High Total Organic Content Research Articles

Characterization of carbonate mudrocks of the Jurassic Tuwaiq Mountain Formation, Jafurah basin, Saudi Arabia: Implications for unconventional reservoir potential evaluation

Organically rich mud rocks are currently targeted for unconventional oil and gas exploration and development in many places around the world, including Saudi Arabia. The Jurassic Tuwaiq Mountain Formation in the Jafurah basin, located east of the giant Ghawar oil field is the primary focus of this paper. The formation has been divided into 3 Tiers possessing varying reservoir qualities. Of these Tiers, the bottom Tier 1 possesses the most excellent shale gas characteristics such as high total organic content (TOC), low clay content and high hydrocarbon saturation. The formation of interest is also in the proper maturity window for hydrocarbon generation and relatively shallow, making it attractive for an economic unconventional shale gas play. To expedite shale gas development in Saudi Arabia, a phased de-risking strategy has been implemented. The strategy consists of four phases; exploration, appraisal, pilot and development. Three wells, representing the first unconventional reservoir exploration wells drilled in the Jafurah basin have been selected for this study. The wells were drilled vertically, cored and logged. Wells were then sidetracked with 5000 ft horizontal laterals and stimulated through multistage hydraulic fracturing. All stimulated wells flowed gas and condensate to surface. This paper summarizes, with examples, a workflow for characterizing the Tuwaiq Mountain Formation as a potential unconventional liquid rich gas play. Crucial to this, is the development of a reservoir quality predictive model for acreage grading, sweet spot identification and fracturing stage selection. This methodical approach is applicable to the evaluation of any emerging unconventional play.

The lithofacies and reservoir characteristics of the Upper Ordovician and Lower Silurian black shale in the Southern Sichuan Basin and its periphery, China

The black shale of the Upper Ordovician and Lower Silurian is a significant target for shale gas exploration in the Southern Sichuan Basin. In this study, we introduced a lithofacies classification for shale based on rock mineral composition. Because the pore structure of gas shale reservoirs are complex and greatly affect the gas storage and transport in shale, four different methods of low-pressure nitrogen gas adsorption, high-pressure mercury intrusion, scanning electron microscopy (SEM) and gas expansion methods were used to investigate the reservoir pore structure and storage space. Combined with X-ray diffraction, total organic matter content (TOC), gas content, methane adsorption, porosity and permeability and wireline data, the key factors that affect shale gas content and storage of shale gas were analyzed.According to our shale classification, three main lithofacies, i.e., calcareous mudstone (CM), high calcareous mixed mudstone (HCMM) and low calcareous mixed mudstone (LCMM), were identified in our study area. The experiment indicates that the shale has a high TOC, thermal maturity and gas content. The methane adsorption isotherms show that the sorbed gas content has a positive correlation with TOC. Difference of TOC between the three is small. Nitrogen adsorption indicates that mesopores dominate the shale pore composition and organic matter is the main source of mesopores. Mercury injection shows that the macropore volume accounts for approximately 14–22% of the total pore volume. No obvious pore structure differences were found for different lithofacies. However, taking the porosity into consideration, LCMM has the largest macropore volume. The SEM observations revealed that organic matter pores, interparticle pores and intraparticle pores are the main pore types. Interparticle pores mainly develop in LCMM which has a relatively high quartz and low carbonate content, it may be the major reason for high porosity, high macropore volume, and high free gas content of LCMM. Free gas and absorbed gas are the major storage form of shale gas. Given similar temperature and pressure conditions, the total organic matter content is the major factor that affects the adsorbed gas content. Therefore, with high free gas and adsorbed gas content, LCMMs with high total organic matter contents would be the most favorable type of lithofacies in this region.

Next steps to crack the code on tight Permian Toolachee and Patchawarra sandstones of the Cooper Basin, southwest Queensland

Historic wells drilled by Real Energy Corporation Limited (Real Energy) in the Windorah Trough (Cooper Basin, southwest Queensland) characterised the Toolachee and Patchawarra formations as being gas-charged, tight-gas, sandstone/lacustrine shale sequences having layers of coaly source rock with high total organic content and moderate hydrocarbon indices. Consistent with being tight-gas reservoirs, drill stem tests have mostly either failed to produce gas or resulted in non-commercial flow rates. To date, North American methodologies for tight and shale gas extraction have not been consistently successful when applied in non-normal stress regimes outside of North America (i.e. Cooper Basin, China, Poland, Middle East, etc). Real Energy anticipated that North American technologies and practices were not likely to be directly applicable, as noted by published case studies for Australian shale gas wells (Johnson and Greenstreet, 2003; Pitkin et al, 2012; Scott et al, 2013; Johnson et al, 2015). Thus, it became an imperative to evaluate any methodologies or technologies more applicable for the Australian strike-slip to transpressional stress regimes to prevent fracture misalignment or disorientation, effects that result in ineffective fracture stimulation. Overall, a more scientific approach must be applied to developing and understanding the most efficient reservoir stimulation processes (e.g. drilling techniques, rock mechanical properties determination, well azimuth, perforating schema, and well interval selection) to optimise the stimulated reservoir volume (SRV). In this extended abstract the authors take the first steps at defining the stimulation strategies required for these tight sandstones using data and results from two case study wells. The authors outline the well observations and report key lessons in a cooperative spirit to solicit industry feedback and further technologies that can aid development of fit-for-purpose technologies to facilitate extraction of these largely untapped resources across the undeveloped troughs and flanks of the Cooper Basin.

The Slottsmøya marine reptile Lagerstätte : depositional environments, taphonomy and diagenesis

Abstract The Late Jurassic Slottsmøya Member Lagerstätte on Spitsbergen offers a unique opportunity to study the relationships between vertebrate fossil preservation, invertebrate occurrences and depositional environment. In this study, 21 plesiosaurian and 17 ichthyosaur specimens are described with respect to articulation, landing mode, preservation, and possible predation and scavenging. The stratigraphic distribution of marine reptiles in the Slottsmøya Member is analysed, and a correlation between high total organic content, low oxygen levels, few benthic invertebrates and optimal reptile preservation is observed. A new model for 3D preservation of vertebrates in highly compacted organic shales is explained. Supplementary material: A taphonomic description of each marine reptile specimen is available at https://doi.org/10.6084/m9.figshare.c.2133549

Hydrocarbon generation and expulsion characteristics of Lower Permian P1f source rocks in the Fengcheng area, northwest margin, Junggar Basin, NW China: implications for tight oil accumulation potential assessment

AbstractCombined with the actual geological settings, tight oil is the oil that occurs in shale or tight reservoirs, which has permeability less than 1 mD and is interbedded with or close to shale, including tight dolomitic oil and shale oil. The Fengcheng area (FA), at the northwest margin of the Junggar Basin, northwest China, has made significant progress in the tight oil exploration of the Fengcheng (P1f) Formation recently, which indicates that the tight oil resources have good exploration prospects. Whereas the lack of recognition of hydrocarbon generation and expulsion characteristics of Permian P1f source rocks results in the misunderstanding of tight oil resource potential. Based on the comprehensive analysis of geological and geochemical characteristics of wells, seismic inversion, sedimentary facies, tectonic burial depth, etc., the characteristics of P1f source rocks were investigated, and the horizontal distributions of the following aspects were predicted: the thickness of source rocks, abundance and type of organic matter. And on this basis, an improved hydrocarbon generation potential methodology together with basin simulation techniques was applied to unravel the petroleum generation and expulsion characteristics of P1f source rocks in FA. Results show that the P1f source rocks distribute widely (up to 2039 km2), are thick (up to 260 m), have high total organic content (TOC, ranging from 0.15 to 4 wt%), are dominated by type II kerogen and have entered into low mature–mature stage. The modeling results indicate that the source rocks reached hydrocarbon generation threshold and hydrocarbon expulsion threshold at 0.5% Ro and 0.85% Ro and the comprehensive hydrocarbon expulsion efficiency was about 46%. The amount of generation and expulsion from the P1f source rocks was 31.85 × 108 and 15.31 × 108 t, respectively, with a residual amount of 16.54 × 108 t within the source rocks. Volumetrically, the geological resource of shale oil is up to 15.65 × 108 t. Small differences between the amounts calculated by the volumetric method compared with that by hydrocarbon generation potential methodology may be due to other oil accumulations present within interbedded sands associated with the oil shales. Copyright © 2015 John Wiley & Sons, Ltd.

Proppant Fracture for Unconventional Carbonate Source Rock in Saudi Arabia

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper IPTC 17765, “First Successful Proppant Fracture for Unconventional Carbonate Source Rock in Saudi Arabia,” by Nayef Ibrahim Al-Mulhim, SPE, Ali Hussein Al-Saihati, SPE, Ahmed M. Hakami, SPE, Moataz Al-Harbi, SPE, and Khalid Saeed Asiri, SPE, Saudi Aramco, prepared for the 2014 International Petroleum Technology Conference, Kuala Lumpur, 10–12 December. The paper has not been peer reviewed. A type of unconventional play currently being evaluated is a carbonate source rock with nanodarcy permeability and very low porosity. This paper will discuss the hydraulic-fracturing- stimulation design, execution, and evaluation for the first successful proppant-fracturing treatment in an unconventional carbonate source rock in Saudi Arabia. The successful two-stage treatment proved that proppant-fracturing techniques could be used to stimulate carbonate formations after modifying the stimulation design (specifically, the perforation strategy, fracturing fluids, and proppant type). Introduction The operator has embarked on an exploration-and-appraisal project to assess unconventional-resource potential in three geographic areas: northwest, South Ghawar, and East Ghawar. Hydraulic-fracturing techniques will be used to enhance production by connecting natural fissures and creating high-connectivity pathways through which gas can flow into the well. The initial focus is in the northwest and in the area of Ghawar. Initial knowledge building from similar plays in North America is being supplemented with internal technical studies and research programs to help solve geological and engineering challenges unique to Saudi Arabia and to locate specific wells planned for 2014. Acid vs. Proppant Fracturing The operator has used mainly acid fracturing and matrix acidizing to increase production rates from carbonate formations in conventional gas fields, while proppant fracturing was used predominantly in sandstone formations. This methodology, coupled with the fact that all previous attempts to stimulate carbonate formations in Saudi Arabia resulted in premature screenouts after only 10% of the proppant had been placed in the formation, clearly demonstrates the significance of the first successful proppant-fracturing treatment in an unconventional carbonate source rock in Saudi Arabia. Jafurah Basin Source Rocks The Jurassic sediments being targeted in the Jafurah basin as unconventional reservoirs are carbonate source rocks within the Tuwaiq Mountain, Hanifa, and locally basal Jubaila formations (please see the complete paper for a detailed geological description). The H-1 well is the first well drilled on a seismic anomaly, and it encountered a thick organicrich Jurassic source rock. The thick sequence of source rock in the H-1 well, as well as other areas within the basin, may suggest the possibility of a commercially viable unconventional play. As a followup to the drilling of the H-1 well, a geophysical forward-modeling project was initiated to investigate the cause of the seismic-amplitude anomaly in the Jafurah basin. The study revealed that the formation encountered in the H-1 well has an overall lower acoustic impedance, which appears to be the result of its high total organic content. Drilling and Coring The H-2 well, east of the giant Ghawar field, was drilled to evaluate several Jurassic source-rock targets. The well was completed with 4½-in. tubing, a 7-in. liner with a 7-in. permanent packer, and a 25-ft sealbore receptacle. The tubing and annulus were displaced with 65-lbm/ft3 brine. The well was designed to be re-entered for horizontal sidetracking. Five cores were cut for laboratory testing and analysis. Acid-solubility tests were performed on the core-plug samples to determine their solubility in hydrochloric acid (HCl). X-ray-diffraction analysis was performed on four core samples before and after the acid-solubility tests, showing that the four samples analyzed consisted mainly of calcite with smaller fractions of dolomite, quartz, anhydrite, pyrite, and clays. Perforation-Design Strategy Deep-penetrating charges were used in Well H-2, in conjunction with underbalanced perforating to minimize perforation damage and ensure clean perforations. In addition, 3,000 gal of 15% HCl was pumped as a preflush before pumping the pad in each stimulation treatment to further aid in removal of debris from the perforation tunnels.

Diversity of thermophiles in a Malaysian hot spring determined using 16S rRNA and shotgun metagenome sequencing.

The Sungai Klah (SK) hot spring is the second hottest geothermal spring in Malaysia. This hot spring is a shallow, 150-m-long, fast-flowing stream, with temperatures varying from 50 to 110°C and a pH range of 7.0–9.0. Hidden within a wooded area, the SK hot spring is continually fed by plant litter, resulting in a relatively high degree of total organic content (TOC). In this study, a sample taken from the middle of the stream was analyzed at the 16S rRNA V3-V4 region by amplicon metagenome sequencing. Over 35 phyla were detected by analyzing the 16S rRNA data. Firmicutes and Proteobacteria represented approximately 57% of the microbiome. Approximately 70% of the detected thermophiles were strict anaerobes; however, Hydrogenobacter spp., obligate chemolithotrophic thermophiles, represented one of the major taxa. Several thermophilic photosynthetic microorganisms and acidothermophiles were also detected. Most of the phyla identified by 16S rRNA were also found using the shotgun metagenome approaches. The carbon, sulfur, and nitrogen metabolism within the SK hot spring community were evaluated by shotgun metagenome sequencing, and the data revealed diversity in terms of metabolic activity and dynamics. This hot spring has a rich diversified phylogenetic community partly due to its natural environment (plant litter, high TOC, and a shallow stream) and geochemical parameters (broad temperature and pH range). It is speculated that symbiotic relationships occur between the members of the community.

Hydrocarbon Generation and Expulsion of the Upper Triassic T3x5 Source Rocks in the Western Sichuan Depression: Assessment for Unconventional Natural Gas

AbstractTight‐sand gas in the Jurassic and shale gas within the fifth member of Xujiahe Formation (T3x5) in the Western Sichuan Basin (WSD) are currently regarded as the most prolific emerging unconventional gas plays in China. This study conducted a conventional evaluation of T3x5 source rocks in the WSD, and investigated their hydrocarbon generation and expulsion characteristics, including intensity, efficiency and amount. The results show that, the T3x5 source rocks are thick (generally >200 m), and have a high total organic content (TOC), ranging from 2.5 to 4.5 wt%. It is thus indivative of a great hydrocarbon generation potential when they underwent high thermal evolution (Ro>1.2%) in the area. In addition, an improved method of hydrocarbon generation potential is applied, indicating that the source rocks reached a hydrocarbon expulsion threshold with vitrinite reflectance (Ro) reaching 1.06%, and that the comprehensive hydrocarbon expulsion efficiency is about 60%. The amount of hydrocarbon generation and expulsion from T3x5 source rocks is 3.14×1010 t and 1.86×1010 t, respectively, with a residual amount of 1.28×1010 t within them. Continuous‐type tight‐sand gas is predicted to have developed in the Jurassic in the Chengdu Sag of the WSD because of the good source‐reservoir configuration; the Jurassic sandstone reservoirs are tight, and the gas expelled from the T3x5 source rocks migrates for very short distances vertically and horizontally. The amount of gas accumulation in the Jurassic reservoirs derived from T3x5 source rocks is up to 9.3×108 t. Geological resources of shale gas are up to 1.05×1010 t. Small differences between the amounts calculated by the volumetric method and those obtained by hydrocarbon generation potential method may be due to other gas accumulations present within interbedded sands associated with gas shales.

An integrated paleomagnetic, rock magnetic, and geochemical study of the Marcellus shale in the Valley and Ridge province in Pennsylvania and West Virginia

AbstractAn integrated paleomagnetic, rock magnetic, and diagenetic study of the Devonian Marcellus Subgroup from threefolds in the Valley and Ridge province in Pennsylvania and West Virginia indicates that the unit contains an intermediate temperature chemical remanent magnetization (CRM) with south‐southeast declinations and shallow negative inclinations residing in pyrrhotite and a CRM with more southerly declinations and shallow positive inclinations residing in magnetite. Rock magnetic results confirm the presence of pyrrhotite and magnetite. Tilt tests indicate that pyrrhotite and magnetite CRMs are syntilting to posttilting, and paleopoles for both CRMs are similar and plot on the Permian part of the apparent polar wander path for North America. The Marcellus Subgroup has a complex paragenetic sequence which includes bitumen deposition and vein formation. The magnetite and pyrrhotite CRMs formed in the Permian, probably due to burial diagenetic processes and not orogenic fluids. The base of the unit contains the highest total organic content (TOC) values and highest magnetic intensities, both of which decrease up section. This connection between TOC and magnetic intensity suggests that the magnetite formed as a result of the maturation of the organic matter although more work is needed to test this hypothesis. The pyrrhotite may have formed as a result of thermochemical sulfate reduction involving organic matter during the production of methane in this gas reservoir. The similar Permian CRM ages may be explained by thrusting which resulted in rapid burial of the Marcellus Subgroup as it passed through the oil window and into the gas window quickly producing magnetite and pyrrhotite, respectively.

Dynamic elastic properties of the Wufeng–Longmaxi formation shale in the southeast margin of the Sichuan Basin

In spite of the growing interest in Late Ordovician to the Early Silurian Wufeng–Longmaxi black shale for gas production in the southeast of the Sichuan Basin, little data is available on the acoustic properties of these shale reservoirs. The dynamic elastic properties of a suite of shales from this formation with different organic matter content were measured using the ultrasonic transmission technique at a range of confining pressures. The mineralogical features and reservoir space types were studied with the goal of analyzing their influence on the acoustic properties of the shale samples. The TOC (total organic content) is found to have a positive correlation with the quartz content and a negative correlation with the clay content. Organic matter pores and inter-crystal micro-pores are the main pore types. Organic-rich shales show a low P-wave impedance (Ip) and Vp/Vs ratio due to relatively higher TOC and quartz content; nonetheless, high P-wave (Ip) is also observed when the quartz content is very high resulting from the variation of load-bearing grains. The velocities and anisotropy of different shale samples show varying pressure dependence. A strong positive correlation is found between the anisotropy and the clay content. Three different types of microfabric can be observed in the shale samples, giving a qualitative explanation for the correlation between the anisotropy and the clay content. The occurrence of preferential alignment of the clay minerals requires that the clay content exceeds a critical volume, and this value is about 25%–30% in this study.

Effect of Some Input Parameters on 3D Basin and Petroleum Systems Modelling: A Case Study of the Norwegian Section of the Northern North Sea

The objective of this study is to test the influence of some key input parameters in basin modelling and to evaluate the resultant effect of varying these parameters on the model. 3D basin modelling and petroleum system analysis of the northern North Sea has been carried out using the PETROMOD software. The model was calibrated using well 34/8-7 in the Visund field. Different input parameters such as heat flow, source rock properties, fault properties, paleo water depth, source rock kinetics, migration methods and different erosion scenarios have been varied and their effects on the model assessed. The effect of the various input parameters has been assessed in terms of hydrocarbon volumes in the Kvitebjorn and Visund fields, source rock maturity, transformation ratios, hydrocarbon saturations and the time hydrocarbon generation began in the Draupne and Heather Formation source rocks. Increase in heat flow increases source rock maturity, the start of hydrocarbon generation, transformation ratios and results in the generation of a lot more gas than oil. Hydrocarbon generation starts at shallower depths with higher heat flow. Increasing Total Organic Content (TOC) and Hydrogen Index (HI) generally results in increase in the volume of hydrocarbons generated. The increase in HI, however, results in the generation of a lot more oil than gas. High TOC and HI also increase the hydrocarbon saturations in the source rock. Increasing Paleo Water Depth (PWD) has a marginal effect on the model. It increases the volume of oil and decreases the volume of gas marginally. Varying the PWD has no significant effect on source rock maturity, transformation ratios and hydrocarbon saturations. Opening the fault planes resulted in an increase in the volume of hydrocarbons generated. The increase was more evident in the volume of oil than gas. This increase in volumes is a consequence of additional migration pathways created by the faults. Varying the erosion thickness of the Draupne Formation did not have any effect on the model.

Petroleum system analysis of the Khatatba Formation in the Shoushan Basin, north Western Desert, Egypt

The Middle Jurassic Khatatba Formation is an attractive petroleum exploration target in the Shoushan Basin, north Western Desert, Egypt. However, the Khatatba petroleum system with its essential elements and processes has not been assigned yet. This study throws the lights on the complete Khatatba petroleum system in the Shoushan Basin which has been evaluated and collectively named the Khatatba-Khatatba (!) petroleum system. To evaluate the remaining hydrocarbon potential of the Khatatba system, its essential elements were studied, in order to determine the timing of hydrocarbon generation, migration and accumulation. Systematic analysis of the petroleum system of the Khatatba Formation has identified that coaly shales and organic-rich shales are the most important source rocks. These sediments are characterised by high total organic matter content and have good to excellent hydrocarbon generative potential. Kerogen is predominantly types II–III with type III kerogen. The Khatatba source rocks are mature and, at the present time, are within the peak of the oil window with vitrinite reflectance values in the range of 0.81 to 1.08 % Ro. The remaining hydrocarbon potential is anticipated to exist mainly in stratigraphic traps in the Khatatba sandstones which are characterised by fine to coarse grain size, moderate to well sorted. It has good quality reservoir with relatively high porosity and permeability values ranging from 1 to 17 % and 0.05–1,000 mD, respectively. Modelling results indicated that hydrocarbon generation from the Khatatba source rocks began in the Late Cretaceous time and peak of hydrocarbon generation occurred during the end Tertiary time (Neogene). Hydrocarbon primarily migrated from the source rock via fractured pathways created by abnormally high pore pressures resulting from hydrocarbon generation. Hydrocarbon secondarily migrated from active Khatatba source rocks to traps side via vertical migration pathways through faults resulting from Tertiary tectonics during period from end Oligocene to Middle Miocene times.

Shale Gas-in-Place Calculation from Sichuan Basin, China

The methods of shale gas content measurement and shale Gas-in-place calculation are introduced in detail. The shale gas content is form 1.05 to 1.84 m3/t. From Gas-in-place calculation the adsorption gas content is a little more than free gas content. The advantage of shale gas accumulation areas are high formation pressure, low water saturation, high porosity and high total organic content. There are some discrepancy between shale gas content testing and gas in place calculation and three reasons may cause this phenomenon.

Evaluation of Upper Triassic T3x5 Source Rocks (Western Sichuan Depression, Sichuan Basin) and their Hydrocarbon Generation and Expulsion Characteristics: Implication for Tight-Sand Gas and Shale Gas Accumulation Potential Assessment

An unconventional, continuous petroleum system consists of an accumulation of hydrocarbons that is found in low-matrix-permeability rocks and contain large amounts of hydrocarbons. Tight-sand gas in the Jurassic and shale gas within the fifth member of Xujiahe Formation (T3x5) are currently regarded as the most prolific emerging unconventional gas plays in China. The conventional and systematical evaluation of T3x5 source rocks was carried out for the first time in the western Sichuan basin (WSD). Hydrocarbon generation and expulsion characteristics (including intensity, efficiency, and amount) of T3x5 source rocks were investigated. Results show that T3x5 source rocks are thick (generally >200 m), have high total organic content (TOC, ranging from 2.5 to 4.5 wt%), and dominated by III-type kerogen. These favorable characteristics result in a great hydrocarbon generating potential under the high thermal evolution history (Ro > 1.2%) of the area. An improved hydrocarbon generation potential methodology was applied to well data from the area to unravel the hydrocarbon generation and expulsion characteristics of T3x5 source rocks in the WSD. Results indicate that the source rocks reached hydrocarbon expulsion threshold at 1.06% Ro and the comprehensive hydrocarbon expulsion efficiency was about 60%. The amount of generation and expulsion from T3x5 source rocks was 3.14 × 1010 and 1.86 × 1010 t, respectively, with a residual amount of 1.28 × 1010 t within the source rocks. Continuous-type tight-sand gas was predicted to develop in the Jurassic in the Chengdu Sag of the WSD because of the good source-reservoir configuration (i.e., the hydrocarbon generation and expulsion center was located in Chengdu Sag), the Jurassic sandstone reservoirs were tight, and the gas expelled from the T3x5 source rocks migrated for very short distances vertically and horizontally. The amount of gas accumulation in the Jurassic reservoirs derived from T3x5 source rocks is up to 9.3 × 108 t. The T3x5 gas shale has good accumulation potential compared with several active US shale-gas plays. Volumetrically, the geological resource of shale gas is up to 1.05 × 1010 t. Small differences between the amounts calculated by volumetric method compared with that by hydrocarbon generation potential methodology may be due to other gas accumulations present within interbedded sands associated with the gas shales.

Hyphenation of a carbon analyzer to photo-ionization mass spectrometry to unravel the organic composition of particulate matter on a molecular level

The carbonaceous fraction of airborne particulate matter (PM) is of increasing interest due to the adverse health effects they are linked to. Its analytical ascertainment on a molecular level is still challenging. Hence, analysis of carbonaceous fractions is often carried out by determining bulk parameters such as the overall content of organic compounds (OC) and elemental carbon (EC) as well as the total carbon content, TC (sum of OC and EC), however, no information about the individual substances or substance classes, of which the single fractions consist can be obtained. In this work, a carbon analyzer and a photo-ionization time-of-flight mass spectrometer (PI-TOF-MS) were hyphenated to investigate individual compounds especially from the OC fractions. The carbon analyzer enables the stepwise heating of particle samples and provides the bulk parameters. With the PI-TOF-MS, it is possible to detect the organic compounds released during the single-temperature steps due to soft ionization and fast detection of the molecular ions. The hyphenation was designed, built up, characterized by standard substances, and applied to several kinds of samples, such as ambient aerosol, gasoline, and diesel emission as well as wood combustion emission samples. The ambient filter sample showed a strong impact of wood combustion markers. This was revealed by comparison to the product pattern of the similar analysis of pure cellulose and lignin and the wood combustion PM. At higher temperatures (450°C), a shift to smaller molecules occurred due to the thermal decomposition of larger structures of oligomeric or polymeric nature comparable to lignocelluloses and similar oxygenated humic-like substances. Finally, particulate matter from gasoline and diesel containing 10% biodiesel vehicle exhaust has been analyzed. Gasoline-derived PM exhibited large polycyclic aromatic hydrocarbons, whereas diesel PM showed a much higher total organic content. The detected pattern revealed a strong influence of the biodiesel content on the nature of the particulate organic material.

The Physico-chemistry and Distribution of Water Hyacinth (<i>Eichhornia cressipes</i>) on the river Nun in the Niger Nelta

The physicochemical studies and phytochemical investigations of River Nun and the water hyacinth (Eichhornia crassipes) were carried out in relation to the distribution of Eichhornia crassipes (Mart) Solms, Family Pontederiaceae in the River Nun.. The physicochemical studies of the water showed that dissolved oxygen (DO), biochemical oxygen demand (BOD), nitrate (NO3), salinity and alkalinity (pH) had mean + SDvalues of 6.94 + 0.22, 5.86 + 0.42mg/L,13.76 + 5.76 mg/L, 0.237 + 0.082 mg/L, 7.25 + 0.37 mg/L and 5.92 + 0.32 mg/L respectively. Phosphate (PO4) and sulphite (SO3) were not detected. The pH and DO levels appeared to favour the growth of E. crassipes.The BOD values were relatively higher than those of the control. The phytochemical studies showed that E. crassipes contains flavonoids (luteolin, apigenin, tricin, chrysoeriol, kaempferol, azaeleatin, gossypetin and orientin), amino acids (methionine, valine, glutamic acid theonine, tryptophan, tyrosine, leucine and lysine), phosphorous, protein, organic matter and cyanide. Some of these phenolic compounds and cyanide contribute to the negative impact associated with the proliferation of E.crassipes, in aquatic systems in addition to blocking water ways. The high protein and total organic matter content of Eichhornia crassipes, however, make E. crassipes a potential raw material for the production of animal feed and organic fertilizers. The study also shows that this plant prefers an almost neutral pH aquatic environment with a substantial concentration of dissolved oxygen, an increased rate of biochemical oxygen demand with a substantial concentration of nitrates. These conditions explain why this plant thrives in freshwater habitats such asthe River Nun

Polychaete assemblage of an impacted estuary, Guanabara Bay, Rio de Janeiro, Brazil

Thirty-eight stations were sampled in Guanabara Bay, Rio de Janeiro, Brazil, to assess the spatio-temporal diversity and biomass of sublittoral polychaetes. Samples were collected during the dry (September 2000) and rainy season (May 2001) in shallow sublittoral sediments. The polychaete spatial composition showed a heterogeneous distribution throughout the bay. A negative gradient of diversity and biomass was observed towards the inner parts of the bay and sheltered areas. A wide azoic area was found inside the bay. Some high-biomass and low-diversity spots were found near a sewage-discharge point. In these areas, the polychaete biomass increased after the rainy season. A diversified polychaete community was identified around the bay mouth, with no dramatic changes of this pattern between the two sampling periods. Deposit-feeders were dominant in the entire study area. The relative importance of carnivores and omnivores increased towards the outer sector, at stations with coarse sediment fractions. Guanabara Bay can be divided into three main zones with respect to environmental conditions and polychaete diversity and biomass patterns: A) High polychaete diversity, hydrodynamically exposed areas composed of sandy, oxidized or moderately reduced sediments with normoxic conditions in the water column. B) Low diversity and high biomass of deposit and suspension-feeding polychaete species in the middle part of the bay near continental inflows, comprising stations sharing similar proportions of silt, clay and fine sands. C) Azoic area or an impoverished polychaete community in hydrodynamically low-energy areas of silt and clay with extremely reduced sediments, high total organic matter content and hypoxic conditions in the water column, located essentially from the mid-bay towards the north sector. High total organic matter content and hypoxic conditions combined with slow water renewal in the inner bay seemed to play a key role in the polychaete diversity and biomass. Sedimentation processes and organic load coming from untreated sewage into the bay may have negatively affected the survivorship of the fauna.

Benthic oxygen fluxes and sediment properties on the northeastern New Zealand continental shelf

We examined spatial variations in benthic remineralisation (measured as sediment oxygen consumption (SOC)) and sediment properties on the northeastern New Zealand continental shelf and slope to assess the importance of benthic mineralisation in this ecosystem and to provide data for more complete global carbon budgets. SOC measured in dark incubations conducted in early summer ranged from 128 μmol m −2 h −1 at the deepest (360 m) to 1222 μmol m −2 h −1 at the shallowest (4.2 m) site and decreased significantly with water depth ( p<0.001, r 2=0.78, SOC=1222.8−456.3×log 10[water depth], n=14 sites). These rates were in the range found on continental shelves elsewhere (64–1750 μmol m −2 h −1, n=30 studies) and had a very similar distribution with water depth. SOC was also measured in light incubations at seven sites (4.2–35 m water depth) to examine the effects of microphytobenthos and accounted for 42–106% of rates measured in the dark. Measurements of near-bed light intensities suggested that microphytobenthos production was not solely regulated by light intensity but evidently influenced by other factors. A two-dimensional PCA ordination of surface sediment properties accounted for 83.3% of the total variance in the data and divided the study area into three clusters that corresponded well to its spatial division into the shallow (<30 m) Firth of Thames, the Hauraki Gulf (30–50 m) and the northern shelf-slope region. In the Firth of Thames sediments were very fine-grained with low CaCO 3 and high total organic matter and pigment content, and low C:N ratios. The northern shelf-slope sediments showed the opposite trends to the Firth of Thames and those in the Hauraki Gulf had mostly intermediate values. Dark SOC was significantly correlated with sediment organic matter, carbon, nitrogen, pigments and silt/clay content ( p<0.05, r=0.55–0.85) but a multiple linear regression revealed that water depth was the only significant predictor. Calculations suggest that approximately 13%, 10% and 34% of primary production is remineralised in the sediments of the northern shelf-slope region, Hauraki Gulf and Firth of Thames, respectively, indicating a strong benthic–pelagic coupling on the northeastern New Zealand continental shelf that was particularly pronounced in the Firth of Thames due to its shallow depth and significant terrestrial and riverine inputs.

PHYSICAL AND STRATIGRAPHIC CHARACTERISTICS OF SEDIMENTS IMPOUNDED WITHIN A FLOOD CONTROL RESERVOIR IN OKLAHOMA

Since 1948, the USDANRCS has constructed almost 11,000 upstream flood control dams across the U.S., andmany of the reservoirs are filling with sediment as they near the end of their 50year economic life. Removing the sedimentremains a viable option for dam rehabilitation, yet little information exists on the physical and spatial characteristics ofsediments impounded by these small reservoirs. To this end, the characteristics of sediment impounded in a flood controlreservoir in Oklahoma were defined. Ten continuous, undisturbed sediment cores were obtained using vibracoring equipment,and the subsurface sediment distributions were imaged using an acoustic profiling system. Stratigraphic analyses showed thatsilt and claysized sediments dominate the deposits within the reservoir pool, relatively high silt and clay contents wereassociated with relatively high total organic contents (about 2% by mass), and sand deposition was restricted to tributaryand surface erosion sources. Stratigraphic correlation of sediment units across the reservoir was possible using the acousticprofiling results, preimpoundment sediment was discriminated from postconstruction deposition, and a map showing totalthickness of deposited sediment was constructed. These results provide detailed information on sedimentation characteristicswithin a typical USDANRCS flood control reservoir. Moreover, the methods used herein were shown to effectively quantifyreservoir sedimentation, which is critically important in reservoir management and rehabilitation programs nationwide.

TEM-EDX investigation on Zn- and Pb-contaminated soils

Lead and zinc contaminated soils from a smelter area in the northern part of France have been studied by transmission electron microscopy (TEM). This study was carried out with 4 different soils contaminated by Pb and Zn but with different chemical and physical characteristics. Two soils are tilled and have a neutral or slightly basic pH, one is a wooded soil and the last one is a meadow soil with acidic pH and high total organic content . TEM images of the soil samples have been coupled with focused energy dispersive X-ray (EDX) analyses and chemical mapping on a few micron-sized windows. This study demonstrates that TEM is a particularly efficient method to investigate metal speciation in the fine fractions of the contaminated soils. Zinc could be detected locally in sulphide minerals probably coming from the smelter emissions, but the major phases retaining Zn are Fe-oxyhydroxides and smectites. Lead could be detected in small aggregates which were characterized by EDX and selected area electron diffraction. Their structural formulae correspond to a pyromorphite-like mineral in which Pb is partly substituted by Ca and Na. Pyromorphite is present only in the wooded and meadow soils where it forms partly from amorphous Si-rich phases (slags) coming from the smelter. These results are compared with data previously obtained by spectroscopic methods on the same samples.