omotoye s. j.1, fadiya s. l.2 , adesiyan t. a.3 and akinsanpe o.t.4

Sedimentological Study and Heavy Mineral Analysis of Sediment Samples from Well-S, Niger Delta, Nigeria

BYOmotoye S. J.1, Fadiya S. L.2 , Adesiyan T. A.3

and Akinsanpe O.T.4

Department of Geology, Obafemi Awolowo University, Ile-Ife, Nigeria.

OUTLINEOUTLINE INTRODUTIONINTRODUTION

AIM AND OBJECTIVESAIM AND OBJECTIVES

METHODOLOGYMETHODOLOGY

RESULTS AND DISCUSSIONRESULTS AND DISCUSSION

CONCLUSIONCONCLUSION

INTRODUCTIONINTRODUCTION Sediments are derived from the pre-existing rocks that have been

weathered, transported and deposited in basins.

The Niger Delta is one of the depositional basins in Nigeria and it has been accommodating sediments since the Paleocene.

The understanding of the sedimentary processes most importantly the environmental factors that have influence on the weathering, transportation, deposition and subsequent modification of the sediments are crucial in knowing their source and reconstructing the environment in which they were.

Sedimentologists are saddled with the responsibility of studying the properties of the sediments such as texture, structure, chemical and mineralogical composition to uncover the natural history of the sediments.

Introduction cont’dIntroduction cont’d

Figure 1a: Showing rock cycle

Figure 1b: Illustration of how sediments move in a stream

Sourced from Google

LOCATION OF THE STUDY AREA

2 4 6 8 10o E

o Eo Eo E

o E

2o N

4 o N

6

Ibadan

Study Area

Figure 2: Map of Niger Delta showing location of the study area (Modified after Whiteman 1982).

AIM AND OBJECTIVES

The aim of this study is to determine the provenance and environment

of deposition of the sediments from well-S in the Niger Delta using

grain size distribution and heavy minerals composition, with a view of

achieving the following objectives:

Determine the particle size distribution of the sediments.

Identify the heavy minerals composition of the samples.

Establish the provenance and environment of deposition of

the sediments.

METHODOLOGYMETHODOLOGY

Thirty (30) ditch cutting samples from 10700-11570 m, collected at 30

m interval from Well-S, Niger Delta were obtained for

sedimentological studies from a Nigeria deepwater operator (Oil Company).

Methodology cont’d

The analyses carried out in the laboratory involved:

Soxhlet Extraction of Soluble Organic Matter.

Wet Sieving.

Particle size distribution of the sediments using pipette analysis for Clay/Silt fraction and Emery’s sedimentation analysis for Sand sized fraction.

Heavy Mineral Separation.

RESULTS AND DISCUSSION

.

Sample 10880

Representative of Pipette Analysis result

Results and Discussion Cont’d

.

Sample 10880

Representative of Emery Sedimentation result

Results and Discussion Cont’d

Figure 3a. Representative of Histogram Curve plotted for each sample.

Figure 3b. Representative of Cumulative curve for each sample.

Results and Discussion cont’d

Figure 4. Representative of Probability Plot for each sample.

Results and discussion cont’dResults and discussion cont’d

Sample No

Ø5 Ø16 Ø25 Ø50 Ø75 Ø84 Ø95

1 0.80 1.36 1.60 2.06 2.80 3.20 3.61

2 0.92 1.80 2.03 2.48 2.87 3.40 3.68

3 1.67 1.00 1.41 1.80 2.19 2.40 2.83

4 0.00 0.00 0.21 1.68 2.50 2.82 3.50

5 0.87 1.81 1.87 2.35 3.02 3.30 3.63

6 1.18 1.64 2.00 2.52 3.20 3.38 3.72

7 0.82 1.28 1.53 2.20 2.77 3.31 3.59

8 0.88 1.82 2.08 2.62 3.10 3.40 3.71

9 0.70 0.91 1.00 2.00 2.62 3.00 3.70

10 0.82 1.73 2.07 2.68 3.18 3.52 3.61

11 1.23 1.49 1.71 2.48 3.39 3.61 3.77

12 0.22 0.87 1.68 2.53 2.91 3.20 3.68

13 0.91 1.20 1.50 2.33 2.89 3.27 3.70

14 0.87 1.28 1.60 2.42 3.10 3.31 3.87

15 0.00 0.75 1.22 2.00 2.58 2.85 3.42

Table 1: Percentile values for each sample.

Table 1 cont’dTable 1 cont’d

16 0.00 0.20 0.57 1.47 1.83 2.03 2.43

17 0.00 0.00 0.00 0.53 1.30 1.68 2.00

18 0.48 0.80 1.49 2.02 2.58 2.88 3.51

19 0.00 0.00 0.00 1.01 1.80 2.10 2.91

20 0.00 0.00 0.12 1.80 2.31 2.60 3.28

21 0.27 1.58 0.87 2.43 1.83 2.87 3.20

22 1.20 1.62 1.69 2.28 2.71 2.80 3.08

23 0.00 0.80 1.42 1.91 2.28 2.59 3.00

24 0.58 1.47 1.70 2.23 2.60 2.87 3.42

25 0.41 1.29 1.63 2.22 2.37 2.68 3.32

26 0.72 1.68 1.89 2.43 2.81 3.01 3.48

27 1.12 1.51 1.70 1.97 2.38 2.92 3.39

28 0.60 1.30 1.58 2.00 2.30 2.70 3.30

29 0.78 1.02 1.20 1.68 2.01 2.31 3.02

30 1.02 1.52 1.72 1.98 2.40 2.59 3.30

Results and Discussion Cont’d

The Statistical parameters derived from the results include;

Graphic mean

Inclusive graphic standard deviation

Inclusive graphic skewness

Graphic kurtosis

.

Results and discussion cont’dResults and discussion cont’d Folk and Ward (1957) proposed equations for the statistical parameters;

Graphic Mean (MZ) = Ø16 + Ø50 + Ø84 3

The values obtained from graphic mean ranges between 0.74 and 2.64Ø. This shows that sediments are fine to coarse grained.

Results and discussion cont’dResults and discussion cont’d

Inclusive Graphic Standard Deviation (SD) = Ø84 - Ø16 + Ø95 - Ø5 4 6.6

Calculated values ranges from 0.53 to 1.24Ø , an indication of moderately sorted to moderately well sorted sediments.

Results and discussion cont’dResults and discussion cont’d

Inclusive Graphic Skewness (SK) = Ø16 + Ø84 -2 Ø50 + Ø95+ Ø50 -2 Ø50 2(Ø84 - Ø16) 2(Ø95 - Ø50)

The values of the graphic skewness ranges from 0.29 to 0.70

Results and discussion cont’dResults and discussion cont’d

Graphic kurtosis (K)= Ø95 –Ø5 2.44(Ø75-Ø25)

The graphic kurtosis values obtained for the samples range from 0.61 to 1.54

Results and discussion cont’dResults and discussion cont’d

ENVIRONMENT OF DEPOSITION Sahu’s (1964) equation expressed as;

Ysh.mari flu = 0.2852Mz – 8.76040 ز – 4.8432SKI + 0.0482Kg

Where: Mz = Average graphic mean ز = Square of the average graphic standard deviation SKI = Average graphic skewness Kg = Average graphic kurtosis

He further proposed a limit value which he used to distinguish the environments, thus;

Yu <- 7.1490 indicates fluvial environment.

Yu > - 7.1490 indicates shallow marine environment.

The value derived for the analysed samples is – 8.0471 which indicate that they are fluvial sediments.

Results and discussion cont’dResults and discussion cont’d

HEAVY MINERAL ANALYSIS

Results and discussion cont’dResults and discussion cont’d

PETROGRAPHY

Figure 5a. Photomicrograph of sample 1.

Results and discussion cont’dResults and discussion cont’d

Figure 5b. Photomicrograph of sample 2.

Results and discussion cont’dResults and discussion cont’d

Figure 5b. Photomicrograph of sample 10.

Results and discussion cont’dResults and discussion cont’d

Results and discussion cont’dResults and discussion cont’d

ConclusionConclusionThe data obtained from the statistical parameters show that the sands from well-S are predominantly fine grained, moderately sorted to moderately well sorted, strongly fine skewed and very platykurtic. This implies that the sediments were deposited in a relatively low energy fluvial environment.

It was revealed by the statistical parameters that the sediments were transported mainly by saltation and suspension with a greater population of the sediments transported by saltation.

The sediments in the sequence studied have been found to be deposited in a fluvial environment as deduced from the application of Sahu’s (1964) equation.

The heavy mineral suite indicates that the sediments of the study area are likely to have been derived from acid igneous and metamorphic rocks which form part of the Basement Complex rocks of Nigeria. The co- occurrence of stable heavy minerals like Tourmaline, Zircon, Rutile, and Garnet indicate that the sediments are mineralogically mature.

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