A. Akinlua

Microwave-assisted nonionic surfactant extraction of aliphatic hydrocarbons from petroleum source rock.

The extraction of aliphatic hydrocarbons from petroleum source rock using nonionic surfactants with the assistance of microwave was investigated and the conditions for maximum yield were determined. The results showed that the extraction temperatures and kinetic rates have significant effects on extraction yields of aliphatic hydrocarbons. The optimum temperature for microwave-assisted nonionic surfactant extraction of aliphatic hydrocarbons from petroleum source rock was 105°C. The optimum extraction time for the aliphatic hydrocarbons was at 50 min. Concentration of the nonionic surfactant solution and irradiation power had significant effect on the yields of aliphatic hydrocarbons. The yields of the analytes were much higher using microwave assisted nonionic surfactant extraction than with Soxhlet extraction. The recoveries of the n-alkanes and acyclic isoprenoid hydrocarbons for GC-MS analysis from the extractant nonionic surfactant solution by in-tube extraction (ITEX 2) with a TENAX TA adsorbent were found to be efficient. The results show that microwave-assisted nonionic surfactant extraction (MANSE) is a good and efficient green analytical preparatory technique for geochemical evaluation of petroleum source rock.

Determination of Selected Metals in Niger Delta Oils by Graphite Furnace Atomic Absorption Spectrometry

Abstract Graphite furnace atomic absorption spectroscopic (GFAAS) analysis of oil samples from the onshore and offshore fields in the Niger Delta was carried out in order to determine their trace element contents. The concentrations of the elements (Cr, Co, Cu, Fe, Mn, Ni, Pb, and V) determined ranged from 0.151–941.199 ppb with an average of 30.190 ppb (% RSD<5) for the oil samples analyzed. The pattern of occurrence of each element was in agreement with studies conducted employing neutron activation analysis and flame atomic absorption spectroscopy. From the cluster analysis of the data, two groups of oils were evident. The groups are correlated with each other, indicating common or similar genetic origin. Trace metal parameters indicate that the oils were generated from organic matter of strong terrestrial input. GFAAS proved to be a good method for the analysis of elemental composition and classification of Niger Delta oils. A. Akinlua is on a postdoctoral research visit from the Department of Chemistry, Obafemi Awolowo University, Ile‐Ife, Nigeria.

Subcritical water extraction of trace metals from petroleum source rock

The extraction of trace metals from petroleum source rock by superheated water was investigated and the conditions for maximum yield were determined. The results showed that no significant extraction was attained at 100 degrees C but the extraction was enhanced at higher temperatures. The optimum temperature for superheated water extraction of the metals from petroleum source rocks was 250 degrees C. Extraction yields increased with enhanced extraction time. Exhaustive extraction time for all the trace metals determined in this study was attained at 30min. Comparison of results of leaching these trace metals by superheated water with those of acid digestion revealed that cadmium, chromium, manganese and nickel had better yields with superheated water while vanadium had better yield with acid digestion. The results showed that the temperature and kinetic rates have significant effects on superheated water extraction of metals from petroleum source rocks. The results also revealed that effective leaching of some metals from petroleum source rocks by superheated water can be achieved without any modification except for vanadium.

Source rock potential of selected Cretaceous shales, Orange Basin, South Africa

Twenty Cretaceous shale samples from two wells in the Orange Basin of South Africa were evaluated for their source rock potential. They were sampled from within a 1400 m-thick sequence in boreholes drilled through Lower to Upper Cretaceous sediments. The samples exhibit total organic carbon (TOC) content of 1.06–2.17%; Rock-Eval S2 values of 0.08–2.27 mg HC/g; and petroleum source potential (SP), which is the sum of S1 and S2, of 0.10–2.61 mg HC/g, all indicating the presence of poor to fair hydrocarbon generative potential. Hydrogen index (HI) values vary from 7 to 128 mg HC/g organic carbon and oxygen index (OI) ranges from 37 to 195 mg CO2/g organic carbon, indicating predominantly Type III kerogen with perhaps minor amounts of Type IV kerogen. The maturity of the samples, as indicated by T max values of 428–446°C, ranges from immature to thermally mature with respect to oil generation. Measured vitrinite reflectance values (%Ro) of representative samples indicate that these samples vary from immature to mature, consistent with the thermal alteration index (TAI) (spore colour) and fluorescence data for these samples. Organic petrographic analysis also shows that amorphous organic matter is dominant in these samples. Framboidal pyrite is abundant and may be indicative of a marine influence during deposition. Although our Rock-Eval pyrolysis data indicate that gas-prone source rocks are prevalent in this part of the Orange Basin, the geochemical characteristics of samples from an Aptian unit at 3318 m in one of the wells suggest that better quality source rocks may exist deeper, in more distal depositional parts of the basin.

A new approach to sample preparation for the determination of trace metals in petroleum source rocks

The dissolution and extraction of petroleum source rocks using a nonionic surfactant to determine their trace metal (V, Ni, Co, Mn, and Mo) content with the assistance of microwave irradiation were investigated and the conditions for obtaining the optimum yield were determined. A complementary microwave-assisted acid dissolution method was also optimized. The results showed that the temperature and time have significant effects on yields of the trace metals. Factors such as surfactant concentration and sample/solvent ratio had little influence on the digestion and extraction efficiencies for these metals. The optimum temperature for microwave-assisted nonionic surfactant dissolution of petroleum source rocks for trace metal determination was 200 °C and the best yields of the metals were obtained in 40 min. The optimum temperature and time for nonionic surfactant extraction of trace metals from petroleum source rocks were 90 °C and 45 min, respectively. The microwave-assisted acid digestion gave optimum yields of the trace metals in 70 min. The new nonionic surfactant digestion and extraction methods showed efficiencies comparable to those afforded by using the acid digestion method for three out of five elements determined in this study, although the recoveries of vanadium and manganese were relatively low, but the reduction of the digestion/extraction time and environmentally friendliness of the new nonionic surfactant based methods are clear advantages. The new method showed a very good reproducibility. The results of this study also show that the microwave-assisted nonionic surfactant digestion method is a good, efficient and better alternative green analytical preparatory technique for the determination of some trace metals in petroleum source rocks.

Light hydrocarbon geochemistry of crude oils from Eastern Niger Delta

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.

Rare earth and trace element geochemistry of Cretaceous kerogens

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.

Geochemistry, heavy mineral and sedimentological analyses of potential reservoir sand samples from Kolmani River-1 well, Northern Benue Trough, Nigeria

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 2414 m and 2785 m. 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 (135–1629 ppm) and Zn (233–1411 ppm) 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.

Natural radionuclides in Niger delta sedimentary organic rock samples

Thirty sedimentary organic rock samples were collected at different depths from three oil wells in the Niger Delta. The natural radionuclides in the samples were measured in order to determine their geochemical significance and radiological effect. The radionuclides were measured using gamma spectrometric technique. Natural occurring radionuclides identified were uranium, thorium and potassium. The average activity concentrations obtained were 2441.65±753.00, 28.31±8.83 and 14.49±4.46 Bq/kg for 40K, 232Th and 238U, respectively. The equivalent doses calculated from activity concentrations of the radionuclides ranged from 0.69–1.25, 0.89–1.18, and 1.19–1.38 mSv/year for Meji, Malu and Mefa oil wells, respectively. These values are slightly higher than the normal background radiation value of 1 mSv/year. The background radiation of 40K detected in these samples was high, the absorbed dose rate and equivalent dose was slightly high, which could pose intrinsically radiological health hazard because of their cumulative radiological effect in the environment.

The role of analytical chemistry in Niger Delta petroleum exploration: A review

Petroleum and organic matter from which the petroleum is derived are composed of organic compounds with some trace elements. These compounds give an insight into the origin, thermal maturity and paleoenvironmental history of petroleum, which are essential elements in petroleum exploration. The main tool to acquire the geochemical data is analytical techniques. Due to progress in the development of new analytical techniques, many hitherto petroleum exploration problems have been resolved. Analytical chemistry has played a significant role in the development of petroleum resources of Niger Delta. Various analytical techniques that have aided the success of petroleum exploration in the Niger Delta are discussed. The analytical techniques that have helped to understand the petroleum system of the basin are also described. Recent and emerging analytical methodologies including green analytical methods as applicable to petroleum exploration particularly Niger Delta petroleum province are discussed in this paper. Analytical chemistry is an invaluable tool in finding the Niger Delta oils.