elevation of 2 to 3m above the sea level in Apapa area of Lagos State, Southwestern Nigeria. The following applications of geophysical well logging methods in shallow boreholes have been dealt with by a large number of publications over the last several years: geological investigations determination of physical properties (Hearst et al. 2000), hydrogeological investigations coastal aquifers and fresh/salt water boundaries and environmental investigations.


1.3 Objectives of the Study

The main objective of this study is to examine the use of single-point resistance and SP logging in groundwater investigation.

Specific objectives include;

  1. To determine the lithology of the subsurface using spontaneous potential log.
  2. To determine or identify the aquifer, depths and thickness of the rock using spontaneous potential log.
  3. To determine the quality of water based on total dissolved solids using single point resistance log.
  4. To determine the portability of the water.

1.4 Research Questions

  1. What is the lithology of the subsurface using spontaneous potential log?
  2. What is the aquifer, depths and thickness of the rock using spontaneous potential log?
  3. What is quality of water based on total dissolved solids using single point resistance log?

1.5 Research Hypotheses

Hypothesis I
  • H0: There is no lithology of the subsurface using spontaneous potential log.
  • H1: There is lithology of the subsurface using spontaneous potential log.
Hypothesis II
  • H0: There is no aquifer, depths and thickness of the rock using spontaneous potential log
  • H1: There is aquifer, depths and thickness of the rock using spontaneous potential log
Hypothesis III
  • H0: There is no quality of water based on total dissolved solids using single point resistance log
  • H1: There is quality of water based on total dissolved solids using single point resistance log

1.6 Significance of the Study

This study will be of immense benefit to other researchers who intend to know more on this study and can also be used by non-researchers to build more on their research work. This study contributes to knowledge and could serve as a guide for other study.


1.7 Scope of the Study

This study is on the use of single-point resistance and SP logging in groundwater investigation.


1.8 Limitations of the Study

The demanding schedule of respondents at work made it very difficult getting the respondents to participate in the survey. As a result, retrieving copies of questionnaire in timely fashion is very challenging. Also, the researcher is a student and therefore has limited time as well as resources in covering extensive literature available in conducting this research. Information provided by the researcher may not hold true for all institutions but is restricted to the selected organization used as a study in this research especially in the locality where this study is being conducted.

  • Financial constraint: Insufficient fund tends to impede the efficiency of the researcher in sourcing for the relevant materials, literature or information and in the process of data collection (internet, questionnaire and interview).
  • Time constraint: The researcher will simultaneously engage in this study with other academic work. This consequently will cut down on the time devoted for the research work.
  • Finally, the researcher is restricted only to the evidence provided by the participants in the research and therefore cannot determine the reliability and accuracy of the information provided.

1.9 Definition of Terms

Single -Point Resistance:

The standard unit of resistance is the ohm, sometimes written out as a word, and sometimes symbolized by the uppercase Greek letter omega: When an electric current of one ampere passes through a component across which a potential difference (voltage) of one volt exists, then the resistance of that component is one ohm

SP Logging:

The spontaneous potential log (SP) measures the natural or spontaneous potential difference between the borehole and the surface, without any applied current.

Groundwater:

Groundwater is water that exists underground in saturated zones beneath the land surface. If groundwater flows naturally out of rock materials or if it can be removed by pumping (in useful amounts), the rock materials are called aquifers.


Chapter Five


Summary, Conclusion and Recommendations

5.1 Summary of Findings

The purpose of this study was to examine the use of single-point resistance and SP logging in groundwater investigation.

Hypotheses were formulated (generated) to guide the researcher.

Hypothesis I
  • H0: There is no lithology of the subsurface using spontaneous potential log.
  • H1: There is lithology of the subsurface using spontaneous potential log.
Hypothesis II
  • H0: There is no aquifer, depths and thickness of the rock using spontaneous potential log
  • H1: There is aquifer, depths and thickness of the rock using spontaneous potential log
Hypothesis III
  • H0: There is no quality of water based on total dissolved solids using single point resistance log
  • H1: There is quality of water based on total dissolved solids using single point resistance log

The objectives of the study were to;

  1. To determine the lithology of the subsurface using spontaneous potential log.
  2. To determine or identify the aquifer, depths and thickness of the rock using spontaneous potential log.
  3. To determine the quality of water based on total dissolved solids using single point resistance log.
  4. To determine the portability of the water.

5.2 Conclusion

Water is one of the abundant and widely used natural resources available to man. Many communities obtain the water they need from rivers, lakes, or reservoirs, sometime using aqueduct or canals to bring water from distant surface sources. Another source of water lies directly beneath most towns. This resource is groundwater, the water that lies beneath the ground surface. The origin of water is traced to the process of the hydrologic cycle. When rain falls on the land surface as precipitation, more than half of the water returns rather rapidly to the atmosphere by evaporation or transportation from plants. The remainder either flows over the land surface as runoff to streams, rivers, and lakes, or soaks into the ground by infiltration to form groundwater. Rivers stream and lakes make up the surface occurrence while those that sink into the ground make up subsurface occurrence called ground water.

Groundwater is the water that lies beneath the ground surface, filling the pore spaces between grains in bodies of sediment and clastic sedimentary rocks and filling cracks crevices in all types of rocks (Plummer et al 1999). The subsurface zone in which all rocks opening are filled with water is saturated zone. The upper surface of the saturated zone is the water table. Groundwater is unfortunately not evenly distributed everywhere. The distribution of ground water depends on large extent upon the types and depth of occurrences (Oseji, 2010). Ground water in its natural state tends to be relatively free of contaminants in most areas. Because it is a widely used source of drinking water, the contamination of groundwater can be a very serious problem (Plummer et al., 1999). Groundwater can be contaminated by pesticides and herbicides (such as diazion, atarzine DEA and 2, 4, D) applied to agricultural crops Can find their way into groundwater when rain or irrigation water leaches the contaminants downward into the soil; Liquid and solid wastes from septic tanlas, sewage plants and animal. Feedlots and slaughterhouse may contain bacteria viruses, and parasite that can contaminate groundwater.


5.3 Recommendations

The hydrogeological studies of Apapa have been investigated with combined well logs and the ditch cuttings. Our results show that aquifer units occur below 150 m depth in most of the boreholes and we interpreted that the lowest unit fresh water aquifers in the deepest parts of the boreholes are the best suitable to be screened for groundwater extraction in the Apapa area. The depths to these aquifers are between 144m-198m in the Tin Can Island Area and 169-250m in the Snake Island. Therefore, we recommend that groundwater boreholes in the Apapa area should be significantly deep, minimum of 220m and 280 m depths in Tin Can Island and Snake Island, respectively, and must geophysically logged to maximize aquifer potential and reduce risk of screening a pollution prone aquifer


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