The distribution pattern and occurrence of aromatic hydrocarbons as influenced by thermal maturity and the nature of Aptian to Campanian source rocks from the Orange Basin were investigated to gain more understanding of the petroleum generation and accumulation potential of the basin. Gas chromatography- mass spectrometry was used to determine the aromatic hydrocarbon content of rock extracts. The aromatic hydrocarbon composition showed abundant alkylated aromatic hydrocarbons. The most abundant of the naphthalene series is trimethylnaphthalene, and the most abundant of the phenanthrenes is methylphenanthrene. The distribution of the aromatic hydrocarbons across the seven wells investigated in this basin revealed that the naphthalenes are relatively more abundant than the phenanthrenes. Both the naphthalene and the phenanthrene distribution patterns are strongly controlled by thermal maturity of the organic matter. The type of organic matter and age of the rock also have a significant impact on the distribution and abundance of the aromatic hydrocarbons. The distribution of both naphthalenes and phenanthrenes indicates strong input of marine organic matter. The rock samples have enhanced concentrations of 1,2,5-trimethylnaphthalene compared with 1,2,7-trimethylnaphthlene, which is a typical characteristic of mature rocks. The values of methylnaphthalene ratio and dimethylnaphthalene ratio of the rock samples from the seven wells investigated revealed that Coniacian, Albian, and Aptian source rocks are more thermally mature than other source rocks in this basin that are not of these ages. Phenanthrene thermal maturity indices indicate that Turonian source rocks are the least thermally mature, whereas Santonian, Coniacian, Albian, and Aptian source rocks have a relatively higher thermal maturity. The effect of burial depth on thermal maturity of the source rocks appears to be more significant than the age of the rocks.

A new green method for extraction of carbazoles from petroleum source rocks was developed using surfactant solution. A three-level full factorial design of experiment (DoE) which involved extraction temperature, extraction time and concentration of surfactant solution led to the development of a new extraction method avoiding organic solvents. All carbazoles extraction experiments were carried out with the assistance of a microwave oven. The carbazoles in the surfactant extracts were determined by high performance liquid chromatography-mass spectrometry (HPLC-MS). The results showed that temperature, time and concentration of surfactant solution have significant influence on the extraction yields of the carbazoles. The highest extraction yields for most of the carbazoles were obtained at the optimal conditions of extraction temperature of 110 degrees C, extraction time of 25 min and surfactant concentration of 0.02 M. In comparison with a fast organic solvent-based extraction method (accelerated solvent extraction, ASE) the microwave assisted surfactant extraction (MASE) method was more efficient with a very good reproducibility.

Petroleum geochemistry of oils in several depobelts of the world has been well documented based on biomarkers. However, there is paucity of data regarding the use of multi-variate statistics in oil-oil correlation study, particularly in the Sub-Saharan African region. The purpose of the study was to gain an insight into the geochemical differences and identify their cause(s) through the application of bulk properties, biomarker indices and multi-variate statistics. Correlation of oils from eight wellheads of three stratigraphic units within the Central and Eastern onshore Niger Delta Basin fields (AG and AS) were undertaken by gas chromatography-flame ionization detector. Utilization of bulk properties, biomarker indices and cross plot parameters somewhat separated the mature AG1-4, AS3 and AS4 oils deposited in oxic/suboxicshaly environment from AS2 oil deposited in anoxic fluvio deltaic environment. In-reservoir alteration and migration differences were the major factors responsible for the observed slight geochemical variability in the studied oils. Nevertheless, multi-variate principal component analysis indicated that the Central and Eastern onshore Niger Delta Basin oils were principally generated from similar organic matter sources. The implication here was that the geochemical variations in the studied oils were not significant, a conclusion corroborated by Pearson correlation model data.

The influence of origin, depositional environment and thermal maturity of organic matter on the occurrence of aromatic hydrocarbons in source rocks from the central and northwestern Niger Delta was investigated. Eighty two source rock samples from four oil wells in the central and northwestern Niger Delta were analyzed for the aromatic hydrocarbon content using gas chromatography-mass spectrometry (GC-MS). The results of analysis of aromatic hydrocarbon fractions of the source rock extracts show the presence of many classes of aromatic hydrocarbons, which include naphthalenes, phenanthrenes, biphenyls, dibenzothiophenes and fluorenes. Trimethylnaphthalene (TMN) is the most abundant among the naphthalenes while dimethylphenanthrene (DMP) is the most abundant among the phenanthrenes. Among the biphenyls, 3-methylbiphenyl (3 MB) is the most abundant while 4-methyldibenzothiophene (4MDBT) is the most abundant among the dibenzothiphenes. Only two fluorenes were detected, and fluorene is more in abundance than 1-methylfluorene (1 MF). Depositional environment indicators of aromatic hydrocarbon organic matter reveal that the organic materials in the source rocks in these wells were deposited in marine-to-swamp depositional environments under reducing to suboxic conditions. Thermal maturity indicators calculated from the abundance of the aromatic hydrocarbons indicate that the source rock samples are thermally mature. Most of the source rocks are at the peak of oil window while a few at the early oil window. Source rocks from wells GB, OP and OT in the central Niger Delta are thermally more mature than those from well AW in the northwestern Niger Delta.

Abstract The extraction of trace metals (manganese, nickel, vanadium and molybdenum) from petroleum source rock using nonionic surfactant solutions with the assistance of oven heat was investigated. The results revealed that time, temperature and pH have significant influence on the extraction yields of the trace metals. The effect of sample/solvent ratio was significant for extraction of some trace metals. The optimum extraction temperature using both polyoxyethylene(23)dodecyl ether (Brij 35) and polyoxyethylene(10)dodecyl ether C12E10) solutions as extracting solvents was 150°C except nickel that had highest yield at 90°C when C12E10 solution was used. For both Brij 35 and C12E10, most of the trace metals had highest yields at 3 hr. The yields of the trace metals were more significant in acidic medium. The yields of the trace metals were significantly higher using Brij 35 than C12E10. Validation of the new oven-assisted nonionic surfactant extraction (OANSE) method using SGR-1b standard reference material revealed excellent recoveries for the trace metals except vanadium that had an average recovery, which indicates that the new method is very efficient for leaching of manganese (Mn), nickel (Ni) and molybdenum (Mo) from petroleum source rock while the recovery of vanadium can be improved in acidic medium. This study revealed that OANSE is efficient and readily available green analytical protocol for the determination of trace metals in source rock.

Trace elements characterization of selected tar sand samples from tar sand belt of southwestern Nigeria was carried out. This was done in order to determine the origin, depositional environment of organic matter from which the hydrocarbons in the tar sands were derived and thermal maturity of the sediments. Nineteen tar sand samples were collected from different locations in Ondo and Ogun States section of the Benin (Dahomey) Basin. The tar sand samples were extracted with dichloromethane. The extract was digested with concentrated sulphuric acid, concentrated nitric acid and hydrogen peroxide. The trace elements in the digested samples were determined using the inductively coupled plasma mass spectrometry (ICP-MS). The average concentrations of the trace elements in the tar sand samples varied from 13.25 to 529.4 ppm. Cr is the most abundant element followed by Ni, Cu, Fe, Mn, Co, Mo and V. The values of Co/Ni, V/Ni and V/(Ni+V) ratios suggest terrestrial organic matter input. The concentrations of redox-sensitive elements, V, Ni, Cu, Cr, Fe, Co, Mo, Mn and V/Ni, V/(V+Ni) and V/Cr ratios in the samples suggested that the organic materials were deposited under oxic conditions. Co/Ni and V/Ni values indicated that organic materials are thermally mature. Fe/V showed decrease concentration with increasing thermal maturity of the organic matter. The study demonstrated that the hydrocarbons in the studied tar sand samples were derived from thermally mature organic matter of mainly terrestrial origin and were deposited under oxic conditions.

Investigation on the use of diamondoids to assess the extent of thermal maturity, depositional environment, and origin of Niger Delta source rocks was carried out. This was done to evaluate the significant of diamondoids in petroleum exploration in the basin. Pulverized rock samples selected from four Niger Delta oil wells, were extracted with Soxhlet extraction technique. The biomarkers content of saturated hydrocarbons fraction was assayed by gas chromatography-mass spectrometry (GC-MS) while the diamondoids content was analyzed using GC-MS-MS. The distribution of saturated hydrocarbons; n-alkanes, pristane, pyhtane, steranes, and terpanes revealed that samples from well AW were sourced from mixed terrestrial/marine organic matter while samples from wells OP, GB, and OT were sourced largely from terrestrial organic matter origin. The Pr/Ph ratio values indicated that the organic matter of wells AW and OP samples were deposited under suboxic conditions while those of wells GB and OT were deposited under anoxic conditions. Hopane and sterane thermal maturity geochemical parameters showed that the organic matter in source rocks from the four wells are thermally mature. Diamondoids source parameters indicated that well AW source rock samples had mixed marine/terrestrial organic matter input, while samples from wells OP, GB, OT were sourced from terrestrial organic matter, which is in perfect agreement with the results of other source geochemical parameters, thus indicating that diamondoids are good tools in determining the origin of petroleum. Diamondoid maturity parameters showed that all the samples from the four wells are thermally mature with maturity level ranging from early to main oil window. This study revealed that diamondoids can be used to evaluate petroleum occurrence in the study area or any other sedimentary basins.

Crude oil and produced water samples obtained from ten wells in an offshore field, Niger Delta, were analyzed, in order to determine the occurrence of naphthenates deposition in the field. Total acid number (TAN) and °API of the crude oil samples, pH and metal ions concentrations of the produced water samples were determined. The results revealed that TAN values ranged from 0.47 to 1.01 mgKOH/g with pH of 6.9–8.9, which were above established threshold. The metal ions concentrations especially for Ca++ and Na+ were relatively high. These imply a high possibility of metal-naphthenate precipitation in the oil production facilities in this field.

Gombe Formation is one of the promising potential source-rock of petroleum in the Gongola basin based on its appreciable amount of organic matter. The present study is therefore aimed at evaluating the hydrocarbon potential of Gombe Formation. Ditch-cutting samples were collected from the depth of 731.5 m to 1554.5 m from Gombe Formation that penetrated the Kolmani River-1 well. The source-rock potential was evaluated based on kerogen analysis and soluble organic matter content using Fourier Transform- Infra red spectroscopic (FT-IR) and Gas chromatography-Mass spectrometric (GC-MS) techniques respectively. There is presence of peak at 900-1000 cm-1 which is due to CH2 rocking vibration in long chain aliphatic substances, which is characteristic of liptinite macerals indicating good potential source-rock for oil and gas. The n-alkane ranges from C11-C33 maximizing at nC16 which suggests that the organic matter are majorly derived from marine organic matter. The Pr/Ph (1.49-1.92) shows that the organic matter was deposited under sub-oxic condition. The distribution of hopanes, homohopanes (C27-C29) steranes, (C0-C4) alkylated naphthalenes and (C0-C3) alkylated phenanthrenes indicate the presence of angiosperm, gymnosperm, algae, marine and bacteria input to the organic matter contained in the samples. Also the plot of DBT/P vs. Pr/Ph classifies the samples into zone 3 (i.e. marine shale and other lacustrine). Various maturity parameters computed from saturate biomarker and polycyclic aromatic hydrocarbon distributions shows that the samples are low mature with the moderately mature zone at the bottom (>1408.2 m) of Gombe Formation. In conclusion, the kerogen was probably derived from type II/III organic matter capable of generating both oil and gas and the moderately mature zone lies at the bottom of the Formation. Key words: Lacustrine, Gombe formation, Maturity, Hydrocarbon, Kerogen

Extraction of adamantanes and diamantanes from petroleum source rock using nonionic surfactant was investigated and the optimum conditions for yields of the diamondoids were determined. The conventionally used accelerated solvent extraction method was compared to an innovative microwave-assisted nonionic surfactant extraction (MANSE). A three-level full factorial design of experiment (DoE) was adopted for the optimization of MANSE, involving solvent concentration, extraction temperature as well as extraction time. In-tube extraction (ITEX-2) using TENAX TA as sorbent in combination with gas chromatography-mass spectrometry (GC-MS) was used to determine the diamondoids in the extract. The results revealed that solvent concentration, extraction temperature and time have significant effects on extraction yields of the diamondoids. 0.04 M was the optimum surfactant concentration for extraction of both, adamantane and diamantane. The highest yields of the diamondoids were obtained at extraction temperature of 80 °C. The optimum extraction time for both adamantane and diamantane was 10 min. In comparison with the accelerated solvent extraction method, the results showed that MANSE is more efficient. This study has revealed that MANSE is a robust and efficient environmentally benign sample preparation method for geochemical evaluation of petroleum source rock.

Forty ditch cutting samples were worked on, twenty each for trace elements and sedimentological analyses. A few of these samples were selected for the analysis of heavy minerals within the Bima sandstone and shale sandstone units. The samples were obtained from Shell Nigeria Exploration and Production Company from a depth of between 2414m and 2785m. The results showed high concentration values of Ca and K which indicate a low degree of weathering in the source area of the material forming the reservoir rock. A high concentration of Fe and Ti implies the presence of Fe and Ti bearing minerals in the source materials, and the abundance of metals like Cu (135-1629ppm) and Zn (233-1411ppm) implied a fine grain size for the sediments as this supports metal absorptivity. The probability curves indicate that the sediments were transported by saltation and suspension in shallow marine environment. The heavy mineral assemblage indicates that the sediments were mineralogically mature and suggest igneous and metamorphic sources. The sorting pattern shows that the distance of transport of materials was intermediate to far from their source. The reservoir rock of Bima Formation shows evidence of having fair to good potential and can hence hold fluids if other petroleum systems are in place.

Particle-induced x-ray emission (PIXE) spectroscopy has been used to characterize soil samples from two relatively old gold mine sites (Iperindo and Itagunmodi) in the Ilesha schist belt of Southwestern Nigeria. This is with a view to identifying the indicator or pathfinder elements of gold for fingerprinting and toxicity potential assessment purposes. Average elemental concentrations of 19 major, minor, and trace elements were determined, and the geochemical data of Mn, Ni, Cu, Zn, Ag, As, Pb, and Au together with multivariate factor and cluster statistical analyses allowed to identify As and Ag as the pathfinder elements of gold. The high concentration of the determined pathfinder elements (As and Ag) as well as other toxic metals (Pb and Cu) implies a relatively high metal contamination risk to the miners and the ecosystem. The major hazard is represented by the abandoned mining wastes, pits, and ponds, already serving as fish ponds.

Trace elements in kerogens isolated from shale samples obtained from oil wells in the central Niger Delta were determined using atomic absorption spectrometry, with the aim to determine the depositional environment and source of the organic matter. The results showed that the concentrations of the elements in the kerogens ranged from 1.50 to 6470.00 ppm and 3.50 to 7946.00 ppm for Wells X and Y, respectively. In both wells, Fe was the most abundant element, while cobalt had the least concentration. Nickel had an enhanced concentration over vanadium in Well X, while the reversed was the case in Well Y. The distribution patterns of the trace elements indicate that most of the kerogens from the two wells have similar origin. The geochemical ratios calculated from the concentrations of the trace elements revealed kerogens from Well X have terrestrial organic matter input, while kerogens from Well Y have both mixed marine/terrestrial organic matter and terrestrial inputs. The concentrations of the trace elements also revealed that the organic materials of samples from Well X were deposited under oxic conditions, while those from Well Y were deposited under oxic–suboxic conditions.

The relationship between rare earth elements (REEs) and the age of Cretaceous kerogens or petroleum source rocks is not known. In this study, kerogen samples isolated from petroleum source rocks from the Cretaceous Orange Basin, South Africa were analyzed for rare earth elements (REEs) and trace elements using inductively coupled plasma-mass spectrometry (ICP-MS). The rare earth elements were profiled in order to determine their relationship to the origin, depositional environment, and age of petroleum source rocks. Most of the rare earth elements identified are of the light REEs series (La, Ce, Pr, Nd, Sm, and Eu) while the trace elements (V, Ni, Mo, and Co) determined are those that are known to have influence on the origin and depositional environment. The results show that the kerogens are mainly of marine origin. The ratios calculated from the concentrations of the elements were able to discriminate marine organic matter from lacustrine organic matter, and also indicate that the organic matter was deposited under anoxic conditions. All the kerogen samples irrespective of the age have similar elemental distribution pattern, indicating a similar genetic origin that could be a reflection of similar organic matter input and depositional environment. The kerogen age has a significant effect on the concentration of the REEs; concentrations of the REEs increase with age. That is, the older the kerogen the greater the content of rare earth elements. Furthermore, the abundance of cerium may be a good indicator of the origin of organic matter. The study also showed that the REEs provide a unique geochemical signature of the kerogens, which can be used for fingerprinting petroleum source rocks.

Abstract Geochemical evaluation of oil samples from the eastern part of the Niger Delta divided into western, eastern, and central sections of the study area was carried out for the characterization of their light hydrocarbons content in order to correlate oils from different parts. The hydrocarbons in the oil samples were determined using gas chromatographic (GC) technique. The results obtained showed that CPI, Pr/Ph, Pr/nC17, and Ph/nC18 ratios ranged from 0.99–1.55, 2.19–4.79, 0.92–2.35, and 0.27–0.47, respectively. The Pr/nC17 versus Ph/nC18 plot showed that the oils were derived from terrestrial organic materials that were deposited under oxic to suboxic conditions. They are moderately matured with minimal effect of biodegradation on most of the oil samples although two of the oils showed relatively higher degradation. Both bivariate and multivariate plots of the light hydrocarbon ratios differentiated the western and central oils from the eastern oils. The classification of the oils into families was not based on origin but rather on post generative alterations that include reservoir conditions and possibly migration effects. The light hydrocarbon parameters identified can be used in the correlation tools.

This distribution of tricyclic terpanes in source rocks from the northwestern and central Niger Delta was used to evaluate their origin, depositional environment and thermal maturity. The rock samples were extracted using Soxhlet extraction method and the saturated hydrocarbon fraction was analysed for biomarkers using gas chromatography-mass spectrometry (GC-MS). The values of soluble organic matter (SOM) and total hydrocarbons for wells AW and OP source rock samples exceeded the minimum 500 ppm and 300 ppm, respectively with values indicating very good to excellent potential source rocks. The tricyclic terpane source parameters and the complementary distribution of hopanes, regular C27-C29 steranes, n-alkanes and acyclic isoprenoid hydrocarbons showed that samples from well AW consist of mixed marine/terrestrial organic matter while those from well OP consist of organic matter largely from terrestrial origin. The values of Pr/Ph ratio for source rock samples from wells AW and OP indicate deposition of the organic matter under suboxic conditions. Sterane and hopane biomarker maturity parameters indicated that the source rock samples from wells AW and OP are at onset of oil generation and main oil window, Most of the source rock samples from well AW are more thermally mature than those from well OP. The results of tricyclic terpane maturity parameters indicated low thermal maturity for the rock samples from both wells with samples from well AW more thermally mature than those from well OP.

A total of 17 crude oil samples from producing wells in the eastern Niger Delta were analyzed for their thermal maturity status. The study is aimed at establishing maturity trends across the area and identifying maturity parameters that can be reliably used for maturity assessment of the area. On the basis of the geography, the study area has been subdivided into eastern, western, and central areas. The oils were analyzed using gas chromatography (GC) and gas chromatographymass spectrometry (GCMS). The results showed that the pristane/phytane (Pr/Ph) ratio ranges from 2.3 to 5.1, which indicates that the oils were derived from mixed terrigenous/marine organic matter. The sterane and hopane results based on thermal maturity parameters were unreliable for oil maturity assessment. Aromatic maturity parameters worked better for thermal maturity assessment of the oil samples analyzed. The conclusion was based on the plots of 4-methyl dibenzothiophene/1-methyl dibenzothiophene (MDR), C-27 17 alpha (H)/C-27 18 alpha (H) (Tm/Ts), methyl phenanthrene ratio (MPR), monoaromatic steroid C-21/triaromatic steroid C-21 + monoaromatic steroid C-28 (MAC(21)/TAC(21) + MAC(28)), and 20S/(20S + 20R)C-27 maturity parameters, which are in good agreement with regard to the maturity status of the oils analyzed and are, therefore, suitable for use in the thermal maturity assessment of oils in the study area. Maturity of the oils is found to increase from the east to west area.