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Structural High (structural + high)
Selected AbstractsBURIAL AND MATURATION HISTORY OF THE HEGLIG FIELD AREA, MUGLAD BASIN, SUDANJOURNAL OF PETROLEUM GEOLOGY, Issue 1 2000A. Y. Mohamed The NW-SE trending Muglad Basin (SW Sudan) is one of a number of Mesozoic basins which together make up the Central African Rift System. Three phases of rifting occurred during the Cretaceous and Tertiary, resulting in the deposition of at least 13 km of sediments in this basin. Commercial hydrocarbons are sourced from the Barremian-Neocomian Sharaf Formation and the Aptian-Albian Abu Gabra Formation. The Heglig field is located on a NW-SE oriented structural high in the SE of the Muglad Basin, and is the second-largest commercial oil discovery in Sudan. The high is characterised by the presence of rotated fault blocks, and is surrounded by sub-basinal structural lows. We modelled the geohistories of three wells on different fault blocks in the Heglig field (Heglig-2, Barki-1 and Kanga-1) and one well in the Kaikang Trough (May25,1). The models were calibrated to measured porosity-depth data, temperature and vitrinite reflectance measurements. Predicted present-day heat flow over this part of the Muglad Basin is about 55 mW/m2. However, a constant heat-flow model with this value did not result in a good fit between calculated vitrinite Ro and measured Ro at the wells studied. Therefore a variable heat-flow model was used; heat flow peaks of 75, 70 and 70 mW/m2 were modelled, these maxima corresponding to the three synrift phases. This model resulted in a better fit between calculated and measured Ro. The source rock section in the Sharaf and Abu Gabra Formations was modelled for hydrocarbon generation in the four wells. Model results indicate that the present-day oil generation window in the Hegligfield area lies at depths of between 2 and 4 km, and that oil and gas generation from the basal unit of the Abu Gabra Formation occurred between about 90 and 55 Ma and from the Sharaf Formation between 120 and 50 Ma. The results suggest that the oils discovered in the Heglig area have been generated from a deep, mature as-yet unpenetrated source-rock section, and/or from source rocks in nearby sub- basinal areas. [source] Stratigraphic and structural expression of the lateral growth of thrust fault-propagation folds: results and implications from kinematic modellingBASIN RESEARCH, Issue 2 2003Kate A. Cooper In order to better understand the development of thrust fault-related folds, a 3D forward numerical model has been developed to investigate the effects that lateral slip distribution and propagation rate have on the fold geometry of pre- and syn-tectonic strata. We consider a fault-propagation fold in which the fault propagates upwards from a basal decollement and along-strike normal to transport direction. Over a 1 Ma runtime, the fault reaches a maximum length of 10 km and accumulates a maximum displacement of 1 km. Deformation ahead of the propagating fault tip is modelled using trishear kinematics while backlimb deformation is modelled using kink-band migration. The applicability of two different lateral slip distributions, namely linear-taper and block-taper, are firstly tested using a constant lateral propagation rate. A block-taper slip distribution replicates the geometry of natural fold-thrusts better and is then used to test the sensitivity of thrust-fold morphology to varied propagation rates in a set of fault-propagation folds that have identical final displacement to length (Dmax/Lmax) ratios. Two stratigraphic settings are considered: a model in which background sedimentation rates are high and no topography develops, and a model in which a topographic high develops above the growing fold and local erosion, transport and deposition occur. If the lateral propagation rate is rapid (or geologically instantaneous), the fault tips quickly become pinned as the fault reaches its maximum lateral extent (10 km), after which displacement accumulates. In both stratigraphic settings, this leads to strike-parallel rotation of the syn-tectonic strata near the fault tips; high sedimentation rates relative to rates of uplift result in along-strike thinning over the structural high, while low sedimentation rates result in pinchout against it. In contrast, slower lateral propagation rates (i.e. up to one order of magnitude greater than slip rate) lead to the development of along-strike growth triangles when sedimentation rates are high, whereas when sedimentation rates are low, offflap geometries result. Overall we find that the most rapid lateral propagation rates produce the most realistic geometries. In both settings, time-equivalent units display both nongrowth and growth stratal geometries along-strike and the transition from growth to nongrowth has the potential to delineate the time of fault/fold growth at a given location. This work highlights the importance of lateral fault-propagation and fault tip pinning on fault and fold growth in three dimensions and the complex syn-tectonic geometries that can result. [source] Origin of the Silurian Crude Oils and Reservoir Formation Characteristics in the Tazhong UpliftACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 5 2010YANG Haijun Abstract: The Silurian stratum in the Tazhong uplift is an important horizon for exploration because it preserves some features of the hydrocarbons produced from multi-stage tectonic evolution. For this reason, the study of the origin of the Silurian oils and their formation characteristics constitutes a major part in revealing the mechanisms for the composite hydrocarbon accumulation zone in the Tazhong area. Geochemical investigations indicate that the physical properties of the Silurian oils in Tazhong vary with belts and blocks, i.e., heavy oils are distributed in the TZ47,15 well-block in the North Slope while normal and light oils in the No. I fault belt and the TZ16 well-block, which means that the oil properties are controlled by structural patterns. Most biomarkers in the Silurian oils are similar to that of the Mid-Upper Ordovician source rocks, suggesting a good genetic relationship. However, the compound specific isotope of n -alkanes in the oils and the chemical components of the hydrocarbons in fluid inclusions indicate that these oils are mixed oils derived from both the Mid-Upper Ordovician and the Cambrian,Lower Ordovician source rocks. Most Silurian oils have a record of secondary alterations like earlier biodegradation, including the occurrence of "UCM" humps in the total ion current (TIC) chromatogram of saturated and aromatic hydrocarbons and 25-norhopane in saturated hydrocarbons of the crude oils, and regular changes in the abundances of light and heavy components from the structural low to the structural high. The fact that the Silurian oils are enriched in chain alkanes, e.g., n -alkanes and 25-norhopane, suggests that they were mixed oils of the earlier degraded oils with the later normal oils. It is suggested that the Silurian oils experienced at least three episodes of petroleum charging according to the composition and distribution as well as the maturity of reservoir crude oils and the oils in fluid inclusions. The migration and accumulation models of these oils in the TZ47,15 well-blocks, the No. I fault belt and the TZ16 well-block are different from but related to each other. The investigation of the origin of the mixed oils and the hydrocarbon migration and accumulation mechanisms in different charging periods is of great significance to petroleum exploration in this area. [source] Tectonic and climatic control on growth and demise of the Phanh Rang Carbonate Platform offshore south VietnamBASIN RESEARCH, Issue 2 2009Michael B. W. Fyhn The Phan Rang Carbonate Platform located offshore south Vietnam covers more than 15 000 km2, making it one of the largest carbonate platforms in the South China Sea. Based on 2-D seismic analysis, this paper outlines the platform evolution and analyzes the regional tectonic, climatic and oceanic factors that controlled the platform growth and demise. This study of the Phan Rang Carbonate Platform therefore provides an analogue to the regions late Neogene carbonates that form important targets for petroleum exploration. Platform growth initiated during the late middle Miocene along the open marine Vietnamese margin and continued throughout the late synrift to early postrift period of the area terminating around Pliocene time. During this period, the structural grain, local and regional tectonics as well as oceanographic effects exerted major controls on carbonate deposition. Optimal growth conditions existed during initial platform deposition and locally accumulation rates reached ca. 230 m Ma,1. Late Miocene regional uplift caused subaerial exposure that interrupted platform growth and caused intense karstification. A gradual reestablishment of marine conditions promoted renewed platform growth. However, carbonate production was stressed by increased terrigenous input caused by onshore uplift and by inorganic nutrification of the surface waters. Nutrification probably occurred in response to increased nutrient influx derived from onshore denudation, enhanced periodically by soil ravinement during transgression. The onset or intensification of summer upwelling along the southern platform margin occurred in response to the onshore uplift and most likely contributed to the nutrification. The deteriorated growth conditions and fast subsidence resulted in platform split-up, backstepping and local drowning. Subsequently, isolated platforms nucleated on structural highs as transgression continued. The remaining platforms thrived for a period but eventually failed to keep pace with subsidence, backstepped and drowned. The longest surviving platform now crops out at the seafloor at ca. 500 m depth. [source] Structural Analysis of the Multi-layer Detachment Folding in Eastern Sichuan ProvinceACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 3 2010Zongxiu WANG Abstract: A serial of "comb-like and trough-like" folds developed in eastern Sichuan, controlled by the multi-layer detachment folding, is different from the classical Jura-type structure in their development. The key factor resulting in the development of these structures is the occurrence of detachment layers in different parts of Neoprotozoic to Mesozoic stratigraphy of study area, which, from the bottom to the top, are the lower part of Banxi Group, Lower Cambrian (Niutitang Formation), Lower Silurian (Longmaxi Formation and Luoreping Formation), Upper Permian (Wujiaping Formation) and Lower Triassic (Daye Formation). On the basis of field survey combined with sand-box modeling, this study argued that the detachment layer of the lower part of Banxi Group controlled the development of the "comb-like" folds, and the lower part of Cambrian detachment layer controlled the development of "trough-like" folds. Because of several detachment layers occurring in the study area, the development of duplex structures different scales is an important deformation mechanism, and the duplexes are the important structures distinguished from the typical detachment folding structures. Due to these duplexes, the surface structures and structural highs may not be the structural highs in the depth. Meanwhile, the detachment layers are good channels for oil/gas migration benefiting the understanding of accumulation and migration of oil and gas. [source] | ||||||||||