Structural controls on sandstone compaction within the anticline crest and flank: An example from the Xihu Sag, East China Sea Basin
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Oil and gas are produced from Tertiary sandstone reservoirs in deltaic and related depositional systems in the United States Gulf Coast, Niger, and MacKenzie-Beaufort basins. In each area there is an orderly, predictable interrelationship of sedimentation, stratigraphy, depositional environment, and structure, with the characteristics, ages, and distribution of producing trends. In comparing and contrasting the three areas, it is apparent that they have many aspects in common, resulting from the fact that they are relatively young, subsiding paralic basins on Atlantic-type margins. They contain thick accumulations of deltaic sediments that have prograded in regressive basin-filling sequences as the basins subsided. Therefore each has a vertical gross lithologic sequence that has shale at the base, overlain by interbedded sandstones and shales, overlain by massive sandstones. The vertical sequence is repeated laterally from basin to land. In each basin the stratigraphic units thicken basinward across a series of normal, listric, down-to-the-basin syndepositional faults, with which are associated anticlines that form traps. Trapping associated with diapiric structures is also characteristic. Significant differences are related to the different geologic settings and geologic histories of the basins. For example, the presence of salt in the Gulf Coast basin has resulted in a wide variety of salt-dome-related trapping mechanisms in addition to the shale diapirs and rollover anticlines common to all three areas. Pre-Tertiary tectonic settings, different in each case, control basin configurations and affect structural trends. Vertical and lateral differences in depositional systems and sequences, and in sandstone geometries, result from variations in ratios of rates of sedimentation to rates of subsidence that are, in part, tectonically controlled. The framework for the occurrence of oil and gas is well understood in the maturely explored and intensively studied Gulf Coast Tertiary basin. Concepts developed there can be applied to developing the less-explored Niger basin and to exploring the frontier Mackenzie-Beaufort basin. End_of_Article - Last_Page 1680------------
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Kumukol Basin,located at the north margin of the Tibetan plateau,is separated from the Qaidam Basin by the Qimantag Range geographically. It is the transitional region between the Tibetan plateau and Qaidam Basin,and also the leading edge of the growing main body of the plateau. Nowadays,East Kunlun Fault and Altyn Tagh Fault,two significant strike-slip faults of Tibetan plateau,as well as the compressional Qimantag folding thrust system,delimit the southern,western and northern borders of the basin,respectively. Therefore,the study on the tectonic deformation and tectonic evolution of the basin will play an important role in understanding the style and mechanism of the eastward expanding of Tibetan plateau.Although Kumukol Basin is delimited by strongly active strike-slip faults,a very large anticline is growing in the basin,with a similar strike of NWW-SEE to the Qimantag folding thrust system and the folds in Qaidam Basin,such as Youshashan fold,suggesting that the basin is compressional. In this study,the lateral growth of this anticline is revealed by the analysis on the topographic profiles and distribution of terraces. A conclusion,as well,is made that the large proluvial fan at the east segment of the anticline is a result of the glacier melt water based on the field survey and dating of terrace samples. According to the OSL and10Be exposure ages,the age of the fan is 87. 09±2. 31ka ~102. 4±3. 7ka,and accordingly,we can get a maximum uplift rate of(2. 78±0. 28)mm /a ~(3. 28±0. 28)mm /a for the anticline since late Pleistocene. Tectonically,Kumukol Basin is highly similar to Qaidam Basin on its north,both are strongly active and controlled by the regional NEE compression stress field of the Altyn Tagh Fault at its south.
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Abstract The Dongying anticline is an E-W striking complex fault-bounded block unit which located in the central Dongying Depression, Bohai Bay Basin. The anticline covers an area of approximately 12 km 2 . The overlying succession, which is mainly composed of Tertiary strata, is cut by normal faults with opposing dips. In terms of the general structure, the study area is located in a compound transfer zone with major bounding faults to the west (Ying 1 fault) and east (Ying -8 and -31 faults). Using three-dimensional seismic data, wireline log and checkshot data, the geometries and kinematics of faults in the transfer zone were studied, and fault displacements were calculated. The results show that when activity on the Ying 1 fault diminished, displacement was transferred to the Ying -8, Ying -31 and secondary faults so that total displacement increased. Dynamic analysis shows that the stress fields in the transfer zone were complex: the northern portion was a left-lateral extensional shear zone, and the southern portion was a right-lateral extensional shear zone. A model of potential hydrocarbon traps in the Dongying transfer zone was constructed based on the above data combined with the observed reservoir rock distribution and the sealing characteristics of the faults. The hydrocarbons were mainly expulsed from Minfeng Sag during deposition periods of Neogene Guantao and Minghuazhen Formations, and migrated along major faults from source kitchens to reservoirs. The secondary faults acted as barriers, resulting in the formation of fault-bound compartments. The high points of the anticline and well-sealed traps near secondary faults are potential targets. This paper provides a reservoir formation model of the low-order transfer zone and can be applied to the hydrocarbon exploration in transfer zones, especially the complex fault block oilfields in eastern China.
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Echelon formation
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Recent hydrocarbon discoveries in the Southern Apennines of Italy have focussed attention on the importance of studying fracturing and cataclasis in carbonate rocks because of their fundamental impact on reservoir permeability and connectivity. The Narni Anticline in the central Apennines consists of a stack of easterly‐verging carbonate thrust sheets compartmentalized by extensional and strike‐slip fault zones. The structure provides afield analogue for studying the evolution of superimposed fold‐ and fault‐related fractures in carbonate reservoir rocks. The fracture pattern at the Narni Anticline developed as a result of three mechanisms: (a) layer‐parallel shortening predating folding and faulting; (b) thrust‐related folding and further thrust breakthrough; and (c) extensional and strike‐slip faulting. Along‐strike (longitudinal) fractures developed during progressive rollover fault‐propagation folding, and their intensity depends on the precise structural position within the fold: fracture intensity is high in the forelimb and low in the crest. The 3‐D architecture of the mechanical anisotropy associated with thrusting, folding, and related fracturing constrained the location and geometry of subsequent extensional and strike‐slip faulting. The superimposition in damage zones of a fault‐related cleavage on the pre‐existing fracture pattern, which is associated with layer‐parallel shortening and thrust‐related folding, resulted in rock fragmentation and comminution, and the development of cataclastic bands. The evolution of fracturing in the Narni Anticline, its role in constraining thrust breakthrough trajectories and the location of extensional and strike‐slip faults, and the final development of low‐permeability cataclastic bands, will be relevant to studies of known oilfields in the Southern Apennines, as well as for future exploration.
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