bluuebunny/crossref_metadata_2025_split huggingface dataset:
THE CONFIGURATION OF THE BASEMENT BENEATH THE ZAGROS BASIN
Authors: Bahroudi A. , Talbot C. J. 
Published: March 2006

It has long been recognised that the deposition and deformation of the Phanerozoic cover in the Zagros Basin (mountains plus foreland) was strongly influenced by the reactivation of old tectonic fabrics in its basement. Facies boundaries and structures trending north‐south and NW‐SE can be attributed to the reactivation of Pan‐African sutures and Najd faults which are exposed in the Nubian‐Arabian Shield. However, to the east of a projection of the Oman line SWwards into the Rhub Al Khali Basin, cover structures have a NE‐SW trend which is not seen in Arabia. This boundary may overlie a Pan‐African suture between Arabia and India (Somalia or Pakistan).Data including magnetic intensities, geothermal gradients and isopach maps are used here to distinguish old faults which were reactivated in the basement from more recent faults formed in the cover by Zagros shortening. Old faults trending NW‐SE are interpreted as having reactivated episodically since the Permo‐Triassic opening of Neo‐Tethys; perhaps more significantly, the basement faults that reactivated in the East Arabian Block since then trend north‐south. The basement configuration is clarified by extending a modified East Arabian Block across the Zagros to an “East Arabian‐Zagros block” in which the NW trend of the Zagros lies between two syntaxes. This suggests a new tectonic framework for the region. The repeated reactivation of basement faults throughout the East Arabian‐Zagros Block controlled source rocks, traps and seals for the supergiant and giant oil and gas reserves which are present at various stratigraphic levels in different areas.
HYDROTHERMAL LAUMONTIZATION AND MICROFRACTURE FORMATION IN RESERVOIR ROCKS AT THE YUFUTSU FIELD, HOKKAIDO, NORTHERN JAPAN
Authors: Yanagimoto Y. , Iijima A. 
Published: March 2006

Reservoir rocks at the Yufutsu oil‐ and gasfield (southern Hokkaido, Northern Japan) comprise Eocene conglomerates and Early Cretaceous granitoids in which networks of fractures < 0.02 mm across are widespread. These basement reservoir rocks were fractured during normal faulting in the late Oligocene — early Miocene. In the early to middle Miocene, the fractured rocks are thought to have been permeated by acidic formation waters derived from Eocene coal measures. Laumontite (a Ca‐rich zeolite) and smectite/illite (S/I) mixed‐layer clay minerals were precipitated in the microfractures and occluded them.The Yufutsu field is located on the western margin of a duplex structure formed during Pliocene or later shortening. As a result of this regional compression, the preexisting “early” microfractures which had been occluded with structurally‐weak laumontite and S/I mixed‐layer clay mineral aggregates reopened as “late” microfractures. Natural gas, which had been generated in deeply‐buried Eocene coal measures in the synclinal area to the east of Yufutsu field, migrated westwards and accumulated in the re‐fractured reservoir rocks.The duplex structure in central Hokkaido probably extends to the unexplored offshore Iburioki structure to the south. Fractured reservoir rocks similar to those at the Yufutsu field may also occur at Iburioki.
DIAGENESIS OF SILURIAN REEFAL CARBONATES, KUDIRKA OILFIELD, LITHUANIA
Authors: Stentoft N. , Lapinskas P. , Musteikis P. 
Published: March 2006

Upper Silurian carbonate reservoir rocks at the Kudirka oilfield, southern Lithuania, have a complex diagenetic history. This consists of the following stages: compaction and dewatering; early lithification; minor fracturing? first generation leaching; precipitation of first‐ and second‐generation inter‐ and intragranular calcite cements; recrystallization of lime mud, sparry calcite cement and bioclastic grains; chemical compaction and the formation of stylolite‐associated fractures; precipitation of dolomite, pyrite and silica; a second phase of leaching, with stylolite surfaces acting as conduits for aggressive fluids; and finally oil emplacement.The Upper Silurian carbonates are interpreted to correspond to a variety of reefal deposits. In all the types of reef rock analysed, late diagenetic leaching has enhanced reservoir quality. However, no clear correlation could be found between rock texture and reservoir quality. This is mainly because the very common crinoid fragments acted as substrates for the growth of pore‐occluding syntaxial calcite cement. The lack of correlation between rock texture and reservoir quality can also be attributed to subordinate localized stylolite‐related dolomitization.
BURIAL HISTORY RECONSTRUCTION AND THERMAL MODELLING AT KUH‐E MOND, SW IRAN
Authors: Kamali M. R. , Rezaee M. R. 
Published: March 2006

At the Kuh‐e Mond anticline (Fars Province, SW Iran) and in nearby offshore structures, large volumes of natural gas are reservoired in the Permian — Early Triassic Dehram Group while heavy oil has been discovered in the Cretaceous Sarvak and Eocene Jahrum Formations. In this paper, we use data from six exploration wells and from nearby surface exposures to reconstruct the burial history at Kuh‐e Mond. Regional observations show that the thick sedimentary fill in this part of the Zagros Basin was subjected to intense tectonism during the Zagros Orogeny, with a paroxysmal phase during the late Miocene and Pliocene. Thermal modelling and geochemical data from Kuh‐e Mond and adjacent fields allows possible hydrocarbon generation and migration mechanisms to be identified. Maturities predicted using Lopatin's TTI model are in accordance with maturities obtained from vitrinite reflectance measurements.We show that formations which have source potential in the nearby Dezful Embayment (including the Pabdeh, Gurpi, Gadvan and Kazhdumi Formations) have not reached the oil window in the Mond wells. Moreover, their organic carbon content is very low as they were deposited in oxic, shallow‐water settings. Underlying units (including the Ordovician and Cambrian) could have reached the gas window but contain little organic matter. Silurian shales (Sarchahan Formation), which generate gas at Kuh‐e Gahkum and Kuh‐e Faraghan (north of Bandar Abbas) and in Saudi Arabia and elsewhere in the Middle East, are absent from the Mond structure.The absence of source rocks suggests that the gas and heavy oil accumulations at Kuh‐e Mond and at nearby fields have most probably undergone long‐distance lateral migration from distant source kitchens.
MESOSCALE HETEROGENEITY OF FLUVIAL‐LACUSTRINE RESERVOIR ANALOGUES: EXAMPLES FROM THE EOCENE GREEN RIVER AND COLTON FORMATIONS, UINTA BASIN, UTAH, USA
Authors: Taylor A. W. , Ritts B. D. 
Published: March 2006

The Eocene Uinta Basin of Utah is a dominantly lacustrine basin that affords the opportunity to survey analogue sandstone reservoirs developed within and adjacent to the lacustrine system. From its SW to NE margin, Eocene strata in the Uinta Basin record fluvial, deltaic, profundal lacustrine, and wave‐dominated shallow‐lacustrine environments. Of these depositional systems, analogue sandstone reservoirs are well‐exposed in outcrop in the fluvial‐deltaic and wave‐dominated intervals. Field and petrographic examination of selected fluvial‐lacustrine reservoir analogues are used to document the mesoscale facies architecture and heterogeneity. Complex depositional geometries and heterogeneity exist at a variety of scales, both within single subenvironments and between opposite sides of the basin.Three outcrops in the Uinta Basin were studied. Outcrops One and Two are located in the SW portion of the basin in Nine Mile Canyon, and represent the interface between fluvial rocks of the Colton Formation and dominantly lacustrine strata of the Green River Formation. Outcrop Three is located at Raven Ridge in the NE of the basin, a shallow wave‐dominated lacustrine margin. Photomosaics and multiple vertical measured sections were described for each outcrop, and were utilized to document lithofacies assemblages, bounding surfaces, and sandbody architecture and heterogeneity. Sandstone samples from each outcrop were analyzed petrographically to capture the small‐scale heterogeneity characteristic of the three outcrops.Sedimentary rocks at Outcrops One and Two consist of lenticular, tabular, or undulatory channel, distributary channel, and bar deposits that are partially to entirely compartmentalized, or encased, by mudstone units. These sandstone units, analogous to reservoir intervals in lacustrine basins, show various types of lateral and vertical connectivity which are dependent on the degree of amalgamation and the sand:mud ratio. Within these sandbodies, mud chip lags, large mud clast horizons, discontinuous finer‐grained beds, accretion sets and amalgamation surfaces represent internal heterogeneity which could be expected to affect transmissibility in an actual reservoir. The complex geometry and heterogeneity characteristic of these reservoir analogues confirms the need for detailed reservoir characterization studies on all scales in order to improve production efficiency in such systems.Outcrop Three is dominated by tabular and laterally extensive offshore bar and sandsheet deposits which are separated by thick mudstone units. Large‐scale heterogeneity is minimized within these reservoir analogues, in that sandbodies exhibit excellent lateral continuity and less complex amalgamation. Therefore, documentation of heterogeneity at the bed‐ and petrographic‐scale is necessary to better address production potential in these types of reservoirs.
RESERVES/RESOURCE CLASSIFICATION SCHEMES USED IN RUSSIA AND WESTERN COUNTRIES: A REVIEW AND COMPARISON
Authors: Poroskun V. I. , Khitrov A. M. , Zaborin O. V. , Zykin M. Y. , Heiberg S. , Sondenå E. 
Published: March 2006

The international oil industry currently uses a number of schemes for hydrocarbon reserves and resources classification. These serve different purposes and are used variously by Governmental agencies, oil companies, scientific societies, research institutes and by the US Securities and Exchange Commission (McKelvey, 1975; Grishin, 1993; Nemchenko et al., 1996). Although the schemes have many features in common, attention has been paid in recent years to the development of a single, universal classification (McKelvey, 1975).Russia, unlike many other countries, uses only one reserves classification scheme (Anon., 1983; Nemchenko et al., 1996; Stasenkov and Gutman, 1989). Interest is growing in the comparison of the Russian scheme with those used elsewhere. A number of Russian oil and gas companies (e.g. Lukoil, Yukos and Gazprom) have already introduced Western standards for reserves evaluation in order to facilitate foreign investment. Conversely, Western companies operating in the Russian Federation are translating the Russian classification scheme into more familiar terms and definitions.
UPPER ORDOVICIAN CARBONATE MOUNDS ON GOTLAND, CENTRAL BALTIC SEA: DISTRIBUTION, COMPOSITION AND RESERVOIR CHARACTERISTICS
Authors: Sivhed U. , Erlström M. , Bojesen‐Koefoed J. A. , Löfgren A. 
Published: March 2006

We present a multidisciplinary description of the Upper Ordovician carbonate mounds which are found throughout the central Baltic Sea and which were studied in detail on the island of Gotland. These mounds were the subject of intense exploration between 1974 and 1992 and a total of 323 shallow wells were completed in more than 100 mounds on Gotland. Many of these were put into production and a total of 100,000 cu. m of high quality oil was produced. In this paper, we discuss the mounds’occurrence, lithological characteristics, age, faunal composition, petroleum chemistry and reservoir properties.The study is based on analyses of core material from wells in the northern part of Gotland. Upper Ordovician mound reservoirs here contain oil which has a similar geochemical signature to that in Lithuania and in the Kaliningrad district (Russia). The oil was probably derived from marine anoxic shales and migrated up‐dip from more central parts of the Baltic Syneclise where oil‐prone shales are known to occur. An intraformational origin for the oil is unlikely.The mounds contain large numbers of vugs and moulds which communicate mainly through dissolution fractures and surfaces and probably reflect a marine regression. Various lithofacies were recognized from petrographic studies including sub‐mound, intra‐mound, cap and flank, and supra‐mound facies. Algae and stromatolites dominate the intra‐mound facies, providing an organic framework for the entire structure. Consequently, the mounds are not merely poorly defined buildups of mud and micrite, as has previously been assumed. Biostratigraphic data indicates a late Caradoc to Ashgill age for the mounds and their associated lithologies.
STRATIGRAPHIC CONTROLS ON PALAEOZOIC PETROLEUM SYSTEMS, GHADAMES BASIN, LIBYA
Authors: Dardour A. M. , Boote D. R. D. , Baird A. W. 
Published: March 2006

The distribution of oil‐ and gasfields in the Libyan Ghadames Basin is strongly influenced by the stratigraphic architecture of the Silurian‐Devonian succession. This interval encompasses part of two (second‐order) super‐sequences separated by the Caledonian unconformity: (i) a late Ashgillian‐Silurian super‐sequence, comprising the Melez Chograne‐Memouniat periglacial lowstand, the Tanezzuft transgressive to early highstand shales and the Acacus Formation late highstand systems tracts; and (ii) the lower part of a composite Devonian‐Carboniferous super‐sequence terminated by the Hercynian unconformity, which includes the lowstand Tadrart fluvial‐shallow marine sands, the Ouan Kasa (transgressive) and the Aouinet Ouinene transgressive to early highstand systems tracts of Devonian age.Hydrocarbon accumulations in Acacus, Tadrart and later Devonian reservoirs have been charged from a basal Silurian (Tanezzuft Formation) “hot” radioactive shale source rock. The Acacus and Tadrart sandstones provided regional migration conduits sealed by intra‐Acacus, intra‐Devonian (Emghaet Formation) and Permian (Bir Al Jaja Formation) shales. Regional stratigraphic continuity of these migration conduits permitted the development of low to moderate impedance petroleum systems dominated by lateral migration.Basin reconstructions and burial history modelling suggest three expulsion peaks from the basal Tanezzuft Formation source rock, preceding major periods of Hercynian, Austrian and Alpine (mid‐late Tertiary) uplift and exhumation. Hydrocarbons trapped prior to the Hercynian event were dispersed during later periods of structural deformation. Some pre‐Austrian accumulations may have survived locally in more robust traps. However, most if not all of the oil‐ and gasfields discovered in the Late Silurian ‐ Devonian succession were probably charged during the Late Cretaceous—Early Tertiary, only to suffer partial dispersal during later uplift, tilting and flushing. Three petroleum systems can be distinguished within the basin: (i) a Tanezzuft ‐Acacus system to the north; (ii) a Tanezzuft ‐ Tadrart system to the south; and (iii) a Tanezzuft ‐Acacus/Tadrart(+) system in the centre, with some leakage into overlying Devonian and Carboniferous sandstones locally.
TEMPESTITE DEPOSITS ON A STORM‐INFLUENCED CARBONATE RAMP: AN EXAMPLE FROM THE PABDEH FORMATION (PALEOGENE), ZAGROS BASIN, SW IRAN
Authors: Mohseni H. , Al‐Aasm I. S. 
Published: March 2006

The Pabdeh Formation is part of a thick carbonate‐siliciclastic succession in the Zagros Basin of SW Iran which includes carbonate reservoirs of Cretaceous and Cenozoic ages. From field observations and petrographic and facies analysis of exposures in the type section of the Pabdeh Formation, four lithofacies were recognized. These are from oldest to youngest: (i) a mottled, bioturbated bioclastic wackestone/mudstone facies; (ii) a wackestone/packstone facies with horizontal burrows on bedding planes; (iii) a thin‐bedded bioclastic wackestone/mudstone facies alternating with thin bioclastic‐oolitic‐intraclastic intervals; and (iv) a bioclastic foraminiferal / algal / peloidal packstone facies. These observations indicate that facies evolved upwards from deep outer‐ramp deposits to inner‐ramp deposits within a shoal complex, suggesting progradation of the ramp depositional system.Storm events significantly influenced the ramp system. Storm‐generated surges transported sediments from nearshore to the deeper outer‐ramp environment where they were deposited as shell‐lags, composed mostly of bioclastic packstones, rich in pelagic microfauna with sharp, undulatory erosional basal contacts. The packstones rest on outer ramp mudstones deposited below storm base level. Sedimentary structures in the Pabdeh Formation are those typical of storm deposits, such as hummocky cross‐stratification, ripple cross‐lamination, ripple marks, escape burrows on the tops of the beds, couplets of fine‐ and coarse‐grained laminae and mixed fauna, as well as intraclasts derived from underlying facies. These distinctive sequences are interpreted to have been generated by waning storm‐generated currents. The dominance of fine‐grained sediments (medium to fine sand); the lack of large‐ scale hummocky cross‐stratification; the minor amounts of intraclasts derived from underlying facies; the paucity of amalgamated tempestite beds; and the finely‐laminated (mm to cm scale) couplets of coarse and fine lamina all suggest a distal tempestite facies. Palaeogeographic reconstruction of the Zagros Basin during the Eocene indicates that the study area was situated in tropical, storm‐dominated palaeolatitudes.
DEPOSITIONAL HISTORY AND SEQUENCE STRATIGRAPHY OF OUTCROPPING TERTIARY CARBONATES IN THE JAHRUM AND ASMARI FORMATIONS, SHIRAZ AREA (SW IRAN)
Authors: Nadjafi M. , Mahboubi A. , Moussavi‐Harami R. , Mirzaee R. 
Published: March 2006

The Oligo‐Miocene Asmari Formation is one of the most important petroleum reservoir units in the Zagros Basin of south and SW Iran. It mainly consists of limestones and dolomitic limestones with interbedded shales, together with a few intervals of sandstone and gypsum assigned to the Ahwaz and Kalhur Members, respectively. The Asmari Formation rests on the thin‐bedded limestones of the Jahrum Formation (Paleocene‐Eocene). In this paper, we report on the lithofacies characteristics of these two formations using data from three measured outcrop sections near Shiraz in SW Iran. From field and petrographic data, we have identified four major lithofacies and twelve subfacies which are interpreted to have been deposited in open‐marine, shoal, lagoon and tidal flat settings.We show that the Asmari and Jahrum Formations constitute two separate depositional sequences which are separated by a thin palaeosol, representing a type‐one sequence boundary which can be correlated with global curves of relative sea‐level. Each depositional sequence is composed of many metre‐scale shallowing‐upward parasequences. This is the first time that the Asmari and Jahrum Formations have been differentiated in the study area. We hope that this study will lead to a better understanding of the Asmari Formation in the subsurface in other parts of the Zagros Basin.
FACIES AND POROPERM CHARACTERISTICS OF A CARBONATE SHOAL (MUSCHELKALK, SOUTH GERMAN BASIN): A RESERVOIR ANALOGUE INVESTIGATION
Authors: Ruf M. , Aigner T. 
Published: March 2006

Outcrop analogue investigations contribute to the understanding of the architecture and behaviour of subsurface hydrocarbon reservoirs. This study was designed to provide input for static reservoir modelling of shoal bodies on carbonate ramps.We investigated an oolitic and shelly carbonate shoal of Late Muschelkalk (late Ladinian) age, about 30 km long and 15 km wide, exposed in a series of quarries in southern Germany. The dimensions of this shoal body correspond to both modern analogues in the Persian Gulf and to oilfields in the Middle East.Fifteen outcrop locations were chosen to cover the entire shoal. A regional correlation based on facies, sequence analysis and outcrop gamma‐ray logs was used as a framework for mapping the distribution of shoal (i. e. reservoir) facies and associated reservoir properties.Three major depositional environments were recognized: foreshoal, shoal and backshoal. In each environment, specific vertical facies successions composed of thick shallowing‐upward units and thin deepening‐upward units forming metre‐scale cycles were deposited. These small‐scale cycles are stacked and form large‐scale shallowing and deepening trends. Shoal facies developed preferentially in the regressive parts of small‐scale cycles and were found to be laterally continuous over distances of at least several kilometres.Porous intervals within the shoal facies are concentrated along the tops of the small‐scale shallowing‐upward cycles. The porous intervals in successive small‐scale cycles increase in thickness and in absolute values of porosity upwards through the large‐scale shallowing trend. Separate vug pore types are characterized by relatively low permeabilities (0 to about 10 mD) in spite of the high porosity (up to 20%). The combined occurrence of separate vug and interparticle porosity leads to higher permeabilities (tens of mD).Isolines of porosity, permeability and net/gross follow the contours of the carbonate shoal complex. The highest values of porosity appear more or less at the centre of the shoal, while the highest values of permeability are found at the shoal margins. The distribution of maximum porosity and maximum permeability zones are thus controlled by the cyclic seaward‐stepping and landward‐stepping of the shoal body.The systematic variations in extent, stacking pattern and related petrophysical characteristics of the carbonate shoal bodies may be used for modelling shoal reservoirs in producing oilfields.