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Hydrocarbon Exploration (hydrocarbon + exploration)
Selected AbstractsCYLINDRICAL AND CONICAL FOLD GEOMETRIES IN THE CANTARELL STRUCTURE, SOUTHERN GULF OF MEXICO: IMPLICATIONS FOR HYDROCARBON EXPLORATIONJOURNAL OF PETROLEUM GEOLOGY, Issue 3 2006J. J. Mandujano V. The NW-SE trending Cantarell structure in the Gulf of Campeche hosts the largest oilfield in Mexico. The oil occurs predominantly in latest Cretaceous , earliest Tertiary breccias with subsidiary reserves in Upper Jurassic (Oxfordian and Kimmeridgian) and Lower Cretaceous oolitic and partially dolomitized limestones, dolomites and shaly limestones. Cantarell has been interpreted both as a fold-and-thrust zone and as a dextral transpressional structure. Analysis of structure contours at 100m intervals, on the tops of the Tertiary breccia and the Kimmeridgian (Upper Jurassic) dolomite, indicates that the structure is an upright cylindrical fold with gently plunging conical terminations; there is also a conical portion in the central part of the structure. The axes of the central, NW and SE cones are subvertical. This geometry indicates that the two fold terminations and the central cone are aprons rather than points, with the NW and central cone axes intersecting the cylindrical fold axis at the point where the geometry switches from conical to cylindrical. The apical angle (i.e. the angle between the fold and cone axes) varies as follows: (i) in the NW cone, it is ,70° in the breccia and ,76° in the Kimmeridgian dolomite; (ii) in the central cone, it is ,77° in the breccia and ,73° in the Kimmeridgian dolomite; and (iii) in the SE cone, it is ,64° in the breccia and ,57° in the Kimmeridgian dolomite. This indicates that whereas the fold opens with depth in the NW cone, it tightens with depth in the central and SE cones. Assuming a parallel fold geometry, these apical angles indicate an increase in volume in the NW cone (i.e. larger hydrocarbon reservoirs), compared to the central and SE cones. Theoretical considerations indicate that the curvature increases dramatically towards the point of the cone. In the case of the Cantarell structure, the apices of the cones are located at the conical-cylindrical fold junctions, where the highest curvature may have resulted in a higher degree of fracturing. The coincidence of maximum curvature and the intersection of the conical and cylindrical fold axes in the fold culminations with porous and permeable reservoir rocks may have made these locations favourable for the accumulation of hydrocarbons. [source] BURIAL HISTORY RECONSTRUCTION USING LATE DIAGENETIC PRODUCTS IN THE EARLY PERMIAN SILICICLASTICS OF THE FARAGHAN FORMATION, SOUTHERN ZAGROS, IRANJOURNAL OF PETROLEUM GEOLOGY, Issue 2 2009S. M. Zamanzadeh In spite of the increasing importance to hydrocarbon exploration and production of the Palaeozoic succession in the Zagros area of SW Iran, few burial history and palaeothermal modelling studies of the interval have been carried out. This paper attempts to assess the burial and palaeotemperature history of the Lower Permian Faraghan Formation which is composed of stromatolitic dolomites overlain by mainly cross-bedded sandstones. The formation grades up into the thick bedded carbonates of the Upper Permian Dalan Formation. The Faraghan and Dalan Formations are major hydrocarbon reservoir units in SW Iran and are time-equivalents of the Unayzah and Khuff Formations in Saudi Arabia, respectively. The Faraghan Formation consists of shallow-marine siliciclastics and foreshore deposits, including tidal-flat and tidal-channel, estuarine, sabkha, shoreface and offshore facies. In this study, diagenetic constituents are used to evaluate the formation's burial history in the Southern Zagros, an area for which only limited subsurface data is available. A burial history diagram for the formation was constructed for well Finu # 1 using WinBuryTM software. The diagram shows that the formation underwent progressive burial at variable rates between its deposition and the mid-Tertiary, since when it has undergone rapid uplift. Burial diagenetic products in the Faraghan Formation comprise saddle, ferroan and zoned dolomites, together with dickite, illite/sericite and chlorite minerals. Additional burial-related features include stylolites and dissolution seams. Isotopic signatures (,18O versus ,13C) of the ferroan dolomites suggest a burial trend for the formation. Reconstruction of the paragenetic sequence together with the burial history diagram suggests a maximum burial depth of about 5000 m and a wide palaeotemperature range of 80-160°C. However considering the saddle dolomites as a palaeothermometer, the temperature range narrows to 78 to 138 °C. The burial depth and temperature ranges closely correlate with the main stage of oil generation to the dry gas zone. [source] AN INTEGRATED STUDY OF DIAGENESIS AND DEPOSITIONAL FACIES IN TIDAL SANDSTONES: HAWAZ FORMATION (MIDDLE ORDOVICIAN), MURZUQ BASIN, LIBYAJOURNAL OF PETROLEUM GEOLOGY, Issue 1 2009A. Abouessa Studies of the impact of diagenesis on reservoir quality in tidal sandstones can be of great importance in successful hydrocarbon exploration. The study reported here shows that diagenetic alterations and bioturbation have induced considerable deterioration and heterogeneity in the reservoir quality of the sand-dominated tidal deposits of the Middle Ordovician Hawaz Formation in the Muruq Basin, Libya. Comparison is made between the diagenetic evolution of samples from the subsurface (present-day depth 1500 m) and from surface outcrops in order to study the impact of burial and uplift on the spatial and temporal distribution of reservoir quality in the Hawaz Formation sandstones. Eogenetic alterations, which were mediated by meteoric water circulation, included kaolinitization and dissolution of framework silicates and mechanical compaction. Mesogenetic alterations (T > 70°C; depth > 2 km) included pressure dissolution of quartz grains and concomitant quartz cementation, conversion of kaolinite into dickite, illitization of kaolinite and of grain-coating clays, and the precipitation of Mg-rich siderite cement. Reduction of intergranular porosity was due more to compaction than to cementation, yet quartz overgrowths are up to 16% in some of the sandstones. Bioturbation has resulted in a greater reduction in sandstone permeability in the lower part of the formation than the upper part. A higher ratio of dickite to kaolinite in subsurface samples than in outcrop samples is attributed to the longer residence time of the former sandstones under mesogenetic conditions. Telodiagenesis has not resulted in enhancement of reservoir quality of the Hawaz Formation Sandstones but in pseudomorphic calcitization of siderite and oxidation of pyrite to goethite. This study shows that the reservoir-quality evolution of tidal sandstones can best be elucidated when linked to depositional facies and distribution of diagenetic alterations. [source] IDENTIFICATION OF SALT FEATURES IN SEISMIC DATAJOURNAL OF PETROLEUM GEOLOGY, Issue 4 2008M. K. Jenyon Deciding on the viability of a salt deposit as a possible site for storage-cavern solution mining requires detailed geological studies of the salt and of its confining formations. Borehole data alone can seldom deliver the information required for such a study. It can impart great detail of the subsurface but only at the actual borehole location in an area. The most practical approach to developing 3D information is to carry out a seismic survey tied in to one or more boreholes which have been logged geophysically Ideally, a high-resolution seismic survey is needed to study relatively shallow zones of the subsurface and resolve the top and base of fairly thin beds. However in some cases it is possible to use "reach-me-down" seismic data acquired previously during hydrocarbon exploration. Although these data were not designed to meet the requirements of salt deposit studies, they may still be adequate for the purpose. Their use will lead to quicker and lower-cost results than the commissioning of a full field seismic survey with concomitant processing, although in both cases a seismic interpretation would be required. [source] POTENTIAL STRUCTURAL TRAPS ASSOCIATED WITH LOWER CARBONIFEROUS SALT IN THE NORTHERN TARIM BASIN, NW CHINAJOURNAL OF PETROLEUM GEOLOGY, Issue 1 2004Jiangyu Zhou In the Aixieke-Santamu area of the northern Tarim Basin (NW China), 45 relatively low amplitude structures related to the plastic flow of Lower Carboniferous salt have been discovered in the Lower Carboniferous Kalashayi Formation and the Middle-Upper Triassic Akekule and Halahatan Formations. Three small hydrocarbon accumulations have so far been located at the margins of a Lower Carboniferous salt body (measuring about 55km x 75km and 115,225m thick, controlled by wells and 2D and 3D seismic sections). In this paper, we consider the development of this salt body and discuss possible reasons why vertical diapirs are absent from the study area. We attempt to develop a model of salt flow and we investigate the relationship between salt flow and the occurrence of oil and gas traps. Using recently-acquired high-resolution 2D and 3D seismic profiles, we show that the Lower Carboniferous salt has undergone three separate phases of plastic flow. At the end of the Early Permian, the salt flowed southwards by 2.0,2.8 km; then, during the Late Triassic,Early Jurassic, it flowed in the same direction by 1.0,1.8 km; and finally at the end of the Tertiary, it flowed northwards by 0.6,1.5 km. These movements resulted in the formation of various types of structural trap in the Kalashayi, Akekule and Halahatan Formations including salt ridge anticlines, domes and marginal troughs. Salt ridge and salt edge low-amplitude anticlines are probably the most important targets for future hydrocarbon exploration. [source] TIMING AND MODES OF DEFORMATION IN THE WESTERN SICILIAN THRUST SYSTEM, SOUTHERN ITALYJOURNAL OF PETROLEUM GEOLOGY, Issue 2 2001L. Tortorici Imbricate units in the western Sicilian fold-and-thrust belt originated on the southern continental margin of Neotethys, and were deformed during the Neogene-Recent in response to convergence between the African and European Plates. Neogene-Pleistocene synorogenic sediments, deposited in flexural foredeeps and satellite piggy-back basins, contain a record of the belt's evolution. Progressive migration of the thrust front southwards into the foreland has been documented, beginning in the Tortonian and continuing to the present-day particularly in western parts of the belt. In the eastern part, activity on Quaternary strike-slip fault zones has produced asymmetric flower structures and other interference structures. In this paper, we present two regional sections across the western Sicilian foreland-thrust belt system. These structural cross-sections extend down as far as the top of the Hercynian basement and integrate our field observations with previously-acquired well log, magnetic and seismic data. We show that complex interactions between the foreland-migrating thrust belt, which developed between the Late Miocene and the Pleistocene, and Pleistocene strike-slip faults led to the development of structural traps which constitute potential targets for hydrocarbon exploration. [source] Three-dimensional seismic characterisation of large-scale sandstone intrusions in the lower Palaeogene of the North Sea: completely injected vs. in situ remobilised sandbodiesBASIN RESEARCH, Issue 4 2010Ewa Szarawarska ABSTRACT A large number of km-scale, saucer-shaped sandstone bodies of enigmatic origin have recently been documented in the North Sea and the Faroe Shetland Basin. This study utilises three-dimensional seismic data, calibrated by well data, to examine two such bodies that exhibit very similar saucer-shaped geometries in cross-section. The Volund and Danica structures, located 250 km apart are interpreted as end members of a spectrum of large-scale remobilised and injected sandstones present in the North Sea Palaeogene. Both are characterised by a central 1,2 km-wide low area surrounded by a discordant, 2,300 m tall inclined dyke complex, that tips out into a bedding concordant body interpreted as a shallow-level sill and/or partly extruded sandstone. The origin of the central concordant sandstone body as either injected (laccolith) or depositional is of key importance to a complete understanding of the origin and prospectivity of these structures. The key criteria for recognising an injected vs. depositional origin for the central concordant sandbody are: (1) a flat, nonerosional base; (2) ,jack-up' of the overburden equal to the underlying sand thickness; (3) equally thick layers of encasing mudstones; and (4) paleogeographic context. This study suggests that the Danica structure was deposited as a channel sandstone and remobilised in situ; this led to the formation of wing-like intrusions along the channel margins. In contrast, the Volund structure overburden displays a forced-fold geometry, arguably a diagnostic feature of an intrusive origin. The ability to recognise and differentiate completely injected vs. in situ remobilised sandbodies is important both from a basin analysis, hydrocarbon exploration and rock mechanics points of view. An improved understanding of these aspects will lead to a reduction of risks associated with the exploration and development of such a sandbody and an enhanced understanding of sediment remobilisation and fluid flow on a basin scale. [source] Alteration and Reformation of Hydrocarbon Reservoirs and Prediction of Remaining Potential Resources in Superimposed BasinsACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 5 2010PANG Hong Abstract: Complex hydrocarbon reservoirs developed widely in the superimposed basins of China formed from multiple structural alterations, reformation and destruction of hydrocarbon reservoirs formed at early stages. They are characterized currently by trap adjustment, component variation, phase conversion, and scale reformation. This is significant for guiding current hydrocarbon exploration by revealing evolution mechanisms after hydrocarbon reservoir formation and for predicting remaining potential resources. Based on the analysis of a number of complex hydrocarbon reservoirs, there are four geologic features controlling the degree of destruction of hydrocarbon reservoirs formed at early stages: tectonic event intensity, frequency, time and caprock sealing for oil and gas during tectonic evolution. Research shows that the larger the tectonic event intensity, the more frequent the tectonic event, the later the last tectonic event, the weaker the caprock sealing for oil and gas, and the greater the volume of destroyed hydrocarbons in the early stages. Based on research on the main controlling factors of hydrocarbon reservoir destruction mechanisms, a geological model of tectonic superimposition and a mathematical model evaluating potential remaining complex hydrocarbon reservoirs have been established. The predication method and technical procedures were applied in the Tazhong area of Tarim Basin, where four stages of hydrocarbon accumulation and three stages of hydrocarbon alteration occurred. Geohistorical hydrocarbon accumulation reached 3.184 billion tons, of which 1.271 billion tons were destroyed. The total volume of remaining resources available for exploration is ,1.9 billion tons. [source] Pressure Prediction for High-Temperature and High-Pressure Formation and Its Application to Drilling in the Northern South China SeaACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 3 2004WANG Zhenfeng Abstract, There are plentiful potential hydrocarbon resources in the Yinggehai and Qiongdongnan basins in the northern South China Sea. However, the special petrol-geological condition with high formation temperature and pressure greatly blocked hydrocarbon exploration. The conventional means of drills, including methods in the prediction and monitoring of underground strata pressure, can no longer meet the requirements in this area. The China National Offshore Oil Corporation has allocated one well with a designed depth of 3200 m and pressure coefficient of 2.3 in the Yinggehai Basin (called test well in the paper) in order to find gas reservoirs in middle-deep section in the Miocene Huangliu and Meishan formations at the depth below 3000 m. Therefore, combined with the "863" national high-tech project, the authors analyzed the distribution of overpressure in the Yinggehai and Qiongdongnan basins, and set up a series of key technologies and methods to predict and monitor formation pressure, and then apply the results to pressure prediction of the test well. Because of the exact pressure prediction before and during drilling, associated procedure design of casing and their allocation in test well has been ensured to be more rational. This well is successfully drilled to the depth of 3485 m (nearly 300 m deeper than the designed depth) under the formation pressure about 2.3 SG (EMW), which indicate that a new step in the technology of drilling in higher temperature and pressure has been reached in the China National Offshore Oil Corporation. [source] | ||||||||||