Features Of Mesozoic Unconformity And Its Controlling Affect On The Hydrocarbon Accumulation In Gaoqing Area

The Gaoqing area is located in the southwestern margin of the Dongying depression,and is adjacent to the Boxing oil-depression depression in the east.It has good oil source conditions.Drilling results in recent years have confirmed that the control of oil and gas in the Mesozoic unconformity is obvious.But at present,the research on the unconformity of Jiyang depression is mainly concentrated in the Cenozoic,but the research on the unconformity of the Mesozoic is not deep enough.In view of this problem,this paper integrates core observation,microscopic observation,mineral and elemental content test,seismic data analysis,well logging data analysis and other methods,this paper studies the unconformity structure characteristics,unconformity structure identification,unconformity structure distribution characteristics and unconformity structure controlling effect on the hydrocarbon accumulation of Mesozoic in Gaoqing area,and obtains the following main achievements and understandings:(1)There are 10 unconformity in the Mesozoic of the Gaoqing area,divided into 3 levels.The Mesozoic unconformity is divided into 3-layer structure vertically,and the top unconformity structure of Mesozoic is mudstone-mudstone-sandstone,while the inner unconformity structure is sandstone-sandy mudstone-sandstone.The content of quartz and kaolinite in weathered clay layer is high.The content of feldspar in semi-weathered rocks is more than that of weathered clay,petrophysical properties deterioration;mineral elements of semi-weathered rocks show the characteristics of rich Al poor Ca and Na,the enrichment and loss of elements are lower than that of weathered clay layer,and the physical property improved obviously.(2)According to the identification criteria for the unconformity of structural minerals in the Mesozoic in the Gaoqing area: the content of feldspar and calcite in weathered clay layer is less than 10%,the content of feldspar and calcite in semi-weathered rocks is between 10%-25%,the content of feldspar and calcite in unweathered rock is more than 25%.The method of chemical weathering index can accurately identify the semi weathered rocks and unweathered rocks.The logging classification standard of Mesozoic unconformity structure in Gaoqing area is established,by analyzing the effect of some wells,it is found that this method can effectively identify the unconformity structure.(3)The distribution characteristics of Mesozoic unconformity structure in Gaoqing area indicate: Rocks above the unconformity is thinner from north to south,and the thickness is generally larger than 20 m.The thickness of weathered clay layer is between 2-20 m,the whole region is widely developed,it is thicker in the west and east,the thickness is thinnest in the middle.The thickness of semi weathering rock is inversely proportional to weathering clay layer,and the average thickness is about 30 m.(4)The transformation mechanism of Mesozoic unconformity development on reservoir physical property in Gaoqing area shows that: Freshwater dissolution is the main reason for the improvement of the property of semi weathered sandstone.The physical property improvement of weathered clay layer and semi weathered mudstone is basically zero,while the modification of the semi-differentiated sandstone is basically preserved and the pore infiltration is improved greatly.(5)The analysis of the oil-controlling factors of unconformity structure shows that mudstone above the unconformity,weathered clay layer and semi weathered mudstone are mainly used as shielding layer,but sandstone above the unconformity,igneous rock and semi weathered sandstone can be used as good channel and place for hydrocarbon migration and accumulation.There are mainly two ways of Mesozoic unconformity structure oil-Controlling in Gaoqing area: The lateral transport mode of unconformity structure and the occlusion mode of unconformity structure.