| Ordos Basin tectonic area was located in the west in China by landing zone of east and west structure in many times, alternately repeatedly pull zhang and extrusion effect with unconformity, forming the many tectonic system for boundaries, evolutionary stages and sedimentary system and more complex basin superposition prototype basin in China, administrative divisions over the shaanxi, gansu, ningxia, Inner Mongolia, shaanxi 5 provinces, an area of about 37×10~4km~2. The tectonic units can be divided into YiMeng uplift, considered uplift, west margin foreland thrust belt and tianhuan depression, shanbei slope and jinxi fold belt, including shanbei slope area, constitute a huge oil and gas exploration in the basin subject area Triassic.Ordos basin, after decades of exploration and development, has been found and put in oilfield shows: basin internal Mesozoic strata large thickness, distribution scope, main birth, porosity are late Triassic to extend groups, among which chang 7 reservoir group, chang 4+5 reservoir development section of the dark mudstone, to half deep lake - deep lake sedimentation; chang 6 reservoir group and chang 8 in sandstone reservoir development mainly of reservoir; Reservoir sandbody mainly northeast river delta depositional system and slope southwest steep slope area braided delta depositional system, in the northwestern and south fan delta depositional system development, a semi-deep-lake deep-water - deep-water part in half regional development turbidite fan deposition; Stratigraphic traps and lithologic trap is composed of upper Triassic prolong the subject of hydrocarbon accumulation.Ordos basin late Triassic to prolong the deposition of the filling record semi-deep-lake to produce, intermittent concussion type lake lake withdrew into, and evolution history of and extinct. The provenance analysis research shows that basin during the deposition in prolonging the group is more than a stream large catchment basin, ancient water system mainly northeast 190°~250°and 50°~65°southwest to two mainstream in basin, the flow of the field profiles at 105°~ 135 basic°and south direction, in basin in the south north direction strands of flow; Light and heavy mineral research and rare earth elements stable REE distribution pattern characteristics also suggests that the late Triassic depositional period basin the primary provenance direction as north east to the west and south material sources, but also the existence the provenance and northwest, but south south the provenance is the provenance influenced range. Combined with the basin sedimentation, can determine the research for border late Triassic provide extended the deposition of the material sources of the parent rocks northeast of yinshan for ancient land castrated2 mountains, JiNing group, the ancient land ALaShan northwest, southwest direction ALaShan group of ancient land, from west gansu qinling - a set of ancient land dang senior metamorphic rocks and granite, suffer its control in basin formed inside the corresponding development of composite northeast large slope river delta depositional system, northwest fan delta depositional system, southwest large steep type composite braided river triangle and fan delta depositional system.Diagenesis aspects: extend the sandstone of the experience of heavy rain and high winds compaction effect rock period and cementation, late diagenetic stage of dissolition and explaination role, precocious rock period compaction effect and cementation cause sand body reservoir property is reduced, dissolition and explaination role improved sand body reservoir pore structure and properties, but overall extend group sand body still have extra-low permeability and porosity features. Of clastic reservoir porosity is buried depth and secondary porosity function, is also subject to the provenance conditions and sedimentary environment control of sediments composition and structure, by structural motion control sedimentary clastic particle burial history, hydrodynamic conditions and pore fluid properties and evolutionary stages, geothermal field, and reservoir rock within the sedimentary system related to organic matter and clay mineral and so on a series of diagenetic evolution related factors the result of joint action.The provenance and sedimentary environment control in composition and structure, experience sediments buried, diagenetic process, extend for different objects of sand body source and sedimentary environment, the diagenesis of depositional system also has difference, the characteristics of ancient land content source control west-to-east deelopment of type of large slope sedimentary system northeast sand body feldspar and mica content high, compaction effect, turbidity zeolite cementation is strong in the main characteristics of cementation, dissolition stage of feldspar dissolution mainly in delta plain distributary channel sand, hydrocarbon source rock hydrocarbon generation when from the center to organic along the northeast edge of turbidity zeolite when migration on dissolution dissolution degree form different band, and feldspar dissolution and turbidity zeolite dissolution has greatly improved the reservoir properties. Southwest sand body and south sand body compared to the northeast sand body speaking, quartz content is higher, rigid particle on the overlying strata support action, stronger, but the upper stratum of the northeast to more than thick, and still a large number of thousand pieces rock cuttings compaction effect, so southwest stronger also, precocious rock formation of ring (for part edge chlorite primary porosity of sand body has certain protective effect. Northwest things by source shallow metamorphic rock, and volcanic rocks control sedimentary system long and six reservoir group than in the development of reservoir long 8 narrowed down a lot, shallow metamorphic rock in compaction effect easily in the miscellaneous base and jam formed false pore, so rigid particles with the amount of quartz reservoir physical property has a very good correlation. |
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