The Coupling Relationship Between The Diagenetic Evolution And Oil Accumulation Of Tight Sandstone Reservoir In Xin Anbian Oilfield,Ordos Basin

The Mesozoic tight oil resources in the Ordos Basin are abundant.The resources of the Chang-7 reservoir of the Yanchang Formation,Triassic,reach 3 billion tons,most of which are distributed in the Semi-Deep Lake sedimentary area and the Lake-Deep sedimentary area of the basin,showing geological characteristics of symbiosis and near-source accumulation in the source and reservoir.It is an important strategic area for hydrocarbon resources in China.Xin’anbian area has become the first billion-ton large-scale tight oil field in China,which was newly discovered in the deep lake region in northeastern part of the Lake Basin in 2014.Its sedimentary environment and reservoir characteristics,especially the hydrocarbon accumulation process,are different from the tight oil in the lake-basin center.The present study starts with the characteristics of tight oil reservoirs in Xin’anbian,analyzes the diagenetic evolution process of reservoirs,discusses the coupling relationship between diagenetic evolution and hydrocarbon accumulation,and determines the dynamic process of tight oil accumulation in the Ordos shallow lake region.It will provide the basis for the evaluation of the tight oil exploration target in the Ordos Chang-7 Lake Bank area.Based on the typical field profiles and key cores in the basin,the present study uses the analysis and test data of cast thin sections,scanning electron microscopy,particle size,mercury intrusion,and fluid inclusion temperature measurement to develop the dynamic evolution of diagenesis-forming reservoirs.The characteristics and diagenesis of Chang 7 tight oil reservoir in Xin’anbian area,Ordos Basin,establishes the diagenetic evolution sequence of the study area,combines the history of hydrocarbon charging,analyzes the filling period and the accumulation process of tight oil,and clarifies the tight evolution of reservoir diagenesis and oil and gas.Filling the coupling relationship.1、The study shows that:the main body of tight oil in the Xin’anbian area is located in the Chang-7₂ sub-section,which is an underwater distributary channel of delta front.The types of main sandstone are debris sandstone and feldspar sandstone,and the interstitial material is mainly kaolinite,chlorite,hydromica,and calcite.The reservoir physical property is poor,the permeability is 0.03-0.8×10^-3μm²,and the porosity is low（5-8%）.The residual intergranular pores are dominant,with the dissolution pores developed in some areas.The connectivity between the pores and throat is poor,which is a typical tight reservoir.2、A analysis suggests that the diagenetic sequence of the Chang-7₂ reservoir in the Xin’anbian Oilfield is:compaction→chlorite membrane→siliceous cementation→hydrocarbon charging→feldspar corrosion→kaolinite and illite cementation→calcite cementing→hydrocarbon charging continuously→calcite corrosion,generally up to the stage A of the middle diagenetic stage.3、The analysis of fluid inclusions shows that the homogenization temperature of the brine inclusions associated with hydrocarbon inclusions in the Chang-7₂ tight oil reservoirs in the Xin’anbian area is between 100°C and 115°C,indicating that the target layer was the one stage charging continuous accumulation and a relatively continuous process.The capture time of hydrocarbon inclusions in the reservoir is between 125and 100 Ma.The migration and filling period of liquid hydrocarbons is Early Cretaceous.At the end of the Late Jurassic-Early Cretaceous,the overall porosity of the sandstone in the study area was decreased,and the reservoir has been tight.The accumulation is obviously later than the reservoir tight,shown that the reservoir tighten period is prior to oil accumulation.