A Structural Study Of The Northern Part Of Bayanhaote Basin,Inner Mongolia

The study area of this thesis is located at the northern part of Inner Mongolia Bayanhaote basin, constructed in Alashan, Ordos block and Qilian fold belt interchange. Although the oil and gas of this area is rich, the research of tectonic framework and evolution of the area are still lacking and restricting the exploration and development of oil and gas. Therefore, systematically analyzing the development of the northern part of the basin evolution of the area, from geometry, kinematics point, is particularly important.Firstly, the2D seismic data of drilling, seismic, regional document is interpreted with Discovery2004and four layer calibrations, Carboniferous bottom, Jurassic bottom, Cretaceous bottom and Paleogene bottom, are been marked referenced on Changqing Research. Then found the geometric characteristics of the study area: eastern fault zone, western depression zones. On this basis, from north to south the area is divided into two secondary tectonic units:Tonggulou bulge and Xiling depression. And they can be divided into the lower structural layer and the upper structural layer separated by Paleogene bottom. The lower structural layer includes Paleozoic-Mesozoic strata, developmental closed folds and gently fold normal fault system and reverse fault system. The upper structural layer includes mainly consist of Cenozoic strata, including development of the gentle folds, normal faults and few reverse faults.Secondly, profile interpretation on kinematic characteristics and evolution of the study area show that there was a horizontal compression in the late Cretaceous period and construct some closed folds and gently fold and a lot of NE-SW trending normal faults and reverse faults. Some of the faults in the lower structural layer are synsedimentary faults. Some of them are receiving the deposition side off the wrong move but stop in the Cretaceous Period, and some of them active again by the regional campaign at the end of the Cretaceous Period or in the Cenozoic Era Period, and the rest of them construct reverse faults by extrusion at the end of the Cretaceous Period and few still stay active. The upper structural layer experienced two campaigns: extensional activities of the Paleogene period or the Neogene period and compressional thrust movement of the end of the Neogene period and constructs gentle fold. The study show that a lot of faults of the upper structural layer are faults of the lower structural layer with one or two times of activities. Few faults has diastrophism only in the Neogene period.From the interpretation of sections we can see that the difference is significant:the activities of Tonggulou bulge is more strong than Xiling depression. As a result, activities of the area is weaker from south to north. There are also a lot of tectonic styles in the area. The tectonic style of region or the basement of the basin not only control the Sedimentary model and grown mechanism of the basin but also the type and distribution of the Oil and gas traps of the basin. With detailed analyzing of the interpretation of seismic profiles, we can find two main type of structure style:the extensional structures style and the extrusion tectonic style. Examples of the former are Graben-horst, Half-grabens, Step fault combination and tilted fault blocks. And examples of the extrusion tectonic style are Imbricated thrust fault combination and back thrust combination. Almost all the two types are developed in the lower structure layer.Finally, by using the analysis on the regional geological data, we can analyze the history of the study area. Before lower Ordovician, the area is Helan aulacogen. Being in transgression, deposition and regional activities extrusion, it gets erosion. There misses Ordovician and Devonian. In Carboniferous Period, the area is squeezed by the north-south in the Qilian movement and constructs some north-south or NE-SW direction extension fractures. A large area of the area uplift. There misses Permian system and Triassic system. In the Jurassic period, there are magmatic activity and parts of it has dome collapse. Near the end of the Jurassic period, the fold of Helan Mountain uplift, and produces some ladder normal faults. At end of the Cretaceous period, the region is squeezed again by the Yanshan movement, produces folds and reverse faults and unconformity contact with the overlying strata angle. After this, the area has been in a stable settlement, also develops a number of normal faults. To the end of the Neogene period, the study area is slightly squeezed by the Himalayan movement and produces some gentle folds. After that the area is stable.It is publicly accepted that basin tectonic style and type of hydrocarbon traps are closely linked. The main style of the study area are compressional tectonic style and extensional tectonic style. The area forms two corresponding types of traps:4faulted anticline and4fault block traps, which are commonly exist and developed in the study area. Faulted anticline is anticline which is closed and breaked by multiple faults and located between two faults. It consist the thrust tectonic wedge and the faulted anticline is split into few fault blocks. The key of fault trap to gather oil and gas is closure. When the fault is closed, the fault trap is a good hydrocarbon trap. According to this interpretation the area in Carboniferous period has well developed structural traps and good preservation, especially Jingyuan group and Yanghugou group, and it is good for Carboniferous accumulation. So the layer in Carboniferous system is used for exploration. Further more, with layers in Jurassic period and Cretaceous period covering on the layer of Carboniferous period, it is another profit condition. After the end of the Cretaceous period, the study area get stable, get little influence from regional tectonic movement, has low active fault developing and less structural traps damage, all these let it to be more fit to storage oil.All the traps of the study area are located in the lower structural layer of Tonggulou bulge and formed in the late Cretaceous period. the couniugou Formation of Lower Carboniferous begins mature from the beginning of the Tertiary period and Benxi Formation of Middle Carboniferous begins mature from the end of the Tertiary period. This means that the trap constructs significantly earlier than the maturity of organic matter and so all the traps are likely to accumulation.