Characteristics Of Oil And Gas Reservoirs Related To Sag Uplift Combination Structure Of Source Rocks In Yanchang Formation,Ordos Basin

In recent years,due to the increasing difficulty of exploration of conventional sandstone oil and gas reservoirs in Ordos Basin,the new reserves of conventional sandstone oil and gas reservoirs are difficult to meet the increasing demand of domestic oil and gas resources.The exploration of source rock oil and gas reservoirs and their related oil and gas reservoirs has gradually become a new direction of oil and gas exploration in Ordos Basin.Predecessors used various means to study the reservoir characteristics of the reservoir.They mainly studied and tested the rock structural characteristics and physical properties of the reservoir.They mainly took the lower limit value of physical properties as the standard to judge whether it is a high-quality reservoir.Most of their studies focused on the analysis of physical parameters of a single layer in a certain area under production pressure,There is not enough research on how to find regions with relatively good reservoir performance in large areas of distributed source rocks and related strata under the environment of original formation pressure.Based on the concave uplift combination structure and fault fracture rock combination structure,this paper preliminarily discusses the reservoir characteristics of Mesozoic Yanchang Formation in Ordos basin according to a large number of core,thin section,logging,logging and seismic data.It provides a new idea for finding areas with good relative reservoir performance in large-scale distributed source rocks and their related strata.The main achievements are as follows:(1)Reservoir characteristics of source rocksThe source rock of Yanchang formation is a set of dark shale developed in Chang 7member.In recent years,a large number of industrial oil flows have been found in the source rock section.The industrial shale reservoirs found in Luo 190 well,Liuping 177 well,yanyeping 1 well and Geng 295 well all belong to this type.The fracture space formed under the formation pressure environment in the fault fracture body rock stratum combination structure is the main reservoir space of the source rock reservoir,and the formation scale and shape of the fracture are affected by the type of fault fracture body rock stratum combination structure,the lithology at both ends of the fault fracture body and its evolution process.(2)Characteristics of reservoirs adjacent to source rocksThe adjacent reservoirs of Yanchang Formation and source rocks are mostly fine-grained rock sandstone combination type in lithologic association.There are obvious differences in grain size between the two ends of the interface,and the interface is clearly visible.A large number of fractures are often developed on the lithologic interface,which makes a great contribution to the porosity and permeability of the reservoir and can improve the reservoir and connectivity.Through the observation of the core thin section of this section and the study of the characteristics of the continuous well section with acoustic time difference,the structural deformation of the reservoir adjacent to the source rock of Yanchang formation is divided into two categories: one is shallow buried depth,the rock is mainly plastic compacted,the variation range of porosity with depth is small,and the rock is not broken;The other type has a large buried depth,the rock has elastic-plastic change or fracture on the lithologic interface,the acoustic time difference has cycle jump,and the porosity changes greatly.Combined with the corresponding relationship between gas logging total hydrocarbon curve and lithology,it is found that the reservoir with fine-grained rock sandstone combination has better gas logging display in the sand mud superimposed section.The reservoir adjacent to the source rock has natural reservoir forming advantages.In a single sag uplift combination structural unit,the sandstone(or other reservoirs)in contact with the source rock is an important reservoir for oil and gas accumulation.The spatial distribution of these reservoirs in a single sag uplift combination structural unit in a key period has a very important impact on the accumulation and distribution of oil and gas.Combined with the strike characteristics of sedimentary sand bodies in Ordos Basin,It is found that lens sand body and reverse slope sand body are blocked by mudstone lithology in the direction of oil and gas escape,so they have better oil and gas filling.By analyzing the matching changes of sand body and concave uplift combination structure in different periods,we can further evaluate the favorable zones for oil and gas accumulation.(3)Reservoir characteristics controlled by fault fracture rock combination structureIn the Yanchang Formation reservoir,in addition to the source rock reservoir and the reservoir in contact with the source rock,there are also considerable oil and gas enrichment in some horizons such as Chang 2 and Chang 8 that are not vertically adjacent to the source rock series.In a structural unit,due to the influence of unified driving force,hydrocarbons are enriched along the migration channel to the high part of the structure.At this time,if there is fault development,oil and gas will migrate along the fault.At the same time,it is found that in the reservoir controlled by fault rock combination structure,oil and gas migrate to the reservoir that is not in contact with the source rock through the fault and are filled.In this process,oil and gas are preferentially filled to the part with the best physical properties of the reservoir,while the rest parts that can be used as high-quality reservoirs according to the conventional reservoir discrimination method are often rarely filled with oil and gas.That is,in this kind of reservoir,the favorable area of the reservoir should be the layer series with the best physical parameters.