The molecular composition and geochemical applications of asphaltenes

PhD ThesisAsphaltenes are the heaviest components of petroleum and bitumen consisting of a complex mixture of heteroaromatic substances that have been associated with various deposition problems in both upstream and downstream sectors of the petroleum industry. This thesis describes characterisation of asphaltenes from a variety of sources and geographical areas using FTIR, NMR, as well as selective chemical degradation methods in combination with GC/MS & GC/IRMS with the aim of understanding how their compositions vary with source and geochemical history. Asphaltenes were observed to co-precipitate with substances such as waxes that are components of the maltene fraction. Quantitative removal of the co-precipitated substances requires Soxhlet extraction of the asphaltenes for several hours. The extraction time was found to vary with different asphaltenes. The so-called occlusion or physical entrapment of biomarkers in the cage-like structure of the asphaltenes is more than likely a consequence of the co-precipitation of the waxes. Analysis of mid-infrared spectra of the asphaltenes revealed that petroleum asphaltenes consist predominantly of aliphatic moieties bonded to condensed aromatic structures with relative proportions of aromatic carbon in range of 30 to 40% for non-biodegraded petroleum asphaltenes as revealed by 13C NMR. Biodegraded asphaltenes are less aromatic with relative aromatic carbon being 27% or less although the aromatic moieties tend to have relatively greater degree of condensation than asphaltenes from ono-degraded oils . Although n-alkyl and iso-alkyl groups are the dominant aliphatic moieties, naphthenic groups, mainly in form of homohopanoids and steroids, are significantly present. Oxygen functionalities are mainly in form of hydroxyl, ether, ester, and carboxyl as well as conjugated ketone groups. Ester groups were detected only in coal and black shale asphaltenes. Carboxyl groups were detected in all the asphaltenes irrespective of source and geographical region, although they were particularly prominent in black shale and coal asphaltenes even at a relatively high rank of Ro = 1.5%. Nitrogen functionalities were present as pyridinic and pyrrolic heteroaromatic systems in addition to tertiary aromatic amines. With increasing thermal stress, asphaltenes were observed to evolve towards an equilibrium structure or composition in which aromatic moieties become dominant over aliphatic moieties as a result of increasing condensation and dealkylation. Distribution of alkyl moieties shifts towards increasing proportions of the lower molecular weight homologues with increasing thermal maturity. The thermal stress also results in loss of oxygen functionalities mainly from ester and carboxyl groups. At the molecular level, isomerisation of bound hopanoids and steroids to form an equilibrium composition was observed with increasing maturity. However, while isomerisation of bound hopanoids in asphaltenes appear to be in phase with the corresponding isomerisation of hopanes in the maltene fraction, the isomerisation of bound steroids lags significantly behind the corresponding isomerisation of the steranes in the maltenes. There is good potential in using multivariate pattern recognition tools in oil/oil correlations based on asphaltene bulk composition as measured using FTIR. Notwithstanding some misclassification, the techniques tend to correlate asphaltenes with common source. Similarly, the aliphatic moieties of asphaltenes also reflect the organic matter sources of the asphaltenes. The n-alkyl moieties from asphaltenes with common source not only show similar distributions, but also similar δ13C trends even in asphaltenes from biodegraded oils. Likewise, bound hopanoids also reflect the organic matter source such that asphaltenes with common source show similar hopanoid distributions. The aliphatic moieties therefore have good potential that may be comparable to the conventional hydrocarbon-based biomarkers in oil/oil correlations. In general, the composition of asphaltenes is controlled by the source organic matter and its thermal evolution. The effect of biodegradation is not yet completely understood but, with the exception of steroids, it does not appear to affect the aliphatic composition of the asphaltenes. There is therefore a significant potential in using asphaltenes in discrimination/correlation of oils particularly where the hydrocarbons in the maltene fraction are lost to biodegradation.Petroleum Technology Development Fund (PTDF), Nigeri

Geochemical Investigation of Vertical Migration of Petroleum through Mudstones I: Origin of the Hydrocarbon Shows

Hydrocarbon shows and seeps are frequently associated with petroleum migration through caprocks. However, leakage of petroleum from reservoirs does not necessarily result in surface seeps, nor do all occurrences of surface petroleum result from trap leakage. Cretaceous Shetland Group mudrocks which serves as caprock (seal) for the petroleum reservoir of the Heidrun Field was observed to contain liquid hydrocarbon as evidenced from UV florescence. Is this oil indigenous of the caprock or from the underlying reservoir thereby indicating possible failure of the seal? Samples from the caprock were analysed with the aim of establishing the origin of the oil stains. The investigation comprised bulk geochemical analyses in order to estimate various leakage indicators (S1 & PI). High Extractable Organic Matter (EOM) values of up to 6 mg/g rock were obtained in most of the samples. The high S1 and PI values obtained from the samples suggest oil staining. Furthermore, Iatroscan SARA analysis was used to identify compositional variability between the oil present in the caprock and the reservoir oil. The reservoir oil predominantly consisted of saturated hydrocarbons, which, in contrast, represent only a fraction of the caprock EOM. The caprock EOM is dominated by polar compounds, and the saturate fraction increases with increasing proximity to the caprock/reservoir boundary. High gas wetness of more than 80% was recorded at caprock/reservoir boundary, suggesting a good relationship between the distribution of gaseous hydrocarbons in the caprock and the gas content of the reservoir oil. The oil stains in the caprock are therefore established to be sourced from the reservoir.Keywords: Leakage; Mudrock; Extractable organic matter; Production index; Gas wetnes

Examination of Surface Water Along River-Rima Floodplain in Wamakko, Sokoto State, Nigeria

This study examined the hydrochemistry of surface water along the River-Rima floodplain area. Five sampling locations were purposively selected, and, in each point, three samples were taken from surface water (river).The sampling was repeated after 20 days. Thus, a total of 30 samples werecollected. Water samples obtained were subjected to laboratory tests. Results revealed that BOD, TDS, Mg2+, and Fe3+ are above the World HealthOrganization (WHO) and Standard Organization of Nigeria (SON) reference guidelines for drinking water quality. Isolates detected from the coliform bacteriological analysis include Enterobacter aerogene, Escherichiacoli, and Citrobacter freundii with most of the samples showing coliform bacteria growth above the SON standard for drinking water. Hence, the water in the River-Rima floodplain of the Wamakko area is of low quality and unsafe for drinking. Results of principal component analysis (PCA)revealed external influences such as pollutant wash off and rock weatheringas controls on hydrochemistry of surface water. There is some indication of anthropogenic inputs (Cl- , NO3- , and PO4 2-) based on hierarchical cluster analysis. Elements including Cl-, NO3-, and PO42- are increasingly added into surface water from human activities, mainly agriculture, and municipal sewage

Empirical investigation of precipitation of hexadecanoic acid from toluene/brine system: Implication to naphthenic acid precipitation from crude oils

<p>Naphthenic acids, due to their tendency to precipitate out of solution when in contact with formation water, present a formidable challenge for the petroleum industry. In this study, precipitation of hexadecanoic acid from an idealized oil-water (toluene/brine) system was investigated. The FTIR results revealed that the acid was mainly precipitated as calcium hexadecanoate. Experiments designed to study the effect of water cut, acid concentration, brine concentration, and pH of the brine on the amount of the precipitate formed revealed that the amount of precipitate formed increased with increase in brine pH, concentration of the acid and calcium ions. Similar effect was observed with respect to water cut but with maximum amount of the precipitate formed at water cut of about 40%, below and above which relatively lower amount of the acid was precipitated irrespective of the levels of the other factors. In general, the observed effects of the factors suggest that precipitation of the naphthenic acid can be minimized with acidic formation water that contains relatively low concentration of calcium ions particularly when the concentration of the acid in the oil is as low as possible.</p

Effect of Soil Contamination with Crude Petroleum on Cowpea: An Insight into the Prospects of Crop Production in Nigerian Frontier Basins

Petroleum hydrocarbon contamination remains a major challenge confronting soil health, environmental sustainability, and food security in oil exploration areas. In this study, the effect of Bonny Light crude oil on cowpea (Vigna unguiculata L. Walp.) was investigated with a view to assessing its toxicity to plant growth and performance. Pristine soil samples were collected in different pots and contaminated with crude oil to achieve 0.0%, 2.5%, 5.0%, 7.5% and 10.0% v/w contamination levels. Viable seeds of cowpea were planted and monitored for the emergence and subsequent growth for a period of 12 weeks. Results showed that the crude oil extended the period of seed germination and delayed the emergence of sprouts by 2 days at a rate of 96.7%, 80.0%, 50.0%, 96.7%, and 73.3% emergence respectively. The plants’ shoots, roots, and leaves lengths were longer in control than in the contaminated soil. Phytotoxicity study showed that shoots, roots and leaves lengths of the plants were significantly reduced by ≥ 50% of the control. The relative plants' weights, chlorophyll, and the number of leaves were worst affected especially in plants grown in higher crude oil concentrations where fewer or absence of leaves was observed at the end of the experiments. No yield parameter was observed in all plants grown in contaminated soil as opposed to the control where flowers, fruits, and seeds were produced. The findings illustrated that the growth rate of V. unguiculata was severely affected due to hydrocarbon contamination in a concentration-dependent manner. It further demonstrated the imminent danger to food security especially in frontier basins with impending oil exploration activities. Therefore, there is a need to identify and integrate effective measures that minimize or prevent oil spillage in the course of oil exploration activities with a view to avoiding the repeat of persistent pollution problems disturbing host communities

Black shale deposition in an Upper Ordovician–Silurian permanently stratified, peri-glacial basin, southern Jordan

The Lower Palaeozoic (Upper Ordovician-Silurian) succession of North Africa contains one of the world's most prolific black shale source rocks, yet the origin of these rocks remains contentious. The black shale of the Batra Formation in Jordan was deposited at high palaeolatitude during rapid Hirnantian to early Silurian deglaciation. Here we report geological and organic geochemical results that provide evidence for an increase in photic zone primary productivity during ice melting. The decay of this organic matter through oxidative respiration resulted in euxinia, which enhanced the potential for organic matter preservation. The occurrence of isorenieratane in all samples indicates euxinia extended from the photic zone to the sediment water interface. The stratified basins and fjords of east Antarctica provide a likely modern analogue