Prasanta K. Mukhopadhyay

Organic facies and maturation of Jurassic/Cretaceous rocks, and possible oil-source rock correlation based on pyrolysis of asphaltenes, Scotian Basin, Canada

Abstract This paper establishes source rock characterization and oil-oil and oil-source rock correlations of selected organic-rich shale source rocks and selected light oils and condensates from Jurassic and Cretaceous formations of the Scotian Basin. Multiple source rocks of Kerogen Types IIA (oil-prone), IIA-IIB (oil- and condensate-prone), IIB (condensate and gas prone), III (gas-prone), and IV (nonsource) are identified in various stratigraphic horizons. Vitrinite reflectance and T inmax data indicate variable maturation histories, in different parts of the basin, which are related to differences in lithology-related heat conductivity and the presence of older sediments closer to areas of rifting. Multiple linear regression and cluster analyses of aromatic hydrocarbon ratios reveal two oil families. Some Kerogen Type IIB rock extracts match many of the light oil and condensates in terms of the aromatic hydrocarbon distributions. A second family of oils could not be correlated with any of the analyzed source rock extracts. Pyrolysis-gas chromatography of asphaltenes from the Cohasset A-52 and Sable Island 3H-58 wells are significantly different in n -alkane, aromatics and phenol content. The asphaltene pyrolyzates of samples from Venture B-52 and S. Desbarres O-76 have a high aromatic content, low content of n -alkanes, and high phenol values (S. Desbarres), which is typical of a terrestial source. They correlate well with one another and also with Sable Island light oil. The N. Triumph G-43 whole rock and extract asphaltene pyrolyzates are dominated by normal hydrocarbons, with aromatic, phenolic and thiophenic compounds in low concentrations suggesting an algal source. Algal type organic matter may have made a contribution to the Cohasset petroleum, as its asphaltene pyrolyzate is also dominated by normal hydrocarbons.

Comparison of coal composition and elemental distribution in selected seams of the Sydney and Stellarton Basins, Nova Scotia, Eastern Canada

Selected high to medium volatile bituminous coal seams of Carboniferous age from the Sydney and Stellarton Basins, Nova Scotia, Eastern Canada were analyzed for their organic and inorganic components. These studies evaluated: (a) the evolution of the ancestral mires (coal facies) that formed various seams; (b) the lateral and vertical distribution of various elements within coal facies (lithotypes); and (c) the mode of occurrence of various elements. Coal facies fluctuated between rheotrophic and minerotrophic mires with occasional flooding or drowning of the mire forming inorganic partings. These partings are the source for most lithophile elements including B, Cr, U, V, and rare earth elements. Most of the lithophile elements are associated with a distinct, mainly syngenetic, mineral phase (associated with the clay minerals), which is derived from the erosion of a hinterland source. Chlorine, Ca and minor amounts of As and Mn are organically bound. Arsenic is mostly associated with fine-grained framboidal pyrite as solid solution. Other chalcophile elements such as Cu, Pb, and Zn in the Sydney Basin occur as a syngenetic sulfide mineral phase, whereas these elements in the Stellarton Basin are associated with syngenetic and epigenetic sulfides. Arsenic, Cl, and Mo and part of the Cu and Pb are possibly derived from a mineralized brine that was originated from the dissolution of Windsor Group evaporites. The lateral variation of elements suggests that the coal beds in the Sydney Basin are enriched in As, Cl, Mn, and Pb whereas those of the Stellarton Basin are enriched in Cr and Ni. The Donkin resource block of the Sydney Basin has the lowest concentration of As, Mn, Ni, and Pb, which make it attractive from a development perspective.

Hydrocarbon generation from deltaic and intermontane fluviodeltaic coal and coaly shale from the Tertiary of Texas and Carboniferous of Nova Scotia

Abstract Selected samples of coal and coaly shale from southeastern Texas (depositional environment: deltaic; Age: Paleocene-Eocene; Ro: 0.25–0.75%) and Nova Scotia (depositional environment: intermontane swamp, delta and lacustrine; Age: Carboniferous-Westphalian A-D; Ro: 0.67–0.70%) were analyzed by fluorescence microscopy, Rock-Eval pyrolysis, NMR, anhydrous pyrolysis (temperature programed and flash) and hydrous pyrolysis to evaluate the hydrocarbon potential and hydrocarbon types. Based on maceral assemblages, palynofacies and hydrocarbon potential, these coal and coaly shale samples are classified as humic, mixinitic (mixed), and sapropelic compared to humic and sapropelic as defined by Stach et al. (Coal Petrology. Gebruder Borntraeger, Berlin, 1982). Mixinitic (or mixed) coal and coaly shale containing mainly humodetrinite and lipodetrinite generated more than 10% pyrolysate (expelled oil + oil in wash fraction + remaining coal extract) and show a bimodal n-alkane distribution (derived from cutinite, suberinite and alginite). Pyrolysis of humotelinite/humocollinite-rich and liptinite-poor humic coals generated low amounts (

A molecular evaluation of contaminants and natural organic matter in bottom sediments from western Lake Ontario

Abstract Py–GC/MS analysis of bottom sediment from Lake Ontario was shown to be effective in assessing organic contaminants, especially attractive as it is a rapid technique requiring little sample preparation. Pyrolyzates of samples richer in organic matter (OM) were relatively enriched in aliphatic hydrocarbons and pyrrolic nitrogen compounds, while leaner samples were more aromatic and pyridinic. Alkylbenzene and alkylphenol distributions in the pyrolyzates were most compatible with derivation from aquatic (algal, bacterial) OM. The organonitrogen compounds indicated the presence of degraded proteinaceous material from aquatic sources and/or sewage. Normal and polycyclic aromatic hydrocarbon distributions indicate, at least in part, contributions of fossil fuels and combustion residues. These observations were confirmed by organic petrologic examination. The ubiquitous input of aquatic OM to the sediments (enhanced by anthropogenic nutrient oversupply) was supplemented by fossil fuel-derived contamination, in proportions varying with proximity to industrial sites and shipping lanes.

Hydrocarbon involvement in the genesis of ore deposits; an example in Cretaceous stratabound (manto-type) copper deposits of central Chile

The analysis of the empirical association of organic carbon in its various forms (e.g., oil, gas, coal) with a variety of ore-deposit types can be a rewarding exercise in the formulation of genetic models and exploration. In many ore provinces, organic matter, residing in its source rocks, migrating in the form of hydrocarbons, or in transient, permanent, leaking, or degrading reservoirs, is likely to have interacted with ground waters, with hydrothermal solutions of diverse origin, or with magmas. After a brief review of these associations, we describe the ubiquitous occurrence of remnant petroleum in two representative “manto-type” stratabound copper deposits in Chile and suggest its possible genetic role and exploration significance. Overmature petroleum (solid bitumen, pyrobitumen) is found in association with copper ores in the southern orebodies of the El Soldado copper deposit in central Chile. Textures indicate that petroleum occupied the host-rock porosity before copper mineralization. Isotopic d...

Metals and polyaromatic hydrocarbons in the drinking water of the Sydney Basin, Nova Scotia, Canada: a preliminary assessment of their source

Abstract Twenty-five drinking water samples collected from the household property and from the Sydney Regional Municipality well bores and lakes were analyzed to evaluate the various inorganic parameters, level of concentrations of the priority elements and polyaromatic hydrocarbons (PAHs). The pH of the majority of the water samples was below the guidelines adopted by Health and Welfare Canada (1996) , although the drinking waters supplied by the Sydney Regional Municipality were within the guidelines. Only three water samples (13 and 14: Point Aconi area and 16: Port Morien fish plant) have elevated concentrations of various PAHs compared to the detection limit. Eight samples have higher concentrations of manganese and two samples (number 7: Sydney Airport and number 1: RCMP Office; Reserve Mines) have higher concentrations of priority elements (especially lead) than the recommended guidelines (>0.05 mg/l). These priority elements and the PAHs in the drinking water samples may have originated from the leaching of the individual coal seams within that part of the Sydney Basin. Other potential sources of these elements and PAHs (Power Plant disposal, Sydney Tar Pond, metalliferous rocks, hydrocarbon reservoir rocks) are not located close enough to the sampling sites of the water samples. Therefore, they are not considered the source of these elements and PAHs.

Characterization of amorphous and other organic matter types by microscopy and pyrolysis-gas chromatography

Abstract According to a modified classification of dispersed organic matter, nine whole-rock and isolated kerogens chosen from different organic facies of Tertiary and Mesozoic sedimentary rocks ( R o between 0.25 and 0.65%), were analyzed by microscopy, Rock-Eval pyrolysis, and pyrolysis-gas chromatography. These rocks contained five amorphous maceral types which are associated with other structured maceral types and showed different hydrocarbon potentials and hydrocarbon distribution patterns in pyrolysis gas chromatography. Higer yield of hydrogen index (Roc-Eval pyrlysis) and the dominance of high molecular weight hydrocarbons (greater than C 10 ) were observed in isolated kerogens than in the whole rocks. Normalized area percentage of low molecular weight aromatics (benzene, toluene, and m , p -xylene) increased from amorphous liptinite I to micrinite rich kerogens. Residues after pyrolysis are microscopically different.

Comparison of Mesozoic carbonaceous claystones in the western and eastern North Atlantic (DSDP Legs 76, 79 and 93)

Summary Mesozoic carbonaceous claystones were recovered on both margins of the North Atlantic Ocean in a number of holes drilled by the Deep Sea Drilling Project (DSDP). Geochemical investigation revealed that the organic matter in these sediments belongs to different organofacies types, as indicated by varying degrees of preservation and mixing of marine and terrigenous material. The intensity of terrigenous organic matter supply, coastal upwelling, downslope transport events, and local oxygen depletion are major factors controlling the composition and preservation of the organic matter in most of the Mesozoic carbonaceous claystones, whereas an ocean-wide anoxic event, if at all, can only be invoked for the organic-matter-rich sediments deposited at the Cenomanian-Turonian boundary. Examples discussed are from the Mazagan Escarpment (Site 547, DSDP Leg 79), the Blake Bahama Basin (Site 534, DSDP Leg 76), and the continental rise off Cape Hatteras (Site 603, DSDP Leg 93).

Waters and organic-rich waste near dumping grounds in the New York Bight

Abstract The New York Bight is a sector of the Middle Atlantic continental shelf. The Bight consists of a part of the Atlantic Ocean offshore of the New York and New Jersey metropolitan area. This area includes the most populated coastal setting in North America. The Atlantic shelf and its estuaries are used for waste disposal, dredging, commercial fishing, and recreation; activities that contribute to the contamination of associated bottom sediments. Existing data for toxicants are still inadequate. Improvements in sediment and water quality will require a more detailed knowledge and understanding of sediments and water in the Bight. Eleven coring stations were established in New York Bight. Decreases in pH and Eh both above and below the water/sediment interface are attributed to the activity of anaerobic bacteria. Sulfate reduction is one of the important processes in lowering pH. Low Eh values of up to −443 can be related to sulfate-reducing bacteria. The highest negative Eh generally occurs with the highest organic carbon concentration. Core samples yielded up to 4.00% organic carbon compared to 0.8 to 1.2% in sediments of the natural nearshore environment. Twenty-seven different aliphatic hydrocarbons, fourteen PAHs, five cyclic hydrocarbons, and eight dicarboxylic acids were identified in the Bight pore waters. Sediment located deeper in the Hudson Shelf Valley has a greater abundance of aliphatic hydrocarbons as adsorbed pollution on clay and silt. The presence of dicarboxylic acids leached from plastic came from anthropogenic activities (mostly sewage). PAHs have two sources: coal ash (observed in sediments) and petroleum (part of the sewage, run-offs, and oil spills). The rest of the hydrocarbons have a petroleum or biogenic origin. The high amount of organic carbon may be the result of sewage sludge or originated from natural sources. The main sources of contaminants are dumpsites, emergency releases after heavy rainstorms from sewage-treatment plants, tanker washing, storage transfer spills, run-off, and air-borne pollution. The relatively high accumulation of organic matter causes oxygen depletion, which creates anaerobic conditions. The presence of hydrogen sulfide makes the environment toxic for most of the biota. Detected hydrocarbons, especially PAHs easily enter the food chain and may cause cancer and mutagenic reactions of biota and humans. Organic petrology of six organic-rich sediments from New York Harbor illustrates a diverse population of anthropogenic and natural organic components. Three core samples (V-2, AC-4, and HV-3) contain coarse-textured organic matter. A slim majority of those components are anthropogenic. They are derived mainly from coal combustion by-products. The other two core samples (AC-6 and T-1) contain mainly very fine-grained organic matter. A majority of them are amorphous organic matter (AOM) that is derived from bacterial degradation of modern organic matter. Radionuclide dating ( 137 Cs , K-40, Pb-210) shows post-1950 components for the shallowest intervals in the cores (

Comparison of source rock geochemistry of selected rocks from the Schei Point Group and Ringnes Formation, Sverdrup Basin, Arctic Canada

Abstract Organic-rich from the Schei Point group (middle to late Triassic in age) and the Ringnes formation (late Jurassic) from the Sverdrup basin of the Canadian arctic archipelago have been geochemically evaluated for source rock characterization. Most samples from the Schei Point group are organic-rich (> 2% TOC and are considered as immature to mature oil-prone source rocks [kerogen types I, I–II (IIA) and II (IIA)]. These kerogen types contain abundant AOM1, AOM2 and alginite ( Tasmanales, Nostocopsis, Leiosphaeridia , acritarch and dinoflagellate) with variable amounts of vitrinite, inertinite and exinite. Samples from the Ringnes formation contain dominant vitrinite and inertinite with partially oxidized AOM2, alginite and exinite forming mostly immature to mature condensate- and gas-prone source rocks [kerogen type II–III (IIB), III and a few II (IIA)]. Schei Point samples contain higher bitumen extract, saturate hydrocarbons and saturate/ aromatic ratio than the Ringnes samples. Triterpane and sterane (dominant C 30 ) distribution patterns and stable carbon isotope of bitumen and kerogen suggest that the analyzed samples from the Schei Point group are at the onset of oil generation and contain a mixture of sapropelic (algal) and minor terrestrial humic organic matter. Sterane carbon number distributions in the Ringnes formation also suggest a mixed algal and terrestrial organic matter type. There are some variations in hopane carbon number distributions, but these are apparently a function of thermal maturity rather than significant genetic differences among samples. Pyrolysis-gas chromatography/mass spectrometry of the two samples with similar maturity shows that the Schei Point sample generates three times more pyrolyzate than the Ringnes sample. Both samples have a dominant aliphatic character, although the Ringnes sample contains phenol and an aromaticity that is higher than that of the Schei Point sample.