bluuebunny/crossref_metadata_2025 huggingface dataset:
THE STRUCTURE OF A MONOCLINE IN THE SYRIAN ARC SYSTEM, MIDDLE EAST‐SURFACE AND SUBSURFACE ANALYSIS
Authors: Reches Ze'ev , Hoexter David F. , Hirsch Francis
Published: December 2007

The long Syrian Arc belt in the Middle East consists of tens of folds and monoclines with their associated faults. The structure of one monocline of this belt, the Hebron monocline in Israel, is analyzed by construction of accurate structural traverses, measurement of the internal strain of the rocks, and geological mapping. The surface structure indicates that three modes of monocline development, draping, buckling and kinking, operated in the Hebron monocline. The subsurface structure, which includes a steep reverse fault, is deduced through mechanical and tectonic models, and structural similarity with other monoclines in Israel.
SEDIMENTOLOGY OF THE BRAE OILFIELD, NORTH SEA: FAN MODELS AND CONTROLS
Authors: Stow Dorrick A. V. , Bishop Clive D. , Mills Stephen J.
Published: December 2007

Submarine fans are important to the petroleum industry for their reservoir and source‐rock potential. There are a variety of fan types that can be characterized by different fan models. In assessing which model, if any, is appropriate for a particular area or field it is important to evaluate the controls that operate to determine the type of fan developed. Most present‐day fans that have been studied are deep‐water oceanic; more work is required on modern examples of shallow‐water, small‐basin fans which are particularly relevant to hydrocarbon exploration.

Jurassic and Tertiary objectives are important in the North Sea and include both nearshore‐sandstone and submarine fan reservoirs. The Brae oilfield is an Upper Jurassic reservoir on the western faulted margin of the North Sea Central rift system. Detailed core, electric log, dipmeter and seismic data have been examined. The Brae field comprises at least three small overlapping submarine fans that form a sediment apron along the scarp margin and that were deposited by a variety of gravity‐flow processes in a shallow basin below wave base. Tectonic control on fan development has resulted in up to six fining upwards megasequences (50‐150m) within the overall fining upwards basin fill (300–600 m). There has been a large intermittent supply of coarse detritus across a narrow littoral zone and down a steep slope. Short, sedimentladen rivers supplied mud and plant débris, and a complex interdigitation of coarse‐and fine‐grained facies has resulted.

The Brae fans are an important example of the fault‐controlled, shallow, small‐basin type and are most closely analogous to the Jurassic fans of East Greenland. Reservoir characteristics are dependent on diagenesis, facies and fault distribution, and vary markedly along the fault margin. A clear understanding of the controls and models is essential for continued exploration and development in this part of the North Sea.
THE NATURE OF THE UPPER 400 KM OF THE EARTH AND ITS POTENTIAL AS THE SOURCE FOR NON‐BIOGENIC PETROLEUM
Authors: Giardini A. A. , Melton Charles E. , Mitchell Richard S.
Published: December 2007

It has been reported that the upper 400 km of the Earth outgassed 1015 tons of petroleum‐related fluid over the past 3 billion years. By assuming Fischer‐Tropsch reactions and crustal entrapment, 0.1% of this quantity can account for the entire amount of petroleum estimated to be in the Earth's crust. In this paper, the authors attempt to define in some detail the past and present nature of this deep‐source for non‐biogenic petroleum. The principal data used are seismic, and the nature of the matter that is found totally enclosed in natural diamonds from world‐wide continental sources. New data are presented on matter included in diamond cubes from Zaire, Africa, noteworthy among which are the identification of plagioclase, silicate glass, and solid hydrocarbon inclusions. The general conclusions on the upper 400 km of the Earth are: (1) Diamonds, the sample carriers from the inner Earth, formed over the depth range ≤ 70 ≤ 370 km in a partially molten silicate environment that contained C and H components. (2) From top to bottom, the growth environment varied from aqueous, carbonate‐rich and felsic to aqueous, hydrogen‐rich and ultramafic. (3) Petroleum and petroleum forming constituents were present throughout. (4) The depth range of diamond formation is found to correlate with the present depth profile of the suboceanic asthenosphere. Because of this, it is concluded that the general nature of this region of the Earth has not changed much since the earliest known time of diamond formation (˜ 3 b.y. ago) in spite of material transport to the surface and isostatic adjustment of the lithosphereasthenosphere boundary. The discovery of significant solid hydrocarbon in a diamond cube suggests that the hydrocarbon content of the upper region of the asthenosphere may be twice that indicated by occluded fluid alone. This tends to support a suggestion based on the quantity of occluded fluid in kimberlite that 1016 rather that 1015 tons of petroleum and petroleum forming material have outgassed from the Earth during the past 3 billion years. An outgassing of 1016 tons would have permitted crustal accumulation of up to 105 tons per km2 in a 10‐million year span of Cenozoic time, consistent with the existence of Cenozoic petroleum fields. By analogy with N2 outgassing, it is estimated that about 1015 tons of non‐biogenic petroleum remain to be outgassed from the Earth.
SOME ASPECTS OF THE OCCURRENCE OF PROTO‐KEROGEN IN RECENT OOIDS
Authors: Ferguson J. , Ibe A. C.
Published: December 2007

Recent oolites from the Bahama Banks are shown to contain 1.23–4.13 wt% organic carbon of algal origin, chiefly in the form of proto‐kerogen. Characterization of the ogranic matter by routine optical and chemical means revealed that, although it is immature, it has a very high potential for generating petroleum hydrocarbons.

It is suggested that with rise in temperature due to burial, and perhaps to catalytic influence of the host sediments, this proto‐kerogen of algal‐amorphous facies would, through time, generate significant amounts of hydrocarbons. In those oolite deposits with adequate porosity, the hydrocarbons could accumulate as petroleum.
RELATIONSHIP BETWEEN DIAGENESIS AND PORE FLUID CHEMISTRY IN NIGER DELTA OIL‐BEARING SANDS
Authors: Lambert‐Aikhionbare D. O.
Published: December 2007

The sandstones of the Niger delta oil reservoirs are predominantly quartz arenites, yet silica cementation in the form of quartz overgrowth is at a minimum. This apparent lack of cementation is attributed among other things to the low concentration of silica in formation water, which results in low bulk‐volume reduction, little pressure‐solution and consequently, under‐compaction.

Under‐compaction is aided by early calcite cementation which probably occurs at the boundary between the fresh waters of the Benin formation and the brackish to saline pore‐waters of the paralic sequence. Early cementation may have aided the discriminate entry of hydrocarbons into the reservoirs of the area.

Entry of hydrocarbon into reservoirs appears to inhibit diagenetic processes as significant differences in mineral assemblages exist between hydrocarbon and non‐hydrocarbon reservoirs. Kaolinite is the dominant authigenic mineral in most hydrocarbon reservoirs whereas kaolinite, siderite, pyrite, calcite as well as minor amounts of smectite and illite occur in many non‐hydrocarbon reservoirs. The presence of mainly kaolinite in most reservoir rocks is suggestive of early entry of hydrocarbons into them. This deduction is at variance with the presently‐accepted theory of hydrocarbon generation within the deeply buried section of the paralic Agbada formation and the overpressured marine Akara shales. Instead, it suggests generation and migration of hydrocarbons from the paralic shales adjacent to the reservoirs.

Lack of cemetation in most hydrocarbon reservoirs results in the production of very fine materials (“fines”) with the oil. It is proposed that most of the kaolinite present in many petroleum reservoirs is produced with such fines. The removal of kaolinite, in this way, reduces the hazard of permeability loss which would have occurred due to blocking of throat‐passages by floating kaolinite platelets.
ESTIMATION OF IRREDUCIBLE WATER SATURATION AND EFFECTIVE PORE SIZE OF MUDSTONES
Authors: Honda Hiromi , Magara Kinji
Published: December 2007

A theoretical consideration of immobile water saturation in mudstone is made by means of a capillary model of a porous medium using the air and water absolute permeabilities of a sample. The calculated values of immobile water saturation of the Tertiary mudstones from Japan tend to support a generally‐accepted concept; virtually all the water in mudstones is irreducible. Immobile or irreducible water saturation increases gradually with decrease of porosity of mudstones; 15% porosity is a critical value beyond which mudstones contain 100% immobile water in the pores.

Pore sizes of the mudstones estimated by the same model are considerably greater than those estimated by Welte (1972), and are more comparable with Momper's (1978) atypical pore size range of mudstone. The result of analysis indicates that radius of principal pores of the mudstones, which are effective on fluid flow, ranges from about 0.1–0.5 μm. The result thus suggests that even relatively large hydrocarbon molecules can effectively pass through the rock.
HYDROCARBON POTENTIAL OF THE EASTERN ALBORZ REGION, NE IRAN
Authors: Rad F. K.
Published: December 2007

The Lower‐Middle Jurassic Shemshak Formation is widely distributed in North, Central and East Iran. Being of great thickness and regional extent, the Formation is a significant source rock in the Eastern Alborz region and is considered as the most probable source for the Khangiran gas (NE Iran) as well as for the eastern Caspian oilfields in Russian Turkmenistan. A detailed geochemical analysis of outcrop samples from this Formation shows that it is an immature source rock, containing dominantly type III kerogen of terrestrial origin. Nevertheless, the depth of burial of the Shemshak Formation in the Dasht‐e Gorgan and the southern Caspian depression suggests that it might have reached the level of thermal maturity required for the generation of hydrocarbons. It is concluded that although the hydrocarbon‐generating potential of the sediments is relatively low, under favourable conditions this Formation is capable of generating enough crude oil and gas to supply a giant field.
THE RECENT (MIOCENE‐QUATERNARY) REGMATIC SYSTEM OF THE WESTERN MEDITERRANEAN REGION: A New Model of Ensialic Geodynamic Evolution, in a Context of Plastic/Rigid Deformation
Authors: Boccaletti M. , Conedera C. , Dainelli P. , Gočev P.
Published: December 2007

By comparing the features observed on Landsat images with the known geological data, a regmatic system that controlled the entire Neogene to Recent structural evolution of the Western Mediterranean area has been recognized.

The system consists of two principal conjugated shear trends, reactivating old fractures, the NE‐SW, or Moulouya, and the NW‐SE, or Gafsa. With these, an E‐W trend of prevailing shear character (Gibraltar) and a N‐S trend with mostly tensional movements (Tyrrhenian), are associated. The trends that characterize the system are always present in all the segments of the circum‐Mediterranean chains and continue in the forelands and in the marine areas, although some may prevail.

The orientation and the relative movements of the fractures of the system are consistent with the slip‐line field that develops in a plastic‐rigid mobile area, when this is placed between two non parallel converging rigid blocks. The system evolves according to a monoclinic scheme, which is in turn complicated by the variations of the crustal thickness in the deformed zone and by some pre‐existing discontinuities. A progressive migration in time of the major deformations towards the SE is also observed. Mechanisms of intracontinental subduction induced by the shear system are then postulated. The new proposed model may open up new leads for the identification of prospects in the exploration for hydrocarbons, particularly along the orogenic belts.
FACIES DISTRIBUTION AND PETROLEUM GEOLOGY OF THE BOMBAY OFFSHORE BASIN, INDIA
Authors: Basu D. N. , Banerjee A. , Tamhane D. M.
Published: December 2007

In view of the recent oil and gas dicoveries in the Bombay Offshore basin, its detailed geology has been worked out in terms of its source rock and reservoir potential. An agewise, layer‐cake lithofacies analysis and five depositional model maps from Paleocene to Middle Miocene age, together with a number of paleotectonic sections has led to the reconstruction of a xeneralized depositional model of the basin as a whole. This proposed depositional model envisages the Bombay Offshore basin as a shelf‐to‐basin carbonate model. During Paleogene and Early Neogene time the clastic supply by the proto‐Narmada river from the NE resulted in delta progradation up to the Dahanu depression, which was a region of pro‐deltas and lagoons with a considerable thickness of finer clastics. Beyond the Dahanu depression, the Bombay High and Bassein‐Alibag‐Ratnagiri shelf remained open carbonate platforms, while the DCS area was the locale of shelf‐edge carbonate build‐up.

The potential targets for exploration are the deltaic sandstone to the north in the Tapti area—particularly where the sandy facies interfingers with the shales and the porous limestone horizons in the Bombay Platform, Bassein‐Alibag‐Ratnagiri shelf and the DCS trend. The Dahanu depression is thought to be the main source rock area.
ABUNDANCE OF SOURCE ROCKS FOR OIL AND GAS WORLDWIDE
Authors: Grunau Hans R.
Published: December 2007

Source rock abundance through geological time cannot be measured in absolute quantitative terms. The source rocks of giant fields, which are known in most cases, can serve as an appropriate yardstick for a percentage allocation of source rocks to geological time intervals, based on ultimately recoverable reserves. This yardstick is used to relate source rock percentages per time interval to in situ reserves and resources of oil and gas worldwide, both conventional and unconventional. Necessary corrections are made. On this basis it appears that the Cretaceous is the most important oil‐generating period (49%), while the Tertiary is the most important gas‐generating period (76%). For total hydrocarbons in terms of oil equivalents, the most important hydrocarbon‐generating intervals are the Tertiary (69%), followed by the Cretaceous (25%), the Jurassic (4%) and the Triassic to Paleozoic (2%). The percentages refer to source‐rock age and not to time of generation. All estimates have to be regarded with much caution. They represent an approach to the problem rather than a solution. Major uncertainties still exist. It must be stressed that the problem of source rock abundance should be seen in a wider hydrocarbon habitat context, especially in the light of retention. The important role of bacterial gas and gas hydrates is emphasized.
SPECIFIC GRAVITY AS A KEROGEN TYPE AND MATURATION INDICATOR WITH SPECIAL REFERENCE TO AMORPHOUS KEROGENS
Authors: Kinghorn R. R. F. , Rahman M.
Published: December 2007

Mineral‐free kerogen concentrates have been fractionated into their components by the use of differential and sequential gravity separation methods. The density of each component within a kerogen depends upon its chemical composition which is a function of the original organic matter and its level of organic maturation.

The mineral‐free kerogen concentrates were analysed for the elements carbon, hydrogen and oxygen and these results, combined with visual kerogen examination, allowed estimations of kerogen type and degree of maturation to be made.

The separation procedure also allows the composition of the sedimentary organic matter to be assessed and thus, with the knowledge of the level of maturity and the possible convertibility of each component into fluid hydrocarbons, a more accurate assessment of the hydrocarbon potential of the kerogen can be obtained.

The quantity of unproductive carbon can be identified by density separation, and the different types of amorphous kerogen can also be identified and separated by means of this method. The oil‐prone amorphous kerogens have lower specific gravities than the amorphous gas‐prone material.
PETROLEUM GEOCHEMISTRY OF LATE CRETACEOUS AND EARLY TERTIARY SHALES PENETRATED BY THE AKUKWA‐2 WELL IN THE ANAMBRA BASIN, SOUTHERN NIGERIA†
Authors: Ekweozor Chukwuemeka M. , Gormly James R.
Published: December 2007

The concentration, type and thermal maturity of organic matter from the Imo Shale, Nkporo Shale and the upper parts of the Nkalagu Formation which were penetrated by the Akukwa‐2 well are presented. The organic carbon content ranged from 0.4–3.5%. The kerogens from the various formations were of the humic and mixed varieties. Evidence from independent thermal maturity parameters (namely, average vitrinite reflectance (R0%), Tmax and transformation ratio from Rock‐Eval, n‐alkanes distribution pattern, and hopane “fingerprint”) combined to locate the top of the ‘oil window’ within the Nkporo Shale at a depth of approximately 2,000 m from the surface. This corresponds to a threshold temperature of circa 65°C.

Sedimentary organic matter which is favourable for both gas and oil generation is therefore probably abundant in the Anambra basin. Hydrocarbon reservoirs are possibly located at relatively shallow depths where accumulations of heavy oils may also be expected.
EVIDENCE FOR IN‐SITU GENERATION OF METHANE IN CARBONATE OOIDS
Authors: Ferguson J.
Published: December 2007

The results reported here are from a series of simple experiments designed to test the hypothesis that algal material associated with modern carbonate ooids is capable of regeneration after prolonged periods of desiccation. Although they do not provide any positive proof of this, they do show evidence for the generation of methane gas associated with ooids, as well as possible evidence for the consumption of methane by sulphate reducing bacteria. The implication is that the ooids themselves provide a suitable anaerobic environment in which methanogenic bacteria can live. These results are in line with the conclusions of Ferguson and Ibe (1981), that there is some process acting within the individual ooids which allows the formation of hydrocarbons in an otherwise aerobic marine environment.
GASFIELDS, NW GERMAN BASIN: SECONDARY GAS MIGRATION AS A MAJOR GEOLOGIC PARAMETER
Authors: Pratsch J.‐C.
Published: December 2007

The observable concentration of the major deep gas accumulation areas in the NW German Basin is the result of focused secondary migration. Gas generated in several effective depocenters (regional structural lows) from Late Carboniferous source beds migrated into adjacent regional structural highs. The preferred migration paths are qualitatively predictable on the basis of present basin geometry. Optimal conditions for gas accumulations exist where the presently trapping regional highs have also been sites of favorable reservoir development. On‐going and future deep‐gas exploration efforts in the basin can be regarded as quite hopeful.
PETROLEUM PROSPECTS OF CRETACEOUS SEDIMENTS OF THE CAMBAY BASIN, GUJARAT, INDIA
Authors: Mukhejee Manoj K.
Published: December 2007

The Cambay Basin in the NW part of the Indian Peninsula is a commercial petroleum producer from Tertiary sediments resting on the basic lava flows known as Deccan Traps. Cretaceous sediments which underlie the Deccan Traps are exposed in the eastern and western margins of the basin and are also encountered in the subsurface. The paleogeographic reconstruction of the Cambay Basin suggests that the northern part, possessing a thin cover of Cretaceous sediments, has meagre petroleum prospects. However, the southern part of the basin, where more than 1,000 m of Cretaceous sediments were deposited by two independent drainage systems, may be more lucrative. Suitable facies for generation and accumulation of petroleum are expected in this part of the basin.
MOZAMBIQUE‐MADAGASCAR GEOSYNCLINE, II: PETROLEUM GEOLOGY
Authors: Kamen‐Kaye Maurice
Published: December 2007

The Mozambique‐Madagascar geosyncline may rank above congeneric borderland down warps along the western Indian Ocean in its hydrocarbon exploration quality. On the Mozambique flank, gas in significant quantities has been produced on test. On the Madagascar flank, bitumen in equally significant quantities has been outlined. Exploration of the geosyncline as a whole has included the drilling of more than 30 wells on the Mozambique flank, and more than 40 wells on the Madagascar flank. Of this total of more than 70 wells, 15 exceed 4,000 m in depth. Objectives almost untouched by the drill are the Karroo strata below basalt on the Mozambique flank, Karroo strata below marine Jurassic onlap on the Madagascar flank, and Karroo strata that this writer believes should exist in continental and mixed facies at the center (below deep waters of the present Mozambique Channel). Considerable depth of burial of all these Karroo objectives should enhance the maturation of their original organic matter to the hydrocarbon stage, even though that matter was initially vegetal and palynomorphic. Post‐Karroo objectives may be limited to the geosynclinal flanks, because pelagic facies may have dominated the center throughout post‐Karroo time. Limitation to the flanks, however, does not adversely affect depth of burial in many areas. Post‐Karroo strata, in fact, may rival their Karroo predecessors, especially considering the presence of marine intercalations. Principal exploration parameters such as sedimentary volume, source rock, reservoirs, and present density of drilling, are favorable or good. They suggest that the Mozambique‐Madagascar geosyncline is a prospect worthy of much additional deep drilling to find major reserves of petroleum.
DEVELOPMENT OF METHODS FOR THE QUANTITATIVE EVALUATION OF PETROLEUM POTENTIAL IN THE USSR
Authors: Maximov S. P. , Vinnikovski S. A.
Published: December 2007

The paper deals with the history of the development of methods used for the prognostic evaluation of hydrocarbon resources in the USSR, their modern classification, and the calculation techniques involved. Ultimate resources are divided into discovered reserves and predicted resources. The latter are divided into D1 and D2 sub‐groups, according to the presence or absence of production from the formation under evaluation. Prognostic resources include identified and unidentified components. The modern system of forecasting provides a review of adequate information and the determination of requirements for: (i) the quality of prediction; (ii) the creation of theoretical models for oil and gas generation and accumulation processes in the region under evaluation; (iii) the determination of quantitative functional relations as a forecasting tool; (iv) resources estimation using different models; and (v) the correlation of the results obtained and the differentiation of the resources in terms of the efficiency of capital investment required for their development.
A PROPOSED GAS POOL IN THE PLEISTOCENE BOSUMTWI IMPACT CRATER, GHANA
Authors: Jones W. B.
Published: December 2007

It is believed that the sediments of Lake Bosumtwi in Ghana are underlain by a body of fallback breccia and a highly fractured basement uplift which could form a significant trap. The lake sediments wouldprovide a rich source of biogenicgas and also seal the reservoir. Reserves of 7 cu km (250 billion cubic feet) of gas are estimated.
SOURCE ROCK ANALYSIS IN TWO KARROO BASINS OF COASTAL TANZANIA
Authors: Kreuser T.
Published: December 2007

Two Karroo basins in the coastal area of Tanzania were selected for source‐rockn analysis i.e. for analysis of potential or probable oil and gas generation. A several hundred ft thick middle section, of a mostly terrestrial, fluviatile‐lacustrine nature up to a deltaic sequence with a minor marine intercalation, showed many laminated fine, pelitic‐lutitic strata in a generally fine sedimentary cycle with large quantities of organic residues. Source‐rock evaluation and geochemical analysis were carried out and yielded moderate values of organic carbon content (up to 2.4%), with maceral composition of mainly structureless organic matter and some vitrinite. They probably represent marginal source rocks for oil and gas which have been “overcooked” during organic metamorphism, and are now post‐mature.
THE ROLE OF ORGANIC MATTER IN THE EARLY DIAGENESIS OF CARBONATE OOIDS ‐ AN EXPERIMENTAL STUDY
Authors: Ferguson J. , Bush P. R. , Clarke B. A.
Published: December 2007

The results of a number of experiments simulating the early diagenesis of carbonate ooids are presented and discussed. consideratin of both inorganic and organic reactions indicate that the presence and maturation of organic matter i scritica. It is suggested matter, while the inorganic reactions are likely to be controlled by the by‐products of the maturation of the oraganic matter. In gernral the results obtained show a marked similarily to the geilogical situation.
IN SITU FORMATION OF PETROLEUM IN OOLITES, PART I: SCHEME OF HYDROCARBON GENERATION AND ACCUMULATION
Authors: Ibe A. C.
Published: December 2007

Published data from an organic geochemical study of Recent oolites from the Bahamas and teh kPersian Gulf suggest that petroleum‐bearing oolites may be the source, as well as the reservoir, of the hydrocarbons they contain. This paper advances a scheme for the generation of leached oolites with oomodic porosity, petroleum‐bearing oolites could be viewed as integrated source‐resrvoir rocks.
THE APPLICATION OF FACIES PARAMETERS ADN MAPPKING TECHNIQUES TO EXPLORATION OF THE SUBSURFACE LOWER CRETACEOUS OF THE QUATTARA DEPRESSION, WESTERN DESERT EGYPT
Authors: Elzarka Mohamed Hossny
Published: December 2007

The occurrence of oil in some fields of the Qattara Deprrssion is largely controlled by the lithological composition of the Lower Cretaceous succession. The lithologic percentage adn ratio; classifying, entropy and distance functions; entropy ratio, relative centre of gravity, variance, covariance adn relative standard deviation; adn tripartite and entropy facies parameters have been calculated for sections studied. They have then been correlated with optimum parameters, i. e. teh average composition fo four oil‐bearing sections. Similarity or departure of the calculated parameters from those of of the optimum composition facilttates delineation of areas favourable for finding oil.

Thus, this tool provides a valuable means for the prospecting for and explorastion of new oil and gas deposits, as indicated in teh case study presented.
THE SE AFRICA TRIPLE JUNCTION AND THE DRIFT OF MADAGASCAR
Authors: Flores Giovanni
Published: December 2007

In a paper published in 1970, the Author expressed the view that the Mozambique Channel originated as Madagascar drifted to the NE from the Mozambique‐Natal coast. A further analysis of that view in the light of recently acquired data now enables him to formulate the hypothesis set out in this paper, namely that:

(a). The geometry and tectonics of the Lebombo‐Zoutspansberg‐Buzi elongated fractures accompanied by Jurassic and Cretaceous effusives define a triple junction similar to the present‐day Red Sea‐Afar‐Gulf of Aden triple junction;

(b). An initial rifting of the Channel occurred as the swell originating the triple junction produced a stretching of the continental crust and the initial separation of the Indo‐Malgache Landmass from Africa along the two eastern branches of the triple junction, while the middle one (Zoutspansberg) was being reduced to an abortive rift; and

(c). Only when the thinned continental crust was stretched to the point of rupture did the oceanization process set in, with the production of “classical” spreading centres and magnetic anomalies.

The latter process probably began in the Cretaceous, and was accompanied by impressive flows of alkaline lavas on the continental side and basalts in the oceanic area.

Considering that, if this hypothesis is correct, the proto‐channel in Early Jurassic time was a narrow seaway, as suggested also by the juxtaposition of the major Mozambique and Madagascar fault lineaments; and considering that Madagascar has numerous shows and seepages of petroleum, probably of Jurassic age, the hypothesis discussed may have considerable bearing on the petroleum possibilities of the deeper Mozambican, Jurassic section, whose existence is indicated by several of the offshore seismic profiles recently run. Any oil generated in that section is likely to have migrated up‐dip on both sides of the proto‐channel.
A SOURCE BED STUDY OF THE OLIGO‐MIOCENE ASMARI LIMESTONE IN SW IRAN
Authors: Kashfi Mansour S.
Published: December 2007

Detailed geological and geochemical investigations in the folded belt of the Zagros geosyncline reveal that the source rocks for the very large Asmari oil accumulations may not be the PabdehGurpi and/or Kazhdumi formations as has been suggested; the hydrocarbons are more likely to be indigenous to the Asmari. Most previous investigators have assumed that only organic‐rich marls and shales serve as effective source rocks. However, geochemical analysis shows that the organic content of the Asmari carbonate, although not very rich, compares favourably with the source beds proposed by earlier workers.

A rock should not be considered an oil source bed if it does not currently contain at least traces of oil. If the oil had been generated in the Pabdeh‐Gurpi and/or Kazhdumi formations, some hydrocarbons should still be present within these rocks.

For all source rocks, there must be a positive relationship between thermal history and oil generation. Consequently, temperature and depth of burial are essential factors in petroleum genesis. The temperature history of the Asmari Formation is related to the thickness of the overlying Teritiary rocks. Maximum burial of the oligo‐Miocene Asmari, throughout most of the folded belt, is assumed to have occured during Early Pliocene time before the last phase of Zagros orogeny.

Asmari limestone, therefore, qualifies as a source rock where it is buried deep enough to reach the optimum temperature needed to release its hydrocarbons. Under conditions of lower temprature and shallower burial, the limestones serve only as reservoir rocks.
GEOLOGY AND EXPLORATION IN THE TAKUTU GRABEN OF GUYANA BRAZIL
Authors: Crawford F. D. , Szelewski C. E. , Alvey G. D.
Published: December 2007

The Takutu basin is a Mesozoic graben 280 km long and 40 km wide in northern Brazil and adjoining Guyana. It occupies an ancient Pre Cambrian shear zone within the heart of the Archean Guyana shield. Metavolcanic rocks and thick Proterozoic quartzites crop out north of the basin. Granitic rocks border the graben on the south and east. Mesozoic basalt forms a band of outcrop along the southern and eastern margins of the modern‐day valley. The basin is filled with up to 5,400m (18,000 ft) of Mesozoic sedimentary rocks, underlain by more than 1,700m (5,600 ft) of mafic volcanics of Jurassic and possibly older (i.e, Proterozoic) ages. Six regional unconformities were recognized within the basin fill.

The geologic history of the graben is characterized by one volcanicphase and three depositional phases. Rifting began in Late Triassic to Early Jurassic time with the extrusion of thick Apoteri flow basalts. Lower Jurassic non‐marine clastics of the Manari Formation overlie the eroded basalt. They are overlain by the thick Lower and Middle Jurassic non‐marine salt and gray shale of the Pirara Formation. These sediments were deposited over most of the basin and contain good oil source‐rocks. Middle and Upper Jurassic non‐marine clastics of the Takutu Formation overlie the evaporites. They were deposited in lacustrine and deltaic environments, as interpreted from seismic and well data.

There are two contrasting structural styles, of Late Triassic to Early Jurassic, and Cretaceous to Tertiary ages. Block‐faults are common in the pre‐salt section, and non‐piercement halokinetic structures in thepost‐salt rocks. The graben contains a cross‐basin arch, evidence of wrench faults and minor salt solution.

Four exploratory wells have been drilled to date. Home Karanambo No. 1 discovered highquality crude oil in the fractured volcanic basement. Seismic stratigraphic interpretations indicate that alluvial fan and deltaic reservoirs may overlie undrilled structures elsewhere in the basin.
LAGOA FEIA FORMATION (LOWER CRETACEOUS), CAMPOS BASIN, OFFSHORE BRAZIL: RIFT VALLEY STAGELACUSTRINE CARBONATERESERVOIRS ‐ I
Authors: Bertani Renato T. , Carozzi Albert V.
Published: December 2007

The Campos Basin is one of the coastal basins of eastern Brazil formed during the separation of the African and South American continental blocks. The Lagoa Feia Formation consists of the sediments deposited during the rift valley stage of the Campos Basin, and varies from 200 m to more than I, 500m in thickness. 17 microfacies were recognized, and are grouped into four main sequences, dominated respectively by terrigenous supplies, ostracods, pelecypods and basic volcaniclastics.

The vertical sequence of microfacies and the associations of syndepositional diagenetic minerals were used to reconstruct the general environment of deposition. It consisted of saline alkaline lakes, oscillating between a playa lake stage with ostracod microfacies and a pluvial lake stage with pelecypod microfacies.

Five diagenetic stages were recognized: syndepositional alteration of lithics to trioctahedral smectites, early dolomitization, early silicification, early cementation by bladed rim calcite and zeolites; fresh water vadose, consisting mainly of dissolution of bioclasts and lithics; fresh water phreatic, with sparite cementation and neomorphism; mixed saline‐fresh water, represented mainly by silicification; and burial with compaction, late dolomitization and partial conversion of smectites to illite.

Pelecypod‐rich limestones with primary interparticle, secondary intraparticle, moldic and moldic‐enlarged porosities constitute the main potential reservoirs. The ideal conditions for the generation and preservation of such reservoirs consisted of periods of exposure followed by rapid lake expansion and burial. In this manner, the secondary porosity formed in the vadose fresh water environment was preserved or only partially occluded by calcite cementation during fresh water phreatic conditions.
PLATE TECTONICS WITH FIXED CONTINENTS: A TESTABLE HYPOTHESIS ‐ I
Authors: Jr. Paul D. Lowman
Published: December 2007

This paper proposes that plate‐tectonic processes do not necessarily cause continental drift, and that sialic blocks the size of Australia or larger are fixed relative to eachother. Continental drift has not yet been geodetically demonstrated and the geologic evidence for it has been repeatedly challenged or refuted. New lines of evidence presented here against drift include: absence of the low‐velocity zone under Shields; deep continental lithospheric roots; absence of continental hot‐spot trails; absence of significant offset between Greenland and Ellesmere Island; internal contradictions in paleomagnetic data, and between paleomagnetic and paleogeographic data; Cenozoic tectonism and horizontal compression at supposed passive margins; and absence of an adequate plate‐driving force for plates with continental (non‐subductable) leading edges. The hypothesis of plate tectonics with fixed continents predicts that high‐precision geodetic measurements now in progress will find no separation of Eurasia and North America no matter how long they are continued. It implies some form of slow subduction at supposed passive margins such as the east coast of North America.
JURASSIC FORAMINIFERAL FACIES IN THE STATFJORD AREA, NORTHERN NORTH SEA ‐ II
Authors: Nagy Jenö
Published: December 2007

In the first part of this paper, which appeared in Journ. Petrol. Geol. 8, (3) 273–295, five foraminiferal assemblages found in core samples recovered from the Lower‐Middle Jurassic boundary (Dunlin and Brent Formations) were identified and discussed.
A PERMIAN BEACH IN THE ZECHSTEIN DOLOMITES FO WESTERN POLAND: INFLUENCE ON RESERVOIRS
Authors: Peryt Tadeusz Marek
Published: December 2007

Zechstein ooid grainstones, which have formed a narrow belt (several hundered meters in width) along the basin‐facing platform margin, have been greatly affected by fresh‐water diagenesis, resulting in contrasting resrvoir characteristics. fresh‐water diagenesis, which was related to a beach environment, was closely accompanied by dolomitization; there was competition between the dissolution of aragonitic ooids and their dolomitiztion. Dissolution of aragonitic ooids can produce an excellent intragranular porosity when early diagenetic dolomite cements form prior to dissolution (Kaldi and Gidman, 1982), or it can produce a non‐porous fabric of overcompacted deformed “spastoliths”. Although burial diagenesis significantly modified the reservoir characteristics of the Zechstein ooid grainstones, a very irregular pattern of early meteoric‐related diagenesis is the main reason why discoveries are so unpredictable in the Zechstein.
THE PETROLEUM RESOURCES OF THE MIDDLE EAST: A REVIEW
Authors: Beydoun Z. R.
Published: December 2007

The area under review is the Arabian Peninsula, Fertile Crescent and parts of SE Turkey and SW Iran (Arabian Plate plus Levant). Petroleum production is essentially from the eastern part or the Iraq‐Iran‐Arabia basin. Published proved oil reserves at the start of 1985 were estimated at 398.7 B† brl (barrels) and those for natural gas at 869.95 T‡ cu. ft (53 B tonnes and 24.8 T cum respectively) amounting to 57% of estimated world oil reserves and 25.6% of world gas reserves. The region produced 21.2% of world production in 1984 (but had produced 38.8% in 1974, the drop being due to non‐technical reasons). The oil reserves are attributable to some 290 producing fields and undeveloped discoveries, 25 of which are “supergiant” and 69 of which are “giant” in size. Only about 122 of these fields and discoveries are actually producing (excluding Turkey's 30 which account for little of the total).

The reasons for the prolific oil abundance lie principally in the repeated extensive deposition of organically‐rich source rocks under anoxic conditions in the right juxtaposition with very permeable extensive reservoirs and sealed by regionally extensive efficient seals over several intervals of geological time, charging extremely large anticlinal traps formed by a variety of structure‐forming mechanisms available at optimum hydrocarbon maturation and migration times. Accumulations occur in Paleozoic sands in southern Oman charged from Infra‐Cambrian source rocks, and in Middle and Upper Jurassic carbonates and Lower and Middle Cretaceous carbonates and sanhtones in the central part of the basin (the Gulf), and the Zagros fold belt, as well as in the Oligo‐Miocene carbonates in the latter charged by vertical migration from the Cretaceous. The NW‐most part has heavier Middle‐Upper Cretaceous and some Miocene oil of differing origin and Triassic light oil, gas and condensate extending into central Syria. Subordinate Paleogene heavy oil occurs in the Kuwait‐Basra area. Other new discoveries of Mesozoic and Paleogene age have occurred in Jordan and North and South Yemen.

All Middle East countries with the exception of Lebanon now either have established production or discoveries under assessment. Even in the main basin, exploration has not been intensive and future efforts including enhanced recovery methods will lead to considerable success and are expected to add new reserves equal to those now established for oil and probably more than those now estimated for gas, with a 50% chance of success. Saudi Arabia, Iraq and UAE are ranked highest, but small basins outside the main area will yield important finds by utilisation of the latest in geophysical and geochemical methods.
PATTERNS OF HYDROCARBON OCCURRENCES IN THE VIKING FORMATION, ALBERTA, CANADA
Authors: Amajor L. C.
Published: December 2007

Most NW‐SE trending, offshore, tide‐generated reservoir sandstones in the Lower Cretaceous Viking Formation of Alberta and Saskatchewan produce oil and/or gas from their NE flanks. This is because stronger tidal currents sorted and shifted finer sediments from the NE to the SW in the direction of sandbody migration. Thus, the NE flanks are older, thinner, coarser and better sorted with good reservoir characteristics. Post‐despositional tilting, however, provided optimal conditions for oil and gas entrapment.

This pattern of hydrocarbon occurrence may be more profitable if applied to the exploration and development of oil and gas in the less‐developed sand units.
NEW EVIDENCE FOR A PETROLEUM SOURCE ROCK IN A MIOCENE EVAPORITE SEQUENCE, GULF OF SUEZ, EGYPT
Authors: Kholief M. M. , Barakat M. A.
Published: December 2007

Anhydrite, gypsum and halite evaporites of Middle Miocene age occurring in the Gulf of Suez area constitute more than 50% of the total rock components. They are intercalated mainly with shales and also subordinate carbonate and sandstone layers. Examination of several evaporite samples under both binocular and petrographic microscopes reveals the presence of inclusions of various types hosted by gypsum crystals. Solid inclusions are composed mainly of minute calcareous particles, fine pyrite crystals and residual organic matter, while liquid inclusions, which are more frequent, exist in a uniphase or biphase state. A light hydrocarbon in the form of oil or gas constitutes one of these phases, while the other is a brine. Most of these inclusions are of primary origin and have been developed during the growth of the hosted minerals.

Based on the assemblage of these inclusions, it can be assumed that the evaporitic environment of deposition, with its reducing condition and high salinity, is favourable for the generation of oil from accumulated organic matter. Also, the presence of a carbonate mineral trapped by gypsum indicates the possible mixing of marine water with a brine of restricted occurrence.
SUBSURFACE GEOLOGY OF THE MIOCENE GHARANDAL GROUP IN THE SOUTH BAKR OILFIELD, GULF OF SUEZ, EGYPT
Authors: Elzarka Mohamed Hossny , Wally Mokhless M.
Published: December 2007

The mineralogical composition of the Miocene Gharandal group has been studied petrographically, and has been confirmed by chemical analyses and Differential Thermal and X‐Ray Diffraction analyses (DTA andXRDA). These investigations have been supplemented by geological mapping, which has revealed the geological setting and paleoenvironmental conditions of the Lower Miocene Gharandal group at the South Bakr oilfield.

The lithic association of the Nukhul and Rudeis formations indicates that deposition took place in a shallow‐marine environment in the sublittoral zone. The mineral association of the rocks of the Kareem Formation suggests a semirestricted environment, where the chemical conditions changed from weakly‐oxidising to slightly reducing during the deposition of these sediments. The lithic association of the rocks of the Kareem Formation indicates that their deposition occurred in a barred basin. The basin was affected by gentle subsidence, which might be associated with post Early Miocene growth‐faulting in its western section.

The rocks of the Gharandal group represent the lower section of an evaporite cycle of deposition.

The structure and variation of the thickness and facies has led the Authors to present some deductions concerning the paleoenvironmental conditions under which the investigated rocks were formed.
THE DISTRIBUTION OF MAJOR OIL AND GAS RESERVES IN REGIONAL BASIN STRUCTURES – AN EXAMPLE FROM THE POWDER RIVER BASIN, WYOMING, USA
Authors: Pratsch J.‐C.
Published: December 2007

The location and geographic distribution of oil and gas reserves within a producing basin often indicate that a remarkable concentration of reserves has taken place in a small area. The concentration of reserves is the result of secondary hydrocarbon migration, itself governed by the basin‐wide regional structure which was present at the time of migration. These factors permit the definition of the most prospective areas of a new basin or play at an early stage in the exploration cycle. Basic geochemical data are required for the definition of critical details of the effective generative depocentre, and regional geological‐geophysical data are required to establish regional structures near particular source‐bed levels, or near top Basement as the deepest prospective level. Other data commonly utilized in the early stages of exploration, such as basin classification schemes, reservoir bed studies and tectonic analyses, are rather less important in forward basin evaluation.

A particularly clear example of the importance of the regional basement structure in the concentration of oil reserves exists in the Powder River Basin, Wyoming, USA. Cumulative oil production here was over 1.9 B brls** in 1984 from more than 460 oilfields and pools. However, 1.5 B brls (79% of the basin output) were produced from only 22 fields (4.7% of the number of fields and pools in the basin). It is also remarkable that all 22 major oilfields in the Powder River Basin are located on positive Bouguer gravity anomalies, which are expressions of deep basement irregularities. Regional lateral oil migration in the Powder River Basin appears to have utilized routes resulting from Laramide deformation (Late Cretaceous ‐ Paleocene).

The resultant basin structure was accentuated by regional structural‐topographic anomalies, which became sites of major structural and stratigraphic traps. In this case regional gravity maps seem to show sufficient details of the deep structure for the accurate definition of major exploration targets.

The Powder River Basin is thus an excellent example of the importance of regional geological and geophysical reconnaissance data aimed at, and available for, the definition of major migration pathways at an early stage of hydrocarbon exploration. When combined with geochemical data, such an approach will become the basis for forward exploration in all known basins.
A TILTED CRUSTAL BLOCK BOUNDED BY LINEAMENTS, SHOWN BY REMOTE SENSING
Authors: Khatieb S. O. Al , Norman. J. W.
Published: December 2007

From a remote‐sensing study here reported, a block of Mesozoic sediments (about 160 km by 40 km) in the Arabian Peninsula appears to have been tilted, and the boundaries of the tilted rocks were seen to be bounded by lineaments detected on satellite imagery. Fieldwork has shown supporting evidence of increased dips, and the movement of the block was confirmed by carrying out a trend surface analysis of the positions of key horizons in water bore‐holes, and their outcrops at the surface.
WHAT WILL THE DEEP DRILLING AT SILJAN, SWEDEN, PROVE?
Authors: Gibbs Allan K.
Published: December 2007

The following highly‐topical contribution is concerned with the experimental deep‐drilling programme which has been initiated in the Siljan Ring in Sweden. Readers will recall that according to the theories of Professor Thomas Gold of Cornell University, which were first propounded in our January 1979 issue (1 (3) 3–19), deep‐seated abiogenic hydrocarbon gases may be encountered at this site, where a meteoric impact is believed to have produced a structure favourable for hydrocarbon accumulation. Dr Gibbs, however, here suggests an alternative, more conventional explanation for any hydrocarbon gases that may be found as drilling, which commenced in June 1986, progresses.