Structural Evolution And Its Control On Accumulation Of Shale Gas In Ningwu Basin

Ningwu is an important coal basin in northern Shanxi Province. Organic-rich shale is very developed in Carboniferous-Permian and Jurassic formations, which provides a wealth of material foundation for shale gas accumulating. Researching the tectonic development characteristics, evolution, shale gas geological characteristics and the control action on shale gas accumulation of tectonic evolution in Ningwu basin has important implications for researching tectonic evolution of Ningwu basin and further exploration and development of shale gas. Based on studying area geological structure fully, mainly guided by plate tectonics theory, this paper launched a comprehensive study on the geometry features and kinematic characteristics of the main geological structure and its formation mechanism by using traditional geological structure methods, with the interior structural geology, the using of simulation software and other experimental methods. At last this paper discussed the control action of tectonic evolution on shale gas accumulation and its mode of occurrence. This paper access to the main following understanding:(1)The formation of under Paleozoic Cambrian to Cenozoic Quaternary were developed in Ningwu area. The region purpose floor mainly experienced multi period tectonic cycle, such as Hercynian period, Indo-China period, Yanshan period, Himalayan period and so on.(2)The mainly fold structure is Ningwu-Jingle syncline in Ningwu basin, which is in the center of basin. Faults are mainly distributed in the east and west edges of the basin. Faults are not developed in the internal of basin. The preferred orientations of jointed in study area are mainly NE, NEE, NW, NS, followed by NWW.(3)There is a big difference in the spatial distribution of tectonic in Ningwu basin. There are the multiple times, multi-directional, multi-stage, multi-nature developmental courses of tectonic evolution.(4) Since Mesozoic, the tectonic evolution of Ningwu basin can be divided into five phases: the nearly NS squeeze in Indo-china period, the NW-SE squeeze in the early-mid of Yanshan period, the E-W squeeze in the late of Yanshan period, the nearly NS squeeze in Sichuan period and new rift forming stage in Himalayan period. The dynamics of Ordos and the uplift of Taihang plays a decisive control role in dynamics of the main tectonic evolution in Ningwu basin.(5)The thickness of purpose floor measured in the field profile in the study area is between 30~100m. TOC is ranged from 0.11%~7.87%, the average of 1.92%.The organic maturity is >0.5%. The deposition and burial of purpose layer can be mainly divided into five stages: the rapid burial in Hercynian-Indo period, the rapid uplift in the late of Indo period, the rapid burial in early-mid of Yanshan period, the slowly uplift and fold in late of Yanshan period, the rapid uplift to erosion in Sichuan-Himalayan period. The thermal evolution of organic can be divided into three major phases: the rapid burial stage in early-mid of Indo-china period, the stop evolutionary stage in late of Indo-china period, the further evolution stage in early-mid of Yanshan period. The organic evolution of the study area is mainly finalized in early-mid of Yanshan period, whicn is the main period of shale gas accumulation. The fault in the eastern margin of Ningwu basin exists negative inversion of structure, which lead to the escaping of a large number of hydrocarbon gas. The thrust fault of the western edge and the syncline provide the effect of blocking and trapping, which form a good shale gas reservoir of structure.