Barry J. Katz

Limitations of ‘Rock-Eval’ pyrolysis for typing organic matter☆

Abstract Laboratory experimentation on whole-rock ‘Rock-Eval’ pyrolysis has shown that the characterization of organic matter through the use of a modified van Krevelen diagram, in which the hydrogen and oxygen indices are substituted for the atomic H/C and O/C ratios, produces questionable results. The hydrogen and oxygen indices have been found to be strongly affected by both matrix mineralogy and level of organic enrichment. It appears, therefore, that although the modified van Krevelen diagram maybe useful for tracing evolutionary pathways as organic matter matures, it can be very misleading when used to assess kerogen type.

Petroleum source rocks

Petroleum Source Rocks - an Introductory Overview.- The Exshaw Formation: a Devonian/Mississippian Hydrocarbon Source in the Western Canada Basin.- Geological Controls of Source Rock Geochemistry Through Relative Sea Level Triassic, Barents Sea.- The Schistes Carton - the Lower Toarcian of the Paris Basin.- Geochemistry of the Upper Jurassic Tuwaiq Mountain and Hanifa Formation Petroleum Source Rocks of Eastern Saudi Arabia.- The Kimmeridge Clay Formation of the North Sea.- The Egret Member, a Prolific Kimmeridgian Source Rock from Offshore Eastern Canada.- Petroleum Generation in the Nonmarine Qingshankou Formation (Lower Cretaceous), Songliao Basin, China.- Sedimentological and Geochemical Characterization of the Lagoa Feia Formation, Rift Phase of the Campos Basin, Brazil.- The Napo Formation, Oriente Basin, Ecuador: Hydrocarbon Source Potential and Paleoenvironmental Assessment.- The Albian Kazhdumi Formation of the Dezful Embayment, Iran: One of the Most Efficient Petroleum-Generating Systems.- Organic-Rich Chalks and Calcareous Mudstones of the Upper Cretaceous Austin Chalk and Eagleford Formation, South-Central Texas, USA.- Petroleum Geochemical Characterisation of the Lower Congo Coastal Basin Bucomazi Formation.- Source Rock Characterization of the Late Cretaceous Brown Limestone of Egypt.- Brown Shale Formation: Paleogene Lacustrine Source Rocks of Central Sumatra.- The Green River Shale: an Eocene Carbonate Lacustrine Source Rock.

Organic geochemistry of DSDP Site 467, offshore California, Middle Miocene to Lower Pliocene strata

Abstract Results of the analyses of twenty-three samples from the Middle Miocene to Lower Pliocene strata from DSDP Site 467, offshore California, are presented. The analyses were performed with the aim of determining the origin of the organic matter, the stratigraphic sections hydrocarbon generation potential and extent of organic diagenesis. Organic carbon contents are an order of magnitude greater than those typically found in deep sea sediments, suggesting an anoxic depositional environment and elevated levels of primary productivity. Hydrocarbon generation potentials are above average for most samples. The results of elemental analyses indicate that the kerogens are primarily composed of type II organic matter and are thermally immature. Analysis of the bitumen fractions confirms that the samples are immature. In cores from 541 to 614 meters, the gas chromatograms of the C 15+ non-aromatic hydrocarbon fractions are dominated by a single peak which was identified as 17α(H), 18α(H), 21β(H)-28, 30-bisnorhopane. This interval is the same area in which the highest degrees of anoxia are observed as reflected by the lowest pristane/phytane ratios. This correlation may have some implications with regard to the origin of the bisnorhopane and its possible use as an indicator of anoxic depositional conditions within thermally immature sediments.

Petroleum Systems of South Atlantic Margins

“Giant oil and gas fields have been discovered through recent exploration in the deep and ultra-deep water regions of Angola, Brazil, and Nigeria. This volume includes 1. Descriptions of the petroleum geology of more than 12 basins along the two margins 2. Discussion of various components of the petroleum systems within these basins 3. Discussion on the use of the petroleum systems concept in the South Atlantic marginal basins to classify and characterize the diversity of the systems 4. Methodologies used in the assessment of petroleum system components 5. Overviews of the different components of the regions petroleum systems. Petroleum explorationists and researchers working in the South Atlantic will welcome this addition to their libraries. The printed version of Memoir 73 was the Winner of the 2000 Dott Award for best AAPG Special Publication.”

Lacustrine basin hydrocarbon exploration – current thoughts

Although much of the worlds petroleum resource-base is associated with marine systems, regionally lacustrine petroleum systems are important. Individual accumulations may exceed several billion barrels. In each of these cases the oil is derived from a lacustrine source rock and may be produced from either nonmarine or marine reservoir rocks. The purpose of this paper is to describe the factors that control lacustrine source rock development and the nature of lacustrine reservoirs. Lacustrine oils display different physical and chemical characteristics than their marine counterparts. These differences can be related to the nature of their precursor material. Although the nature of the products are different, the geochemical threshold criteria for defining source rocks in both settings are the same because of common expulsion requirements. Commercially significant lacustrine systems require the presence of large, long-lived lakes. Such lake settings are tectonic in origin and restricted to climatic settings where precipitation exceeds evaporation. Within these large lake systems three primary factors determine source rock potential and quality. These factors are primary productivity level, organic preservation potential, and matrix sedimentation rate, which controls the dilution of preserved organic matter. Source rock potential is maximized where both productivity and preservation potential are maximized and sedimentation rate is minimized. To some degree these factors can compensate for each other. Hydrocarbon reservoir potential within lacustrine basins is partially impacted by overall tectonic setting. Within extensional settings, transport distances tend to be limited, with much of the sediment being transported away from the basin. The sediments delivered to the lake are poorly sorted and sedimentologically immature, commonly resulting in poor reservoirs due to both primary properties and their susceptibility to diagenesis. Within rifts better reservoirs tend to develop along platform or flexural margins. Stacking of reservoirs is important in lacustrine systems but baffles and barriers are often present between individual sand units. These barriers form as a result of lake level fluctuations. In compressional settings transport distances tend to be longer, resulting in more mature, better sorted sediments leading to higher quality reservoirs. These reservoirs typically develop in fluvial-deltaic and wave-dominated shoreline settings. Lacustrine carbonate reservoirs are locally important. These carbonates tend to develop during lake level lowstands and are dependent on diagenesis (dissolution and karstification) for porosity and permeability development. Lacustrine reservoirs are often stratigraphically and areally limited and display low individual well production rates. Within ‘pure’ lacustrine systems exploration opportunities appear to be often restricted by either reservoir presence or quality (i.e., production rates). The best exploration opportunities in lacustrine basins appear to be associated with hybrid systems where a lacustrine source and marine reservoir exist.

Predicting CO2 occurrence on a regional scale : Southeast Asia example

Abstract Prediction of CO 2 occurrence in natural gases is difficult owing to the interplay among basinal sources (e.g. volcanic emanations, carbonate hydrolysis and metamorphism, organic diagenesis and maturation), reservoir processes (e.g. mineralogical transformations), and poorly understood physicochemical phenomena (e.g. differential solubility of gas components, carbonate buffering, phase segregation). Published approaches to assessing CO 2 risk are based either on circumstantial evidence of basinal influences or statistical analysis of reservoir attributes. The present study presents the results of empirical, statistical and neural network analysis of CO 2 abundance in natural gas and discusses potentially influential basinal and reservoir attributes to quantify risk factors for anomalous CO 2 occurrences in Southeast Asia. The results of this study indicate that tectonic setting (including basement crustal age), basement fault density, reservoir temperature and reservoir pressure are key elements controlling CO 2 abundance. Assignment of CO 2 risk at the basin level can be roughly approximated using the results of this study. More accurate assessments of CO 2 risk at the basin, play, field and reservoir levels require more comprehensive geological and geochemical data as well as consideration of potentially influential physico-chemical processes.

Hydrocarbon products of coals as revealed by pyrolysis-gas chromatography

Abstract The hydrocarbon products generated and released from coals continue to be debated. The Mesozoic and Cenozoic southern hemisphere coals have been described as being capable of generating significant quantities of heavy hydrocarbons (oil-like material) when compared to the Paleozoic coals of the northern hemisphere because of changes in the coal forming community. This hypothesis was examined by comparing the pyrolysis-gas chromatography results of a collection of coals. Preliminary results indicate that the most significant difference in pyrolytic products is in the less than nC15 fraction. The data further indicate that coals generate similar types of hydrocarbons independent of age or geographic position if they contain similar bulk maceral content. Coals rich in vitrinite generate predominately aromatic hydrocarbons with lesser amounts of n-paraffins. Coals rich in algae and other exinites generate largely paraffinic hydrocarbons. Coals rich in resins generate naphthenic and aromatic hydrocarbons. The petroleum generating potential of coals also depends on the coals expulsion efficiency, which is not addressed by this study.

A survey of rift basin source rocks

Abstract Various studies reveal that rift basins contain a disproportionate amount of petroleum based on their area and sediment volume. In part, this results from the excellent petroleum source rocks found in many of these basins. The presence of these sources not only influences the petroleum potential of the rift sequence, but may also influence the petroleum potential the post-rift succession. These high quality source rocks can be partially explained by the low width: depth ratios and high subsidence rates associated with rift basins. However, not all rifts contain these organic-rich deposits, nor are all the organic-rich deposits volumetrically significant. Other factors, such as climate and sedimentation rate, strongly influence the deposition of these organic-rich sediments. Within individual basins sub-basins may display dramatically different oil- vs gas-prone tendencies due to different subsidence rates. High subsidence rates favour oil source rock development, while low subsidence rates favour gas source development. Many, but not all, of these petroleum source rock systems are lacustrine. Restricted marine source rocks are also present within rift sequences. This study focuses on three elements of rift basin source rocks: (1) their distribution; (2) the factors controlling their deposition, distribution and quality; and (3) their geochemical attributes.

Summary of the AAPG Research Symposium on Lacustrine Basin Exploration in China and Southeast Asia

In this paper, we review the work presented at the AAPG-Shengli Petroleum Administration Research Symposium dealing with lacustrine basin exploration in China and southeast Asia. This meeting, held in the fall of 1995, revealed that there has been an expansion of the available knowledge base associated with these basins. This increase in information has resulted in a better understanding of lacustrine basin-fill properties and characteristics, even though many of the causal mechanisms for these properties have not yet been established. The many papers presented suggest that there are two primary causes for economic failure within many of these basins: (1) communication between source and reservoir and (2) the limited reservoir potential within the lacustrine sequence of these basins. More effective petroleum systems are found in basins where marine sandstones are in communication with lacustrine sources. The discussions also clearly demonstrated that lacustrine basins are sensitive to environmental changes, causing complex sedimentary facies successions. Each facies, however, displays unique characteristics that can be mapped. Several presenters also suggested that within extensional lacustrine settings the stratigraphic succession follows a distinct pattern. Although most of these basins are predominantly oil prone, several lacustrine basins within the region contain significant volumes of gas. Included within these gas reserves are biogenic accumulations that appear to have formed nearly penecontemporaneously with deposition. Recent work on several of the Chinese basins suggests the possibility for immature hydrocarbon generation and expulsion in a manner different than that associated with marine type II-S kerogens. Even with the progress that this symposium revealed there are several key questions that remain, including questions associated with how technology might be used to improve the economics of many of these systems that display limited reservoir potential.

Petroleum Generation in the Nonmarine Qingshankou Formation (Lower Cretaceous), Songliao Basin, China

The Songliao basin, covering an area of 260 000 km2 in northeast China, is known as one of the world’s most prolific oil- and gas-producing basins. The super giant Daqing oil field is located in the center of the basin with major oil plays in the Lower Creataceous Yaojia and Qingshankou Formations.