ABSTRACT A migration geochemical study was conducted over an area of approximately 15,000 km 2 (5792 mi 2 ) in northeast Saudi Arabia to define regional migration patterns and de-risk oil charge away from the Late Jurassic source kitchen of the Gotnia Basin to prospects further to the south and west on the shelf margin and Summan Platform. Discovered accumulations range in depth from more than 10,000 ft (3048 m) subsea on the shelf margin in the north to around 5000 ft (1524 m) on the Summan Platform in the south. Shallowing south/southwestward is associated with a wide API gravity variation (15–35°) and gentler molecular and isotopic maturity trends. Defining migration patterns based on bulk, isotopic, and saturated and aromatic hydrocarbon distributions alone proved ineffective, especially given that all oils examined from the target Arab-A reservoir have a narrow peak-oil window maturity and a largely common source, that is sulfur-rich (up to 6.1 wt.%) anoxic marine carbonate, presumably within the Hanifa/Tuwaiq Mountain formations or their equivalent Najmah/Sargelu formations in the Gotnia Basin. Molecular geotracers, based primarily on compositional correlation coefficients of aromatic nitrogen compounds, identified several southwest-trending migration pathways that have charged traps in the Late Jurassic Arab Formation. Prospects falling along inferred migration pathways or entry/spill routes are therefore high-graded.

ABSTRACT Determination of petroleum charge history in a field is a critical segment to resolve within regional migration analysis. This, however, is often complicated by a number of alteration processes, such as density segregation. Later charges can disturb chemical equilibrium and compositional grading of oil columns. Controls over fluid compositional variations of oil field H in the northern part of Saudi Arabia were investigated to help predict fluid properties of future delineation and development wells and help constrain regional migration scenarios. Combined effects of charge history, density segregation, and compartmentalization appear to have been key controls on fluid compositional variations in this field, with density segregation manifested at bulk and molecular levels in this single-phase, undersaturated fluid system. The molecular and isotopic maturity profiles mirror the API gravity–asphaltene–depth profiles, which indicate the combination of multiple charging and density segregation. Density segregation within the reservoir has apparently expanded the API gravity range originally entered the trap, resulting in a mismatch between the wide API gravity range (15–26°) and the narrow maturity range (0.78–0.81% calculated vitrinite reflectance). Due to possible interference from molecular segregation, maturity parameters that rely on compounds of differing molecular densities and chemical reactivities should be used with caution. Sterilization of the oil column at temperatures greater than 80°C (176°F) during its deepest burial events in the Eocene and Miocene times may explain the nonbiodegraded nature of this shallow (<5400 ft [1646 m] depth) and relatively cool (54–63°C [129–145°F]) accumulation.

Abstract The southern Arabian (Persian) Gulf is at present the site of extensive carbonate sedimentation, as was the case during Pléistocène interglacial marine highstands. During glacial lowstands the basin was subaerially exposed, and aeolian sedimentation predominated. Most of the southern Arabian Gulf floor is underlain by Quaternary carbonates, and scattered outcrops may be found onshore. These belong to three formations: the aeolian Ghayathi Formation, the continental Aradah Formation and the marine Fuwayrit Formation. The Fuwayrit Formation consists of three members, separated by subaerial exposure surfaces. These are, from the base upwards, the shallow marine Futaisi and Dabb'iya Members, and the aeolian Al Wusayl Member. Offshore, at least six Quaternary sequences are present within the uppermost 50 m of sediment. No reliable direct age dates have been acquired from Pléistocène shallow marine or coastal deposits in the southern Arabian Gulf. It has therefore been necessary to infer the ages of these sediments by a comparison of their stratigraphy and elevation with deposits known from other parts of the world. We regard this approach as valid because the southern Gulf coastline lacks evidence for significant widespread neotectonic uplift, and halotectonic effects are localized. This comparison indicates that the Fuwayrit Formation was deposited during the last interglacial (oxygen isotope substage 5e), as (1) these sediments represent the youngest pre-Holocene marine deposits, and (2) they are found at an elevation correlative with many substage 5e deposits from other parts of the globe. Sedimentary evidence reveals two highstands during this period, peaking at around 1.5 m and 6 m above present sea level, respectively. Offshore sediments indicate that sea level did not fall as far as 24 m below present level in the intervening regression. Following the second highstand, sea level fell to more than 23 m below present level, before briefly rising once again (late isotope stage 5). This later highstand probably peaked between 17 and 7 m below present level. The sequence underlying the Fuwayrit Formation was probably deposited during the penultimate interglacial (late oxygen isotope stage 7). It is also likely that the Ghayathi Formation aeolianites were largely sourced from this sequence. Facies analysis of offshore core sediments indicates that sea level reached at least 15 m below present level during this period. Widespread evidence exists for a Holocene sea level higher than at present in the southern Arabian Gulf, indicating that it peaked at 1 -2 m above present level, c . 5.5 ka bp. Pléistocène deposits preserved in the southern Arabian Gulf provide a record of changing palaeowinds and palaeoclimates. Currently, the region experiences a hyper-arid to arid climate, with facies patterns dominated by the northwesterly shamal wind. The Ghayathi Formation was originally deposited under an arid climatic regime, which allowed the sediments to remain unconsolidated. The dunefield was later remodelled under conditions of increasing wind speed, with a change in wind direction from NNW to WNW. These changes are thought to reflect the onset of glaciation. Palaeocurrent directions from the Al Wusayl Member, combined with sedimentary evidence from the Futaisi and Dabb'iya Members, indicate that during the peak of the last interglacial the prevailing wind (the 'palaeo-shamal') blew from the NE. Compelling evidence for a pluvial episode during this period is provided by abundant and widespread dissolution (palaeokarstic) pits found in the top surface of the Futaisi Member, believed to represent the former positions of abundant trees or large plants.

Abstract Quaternary carbonate eolianites, accumulated through eolian reworking of marine sediments, occur extensively in the southern Arabian Gulf. In Abu Dhabi and Qatar these include widespread deposits belonging to the middle-late Pleistocene Ghayathi Formation, scattered coastal outcrops belonging to the Sangamonian Fuwayrit Formation, and semilithified deposits believed to be Wisconsin-Holocene in age. Deposition of these eolianites was intimately linked to fluctuations of sea level and climate. Sea level has controlled the amount and the nature of sediment available for eolian deposition, whereas paleoclimate has been the main factor influencing the size and location of the eolianites. The Ghayathi Formation provides an example of “regressive eolianites,” which were deposited through deflation of the shoreface during and following sea-level fall, accompanied by inland migration of eolian sediment. In contrast, the Fuwayrit Formation eolianites were deposited during highstand. The Wisconsin-Holocene semilithified eolian sands are best explained in terms of deposition during transgression. Negligible subsidence is believed to have occurred since the eolianites were deposited. Modern carbonate dune accumulations are rare in the southern Arabian Gulf. In Abu Dhabi this seems to be largely a result of the present-day coastal geomorphology, with deposits limited by the size of barrier islands. In Qatar the buildup of eolianites is currently prevented by offshore deflation on the eastern coast. In a ramp-like setting, such as the Arabian Gulf, eolian reworking of marine sediment can take place over a much longer period than in isolated platform settings, because sediment production is less dependent upon high sea levels. In addition, subaerial lithification of aragonitic sediments is retarded by the predominantly arid climate of the Arabian Gulf. In this respect, southern Gulf eolianites may be more analogous to ancient carbonate deposits than those from more humid Quaternary settings.

ABSTRACT Sequence stratigraphic concepts have long been used to integrate core and well log data with 3D seismic data to establish predictive reservoir models. This paper documents a new technique to systematically evaluate large scale log patterns in order to identify key chronostratigraphic surfaces with confidence. Linked closely to 3D seismic structural and stratigraphic interpretations, this technique has been applied in several reservoir modelling studies in the Niger Delta. Special emphasis has been given to the influence of growth faults on reservoir development. The resulting tectonosedimentary framework has led to semi-quantitative predictions about sediment geometry and distribution which were subsequently utilized to constrain 3D models of the reservoirs. Such 3D models improve the quality and success of appraisal drilling as well as field development planning.

Abstract The Phanerozoic evolution of eastern Canada involved the rifting and passive development of an early Paleozoic continental margin that bordered an Iapetus ocean. The closing of Iapetus and the destruction of its North American margin led to the development of the Appalachian Orogen (Bird and Dewey, 1970). Opening of the modern Atlantic began in Jurassic time. Its axis split the Appalachian Orogen longitudinally and it lay well east of the Iapetus suture. Thus a variety of suspect terranes were left clinging to the North American Paleozoic margin. Recently published reviews on the development of the northern Appalachians include those of Williams (1979), Dewey and others (1983), and Williams and Hatcher (1983). The record of the Paleozoic margin of Iapetus is contained in rocks of western Newfoundland.Initiation of the margin involved the rifting of Grenvillian basement with coeval mafic dike intrusion, mafic volcanism, and the accumulation of thick clastic sequences (Rodgers, 1968; Stevens, 1970; Williams and Stevens, 1974). These events were initiated in the late Precambrian, as indicated by isotopic ages of mafic dikes (Pringle and others, 1971; Stukas and Reynolds, 1974). A thinner sequence of mainly carbonate rocks formed at the continental shelf from Early Cambrian to latest Early Ordovician time. These sediments thicken eastward and record an upward transition from immature arkosic sandstones to mature quartz sandstones, and then limestones and dolomites. Rocks deposited at the continental slope and rise are now represented in allochthonous sequences above the carbonate shelf. These consist of coarse limestone breccias and turbidites and

Abstract DNAG Transect D-1. Part of GSA’s DNAG Continent-Ocean Transect Series, this transect contains all or most of the following: free-air gravity and magnetic anomaly profiles, heat flow measurements, geologic cross section with no vertical exaggeration, multi-channel seismic reflection profiles, tectonic kindred cross section with vertical exaggeration, geologic map, stratigraphic diagram, and an index map. All transects are on a scale of 1:500,000.