bluuebunny/crossref_metadata_2025 huggingface dataset:
PETROLEUM IN TIBET AND THE INDIA‐ASIA SUTURE (?) ZONE
Authors: Meyerhoff A. A.
Published: December 2007

During 1976, three separate drill sites were reported from parts of central and southern Tibet, the People's Republic of China. The ages of the formations penetrated are not known, but possible commercial hydrocarbon shows were reported at each of the three drill sites. The shows were in either late Paleozoic or Mesozoic Tethyan facies, north of the Yalu Tsangpo (Brahmaputra) River. Similar Tethyan facies crop out south of the river.

The Yalu Tsangpo River strikes W‐Eacross S Tibet, and its trace has been interpreted by some geologists to be a suture zone where the Indian plate is alleged to have collided with Asia. The presence of identical rock formations north and south of the Yalu Tsangpo appears to negate this conclusion.

However, Chinese geologists hold differing opinions concerning the presence or absence of a suture zone along the Yalu Tsangpo River line‐one group holding that the line is a suture zone; another group denying the existence of a suture zone; and a third group taking an intermediate position. The views of the different groups are reviewed here for the benefit of non‐Chinese geologists and geophysicists who may be interested in this area. Present non‐Chinese literature on the area is woefully lacking in factual data and, as a consequence, serious misunderstandings exist regarding the geology, tectonics, and petroleum potential of this region.
TERRESTRIAL SOURCES OF CARBON AND EARTHQUAKE OUTGASSING
Authors: Gold Thomas
Published: December 2007

The Earth has replenished its surface with carbon throughout geologic time. The supply may have come from hydrocarbons originally included in the body and outgassing largely through faults in the crust. Combustible gases are frequently released in earthquakes and seem to be an essential part of that phenomenon. New sources of fuel and improved earthquake prediction may come from a better understanding of the processes.
SEGMENTATION OF ISLAND ARCS AND APPLICATION TO PETROLEUM GEOLOGY†
Authors: Ranneft T. S. M.
Published: December 2007

Island arcs are commonly depicted as smoothly curved or sinuous structures. This presentation almost certainly is incorrect. Most island arcs, perhaps all, are composed of more or less straight segments whose trend changes direction suddenly at specific hinge or boundary zones; these zones seem to consist of multiple transverse faults. Each straight segment itself is cut by transverse faults. The presence of the transverse structural systems is evident from geological and geophysical data.

Examples of segmentation include island arcs in Indonesia, the Philippines, Solomons, New Hebrides, Kuril‐Kamchatka, Lesser Antilles, Central America, Mexico, Tonga, Alaska, Japan, Chile, Andaman‐Nicobar Islands, New Britain, Marianas, Greece, and the Himalayas. The fracture system may be related to structural, morphological, or movement aspects of an underthrusting slab, or it may be the result of movement in the backdeep or of the overthrusting sheet in general. Some of the transverse faults may be old ones that have been rejuvenated within the island‐arc area.

Transverse structural systems seem to have had a pronounced effect on the petroleum accumulations of island‐arc regions, both from a stratigraphic and structural viewpoint; they therefore affect petroleum‐exploration procedures. Such systems are also likely to be found in ancient basins that went through an island‐arc stage. Knowledge of the segmentation of island arcs should aid future exploration.
OUTLOOK FOR MINERAL RAW MATERIALS
Authors: Meyerhoff Howard A.
Published: December 2007

No better summary of the outlook for the mineral raw materials industry during the next two decades can be offered than the oft‐repeated aphorism, “The more things change, the more they remain the same”. Each mineral commodity will pursue its own individual course, but overall, the growth and increasing sophistication of the world population will double consumption and narrow such gaps as exist between supply and demand. Sources of supply will be found over a widening geographic range and will cross an increasing number of political boundaries. Although the need for an international mineral policy is obvious, confrontation between the industrial nations of the West and the anti‐colonialism and nationalism of Third World countries offers little hope of anything better than ad hoc solutions in the form of bilateral agreements or cartelization of specific commodities involving several producing nations with common interests. Japan has shown the efficacy of bilateral agreements; the International Tin Council and OPEC are examples of cartelization. Although its mineral resources make the USSR all but self‐sufficient, analysis of its military and maritime programmes indicates that one of its aims is to fill the vacuum created by the lack of an international mineral policy. It is following closely a modernized formula for world domination set forth by Sir Halford Mackinder in 1904. Success would enable it to impose a mineral “policy” on the rest of the world, which will be well advised to ponder this possibility.
SHIFTING DEPOSITIONAL AXES OF IRAQ: AN OUTLING OF GEOSYNCLINAL HISTORY
Authors: Ibrahim M. W.
Published: December 2007

Isopach‐lithofacies maps, presented in this paper as maps showing depositional axes (depo‐axes) for successive informal lithostratigraphic groups of sedimentary units, are applied to outline the tectonic history of Iraq. Five geosynclinal stages are recognistd:(a) Intra‐Cratonic Bacinal stage, (b) Early Orthogeosynclinal stage, (c) Late Orthogeo‐synclinal stage, (d) Idiogeosynclinal stage and (e) Exogeosynclinal stage. In general, throught those stages, depo‐axes were always migrating away from the tectonically‐elevated crustal elements during tectomic events and advancing towards them after the lapse of each tectonic pulse when normal sedimentation was resumed. The pattern. History and position of the axes of deposition determined the hydrocarbon migration directions:these were generally from the ENE towards the WSW of iraq.
BOOK REVIEW
Authors: Hobson G. D.
Published: December 2007

S. Yuriv and H. Cross, 1979. Geochemistry of Colloid Systems for Eurth Scientists: Berlin. Heidelberg, New York, Springer‐Verlug. 86
THE DENSITY SEPARATION OF DIFFERENT MACERAL GROUPS OF ORGANIC MATTER DISPERSED IN SEDIMDENTARY ROCKS
Authors: Kinghorn R. R. F. , Rahman M.
Published: December 2007

Macerals of ancient sedimentary organic matter, comprising sporinites, alginites. vitrinites and inertinites have been separated by sequential centrifuging in zinc bromide solutions of progressively higher specific gravities.

Marine organic matter. composed of structureless platy constituents, is separated by low‐density, heavy‐liquid solutions (S.G. 1.12‐1.34), whereas material from terrestrial and land influenced sources separates out at higher specific gravities (S.G. 1.45‐1.65). The various structured constituents of the latter can then be isolated by virtue of their different specific gravity ranges (alginite < 1.53, sporinite 1.53‐1.65 and vitrinite/ inertinite > 1.65): the density increases within each of these ranges with the darkening of their colour, reflecting increasing diagenesis.
GEOLOGY OF THE MUSANDAM PENNINSULA (SULTANATE OF OMAN) AND ITS SURROUNDINGS
Authors: Ricateau R. , Riché P.H.
Published: December 2007

The Musandam peninsula (Sultanate of Oman) is a vast outcrop of carbonate rocks of Permian to Middle Cretaceous age. The facies of these formations relates them without doubt to the contemporaneous formations of the Arabian platform and there is a good analogy with the formations encountered in the wells drilled in the Persian Gulf west of the Musandam outcrops. After the deposition of these platform formations, several tectonic events deepb affected this area, and led to the present configuration: at the end qf the Middle Cretaceous, a wide area emerged on the E edge of the Arabian platform. whereas on the W side of the Peninsula important halokinetic movements of the structures of thePersian Gulf persisted.

Following that tectonic event, the sedimentary domain of the platform withdrew towards the Arabian shield during the Upper Cretaceous, whereas the orogenic activity spread out into the oceanic domain. The Musandam peninsula was located between those two domnins, in a sedimentary basin which successively received first the turbidites of'the Muti Formation (Coniacian ‐ Santonian), mainly produced by the erosion of the Middle Cretaceous emerged area, and then the Hawasina nappes, mainly formed by abyssal sediments of earlier Mesozoic age.

Itis not firmly established whether the Semail nappe of the ophiolitic complex was emplaced over the Musandam as it was over the greater part of the Oman mountains. During and after the setting of the nappes, E‐W compression caused the series of overthrusts, creating in the Musandam area a ridge edged on the W by a subsidmr foredeep which received materials from the ridge, and on the E by an oceanic zone in which the sedimentation was far more reduced. The same pattern continued until the end of the Lower Miocene, when a very important compressive movement from E to W gave their present shape to most structures.

During the Upper Miocene, vertical movements of compensation took place and continued to thepresent time over Musandam, while on the E flankof the Peninsula, in the subsiding Gu(fof Oman, sedimentation became very important.
AN OIL MIGRATION AND RE‐ENTRAPMENT MODEL FOR THE MARDIN GROUP RESERVOIRS OF SOUTHEAST ANATOLIA
Authors: Erdogan L. Tufan , Akgül Azat
Published: December 2007

Oil migrates from a source into a reservoir rock and then, inside the reservoir rock, into a trap, and from the trap into a series of traps and reservoir rocks. The movement of oil is continuous and the interchange of oil between several reservoir rocks is totally independent of the source rock after a certain stage of migration. Each migration stage may cause quality changes in the properties of oil. A model is devised to account for oil migration and re‐entrapment, and to explain the distribution of different quality oils in time and space. Variations in the API‐gravity of oil, formation‐water salinity, reservoir temperature and pressure, sulphur‐content of oil, initial water content and recoverable oil reserves of oilfields can be important clues for the determination of migration directions and new prospects. These concepts were applied in a petroleum migration study of the Mardin Group (Aptian‐Turonian) which is the most important reservoir rock of SE Anatolia.

Quantitative modelling shows that oil migration is directed towards two main uplifts which control the distribution of oilfields in SE Anatolia. Active water movement inside the reservoir rock has resulted in the accumulation of oil inside very young structural traps. Because almost all the fields have tilted oil‐water contacts, wildcat locations must be selected with special emphasis on hydrodynamics.
THE GEOLOGY OF THE ASL OILFIELD, WESTERN SINAI, EGYPT
Authors: Thiébaud C. E. , Robson D. A.
Published: December 2007

Surface mapping in the Asl area of Sinai, which was carried out in the year 1937, established the presence of 18 gypsum beds alternating with shales, marls and sandy beds, folded into gentle flexured structures with very little faulting. In contrast, the structures at depth, as revealed by the information from 28 wells, consist of numerous tilted blocks bounded by faults; most of these faults die out before reaching the surface.

The task of finding locations for producing wells proved difficult; only 12 of the wells drilled have yielded commercial supplies of oil. The value of seismic records is limited in such a geological environment, where deep‐seated, block‐faulted structures are overlain by a thick evaporite succession.

Three producing horizons, two of Miocene age and one at the top of the Eocene, have yielded an aggregate of more than six million tons of oil.
LITHOSTRATIGRAPHY AND SUBSURFACE GEOLOGY OF THE ALBIAN ROCKS OF SOUTH IRAQ
Authors: Ibrahim M. W.
Published: December 2007

The Nahr Umr Formation is argued here to be in physical and possible chronological continuity with the exposed Rutbah Sandstone Formation of Western Iraq. This stratigraphic relation is postulated on the basis of subsurface mapping.

The presently available information, i.e. lithofacies data, well logs, petroleum occurrences, and structural traps availability were evaluated in order to present a preliminary prospect evaluation. It appears that the Albian petroliferous belt coincides with: a marginal‐marine environment of deposition, a sand/shale ratio of > 1 < 8, and a Cretaceous growth of structural traps.
A FURTHER GEOLOGIC STUDY ON THE TRIASSIC FORMATIONS OF NORTH‐CENTRAL ALGERIA WITH SPECIAL EMPHASIS ON HALOKINESIS
Authors: Assaad Fakhry A.
Published: December 2007

Up‐to‐date lithostratigraphic classifications of the Triassic detritals of the Upper Triassic and Lower Jurassic evaporitic series have been made in North‐Central Algeria. It is believed that the formation of the Lower Triassic fluvio‐deltaic deposits and the principal Upper Trias‐Lias evaporites may be explained in terms of plate tectonics. Correlation of the Triassic formations were found possible between the two different tectonic units known in Algeria. The Epihercynian and Pre‐cambrian platforms attained their main tectonic features after the Early Alpine “Post‐Liassic” orogenic movements; whereas the successive southerly migrations of the Equator during Later Triassic time led to the formation of several lagoons.

To the E of the High Plateaux, a NE‐SW lagoonal basin probably existed in the central part of which salt accumulated, overlain by shales and anhydrites, whereasat the edges only anhydrites were deposited. In the NW of the Algerian Sahara‐studied area, open Tethys sea sedimentation partly prevailed and carbonate rocks were deposited during Late Triassic.

Triassic‐Liassic diapirs of different ages of emplacement are known in N Algeria and are represented on the surface by saliferous shales and other associated rocks mainly produced by halotectonic processes. Precise photogeologic and seismic studies may reveal the presence of salt‐dome structures in areas of halokinetic piercing diapirs, as well as in other areas away from the direct effects of regional tectonics. No Triassic‐Liassic outcrops or diapirs are known on the Saharan platform, the Triassic basins having developed on the Paleozoic craton.
EXPERIMENTALLY‐BASED ARGUMENTS SUPPORTING LARGE CRUSTAL ACCUMULATIONS OF NON‐BIOGENIC PETROLEUM
Authors: Giardini A. A. , Melton Charles E.
Published: December 2007

The evolution of the Earth's atmosphere has been explained by a diffusion model that obeys first order kinetics. By assuming that the same rate law governs the diffusion of petroleum compounds that are known to exist in the upper mantle, we find that 1.5 × 1015 tons have diffused out during the past 3.1 billion years. If 0.1% of this primordial petroleum has undergone crustal migration and entrapment, deposits totalling 1.5 × 1012 tons are now present in the Earth's crust. Assigning a 0.3 recovery factor, this is equivalent to about 3 trillion barrels.
AQUEOUS SOLUBILITY OF CRUDE OIL TO 400°C AND 2,000 BARS PRESSURE IN THE PRESENCE OF GAS*
Authors: Price Leigh C.
Published: December 2007

This study reports aqueous solubilities of crude oil distillation fractions over the carbon number range C1‐C34as a function of: temperature (100° to 400° C), pressure (100 to 2,000 bars), NaCl concentration, and gas in solution (N2, CO2, CH4). Experimental parameters were designed so that conditions within a petroleum basin would be duplicated. Increases in temperature increased crude oil solubility, and the higher molecular weight species were affected more positively than lower molecular weight species. Increases in pressure or salinity decreased solubility. The presence of gas in solution increased the solubility of high molecular weight hydrocarbons (> C24) over all temperatures, and increased the solubility of lower molecular weight hydrocarbons at high temperatures (> 180–260°C). Gas decreased the solubility of low molecular weight hydrocarbons at low temperatures.

Hydrocarbon solute compositional changes were also examined as a function of the above parameters. At high temperatures, both increasing gas concentration and increasing temperature caused hydrocarbon solutes to become compositionally more similar and eventually identical to the original distillation fraction. The high molecular weight hydrocarbons and saturated hydrocarbons, especially the n‐paraffins, were taken into solution in progressively greater concentrations over the aromatic and low molecular weight hydrocarbons. Thus, the strong preferential uptake of low molecular weight and aromatic hydrocarbons into solution at lower temperatures was reversed.
GREAT CARBONATE BANK OF YUCATÁN, SOUTHERN MEXICO
Authors: Viniegra‐O Francisco
Published: December 2007

Since 1972, numerous large and giant fields have been discovered in the Reforma area of Chiapas and Tabasco States, southern Mexico, and on the offshore Campeche shelf west of Campeche State. The huge carbonate bank with which these discoveries are associated is called the Great Carbonate Bank of Yucatán. Most of the Reforma fields produce from bank‐edge talus, now largely dolomitized, of Late‐Jurassic and Early‐ to Middle‐Cretaceous ages, and drilling depths to the tops of the reservoirs generally range from 3,800‐4,500m. The offshore discoveries include fields which are productive mainly in bank‐edge talus of Paleocene and Late‐Jurassic ages, and depths to the top of production generally are shallower than onshore‐1,260‐3,500m. The petroleum source materials for the Jurassic, Cretaceous, and Paleocene fields are believed to be mainly in Late‐Jurassic strate, but some Early‐Cretaceous sources cannot be eliminated. Middle‐Cretaceous rocks have not yet been identified beneath the offshore shelf from Tampico (Arenque) to Samaria (A. J. Bermúdez) and Conduacán. Although most of the discovered fields contain mainly oil, some of the fields contain gas and condensate.

Some porosity and permeability is primary, and most is secondary‐the result of solution, dolomitization, and intense microfracturing. The original trap for the Late Jurassic‐Middle Creataceous fields appears to have been stratigraphic, but the present traps are mainly fractured and faulted domal salt pillows created during the Laramide orogeny.

The basis for the discovery of the fields was the widespread presence on the Yucatán Peninsula, and in the States of Campeche, Chiapas, and Tabasco, of Cretaceous through Tertiary backreef or lagoonal facies‐carbonates, anhydrite, and some halite, The drilling of the Pichucalco well in 1971 for the first time showed that reef and/or bank‐edge facies were present. In addition, more than 200 oil seeps were known in a linear zone along the foot of the Sierra de Chiapas, south of and adjacent to the coastal plain. If one assumes a facies distribution similar to that of the Golden Lane, it can be concluded that an extensive bank‐edge talus deposit should lie gulfward from the lagoonal facies. With this geologic concept in mind, seismic work was commenced, and drilling during 1971–1972 led to the dual discoveries of the Sition Grande and Cactus oil fields in 1972. The first offshore discovery, Chac, was made in 1976.

The Great Carbonate Bank of Yucatán is believed to include not just the Yucatán Peninsula, but also a part of coastal Veracruz State, where several discoveries have been made in carbonate rocks of Early‐ to Middle‐Cretaceous ages in thrust sheets along the western margin of the Veracruz basin, which are now buried beneath the coastal plain. It is probable that large, subthrust, anticlinal structures underlie the thrust sheets along the western margin of the Veracruz basin. These, when drilled, may contain important hydrocarbon accumulations.
OIL AND GAS OCCURRENCES ON THE EAST‐EUROPEAN PLATFORM AS RELATED TO ITS TECTONIC HISTORY
Authors: Maximov S. P.
Published: December 2007

Phanerozoic deposits on the East‐European platform are represented by four megasequences: Lower Paleozoic, Middle‐Upper Paleozoic. Mesozoic and Cenozoic. Each megacycle includes several depositional cycles. A correlation may be established between the distribution of oil and gas source rocks and commercial production and the depositional and geotectonic megacycles and cycles. The formation of major gasfields (Orenburg, Shebelinka, Astrakhan and Vuktyl) during the periods of upward tectonic movement is discussed.
ON THE THEORY OF GROWTH FAULTING PART II (c): GENESIS OF THE “UNIT”
Authors: Crans W. , Mandl G.
Published: December 2007

This paper forms the third and concluding section of the second part of a detailed and rigorous geomechanical analysis of the stability of overpressured, gently‐sloping sediment layers presented in the Journal of Petroleum Geology, 2, 3, 1980 and 3, 2, and 3, 3, 1981. Parts II(a) and (b) considered stress equilibrium, related stress equations, types of overpressure, the representation of the stress state in Mohr space, and the plastic/elastic states of frictional materials in long fluid‐filled layers, together with numerical and analytical examinations of slip lines and considerations of plastic flow and slip.

This concluding section introduces the effects of peak‐strength and liquefaction phenomena, together with a consideration of the behaviour of purely cohesive materials, and contains also the six important conclusions derived from this study.
GURI LIMESTONE, A NEW HYDROCARBON RESERVOIR IN SOUTH IRAN
Authors: Kashfi Mansour S.
Published: December 2007

The Guri Limestone Member of the Mishan Formation of Early to Middle Miocene age produces gas in the SE portion of the Zagros geosyncline. The Mishan Formation, which is predominantly marl in its type section near Khuzestan Province, becomes more argillaceous with an increase in organic content towards the SE where the sequence thickens. In the SE portion of the Zagros geosyncline, the lower part of the Mishan changes to a highly‐resistant, fossilqerous limestone which is called the Guri Limestone. This is of Late‐Early Miocene age in most of the SE Zagros and rises in stratigraphic position towards the NW, becoming of Middle Miocene age in Khuzestan Province. The Guri thickens considerably with massive reefal‐type deposits towards the eastern end of the Fars Province near the Oman high.

Lithological and geochemical studies support the hypothesis that the Mishan Formation could serve as a source rock for the hydrocarbons which have been found within the Guri. However, subsidence has failed to place the Mishan Formation within the thermal zone thought to be necessary for liquid hydrocarbon formation, and it is more likely that the deposits will produce gas.
MOZAMBIQUE‐MADAGASCAR GEOSYNCLINE, I: DEPOSITION AND ARCHITECTURE
Authors: Kamen‐Kaye Maurice
Published: December 2007

The Mozambique‐Madagascar geosyncline consists of an open‐ended non‐compressional NNE‐SSW downwarp 1,700 km long in the area of the present Mozambique Channel and its bordering coastal regions. Exposed basement marks the lateral boundaries of the geosyncline, and embayments rather than discrete basins modify its regional geometry. A sedimentary volume of more than 5,000,000 cu km resulted from subsidence and hypersubsidence, not only in the Mozambique Channel but also on the coastal borders, in places relatively close to exposed basement.

Continental facies of South African Karroo type dominates the sedimentary columns of the geosynclinal flanks in the Upper Carboniferous to Middle Jurassic interval, but is not yet documented beneath the bathyal and abyssal waters of the intervening Mozambique Channel. Marine facies, mixed facies, and a few continental facies occupy the sedimentary columns of the flanks above the Middle Jurassic. Pelagic facies may be dominant in contemporaneous strata now below the bottom of the Channel.

As part of the vast non‐compressional province of the Indian Ocean the Mozambique‐Madagascar geosyncline has been subjected only to epeirogeny. The structural response has been normal faulting, in some places, with major downthrow and in others antithetic with patterns of graben and horst. Volcanism is known to have accompanied the faulting from Late Triassic time onward.

Modern consensus invokes a separation of Madagascar from Africa followed by drift along southward, eastward, or NE paths, depending upon individual tectonophysical interpretation, each of the three of which displays weakness. The alternative of separation by subsidence only needs the test of deep drilling under the present Mozambique Channel for support orproof Until then, a tentative scheme of stratal succession is proposed, namely, a relatively‐thin post‐Karroo column in pelagic facies and a relatively‐thick Karroo column in continental and mixed facies.

Confirmation of the succession by drilling would provide strong support of a model presenting paleo‐Madagascar as the eastern sector of an Africa that bulged more than once toward the east in post‐Carboniferous time. The corollary of a broad band of reservoir Karroo, under a broad cover of pelagic post‐Karroo, all under the waters of the present Mozambique Channel would be of considerable interest to explorationists.
A SCIENTIFIC EXPLANATION FOR THE ORIGIN AND LOCATION OF PETROLEUM ACCUMULATIONS
Authors: Giardini A. A. , Melton Charles E.
Published: December 2007

The general concept of petroleum formation by biogenic mechanisms has been firmly entrenched for a long time, but there has been no accumulation of convincing experimental evidence in support of this belief. If, on the other hand, a juvenile origin is considered, rigorous mathematical and experimental treatments are possible. This is done here. The mathematical foundation of the juvenile petroleum model is drawn from the model that has quantitatively explained the formation of the atmosphere, the oceans, and surficial carbonaceous matter by outgassing of the Earth. Experimental data for the abundance of juvenile precursors of petroleum — H2, CO, alcohols and hydrocarbons — are obtained from diamond carriers which crystallized in the upper mantle 3.1 billion years ago. The correlation that exists world‐wide between the distribution of petroleum accumulations and regions that have experienced diastrophism is interpreted as demonstrating a direct relationship between plate tectonics and channels of precursor outflow from the upper mantle to crustal traps. The conversion of precursors to petroleum is assigned to maturation processes. The theoretical coefficient of juvenile petroleum production is compared with coefficients of petroleum accumulation derived from published data on 78 giant petroleum accumulations. Agreement is found in all cases. The various “proofs” of a biological origin for petroleum are examined and found to be inconclusive. It is concluded that recognition of a mainly juvenile origin has been clouded by traces of biologically‐derived compounds and fossils that are merely intrinsic to the sedimentary nature of “source rock” and reservoirs. Limitations of the juvenile petroleum model and its possible value for petroleum exploration are discussed.
GEOLOGY AND ENTRAPMENT HISTORY OF THE PORTACHUELO SALINA POOL, TALARA BASIN, PERU
Authors: Hay‐Roe H. , Zuniga J. F. , Montoya A.
Published: December 2007

Maps of pressure measurements and fluid distribution are important tools in deciphering the geology of complex reservoirs. To understand the original entrapment and present‐day distribution of hydrocarbons in the Salina Pool of Portachuelo Field, NW Peru, we used pressure and production data, in conjunction with a detailed analysis of how the pool is put together structurally and stratigraphically. In Portachuelo up to 45 Lower Eocene (Salina) sands, which can be oil‐, gas‐, or water‐bearing in different wells, have been offset by a veritable maze of normal faults. To reconstruct this jig‐saw puzzle we used “composite” electric logs that provided a close approximation of the Salina sequence prior to faulting.

The Salina Pool of Portachuelo offers a challenging place to hunt for commercial oil in a 490‐m sequence of multiple thin (2–10 m) sands within small fault‐blocks. In this search it is helpful to consider the pool as a fluid system in which the reservoir geometry, defined by both stratigraphy and structure, is only one major element; the other two elements are the fluid content of the system and its internal energy, as reflected in the reservoir pressure.

Because of the remarkable complexity of the reservoir geometry, it was the present‐day distribution of fluids and pressures that eventually provided the key to the pool's history of entrapment. Only after fluid and pressure variations were interpreted in terms of the structural evolution did it become clear that Portachuelo's oil originally accumulated in a well‐defined anticline. This simple distribution was destroyed by faulting, which thinned and collapsed the anticlinal crest while raising the flanks. Gas, because of its higher mobility, was more widely redistributed than oil or water.
FORMATIONAL WATER CHARACTERISTICS AS AN INDICATOR FOR THE PROCESS OF OIL MIGRATION AND ACCUMULATION AT THE AIN ZALAH FIELD, NORTHERN IRAQ
Authors: EIzarka Mohamed Hossny , Ahmed Walid Abdel Majid
Published: December 2007

Formational water characterization denotes a chloride‐calcium type in the S1S2A2 class. It indicates a hydrodynamic zone unfavourable for hydrocarbon preservation in the eastern block of the field. These waters have an index of base exchange (IBE) greater than 0.129, indicating connate oil reservoir waters, migrating with oil from the oil source‐beds at the southern parts of the field through connected openings and fault planes.

The entrapment of oil took place at the crestal parts of the folded structure to the west and NW of the field. The water moved down‐dip along the eastern flank, creating capillary pressure, forcing the oil to accumulate in subcapillary pores at the top‐most parts of the upper pay‐zone. The latter section became oil‐wet. The oil wettability led to entrapment of a quantity of oil in the subcapillary pores that was then left behind during oil production operations, necessitating secondary recovery methods.

The occurrence of more lighter constituents in crudes of the upper pay‐zone than in the lower one is due to fractionation and differentiation during migration.
THE SUBSURFACE GEOLOGY OF THE MEER AREA IN FORTH BELGIUM, AND ITS SIGNIFICANCE FOR THE OCCURRENCE OF HYDROCARBONS
Authors: Vandenberghe N.
Published: December 2007

In North Belgium, unusually thick Namurian strata are shown to be rrelate to the existence of deep basin. The presence of a listric growth fault is demonstrated in the Upper Carboniferous, somewhat limiting the Namurian Basin.

The associated roll‐over structure may contain sandstones with sufficient porosity to become an attractive exploration target for gas.
SEDIMENTARY FACIES VARIATION AND HYDROCARBON RESERVOIRS IN CNTINENTAL SEDIMENTS–A PREDICTIVE MODEL
Authors: Blackbourn Graham A.
Published: December 2007

A simple model is outlined which links continental sedimentary environments and facies with their relative position within a basin, and with the prevailing climate. The model may be used for predicting vertical and lateral facies changes within a succession of continental sediments. It is a useful tool both in the search for hydrocarbon reservoirs, and in the understanding of reservoir properties.
EVIDENCE FOR VERTICAL MOVEMENS IN THE SOUTHERN PART OF THE ZAGROS GEOSYNCLINE, IRAN
Authors: Kashfi Mansour S.
Published: December 2007

Detaile dgeological field investigations in the SE Zagros Mountains reveal that this portion of the Zagros was formed by epeirogenic vertical uplifyt. This vertical movement probably started in the Early Paleozoic and continued through geologic time, as shown by disconformities and dominantly shallow‐water sedimentary rocks. Movements of Infra‐Cambrian salt may have contributed to this vertical uplift to produced box‐type folds which are geometrically and genetically different from folds in the NW segment of the Zagros geosyncline. Three late stage of vertical uplift with different magnitudes were measured and studied. Terraces along the mehran River, elevated alluvial cones, and elevated ancient shorelines are among the most spectacular features supporting the vertical uplift of this region.
DISCOVERY OF A VERTEBRATE FAUNA AT THE DEVONIAN‐CARBONIFEROUS BOUNDARY IN SE TURKEY (HAKKARI PROVINCE)
Authors: Janvier Ph. , Lethiers F. , Monod O. , Balkaş Ö.
Published: December 2007

The rich vertebrate assemblage recovered from the base of the Köprülü shales at the top of the Devonian Red Sandstones in the Border Folds of SE Turkey has proved to be exceptional in its composition and stratigraphic emplacement. For the first time, several fish species that were previously restricted either to the Late Devonian or to the Early Carboniferous were found together. In association, rich Ostracode assemblages indicate a Strunian (Latest Devonian) age for this fauna and a transition from supratidal to infralittoral environments. Due to the wide distribution of the Devonian‐Carboniferous formations in SE Turkey, Iraq and Iran, this fauna should become a good marker for this major stratigraphical boundary in the Middle East.
EFFECTS OF EPIDIAGENESIS ON RESERVOIR CHARACTERISTICS OF ROCKS BENEATH CONCEALED UNCONFORMITIES IN ENGLAND AND THE WESTERN DESERT, IRAQ
Authors: Al‐Gailani M. B. , Ala M. A.
Published: December 2007

Petrographic and reservoir characteristic studies (porosity and permeability measurements) were carried out on 447 core samples from seven boreholes penetrating concealed unconformities in England and the Western Desert of Iraq. In England, the unconformities occur at the following boundaries: (a) Cretaceous/Devonian; (b) Lower Lias/Rhaeto‐Liassic/Beds of unknown age/Carboniferous Limestone Series; (c)Triassic/Lower Carboniferous; (d) Triassic/Upper Coal Measures (equivalent to Upper Pennsylvanian); and (e) Triassic/Permo‐Trias/Permian. The borehole in the Western Desert of Iraq encountered five unconformities, in successions ranging in age from the Carboniferous to the Cretaceous.

The results showed great variations in porosity and permeability in the vicinity of these unconformities. These variations are attributed to diagenetic and epidiagenetic processes which may be summarized as follows: (1) early alteration of unstable components such as feldspars; (2) filling of pores and coating of grains by authigenic clay materials; (3) development of pyramidal or bipyramidal overgrowths on quartz grains; and (4) introduction of late diagenetic poikilotopic sparry calcite and/or dolomite cement.

Carbonate rocks are affected by: (1) early dissolution and development of vuggy porosity; (2) dolomitization and dedolomitization; (3) vadose and phreatic cementation; (4) silicification; and (5) modification of porosity and permeability through the growth of new minerals.

Finally, on the basis of the results obtained, three models illustrating the evolution of porosity beneath unconformities are proposed.
THE HYDROCARBON EXPLORATION OF THE BASINS OF THE ROSS SEA, ANTARCTICA, FROM MODELLING OF THE GEOPHYSICAL DATA†
Authors: Cook Richard A. , Davey F. J.
Published: December 2007

Geophysical definition of the three major sedimentary basins of the Ross Sea and scientific drilling on their margins have provided enough information for conceptual models of hydrocarbon generation and source rock character to be applied.

The Waples‐Lopatin geochemical model used is an accepted part of preliminary exploration in petroleum frontier areas where data are limited. The model has only a narrow empirical base despite widespread use by the exploration industry, but its value is in the collation and utilization of a variety of parameters which control the physical environment of hydrocarbon generation. This modelling evaluation attempts to overcome the condemnation of a region because of the lack of data rather than the lack of true petroleum potential.

In the Ross Sea, the Deep Sea Drilling Project (DSDP) holes 270–273 showed that methane and heavier hydrocarbons are present in the drilled sequences. However, to be significant, they must be indicative of regional generation and not just the result of local anomalies. Modelling shows that there are areas of the Ross Sea where the conditions for hydrocarbon generation should be present and these areas are worthy of future exploration.
A RIFT‐RELATED STRATIGRAPHIC TRAP
Authors: Fagerland Nils
Published: December 2007

During the prospectivity analysis of the 40 blocks of the 8th Norwegian round of licensing, a potential “giant” stratigraphic trap was discovered. Its evolutionary histroy makes it especially interesting from a regional point of view.

Well information from neighbouring blocks and high quality seismic data has made this possible.

In block 16/4 in the southern part of the Viking Graben, a combined stratigraphic/structural trap was formed during the Late Paleocene‐Early Eocene.

A submarine fan sequence reached across the viking Graben from the Shetland Platform onto the western flank of the Utsira High of block 16/4 during the Early Paleocene. Later, the Tertiary basins sank with the depo‐centers centered over the old graben. This sinking, together with reactivation of old faults in the southern part of block 16/1 and the northern part of block 16/4 during the Late Paleocene‐Early Eocene, created a large trap. This type of trap is typical for early post‐rift sequences where the post‐rift basin development is governed by the old lines of weakness inherited from the underlying aborted rift.
TECTONIC CONDITIONS FOR OIL AND GAS GENERATION AND DISTRIBUTION ON ANCIENT PLATFORMS
Authors: Maximov S. P. , Zolotov A. N. , Lodzhevskaya M. I.
Published: December 2007

This paper deals with the influence of tectonic factors on teh distribution and generation of oil and gas accumulations in oil‐and gas‐bearing basins ancient platforms. Threee main platform evolutionary stages, with their corresponding structural‐formational associations, may be recognized; the petroleum potential of each stage is different.

Important factors are: the intensity of subsidence; the areal distribution of individual formations, and the presence of sulphate‐saltis in teh section, formation regional seals.

The influence of inversion processes in the development of “giant”l gas‐condensate accumulations is emphasized, adn the petroleum‐bearing basins of ancient platforms are classified according to their oil and gas reserve.
JURASSIC FORAMINIFERAL FACIES IN THE STATFJORD AREA, NORTHERN NORTH SEA ‐ I
Authors: Nagy Jenö
Published: December 2007

Core samples from five wells of the Statfjord area were analysed for foraminifera. The material covers the middle and upper parts of the deltaic marine Dunlin Formation and the basal deposits of the deltaic Brent Formation through an interval ranging in age from Pliensbachian to Toarcian or early Bajocian.

The quantitative distribution of genera and other major faunal parameters define the following five assemblages which reflect successive steps in the evolution of the depositional basin (in ascending order): the Dentalina‐Nodosaria, Ammodiscus‐Dentalina and Marginulina assemblages developed in a delta‐influenced shelf embayment; the Trochammina‐Verneuilinoides assemblage formed under prodelta conditions; the Ammodiscus assemblage deposited in a delta‐front environment. The specific composition of the assemblages is illustrated by quantitative examples.
CONCEPTS ON THE GENERATION AND ACCUMULATION OF BIOGENIC GAS
Authors: Gang Zhang Yi , Jiang Chen Huan
Published: December 2007

To help in the search for biogenic gas, parameters affecting its spatial and temporal distribution are delineated here on the basis of recent developments in microbiology and geochemistry. Methane is produced and dissipated at high rates in uppermost sediments. The key to its accumulation lies in the presence of factors which inhibit the metabolism of bacterial methanogens near the surface, and leave them to flourish at greater burial depths. Favourable controlling factors are as follows: a plentiful nutrient supply (mainly carbohydrates), a high SO‐4 content in the bottom water; a post‐oxic sedimentary environment; frequent transgressions and regressions; low temperatures; high pH values; and high depositional rates and pressures.

In the course of geological history, biogenic gas could be formed whenever transgressions and regressions have occurred frequently due either to tectonics or Ice Ages; when broad coastal plains were supplied with terrigenous non‐lignin carbohydrates by vast river networks; and when cool climates persisted. Accumulations can be grouped into three major genetical types, i. e. West Siberian (coastal marine facies); Black Sea (transitional marine‐lacustrine facies of restricted basins); and Qaidam (inland brackish lacustrine facies). Some case‐ histories from China and additional information from West Siberia are presented. It seems that many biogenic gasfielh remain undiscovered, and exploration prospects are good.
PART 1: ROCK‐EVALFYROLYSIS AND VITRINITE REFLECTANCE1
Authors: Price Leigh C. , Daws Ted , Pawlewicz Mark
Published: December 2007

Detailed organic geochemistry has been performed on a large number of Lower Mississippian‐Upper Devonian Bakken shales from the North Dakota portion of the Williston Basin, and 28 oils mainly from Mississippian Madison Group rocks from different basinal areas. Here we report results of Rock‐Eval pyrolysis and vitrinite reflectance (Ro) analyses. Variable paleoheat flows in the Williston Basin caused the threshold of intense hydrocarbon generation to occur at different depths in different basinal areas. In higher paleogeothermal gradient basinal areas, this event occurred at depths of 7,650‐8,000 ft, and at 10,000 ft or deeper in lower paleogeothermal gradient areas of the Basin. Distinct organic metamorphic imprints in Williston Basin sediments were also caused by extreme, but variable, paleoheat flows in the basin, as well as secondary migration of crude oils from deep basinal source areas. The high paleoheat flows are postulated as being due to a Late Cretaceous — Paleocene aborted rift event. Only a small volume of Bakken shales in restricted areas of the Williston Basin was responsible for the oil found reservoired in Mississippian Madison Group rocks. However, this small shale volume has been responsible for a relatively large amount of crude oil.

R0 profiles in the Tertiary through Middle Jurassic rocks in the Williston Basin had steep, linear Ro versus depth gradients, with strong reversals of R0 values occurring in the Lower Jurassic rocks. The lower Mesozoic through Paleozoic rocks of the Basin had strongly suppressed R0 values compared to the values in the Tertiary through Middle Jurassic rocks. This was especially true of the R0 values in the Bakken shales. This R0 suppression was due to a change in organic matter (OM) type from oxygen‐rich terrestrially derived OM in the younger rocks, to a hydrogen‐rich marine derived OM in the deeper, older rocks. The threshold of intense oil generation (TIHG) occurred in the Bakken shales of the Williston Basin at R0 values somewhere between 0.9 and 1.7% (best estimate 0.9), as would be read in oxygen‐rich OM. Much higher burial temperatures (and consequently R0 values) than usually held to be necessary were required for both the TIHG as well as mainstage hydrocarbon generation in the Bakken shales. These results are most likely applicable in general to source rocks with hydrogen‐rich OM. The data of this study have major implications to petroleum exploration as well as to petroleum resource assessment.
SOME APPEARANCES AND CAUSES OF LINEAMENTS SEEN ON LANDSAT IMAGES
Authors: Onyedim G. C. , Norman J. W.
Published: December 2007

The surface appearance and nature of lineaments showing on Landsat images are described, together with their likely causes. A computer model, based on the finite element method, is employed to show that the strain and stress effects over a deep underlying vertical fault are conducive to the development of two classes of faults, which are usually observed at the Earth's surface as lineaments. Some aspects of the involvement of these failure zones in mineral and petroleum prospecting, water supply and engineering geology are outlined.
THE ORINOCO OIL BELT, VENEZUELA
Authors: Martínez Aníbal R.
Published: December 2007

The Orinoco Oil Belt of Venezuela is a very extensive, non‐discrete, crude‐oil producing area located along the southern third of the Maturín (Eastern Venezuela) basin, north of the Orinoco River and the Guayana Shield. It extends due westwards from Puerto Ordaz for 460km; the main producing areas, defined on the basis of productivity and magnitude of crude oil in‐place, cover 13, 600 sq. km. There are no significant surface indications of petroleum anywhere in the Belt. The first well drilled was La Canoa‐1 in 1936, initiating a stage of exploration which ended in 1967 with publication of a preliminary evaluation of the potential reserves; the Ministry of Energy and Mines, then of Mines and Hydrocarbons, and the State oil company Corporación Venezolana del Petróleo (CVP) completed a second stage of exploration in 1977; Petróleos de Venezuela and its operating companies then drilled 669 wells in five years (1979–83) totalling 643,000 m with 5.5 MM** m of logs, and shot 15,000 km of seismic lines at a cost of $US 615 MM, an effort conservatively estimated as having taken 2,500 man‐years. The main producing areas are, from east to west, Cerro Negro, Pao, Hamaca, San Diego, Zuata, and Machete. Petroleum characterisation in the Belt is based on the study and analysis of 288 samples. Viscosity (dynamic) of the crude oils at reservoir conditions ranges from 2,000 to 7,000 m Pa.s (cp)†.Production rates average 25 cu. m/d(160 b/d), increasing fourfold after steam stimulation. At the end of 1985, production was 13,000 cu.m/d(80,000b/d)†, from the Cerro Negro and Hamaca main producing areas. Operating costs are similar to those in other heavy‐crude oilfields in the basin. The volume of crude oil in‐place is estimated to be 187.8 B cu. m (1,181 B brls), which makes the Orinoco Oil Belt the largest crude oil accumulation in the world. Proved reserves are 4.161 B cu. m (26.170 B brls). and unproved reserves 14.822 B cu. m (93.230 B brls). Investigative activities are underway, particularly in the Cerro Negro and San Diego producing areas.

In subsequent papers of this thematic survey, A. Isea presents a geological synthesis of the Orinoco Oil Belt; G. Don Kiser discusses the exploration results of the Machete area; A. Santos and L. Frontado describes the reservoir geology of the Cerro Negro steam‐injection area; and A. Vega and I. de Rojas summarise exploration results from the Zuata area.