| Bayanhaote basin is located in middle-west Inner Mongolia,Alashan prefecture.It's in the southeast of Alashan block that the three big tectonic units of Helan tectonic belt,Alashan block and Gansu Corridor structural belt.It's the key of the oil and gas exploration that has found the oil and gas with good show in many places,but has not got a significant breakthrough.The main reason is that the complicated tectonic features and the unknown mode of hydrocarbon migration and accumulation due to the multiple periods of tectonic movements,the theoretical demand of petroleum exploration and development cannot be satisfied.The paper takes the Eastern Depression of Bayanhaote Basin as the research object,based on a large number of field outcrops,2D seismic,drilling,well logging and actual test data,using the theory of petroleum structure analysis and hydrocarbon migration dynamics,clear the main type,the scale and level of fracture system,plane combinate the breakpoint of fracture system,analyze and determine the type,characteristics and plane distribution of the main structural style,evaluate the conditions of reservoir,research the hydrocarbon migration direction based on the theory of fluid potential,establish the hydrocarbon migration and accumulation models in the study area following the predecessors' research.The main results are as follows:In the plane of the Eastern Depression of Bayanhaote basin,3 groups of netrending,NNE-trending and near-EW-trending fault systems are developed,among which the NNE-trending faults are the most developed,which is the main faults in the study area.With the Jurassic as the boundary,the upper normal fault and the lower inverse fault systems were developed in the vertical.There are three types of structural styles: extending structural style,compressional structural style and strike-slip structural style.The main source rocks are Carboniferous mudstone with good hydrocarbon generation capacity.The main hydrocarbon expulsion period is Late Cretaceous.The reservoirs are mainly Carboniferous sandstone with low porosity and low permeability.The transport system is a three-dimensional hydrocarbon transport network composed of four types of transport systems: fracture,unconformity,connected sand body and fracture,which cross,overlap and combine with each other.There are three types of source-reservoir-cap assemblages,which are self-generation and self-bearing,up-generating and down-bearing,down-generating and up-bearing.In the Late Cretaceous,the Carboniferous fluid potential decreased from the east and south to the west and southeast of the depression.The high potential area had a small distribution range and it was main located in the east and south of the depression.The general direction of hydrocarbon migration was from the east and southwest to the west and southeast of the depression.The study area can be divided into 3 hydrocarbon migration and accumulation zones and 8 hydrocarbon migration and accumulation units.The traps with good evaluation were mainly developed in the south and central part of the depression.Based on the comprehensive analysis of the factors such as "fault characteristics","tectonic characteristics","reservoir conditions","fluid potential characteristics" and "hydrocarbon accumulation unit",the paper makes a comprehensive evaluation of the structural traps in the study area,and establishes 3 hydrocarbon migration and accumulation modes: near-source,far-source and in-source accumulation.It is considered that the near-source hydrocarbon migration and accumulation mode controlled by the unconformity-connected sand body coupling transport system has a short migration distance and is not easily dispersed,and it can form large reservoirs. |
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