Spectral decomposition' application for stratigraphic-based quantitative controls on Lower-Cretaceous deltaic systems, Pakistan: Significances for hydrocarbon exploration

The Torquay Sub-basin lies to the south of Port Phillip Bay in Victoria. It has two main tectonic elements; a Basin Deep area which is flanked to the southeast by the shallower Snail Terrace. It is bounded by the Otway Ranges to the northwest and shallow basement elsewhere. The stratigraphy of the area reflects the influence of two overlapping basins. The Lower Cretaceous section is equivalent to the Otway Group of the Otway Basin, whilst the Upper Cretaceous and Tertiary section is comparable with the Bass Basin stratigraphy.The Torquay Sub-basin apparently has all of the essential ingredients needed for successful hydrocarbon exploration. It has good reservoir-seal pairs, moderate structural deformation and probable source rocks in a deep kitchen. Four play types are recognised:Large Miocene age anticlines, similar to those in the Gippsland Basin, with an Eocene sandstone reservoir objective;The same reservoir in localised Oligocene anticlines associated with fault inversion;Possible Lower Cretaceous Eumeralla Formation sandstones in tilted fault blocks and faulted anticlines; andLower Cretaceous Crayfish Sub-group sandstones also in tilted fault block traps.Maturity modelling suggests that the Miocene anticlines post-date hydrocarbon generation. Poor reservoir potential and complex fault trap geometries downgrade the two Lower Cretaceous plays.The Oligocene play was tested by Wild Dog-1 which penetrated excellent Eocene age reservoir sands beneath a plastic shale seal, however, the well failed to encounter any hydrocarbons. Post-mortem analysis indicates the well tested a valid trap. The failure of the well is attributed to a lack of charge. Remaining exploration potential is limited to the deeper plays which have much greater risks associated with each play element.

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Characterization and origin of large Campanian depressions within the Chalk Group of the Danish Central Graben – implications for hydrocarbon exploration and development

Geological Society London Special Publications ◽

10.1144/sp509-2019-126 ◽

2020 ◽

pp. SP509-2019-126

Author(s):

Florian W. H. Smit ◽

Lars Stemmerik ◽

Mikael Lüthje ◽

Frans S. P. van Buchem

Keyword(s):

Lower Cretaceous ◽

Current System ◽

Isotope Analysis ◽

Fault Reactivation ◽

Hydrocarbon Exploration ◽

Source Rocks ◽

Bottom Current ◽

Current Activity ◽

Fluid Venting ◽

Gas Bearing

AbstractThis study re-examines large and deep U-shaped reflections (2–4 km wide and 100–200 m deep) within the Upper Cretaceous–Danian Chalk Group in the inverted Roar Basin of the Danish North Sea, previously interpreted as a moat associated with a contour-parallel current system and/or erosive channels formed by gravity-driven turbidites. Improved 3D seismic data quality and seismic interpretation techniques helped to identify overlooked reflection terminations, which suggest that rather than a linear depression, the U-shaped reflections outline several bowl-shaped depressions. In addition, vertical high-amplitude columns and vertical discontinuity zones within and below the depressions were recognized and interpreted to indicate the presence of small fluid pipes, suggesting that the formation of the depressions is more complex. Carbon isotope analysis of high acoustic impedance beds within the underlying Lower Cretaceous chalk showed negative δ13C values down to −20‰, and are interpreted to indicate sediments influenced by methane-derived authigenic carbonates. Permo-Triassic half-grabens seem to have been a major source of gas-bearing fluids, as evidenced by hydrocarbon leakage phenomena within Triassic–Lower Cretaceous strata. In areas where Zechstein salt is present, the leakage root lies at salt welds, causing the formation of focused seismic reflection wipe-out and dim zones. In areas where salt was absent, the leakage root comprises a much more diffuse zone across the fault boundaries of the Permo-Triassic half-graben, and gas chimneys are characterized seismically as broad vertical dim zones up to 10 km wide. Campanian inversion tectonics caused fault reactivation and several hundreds of metres of uplift in the Roar Basin, which created an instability for the trapped gas-bearing fluids. Gentle fluid venting through observed pipes caused sediment suspension and entrainment, which could be carried away by bottom-current activity, causing localized zones of non-deposition and the formation of individual depressions. This model thus does not disregard the role of bottom-current activity in the formation of the depressions, yet it includes a fluid-venting element that fits better with the architecture and overall evidence for fluid-venting features in pre-chalk strata, as well as in the Chalk Group. Importantly, it shows that prior to the thermogenic maturation of the main source rock (i.e. the Bo Member of the Farsund Formation in the Late Miocene), fluid venting had already occurred on the Late Cretaceous seafloor from deeper source rocks that are at present overmature.

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APPLICATION OF TIME-FREQUENCY DECOMPOSITION METHOD FOR GAS RESERVOIR IDENTIFICATION IN THE SERGIPE - ALAGOAS BASIN

Brazilian Journal of Geophysics ◽

10.22564/rbgf.v36i2.943 ◽

2018 ◽

Vol 36 (2) ◽

pp. 189

Author(s):

Alexandre De Jesus Pinho ◽

Milton José Porsani

Keyword(s):

Spectral Decomposition ◽

Reservoir Characterization ◽

Low Frequency ◽

Seismic Attributes ◽

Entropy Method ◽

Hydrocarbon Exploration ◽

Maximal Entropy ◽

Time Frequency ◽

High Attenuation ◽

Frequency Decomposition

ABSTRACT. The sedimentary basin of Sergipe-Alagoas, located on the Brazilian east bank, presents one of the most complete stratigraphic sections of the Brazilian continental margin. Hydrocarbon exploration activities began more than 50 years ago. The recent discoveries of hydrocarbons (gas and oil of high API grade) in turbiditic reservoirs of deep waters have further awakened the exploratory interest of the basin. Problems related to the processing and interpretation of seismic data have always received great attention from the scientific community. Currently, the use of time-frequency decomposition methods of the seismic signal is of great interest. Spectral decomposition has been widely used in reservoir characterization, such as determination of layer thickness, stratigraphic visualization with seismic attributes and identification of low frequency anomalies associated with the presence of gas. The mechanism causing these anomalies is not yet well known, but they are often attributed to the high attenuation of gas filled reservoirs. The approach used for spectral decomposition combines the maximal entropy method and the Wigner-Ville distribution, based on the idea of the Burg method that uses the prediction error operator to extend the Wigner-Ville kernel sequences by applying, then, the Fourier transform to each extended sequence of the Kernel, thus allowing to obtain the Wigner-Ville distribution of maximum Entropy.Keywords: Sergipe-Alagoas Basin, Wigner-Ville distribution, Maximum Entropy, spectral decomposition, seismic attributes, low frequency anomaly.RESUMO. A bacia sedimentar de Sergipe-Alagoas, localizada na margem leste brasileira, apresenta uma das mais completas seções estratigráficas da margem continental brasileira. As atividades exploratórias de hidrocarbonetos foram iniciadas há mais de 50 anos. As recentes descobertas de hidrocarbonetos (gás e óleo de elevado grau API) em reservatórios turbidíticos de águas profundas despertaram ainda mais o interesse exploratório da bacia. Os problemas relacionados ao processamento e `a interpretação de dados sísmicos sempre receberam grande atenção da comunidade científica. Atualmente, desperta grande interesse o uso de métodos de decomposição tempo-frequência do sinal sísmico. A decomposição espectral tem sido bastante utilizada na caracterização de reservatório, como estimativa de espessura de camada, visualização estratigráfica com atributos sísmicos e identificação de anomalias de baixa frequência que podem estar associadas `a presença de gás. O mecanismo causador dessas anomalias ainda não é perfeitamente conhecido, mas é frequentemente atribuído a atenuação das altas frequências nos reservatórios preenchidos com gás. A abordagem utilizada para a decomposição espectral combina o método de máxima entropia e a distribuição de Wigner-Ville, com base na ideia do Método de Burg que usa o operador de erro de predição para estender as sequências do kernel de Wigner-Ville aplicando a transformada de Fourier para cada sequência estendida do kernel, permitindo assim, obter a distribuição Wigner-Ville de máxima entropia.Palavras-chave: Bacia Sergipe-Alagoas, distribuição Wigner-Ville, Máxima Entropia, decomposição espectral, atributos sísmicos, anomalia de baixa frequência. Universidade Federal

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Abstract: Sequence Stratigraphy of the Lower Cretaceous Lake-Sediments of the West African Rift - a Tool for Hydrocarbon Exploration

AAPG Bulletin ◽

10.1306/1d9bd795-172d-11d7-8645000102c1865d ◽

1998 ◽

Vol 82 (1998) ◽

Author(s):

Bate, Raymond H.

Keyword(s):

Lake Sediments ◽

Sequence Stratigraphy ◽

Lower Cretaceous ◽

West African ◽

Hydrocarbon Exploration ◽

The West ◽

African Rift

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Geochemical Inversion Applied to Oil Samples from Lower Cretaceous Reservoirs, Southeast Abu Dhabi: Implications for Hydrocarbon Exploration

10.2118/207558-ms ◽

2021 ◽

Author(s):

Lozano Mario Jorge ◽

Hilario Camacho ◽

Jose Guevara

Keyword(s):

Lower Cretaceous ◽

Oil And Gas ◽

Compositional Data ◽

Structural Evolution ◽

Hydrocarbon Exploration ◽

Source Rocks ◽

Abu Dhabi ◽

Oil Composition ◽

Petroleum Systems ◽

The World

Abstract The Middle East contains some of the most fascinating and prolific oil provinces in the world. The combination of excellent source rocks of different geologic ages, the presence of outstanding reservoirs and ubiquitous seals, optimal thermal history, and structural evolution provides an ideal recipe to produce the largest oilfields in the world. The UAE is currently estimated to hold 6% of global oil reserves, 96% of which are within Abu Dhabi. However, exploration for additional recoverable reserves is becoming more challenging. Finding hydrocarbons for the future is dependent upon a detailed understanding of the petroleum systems and subtle play types. For southeastern Abu Dhabi, several petroleum systems have been proposed to explain the oil and gas accumulations in Lower Cretaceous reservoirs. This study presents the practical application of a geochemical inversion workflow to a set of oil samples from Lower Cretaceous reservoirs collected in two exploration wells recently drilled in southeastern Abu Dhabi. The geochemical inversion workflow is based on stable isotope, biomarker, and oil composition data. Preliminary results and comparisons with previously identified oil families in the UAE suggest that the oils were generated from a carbonate-rich source rock deposited during Jurassic time. Compositional data and detailed stratigraphic and structural analyses support the possibility of multiple episodes of lateral and vertical migrations. The implications and risk associated with the timing of oil generation and trap formation are presented here to define a path forward and guide the prospecting efforts within this exciting region.

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Revised Stratigraphy, Depositional Systems, and Hydrocarbon Exploration Potential for the Lower Cretaceous Muddy Sandstone, Northern Denver Basin

AAPG Bulletin ◽

10.1306/c9ebcda1-1735-11d7-8645000102c1865d ◽

2000 ◽

Vol 84 ◽

Author(s):

John P. Graham2

Keyword(s):

Lower Cretaceous ◽

Hydrocarbon Exploration ◽

Denver Basin ◽

Depositional Systems ◽

Muddy Sandstone

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Palynostratigraphy and paleoecology of a Lower Cretaceous (upper Barremian–lower Aptian) succession in the Shushan Basin, northwestern Egypt: inferences on intra- and inter-basinal correlations

Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen ◽

10.1127/njgpa/2019/0855 ◽

2019 ◽

Vol 294 (2) ◽

pp. 177-195 ◽

Cited By ~ 2

Author(s):

Tarek F. Mostafa ◽

Amr S. Deaf ◽

Maher I. El Soughier ◽

Walid A. Makled

Keyword(s):

Source Rock ◽

Lower Cretaceous ◽

Relative Difference ◽

Hydrocarbon Exploration ◽

Western Desert ◽

The North ◽

Depositional Settings ◽

Assemblage Zone ◽

Local Tectonics ◽

North Western

Recent national and international demand for additional resources of the fossil fuel resulted in extensive hydrocarbon exploration activities in Egypt to further explore possible petroliferous rock units that were conventionally deemed as barren or having non- commercial reserves such as the Alam El Bueib Formation. This increased the stress to enrich the lithological correlation of this formation across the north Western Desert to better understand its regional lithological characteristics and thus its potential regional reservoir/source rock quality. Palynostratigraphic analysis of Lower Cretaceous successions in the Tut-1X and Amoun-1X wells in the Shushan Basin, north Western Desert enabled the recognition of the upper Alam El Bueib Formation in both wells, in contrast to a previous study, which suggested non-deposition of this formation in the Amoun-1X well. This highlights the important role of the palynology as a key stratigraphic tool, which helped effectively in recognising this problematic monotone clastic formation, where other marine microfossils are lacking. This also shows that recognition of this formation based on lithological criteria only was impractical and misleading. Marker terrestrial and marine palynomorph taxa recovered from the upper Alam El Bueib Formation enabled dating it as late Barremian– early Aptian and were used to identify two palynological biozones that can be traced out regionally across the Shushan, Matruh, and other nearby basins. These biozones are the early Aptian Murospora florida – Afropollis operculatus – Pseudoceratium securigerum Assemblage Zone and the late Barremian Stellatopollis barghoornii – Pseudoceratium anaphrissum– Cyclonephelium vannophorum Assemblage Zone. An undifferentiated interval was recorded just below the upper Barremian strata in the Tut-1X well due to very low palynomorph recovery and absence of marker forms. Composition of terrestrial and marine palynomorph assemblages suggests the upper Alam El Bueib Formation was deposited in fluviodeltaic to proximal inner shelf settings. The Alam El Bueib Formation shows notable regional variations in thickness and considerable lateral and verti- cal changes in lithology due to local tectonics and relative difference in its depositional settings in the Shushan and Matruh basins. Regionally, the Alam El Bueib Formation shows dual reservoir/source rock characteristics, where thick and poorly fossiliferous sandstone units act as reservoir rocks, while moderately fossiliferous finer clastics and carbonates already acted as intraformational source rock intervals in some parts of the Shushan and Matruh basins.

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