Petroleum System Concept Research Articles

Exploration for Helium in the Phanerozoic

Almost all the helium discovered worldwide has been found by chance in the drilling for hydrocarbons. Targets were usually anticlinal structures located by seismic surveys. The association of helium and natural gas in reservoirs is purely coincidental because the source rocks for each are different—natural gas is mainly produced from diagenesis of carbon rich shale whereas Helium- 4 is derived mainly from the decay of uranium/thorium in the crust. A new geochemical exploration system for helium in the Phanerozoic is considered highly desirable by industry. The current exploration system in the Phanerozoic uses a modified petroleum system concept that has been used successfully for decades to high-grade plays and de-risk oil and gas prospects. Like a petroleum system, the helium system is identified by its source rock, reservoir, trap, seal, and migration pathways. However, this approach is expensive taking years to complete and can be a limiting factor for countries/provinces/states to develop their resources. As a precursor to ground helium/hydrogen surveys for exploration in the Phanerozoic, hyperspectral (satellite) surveys assess huge areas for their helium potential as well as any associated hydrocarbons. These areas may be even devoid of any previous exploration for hydrocarbons. This is followed with geochemical soil gas surveys of the more prospective trends to locate drilling locations. Both methods ascertain whether helium anomalies, which represent helium reservoirs at depth, are associated with hydrocarbons or nitrogen. Helium reservoirs associated with nitrogen are higher in helium content but are deeper, close to the basement. Hyperspectral and geochemical soil gas surveys are also applicable for projects that begin with helium analysis of old wells followed by seismic and drilling. Typically, exploration companies lease vast areas surrounding the legacy well, but their initial focus is on seismic in the area around the legacy well to determine the size and configuration of the helium reservoir and trap penetrated by the well and this is followed by drilling. It is not known at this point whether this reservoir is the best prospect because the helium discovered is usually associated with hydrocarbon (HC), not with nitrogen with much higher helium concentration in the lower Phanerozoic. Rarely do legacy wells penetrate deep enough to this level. Any cost-effective exploration program for helium is best accomplished by hyperspectral and follow-up geochemical soil gas surveys.

A quantitative probabilistic framework for estimating the critical moment in a petroleum system

The petroleum system concept spans the spatial and temporal extent of all elements and processes required for the generation and preservation of petroleum. The critical moment of a petroleum system is the moment with the highest probability for the generation–migration–accumulation of hydrocarbons. It is an important concept in petroleum exploration risk assessment because the stratigraphic and geographic extents of a petroleum system are determined at the critical moment. In petroleum systems, thermal history data, burial history data, and vitrinite reflectance data may be unavailable, unreliable, or incomplete; this introduces significant uncertainty in the choice of the critical moment. We present here a quantitative probabilistic framework for estimating the critical moment and quantifying the associated uncertainty in such cases. We define a probabilistic early bound and late bound for the critical moment (which, combined together, we term the critical range) and then estimate the moment with the highest numerical probability of generation–migration–accumulation. We define the uncertainty associated with the critical moment as half the absolute value of the critical range. In cases with little ambiguity or duplicity in the timing of petroleum system elements and processes, the critical range converges to one point, which is also the critical moment. The probabilistic framework introduces consistency to the critical moment estimation problem and quantifies the level of uncertainty in the estimation. This reduces the risk involved in petroleum exploration assessment.

Petroleum system assessment of conventional-unconventional oil in the Jimusar sag, Junggar basin, Northwest China

In recent years, petroleum assessment incorporates the petroleum system concept method instead of the play concept method to estimate petroleum resources, because conventional-unconventional petroleum resources are more reliably estimated by the genetic similarities of petroleum fluids in the petroleum system. Conventional-unconventional oil resources co-exist in the Lucaogou-Permian petroleum system in the Jimusar sag of the Junggar basin, Northwest China. The mean in-place resources (IPR) of tight oil of the Lucaogou Formation (LF) were estimated at 2.0billion tons by an integration method in the Jimusar sag. Based on the assessment of the technically recoverable coefficient by drill productivity, it is estimated that the mean technically recoverable resources (TTR) of tight oil are about 0.11billion tons. The mean IPR and TTR of conventional oil of the Wutonggou Formation (WF) were evaluated at 0.36 billion tons and 0.06billion tons by analogy methods, respectively. The ratio of mean IPR of unconventional oil to conventional oil in the Jimusar is about 5:1, but the ratio of mean TTR is only about 2:1. In addition, tight oil development is higher cost than conventional oil so far. Therefore, the development of tight oil in the Jimusar sag should be a careful consideration. Anyway, the integrated resource assessment of unconventional and conventional oil in the Jimusar sag could provide as a classic example for other lacustrine petroleum systems.

Transform margins: development, controls and petroleum systems – an introduction

Abstract This paper provides an overview of the existing knowledge of transform margins including their dynamic development, kinematic development, structural architecture and thermal regime, together with the factors controlling these. This systematic knowledge is used for describing predictive models of various petroleum system concept elements such as source rock, seal rock and reservoir rock distribution, expulsion timing, trapping style and timing, and migration patterns. The paper then introduces individual contributions to this volume and their focus. Supplementary material: Location table and map of specific transform examples, structural elements of the Romanche transform margin and glossary of terms used in this article is available at https://doi.org/10.6084/m9.figshare.c.3276407

Geologic implications of gas hydrates in the offshore of India: Krishna–Godavari Basin, Mahanadi Basin, Andaman Sea, Kerala–Konkan Basin

Gas hydrate resource assessments that indicate enormous global volumes of gas present within hydrate accumulations have been one of the primary driving forces behind the growing interest in gas hydrates. Gas hydrate volumetric estimates in recent years have focused on documenting the geologic parameters in the “gas hydrate petroleum system” that control the occurrence of gas hydrates in nature. The primary goals of this report are to review our present understanding of the geologic controls on the occurrence of gas hydrate in the offshore of India and to document the application of the petroleum system approach to the study of gas hydrates.National Gas Hydrate Program of India executed the National Gas Hydrate Program Expedition 01 (NGHP-01) in 2006 in four areas located on the eastern and western margins of the Indian Peninsula and in the Andaman Sea. These areas have experienced very different tectonic and depositional histories. The peninsular margins are passive continental margins resulting from a series of rifting episodes during the breakup and dispersion of Gondwanaland to form the present Indian Ocean. The Andaman Sea is bounded on its western side by a convergent margin where the Indian plate lithosphere is being subducted beneath southeast Asia.NGHP-01 drilled, logged, and/or cored 15 sites (31 holes) in the Krishna–Godavari Basin, 4 sites (5 holes) in the Mahanadi Basin, 1 site (2 holes) in the Andaman Sea, and 1 site (1 hole) in the Kerala–Konkan Basin. Holes were drilled using standard drilling methods for the purpose of logging-while-drilling and dedicated wireline logging; as well as through the use of a variety of standard coring systems and specialized pressure coring systems.NGHP-01 yielded evidence of gas hydrate from downhole log and core data obtained from all the sites in the Krishna–Godavari Basin, the Mahanadi Basin, and in the Andaman Sea. The site drilled in the Kerala–Konkan Basin during NGHP-01 did not yield any evidence of gas hydrate. Most of the downhole log-inferred gas hydrate and core-recovered gas hydrate were characterized as either fracture-filling in clay-dominated sediments or as pore-filling or grain-displacement particles disseminated in both fine- and coarse-grained sediments. Geochemical analyses of gases obtained from sediment cores recovered during NGHP-01 indicated that the gas in most all of the hydrates in the offshore of India is derived from microbial sources; only one site in the Andaman Sea exhibited limited evidence of a thermogenic gas source. The gas hydrate petroleum system concept has been used to effectively characterize the geologic controls on the occurrence of gas hydrates in the offshore of India.

Natural emissions of methane from geological seepage in Europe

Recent studies have shown that geological emissions of methane are an important greenhouse-gas source. Remarkable amounts of methane, estimated in the order of 40–60 Tg yr −1, are naturally released into the atmosphere from the Earth's crust through faults and fractured rocks. The main source is natural gas, both microbial and thermogenic, produced in hydrocarbon-prone sedimentary basins and injected into the atmosphere through macro-seeps (onshore and offshore mud volcanoes and other seeps) and microseepage, an invisible but pervasive flux from the soil. This source is now evaluated for Europe on the basis of a literature survey, new field measurements and derived emission factors. The up-scaling criteria recommended by the EMEP/CORINAIR guidelines are applied to the local point and area source data. In Europe, 25 countries host oil and/or natural gas reservoirs and potentially, or actually, emit geological methane. Flux data, however, are available only from 10 countries: the onshore or offshore petroliferous sectors of Denmark, Italy, Greece, Romania, Spain, Switzerland, United Kingdom and Black Sea countries (Bulgaria, Ukraine, Georgia). Azerbaijan, whose emissions due to mud volcanism are known to be relevant, is included in the estimate. The sum of emissions, regional estimates and local measurements, related to macro-seeps leads to a conservative total value of about 2.2 Tg yr −1. Together with the potential microseepage fluxes from the petroliferous basins, estimated on the basis of the Total Petroleum System concept (around 0.8 Tg yr −1), the total European seepage is projected to 3 Tg yr −1. This preliminary figure would represent, in terms of magnitude, the second natural methane source for Europe after wetlands. The estimate will have to be refined by increasing the number of seepage measurements both on lands, where there is high potential for microseepage (e.g., Germany, Hungary, Romania, Ukraine, Belarus, Russia, Georgia) and in coastal marine areas (the North Sea, the Black Sea, offshore Greece and Italy) where emission factors and the extent of the underwater seeping area are not completely known.

Petroleum systems in the Damintun Depression, Liaohe Oilfield

There are two different types of oils—high-wax oil and normal oil—found in the Damintun Depression of Liaohe Oilfield after several years of exploration and development, but their distributions and origins had confused the explorers in the oilfield. The introduction of petroleum-system concept shifts the view of geoscientists from geology and geophysics to oil, gas and their related source rocks. After detailed study, two petroleum systems have been identified in the Damintun Depression: (1) the ES42-Ar buried hill petroleum system (called the high-wax oil petroleum system) and (2) the ES41+ES34-ES4 and ES3 petroleum system (called the normal oil petroleum system). Based on the detailed analysis of the basic components, and all the geological processes required to create these elements of the two petroleum systems, it is put forward that targets for future exploration should include the area near Dongshenpu-Xinglongpu and the area near the Anfutun Sag. This provides scientific basis and has theoretical and practical meaning for the exploration and development.

Modification of the petroleum system concept: Origins of alkanes and isoprenoids in crude oils: Discussion

In their recent paper, Collister et al. (2004) presented a statistical analysis of C10–C28 n-alkane and C16–C21 regular isoprenoid distributions of oils and rock extracts from the Timan-Pechora basin. They found that all unaltered to moderately biodegraded samples could be described as mixtures of six end-member compositions that were assigned to five unique biological sources and to one reservoir process (biodegradation). Because the end members appeared to yield no indications of thermal maturation, Collister et al. surmised that these hydrocarbons were generated not from the thermal cracking of kerogen, but from the liquefaction of biopolymers. If this theory is true, our current paradigms of oil generation and source rock potential need to be changed drastically because it suggests that a significant quantity of liquid hydrocarbons can be generated directly from unaltered biological precursors instead of the thermal cracking of kerogen. We respectfully disagree with the conclusions and hypotheses reached by Collister et al. We regard their interpretation of the statistical analysis of the hydrocarbon distribution data to be flawed and their hypotheses concerning the generation of C10+ n-alkanes and isoprenoids during diagenesis from biopolymers to be incorrect. The mathematical procedure (polytopic vector analysis) used by Collister et al. has the ability to extract end-member spectra from mixed systems. They found that six end members were needed to explain most of the variance in the data. This is not a unique solution, however, because the inclusion of additional end members will always improve the overall goodness of fit. Whether these six end-member fluids truly are representative of specific biological precursors, geologic processes, or are merely mathematical constructs cannot be resolved from the statistical analysis alone. Although Collister et al. claim that five of the end members bear the signature of specific biological sources and …

Modifications of the petroleum system concept: Origins of alkanes and isoprenoids in crude oils: Reply

Kerogen, the source material for petroleum, can have a long history of alteration and diagenesis before crude oil forms. A common assumption is that the bulk composition of the expressed oil reflects so much of these progressive alterations that most of the primary biological information of the original fixed carbon has been lost. Exceptions are trace constituents, the biomarkers that comprise only a fraction of the organic material in most pristine crude oils. Analysis of the alkane/acyclic isoprenoid fraction of a large number of crude oils and rock extracts from the Timan-Pechora basin (Russia) suggest that this fraction, the main constituent of most crude oils, is a direct product of liquefaction of biological debris that was preserved essentially unaltered to the point of oil generation. Therefore, the primary biological provenance of this fraction is preserved in the oil fraction.A set of gas-chromatographic analyses of 242 crude oils as well as 83 solvent extracts from upper to middle Paleozoic putative source rocks from the Timan-Pechora basin (Russia) were analyzed by a multivariate data-analytical procedure new to organic geochemistry. The distributions of n-alkanes and acyclic isoprenoids (24 in all) in the 325 samples could be reproduced by linear combinations of six end-member compositions attributed to distinct biological inputs. Four of the six are assigned to primary producers (waxes from higher plants, cyanobacteria, microalgae, and the microorganism Gloeocapsomorpha prisca). These end members account for most of the n-alkanes and acyclic isoprenoids in our samples. The other two represent the products of secondary bacterial alteration of primary organics during sedimentation and low-level bacterial alteration in the reservoir (biodegradation). Each end member is composed of a spectrum of analytes whose abundances are related to one another by fixed ratios. We surmise that each primary end member represents the breakdown of a resistant biopolymer that forms cell walls and partitions of a given biological group. The n-alkanes and acyclic isoprenoids in crude oils represent the weighted signatures of their various ancestors (i.e., their primary organic inputs). If the precursors of most oils are the products of a small set of chemically simple biopolymers, then many of our assumptions concerning the importance of total organic carbon and the nature of the oil window must be reexamined.

Understanding petroleum systems: an overview

Recent developments in petroleum geochemistry and basin modelling have advanced the petroleum system concept linking reservoired hydrocarbons to their source rocks. However, this link is often very complex involving the use of multi-dimensional basinal models to simulate maturation, hydrocarbon generation and fluid flow. New developments and concepts are discussed in this introductory chapter and succeeding section, with their application to both NW European petroleum provinces and frontier exploration areas of the world.

Petroleum in the South Atlantic

The petroleum deposits in the South Atlantic are considered in terms of the contemporary understanding of the formation of petroleum and of the petroleum system concept. These hydrocarbon reserves (7% of the global reserves), contained in the sedimentary rims along the coasts of West Africa and of the Eastern seaboard of South America, result from a favourable geological setting that is essentially the same on both sides of the ocean, giving rise to an almost symmetrical pattern. Their history is described within the general framework of the opening of the South Atlantic Ocean, which began over 140 Ma ago with the breaking up of the proto-continent Pangea. The importance of these concepts for the opening up of deep and ultra-deep offshore prospects in West Africa and Brazil is underlined.

Modification of the petroleum system concept: Origins of alkanes and isoprenoids in crude oils

Modification of the petroleum system concept: Origins of alkanes and isoprenoids in crude oils

Abstract: Application of the Total Petroleum System Concept to Assessing Undiscovered Gas Resources of the Ghaba and Fahud Salt Basin Provinces, North-Central Oman

Abstract: Application of the Total Petroleum System Concept to Assessing Undiscovered Gas Resources of the Ghaba and Fahud Salt Basin Provinces, North-Central Oman

An overview of the petroleum systems of Morocco

Abstract Magoon & Dow’s petroleum system concept is utilized in this paper to evaluate the origin of the proven hydrocarbon resources of Morocco, which lie chiefly in the Essaouria, Prerif and Rharb Basins. Several systems are interpreted, in which the confidence in the source-petroleum tie varies from ‘known’ to ‘speculative’, involving charge from Silurian (eastern Essaouira), Lias (Prerif), Oxfordian (western Essaouira), Cretaceous (Ain Hamra) and an intra-Miocene biogenic system in the Rharb Basin. The origin of the Cap Juby heavy oil accumulation in the offshore Tarfaya basin is uncertain, with a Jurassic carbonate source currently the favoured interpretation. The petroleum system concept is extended in this paper to predict further, currently undrilled and unproven systems. These include areas where the proven source systems referred to above are likely to extend, plus additional systems predicted on the basis of analogues to surrounding regions. An example of the latter is a series of postulated Triassic systems developed in lacustrine deposits in offshore half-grabens. Palaeozoic source rocks may be regionally developed and may still be in the oil and gas windows over wide, generally unexplored, regions. Lower to Middle Jurassic source rocks are predicted in lagoonal settings in platform sags and in outer shelf environments, whereas Cretaceous source beds occur in continental rift complexes and passive margins, with maturity likely to be reached in depocentres and below thrusts. Biogenic gas potential is probably confined to Neogene deposits in foreland and divergent margin basins. Further application of the petroleum system concept should help to significantly reduce geological risk, particularly in frontier exploration areas.

The Petroleum System Concept in the Sergipe Basin, Northeasthern Brazil: ABSTRACT

The Petroleum System Concept in the Sergipe Basin, Northeasthern Brazil: ABSTRACT

Beyond the Petroleum System: GEOHORIZONS

The first joint AAPG/AMGP (Association of Mexican Petroleum Geologists) Hedberg Conference on Geologic Aspects of Petroleum Systems was held October 2-6, 1994, in Mexico City, Mexico. This research conference attracted nearly 150 geoscientists from 15 countries; 41 papers and 27 posters were presented. The opposite response occurred when the petroleum-system concept was presented more than 20 yr ago; it was largely overlooked. In the past decade, however, interest in this concept as an exploration tool has been growing rapidly. The research conference addressed the concept itself, its elements and processes, the tools and methods used to identify a petroleum system, and many case studies. We summarize responses by the participants to the following three questions. First what is gained from using the petroleum-system concept? Second, in what new directions will the petroleum-system concept take us in the future? Third, has anything new come out of this research conference?

A Successful Application of the Petroleum System Concept in the Camamu Basin, Offshore Brazil: ABSTRACT

The characterization of a major petroleum system in the Camamu basin, NE Brazil, was undertaken using a multidisciplinary approach involving geochemical, geological, geophysical and microbiostratigraphic research. This approach has greatly enhanced the level of understanding of the petroleum system concept in the area, allowing the identification of a new exploration target. The hydrocarbons sourced by the lowermost Cretaceous lacustrine fresh to brackish water black shales, started migration during the Early Cretaceous times, continuing up to now in some parts of the basin. The hydrocarbons were accumulated in Lower Cretaceous, Rio de Contas Formation lacustrine sandstone reservoirs, structured during the rifting process, and sealed by deep water lacustrine shales, or trapped in the Dom Joao Stage (Jurassic), Sergi Formation, against the footwall of major regional faults. The geochemical parameters indicate that the Camamu basin is basically oil prone. Mapping the geographic extent of the petroleum system emphasizes the association of the oil fields with the proposed pod of active source rocks. The integration of these data with a 2D-geochemical modelling allowed the prediction and characterization, in time and space, of the petroleum pathways from source to trap in the area. Two major petroleum systems were selected, as the most attractive, inmore » the Camamu Basin: the pre-rift Morro do Barro-Sergi (!) and synrift Morro do Barro-Rio de Contas (!). This approach allowed the identification of a new exploration target, in the latter one, which, after drilling, resulted in a 157 M bbl discovery, and brought a new insight for the hydrocarbon exploration in the basin.« less

Two Petroleum Systems in the Sacramento Basin, California--A Basis for New Discoveries: ABSTRACT

The Sacramento basin is a north-trending fore-arc basin that contains Lat Jurassic to Holocene sedimentary rocks that become thicker to the south and are overpressured at depth. The basin fill is about 300 km long, 80 km wide, and as much as 16 km thick. Two petroleum systems occur in the Sacramento basin. The Dobbins-Forbes( ) gas system, which contained about 2.25 tcf (10[sup 12]ft[sup 3]) of recoverable gas, underlies the Winters-Domingine( ) gas system, which contained about 6.89 tcf of recoverable gas. Gas migrated laterally and to the north as much as 200 km in the Dobbins-Forbes( ) system, whereas in the Winters-Domingine( ) system, gas first migrated vertically and then crossed the Midland fault to the east for up to 40 km. For both systems, depth of gas production from reservoir rocks of Lake Cretaceous to Oligocene in different trap types is less than 3 km. By applying the petroleum-system concept and information about the geology and geochemistry available for this province, this study- provides a new testable hypthesis for the origin, migration, and accumulation of gas in the Sacramento basin. By reinterpreting some of the natural gas information, gas wetness, gas-oil ratio, vectors of migration, hydrocarbon volume,more » and thermal history, two petroleum systems are identified. Understanding of the origin of known accumulations in this province provides a basis for new plays that should lead to discoveries with substantial reserves.« less

The Petroleum System as an Exploration Tool in a Frontier Setting

Use of the petroleum system concept as an exploration tool requires synthesis of the influence of three geological processes connected in space and time to create each petroleum system. These three processes are the generation, migration, and trapping of petroleum. An evaluation procedure that makes this synthesis provides a logical mechanism for ranking the conceptual petroleum systems in a given frontier area with respect to hydrocarbon charge questions. In a frontier area this evaluation procedure starts with a regional geologic model of the area based on a seismic grid calibrated to the available stratigraphic control. This model should go to basement, that is, to a layer deep enough to include all potential source rocks for those conceptual petroleum systems of interest. This model should be developed using seismic stratigraphy methods to define depositional sequences, major transgressions, and regressions related to global sea-level changes, paleo-topography and other characteristics important for predicting and extrapolating source rocks, reservoirs, and seals. If the area has a complex tectonic history, several models may be required, each representing a different stage in the evolution of the area. Considerable experience has been gained over the past 23 years in the application of this approach to evaluate hydrocarbonmore » charge questions in the frontier area of North America. Examples drawn from this experience will be presented to illustrate successes, failures, and difficulties of prediction based on the petroleum system concept.« less