CHAPTER ONE
1.1 INTRODUCTION (GENERAL STATEMENT)
Palynology is the study of micro organic
material such as pollen grains and other spores especially as found in
geological deposits. They are important group of microfossils and in
general, are important tools for the petroleum industry, finding
practical uses in all stages of the exploration process. Prior to
drilling, micropaleontological methods can aid the acquisition of
geological field data and enhance the quality of the reservoir potential
assessment by way of sequence stratigraphic correlation,
paleogeographical and facies analysis, depositional and source-rock
maturation determination as well as migration modeling (Jenkins, 1993).
The accuracy and profitability of the drilling process itself can
benefit from micropaleontological monitoring through the analysis of
ditch cuttings, essentially allowing age determination, correlation of
wells, unconformity evaluation, paleoenvironmental interpretation and
lithostratigraphic as well as depositional sequence characterization.
Finally, in the ”post”-drilling stage
of the exploration, comprising appraisal and development, the evaluation
of microfossils is imperative for setting up detailed stratigraphic
subdivisions and modeling reservoir connectivity. Pollen extracted from
such deposits may be used for radiocarbon dating and for studying past
climates and environment by indenting the plant. Pollen and spores are
transported by wind and water and can travel long distances before final
deposition. They are surprisingly resistant to decay and are common as
fossils. Because of the long transport before deposition, they usually
tell us little about the environment of deposition, but they can be used
for biostratigraphy. Fossil pollen and spores can also give us
information about ancient climates.
Palynological studies in Nigeria are
largely confined to the Tertiary Niger Delta, where numerous studies
have been carried out following the discovery of petroleum resources in
the Niger Delta in the late 1950s. The Niger Delta Basin is economically
important because of its petroliferous nature; the economy of Nigeria
depends largely on the oil and gas derived from it. Up to 12km of Late
Eocene-Recent deltaic and shallow marine sediments have accumulated in
the triangular-shaped basin in a series of southerly prograding off
lapping cycles (Michele et al.). The combination of source rock,
lithologic types, structures and thermal history of the basin are
favorable for the generation, accumulation and retention of hydrocarbons
(Whiteman Stacher Sonibare and Ekweozor).
Additionally, the organic chemicals
which comprise palynomorphs get darker with increased heat. Because of
this color change they can be used to assess the temperature to which a
rock sequence was heated during burial. This is useful in predicting
whether oil or gas may have formed in the area under study, because it
is heat from burial in the Earth that makes oil and gas from original
organic rich deposits (Asheesh, 2008). Some geological fields in which
palynology can be applied to, here are the major fields:
- Geochronology
- Biostratigraphy
- Paleoecology
- Geochronology - dating of rocks. Palynoflora are used to date
rocks. Palynomorphs are great indicators of narrow time ranges because
of the rapid evolution of the samples. Because they are present in
rocks that don't usually have fossils, the microscopic fossils are used
as a time range instead of waiting for complicated lab results.
- Biostratigraphy - correlation of rock sections. This aspect of
palynology is the most important economically. Proper identification of
indicative palynomorphs could lead to the discovery of oil, coal, and
gas deposits. In fact, fossilized pollen was first discovered in a coal
thin section. Because pollen and spores have the tendency of being
dragged along with migrating petroleum through porous rocks - they are
good indicators that petroleum isn't too far away. The small sizes of
palynomorphs are ideal for drill core samples. The coloration and type
of palynomorphs represents the thermal maturity and hydrocarbon
potential of the area.
- Paleoecology - past environments. Because palynomorphs are
sensitive to any minor fluctuation in their surroundings, they are
highly indicative of the environment in which they are deposited. The
advantage of palynomorphs over other fossils is their widespread
distribution; they can be found in either terrestrial, freshwater,
saltwater, or estuary sources of sedimentary rocks.
1.2 AIM AND OBJECTIVES
This study is primarily aimed at using palynomorphs (pollens and spores) in order to achieve the following objectives:
- To establish biostratigraphic zonation
- To determine the relative age of the studied well ( age dating )
- To interpret and reconstruct the depositional environments
1.3 SCOPE AND METHODS OF STUDY
i). Obtain well cutting samples from four wells
ii).Prepare and analyze the samples for their palynological content
iii). Interpret the analyzed samples in line with standard palynological methods
iv). Present the results using statistical models
v). Draw up conclusions from the findings
vi). Present the report as a dissertation.
1.4 LOCATION AND ACCESSIBILITY
The study area is
located in the offshore western Niger Delta area of Nigeria. The Niger
Delta is situated in the Gulf of Guinea on the west coast of Central
Africa. Niger Delta lies between latitudes 4° and 6° N and longitudes 3°
and 9° E in the south-south geo-political region of Nigeria (Ojo et al,
2009). The Cenozoic Niger Delta is situated at the intersection of the
Benue Trough and the South Atlantic Ocean where a triple junction
developed during the separation of South America and Africa in the Late
Jurassic (Whiteman, 1982).
1.5 TOPOGRAPHY AND DRAINAGE
In the drainage of the Niger Delta, the
river Niger drains the eastern flank of the state and discharges into
the sea through its several distributaries such as the forcados,
Escravos and Warri Rivers and creeks such as Bomadi creeks amongst
other. Low relief and poor drainage result to erosion and flooding
leading to coastal area been flooded and low availability of land for
farm purpose.
1.6 CLIMATE, VEGETATION AND OCCUPATION
The vegetation of the Niger Delta
consists mainly of forest swamps. The forest is of two types, nearest
the sea is a belt of saline/brackish mangrove swamp separated from the
sea by sand beach ridges within the mangrove swamp. Numerous sandy
islands occur with fresh water vegetation. Fresh water swamps gradually
supersede the mangrove on the landward side. The Niger delta is a rich
mangrove swamp in the southernmost part of Nigeria covering over
20,000kmsquare.
The major occupation of the people in the region is fishing, agriculture and the region is abundantly blessed in this respect.
1.7 PAST WORK OR LITERATURE REVIEW
Three depositional cycles and
lithostratigraphic subdivision of upper sandy continental Benin
Formation, intervening unit of alternating sandstones and shales (Agbada
Formation) and lower shaly Akata Formation have been identified in the
Niger Delta area (Short & Staüble, 1967; Avbovbo, 1978, etc.). The
structural geology, sedimentology and petroleum geochemistry of the
Niger Delta have been published by several workers (Tuttle, et al.,
1999; Weber & Daukoru, 1975, etc.).The accumulation and retention of
hydrocarbons was published by (Whiteman Stacher Sonibare and Ekweozor).
In addition, the biostratigraphy and sequence stratigraphy of the Niger
Delta have been studied (Ozumba, 1999; Adeniran, 1997; Petters, 1982,
etc