ABSTRACT
Palynofacies analysis and thermal maturation study was carried out on IDM-4 and IDM-5 wells of the Niger Delta Basin. The location of the studied area lies within Latitude 04⁰ 08’ 02’’ N and longitude 06⁰ 08’ 06’’ E for IDM-4 and latitude 04⁰ 08’ 0’’ N and longitude 06⁰ 07’ 06’’ E for IDM-5. The studied depth of the well is 10030 ft– 11700 ft at 30 ft interval. Palynological processing, analysis and interpretations were carried out on forty-nine and forty-seven ditch cutting samples from the IDM-4 and IDM-5 wells, respectively. Kerogen analysis was also carried out on the part samples. Simple acid method of sample preparation was used during the palynofacies analysis. Physical observation and Gamma Ray log were used in determining the lithology of the sedimentary succession. The lithology consists of the fine to medium sized sandstones and sandy mudstones. Abundant species of palynomorphs and palynomacerals were recovered. Some of which are biomarkers such as Zonocostites ramonae, Pachydermites diederixii, Sapotaceodaepollenites sp., Psilatricolporites cassus. Crassoretitriletes vanraadshooveni, Laevigatasporites sp. This is correlatable to early-Miocene to middle- Miocene stratigraphic ages. Two zones were established in IDM-4well. They are Pachydermites diederixizone which falls within the 7000 ft and 7990 ft and Crassoretitrites vanraadshooveniZone which falls within the interval 6030 ft and 7000 ft. Three zones were established in IDM-5 well. They are Polypodiaceoisporites sp. Zone, Magnastriatites howardi Zone and Pachydermites diederixi Zone. The palynofacies associations show the depositional environment of Pachydermites diederixii to be mangrove swamp while Crassoretitrites vanraadshooveni Zone indicates mangrove- shoreface depositional environment for IDM-4 while the depositional environment of the studied interval is interpreted to predominantly range between Mangrove and Channel depositional environments for IDM-5. For IDM-4 well, the intervals such as 6050 ft, 6150 ft, 6400- 6600 ft, 6900- 6950 ft are the intervals that show the mature phase of liquid oil while intervals 6100 ft, 6200- 6400 ft, 6600- 6900 ft, 6950- 7950 ft are the phase of dry gas. For IDM-5 well, intervals 10000 -10950 ft are the phases of dry gas while intervals 10950- 11025 ft and 11450-11700 ft are the phases of mature liquid oil.
CHAPTER ONE
1.0 INTRODUCTION
1.1 Background of the Study
Palynofaciesen compass the total complement of acid-resistant organic matter recovered from a sediment or sedimentary rock by palynological processing techniques, using hydrochloric acid and hydrofluoric acid, as seen under a microscope. (Combaz, 1964). Powell e.t al. (1990) redefined the term as “a distinctive assemble age of palynoclasts whose composition reflects a particular sedimentary environment”. Tyson (1995), however, added that apart from reflecting a specific set of environmental conditions, it is also associated with a characteristic range. of hydrocarbon-generating potential. Other workers have referred to organic components in sediments as organic matter, palynodebris, palynomaceral, and kerogen (Mudie, 1992; Staplin, 1969; Whitaker, 1984; Boulter and Riddick, 1986; Traverse.,1988; Lorente., 1990; Tyson, 1995).
Polynofacies is the total complement of acid resistant particulate organic matter recovered from sediments by palynological processing techniques (Tyson, 1995). Tyson (1995) provided that one of the most widely use definition of the palynofacies as the total particulate organic matter assemble contained in a body of sediments is indicative of a particular type of environmental condition or is associated with a characteristic range of hydrocarbon generating potential.
According to Lucas (2017) palynofacies is a relatively new aspect of palynology; the term connotes the global microscopic image of the organic constituents of the rock after proper carrying out of maceration and mounting under standard conditions of preparation. In other words, palynofacies involves the examination of the. total acid insoluble component of the sedimentary samples (outcrops, cores or ditch cuttings) with focus on the constituent elements, their proportions, diversity of palynomorph, types, sorting and size characteristics and evidence for biological and physical degradation. Muhammed et al. (2008) reported that in source rock quality, palynofacies and the thermal history of the Niger Delta Basin will give a detailed picture of the hydrocarbon generation and the source rock potential of the basin.
Tyson (1995) classified palynofacies into phytoclasts, opaques (black debris), Amorphous organic matter (AOM) and palynomorphs. Kholeif and Mudie (2010) has extensively described the. palynofacies that include spores, pollen, dinoflagellates, acritarchs, chitinozoans, prasinophytes, foraminiferal linings and marine algae These are abundant in fine grained muds, shales, clays, and sometimes in sandstones and limestones (Mudie., 1992).
Pollen and spore assembles from superficial sediments provide useful information that can aid the proper understanding of depositional environments and stratigraphy of geologic formation. Therefore., it is a means of elucidating the environment represented by a particular lithological sequence Onoduku (2014) noted that the study of fossil remains in sedimentary succession had become a valuable tool which is universally accepted to understand the stratigraphy and source rock potential of sedimentary basins. Palynofacies study is advantageous over other fossils studies because palynofacies are widely distributed, they can be found in their terrestrial, freshwater, saltwater, or estuarine source. of sedimentary rocks.
Organic diagenesis or maturation is one of the parameters to be considered in the evaluation of hydrocarbon producing potentials of sediments. Maturation is considered to be controlled by various factors including the temperature, pressure and time, Some other parameters include geothermometry state of preservation of organic matter, vitrinite reflectance studies, organic geochemical studies, clay mineralogy and microscopic studies can be integrated to define a maturation scale or the thermal alteration index.
Thermal alteration index is established specifically relating to the physical alteration observed in the kerogens evaluated. The state of preservation of the organic matter has been used to characterize the degree of organic maturity. Additional to the alteration states of palynomorphs, the zonation has been based on the vitrinite reflectance values, clay mineralogic compositions and pyrolysis.
Tyson (1995), the main uses of palynofacies include:
i. Determining magnitude and location of terrigenous inputs (proximal-distal relationships with respect to source).
ii. Determining depositional polarity (onshore, offshore axes).
iii. Identifying relative shallowing-deepening and regressive-transgressive trends in stratigraphic sequences (and hence Sequence Tracts and Flooding Surfaces).
iv. Characterizing and to subdividing sedimentologically uniform facies, especially shales.
v. Determining hydrocarbon source rock potential and to qualify the bulk rock geochemical parameters.
vi. Estimating differences in primary productivity and water mass stratification (using absolute and relative abundance of different types of organic-walled microplankton).
vii. Discriminating among environments, for example: oxic open marine, dysoxic-anoxic marine, and brackish freshwater.
1.2 Statement of the Research Problem
An accurate. identification of thermally matured sediments/source rocks is a challenge to petroleum exploration (Okeke and Umeji, 2016).
Researchers like Inyang e.t al. (2016), Lucas (2017), Chukwuma-Orji e.t al (2017) and a lot of others have carried out researches on palynofacies and depositional environment of the. Niger Delta Basin, but did not work on thermal alteration indices of the rocks.
Few works have. been done on the use of palynomorphs to identify oil bearing zones, (Okeke and Ume.ji, 2016) more work still need to be done to provide more accurate data on the thermal alteration in identifying productivity levels of oil wells in the Niger Delta Basin. Evamy e.t al. (1987) used Alpha-numeric method to establish biozone which is not in line with the international standard. Therefore, biozone established in line with international standard is needed.
1.3 Justification for the Study
Biostratigraphy studies in the Niger Delta Basin is a very important aspect of research as regards oil exploration. Thermal alteration studies useful in delineating matured source rocks. Biozone done in line with international standard is essential in oil industry for accurate relative dating and correlation of reservoirs.
1.4 Aim
The aim of this research is to carry out palynofacies analysis of the sedimentary succession penetrated by IDM- 4 and IDM-5 wells in order to identify the palynomorph maker species and palynomacerals which would be related to palyzones and sediment maturity of the successions.
1.5 Objectives
The objectives of this research are as follows:
Establish the palynofacies associated with the strata within the field using the recovered palynomorphs and palynomacerals.
Determine the environment of deposition of the succession using the palynofacies association.
Deduct the maturity of the potential source rock intervals (shales) using palynofacies.
1.6 Scope of Work
The work covers palynofacies analysis, depositional environment and thermal maturation analyses of IDM-4 and IDM-5 wells in the Niger Delta Basin.
1.7 Location of the Study Area
The studied wells are part of the Niger Delta Basin’s Central Swamp Depobe lt (Figure 1). The Niger wells are situated in IDM field of the Niger Delta Basin. IDM 4 well is situated on latitude 04 08ˈ 02̎ N and longitude 06° 08ˈ 06 E, while IDM 5 is located within latitude 04 08ˈ 00 N and longitude 06° 07ˈ 06 E
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PALYNOFACIES ANALYSIS AND THERMAL MATURATION STUDY OF SEDIMENTS OF IDM 4 AND IDM 5 WELLS OF NIGER DELTA BASIN, NIGERIA
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