ABSTRACT
Field studies were carried out on outcropping sediments exposed in
Lokoja and its environs to gain insight into reservoir characteristics and
sedimentological characteristics. Sieve analysis and petrographic analysis were
carried out on fresh samples of the sediments to determine their statistical
parameters, paleodepositinal environment and their reservoir quality.
Granulometric analysis of the Filele sands reveals that the sediments are
medium to coarse, moderate to poorly sorted, near symmetrical to positively
skewed and mainly leptokurtic, While the granulometric analysis of the Mount Patti
sands reveals that the sediments are fine to medium, well sorted to moderate
sorting, negatively skewed to positively skewed and mesokurtic to leptokurtic.
The petrographic analysis of the Filele sands reveals that the sediments
consist averagely of 78% Quartz, 17% Feldspar, and 5% Rock fragment, while the
Mount Patti sands consist of 90% Quartz, 6% Feldspar, and 4% Rock Fragment.
Ternary diagram also reveals that the sediments are mainly sub-arkose. The average
mineralogical maturity index (IMM) for the Filele sands is 3.8 indicative of
sub-maturity, while the Patti sands with 11.7 maturity index are indicative of
mature sands. Using Field evidences and Bivariate plots of skewness versus
sorting and mean versus sorting, a fluvial depositional setting was interpreted
for the sediments.
TABLE OF
CONTENTS
CERTIFICATION.. i
DEDICATION.. ii
ACKNOWLEDGEMENT. iii
ABSTRACT. iv
TABLE OF CONTENTS
LIST OF
FIGURES. vii
LIST OF
TABLES. viii
CHAPTER
ONE: INTRODUCTION.. 1
1.1
BACKGROUND TO THE STUDY.. 1
1.2 AIM AND
OBJECTIVES. 1
1.3
LOCATION AND ACCESSIBILITY.. 2
1.4 RELIEF
AND DRAINAGE. 4
1.5 CLIMATE
AND VEGETATION.. 4
1.6
SETTLEMENT AND LAND USE. 4
1.7 SCOPE
OF PRESENT STUDY.. 4
1.8
LITERATURE REVIEW.. 5
CHAPTER
TWO: REGIONAL GEOLOGY.. 8
2.1 THE
GEOLOGY OF MID-NIGER (BIDA) BASIN.. 8
2.2.
TECTONIC HISTORY OF THE AREA.. 8
2.3
STRATIGRAPHIC SETTING AND PALEOGEOGRAPHY.. 9
2.4
STRATIGRAPHIC SUCCESSION OF SOUTHERN BIDA BASIN.. 11
2.4.1
Precambrian basement complex. 11
2.4.2 The
lokoja formation. 11
2.4.3 The
patti formation. 12
2.4.4 The
agbaja formation. 13
CHAPTER
THREE: METHODOLOGY.. 14
3.1 MATERIALS AND
METHODS. 14
3.2 FIELD EQUIPMENT AND
INSTRUMENTS. 14
3.3 LABORATORY
MATERIALS/EQUIPMENT. 14
3.3.1 Granulometric
(sieve) analysis 14
3.3.2 Petrographic
analysis (thin section preparation) 15
3.4 FIELD MAPPING
TECHNIQUE. 15
3.5 SAMPLE COLLECTION.. 16
3.6 LABORATORY ANALYSES. 16
3.7 SEDIMENTOLOGICAL
(SEIVE) ANALYSIS. 16
3.8 PROCEDURE FOR
PETROGRAPHIC SLIDE PREPARATION/ANALYSIS. 17
CHAPTER FOUR: RESULTS
AND INTERPRETATION.. 19
4.1 PRESENTATION OF
RESULTS. 19
4.1.1
Sedimentological results 19
4.1.2 Petrographic
results 26
4.2 INTERPRETATION OF
RESULTS. 28
4.2.1 Sedimentological
and lithofacies description. 28
4.2.2 Paleodepositional
environment 32
4.2.3: Petrophysical
analysis 33
4.2.4
Petrographic interpretation. 34
4.2.5 Provenance and
paleoclimate interpretation. 37
4.3 DISCUSSION OF
FINDINGS. 39
4.3.1: Lithofacies and
depositional environment 39
4.3.2 petrography and
provenance. 40
CHAPTER FIVE:
SUMMARY, CONCLUSION AND RECOMMENDATION.. 41
5.1 SUMMARY.. 41
5.2 CONCLUSION.. 41
5.3 RECOMMENDATIONS. 42
REFERENCES. 43
APPENDICES. 47
LIST OF FIGURES
Figure 1
Geologic map of Southern Bida basin showing (Ojo, 2009). 3
Figure 2
Lithologic section of the Lokoja Formation at Filele along Lokoja – Abuja
Highway (Omali, et al., 2011). 7
Figure 3 :
Stratigraphic Succession in the Bida Basin (After Akande, 2005; Obaje, 2009) 10
Figure 4 :
Photomicrograph of Patti formation sample 5 (A = XP, B = PPL) Q = Quartz, RF = Rock
Fragment. 26
Figure 5 :
Photomicrograph of Patti formation sample 6 (A = XP, B = PPL) Q = Quartz, RF = Rock
Fragment. 26
Figure 6 :
Photomicrograph of Filele sample 2 (A = XP, B = PPL) Q = Quartz, FD = Feldspar. 26
Figure 7 :
Photomicrograph of Filele sample 4 (A = XP, B = PPL) Q = Quartz, FD = Feldspar. 27
Figure 8 :
Photomicrograph of Filele sample 5 (A = XP, B = PPL) Q = Quartz, FD = Feldspar, FQ =
Fractured Quartz RF = Rock Fragment. 27
Figure 9 :
Photomicrograph of Filele sample 6 (A = XP, B = PPL) Q = Quartz. 27
Figure
10 : sequence of very fine to cobbly poorly sorted arkosic sand facies of the
Lokoja Formation unconformably overlying the Precambrian basement exposed on a
road cut at Filele along the Okene-Lokoja road. 29
Figure
11 : Litholog of Filele outcrop. 30
Figure 12 :
Otcropping sediments of the Patti formation exposed at Mount Patti along Lokoja
Agbaja road. 31
Figure
13 : Litholog of Patti formation exposed at Mount Patti 31
Figure 14 :
Bivariate Plot of Skewness versus Standard Deviation (boundary modified after
Friedman, 1967). 32
Figure 15 :
Bivariate Plot of Mean versus Standard (boundary modified after Moiola and
Weiser, 1968) 33
Figure 16 :
Figure Ternary Plot of Framework Minerals (after Adams et al., 1984) 36
Figure 17 :
Framework Classification of Minerals (after Dott, 1964) 37
Figure 18 :
Ternary of Framework Model for Sediments of the Study Area (modified after
Dott, 1964 and Adams et al. 1984). 38
Figure 19 :
QFR Classification of Provenance Fields of the Outcropping Sediments the Study
Area (modified after Dickenson et al.,
1983 and Osae et al., 2006). 38
Figure 20 :
QFR Ternary Plot as a Function of Paleoclimate (modified after Suttner et al., 1981). 39
LIST OF TABLES
Table 1:
Sample Collection Points and Descriptions 16
Table 2: A
Typical Table for Recording Values from Granulometric Analysis 17
Table 3 :
Particle Size Distribution for Mount Patti sample 1. 19
Table 4 :
Particle Size Distribution for Mount Patti sample 2. 19
Table 5 :
Particle Size Distribution for Mount Patti sample 3. 20
Table 6 :
Particle Size Distribution for Mount Patti sample 4. 20
Table 7 :
Particle Size Distribution for Mount Patti sample 5. 21
Table 8 :
Particle Size Distribution for Mount Patti sample 6. 21
Table 9 :
Particle Size Distribution for Mount Patti sample 7. 22
Table 10 :
Particle Size Distribution for Mount Patti sample 8. 22
Table 11 :
Particle Size Distribution for Filele sample 1. 23
Table 12 :
Particle Size Distribution for Filele sample 2. 23
Table 13 :
Particle Size Distribution for Filele sample 3. 24
Table 14 :
Particle Size Distribution for Filele sample 4. 24
Table 15 :
Particle Size Distribution for Filele sample 5. 25
Table 16 :
Particle Size Distribution for Filele sample 6. 25
Table 17 :
Textural Interpretation of the Sediments 28
Table 18 :
Calculated Permeabilities for the Outcropping Sandstone Facies around Lokoja
and environs. 34
Table 19 : Percentage (%) Mineralogical Composition of
the Sediments 35
Table 20 : Percentage (%) Modal Mineralogical Composition
of the Sediments 35
Table 21 :
Mineralogical Maturity Index (IMM) of Sediments (after Nwajide and Hoque, 1985) 36
CHAPTER ONE
INTRODUCTION
1.1 BACKGROUND TO THE STUDY
Sandstones are sedimentary rocks
formed by the cementation of sediment by material cements and they show a great
deal of variation in mineral composition, degree of sorting and roundness and
they possess quality reservoir characteristics and mineralogy. Sedimentological
studies help to determine sediment characteristics of the rocks (sorting,
sedimentary structures, grain size, shape, lithology, porosity, texture,
maturity etc.). Similarly, petrographic studies are very useful in
understanding and interpreting the mineralogical (petrographic) details of
rocks – their composition, abundance, and morphology among others. Together,
sedimentology and petrography are widely used in the reconstruction of the
geological history of rocks – their distances from provenance, paleoenvironmental
and conditions of formation and/or deformation, diagenetic processes acting on
rocks, tectonic history as well as the stratigraphy.
The need to combine
sedimentological and petrographic analyses for paleoenvironmental analyses is
borne out of the fact that relying on textural analysis alone may result in
gross interpretational errors, especially if diagenetic or disaggregation
processes have significantly altered textural properties of such sediments
(Wilson and Pittman, 1979).
The sedimentological investigation of some
outcropping sediment in southern Bida basin and its environs employed the field
mapping and the laboratory studies approach of the sediments sampled and it was
used in deducing the porosity and permeability of the outcropping sediments in
the study area.
This
study involves the determination of the lithology, mineralogy and textural
characteristics of the sandstone facies in order to predict the reservoir
quality of the sandstone using Sedimentological and petrographic data as
obtained from field evidence of some outcropping sediment of southern Bida
basin and its environs.
This study is aimed at
investigating the Sedimentological and petrographic attributes of outcropping
sediments in Lokoja and its environs.
The objectives of this
study include:
i. To determine the lithofacies characteristics of the
sediments of the study area;
ii. To ascertain the mineralogical composition of the
sediments;
iii. To determine the paleodepositional environment in
which the sediments where formed using available sedimentological and
petrographic data sets; and
iv. To characterize the reservoir properties of the
sediments by inferring the porosity and quantitatively determine the
permeability.
The study area is located in Kogi State.
It is bounded by latitudes 070 30’ N - 080 30’
N and longitude 0060 00’E- 0070 00’
E. The area visited include outcrops on road cuts along the Lokoja-Abuja
Express Road and include; Filele and Mount Patti.
The study area was accessible by main
roads and footpaths. The main is the Lokoja-Abuja express road [(fig. 1)Ojo,
2009].
Figure 1 Geologic map of
Southern Bida basin showing (Ojo, 2009).
The
River Niger is present in the study area as the main hydrological element. The
Niger River runs in an ESE direction in the southern marginal area/part of the
basin. Its floodplain is broad and locally up to 20km wide and marked in most
areas by a series of elongated ponds running parallel to the river channel. The
main tributaries of the River Niger are River Kaduna (wuya) and Gurara which
drain the Northern Nigeria Basement Complex.
The
area of study has various elevations above sea level as recorded by GPS and
shown below:
Filele
(169m), Mount Patti (255m) and Agbaja plateau (407m).
The study area has an average maximum
temperature of 33.20C and an average minimum temperature of 22.80C.
It is generally hot throughout the year with an average relative humidity of
68-70 percent. The study area has two distinct weathers, dry and wet seasons.
The dry season occurs between November and February while the rainy season is
between March and October.
The vegetation type in the study area is
Guinea savanna or parkland savanna with tall grasses interspersed shrubs and
some trees. The shrubs shed their leaves during the dry seasons in order to
withstand some amount of drought. Apart from shedding of leaves, some shrubs
have stems with thick bark, thick leaves etc. as adaptive features by the trees
or shrubs in low rainfall regions to check excessive transpiration.
The study area is the headquarters of Kogi
state with various settlements ranging from mainly urban to rural. Main towns
in the study area include Ahoko, Kotonkarfi, Idu and Ozi. The main occupation
of the residents is Agriculture. Trade and other cottage industries are also
common in the area.
11
This
study is focused on determining the reservoir quality from the sedimentological
and petrographic attributes of outcropping sediment in Lokoja and its environs
in southern Bida basin.
The
scope of this study includes:
I. Field
Mapping and sample collection of outcropping sediments in the study area.
II. Laboratory studies
involving sedimentological and petrographic analyses of collected samples
III. Quantitative determination of permeability of the
sediments.
IV. Determination of provenance; and
V. Interpretation of results
The Campanian Maastrichtian Lokoja
Formation, which is chiefly, if not wholly, non-marine clastics, comprises of
conglomerates, massive, pebbly to coarse grained sandstones, claystones,
siltstones, ironstones and lateritic capping (Adeleye, 1971, 1973 and Braide
1992). Lokoja sandstone is the oldest formation in the Southern Bida Basin
being 90-280m thick, overlain by 70-100m
thick Maastritichian Patti Formation and about
5-20m thick of Agbaja ironstones overlaying the middle Patti Formation
(Braide,1992, Ladipo 1994). Lokoja sub-basin of the Bida Basin is a NW-SE
shallow, downwarped trough which resulted from the wrench fault movement
associated with the tectonic framework of the Nigerian sedimentary basins
(Jones, 1953 and Braide, 1992) which was filled with Campanian-Maastritichian
sediments as confirmed by the palaeontological and sedimentological studies
(Ojo, 1992, Abimbola 1993). Alluvial fans and deltaic facies that interfinger
with lacustrine facies provide an amount of reservoir quality for the
formation.
The alternating sandstone and
conglomeratic facies of the Lokoja Formation indicate fluvial sediment
dominated by mass flow and bed-load deposits within an alluvial and braided
stream complex (Braide, 1992; Akande et
al., 2006). The immature clast to matrix supported conglomerates are
interpreted as debris flow deposit, similar to the poorly sorted conglomerates
interpreted as gravity induced alluvial fans of the Upper Benue Trough
(Nwajide, 1980). Interbedded sandstones probably represent braided stream
channel deposits whereas the claystones are probably flood plain deposits
(Pettijohn, 2004). The massive matrix supported conglomerate corresponds to a
debris flow in an alluvial fan setting. The conglomeratic unit with graded
bedded is interpreted as an abandoned channel deposit. The alternating
conglomerates and sandstones of the Lokoja Formation in the lower part of the
section reflect continental deposition influenced largely by alluvial and braided
stream processes (Akande et al.,
2006). The stratified nature of the shales and sandstones provides likely favourable
pathways for migration of fluids into potential reservoir rocks made up mainly
of fluvial, shelf and flood plain sandstones in the Lokoja and the Patti
formation (Obaje, et al. 2011). Outcrop studies have been used by Osokpor et al., (2013), to determine the
sequence stratigraphy and environment of deposition for the Bida Basin, and
inferred that the Lokoja Formation enabled the discrimination of various
subfacies formed in continental paleodepositional settings of dominantly
fluvial systems during the Late Cretaceous out-building of sedimentary
sequences in the Southern Middle Niger Basin and signaled as lowstand systems
tract architecture. The relatively well-sorted sandstones unit of the tidally
influenced facies of the Patti Formation has been observed as better
characterized reservoir rock compared to the fluvial Lokoja sandstones with the
prevalence of alluvial fans, containing poorly sorted massive conglomeratic
sandstone, matrix supported conglomerate [(fig, 2), Omali, et al., 2011], proximal to the basement. These continental
alluvial fans with obvious clogging of the pore throats by clays and
clay-filled minerals will be responsible for the inferred reduced porosity and
permeability in the Lokoja sandstone than in the tidally influenced facies
(obvious from observed herringbone and cross-stratifications) of the Patti
Formation which may provide better reservoir possibilities at greater depths
(Obaje, et al., 2011).
Figure 2 Lithologic section of the Lokoja
Formation at Filele along Lokoja – Abuja Highway (Omali, et al., 2011).
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