bluuebunny/crossref_metadata_2025_split huggingface dataset:
RESERVOIR ARCHITECTURE IN A TERMINAL ALLUVIAL PLAIN: AN OUTCROP ANALOGUE STUDY (UPPER TRIASSIC, SOUTHERN GERMANY) PART II: CYCLICITY, CONTROLS AND MODELS
Authors: Hornung J. , Aigner T. 
Published: March 2006

This outcrop analogue study investigates Triassic fluvial sandstones of the Stubensandstein Formation which were deposited on a terminal alluvial plain under semi‐arid to sub‐humid climatic conditions in the land‐locked South German Keuper Basin. The Stubensandstein may serve as an analogue for reservoir units in comparable continental basins. Data came from studies of 13 large sandpits, together with a subsurface database supported by three well‐log clusters (comprising up to 20 boreholes) and four single wells.Lithofacies types vary along a palaeogeographical gradient from proximal erosion and non‐deposition to fluvial bed‐load, to distal suspended‐load deposits and finally to playas with lacustrine carbonates.Within a three‐fold hierarchy of cyclicity, meso‐ and macro‐scale cycles could be correlated regionally using an approach based on stratigraphic base‐level changes.The observed sedimentary patterns, together with palaeosol types, their stable isotope signals and palynological data, indicate that palaeoclimatic fluctuations exerted the principal control on stratigraphic architecture and cyclicity. Progradation of sand wedges into the basin occurred while climate was arid but becoming more humid. As playa lake levels rose, the alluvial sands retrograded. Shorter and longer‐term palaeoclimatic fluctuations caused systematic changes in reservoir and seal geometries, and in the extent and interconnectedness of sandbodies. Thus, a knowledge of the overall palaeoclimatic trends in comparable continental basins may allow predictions to be made concerning the regional reservoir architecture.Outcrop data were used to generate static reservoir models of sandbody architecture in subsurface well log data sets. A stochastic facies and poro‐perm simulation was run and calibrated with outcrop data. Different stratigraphic levels could be reproduced, as could the scouring and interbedding of the different fluvial systems.
RESERVOIR POTENTIAL OF CRETACEOUS PLATFORM‐MARGIN BRECCIAS, CENTRAL ITALIAN APENNINES
Authors: Casabianca D. , Bosence D. , Beckett D. 
Published: March 2006

In this paper, we report on the characteristics of sedimentary breccias derived from, and deposited adjacent to, the Cretaceous Maiella carbonate platform in central Italy. Previous work has interpreted the northern platform margin to have been inherited from Early Jurassic rifting, and to have remained tectonically passive throughout the Cretaceous. However, our field studies show that the platform margin was segmented by north‐south oriented normal faults in the Late Cretaceous. Thick breccias composed of lithoclastic rudstones and floatstones were derived from the collapse of the shelf margin, and were deposited as rock avalanche and debris flow deposits in hangingwall depocentres.Four breccia units (thicknesses up to 250m, 130m, 60m and 20m) were mapped and studied in detail. Clasts consist of shallow‐water bioclastic limestones; textures vary within each breccia unit from rudstones in the bottom two‐thirds to floatstones above. Vuggy, late stage dissolution porosity is present throughout each unit, and probably developed in a meteoric environment after Pliocene thrusting and exhumation. Much earlier diagenesis, associated with a Late Cretaceous shallow‐marine to meteoric environment, generated the mouldic and intergranular porosity observed in the rudstones. The skeletal floatstones display biomouldic porosity which has likewise been preserved since the Late Cretaceous.Bulk porosity volumes have been estimated for three of the breccias at the time of expected hydrocarbon charge (Miocene‐Pliocene): they range between 72 × 106 and 42 × 106 m3. Oil seepage from these breccias can be observed at the present day in outcrops near to the study area, indicating that migration and charge are still active.The significance of the breccias as potential reservoirs is that high‐porosity platform margin facies clasts were transported into a depositional environment which would otherwise have been occupied by low‐porosity slope facies. This extends the platform margin reservoir fairway beyond the defined platform edge.
DETERMINATION OF PALAEOSTRESSES FROM MESOSCALE SHEAR FRACTURES IN CORE SAMPLES USING THE MULTI‐INVERSE METHOD
Authors: Yamada Y. , Yamaji A. 
Published: March 2006

Palaeostress reconstruction is the key to quantitative characterization of fractured hydrocarbon reservoirs. In order to calculate the palaeostresses responsible for fault activity, faults in oriented core samples can be analysed and the optimal stresses can then be determined from fault‐slip data in a least‐squares sense. Many fractured reservoir rocks, however, include faults generated during a number of different tectonic phases. In these cases, the optimal stresses can be determined for subgroups of faults which are considered to be of approximately the same age. The difficulty with this is that criteria for accurate age‐dating are often absent, especially from core samples.Recently, the so‐called “multi‐inverse” method has been proposed to address this problem. This is a numerical technique for separating palaeostresses within a heterogeneous fault assemblage in the absence of a priori information on the faults’relative ages. In this paper, we apply the method to eighteen faults in two short (9m) cores from an exploration well in Hokkaido, northern Japan. The cores came from a fractured hydrocarbon reservoir and were oriented by correlation with borehole images. Core lithologies included massive Cretaceous basalts in which there was no layering which would show fault offsets; for these samples, we determined the sense of shear by studying asymmetric microstructures on the fault surfaces. The results show that the rocks have experienced six different stress regimes. In general, these are compatible with the tectonic history of the study area as inferred from the regional stratigraphy and from macroscale geological structures.These results show that the multi‐inverse method can be used to extract palaeostress data from cores, thereby providing information which will assist with the exploration of (and production from) fractured hydrocarbon reservoirs.
GEOLOGY AND GEOCHEMISTRY OF SOURCE ROCKS IN THE QAIDAM BASIN, NW CHINA
Authors: Qiang Jin , Ming Zha , Zhen Liu , XianZhi Gao , Dehua Peng , Lamei Lin 
Published: March 2006

In this paper, we discuss the organic geochemistry of source rocks in the Qaidam Basin, NW China, using data generated during a recent four‐year study. This study addressed some basic problems concerning petroleum systems in the basin, problems which persist despite some five decades of exploration. We show that three separate source rocks are present and these are distinct in terms of both age and depositional facies and also geographical distribution.The oldest source rocks are Lower Jurassic fresh‐water lacustrine deposits which are generally confined to northern Qaidam. These are currently thermally mature or highly mature and have generated the oils, condensates and gases which have been discovered in Jurassic and Tertiary reservoirs in the North Qaidam area.By contrast, Tertiary source rocks were deposited in saline lakes. Previous studies have shown that they are characterized by low TOC values (0.2–0.6%). However, we found Tertiary source rocks with TOC > 1.0%; these were deposited in hypersaline lakes around the Manya Depression in western Qaidam. These source rocks have probably generated the oils at fields recently discovered in the western part of the basin.The youngest (gas‐prone) source rocks in the basin are Quaternary. These were deposited in saline lakes in the east and central parts of the basin and are thermally immature. However they are thought to have generated the large volumes of biogenic gas which are present in Quaternary reservoirs.
TUNNEL VALLEYS AND DENSITY FLOW PROCESSES IN THE UPPER ORDOVICIAN GLACIAL SUCCESSION, ILLIZI BASIN, ALGERIA: INFLUENCE ON RESERVOIR QUALITY
Authors: Hirst J. P. P. , Benbakir A. , Payne D. F. , Westlake I. R. 
Published: March 2006

Upper Ordovician syn‐glacial deposits form a gas reservoir at the Tiguentourine field, Illizi Basin, Algeria. The reservoir geology of these glacial deposits has been investigated with the objective of understanding the widely varying thickness of the sequence and the controls on reservoir quality.A general depositional model was developed following a review of outcrops in the Tassili N'Ajjer region, some 200km south of Tiguentourine. In these outcrops, elongate tunnel valleys were observed to be incised into the subglacial surface, and these were interpreted to have been formed by subglacial meltwater flows. The isopach map of the Tiguentourine field syn‐glacial sequence, derived from well penetrations and a 3D seismic survey, indicates there were two elongate depressions analogous to, but broader than, the tunnel valleys observed at outcrop.The sedimentary rocks encountered at outcrop and in the subsurface were broadly similar. Initial sedimentation in the tunnel valleys typically comprised medium‐ to coarsegrained, structured sandstones. These were interpreted as the deposits of glaciofluvial currents flowing along the tunnel valleys. They were succeeded by a range of density flow deposits (muddy and sandy debrites, high‐ and low‐density turbidites). In the outcrops, the turbidites are seen to evolve upwards from an amalgamated sheet complex to sinuous channel forms. Long wavelength (>2m), low amplitude, symmetrical dunes were noted in these high‐density turbidites; they were interpreted to be the products of sustained, possibly hyperpycnal, turbidity currents. In the subsurface, pelagic deposits with graptolites were recorded towards the top of the succession indicating a glacial‐marine environment. At its maximum extent, the ice is believed to have been grounded on the continental shelf. The synglacial succession in the south Illizi Basin was interpreted as a product of glacial retreat, with the hardground at the top of the sequence probably the result of isostatic uplift.
HYDROCARBON GENERATION AND CHARGING IN THE OCTOBER FIELD, GULF OF SUEZ, EGYPT
Authors: El‐Ghamri M. A. , Warburton I. C. , Burley S. D. 
Published: March 2006

Source rocks on‐structure in the October field are not sufficiently mature to have expelled hydrocarbons at the present day. l‐D modelling of a pseudo‐well in the deep October South Trough demonstrates that the Eocene Thebes and Senonian Sudr Formations are presently mature at depths greater than 3km. However, only the carbonate‐rich Sudr Formation has generated sufficient hydrocarbons for expulsion to take place at depths shallower than 3.5km, suggesting that reservoired oil in the October field originates predominantly from source rocks of this unit. Model results indicate that hydrocarbon expulsion from this source may have commenced as early as 20Ma in kitchen depocentres adjacent to the October field, and continued through the Pliocene.Migration routes predicted from 2‐D modelling are complex and require downward expulsion from the Sudr Formation east and west of the October field to charge the Palaeozoic Nubian Sandstone. Mature Sudr Formation in the October South Trough first charges the Nubian and then lower Senonian Matulla Formation reservoirs in the NW compartments of the October field via flow across the NW bounding fault. The mature Sudr Formation in the Baba Trough to the SE charged the Matulla Sandstones on the eastern flanks of the October field which then back‐filled to spill into the Nubian Sandstones. Hydrocarbons generated from the Thebes Formation contribute only minor volumes to the predicted accumulations.The presence of trap‐bounding faults and their sealing properties is shown to be a key sensitivity for charging the October field and related structures. Fault seal is required to charge known accumulations and match known hydrocarbon column heights, but extending shale smear into the Nubian Sandstone prevents the crestal October field structure from charging.The Matulla Formation sandstones are a regional migration fairway providing charge for the Ras Budran field and Nubian Sandstone prospects to the west of the October field. Younger Mesozoic sandstones are charged by vertical migration through seals and along faults. This regional migration sequence as described for the October field is likely to Maher Ayyad of BG Egypt very kindly gave access to the seismic cross section used in the study, as well as guiding our understanding of the regional geology of the Gulf of Suez, and also provided a constructive review of the manuscript. EGPC generously provided access to well data and support for Magdi El‐Ghamri. Colin Harwood (BG Group) and Dan Carruthers and John Bunney (Permedia Research Group Inc.) commented on early drafts of the manuscript. BG Group is thanked for permission to publish.
DIAGENETIC HISTORY OF LATE PALAEOCENE POTENTIAL CARBONATE RESERVOIR ROCKS, KOPET‐DAGH BASIN, NE IRAN
Authors: Mahboubi A. , Moussavi‐Harami R. , Brenner R. L. , Gonzalez L. A. 
Published: March 2006

The Upper Palaeocene (Thanetian) Chehel‐Kaman Formation in the Kopet‐Dagh Basin of NE Iran is principally composed of carbonates with minor siliciclastics and evaporites. Six stratigraphic sections were measured and more than 1,000 samples were collected for petrographic analysis, together with analyses of carbon and oxygen isotopes and trace element content. Four major carbonate lithofacies (and 13 subfacies) have been identified in previous studies and are interpretd in terms of deposition in a shallow‐marine environment.The petrographic analyses indicate that the Chehel‐Kaman Formation carbonates have undergone a complex diagenetic history which includes compaction, cementation, micritization, dissolution, silicification, dolomitization, neomorphism and fracturing. δ18O and δ13C values in Chehel‐Kaman Formation limestones range between +0.8 and ‐15.1%0 PDB, and ‐2.82 and +3.5%0 PDB, respectively. These variations are interpreted to reflect meteoric and burial diagenetic processes. Variations in trace‐element concentrations (Fe and Mn increased while Na decreased) also indicated the effects of meteoric flushing. The limestones appear to have been formed at about 28°C.Chehel‐Kaman Formation dolomites were divided into d1 (finely‐crystalline) and d2 (coarsely‐crystalline) types. Petrographic and geochemical results indicated that the d1 dolomites formed under sabkha conditions from a parental solution at around 26°C, while d2 dolomites formed during burial diagenesis with much hotter pore fluids (around 72°C). The paragenetic sequence indicates that primary porosity decreased during early stages of diagenesis, although secondary porosity was subsequently created improving the reservoir quality of the carbonates.
OIL AND GAS PLAYS IN ALBANIA: DO EQUIVALENT PLAYS EXIST IN GREECE?
Authors: Zelilidis A. , Piper D. J. W. , Vakalas I. , Avramidis P. , Getsos K. 
Published: March 2006

Western Greece and Albania have had a broadly similar geological history and the hydrocarbon potentials of both areas may therefore be comparable. In this paper, we briefly review the stratigraphic and structural evolution of Albania and compare it with that of NW Greece in terms of source rocks, reservoirs, seals, structures and maturation history.In Albania, a number of sizeable oilfields produce from Mesozoic‐Paleogene carbonates assigned to the Ionian Zone; traps are thrust‐related anticlines. Gas is produced from both Mesozoic reservoir rocks and also from Tortonian‐Messinian sandstones along the eastern margin of the Neogene Durres Basin. In both Albania and western Greece, the Mesozoic to Eocene succession includes organic‐rich shales which were deposited on the Apulian margin of the Pindos Ocean. Tertiary closure of that ocean resulted in thin‐skinned thrusting onto the Apulian margin along Triassic evaporite décollements. Thick, late Eocene to Miocene flysch was deposited synchronously in the Pindos foreland basin, and was deformed by the advancing thrust system.The Neogene Durres and Preveza Basins developed on the Apulian foreland as a result of complex plate‐tectonic interactions and block rotations. NE‐trending lineaments played an important role in the evolution of these basins, and also gave rise to dip‐closed anticlines in the Ionian Zone successions in both countries. In Albania, the Vlora‐Elbasan lineament controlled the development of structural traps at producing oilfields, and the Cephalonia transform fault in Greece may have played an analogous structural role. Potential hydrocarbon plays in NW Greece, analogous to producing fields in Albania, are located in the Ionian thrust belt and in the Neogene Preveza Basin. In addition, the middle Tertiary flysch basins of both countries may have some gas potential.
THE APPLICATION OF ELECTRON SPIN RESONANCE AS A GUIDE TO THE MATURATION AND TYPING OF ORGANIC MATTER IN THE NORTH SEA
Authors: McTavish R. A. 
Published: March 2006

In early electron spin resonance (ESR) analysis of North Sea wells, maturation of organic matter (OM) was expressed in terms of maximum palaeotemperature (MPT) based on North American calibrations that did not consider the influences of kerogen composition or overpressure. In the North Sea, the MPTs were anomalous in overpressured sequences and relative to other indices of OM maturation such as vitrinite reflectance, so the ESR method was abandoned there in geochemical studies. However, early empirical study of North Sea ESR data indicated that, in relation to functions that linked temperature and pore pressure, some ESR parameters were predictable without reference to MPTs.In order to re‐evaluate ESR parameters as indices of OM maturation, the physical factors (temperature and pressure) which affect OM maturation are related in the present paper to the ESR parameters “g” (spectral position) and Ng (spin density) at six well locations in the northern North Sea. A third ESR parameter, W (line width), is not an effective guide to maturation levels due to its complex relationship to the physical factors and kerogen types. However, cross‐plots of W versus “g” and Ng appear to be as effective as pyrolysis for kerogen typing. Levels of maturation investigated in the North Sea wells range through the equivalent vitrinite reflectance values of about 0.50–1.50%. The values of “g” and Ng have been differentiated for kerogen type, but undifferentiated values of “g” have also been studied.Regression analysis has shown that there are linear relationships between the ESR parameters “g” and Ng, and the physical factors present‐day temperature (To), “effective” temperature (Te), and differential pressure (Pd). Correlation coefficients for both “g” (undifferentiated and differentiated) and Ng (differentiated) relative to the physical factors are high; the highest values are for “g” and Ng relative to Te and Pd (r =−0.950 for “g” differentiated or undifferentiated, r = 0.944–0.976 for Ng differentiated, respectively). However, correlation coefficients were lower for “g” and Ng relative to To.More frequent high correlation coefficients and larger sample populations suggest that “g” (undifferentiated) is a more reliable index of OM maturation than Ng(differentiated). However, the estimation of levels of OM maturation is improved if both indices are used together.The ESR method appears to be effective both for estimating levels of OM maturation and for kerogen typing. It has a number of potential advantages over other geochemical methods: firstly, it is more sensitive for estimating OM maturation than most other methods; secondly, it can be used to analyze organic matter which is as old as Proterozoic; thirdly, it does not destroy the samples analyzed.
ORGANIC PETROLOGY OF POTENTIAL SOURCE ROCKS IN THE TARIM BASIN, NW CHINA
Authors: Liu Dameng , Tu Jianqi , Jin Kuili 
Published: March 2006

Potential source rocks in the Tarim Basin (NW China) include Cambrian‐Lower Ordovician lagoonal carbonates and mudstones; Middle‐Upper Ordovician platform carbonates; Carboniferous‐Permian shallow‐marine carbonates and mudstones; and Triassic‐Jurassic continental deposits including coals and lacustrine mudstones. Our petrological observations show that the organic components in Cambrian‐Ordovician deposits are mainly alginites andamorphinites with minor vitrinite‐like macerals, zooclasts and solid bitumen (Type I organic matter). The organic carbon content of these rocks is 0.1–2% TOC (averaging 0.9%TOC in deeper‐water fades) and they are mature to overmature in terms of oil generation.Organic macerals in Permian‐Carboniferous source rocks are dominated by alginite with minor quantities of zooclasts andexinite derived from terrestrial higher plants (mainly Type II OM with minor Types I and III). TOC contents are 0.1–1%. These rocks are mature to highly‐mature in terms of oil generation.Macerals in Jurassic‐Triassic source rocks are dominated by vitrinite and inertinite, with V+I > 50% and alginite + amorphinite < 40%; exinite averages 2–5%. This organic matter type is Type III, and the sediments are immature to just mature.We have calculated the original organic matter richness of Ordovician deposits at selected locations. The original OM content appears to have been particularly high around Lunnan (in the North Tarim Uplift), in the Central Tarim Uplift and around Tadong (in the SE Uplift). These areas are therefore suggested to have particularly high exploration potential.
SOURCE ROCK EVALUATION AND GEOCHEMISTRY OF CONDENSATES AND NATURAL GASES, OFFSHORE NILE DELTA, EGYPT
Authors: Sharaf L. M. 
Published: March 2006

Geochemical analyses of mudstones from wells in the NE offshore Nile Delta suggest that the Early Miocene Qantara Formation has “good” potential to generate hydrocarbons at the studied locations. Its generating capability and oil‐proneness increase northwards, towards areas where better organic‐matter preservation and a greater contribution from marine source material can be expected. By contrast, the Middle Miocene Sidi Salem Formation has “poor to fair” potential to generate mixed gas and oil, while the overlying Wakar and Kafr El Sheikh Formations have “poor” capability to generate gas with minor oil. Based on pyrolysis Tmax and thermal alteration index assessments, the Wakar and Kafr El Sheikh Formations are immature in the study area. The Sidi Salem and Qantara Formations are immature in the southern part of the study area, but are within the oil window in the north, around well Temsah‐4.Biomarker distributions based on GC‐MS analyses of two condensate samples from the Wakar and Sidi Salem Formations indicate that hydrocarbons are derived from siliciclastic source rocks containing significant terrestrial material and limited marine organic matter. The condensates were generated during early maturation of Type III kerogen from deeper and more mature source rocks than those encountered in the drilled wells. Geochemical and isotopic data from natural gas produced from the Kafr El Sheikh Formation suggest mixed biogenic and thermogenic sources.