Analysis Of Fault Structural Styles And Evaluation Of Favorable Structural Zones In The Linhe Depression, Hetao Basin

On the basis of fully investigating the success of early exploration in Linhe Depression of Hetao Basin and summarizing the previous research and understanding,Based on the new data of 2-D seismic survey line,drilling logging and outcrop in Linhe Depression,Combined with the theoretical knowledge and technical methods of petroleum structure analysis,the stratigraphic-structural comprehensive interpretation is carried out,with emphasis on the study of fault grade and stage,fault structural style types and their evolution and distribution laws,structural control of oil and gas,and the evaluation of favorable structural zones.Hetao Basin is located in the central part of Inner Mongolia.It is an important oil and gas-bearing basin in eastern China.It is an asymmetric dustpan-shaped fault basin developed and evolved on the basis of Precambrian metamorphic rocks.Linhe Depression is the largest sedimentary depression in Hetao Basin.Under the superposition of multi-stage tectonic movements(Yanshan movement and Himalayan movement),this area has formed a complex fault-fold system with NE and NNE strike-dominated normal faults and fold development.The regional tectonic framework has the characteristics of "east-west division and north-south division".Based on the background of regional tectonic evolution and the study in this paper,it is found that Linhe Depression has obvious Mesozoic-Cenozoic strike-slip pull-apart characteristics,and has experienced Cretaceous weak extension left-slip strike-slip pull-apart stages,Paleogene weak-medium right-slip strike-slip pull-apart stages,Neogene strong right-slip strike-slip pull-apart stages and Quaternary left-slip strike-slip reformation stages.Under the action of multi-stage different tectonic stresses,the area has formed three types of tectonic styles: extension,strike-slip and inversion,which can be further divided into eight types of tectonic styles according to their morphological characteristics.The evolution of structural styles corresponds to different stages of structural evolution.The structural pattern dominated by reverse tilted fault blocks in Cretaceous has gradually evolved into the structural pattern dominated by reverse tilted fault blocks,distributed by middle barrier graben fault blocks,regulated by negative flower structures and fold-type inversion structures.The structural styles are distributed in NE-trending strips as a whole.Based on the analysis of tectonic hydrocarbon control,it is believed that two sets of main source rocks are developed in this area,Guyang Formation of Lower Cretaceous and Linhe Formation of Oligocene.Under the difference of activity of boundary strike-slip faults,the whole source rocks are distributed in an arc shape along the boundary faults,which are thin in the south and thick in the north.Based on the analysis of the transport system and the geometric characteristics of the cross section,it is believed that during the peak period of Neogene hydrocarbon generation and expulsion,the generated oil and gas can migrate well vertically and laterally through the fault-unconformity transport system,and the whole oil and gas migrate from the northwest hydrocarbon generation area to the southeast gentle slope zone.However,many structural traps formed by multi-stage tectonic movements,mainly fault block traps,flower anticline traps and reverse anticline traps,provide good oil and gas accumulation space.Finally,combined with the analysis of evaluation parameters such as local stress state of strike-slip faults,favorable structural zones are predicted,namely,the gentle slope structural zone in the north of Linhe,the gentle slope structural zone in the south of Linhe and the structural zone in the north of Jilantai.