Understanding hydrocarbon migration and accumulation mechanisms is one of the key scientif ic problems that should be solved for effective hydrocarbon exploration in the superimposed basins developed in northwest Chin...Understanding hydrocarbon migration and accumulation mechanisms is one of the key scientif ic problems that should be solved for effective hydrocarbon exploration in the superimposed basins developed in northwest China. The northwest striking No.1 slope break zone, which is a representative of superimposed basins in the Tarim Basin, can be divided into five parts due to the intersection of the northeast strike-slip faults. Controlled by the tectonic framework, the types and properties of reservoirs and the hydrocarbon compositions can also be divided into five parts from east to west. Anomalies of all the parameters were found on the fault intersection zone and weakened up-dip along the structural ridge away from it. Thus, it can be inferred that the intersection zone is the hydrocarbon charging position. This new conclusion differs greatly from the traditional viewpoint, which believes that the hydrocarbon migrates and accumulates along the whole plane of the No.1 slope break zone. The viewpoint is further supported by the evidence from the theory of main pathway systems, obvious improvement of the reservoir quality （2-3 orders of magnitude at the intersection zone） and the formation mechanisms of the fault intersection zone. Differential hydrocarbon migration and entrapment exists in and around the strike- slip faults. This is controlled by the internal structure of faults. It is concluded that the more complicated the fault structure is, the more significant the effects will be. If there is a deformation band, it will hinder the cross fault migration due to the common feature of two to four orders of magnitude reduction in permeability. Otherwise, hydrocarbons tend to accumulate in the up-dip structure under the control of buoyancy. Further research on the internal fault structure should be emphasized.展开更多
Recent studies, focused on dihedral angles and intersection processes, have increased understandings of conjugate fault mechanisms. We present new 3-D seismic data and microstructural core analysis in a case study of ...Recent studies, focused on dihedral angles and intersection processes, have increased understandings of conjugate fault mechanisms. We present new 3-D seismic data and microstructural core analysis in a case study of a large conjugate strike-slip fault system from the intracratonic Tarim Basin, NW China. Within our study area, ＂X＂ type NE and NW trending faults occur within Cambrian- Ordovician carbonates. The dihedral angles of these conjugate faults have narrow ranges, 19~ to 62~ in the Cambrian and 26~ to 51~ in the Ordovician, and their modes are 42~ and 44~ respectively. These data are significantly different from the ~60~ predicted by the Coulomb fracture criterion. It is concluded that： （1） The dihedral angles of the conjugate faults were not controlled by confining pressure, which was low and associated with shallow burial; （2） As dihedral angles were not controlled by pressure they can be used to determine the shortening direction during faulting; （3） Sequential slip may have played an important role in forming conjugate fault intersections; （4） The conjugate fault system of the Tarim basin initiated as rhombic joints; these subsequently developed into sequentially active ＂X＂ type conjugate faults; followed by preferential development of the NW-trending faults; then reactivation of the NE trending faults. This intact rhombic conjugate fault system presents new insights into mechanisms of dihedral angle development, with particular relevance to intracratonic basins.展开更多
The gold orefield studied is located on the south border of the underthrust-collision zone of the Qinling microplate and the North China microplate in the Indosinian epoch. The main ore deposits localized in the area ...The gold orefield studied is located on the south border of the underthrust-collision zone of the Qinling microplate and the North China microplate in the Indosinian epoch. The main ore deposits localized in the area where the WNW-trending compression-shear type fault of the Indosinian epoch intersected the NE-trending tenso-shear type fault of the Yanshanian epoch. The orebody appeared in a chambered or wedged form. The mineral composition is relatively complex. On the southeastern border of the orefield there have developed intermediate-acid anatectic magmatites of the Mesozoic Era. Three-phase inclusions (Lco2, Vco2 and LNaCl-H2O) comprise over 50%, associated with vapor phase consisting of H2O, CO2, CO, CH4, N2 and H2. The ore-forming fluids can be divided into 2 stages (the early and the late). The samples are projected in the area of mixture of initial magmatic and meteoric water on the δD-δ18O diagram, suggesting two types of mineralization, i.e. the re-equilibrated magmatic-hydrothermal type and the circulating geothermal water type of a meteoric water source. The mineralization occurring in this orefield might be a superimposition of 2 tectono-magmatic activities (the Indosinian and Yanshanian movements). Therefore, it is considered a superimposed B-S type gold orefield.展开更多
基金supported by the National 973 Basic Research Program (Grant No.2006CB202308)the Major National Science & Technology Program (2008ZX05008-004-012)
文摘Understanding hydrocarbon migration and accumulation mechanisms is one of the key scientif ic problems that should be solved for effective hydrocarbon exploration in the superimposed basins developed in northwest China. The northwest striking No.1 slope break zone, which is a representative of superimposed basins in the Tarim Basin, can be divided into five parts due to the intersection of the northeast strike-slip faults. Controlled by the tectonic framework, the types and properties of reservoirs and the hydrocarbon compositions can also be divided into five parts from east to west. Anomalies of all the parameters were found on the fault intersection zone and weakened up-dip along the structural ridge away from it. Thus, it can be inferred that the intersection zone is the hydrocarbon charging position. This new conclusion differs greatly from the traditional viewpoint, which believes that the hydrocarbon migrates and accumulates along the whole plane of the No.1 slope break zone. The viewpoint is further supported by the evidence from the theory of main pathway systems, obvious improvement of the reservoir quality （2-3 orders of magnitude at the intersection zone） and the formation mechanisms of the fault intersection zone. Differential hydrocarbon migration and entrapment exists in and around the strike- slip faults. This is controlled by the internal structure of faults. It is concluded that the more complicated the fault structure is, the more significant the effects will be. If there is a deformation band, it will hinder the cross fault migration due to the common feature of two to four orders of magnitude reduction in permeability. Otherwise, hydrocarbons tend to accumulate in the up-dip structure under the control of buoyancy. Further research on the internal fault structure should be emphasized.
基金partly supportedby National Natural Science Foundation of China(Grant No.41472103)
文摘Recent studies, focused on dihedral angles and intersection processes, have increased understandings of conjugate fault mechanisms. We present new 3-D seismic data and microstructural core analysis in a case study of a large conjugate strike-slip fault system from the intracratonic Tarim Basin, NW China. Within our study area, ＂X＂ type NE and NW trending faults occur within Cambrian- Ordovician carbonates. The dihedral angles of these conjugate faults have narrow ranges, 19~ to 62~ in the Cambrian and 26~ to 51~ in the Ordovician, and their modes are 42~ and 44~ respectively. These data are significantly different from the ~60~ predicted by the Coulomb fracture criterion. It is concluded that： （1） The dihedral angles of the conjugate faults were not controlled by confining pressure, which was low and associated with shallow burial; （2） As dihedral angles were not controlled by pressure they can be used to determine the shortening direction during faulting; （3） Sequential slip may have played an important role in forming conjugate fault intersections; （4） The conjugate fault system of the Tarim basin initiated as rhombic joints; these subsequently developed into sequentially active ＂X＂ type conjugate faults; followed by preferential development of the NW-trending faults; then reactivation of the NE trending faults. This intact rhombic conjugate fault system presents new insights into mechanisms of dihedral angle development, with particular relevance to intracratonic basins.
文摘The gold orefield studied is located on the south border of the underthrust-collision zone of the Qinling microplate and the North China microplate in the Indosinian epoch. The main ore deposits localized in the area where the WNW-trending compression-shear type fault of the Indosinian epoch intersected the NE-trending tenso-shear type fault of the Yanshanian epoch. The orebody appeared in a chambered or wedged form. The mineral composition is relatively complex. On the southeastern border of the orefield there have developed intermediate-acid anatectic magmatites of the Mesozoic Era. Three-phase inclusions (Lco2, Vco2 and LNaCl-H2O) comprise over 50%, associated with vapor phase consisting of H2O, CO2, CO, CH4, N2 and H2. The ore-forming fluids can be divided into 2 stages (the early and the late). The samples are projected in the area of mixture of initial magmatic and meteoric water on the δD-δ18O diagram, suggesting two types of mineralization, i.e. the re-equilibrated magmatic-hydrothermal type and the circulating geothermal water type of a meteoric water source. The mineralization occurring in this orefield might be a superimposition of 2 tectono-magmatic activities (the Indosinian and Yanshanian movements). Therefore, it is considered a superimposed B-S type gold orefield.
