Km Of Seismic Data Research Articles

Lateral changes of crustal extension and passive margin type along the Brazilian southeastern margin

For the last half century, studies based on an increasing, diverse data set, have focused on passive continental margin evolution, as a result of a sequence of tectonic processes that occur in crustal scale and in the geological time. Where extensive subsurface data exists, two distinct endmembers of continental margin architectures were first described along specific margins of the North Atlantic: 1) wide continent-ocean transitions or hyper-extended; 2) narrow continent-ocean transitions or hypo-extended. The lateral transition between these endmember margins, which can occur laterally in short distances, is still not fully understood. The same two endmember margin types are observed across passive margins around the world and notably along the South Atlantic margin. In an area known for controversial interpretations about the crustal nature and the limits of thinned continental crust, this investigation integrates crustal thickness, seismic interpretation, and facies analyses across ∼150,000 km of seismic data along the Brazilian southeastern margin. This study has implications for those investigating the crustal geometry variations for basin analysis and results impact hydrocarbon assessments for the southeastern margin of Brazil. We resume continental margin analyses, in a critical moment as hydrocarbon exploration advances from the continental slope to ultra-deep waters. Results indicate a marked change from a narrow, hypo-extended, sub-aerial, Iceland-like, plume-related volcanic crust in the Pelotas Basin, to a hyper-extended, Iberia-like, magma-rich crust in the Santos Basin, which is separated by a pronounced oceanic transform-fault zone. Dextral movement along this NW-oriented fault zone accommodated differential extensional rates between the hypo- and the hyper-extended margins. Lateral variations in magmatic content within these margin types are interpreted as result from the interaction with mantellic plumes. Margin architecture can locally be affected by pre-existing fault zones and be later modified by oceanic transform faults. The interactions between crustal extensional rates, crustal rheology, mantle underplating, and volcanic material exhumed through mantle-derived plumes, are the key controls for the evolution of continental margins. Tectonic framework classification proposed in this study presents an alternative, original model for continental passive margins evolution.

RESULTS OF INTERPRETATION OF SEISMIC SECTIONS DURING ENGINEERING SURVEYS WITHIN OF THE SOUTH-KIRINSKOYE OIL AND GAS CONDENSATE FIELD (SHELF OF SAKHALIN ISLAND)

High-resolution 2D seismic is the main and optimal method in marine engineering geophysics, which for many years has worked well for the production of semi-submersible drilling rigs, self-lifting drilling rigs, construction of berthing facilities and bridges. The main objective of this method is to identify near-surface gas, faults, which are geological hazards. The method used for performing marine research is longitudinal profiling of reflected waves with a 48-fold overlap of the reflecting horizons. To obtain high-quality seismic migrated sections, we have previously developed a unified data processing algorithm for the offshore areas of the South-Kirinskoye oil and gas condensate field (Sakhalin shelf). More than 8,000 line km of seismic data were processed. The article presents the sequence of interpretation, as well as an analysis of the presence of hazards in the project wells (objects). To isolate potentially dangerous objects for each horizon, a dynamic analysis was carried out, which included the definition of the following parameters: maximum and minimum peak amplitude. The systematization and classification of amplitude anomalies was carried out according to such features as a phase change, frequency reduction, the presence of a supply channel and distortion (false deflection) of all underlying boundaries, indicating the possible presence of gas. The probable hazard levels for drilling operations were determined. All the identified anomalies in the process of interpreting seismic sections were mapped to the geological hazards to select the optimal and safe installation point for drilling a prospecting or exploration well.

Developing cost-effective seismic mineral exploration methods using a landstreamer and a drophammer

To be fully embraced into mineral exploration, seismic data require to be acquired fast, cheaper and with minimum environmental impacts addressing also the often brown-field highly noisy environment where these surveys are employed. Since 2013 and through a number of case studies, we have been testing a newly developed for urban environment, digital-based 240 m long, seismic landstreamer for mine planning and mineral exploration purposes. Here, we present a pilot study examining the potential of the streamer for deep targeting a known, down to approximately 850 m depth, iron-oxide mineralization in the Bergslagen mineral district of central Sweden. Combined streamer (100-3C-MEMS (micro-electromechanical system), 2–4 m spacing) and 75 wireless recorders (mixed 10 Hz and MEMS, 10 m spacing) were used. A Bobcat-mounted drophammer, 500 kg, was used to generate the seismic signal. Within 4 days, approximately 3.5 km of seismic data using 2–10 m source and receiver spacing were acquired. Reflection data processing results clearly image the mineralization as a set of strong high-amplitude reflections and likely slightly extending beyond the known 850 m depth. This is encouraging and suggests such a cost-effective exploration method can be used in the area and elsewhere to delineate similar depth range iron-oxide deposits.

Petroleum potential of the offshore southern Carnarvon Basin—insights from new Geoscience Australia data

In 2008–9, under the Offshore Energy Security Program, Geoscience Australia (GA) acquired 650 km of seismic data, more than 3,000 km of gravity and magnetic data, and, dredge samples in the southern Carnarvon Basin. This area comprises the Paleozoic Bernier Platform and southern part of the Mesozoic Exmouth Sub-basin. The new seismic and potential field data provide a new insight into the structure and sediment thickness of the deepwater southernmost part of the Exmouth Sub-basin. Mesozoic depocentres correspond to a linear gravity low, in water depths between 1,000–2,000 m and contain between 2–3 sec (TWT) of sediments. They form a string of en-echelon northeast-southwest oriented depressions bounded by shallow-dipping faults. Seismic data indicates that these depocentres extend south to at least 24°S, where they become more shallow and overprinted by volcanics. Potential plays in this part of the Exmouth Sub-basin may include fluvio-deltaic Triassic sandstone and Lower–Middle Jurassic claystone source rocks sealed by the regional Early Cretaceous Muderong shale. On the adjoining Bernier Platform, minor oil shows in the Silurian and Devonian intervals at Pendock–1a indicate the presence of a Paleozoic petroleum system. Ordovician fluvio-deltaic sandstones sealed by the Silurian age marine shales, Devonian reef complexes and Miocene inversion anticlines are identified as potential plays. Long-distance migration may contribute to the formation of additional plays close to the boundary between the two provinces. With a range of both Mesozoic and Paleozoic plays, this under-explored region may have a significant hydrocarbon potential.

Role of the Wan-Na fault system in the western Nansha Islands (Southern South China Sea)

Since 1987, the South China Sea Institute of Oceanology, Chinese Academy of Sciences, has acquired about 20,000 km of seismic data in Nansha (Spratly) Islands waters, southern South China Sea (SCS). Interpretation and correlation of the profiles crossing the western part of the waters, indicate that the Wan-Na Fault Zone is a dextral strike-slip system composed of the following: (1) Ranai-Sarawak strike-slip-contractional imbricate fan at its southern segment, (2) a strike-slip-extensional imbricate fan at its northern segment in the southwestern end of the Southwest subbasin (SWSB) of the South China Sea, and (3) a strike-slip-pull-apart duplex of the Wan'an basin in the central segment. The northern segment is characterized by the faults that tend to converge toward the side of the Wan-Na fault zone to the southwest and splay toward the Southwest subbasin to the northeast, down-faulted step by step. Lithospheric delamination beneath the South China-Indochina continental margins and seafloor spreading of the South China Sea led to the development of the Wan-Na fault zone as a plate-bounding tectonic element in the region. As a whole, its major activity occurred during the Eocene to Early Miocene. The strike-slip system and pull-apart duplex directly resulted in the generation of the Wan'an basin.

Seafloor Features and Characteristics of the Black Ledges Area, Penobscot Bay, Maine, USA.

ABSTRACT The Black Ledges, a series of islands, shoals, and ledges in East Penobscot Bay, Maine, was mapped with digital sidescan sonar and shallow marine seismic reflection equipmentA total of 38 km2 of sidescan and 600 km of seismic data was collected during four cruises in 2000–2001. The sidescan sonar reveals a surficial geology dominated by muddy sediments with frequent, patchy outcrops of gravel and minor amounts of bedrock. There are seven large concentrations of pockmarks with populations totaling over 3500 in the areas of muddy sediments. Generally circular, pockmarks range in size from five to 75 meters in diameter and up to eight meters deep. Calculations show over 2 × 106 m3 of muddy sediment and pore water were removed from the system during pockmark formation. Seismic data reveal a simple stratigraphy of modern mud overlying late Pleistocene glaciomarine sediment, till and Paleozoic bedrock. Seismic data indicate areas of gas-rich sediments and gas-enhanced reflectors in close association wi...

Seismic stratigraphy of the offshore Indus Basin

Abstract In 1997 Lasmo Oil Pakistan Ltd (Lasmo) gained a significant position in the offshore Indus Basin with the award of the Indus A and B Blocks. The main hydrocarbon play comprises Miocene shelf-delta sands interbedded with intraformational shale seals and sourced by gas-prone offshore equivalents. Approximately 12 000 km of seismic data have been interpreted in the detailed evaluation of these blocks. However, only four wells have tested the preferred play type and no core or rock data were available to provide further insights into facies or age dating. Log data from two key wells in the offshore Indus area record the initial infilling of the basin by shale-dominated basinal or outer shelf sediments, followed by stacked thin-bedded sandstone-shale sequences of a shelf-delta nature. A zone of progradational sequences marks the transition between the two, but no other workable stratigraphic divisions were apparent. Regional seismic correlation established the diachronous nature of the prograding shelf package and this was matched by distinct bands of seismic progrades. A series of simple palaeogeographies of the prograding shelf margin were developed showing initial sediment input from the north and rapid progradation towards the south and west. The Oligo-Miocene basin fill of the offshore Indus Basin appears to be a ‘one-step’ fill process of a significant depocentre created between the Karachi Platform and the Murray Ridge. Canyons are a very distinct feature on seismic profiles and two main phases of development are apparent. The earlier phase is interpreted to be of Early Miocene age. Downcutting at this time rarely exceeded 400 m. The second phase of canyon development occurred during Plio-Pleistocene time, and these younger canyons often dominate the shallow section, with multiple phases of downcutting sometimes exceeding 1000 m. Where drilled, canyons of both ages have been found to be shale prone. These drilled canyons are interpreted to be on the palaeo-slope where erosion and sediment by-pass occurred during the active phase, and were subsequently filled by fine-grained deposits after abandonment. The two phases of canyoning are considered to relate to phases of tectonic activity in the collision zone between the western margin of the Indo-Pakistan plate and the Eurasian plate.

NEW PETROLEUM MODELS IN THE PEDIRKA BASIN, NORTHERN TERRITORY, AUSTRALIA

The northern Pedirka Basin in the Northern Territory is sparsely explored compared with its southern counterpart in South Australia. Only seven wells and 2,500 km of seismic data occur over a prospective area of 73,000 km2 which comprises three stacked sedimentary basins of Palaeozoic to Mesozoic age. In this area three petroleum systems have potential related to important source intervals in the Early Jurassic Eromanga Basin (Poolowanna Formation), the Triassic Simpson Basin (Peera Peera Formation) and Early Permian Pedirka Basin (Purni Formation). They are variably developed in three prospective depocentres, the Eringa Trough, the Madigan Trough and the northern Poolowanna Trough. Basin modelling using modern techniques indicate oil and gas expulsion responded to increasing early Late Cretaceous temperatures in part due to sediment loading (Winton Formation). Using a composite kinetic model, oil and gas expulsion from coal rich source rocks were largely coincident at this time, when source rocks entered the wet gas maturation window.The Purni Formation coals provide the richest source rocks and equate to the lower Patchawarra Formation in the Cooper Basin. Widespread well intersections indicate that glacial outwash sandstones at the base of the Purni Formation, herein referred to as the Tirrawarra Sandstone equivalent, have regional extent and are an important exploration target as well as providing a direct correlation with the prolific Patchawarra/Tirrawarra petroleum system found in the Cooper Basin.An integrated investigation into the hydrocarbon charge and migration history of Colson–1 was carried out using CSIRO Petroleum’s OMI (Oil Migration Intervals), QGF (Quantitative Grain Fluorescence) and GOI (Grains with Oil Inclusions) technologies. In the Early Jurassic Poolowanna Formation between 1984 and 2054 mRT, elevated QGF intensities, evidence of oil inclusions and abundant fluorescing material trapped in quartz grains and low displacement pressure measurements collectively indicate the presence of palaeo-oil and gas accumulation over this 70 m interval. This is consistent with the current oil show indications such as staining, cut fluorescence, mud gas and surface solvent extraction within this reservoir interval. Multiple hydrocarbon migration pathways are also indicated in sandstones of the lower Algebuckina Sandstone, basal Poolowanna Formation and Tirrawarra Sandstone equivalent. This is a significant upgrade in hydrocarbon prospectivity, given previous perceptions of relatively poor quality and largely immature source rocks in the Basin.Conventional structural targets are numerous, but the timing of hydrocarbon expulsion dictates that those with an older drape and compaction component will be more prospective than those dominated by Tertiary reactivation which may have resulted in remigration or leakage. Preference should also apply to those structures adjacent to generative source kitchens on relatively short migration pathways. Early formed stratigraphic traps at the level of the Tirrawarra Sandstone equivalent and Poolowanna Formation are also attractive targets. Cyclic sedimentation in the Poolowanna Formation results in two upward fining cycles which compartmentalise the sequence into two reservoir–seal configurations. Basal fluvial sandstone reservoirs grade upwards into topset shale/coal lithologies which form effective semi-regional seals. Onlap of the basal cycle onto the Late Triassic unconformity offers opportunities for stratigraphic entrapment.

Basin dynamics and mineralisation, McArthur Basin, northern Australia

The Broadmere Structure is a concealed complex inversion structure that developed in a well preserved part of the Batten Trough in the southern McArthur Basin of northern Australia. The structure formed in response to a number of major tectonic events over a period of at least 600 million years. Evaluation of more than 300 km of seismic data gathered across the structure has provided significant insight into the evolution of the basin architecture which, in turn, has provided a framework for understanding the spatial and temporal distribution of mineralisation. The Palaeoproterozoic McArthur Basin, a polyphase basin with a long and complex evolutionary history, was initiated some time after 1.8 Ga as a sag basin following mantle activity associated with supercontinent assembly. This shallow sag then began to accumulate a relatively mature clastic sedimentary succession with interspersed basic volcanics. Subsequent extension of the weakened crust, beginning at approximately 1730 Ma, led to the development ...

Basin dynamics and mineralisation, McArthur Basin, northern Australia

The Broadmere Structure is a concealed complex inversion structure that developed in a well preserved part of the Batten Trough in the southern McArthur Basin of northern Australia. The structure formed in response to a number of major tectonic events over a period of at least 600 million years. Evaluation of more than 300 km of seismic data gathered across the structure has provided significant insight into the evolution of the basin architecture which, in turn, has provided a framework for understanding the spatial and temporal distribution of mineralisation. The Palaeoproterozoic McArthur Basin, a polyphase basin with a long and complex evolutionary history, was initiated some time after 1.8 Ga as a sag basin following mantle activity associated with supercontinent assembly. This shallow sag then began to accumulate a relatively mature clastic sedimentary succession with interspersed basic volcanics. Subsequent extension of the weakened crust, beginning at approximately 1730 Ma, led to the development of a series of normal faults and half grabens within zones (e.g. Batten Trough) defined laterally by major strike slip fault complexes. The half grabens were filled initially by volcaniclastic sediments with associated bimodal volcanics that were later followed by mixed carbonate and clastic sediments exceeding 8 km in thickness. A major change in basinal and regional dynamics between 1575 and 1500 Ma (Isan Orogeny) led to the inversion of the thickened succession overlying the half grabens and extensive erosion of earlier depositional units, followed by deposition of a further 3 km of shallow marine clastic sediments. The analysis of the Broadmere Structure has provided a simple framework in which to evaluate prospectivity. The primary northwest striking half grabens formed localised anoxic, sediment starved depocentres in which organic rich sediments that potentially host mineralisation accumulated. The distribution of subsequent ore bodies is a function of the timing of fluid movement and the nature of fluid pathways, as determined by the evolving basin architecture. Fluids moved laterally through the permeable channels into the Batten Trough in two stages. Spatial data show that Pb and Zn occurrences lie close to the bounding faults, while Cu occurrences are distributed across the width of the Batten Trough, supporting a more or less syngenetic origin for the former and a much later, post inversion, epigenetic origin, for the latter. Mineralisation thus occurred in association with inversion structures formed above the primary half grabens that were generally concealed by later sedimentation. Because the half grabens occur at regularly spaced intervals along the Batten Trough there may well be more mineral occurrences similar to the McArthur River deposit. Clearly, these conclusions must be integrated into any exploration strategy.

Seismic stratigraphy of the Upper Pliocene and Quaternary deposits in the South Caspian Basin

More than 10,000 km of seismic data were used for seismic stratigraphic analysis and differentiation of major depositional environments of Upper Pliocene and Quaternary strata in the central deepwater and eastern parts of the South Caspian Basin (SCB). The study shows that the conventional sequence stratigraphy concept works well in the South Caspian Basin. Clinoform complexes within Paleo-Amudarya shelf margin are bounded by regionally, seismically expressed sequence boundaries and flooding surfaces that can be traced to the deep basin. Sequence analysis and seismic facies interpretation showed that deposition of prograding clinoforms and deep-water turbidite systems were controlled by the relative lake-level change. Depositional interpretation of sediment infill indicates that in the South Caspian Basin, as in other closed basins with high terrigineous input, basinal deposition is from turbidity currents and slumps generated from large shelf-edge deltas. There are two distinct stratigraphic complexes interpreted from seismic data: lower, interpreted as homogeneous infill of mud-rich turbidites and deepwater lacustrine deposits (Upper Pliocene, i.e. Akchagyl and Aspheron), and upper, consisting of prograding clinoform packages and coeval deepwater fan systems and slumps (Quaternary). The source of the central basin turbidite infill was primarily the eastern “Paleo-Amudarya” shelf. Growing diapir folds structurally controlled deposition of large-scale fan systems in the central basin. The distribution of these fan systems is tied to location of the coeval thick shelf-margin complexes.

The structural and stratigraphic framework of the Irish Rockall Trough

The Irish sector of the Rockall Trough is the largest of the sedimentary basins offshore Ireland and is virtually unexplored. This study establishes the first regional structural and stratigraphic framework of the Mesozoic and Tertiary fill of the Irish sector of the Trough with the aim of assessing its hydrocarbon potential. Major structural features of the Irish Rockall Trough and the adjacent part of the Irish Continental Shelf have been mapped using a combination of 9000 km of confidential and released regional seismic lines, satellite gravity data and a compilation of marine and aeromagnetic data. A sequence stratigraphic framework for the Mesozoic and Tertiary has been established using the seismic data tied to ten wells in adjacent basins (Erris and Slyne troughs and Porcupine Basin) and to one well in the southern part of the UK Rockall Trough. A major advance was the recognition of new Mesozoic perched basins and tilted fault blocks on both margins of the Trough in areas previously interpreted as shallow basement. A further 12000 km of seismic data acquired in the summer of 1996 indicate that a considerable thickness of sediment is present in these basins containing a fill analogous to the Slyne and Erris troughs. The configuration of the perched basins suggests that a major linked rift system, coincident with the site of the present-day Rockall Trough, existed during the early Mesozoic. Within the Trough, a number of sub-basins have been identified, characterized by syn-rift wedges of interpreted Jurassic to Early Cretaceous age.

Basin Configuration in Konkan Deepwaters: Western Indian Offshore

Abstract The sedimentary patch in Konkan deepwaters, located west of the Konkan continental shelf contains over 3 km thick sediments. Based upon the interpretation of over 11,000 line km of seismic data, gross basin configuration model has been worked out. The basin floor at the base of Tertiary is differentiated into a series of rift zones containing synrift sediments. These zones are superimposed by post-rift sediments deposited as a result of flexurally distributed thermal subsidence. Therefore, the sediments in the basin are divisible into three distinct mega-seismic packages denoting three major tectonic habitats of the evolution of the Konkan continental margin. Based upon the basinal configuration of each mega-seismic package in space and time, tectono-sedimentary evolution of the continental margin is brought out with an assessment of hydrocarbon prospects.

The Woolhope and Usk Basins: Silurian rift basins revealed by subsurface mapping of the southern Welsh Borderland

Subsurface mapping of the southern Welsh Borderland has utilized over 600 km of seismic data and three exploration boreholes to investigate the subsurface of this classic geological area. The survey reveals two Silurian basins, each about 400 km 2 in area, in the western part of the Midland Platform. The Woolhope Basin underlies the Silurian inlier of the Woolhope Anticline. The basin fill is bounded to the northwest by faults of the Neath Disturbance, and was also influenced by WNW-striking extensional growth faults. The fill thins eastward towards the Malvern Line. Lower Silurian sequences thin southward before thickening again, particularly across WNW-striking faults. The resulting Usk Basin, underlying the Usk Inlier, has ill-defined margins, but some additional N-S fault control. The Fownhope-1 and Usk-1 wells indicate that rapid subsidence occurred in both basins during Rhuddanian and Aeronian (Early to Mid-Llandovery) time. Modelling of this subsidence, assuming the finite duration lithospheric extension model, yields stretching factors of between 1.3 and 1.6. The later part of the fill to both basins is marine, but red conglomerates, sandstones and mudstones in their Early Llandovery intervals suggest continental fluvial environments in the initial stages of basin development. The Woolhope and Usk Basins show that the western sector of the Midland Platform rifted during Early to Mid-Llandovery time, perhaps during regional dextral transtension. The rifting is synchronous with, and perhaps genetically related to, an episode of mafic volcanism in the southwest part of the platform. However, this rifting apparently predates the Late Llandovery (Telychian) fault-controlled subsidence seen in the Welsh Basin to the northwest.

The Gulf of Mexico Structural and Stratigraphic Structural Synthesis Project: Introduction and Overview: ABSTRACT

The Gulf of Mexico Structural and Stratigraphic Synthesis Project (GMS3) was organized in the fall of 1987. Its main objective was to map, by means of student research projects, the northern Gulf of Mexico. Included objectives were (1) provide realistic research for graduate students in geology and geophysics, (2) to produce high-quality results suitable for publication and (3) to produce a product of value to the petroleum industry. To date, 25 oil exploration companies have contributed to the financial support of the project, 6 seismic contractors have provided approximately 130,000 line km of seismic data, and other industry service companies have provided data base support, interactive interpretation support and other support too numerous to mention. The project data base currently includes logs from over 700 wells and paleo from a similar number of wells. These data were obtained from the public domain and through contributions from numerous oil companies. Students mapped 5 Plio-Pleistocene and 4 Miocene horizons throughout the northern Gulf. They also mapped a number of Mesozoic horizons in the MAFLA and Mississippi Delta regions, and Oligocene horizons in South Texas. Over 25 students and 4 post-doctoral research associates have participated in the project to date. Most of themore » students completed either M.S. theses or Ph.D. dissertations. Papers read in this session and materials published in the Transactions represent only a small fraction of their output. Having completed the basic mapping of the Gulf, project faculty, post-doctoral associates and students are now focusing their attention on reservoir problems in the Gulf of Mexico.« less

Karoo Rift basins of the Luangwa Valley, Zambia

Abstract An integrated study of the Luangwa Valley Karoo Rift basins of NE Zambia has been carried out. Approximately 3000 km of seismic data were used in addition to gravity and aeromagnetic surveys and data from two exploration wells. The present day Luangwa Valley is underlain by two opposing Karoo half-graben separated by a central accommodation or transfer zone. The basins contain up to 8000m of Permo-Triassic, mainly clastic, sediments. The Lower Karoo consists of basal glacial deposits overlain by a sequence of interbedded coal, shale and siltstone, and capped by a very thick (up to 5000 m) lacustrine section of interbedded siltstone and mudstone. The Upper Karoo consists of interbedded coarse sandstones and siltstones thought to be of braided stream and flood plain origin. Rifting appears to have been initiated in the early Permian. The timing of subsequent rifting and inversion events has been related to strike-slip movements along the Mwembeshi Shear Zone, a major Precambrian lineament. Study of the seismic data has revealed a number of structural and stratigraphic plays in the basin. The best potential for hydrocarbon accumulation occurs within the lowest part of the Karoo section where source rocks and reservoirs are postulated in the Luwumbu Formation and the lowest part of the Madumabisa Mudstone. Since these intervals were not reached by either of the exploration wells drilled it is felt that the hydrocarbon potential of the Luangwa Graben has not yet been fully tested.

Structural framework and tectono-stratigraphic evolution of the Porcupine Seabight Basin, offshore Western Ireland

The Porcupine Seabight Basin is an intra-cratonic rift basin which evolved through recurrent episodes of lithospheric stretching. Structure-contour and isopach maps presented here have been constructed following the interpretation of approx. 10 000 km of seismic data. Together with all the available well data, this integrated database has allowed the tectono-stratigraphic history of the basin to be traced in detail from its earliest inception. The basin was initially formed during the Carboniferous when up to 3.7 km of Autuno-Carboniferous sediments were deposited on a Caledonian and Hercynian structured basement. Late Permian and early Mesozoic sediments at least 1 km thick are preserved in contiguous grabens, and their presence is also inferred within localized sub-basins. Late Liassic crustal doming heralded the onset of the final rifting episode and in the north promoted severe erosion and a rapid discharge of clastic sediments. Rapid subsidence, block faulting and magmatism accompanied the deposition of up to 3.5 km of Middle-Upper Jurassic sediments in asymmetrical sub-basins. The transition from stretching to passive subsidence across the Jurassic-Cretaceous boundary, in combination with localized inversion, abrupt eustatic and environmental changes, generated a basin-wide unconformity. The rift-drift transition in the adjacent proto-Atlantic rift system is recorded in the Porcupine Seabight Basin by voluminous volcanism and a late Lower Cretaceous unconformity. Cretaceous sediments are strongly transgressive and up to 6 km thick. These were superseded during the early Palaeogene by several regressive-transgressive cycles, before the arrival of an upper slope fauna in the mid-Middle Eocene. Cenozoic sediments are up to 4 km thick and record the interplay between (1) the location of the basin Pn the Pyrenean/Alpine foreland, superimposed on the periphery of the Icelandic plume and (2) its development as a marginal Atlantic shelf region. The former is thought to be responsible for Eo-Oligocene faulting, subsidence and igneous activity in the north-east part of the basin and the latter for unconformities and a change in the style of sedimentation, principally due to oceanic circulation changes.

The 1-AB Block Fields: A Giant Oil Accumulation in Eastern Peru

The 1-Ab block fields are located in the northeastern part of Peru. Geologically, the area is the sub-Andean Maranon Basin, a continuation of the Napo Basin from eastern Ecuador. During the 20 years that Occidental has operated Block 1-AB, approximately 11,500 km of seismic data has been recorded and 34 exploratory wells have been drilled, resulting in the discovery of 18 fields, or 53% exploration success. The 1-AB oil accumulation discovered in 1972 is a group of medium to small asymmetric anticlines distributed along six northwest-southeast trending structural alignments: North Capahuari-South Capahuari-Tambo, Carmen-North San Jaacinto and Bartra. This concentration of productive structures in a relative small area is unique within the Maranon basin. The controlling factors include exceptional pre-Cretaceous uplifting and the presence of very good to excellent Cretaceous sandstones reservoirs. The two major Cretaceous producing zones, the Chonta and Vivian sandstones, have been defined within the Coniacian and Campanian ages respectively. The Chonta sands are related to shelfal deposition across Block 1-AB, represented by strand plain and barrier island sediments. The Vivian formation is a massive fluvial sandstone covering all of the Maranon basin and ranging in thickness between 40 and 200 feet. After oil was accumulated, fresh watermore » influxes into the reservoirs of the northern and eastern fields caused oil biodegradation and salinity variation of the reservoir waters, depending upon the intensity of biodegradation. Oil remigration also has been documented for the South Huayari field.« less

Geochemical modelling of the East Irish Sea Basin: its influence on predicting hydrocarbon type and quality

A number of oil discoveries have been made in recent years in the East Irish Sea Basin (EISB). These have renewed industry interest in a basin which many thought to be essentially gas prone. British Gas, over a number of years, has developed and refined a basin model for the area based upon in excess of 23 000 km of seismic data and 40 wells. This model shows that the present-day distribution of oil and gas is controlled by complex interrelationships between the thermal and tectonostratigraphic history of the EISB. An integrated approach has been adopted in creating the model, which includes data generated from many sources including AFTA, detailed diagenetic and geochemical studies and more conventional geological, geophysical, and petrophysical analysis. The paper will address several aspects of the current basin model, including oil–source rock correlation, the origins of hydrogen sulphide within the EISB, and the problems and solutions in validating a basin model when so much of the rock record is missing.

Tectonic Provinces and Different Types of Hydrocarbon Traps in the Maturin Subbasin, Eastern Venezuela Basin

During the Oligo-Miocene, the transcollision of the Caribbean and South American plates, caused the northern flank of the Maturin Sub-basin to deform. This geodynamic process transformed the original passive margin basin into a foreland basin. As a result, the tectonic elements that distinguish this basin can be subdivided into three categories, the allochthonous block, the parautochthonous block and thrust belt, and the authochthonous block. The integrated interpretation of 7000 Km of seismic data and 25 wells has enabled us to elucidate the structural framework of the basin. A [open quotes]forward breaking[close quotes] sequence is proposed starting at the Pirital Thrust in the north and ending at the Furrial-Tejero Thrust in the south. However, the presence of a Post-Middle Miocene unconformity, folding of Early-Middle Miocene sediments and the development of a back thrust and its subsequent delta zone strongly suggests that movement towards the north also occurred. Between the Pirital and Tala faults, a lateral ramp known as the Urica fault, separates two zones that have been deformed by different mechanisms. The Urica fault has been interpreted by several authors as a dextral strike-slip fault. Hydrocarbons occur in three areas. The most important province occurs in the parautochthonous blocks with hydrocarbonsmore » occurring in cylindrical folds associated with the thrusts. To the south, conical folds associated with a strike-slip fault zone form good structural traps. The traditional Oficina fields lie still further south, in an area of normal faulting lightly affected by the Oligo-Miocene plate collision to the north.« less